The Steel Head Rod Mill(sometimes call a bar mill)gives the ore dressing engineer a very wide choice in grinding design. He can easily secure a standard Steel Head Rod Mill suited to his particular problem. The successful operation of any grinding unit is largely dependent on the method of removing the ground pulp. The Steel Head Rod Mill is available with five types of discharge trunnions and each type trunnion is available in small, medium, or large diameter. The types of Rod Mill discharge trunnions are:
The superiority of the Steel Head Rod Mill is due to the all-steel construction. The trunnions are an integral part of the cast steel heads and are machined with the axis of the mill. The mill heads are insured against breakage due to the high tensile strength of cast steel as compared to that of the cast iron head found on the ordinary rod mill. Trunnion Bearings are made of high-grade nickel babbitt, dovetailed into the casting. Ball and socket bearings can be furnished if desired.
Head and shell liners for Steel Head Rod Mills are available in Decolloy (a chrome-nickel alloy), hard iron, electric steel, molychrome steel, and manganese steel. The heads have a conical shaped head liner construction, both on the feed and discharge ends, so that there is ample room for the feed from the trunnion helical conveyor discharge to enter the mill betweenthe rods and head liners on the feed end of the mill. Drive gears are furnished either in cast tooth spur gear and pinion or cut tooth spur gear and pinion. The gears are furnished as standard on the discharge end of the mill, out of the way of the classifier return feed, but can be furnished at the mill feed end by request. Drives may be obtained according to the customers specifications.
The following table clearly illustrates why Steel Head Rod Mills have greater capacity than other mills. This is due to the fact that the diameters are measured inside the liners, while other mills measure their diameter inside the shell.
Rod Mills may be considered either fine crushers or coarse grinding equipment. They are capable of taking as large as 2 feed and making a product as fine as 35-48 mesh. Of particular advantage is their adaptability to handling wet sticky ores, which normally would cause difficulty in crushing operations. Under wet grinding conditions of course the problem of dust is eliminated.
The grinding action of a rod mill is line contact. As material travels from the feed end to the discharge end it is subjected to crushing forces inflicted by the grinding rods. The rods both tumble in essentially a parallel alignment and also spin, thus simulating the crushing and grinding action obtained from a series of roll crushers. The large feed tends to spread the rods at the feed end which imparts still an additional action which may be termed scissoring. As a result of this spreading the rods tend to work on the larger particles and thereby produce a minimum amount of extremely fine material.
The Rod Mill encourages the use of a thick pulp coating both the liners and the rods, thus minimizing steel consumption. Continuous movement of the pulp through the rod mass eliminates the possibility of short circuiting any material. The discharge end of the Rod Mill is virtually open and larger in diameter than the feed end, providing a steep gradient of material flow through the mill. This is described in more detail on pages 20 and 21.
Normally Rod Mills are furnished of the two trunnion design. For special applications they may be furnished of the tire trunnion or two- tire construction. These mills can be equipped with any type of feeder and type of drive, discussed separately in this catalog.
The above tables list some of the most common Open End Rod Mill sizes. Capacities are based on medium hard ore with mill operating in closed circuit under wet grinding conditions at speeds indicated. For dry grinding, speeds and power are reduced and capacities drop 30 to 50%.
The End Peripheral Discharge Rod Mill is designed to produce a minimum amount of fines when grinding either wet or dry. Material to be ground enters through a standard trunnion and is discharged through port openings equally spaced around the mill periphery. These ports are in a separate ring placed between the shell and the discharge head.
The construction of the end peripheral discharge mill emphasizes the principle of grinding. Due to the steep gradient between the point of entry and the point of discharge the pulp flows rapidly through the mill providing a fast change of mill content with a relatively small amount of pulp within the grinding chamber.
The sloping or conical shaped feed head proves ample space for a feed pocket to accommodate large quantities of material and assure their entrance into the grinding rods. Any type of feeder listed on pages 22 and 23 can be furnished for these mills; however, since the mills are not usually operated in closed circuit grinding, the drum or spout feeder is normally preferred.
No other type of mill is so well adapted to dry grinding materials to -4 or -8 mesh in single pass with the production of a minimum amount of fines. A major factor in dry grinding is the rapid removal of finished material to prevent cushioning of the rods. This is accomplished in the End Peripheral Discharge Rod Mill.
The free discharge feature permits the grinding of material having a higher moisture content than with other types of rod or ball mills. Our Peripheral Discharge Mills have found wide application in grinding coke and friable non-metallics, material for glass, pyroborates, as well as gravel to produce sand. Another application is for grinding and mixing sand lime brick materials. The rod action gives a thorough mixture while grinding of the hydrated lime and sand.
For specifications of End Peripheral Discharge Rod Mills use table of standard open end rod mills given on pages 24 and 25. The capacity of the end peripheral discharge rod mill is slightly higher than shown for the Open End Rod Mills.
The CPD (Center Peripheral Discharge) Rod Mill has been developed to produce sand to meet U. S. Government or State specifications. It has also found application in grinding friable non-metallics, and industrial materials and ores which tend to slime excessively. Another application is in the field of abrasion milling on ores such as found on the Mesabi Iron Range. In this latter application true grinding is not desired, but more of a surface scrubbing of the individual particles.
Again with this construction grinding may be done either wet or dry. In this design, however, feed enters both ends by means of feeders and is discharged at the center through rectangular discharge ports equally spaced around the mill periphery. The center discharge openings are generally contained in a separate ring placed between shell halves. The ground material is discharged and directed to either side or directly under the mill by the use of a discharge ring housing.
In standard rod-milling it will be found that rods spread apart at the feed end in the amount of the maximum size of feed entering the mill. In the center peripheral discharge mill the rods are spread at both ends and parallel throughout the length of the mill. This feature results in more space between the rods and thereby lessens the amount of fines produced. Furthermore, fines are also diminished because the material moves rapidly through the mill due to the steep gradient of travel and the distance of travel is reduced by half. Similarly time of contact with the grinding media is reduced by half.
Another center peripheral discharge advantage is that a cubical shaped particle is produced. Maintenance is negligible and grinding media is relatively inexpensive. Other types of sand manufacturing equipment lose efficiency with wear and require excessive maintenance. This loss of efficiency increases rapidly as hardness of feed increases. The Center Peripheral Discharge Rod Mill can be easily maintained at peak operating efficiency by the periodical addition of rods. CPD Rod Mills give a wide range of flexibility to sand plant operation. By changing the rate of feed, pulp dilution (wet grinding), and discharge port area it is possible to produce and blend sand of virtually any fineness modulus and maintain it within Government specifications.
Unlike many crushers or grinders the CPD Mill can easily handle wet or sticky material. When grinding wet, the dust nuisance is completely eliminated. For dry grinding applications the mill is furnished with a dust proof discharge housing.
Various items must be considered in computing the cost of producing manufactured sand. These include wear on the constituent parts, power consumption, lubrication, labor and general maintenance. Maintenance of the center peripheral discharge mill is definitely much lower than that of any other sand manufacturing machine. The greater portion of the wear which takes place is on the inexpensive high carbon steel rods. Field installations show an average of less than 1 # per ton of sand ground as rod consumption, and from 0.08# to 0.10# per ton of sand ground as the steel liner wear. The overall cost of mill operation, exclusive of amortization, is generally less than 30c per ton (year 1958).
Every possible operating convenience has been incorporated in the center peripheral discharge mill design. On most sizes the trunnions are carried in large lead bronze bushed bearings. The interior of the mill is readily accessible through these large trunnion openings. The peripheral ring housing is furnished with a door for inspection and another lower door to facilitate sampling of the mill discharge. Covers for the discharge ports are furnished allowing any variation in discharge area which might be desired.
Given below are approximate capacities for several sizes of the center peripheral discharge mills. Such capacities are expressed in dry tons per hour, based on - x 4 mesh screened feed of medium hard gravel. Mill discharge is generally less than 5% + 4 mesh in wet open circuit operations, for dry grinding work reduce the capacities indicated by approximately 30% to 50%.
A Rod Mill has for Working Principle its inside filledgrinding media, in this case STEEL RODS. These rods run the length of the machine, which is most commonly between eight and sixteen feet in length. The diameter of these rods will range from, when new, between two and four inches. The rods arefree inside the mill. When the mill is turned, the rods tumble against one another grinding all the ore that is between them to aid in the grinding, water is added with the ore as it enters the mill.So from that you can see why it is called a wet tumbling mill. The ore is ground wet and the mill revolves. This causes the grinding media inside of it to tumble grinding the ore.
Historically there has been three basic ways of grinding ore, hammer mills, rolls, or wet tumbling mills. Hammer mills and rolls are not used that often and then usually only for special applications as in lab work or chemical preparation.
The type of mill that is used for grinding ore in a modern concentrator is the wet tumbling mill. These mills may be divided into three types ROD MILLS, BALL MILLS andAUTOGENOUS MILLS. In the first type, the ROD MILL, the ore is introduced into the mill.
From the trunnion liner out wards first we will come to the FACE PLATE. It is slightly concave to create the POOLING AREA for the rock to collect in before entry to the ROD-LOAD. On the outside attached to the face plate is the BULL GEAR. This gear completely circles the mill and provides the interface between the motor and the mill. The bull gear and drive line may be at the other end of the mill instead. There are advantages and disadvantages to either end this will be explained later when we are discussing the motor and drive line. But for now back to the face plate, attached to the other side of the face plate is the SHELL. The shell is the body of the mill. On the inside of the mill there are two layers of material, the first layer is the BACKING for the liners. This is customarily constructed from rubber but wood may be used as well. The purpose of this backing is two-fold, one to absorb the shock that is transmitted through the liners from normal running. And to provide the shell with a protective covering to eliminate the abrasion that is produced by the finely ground rock and water. Without this rubber or wood backing, the life of the mill is drastically reduced due to metal fatigue and simply being worn away.For those of you arent familiar with METAL FATIGUE I will explain. When metal is continually pounded or vibrated, the molecular structure of the metal begins to change, it is said to CRYSTALLIZE, and the metal becomes hard and finally loses all ability to give with the vibration. Thousands of microscopic cracks will begin to appear, as the fatigue of the metal continues, these cracks will grow to become major problems.
Later for interest sake we will explain the difference in some of them, but for now lets stay with identifying the parts of the mill. We have already mentioned the trunnion liner so let start from there.
The trunnion liner may also be referred to as the THROAT LINER. You will find that many of these parts will be called two or even sometimes three names, All I can say is try not to let it confuse you, The name isnt as important as the job that it does. As long as everybody that you work with agree on which name to use, it doesnt matter that much.
Next to this liner is the END LINERS, or to some, the PACE PLATE LINERS.The FILLER RING which is next is not standard in all mills, some mills have them, and some dont. Their job is to fill the corner of the mill up so the shell will not wear at that point. They dont provide any lift to the media, in fact quite often the media will not come into contact with them at all, but what they do is make changing liners that much easier. With different liner designs the replacement of a single liner may be quite difficult and to change one could become a lengthy project.
The liner that butts into the filler liner is known as a BELLY LINER or SHELL LINER, and in some designs LIFTER BARS. These liners and/or lifters give the media its CASCADING action and also receive the most wear. They cover the complete body of the mill and have the largest selection of types to choose from.
As the two ends of the mill are the same there isnt any reason to go over the other face plate. The discharge trunnion assembly is very much like the feed trunnion except that, it wont have a worm as part of the liner. Instead of a feed seal bolted to it, it may have a screen.
This is called a TRUMMEL SCREEN and its purpose is to screen out any rock that didnt get ground as well as any TRAMP METAL or REJECT STEEL that may be coming out of the mill. Reject steel is the old grinding media that has been worn so small that it comes out of the mill. If this tramp metal and steel is allowed to get into pumps and classifiers damage and plug- ups may be caused.
With regards to Rod Mills, let us start by identifying the different portions of the rod load as it goes through one revolution, as you will see, each of these areas will hold interest for the Grinding operator.
As the rod mill turns, the rods are carried by the lifting portion of the liners. The height that they are lifted is referred to as the lift of the liners. As they roll off of the liners, the rods enter the cascade zone. The rods roll through the cascade zone until they come to the toe of the load. At this point the rods come to rest in relation to the shell of the mill. The liners lift the rods back to begin the cascade again. You will notice, that as you go deeper into the rod load, the rod movement becomes less and less until the movement is very slight at the deepest part. This area is called the core of the load. As a description of the normal grinding action, the rods and the ore react together like this. The ore enters-the mill and is deposited in the pooling area directly under the feed trunnion.
This pooling area allows the large rock to fall towards the outside portion of the load, the TOE area. This is the zone with the greatest movement in it, which means the area that will have the highest impact on the ore.
The rock will be carried up by the rods as they go through the CASCADE ZONE reducing the size of the rock. As each particle of ore becomes smaller it will work towards the CORE ZONE while travelling the length of the mill. That makes for a rather neat arrangement doesnt it. The larger rock is deposited in the area where the maximum impact from the rod load occurs and then as each particle gets smaller it slowly travels inwards towards the centre of the load.
This is where the maximum surface contact takes place, producing the finer grind. When the ore has travelled from one end of the mill to the other end it will have completed its grinding cycle in this mill. As it exits the rod load it will be deposited in another POOLING AREA prior to leaving the mill by way of the DISCHARGE TRUNNION. Prom that you can see how a mill will become over loaded. If for some reason the rock begins to separate the rods over their entire length, the larger rock will prevent the intermediate rock from being ground. Which in turn will begin to invade the area that the fine material is being ground in. As the rods become separated through the entire load, the grind will get progressively worse until the unground rock is in the discharge pooling area. At this point, the operator will notice, that large rock is being discharged from the discharge trunnion.
During normal operations there is usually a certain amount of this larger rock that wont get ground. These are known as REJECTS and they serve as one of the tattle tales as to how the mill is grinding. If there is an increase of these rejects then the mill isnt grinding that well and the operator will have to do something about it. If he doesnt the mill load will continue to climb, until the rods in the lifting zone are completely separated. When this happens those rods will have quit grinding.
There is a visual warning of this happening that the operator can take advantage of. The lift on the rods will get higher and higher until they are being carried to the very top of the mill before cascading. I think falling would be a better word for it though. As this is happening, the core of the load will be slowly moving away from the shell towards the center of the mill. This is because the volume of the mill is being filled with unground rock. This will continue until the load hits a critical volume and a critical density. The rock still coming in to the mill will have to have some where to go so it tries pushing the rods out of the mill. Unfortunately they wont make it, the first hunch of rods that get far enough into the discharge trunnion will be- hit by the rest of the load bending and twisting them until they look like SPAGHETTI. This usually shuts the mill down for a couple of days while the millwrights cut the bent rods out of the mill.
On the other end of the scale, if the density is to light, the rod load will become too active, not having the solids in the mill to cushion the impact of rod on rod and rod on liner. As the rods enter the cascade zone, the pattern of the movement of the rods will be different. Instead of having a tightly tumbling mass of rods, the rods will be separated. The lift will be higher and the cascade will form more of an arc. The impact of the rods on the rock will be less because there will be more give in the rod load, with high amount of steel on steel causing the rods to bounce.
Letslook at how these Rod mills work, as I mentioned earlier there are steel rods inside the mill, it is their job to do the actual grinding. If you look at the mill in a cross section of an end view. You will get a very good illustration of the grinding action, of the mill.
The LINERS provide the tumbling action of the rods. When the mill rotates the rods are lifted until they roll off of the liners, this is known as CASCADING. The ore enters the mill at the feed end, as the rods cascade and tumble, the rock is caught between the rods and is ground. The size that the rock will be ground to is dependent on the amount of time the ore is in the mill, how many rods there are in the mill V and the size of the incoming ore.
AG and SAG mills are now the primary unit operation for the majority of large grinding circuits, and form the basis for a variety of circuit configurations. SAG circuits are common in the industry based on:
Though some trepidation concerning AG or SAG circuits accompanied design studies for some lime, such circuits are now well understood, and there is a substantial body of knowledge on circuit design as well as abundant information that can be used for bench-marking of similar plants in similar applications. Because SAG mills rely both on the ore itself as grinding media (to varying degrees) and on ore-dependent unit power requirements for milling to the transfer size, throughput in SAG circuits are variable. Relative to other comminution machines in the primary role. SAG mill operation is more dynamic, and typically requires a higher degree of process control sophistication. Though more complex in AG/ SAG circuits relative to the crushing plants they have largely replaced, these issues are well understood in contemporary applications.
AG/SAG mills grindore through impact breakage, attrition breakage, and abrasion of the ore serving as media. Autogenous circuits require an ore of suitable competency (or fractions within the ore of suitable competency) to serve as media. SAG circuits may employ low to relatively high ball charges (ranging from 2% to 22%, expressed as volumetric mill filling) to augment autogenous media. Higher ball charges shift the breakage mode away from attrition and abrasionbreakage toward impact breakage; as a result, AG milling produces a finer grind than SAG milling for a given ore and otherwise equal operating conditions. The following circuits are common in the gold industry:
Common convention generally refers to high-aspect ratio mills as SAG mills (with diameter to effective grinding length ratios of 3:1 to 1:1), low-aspect ratio mills (generally, a mill with a significantly longer length than diameter) are also worth noting. Such mills are common in South African operations; mills are sometimes referred to as tube mills or ROM ball mills and are also operated both autogenously and semi-autogenously. Many of these mills operate at higher mill speeds (nominally 90% of critical speed) and often use grid liners to form an autogenous liner surface. These mills typically grind ROM ore in a single stage. A large example of such a mill was converted from a single-stage milling application to a semi autogenous ball-mill-crushing (SABC) circuit, and the application is well described. This refers to high-aspect AG/SAG mills.
With a higher density mill charge. SAG mills have a higher installed power density for a given plant footprint relative to AC mills. With the combination of finer grind and a lower installed power density (based on the lower density of the mill charge), a typical AG mill has a lower throughput, a lower power draw, and produces a finer grind. These factors often translate to a higher unit power input (kWh/t) than an SAG circuit milling the same ore. but at a higher power efficiency (often assessed by the operating work index OWi, which if used most objectively, should be corrected by one of a number of techniques for varying amounts of fines between the two milling operations).
In the presence of suitable ore, an autogenous circuit can provide substantial operating cost savings due to a reduction in grinding media expenditure and liner wear. In broad terms, this makes SAG mills less expensive to build (in terms of unit capital cost per ton of throughput) than AG mills but more expensive to operate (as a result of increased grinding media and liner costs, and in many cases, lower power efficiency). SAG circuits are less susceptible to substantial fluctuations due to feed variation than AG mills and are more stable to operate. AG circuits are more frequently (but not exclusively) installed in circuits with high ore densities. A small steel charge addition to an AG mill can boost throughput, result in more stable operations, typically at the consequence of a coarser grind and higher operating costs. An AG circuit is often designed to accommodate a degree of steel media for circuit flexibility. AG mills (or SAG mills with low ball charges) are often used in single-stage grinding applications.
Based on their higher throughput and coarser grind relative to AG mills, it is more common for SAG mills to he used as the primary stage of grinding, followed by a second stage of milling. AG/SAG circuits producing a fine grind (particularly single-stage grinding applications) are often closed with hydrocyclones. Circuits producing a coarser grinds often classify mill discharge with screens. For circuits classifying mill discharge at a coarse size (coarser than approximately 10 mm), trommels can also be considered to classify mill discharge. Trommels are less favorable in applications requiring high classification efficiencies and can be constrained by available surface area for high-throughput mills. Regardless of classification equipment (hydrocyclone, screen, or trommel), oversize can be returned to the mill, or directed to a separate stage of comminution.
Many large mills around the world (Esperanza with a 12.8 m mill. Cadia and Collahuasi with 12.2-m mills, and Antamina. Escondida #IV. PT Freeport Indonesia, and others with 11.6-m mills) have installed SAG mills of 20 MW. Gearless drives (wrap-around motors) are typically used for large mills, with mills of 25 MW or larger having been designed. Several circuits have single-line design capacities exceeding 100,000 TPD. A large SAG installation (with pebble crusher product combining with SAG discharge and feeding screens) is depicted here below, with the corresponding process flowsheet presented in Figure 17.9.
Adding pebble crushing as a unit operation is the most common variant to closed-circuit AG/SAG milling (instead of direct recycle of oversize material ). The efficiency benefits (both in terms of grinding efficiency and in capital efficiency through incremental throughput) are well recognized. Pebble crushers are effective at reducing the buildup of critical-sized material in the mill load. Critical-sized particles are those where the product of the mill feed-size distribution and the mill breakage rates result in a buildup of a size range of material in the mill load, the accumulation of which limits the ability of the mill to accept new feed. While critical-size could be of any dimension, it is most typically synonymous with pebble-crusher feed, with a size range of 1375 mm. Critical-sized particles can result from a simple failure of a mills breakage rates to exceed the breakage rate of incoming particles, and particles generated when breaking larger particles. Alternatively, a second type of buildup of critical-sized material can result due to a combination of rock types in the feed that have differing breakage properties. In this case, the harder fraction of the mill feed builds up in the mill load, againrestricting throughput. Examples of materials in this category include diorites, chert, and andesite. When buildup of these materials does occur, pebble crushing can improve mill throughput even more dramatically than when the critically sized fraction results purely from a breakage rate deficit alone. For these ore types, a pebble-crushing circuit is tin imperative for efficient circuit operation.
Currently, every AG/SAG flowsheet evaluation is likely to consider the inclusion of a pebble crusher circuit. Flowsheets that do not elect to include pebble crushing at construction and commissioning may include provisions for future retrofitting a pebble-crushing circuit. Important aspects of pebble crusher circuit design include:
The standard destination for crushed pebbles has been to return them to SAG feed. However, open circuiting the SAG mill by feeding crushed pebbles directly to a ball-mill circuit is often considered as a technique to increase SAG throughput. An option to do both can allow balancing the primary and secondary milling sections by having the ability to return crushed pebbles to SAG feed as per a conventional flowsheet, or to the SAG discharge. Such a circuit is depicted here on the right. By combining with SAG discharge and screening on the SAG discharge screens, top size control to the ball-mill circuit feed is maintained while still unloading the SAG circuit (Mosher et al, 2006). A variant of this method is to direct pebble-crushing circuit product to the ball-mill sump for secondary milling: while convenient, this has the disadvantage of not controlling the top size of feed to the ball-mill circuit. There have also been pioneer installations that have installed HPGRs as a second stage of pebble crushing.
The unit power requirement for SAG milling (both individually and as a fraction of the total circuit power) is worthy of comment. It can be very difficult operationally to trade grind for throughput in an SAG circuitonce designed and constructed for a given circuit configuration, an SAG mill circuit has limited flexibility to deliver varying product sizes, and a relatively fixed unit power input for a given ore type is typically required in the SAG mill. This is particularly true for those SAG circuits designed with a coarse closing size. As a result, under-sizing an SAG mill has disastrous results on throughput across the industry, there are numerous examples of the SAG mill emerging as the circuit bottleneck. On the other hand, over-sizing an SAG circuit can be a poor utilization of capital (or an opportunity for future expansion!).
Traditionally, many engineers approached SAG circuit design as a division of the total power between the SAG circuit and ball-mill circuit, often at an arbitrary power split. If done without due consideration to ore characteristics, benchmarks against comparable operating circuits, and other aspects of detailed design (including steady-state tests, simulation, and experience), an arbitrary power split between circuits ignores the critical decision of determining the required unit power in SAG milling. As such, it exposes the circuit to risk in terms of failing to meet throughput targets if insufficient SAG power is installed. Rather than design the SAG circuit with an arbitrary fraction of total circuit power, it is more useful to base the required SAG mill size on the product of the unit power requirement for the ore and the desired throughput. Subsequently, the size of the secondary milling circuit is then sized based on the amount of finish grinding for the SAG circuit product that is required. Restated, the designed SAG mill size and operating conditions typically control circuit throughput, while the ball-mill circuit installed power controls the final grind size.
The effect of feed hardness is the most significant driver for AG/SAG performance: with variations in ore hardness come variations in circuit throughput. The effect of feed size is marked, with both larger and finer feed sizes having a significant effect on throughput. With SAG mills, the response is typically that for coarser ores, throughput declines, and vice versa. However, for AG mills, there are number of case histories where mills failed to consistently meet throughput targets due to a lack of coarse media. Compounding the challenge of feed size is the fact that for many ores, the overall coarseness of the primary crusher product is correlated to feed hardness. Larger, more competent material consumes mill volume and limits throughput.
A number of operations have implemented a secondary crushing circuit prior to the SAG circuit for further comminution of primary crusher product. Such a circuit can counteract the effects of harder ore. coarser ore. decrease the size of SAG mill required, or rectify poor throughput due to an undersized SAG circuit. Notably, harder ore often presents itself to the SAG circuit as coarser than softer oreless comminution is produced in blasting and primary crushing, and therefore the impact on SAG throughput is compounded.
Circuits that have used or do use secondary crushing/SAG pre-crush include Troilus (Canada), Kidston (Australia), Ray (USA), Porgera (PNG). Granny Smith (Australia), Geita Gold (Tanzania), St Ives (Australia), and KCGM (Australia). Occasionally, secondary crushing is included in the original design but is often added as an additional circuit to account for harder ore (either harder than planned or becoming harder as the deposit is developed) or as a capital-efficient mechanism to boost throughput in an existing circuit. Such a flowsheet is not without its drawbacks. Not surprisingly, some of the advantages of SAG milling are reduced in terms of increased liner wear and increased maintenance costs. Also, pre-crush can lead to an increase in mid-sized material, overloading of pebble circuits, and challenges in controlling recycle loads. In certain circuits, the loss of top-size material can lead to decreased throughput. It is now widespread enough to be a standard circuit variant and is often considered as an option in trade-off studies. At the other end of the spectrum is the concept of feeding AG mills with as coarse a primary crusher product as possible.
The overall circuit configuration can guide selection of die classification method of primary circuit product. Screening is more successful than trommel classification for circuits with pebble crushing, particularly for those with larger mills. Single-stage AG/SAG circuits are most often closed with hydrocyclones.
To a more significant degree than in other comminution devices, liner design and configuration can have a substantial effect on mill performance. In general terms, lifter spacing and angle, grate open area and aperture size, and pulp lifter design and capacity must be considered. Each of these topics has had a considerable amount of research, and numerous case studies of evolutionary liner design have been published. Based on experience, mill-liner designs have moved toward more open-shell lifter spacing, increased pulp lifter volumetric capacity, and a grate design to facilitate maximizing both pebble-crushing circuit utilization and SAG mill capacity. As a guideline, mill throughput is maximized with shell lifters between ratios of 2.5:1 and 5.0:1. This ratio range is stated without reference to face angle; in general terms, and at equivalent spacing-to-height ratios, lifters with greater face-angle relief will have less packing problems when new, but experience higher wear rates than those with a steeper face angle. Pulp-lifter design can be a significant consideration for SAG mills, particularly for large mills. As mill sizes increases, the required volumetric capacity of the pulp lifters grows proportionally to mill volume. Since AG/SAG mill volume is roughly proportional to the mill radius cubed (at typical mill lengths) while the available cross-sectional area grows only as the radius squared, pulp lifters must become more efficient at transferring slurry in larger mills. Mills with pebble-crushing circuits will require grates with larger apertures to feed the circuit.
No discussion of SAG milling would be complete without mention of refining. Unlike a concentrator with multiple grinding lines, conducting SAG mill maintenance shuts down an entire concentrator, so there is a tremendous focus on minimizing required maintenance time; the reline timeline often represents the critical path of a shutdown (but typically does not dominate a shutdown in terms of total maintenance effort).
Reline times are a function of the number of pieces to be changed and the time required per piece. Advances in casting and development of progressively larger lining machines have allowed larger and larger individual liner pieces.
While improvements in this area will continue, the physical size limit of the feed trunnion and the ability to maneuver parts are increasingly limiting factors, particularly in large mills. The other portion of the equation for reline times is time per piece, and performance in this area is a function of planning, training/skill level, and equipment.
Abroad range of AG/SAG circuit configurations are in operation. Very large line plants have been designed, constructed, and operated. The circuits have demonstrated reliability, high overall availabilities, streamlined maintenance shutdowns, and efficient operation. AG/SAG circuits can handle a broad range of feed sizes, as well as sticky, clayey ores (which challenge other circuit configurations). Relative to crushing plants, wear media use is reduced, and plants run at higher availabilities. Circuits, however, are more sensitive to variations in circuit feed characteristics of hardness and size distribution; unlike crushing plants for which throughput is largely volumetrically controlled. AG/SAG throughput is defined by the unit power required to grindthe ore to the closing size attained in the circuit. Very hard ores can severely constrain AG/SAG mill throughput. In such cases, the circuits can become capital inefficient (in terms of the size and number of primary milling units required) and can require more total power input relative to alternative comminution flowsheets. A higher degree of operator skill is typically required of AG/SAG circuit operation, and more advanced process control is required to maintain steady-state operation, with different operator/advanced process control regimens required based on different ore types.
Many mills have been built based on data from inadequate sampling or from insufficient tests. With the cost of many mills exceeding several hundred million dollars, it is mandatory that geologists, mining engineers and metallurgists work together to prepare representative samples for testing. Simple repeatable work index tests are usually sufficient for rod mill and ball mill tests but pilot plant tests on 50-100 tons of ore are frequently necessary for autogenous or semiautogenous mills.
Preparation and selection of the test sample is of utmost importance. Procedures for autogenous and semiautogenous mill pilot plant tests are relatively simple for those experienced in running them. Reliable and repeatable results can be obtained if simple fundamental procedures are followed.
The design of large mills has become increasingly more complicated as the size has increased and there is little doubt that without sophisticated design procedures such as the use of the Finite Element method the required factors of safety would make large mills prohibitively expensive.
In the past the design of small mills, up to +/- 2,5 metres diameter, was carried out using empirical formulae with relatively large factors of safety. As the diameter and length of mills increased several critical problem areas were identified. One of the most important was the severe stressing which took place at the connection of the mill shell and the trunnion bearing end plates, which is further aggravated by the considerable distortion of the shell and the bearing journals due to the dynamic load effect of the rotating mill with a heavy mass of ore and pulp being lifted and dropped as the grinding process took place. Incidentally the design calculation of the deformations of journal and mill shell is based on static conditions, the influence of the rotating mass being of less importance. An indication of shell and journal distortion is shown in Figure 1.
Investigations carried out by Polysius/Aerofall revealed that practical manufacturing considerations dictated some aspects of trunnion end design. Whereas the thickness of the trunnion in the case of small diameter mills was dictated by foundry practice which required a minimum thickness of metal the opposite was the case in the design of large diameter mills where the emphasis was not to exceed a maximum thickness both from the mass/casting temperature point of view and the cost aspect.
While the deformation of shell and end plates was acceptable in the case of small mills due in some extent to the over stiff construction, the deformation in the large, more flexible, mills is relatively high. The ratio of the trunnion thickness to trunnion diameter in a mill of 2,134 m diameter is almost twice that of a mill of 5,8 m diameter, i.e. a ratio (T/D) of 0,116 to 0,069 for the large mill.
The use of large memory high speed computers coupled with finite element methods provides the means of performing stress calculations with a high degree of accuracy even for the complex structures of large mills. The precision with which the stress values can be predicted makes the use of safety factors based on empirical formulae generally unnecessary.
In the case of large diameter trunnion bearing mills the distortion which takes place is further compounded by the fact that the deformation varies across the width of the bearing journal due to the fact that the end of the journal attached to the mill end plate is less liable to distortion than the outlet free end of the journal. This raises serious complications as far as the development of the hydrodynamic fluid oil film of the bearing is concerned since the minimum oil gap may be only 0,05 mm.
Obviously a thinner oil film is adequate where the deformation of the journal is less while at the unsecured end of the journal widely varying oil film thickness is necessary to maintain the correct oil pressure to support the mill. A solution to this problem has been the advent of the hydrostatic bearing with a supply of high pressure oil pumped continuously into the bearings.
Incorporating the mill bearing journals as part of the mill shell reduced the magnitude of the problem of distortion although there is always out of round deformation of the shell. The variation across the width of the journal surface is less pronounced than is the case with the trunnion bearing.
The replacement of a single bearing with a number of individual self adjusting bearing pads which together support the mill has lessened the undesirable effects of deformation while improving the efficiency of the bearing.
The ability of each individual bearing-pad to adjust automatically to a more localised area of the shell journal gives rise to improved contact of the oil film with both the bearing surface and the journal and in the case of hydrodynamic oil systems makes it unnecessary to supply oil at constant high pressure once the oil film has been established. A cross-section of a slipper pad bearing is shown in Figure 3.
Kidstons orebody consists of 44.2 million tonnes graded at 1.79 g/t gold and 2.22 g/t silver. Production commenced in January, 1985, and despite a number of control, mechanical and electrical problems, each month has seen a steady improvement in plant performance to a current level of over ninety percent rated capacity.
The grinding circuit comprises one 8530 mm diameter x 3650 mm semi-autogenous mill driven by a 3954 kW variable speed dc motor, and one 5030 mm diameter x 8340 mm secondary ball mill driven by a 3730 kW synchronous motor. Four 1067 x 2400 mm vibrating feeders under the coarse ore stockpile feed the SAG mill via a 1067 mm feed belt equipped with a belt scale. Feed rate was initially controlled by the SAG mill power draw with bearing pressure as override.
Integral with the grinding circuit is a 1500 cubic meter capacity agitated surge tank equipped with level sensors and variable speed pumps. This acts as a buffer between the grinding circuit and the flow rate sensitive cycloning and thickening sections.
The Kidston plant was designed to process 7500 tpd fresh ore of average hardness; but to optimise profit during the first two years of operation when softer oxide ore will be treated, the process equipment was sized to handle a throughput of up to 14 000 tpd. Some of the equipment, therefore, will become standby units at the normal throughputs of 7 000 to 8 000 tpd, or additional milling capacity may be installed.
The SAG mill incorporates a design which allowed expedient manufacturing to high quality specifications, achieved by selecting a shell to head to trunnion configuration of solid elements bolted together. This eliminates difficult to fabricate and inspect areas such as a fabricated head welded to shell plate, fabricated ribbed heads, plate or casting welded to the head in the knuckle area and transition between the head and trunnion.
Considerable variation in ore hardness, the late commissioning of much of the instrumentation and an eagerness to maximise mill throughput led to frequent mill overloading during the first four months of operation. The natural operator over-reaction to overloads resulted numerous mill grindouts, about sixteen hours in total, which in turn were largely responsible for grate failure and severe liner peening. First evidence of grate failure occurred at 678 000 tonnes throughput, and at 850 000 tonnes, after three grates had been replaced on separate occasions, the remaining 25 were renewed. The cylinder liners were so badly peened at this stage that no liner edge could be discerned except under very close scrutiny and grate apertures had closed to 48 percent of their original open area.
The original SAG mill control loop, a mill motor power draw set point of 5200 Amperes controlling the coarse ore feeder speeds, was soon found to give excessive variation in the mill ore charge volume and somewhat less than optimal power draw.
The armature, weighing 19 tonnes, together with the top half magnet frame, were trucked two thousand kilometers to Brisbane for rewinding and repairs. The mill was turning again on January 24 after a total elapsed downtime of 14 days. After a twelve day stoppage due to a statewide power dispute in February, the mill settled down to a fairly normal operation, apart from some minor problems with alarm monitoring causing a few spurious trips. One cause of the mysterious stoppages was tracked down to the cubicle door interlocks which stuttered whenever the mining department fired a bigger than usual blast.
The open trunnion bearings are sealed with a rubber ring which proved ineffective in preventing ingress of water, and occasionally solids, from feed chute chokes and spillages. Contamination and emulsification of the oil with subsequent filter choking has been responsible for nearly eighteen percent of SAG mill circuit shutdowns. Despite the very high levels of contamination, no damage has been sustained by the bearings which has at least proved the effectiveness of the filters and other protection devices.
Design changes to date have, predictably, mostly concentrated on improving liner life and minimising discharge grate damage. Four discharge grates with thickened ends have performed satisfactorily and a Mk3 version with separate lifters and 20 mm apertures is currently being cast by Minneapolis Electric.
Cylinder liners will continue to be replaced with high profile lifters only on a complete reline basis. While there is the problem of reduced milling capacity with reduced lifter height towards the end of liner life, it is hoped to largely offset this by operating at higher mill speeds.
Mill feed chute liner life continues to be a problem. The original chrome-moly liners lasted some three months and a subsequent trial with 75 mm thick clamped Linhard (rubber) liners turned in a rather dismal life of three weeks.
Am sure your BallMill is considered the finest possible grinding mill available. As such you will find it is designed and constructed according to heavy duty specifications. It is designed along sound engineering principles with quality workmanship and materials used in the construction of the component parts. YourBallMill reflects years of advancement in grinding principles, materials, and manufacturing techniques. It has been designed with both the operators and the erectors viewpoints in mind. Long uninterrupted performance can be expected from it if the instructions covering installation and maintenance of the mill are carried out. You may be familiar with installing mills of other designs and manufacture much lighter in construction. YourBallis heavy and rugged. It should, therefore, be treated accordingly with due respect for its heavier construction.
The purpose of this manual is to assist you in the proper installation and to acquaint you a bit further with the assembly and care of this equipment. We suggest that these instructions be read carefully and reviewed by everyone whenever involved in the actual installation and operation of the mill. In reading these general instructions, you may at times feel that they cover items which are elementary and perhaps not worthy of mention; however in studying hundreds of installations, it has been found that very often minor points are overlooked due to pressure being exerted by outside influences to get the job done in a hurry. The erection phase of this mill is actually no place to attempt cost savings by taking short cuts, or by-passing some of the work. A good installation will pay dividends for many years to come by reduced maintenance cost.With the modern practice of specialized skills and trades, there is often a line drawn between responsibilities of one crew of erectors and another. Actually the responsibility of installation does not cease with the completion of one phase nor does it begin with the starting of another. Perhaps a simple rule to adopt would be DO NOT TAKE ANYTHING FOR GRANTED. This policy of rechecking previously done work will help guarantee each step of the erection and it will carefully coordinate and tie it into subsequent erection work. To clarify or illustrate this point, take the example of concrete workers completing their job and turning it over to the machinist or millwright. The latter group should carefully check the foundation for soundness and correctness prior to starting their work.
Sound planning and good judgement will, to a great extent, be instrumental in avoiding many of the troublesome occurrences especially at the beginning of operations. While it is virtually impossible to anticipate every eventuality, nevertheless it is the intention of this manual to outline a general procedure to follow in erecting the mill, and at the same time, point out some of the pitfalls which should be avoided.
Before starting the erection of the mill, adequate handling facilities should be provided or made available, bearing in mind the weights and proportions of the various parts and sub-assemblies. This information can be ascertained from the drawings and shipping papers.
The gearing, bearings, and other machined surfaces have been coated with a protective compound, and should be cleaned thoroughly with a solvent, such as Chlorothene, (made by Dow Chemical). Judgement should be exercised as to the correct time and place for cleaning the various parts. Do not permit solvents, oil or grease to come in contact with the roughened top surfaces of the concrete foundation where grouting is to be applied; otherwise proper bonding will not result.
After cleaning the various parts, the gear and pinion teeth, trunnion journals and bearings, shafting and such, should be protected against rusting or pitting as well as against damage from falling objects or weld splatter. All burrs should be carefully removed by filing or honing.
Unless otherwise arranged for, the mill has been completely assembled in our shop. Before dismantling, the closely fitted parts were match marked, and it will greatly facilitate field assembly to adhere to these match marks.
The surfaces of all connecting joints or fits, such as shell and head flanges, trunnion flanges, trunnion liner and feeder connecting joints, should be coated with a NON-SETTING elastic compound, such as Quigley O-Seal, or Permatex to insure against leakage and to assist in drawing them up tight. DO NOT USE WHITE LEAD OR GREASE.
Parts which are affected by the hand of the mill are easily identified by referring to the parts list. In general they include the feeder, feed trunnion liner, discharge trunnion liner if it is equipped with a spiral, spiral type helical splitter, and in some cases the pan liners when they are of the spiral type. When both right and left hand mills are being assembled, it is imperative that these parts which involve hand be assembled in the correct mill.
Adequate foundations for any heavy equipment, and in particular grinding mills, are extremely important to assure proper operation. The foundation should preferably be in one piece, that is, with a reinforced slab footing (so called mat) extending under both trunnion bearing foundations as well as the pinion bearing foundation. If possible or practical, it should be extended to include also the motor and drive. With this design, in the event of some movement, the mill and foundation will tend to move as a unit. ANY SLIGHT SETTLING OF FOUNDATIONS WILL CAUSE BEARING AND GEAR MISALIGNMENT, resulting in excessive wear and higher maintenance costs. It has been found that concrete foundations on a weight basis should be at least 1 times the total weight of the grinding mill with its grinding media.
Allowable bearing pressure between concrete footings and the soil upon which the foundation rests should first be considered. The center of pressure must always pass through the center of the footing. Foundations subject to shock should be designed with less unit pressure than foundations for stationary loads. High moisture content in soils reduces the amount of allowable specific pressure that the ground can support. The following figures may be used for preliminary foundation calculations.
Portland cement mixed with sand and aggregate in the proper proportions has come to be standard practice in making concrete. For general reference cement is usually shipped in sacks containing one cubic foot of material. A barrel usually holds 4 cubic feet. Cement will deteriorate with age and will quickly absorb moisture so it should be stored in a dry place. For best results the sand and gravel used should be carefully cleaned free of humus, clay, vegetal matter, etc.
Concrete may be made up in different mixtures having different proportions of sand and aggregate. These are expressed in parts for example a 1:2:4 mixture indicates one bag of cement, 2 cubic feet of sand, and 4 cubic feet of gravel. We recommend a mixture of 1:2:3 for ball mill and rod mill foundations. The proper water to sand ratio should be carefully regulated since excess water increases the shrinkage in the concrete and lends to weaken it even more than a corresponding increase in the aggregate. Between 5 to 8 gallons of water to a sack of cement is usually recommended, the lower amount to be used where higher strength is required or where the concrete will be subject to severe weathering conditions.
Detailed dimensions for the concrete foundation are covered by the foundation plan drawing submitted separately. The drawing also carries special instructions as to the allowance for grouting, steel reinforcements, pier batter, foundation bolts and pipes. During concrete work, care should be taken to prevent concrete entering the pipes, surrounding the foundations bolts, which would limit the positioning of the bolts when erecting the various assemblies. Forms should be adequately constructed and reinforced to prevent swell, particularly where clearance is critical such as at the drive end where the gear should clear the trunnion bearing and pinion bearing piers.
For convenience in maintenance, the mill foundations should be equipped with jacking piers. These will allow the lifting of one end of the mill by use of jacks in the event maintenance must be carried out under these conditions.
Adequate foundations for any heavy equipment, and in particular Marcy grinding mills, are extremely important to assure proper operation of that equipment. Any slight settling of foundations will cause bearing and gear misalignment, resulting in excessive wear and higher maintenance costs. It has been found that concrete foundations on a weight basis should be approximately 1 times the total weight of the grinding mill with its grinding media.
Allowable bearing pressure between concrete footings and the soil upon which the foundation rests should first be considered. The center of pressure must always pass through the center of the footing. Foundations subject to shock should be designed with less unit pressures than foundations for stationary loads. High moisture content in soils reduces the amount of allowable pressure that that material can support. The following figures may be used for quick foundation calculations:
Portland cement mixed with sand and aggregate in the proper proportions has come to be standard practice in making concrete. For general reference cement is usually shipped in sacks containing one cubic foot of material. A barrel usually consists of 4 cubic feet. Cement will deteriorate with age and will quickly absorb moisture so it should be stored in a cool, dry place. The sand and gravel used should be carefully cleaned for best results to be sure of minimizing the amount of sedimentation in that material.
Concrete may be made up in different mixtures having different proportions of sand and aggregate. These are expressed in parts for example a 1:2:4 mixture indicates one bag of cement, 2 cubic feet of sand, and 4 cubic feet of gravel. We recommend a mixture of 1:2:3 for ball mill and rod mill foundations. The proper water to sand ratio should be carefully regulated since excess water will tend to weaken the concrete even more than corresponding variations in other material ratios. Between 5 to 8 gallons of water to a sack of cement is usually recommended, the lower amount to be used where higher strength is required or where the concrete will be subject to severe weathering conditions.
We recommend the use of a non-shrinking grout, and preferably of the pre-mixed type, such as Embeco, made by the Master Builders Company of Cleveland, Ohio. Thoroughly clean the top surfaces of the concrete piers, and comply with the instructions of the grouting supplier.
1. Establish vertical and horizontal centerline of mill and pinion shaftagainst the effects of this, we recommend that the trunnion bearing sole plate be crowned so as to be higher at the center line of the mill. This is done by using a higher shim at the center than at the endsand tightening the foundation bolts of both ends.
After all shimming is completed, the sole plate and bases should be grouted in position. Grouting should be well tamped and should completely fill the underside of the sole plate and bases. DO NOT REMOVE THE SHIMS AFTER OR DURING GROUTING. When the grout has hardened sufficiently it is advisable to paint the top surfaces of the concrete so as to protect it against disintegration due to the absorption of oil or grease.
If it is felt that sufficient accuracy in level between trunnion bearing piers cannot be maintained, we recommend that the grouting of the sole plate under the trunnion bearing opposite the gear end be delayed until after the mill is in place. In this way, the adjustment by shimming at this end can be made later to correct for any errors in elevation. Depending on local climatic conditions, two to seven days should he allowed for the grouting to dry and set, before painting or applying further loads to the piers.
Pinion bearings are provided of either the sleeve type or anti-friction type. Twin bearing construction may use either individual sole plates or a cast common sole plate. The unit with a common sole plate is completely assembled in our shop and is ready for installation. Normal inspection and cleaning procedure should be followed. Refer to the parts list for general assembly. These units are to be permanently grouted in position and, therefore, care should be taken to assure correct alignment.
The trunnion bearing assemblies can now be mounted on their sole plates. If the bearings are of the swivel type, a heavy industrial water-proof grease should be applied to the spherical surfaces of both the swivels and the bases. Move the trunnion bearings to their approximate position by adjustment of the set screws provided for this purpose.
In the case of ball mills, all internal wearing parts will pass through the manhole, whereas in the case of open end rod mills they will pass through the discharge trunnion opening. When lining the shell, start with the odd shaped pieces around the manhole opening if manholes are furnished. Rubber shell liner backing should be used with all cast type rod mills shell liners. If the shell liners are of the step type, they should be assembled with the thin portion, or toe, as the leading edge with respect to rotation of the mill.
Lorain liners for the shell are provided with special round head bolts, with a waterproof washer and nut. All other cast type liners for the head and shell are provided with oval head bolts with a cut washer and nuts. Except when water proof washers are used, it is advisable to wrap four or five turns of candle wicking around the shank of the bolt under the cut washer. Dip the candle wicking in white lead. All liner bolt threads should be dipped in graphite and oil before assembly. All liner bolt cuts should be firmly tightened by use of a pipe extension on a wrench, or better yet, by use of a torque wrench. The bolt heads should be driven firmly into the bolt holes with a hammer.
In order to minimise the effect of pulp race, we recommend that the spaces between the ends of the shell liners and the head liners or grates be filled with suitable packing. This packing may be in the form of rubber belting, hose, rope or wood.
If adequate overhead crane facilities are available, the heads can be assembled to the shell with the flange connecting bolts drawn tightly. Furthermore, the liners can be in place, as stated above, and the gear can be mounted, as covered by separate instructions. Then the mill can be taken to its location and set in place in the trunnion bearings.
If on the other hand the handling facilities are limited it is recommended that the bare shell and heads be assembled together in a slightly higher position than normal. After the flange bolts are tightened, the mill proper should be lowered into position. Other intermediate methods may be used, depending on local conditions.
In any event, just prior to the lowering of the mill into the bearings the trunnion journal and bushing and bases should be thoroughly cleaned and greased. Care should be taken not to foul the teeth in the gear or pinion. Trunnion bearing caps should be immediately installed, although not necessarily tightened, to prevent dirt settling on the trunnions. The gear should be at least tentatively covered for protection.
IMPORTANT. Unless the millwright or operator is familiar with this type of seal, there is a tendency to assume that the oil seal is too long because of its appearance when held firmly around the trunnion. It is not the function of the brass oil seal band to provide tension for effective sealing. This is accomplished by the garter spring which is provided with the oil seal.
Assemble the oil seal with the spring in place, and with the split at the top. Encircle the oil seal with the band, keeping the blocks on the side of the bearing at or near the horizontal center line so that when in place they will fit between the two dowel pins on the bearing, which are used to prevent rotation of the seal.
Moderately tighten up the cap screws at the blocks, pulling them together to thus hold the seal with its spring in place. If the blocks cannot be pulled snuggly together, then the oil seal may be cut accordingly. Oil the trunnion surface and slide the entire seal assembly back into place against the shoulder of the bearing and finish tightening. Install the retainer ring and splash ring as shown.
In most cases the trunnion liners are already mounted in the trunnions of the mills. If not, they should be assembled with attention being given to match marks or in some cases to dowel pins which are used to locate the trunnion liners in their proper relation to other parts.
If a scoop feeder, combination drum scoop feeder or drum feeder is supplied with the mill, it should be mounted on the extended flange of the feed trunnion liner, matching the dowel pin with its respective hole. The dowel pin arrangement is provided only where there is a spiral in the feed trunnion liner. This matching is important as it fixes the relationship between the discharge from the scoop and the internal spiral of the trunnion liner. Tighten the bolts attaching the feeder to the trunnion liner evenly, all around the circle, seating the feeder tightly and squarely on its bevelled seat. Check the bolts holding the lips and other bolts that may require tightening. The beveled seat design is used primarily where a feeder is provided for the trunnion to trunnion liner connection, and the trunnion liner to feeder connection. When a feeder is not used these connecting joints are usually provided by a simple cylindrical or male and female joint.
If a spout feeder is to be used, it is generally supplied by the user, and should be mounted independently of the mill. The spout should project inside the feed trunnion liner, but must not touch the liner or spiral.
Ordinarily the feed box for a scoop tender is designed and supplied by the user. The feed box should be so constructed that it has at least 6 clearance on both sides and at the bottom of the scoop. This clearance is measured from the outside of the feed scoop.
The feed box may be constructed of 2 wood, but more often is made of 3/16 or plate steel reinforced with angles. In the larger size mills, the lower portion is sometimes made of concrete. Necessary openings should be provided for the original feed and the sand returns from the classifiers when in closed circuit.
A plate steel gear guard is furnished with the mill for safety in operation and to protect the gear and pinion from dirt or grit. As soon as the gear and pinion have been cleaned and coated with the proper lubricant, the gear guard should be assembled and set on its foundation.
Most Rod Mills are provided with a discharge housing mechanism mounted independently of the mill. This unit consists of the housing proper, plug door, plug shaft, arm, and various hinge pins and pivot and lock pins. The door mechanism is extra heavy throughout and is subject to adjustment as regard location. Place the housing proper on the foundation, level with steel shims and tighten the foundation bolts. The various parts may now be assembled to the housing proper and the door plug can be swung into place, securing it with the necessary lock pins.
After the mill has been completely assembled and aligned, the door mechanism centered and adjusted, and all clearances checked, the housing base can be grouted. The unit should be so located both vertically and horizontally so as to provide a uniform annular opening between the discharge plug door and the head liners.
In some cases because of space limitation, economy reasons, etc., the mill is not equipped with separate discharge housing. In such a case, the open end low discharge principal is accomplished by means of the same size opening through the discharge trunnion but with the plug door attached to lugs on the head liner segments or lugs on the discharge trunnion liner proper. In still other cases, it is sometimes effected by means of an arm holding the plug and mounted on a cross member which is attached to the bell of the discharge trunnion liner. In such cases as those, a light weight sheet steel discharge housing is supplied by the user to accommodate the local plant layout in conjunction with the discharge launder.
TRUNNION BEARING LUBRICATION. For the larger mills with trunnion bearings provided with oil seals, we recommend flood oil lubrication. This can be accomplished by a centralized system for two or more mills, or by an individual system for each mill. We recommend the individual system for each mill, except where six or more mills are involved, or when economy reasons may dictate otherwise.
In any event oil flow to each trunnion bearing should be between 3 to 5 gallons per minute. The oil should be adequately filtered and heaters may be used to maintain a temperature which will provide proper filtration and maintain the necessary viscosity for adequate flow. The lines leading from the filter to the bearing should be of copper tubing or pickled piping. The drain line leading from the bearings to the storage or sump tank should be of adequate size for proper flow, and they should be set at a minimum slope of per foot, perferably per foot. Avoid unnecessary elbows and fittings wherever possible. Avoid bends which create traps and which might accumulate impurities. All lines should be thoroughly cleaned and flushed with a solvent, and then blown free with air, before oil is added.
It is advisable to interlock the oil pump motor with the mill motor in such a way that the mill cannot be started until after the oil pump is operating. We recommend the use of a non-adjuslable valve at each bearing to prevent tampering.
When using the drip oil system it is advisable to place wool yarn or waste inside a canvas porous bag to prevent small pieces of the wool being drawn down into the trunnion journal. If brick grease is used, care should be taken in its selection with regard to the range of its effective temperature. In other words, it should be pointed out that brick grease is generally designed for a specific temperature range. Where the bearing temperature does not come up to the minimum temperature rating of the brick grease, the oil will not flow from it, and on the other hand if the temperature of the bearing exceeds the maximum temperature rating of the brick grease, the brick is subject to glazing; therefore, blinding off of the oil. This brick should be trimmed so that it rests freely on the trunnion journal, and does not hang up, or bind on the sides of the grease box.
When replacing the brick grease, remove the old grease completely. Due to the extended running time of brick grease, there is usually an accumulation of impurities and foreign matter on the top surface, which is detrimental to the bearing.
Where anti-friction bearings are supplied, they are adequately sealed for either grease or oil lubrication. If a flood system is used for the trunnion bearings and it is adequately filtered, it can then be used for pinion bearings with the same precautions taken as mentioned above, with a flow of to 1 gallons per minute to each bearing.
These lubricants can be applied by hand, but we highly recommend some type of spray system, whether it be automatic, semi-automatic or manually operated. It has been found that it is best to lubricate gears frequently with small quantities.
Start the lubrication system and run it for about ten minutes, adjusting the oil flow at each bearing. Check all of the bolts and nuts on the mill for tightness and remove all ladders, tools and other obstructions prior to starting the mill.
Before starting the mill, even though it is empty, we recommend that it be jogged one or two revolutions for a check as to clearance of the gear and its guard, splash rings, etc. The trunnion journal should also be checked for uniform oil film and for any evidence of foreign material which might manifest itself through the appearance of scratches on the journal. If there are any scratches, it is very possible that some foreign material such as weld splatter may have been drawn down into the bushing, and can be found imbedded there. These particles should be removed before proceeding further.
If everything is found to be satisfactory, then the mill should be run for ten to fifteen minutes, and stopped. The trunnion bearings should be checked for any undue temperature and the gear grease pattern can be observed for uniformity which would indicate correct alignment.
It should be noted that with an empty mill the reactions and operating characteristics of the bearings and gearing at this point are somewhat different than when operating with a ball or rod charge. Gear noises will be prominent and some vibration will occur due to no load and normal back-lash. Furthermore, it will be found that the mill will continue to rotate for some time after the power is shut off. Safety precautions should therefore he observed, and no work should be done on the mill until it has come to a complete stop.
We have now reached the point where a half ball or rod charge can be added, and the mill run for another six to eight hours, feeding approximately half the anticipated tonnage. The mill should now be stopped, end the gear grease pattern checked, and gear and pinion mesh corrected, if necessary, according to separate instructions.
The full charge of balls or rods can now be added, as well as the full amount of feed, and after a run of about four to six days, ALL BOLTS SHOULD AGAIN BE RETIGHTENED, and the gear and pinion checked again, and adjusted if necessary.
Where starting jacks are provided for the trunnion bearings of the larger sized mills, they should be filled with the same oil that is used for the lubrication of the trunnion bearings. Before starting the mill they should be pumped so as to insure having an oil film between the journal and the bushing.
When relining any part of the mill, clean away all sand from the parts to be relined before putting in the new liners. For the head liners and shell liners you may then proceed in the same manner used at the time of the initial assembly.
Before relining the grate type discharge head, it is advisable to refer to the assembly drawings and the parts list.Because of such limitations as the size of the manhole opening, and for various other reasons, it will be found that the center discharge liner and cone designs vary. The cone may be a separate piece or integral with either the trunnion liner, or the router discharge liner. Furthermore, it will be found in some mills that the center discharge liner is held by bolts through the discharge head, whereas in other cases it depends upon the clamping effect of grates to hold it in position. In any event, the primary thing to remember in assembling the discharge grate head parts is the fact that the grate should be first drawn up tightly towards the center discharge liner by adjusting the grate set screws located at the periphery of the discharge head. This adjustment should be carried out in progressive steps, alternating at about 180 if possible and in such a manner that, the center discharge liner does not become dislodged from its proper position at the center of the mill. These grate set screws should be adjusted with the side clamp bar bolts loosened. After the grates have been completely tightened with the set screws, check for correct and uniform position of each grate section. The side clamp bar bolts may now be lightened, again using an alternate process. This should result in the side clamp bars firmly bearing against the beveled sides of the grates. The side clamp bars should not hear against the lifter liners.
When new pan liners are installed, they should be grouted in position so as to prevent pulp race in the void space between the discharge head and the pan liner. Another good method of preventing this pulp race is the use of the sponge rubber which can be cemented in place.
After the mill is erected, in order to avoid overlooking both obvious and obscure installation details, we recommend the use of a check list. This is particularly recommended for multiple mill installations where it is difficult to control the different phases of installation for each and every mill. Such a check list can be modeled after the following:
No. 1 Connecting Bolts drawn tight. A. Head and Shell flange bolts. B. Gear Connecting, bolts. No. 2 Trunnion studs or bolts drawn up tight. No. 3 Trunnion liner and feeder connecting bolts or studs drawn up tight. No. 4 Feeder lip bolts tightened. No. 5 Liner bolts drawn up tight. No. 6 Gear. A. Concentric B. Backlash C. Runout D. Joint bolts drawn up tight. No. 7 Coupling and Drive alignment and lubrication. No. 8 Bearings and Gearing cleaned and lubricated. No. 9 Lubrication system in working order with automatic devices including alarms and interlocking systems.
We further recommend that during the first thirty to sixty days of operation, particular attention be given to bolt tightness, foundation settlement and condition of the grouting. We suggest any unusual occurrence be recorded so that should trouble develop later there may be a clue which would simplify diagnosing and rectifying the situation.
As a safety precaution, and in many cases in order to comply with local safety regulations, guards should be used to protect the operators and mechanics from contact with moving parts. However, these guards should not be of such a design that will prevent or hinder the close inspection of the vital parts. Frequent inspection should be made at regular intervals with particular attention being given to the condition of the wearing parts in the mill. In this way, you will be better able to anticipate your needs for liners and other parts in time to comply with the current delivery schedules.
When ordering repair or replacement parts for your mill, be sure to identify the parts with the number and description as shown on the repair parts list, and specify the hand and serial number of the mill.
By following the instructions outlined in this manual, mechanical malfunctions will be eliminated. However, inadvertent errors may occur even under, the most careful supervision. With this in mind, it is possible that some difficulties may arise. Whenever any abnormal mechanical reactions are found, invariably they can be attributed to causes which though sometimes obvious are often hidden. We sight herewith the most common problems, with their solutions.
Cause A GROUT DISINTEGRATION. Very often when the grouting is not up to specification the vibration from the mill tends to disintegrate the grouting. In most instances the disintegration starts between the sole plate and the top surface of the grouting near or at the vertical centerline of the mill. As this continues, the weight of the mill causes the sole plate and trunnion bearing base to bend with a resultant pinching action at the side of the bearing near the horizontal center line of the mill. This pinching will cut off and wipe the oil film from the journal and will manifest itself in the same manner as if the lubrication supply had been cut off. If the grout disintegration is limited to about . 050 and does not appear to be progressing further, the situation can be corrected by applying a corresponding amount of shimming between the trunnion bearing base and the sole plate near the centerline of the mill in such a fashion that the trunnion bearing base has been returned to its normal dimensional position. If, on the other hand, the grouting is in excess of . 050 and appears to be progressing further, it is advisable to shut down operations until the sole plate has been re grouted.
Cause B HIGH SPOT ON THE BUSHING. While all BallMill bushings are scraped in the shop to fit either a jig mandrel or the head proper to which it is to be fitted, nevertheless there is a certain amount of seasoning and dimensional change which goes on in the type of metals used. Therefore if high spots are found, the mill should be raised, the bushings removed and rescraped. Bluing may be used to assist in detecting high spots.
Cause C INSUFFICIENT OIL FLOW. Increase the oil supply if it is a flood oil system. If brick grease is used, it is possible that the particular grade of brick may not be applicable to the actual bearing temperature. Refer to the remarks in this manual under the paragraph entitled Lubrication.
Cause E EXCESSIVE RUBBING ON THE SIDE OF THE BUSHING. This comes about due to the improper setting of the bearings in the longitudinal plane. In some cases, particularly on dry grinding or hot clinker grinding mills, the expansion of the mills proper may account for this condition. In any event, it can be remedied by re-adjusting the bearing base on the sole plate longitudinally at the end opposite the drive.
There are many more lubricant suppliers, such as E. F. Houghton and Co. , or Lubriplate Division of Fiske Bros. Refining Co. In making your final selection of lubricants, you should consider the actual plant conditions as well as the standardization of lubricants. New and improved lubricants are being marketed, and we, therefore, suggest that you consult your local suppliers.
A mill is a grinder used to grind and blend solid or hard materials into smaller pieces by means of shear, impact and compression methods. Grinding mill machine is an essential part of many industrial processes, there are mainly five types of mills to cover more than 90% materials size-reduction applications.
Do you the difference between the ball mill, rod mills, SAG mill, tube mill, pebble mill? In the previous article, I made a comparison of ball mill and rod mill. Today, we will learn about the difference between SAG mill vs ball mill.
AG/SAG is short for autogenous mill and semi-autogenous mill, it combines with two functions of crushing and grinding, uses the ground material itself as the grinding media, through the mutual impact and grinding action to gradually reduce the material size. SAG mill is usually used to grind large pieces into small pieces, especially for the pre-processing of grinding circuits, thus also known as primary stage grinding machine. Based on the high throughput and coarse grind, AG mills produce coarse grinds often classify mill discharge with screens and trommel. SAG mills grinding media includes some large and hard rocks, filled rate of 9% 20%. SAG mill grind ores through impact, attrition, abrasion forces. In practice, for a given ore and equal processing conditions, the AG milling has a finer grind than SAG mills.
The working principle of the self-grinding machine is basically the same as the ball mill, the biggest difference is that the sag grinding machine uses the crushed material inside the cylinder as the grinding medium, the material constantly impacts and grinding to gradually pulverize. Sometimes, in order to improve the processing capacity of the mill, a small amount of steel balls be added appropriately, usually occupying 2-3% of the volume of the mill (that is semi-autogenous grinding).
High capacity Ability to grind multiple types of ore in various circuit configurations, reduces the complexity of maintenance and coordination. Compared with the traditional tumbling mill, the autogenous mill reduces the consumption of lining plates and grinding media, thus have a lower operation cost. The self-grinding machine can grind the material to 0.074mm in one time, and its content accounts for 20% ~ 50% of the total amount of the product. Grinding ratio can reach 4000 ~ 5000, more than ten times higher than ball, rod mill.
Ball mills are fine grinders, have horizontal ball mill and vertical ball mill, their cylinders are partially filled with steel balls, manganese balls, or ceramic balls. The material is ground to the required fineness by rotating the cylinder causing friction and impact. The internal machinery of the ball mill grinds the material into powder and continues to rotate if extremely high precision and precision is required.
The ball mill can be applied in the cement production plants, mineral processing plants and where the fine grinding of raw material is required. From the volume, the ball mill divide into industrial ball mill and laboratory use the small ball mill, sample grinding test. In addition, these mills also play an important role in cold welding, alloy production, and thermal power plant power production.
The biggest characteristic of the sag mill is that the crushing ratio is large. The particle size of the materials to be ground is 300 ~ 400mm, sometimes even larger, and the minimum particle size of the materials to be discharged can reach 0.1 mm. The calculation shows that the crushing ratio can reach 3000 ~ 4000, while the ball mills crushing ratio is smaller. The feed size is usually between 20-30mm and the product size is 0-3mm.
Both the autogenous grinding mill and the ball mill feed parts are welded with groove and embedded inner wear-resistant lining plate. As the sag mill does not contain grinding medium, the abrasion and impact on the equipment are relatively small.
The feed of the ball mill contains grinding balls. In order to effectively reduce the direct impact of materials on the ball mill feed bushing and improve the service life of the ball mill feed bushing, the feeding point of the groove in the feeding part of the ball mill must be as close to the side of the mill barrel as possible. And because the ball mill feed grain size is larger, ball mill feeding groove must have a larger slope and height, so that feed smooth.
Since the power of the autogenous tumbling mill is relatively small, it is appropriate to choose dynamic and static pressure bearing. The ball bearing liner is made of lead-based bearing alloy, and the back of the bearing is formed with a waist drum to form a contact centering structure, with the advantages of flexible movement. The bearing housing is lubricated by high pressure during start-up and stop-up, and the oil film is formed by static pressure. The journal is lifted up to prevent dry friction on the sliding surface, and the starting energy moment is reduced. The bearing lining is provided with a snake-shaped cooling water pipe, which can supply cooling water when necessary to reduce the temperature of the bearing bush. The cooling water pipe is made of red copper which has certain corrosion resistance.
Ball mill power is relatively large, the appropriate choice of hydrostatic sliding bearing. The main bearing bush is lined with babbitt alloy bush, each bush has two high-pressure oil chambers, high-pressure oil has been supplied to the oil chamber before and during the operation of the mill, the high-pressure oil enters the oil chamber through the shunting motor, and the static pressure oil film is compensated automatically to ensure the same oil film thickness To provide a continuous static pressure oil film for mill operation, to ensure that the journal and the bearing Bush are completely out of contact, thus greatly reducing the mill start-up load, and can reduce the impact on the mill transmission part, but also can avoid the abrasion of the bearing Bush, the service life of the bearing Bush is prolonged. The pressure indication of the high pressure oil circuit can be used to reflect the load of the mill indirectly. When the mill stops running, the high pressure oil will float the Journal, and the Journal will stop gradually in the bush, so that the Bush will not be abraded. Each main bearing is equipped with two temperature probe, dynamic monitoring of the bearing Bush temperature, when the temperature is greater than the specified temperature value, it can automatically alarm and stop grinding. In order to compensate for the change of the mill length due to temperature, there is a gap between the hollow journal at the feeding end and the bearing Bush width, which allows the journal to move axially on the bearing Bush. The two ends of the main bearing are sealed in an annular way and filled with grease through the lubricating oil pipe to prevent the leakage of the lubricating oil and the entry of dust.
The end cover of the autogenous mill is made of steel plate and welded into one body; the structure is simple, but the rigidity and strength are low; the liner of the autogenous mill is made of high manganese steel.
The end cover and the hollow shaft can be made into an integral or split type according to the actual situation of the project. No matter the integral or split type structure, the end cover and the hollow shaft are all made of Casting After rough machining, the key parts are detected by ultrasonic, and after finishing, the surface is detected by magnetic particle. The surface of the hollow shaft journal is Polished after machining. The end cover and the cylinder body are all connected by high-strength bolts. Strict process measures to control the machining accuracy of the joint surface stop, to ensure reliable connection and the concentricity of the two end journal after final assembly. According to the actual situation of the project, the cylinder can be made as a whole or divided, with a flanged connection and stop positioning. All welds are penetration welds, and all welds are inspected by ultrasonic nondestructive testing After welding, the whole Shell is returned to the furnace for tempering stress relief treatment, and after heat treatment, the shell surface is shot-peened. The lining plate of the ball mill is usually made of alloy material.
The transmission part comprises a gear and a gear, a gear housing, a gear housing and an accessory thereof. The big gear of the transmission part of the self-grinding machine fits on the hollow shaft of the discharge material, which is smaller in size, but the seal of the gear cover is not good, and the ore slurry easily enters the hollow shaft of the discharge material, causing the hollow shaft to wear.
The big gear of the ball mill fits on the mill shell, the size is bigger, the big gear is divided into half structure, the radial and axial run-out of the big gear are controlled within the national standard, the aging treatment is up to the standard, and the stress and deformation after processing are prevented. The big gear seal adopts the radial seal and the reinforced big gear shield. It is welded and manufactured in the workshop. The geometric size is controlled, the deformation is prevented and the sealing effect is ensured. The small gear transmission device adopts the cast iron base, the bearing base and the bearing cap are processed at the same time to reduce the vibration in operation. Large and small gear lubrication: The use of spray lubrication device timing quantitative forced spray lubrication, automatic control, no manual operation. The gear cover is welded by profile steel and high-quality steel plate. In order to enhance the stiffness of the gear cover, the finite element analysis is carried out, and the supporting structure is added in the weak part according to the analysis results.
The self-mill adopts the self-return device to realize the discharge of the mill. The self-returning device is located in the revolving part of the mill, and the material forms a self-circulation in the revolving part of the mill through the self-returning device, discharging the qualified material from the mill, leading the unqualified material back into the revolving part to participate in the grinding operation.
The ball mill adopts a discharge screen similar to the ball mill, and the function of blocking the internal medium of the overflow ball mill is accomplished inside the rotary part of the ball mill. The discharge screen is only responsible for forcing out a small amount of the medium that overflows into the discharge screen through the internal welding reverse spiral, to achieve forced discharge mill.
The slow drive consists of a brake motor, a coupling, a planetary reducer and a claw-type clutch. The device is connected to a pinion shaft and is used for mill maintenance and replacement of liners. In addition, after the mill is shut down for a long time, the slow-speed transmission device before starting the main motor can eliminate the eccentric load of the steel ball, loosen the consolidation of the steel ball and materials, ensure safe start, avoid overloading of the air clutch, and play a protective role. The slow-speed transmission device can realize the point-to-point reverse in the electronic control design. When connecting the main motor drive, the claw-type Clutch automatically disengages, the maintenance personnel should pay attention to the safety.
The slow drive device of the ball mill is provided with a rack and pinion structure, and the operating handle is moved to the side away from the cylinder body The utility model not only reduces the labor intensity but also ensures the safety of the operators.
In all ore dressing and milling Operations, including flotation, cyanidation, gravity concentration, and amalgamation, the Working Principle is to crush and grind, often with rob mill & ball mills, the ore in order to liberate the minerals. In the chemical and process industries, grinding is an important step in preparing raw materials for subsequent treatment.In present day practice, ore is reduced to a size many times finer than can be obtained with crushers. Over a period of many years various fine grinding machines have been developed and used, but the ball mill has become standard due to its simplicity and low operating cost.
A ball millefficiently operated performs a wide variety of services. In small milling plants, where simplicity is most essential, it is not economical to use more than single stage crushing, because the Steel-Head Ball or Rod Mill will take up to 2 feed and grind it to the desired fineness. In larger plants where several stages of coarse and fine crushing are used, it is customary to crush from 1/2 to as fine as 8 mesh.
Many grinding circuits necessitate regrinding of concentrates or middling products to extremely fine sizes to liberate the closely associated minerals from each other. In these cases, the feed to the ball mill may be from 10 to 100 mesh or even finer.
Where the finished product does not have to be uniform, a ball mill may be operated in open circuit, but where the finished product must be uniform it is essential that the grinding mill be used in closed circuit with a screen, if a coarse product is desired, and with a classifier if a fine product is required. In most cases it is desirable to operate the grinding mill in closed circuit with a screen or classifier as higher efficiency and capacity are obtained. Often a mill using steel rods as the grinding medium is recommended, where the product must have the minimum amount of fines (rods give a more nearly uniform product).
Often a problem requires some study to determine the economic fineness to which a product can or should be ground. In this case the 911Equipment Company offers its complete testing service so that accurate grinding mill size may be determined.
Until recently many operators have believed that one particular type of grinding mill had greater efficiency and resulting capacity than some other type. However, it is now commonly agreed and accepted that the work done by any ballmill depends directly upon the power input; the maximum power input into any ball or rod mill depends upon weight of grinding charge, mill speed, and liner design.
The apparent difference in capacities between grinding mills (listed as being the same size) is due to the fact that there is no uniform method of designating the size of a mill, for example: a 5 x 5 Ball Mill has a working diameter of 5 inside the liners and has 20 per cent more capacity than all other ball mills designated as 5 x 5 where the shell is 5 inside diameter and the working diameter is only 48 with the liners in place.
Ball-Rod Mills, based on 4 liners and capacity varying as 2.6 power of mill diameter, on the 5 size give 20 per cent increased capacity; on the 4 size, 25 per cent; and on the 3 size, 28 per cent. This fact should be carefully kept in mind when determining the capacity of a Steel- Head Ball-Rod Mill, as this unit can carry a greater ball or rod charge and has potentially higher capacity in a given size when the full ball or rod charge is carried.
A mill shorter in length may be used if the grinding problem indicates a definite power input. This allows the alternative of greater capacity at a later date or a considerable saving in first cost with a shorter mill, if reserve capacity is not desired. The capacities of Ball-Rod Mills are considerably higher than many other types because the diameters are measured inside the liners.
The correct grinding mill depends so much upon the particular ore being treated and the product desired, that a mill must have maximum flexibility in length, type of grinding medium, type of discharge, and speed.With the Ball-Rod Mill it is possible to build this unit in exact accordance with your requirements, as illustrated.
To best serve your needs, the Trunnion can be furnished with small (standard), medium, or large diameter opening for each type of discharge. The sketch shows diagrammatic arrangements of the four different types of discharge for each size of trunnion opening, and peripheral discharge is described later.
Ball-Rod Mills of the grate discharge type are made by adding the improved type of grates to a standard Ball-Rod Mill. These grates are bolted to the discharge head in much the same manner as the standard headliners.
The grates are of alloy steel and are cast integral with the lifter bars which are essential to the efficient operation of this type of ball or rod mill. These lifter bars have a similar action to a pump:i. e., in lifting the product so as to discharge quickly through the mill trunnion.
These Discharge Grates also incorporate as an integral part, a liner between the lifters and steel head of the ball mill to prevent wear of the mill head. By combining these parts into a single casting, repairs and maintenance are greatly simplified. The center of the grate discharge end of this mill is open to permit adding of balls or for adding water to the mill through the discharge end.
Instead of being constructed of bars cast into a frame, Grates are cast entire and have cored holes which widen toward the outside of the mill similar to the taper in grizzly bars. The grate type discharge is illustrated.
The peripheral discharge type of Ball-Rod Mill is a modification of the grate type, and is recommended where a free gravity discharge is desired. It is particularly applicable when production of too many fine particles is detrimental and a quick pass through the mill is desired, and for dry grinding.
The drawings show the arrangement of the peripheral discharge. The discharge consists of openings in the shell into which bushings with holes of the desired size are inserted. On the outside of the mill, flanges are used to attach a stationary discharge hopper to prevent pulp splash or too much dust.
The mill may be operated either as a peripheral discharge or a combination or peripheral and trunnion discharge unit, depending on the desired operating conditions. If at any time the peripheral discharge is undesirable, plugs inserted into the bushings will convert the mill to a trunnion discharge type mill.
Unless otherwise specified, a hard iron liner is furnished. This liner is made of the best grade white iron and is most serviceable for the smaller size mills where large balls are not used. Hard iron liners have a much lower first cost.
Electric steel, although more expensive than hard iron, has advantage of minimum breakage and allows final wear to thinner section. Steel liners are recommended when the mills are for export or where the source of liner replacement is at a considerable distance.
Molychrome steel has longer wearing qualities and greater strength than hard iron. Breakage is not so apt to occur during shipment, and any size ball can be charged into a mill equipped with molychrome liners.
Manganese liners for Ball-Rod Mills are the world famous AMSCO Brand, and are the best obtainable. The first cost is the highest, but in most cases the cost per ton of ore ground is the lowest. These liners contain 12 to 14% manganese.
The feed and discharge trunnions are provided with cast iron or white iron throat liners. As these parts are not subjected to impact and must only withstand abrasion, alloys are not commonly used but can be supplied.
Gears for Ball-Rod Mills drives are furnished as standard on the discharge end of the mill where they are out of the way of the classifier return, scoop feeder, or original feed. Due to convertible type construction the mills can be furnished with gears on the feed end. Gear drives are available in two alternative combinations, which are:
All pinions are properly bored, key-seated, and pressed onto the steel countershaft, which is oversize and properly keyseated for the pinion and drive pulleys or sheaves. The countershaft operates on high grade, heavy duty, nickel babbitt bearings.
Any type of drive can be furnished for Ball-Rod Mills in accordance with your requirements. Belt drives are available with pulleys either plain or equipped with friction clutch. Various V- Rope combinations can also be supplied.
The most economical drive to use up to 50 H. P., is a high starting torque motor connected to the pinion shaft by means of a flat or V-Rope drive. For larger size motors the wound rotor (slip ring) is recommended due to its low current requirement in starting up the ball mill.
Should you be operating your own power plant or have D. C. current, please specify so that there will be no confusion as to motor characteristics. If switches are to be supplied, exact voltage to be used should be given.
Even though many ores require fine grinding for maximum recovery, most ores liberate a large percentage of the minerals during the first pass through the grinding unit. Thus, if the free minerals can be immediately removed from the ball mill classifier circuit, there is little chance for overgrinding.
This is actually what has happened wherever Mineral Jigs or Unit Flotation Cells have been installed in the ball mill classifier circuit. With the installation of one or both of these machines between the ball mill and classifier, as high as 70 per cent of the free gold and sulphide minerals can be immediately removed, thus reducing grinding costs and improving over-all recovery. The advantage of this method lies in the fact that heavy and usually valuable minerals, which otherwise would be ground finer because of their faster settling in the classifier and consequent return to the grinding mill, are removed from the circuit as soon as freed. This applies particularly to gold and lead ores.
Ball-Rod Mills have heavy rolled steel plate shells which are arc welded inside and outside to the steel heads or to rolled steel flanges, depending upon the type of mill. The double welding not only gives increased structural strength, but eliminates any possibility of leakage.
Where a single or double flanged shell is used, the faces are accurately machined and drilled to template to insure perfect fit and alignment with the holes in the head. These flanges are machined with male and female joints which take the shearing stresses off the bolts.
The Ball-Rod Mill Heads are oversize in section, heavily ribbed and are cast from electric furnace steel which has a strength of approximately four times that of cast iron. The head and trunnion bearings are designed to support a mill with length double its diameter. This extra strength, besides eliminating the possibility of head breakage or other structural failure (either while in transit or while in service), imparts to Ball-Rod Mills a flexibility heretofore lacking in grinding mills. Also, for instance, if you have a 5 x 5 mill, you can add another 5 shell length and thus get double the original capacity; or any length required up to a maximum of 12 total length.
On Type A mills the steel heads are double welded to the rolled steel shell. On type B and other flanged type mills the heads are machined with male and female joints to match the shell flanges, thus taking the shearing stresses from the heavy machine bolts which connect the shell flanges to the heads.
The manhole cover is protected from wear by heavy liners. An extended lip is provided for loosening the door with a crow-bar, and lifting handles are also provided. The manhole door is furnished with suitable gaskets to prevent leakage.
The mill trunnions are carried on heavy babbitt bearings which provide ample surface to insure low bearing pressure. If at any time the normal length is doubled to obtain increased capacity, these large trunnion bearings will easily support the additional load. Trunnion bearings are of the rigid type, as the perfect alignment of the trunnion surface on Ball-Rod Mills eliminates any need for the more expensive self-aligning type of bearing.
The cap on the upper half of the trunnion bearing is provided with a shroud which extends over the drip flange of the trunnion and effectively prevents the entrance of dirt or grit. The bearing has a large space for wool waste and lubricant and this is easily accessible through a large opening which is covered to prevent dirt from getting into the bearing.Ball and socket bearings can be furnished.
Scoop Feeders for Ball-Rod Mills are made in various radius sizes. Standard scoops are made of cast iron and for the 3 size a 13 or 19 feeder is supplied, for the 4 size a 30 or 36, for the 5 a 36 or 42, and for the 6 a 42 or 48 feeder. Welded steel scoop feeders can, however, be supplied in any radius.
The correct size of feeder depends upon the size of the classifier, and the smallest feeder should be used which will permit gravity flow for closed circuit grinding between classifier and the ball or rod mill. All feeders are built with a removable wearing lip which can be easily replaced and are designed to give minimum scoop wear.
A combination drum and scoop feeder can be supplied if necessary. This feeder is made of heavy steel plate and strongly welded. These drum-scoop feeders are available in the same sizes as the cast iron feeders but can be built in any radius. Scoop liners can be furnished.
The trunnions on Ball-Rod Mills are flanged and carefully machined so that scoops are held in place by large machine bolts and not cap screws or stud bolts. The feed trunnion flange is machined with a shoulder for insuring a proper fit for the feed scoop, and the weight of the scoop is carried on this shoulder so that all strain is removed from the bolts which hold the scoop.
High carbon steel rods are recommended, hot rolled, hot sawed or sheared, to a length of 2 less than actual length of mill taken inside the liners. The initial rod charge is generally a mixture ranging from 1.5 to 3 in diameter. During operation, rod make-up is generally the maximum size. The weights per lineal foot of rods of various diameters are approximately: 1.5 to 6 lbs.; 2-10.7 lbs.; 2.5-16.7 lbs.; and 3-24 lbs.
Forged from the best high carbon manganese steel, they are of the finest quality which can be produced and give long, satisfactory service. Data on ball charges for Ball-Rod Mills are listed in Table 5. Further information regarding grinding balls is included in Table 6.
Rod Mills has a very define and narrow discharge product size range. Feeding a Rod Mill finer rocks will greatly impact its tonnage while not significantly affect its discharge product sizes. The 3.5 diameter rod of a mill, can only grind so fine.
Crushers are well understood by most. Rod and Ball Mills not so much however as their size reduction actions are hidden in the tube (mill). As for Rod Mills, the image above best expresses what is going on inside. As rocks is feed into the mill, they are crushed (pinched) by the weight of its 3.5 x 16 rods at one end while the smaller particles migrate towards the discharge end and get slightly abraded (as in a Ball Mill) on the way there.
We haveSmall Ball Mills for sale coming in at very good prices. These ball mills are relatively small, bearing mounted on a steel frame. All ball mills are sold with motor, gears, steel liners and optional grinding media charge/load.
Ball Mills or Rod Mills in a complete range of sizes up to 10 diameter x20 long, offer features of operation and convertibility to meet your exactneeds. They may be used for pulverizing and either wet or dry grindingsystems. Mills are available in both light-duty and heavy-duty constructionto meet your specific requirements.
All Mills feature electric cast steel heads and heavy rolled steelplate shells. Self-aligning main trunnion bearings on large mills are sealedand internally flood-lubricated. Replaceable mill trunnions. Pinion shaftbearings are self-aligning, roller bearing type, enclosed in dust-tightcarrier. Adjustable, single-unit soleplate under trunnion and drive pinionsfor perfect, permanent gear alignment.
Ball Mills can be supplied with either ceramic or rubber linings for wet or dry grinding, for continuous or batch type operation, in sizes from 15 x 21 to 8 x 12. High density ceramic linings of uniform hardness male possible thinner linings and greater and more effective grinding volume. Mills are shipped with liners installed.
Complete laboratory testing service, mill and air classifier engineering and proven equipment make possible a single source for your complete dry-grinding mill installation. Units available with air swept design and centrifugal classifiers or with elevators and mechanical type air classifiers. All sizes and capacities of units. Laboratory-size air classifier also available.
A special purpose batch mill designed especially for grinding and mixing involving acids and corrosive materials. No corners mean easy cleaning and choice of rubber or ceramic linings make it corrosion resistant. Shape of mill and ball segregation gives preferential grinding action for grinding and mixing of pigments and catalysts. Made in 2, 3 and 4 diameter grinding drums.
Nowadays grinding mills are almost extensively used for comminution of materials ranging from 5 mm to 40 mm (3/161 5/8) down to varying product sizes. They have vast applications within different branches of industry such as for example the ore dressing, cement, lime, porcelain and chemical industries and can be designed for continuous as well as batch grinding.
Ball mills can be used for coarse grinding as described for the rod mill. They will, however, in that application produce more fines and tramp oversize and will in any case necessitate installation of effective classification.If finer grinding is wanted two or three stage grinding is advisable as for instant primary rod mill with 75100 mm (34) rods, secondary ball mill with 2540 mm(11) balls and possibly tertiary ball mill with 20 mm () balls or cylpebs.To obtain a close size distribution in the fine range the specific surface of the grinding media should be as high as possible. Thus as small balls as possible should be used in each stage.
The principal field of rod mill usage is the preparation of products in the 5 mm0.4 mm (4 mesh to 35 mesh) range. It may sometimes be recommended also for finer grinding. Within these limits a rod mill is usually superior to and more efficient than a ball mill. The basic principle for rod grinding is reduction by line contact between rods extending the full length of the mill, resulting in selective grinding carried out on the largest particle sizes. This results in a minimum production of extreme fines or slimes and more effective grinding work as compared with a ball mill. One stage rod mill grinding is therefore suitable for preparation of feed to gravimetric ore dressing methods, certain flotation processes with slime problems and magnetic cobbing. Rod mills are frequently used as primary mills to produce suitable feed to the second grinding stage. Rod mills have usually a length/diameter ratio of at least 1.4.
Tube mills are in principle to be considered as ball mills, the basic difference being that the length/diameter ratio is greater (35). They are commonly used for surface cleaning or scrubbing action and fine grinding in open circuit.
In some cases it is suitable to use screened fractions of the material as grinding media. Such mills are usually called pebble mills, but the working principle is the same as for ball mills. As the power input is approximately directly proportional to the volume weight of the grinding media, the power input for pebble mills is correspondingly smaller than for a ball mill.
A dry process requires usually dry grinding. If the feed is wet and sticky, it is often necessary to lower the moisture content below 1 %. Grinding in front of wet processes can be done wet or dry. In dry grinding the energy consumption is higher, but the wear of linings and charge is less than for wet grinding, especially when treating highly abrasive and corrosive material. When comparing the economy of wet and dry grinding, the different costs for the entire process must be considered.
An increase in the mill speed will give a directly proportional increase in mill power but there seems to be a square proportional increase in the wear. Rod mills generally operate within the range of 6075 % of critical speed in order to avoid excessive wear and tangled rods. Ball and pebble mills are usually operated at 7085 % of critical speed. For dry grinding the speed is usually somewhat lower.
The mill lining can be made of rubber or different types of steel (manganese or Ni-hard) with liner types according to the customers requirements. For special applications we can also supply porcelain, basalt and other linings.
The mill power is approximately directly proportional to the charge volume within the normal range. When calculating a mill 40 % charge volume is generally used. In pebble and ball mills quite often charge volumes close to 50 % are used. In a pebble mill the pebble consumption ranges from 315 % and the charge has to be controlled automatically to maintain uniform power consumption.
In all cases the net energy consumption per ton (kWh/ton) must be known either from previous experience or laboratory tests before mill size can be determined. The required mill net power P kW ( = ton/hX kWh/ton) is obtained from
Trunnions of S.G. iron or steel castings with machined flange and bearing seat incl. device for dismantling the bearings. For smaller mills the heads and trunnions are sometimes made in grey cast iron.
The mills can be used either for dry or wet, rod or ball grinding. By using a separate attachment the discharge end can be changed so that the mills can be used for peripheral instead of overflow discharge.
Max Feeding size <25mm Discharge size0.075-0.4mm Typesoverflow ball mills, grate discharge ball mills Service 24hrs quotation, custom made parts, processing flow design & optimization, one year warranty, on-site installation.
Ball mill, also known as ball grinding machine, a well-known ore grinding machine, widely used in the mining, construction, aggregate application. JXSC start the ball mill business since 1985, supply globally service includes design, manufacturing, installation, and free operation training. Type according to the discharge type, overflow ball mill, grate discharge ball mill; according to the grinding conditions, wet milling, dry grinding; according to the ball mill media. Wet grinding gold, chrome, tin, coltan, tantalite, silica sand, lead, pebble, and the like mining application. Dry grinding cement, building stone, power, etc. Grinding media ball steel ball, manganese, chrome, ceramic ball, etc. Common steel ball sizes 40mm, 60mm, 80mm, 100mm, 120mm. Ball mill liner Natural rubber plate, manganese steel plate, 50-130mm custom thickness. Features 1. Effective grinding technology for diverse applications 2. Long life and minimum maintenance 3. Automatization 4. Working Continuously 5. Quality guarantee, safe operation, energy-saving. The ball grinding mill machine usually coordinates with other rock crusher machines, like jaw crusher, cone crusher, to reduce the ore particle into fine and superfine size. Ball mills grinding tasks can be done under dry or wet conditions. Get to know more details of rock crushers, ore grinders, contact us!
Ball mill parts feed, discharge, barrel, gear, motor, reducer, bearing, bearing seat, frame, liner plate, steel ball, etc. Contact our overseas office for buying ball mill components, wear parts, and your mine site visits. Ball mill working principle High energy ball milling is a type of powder grinding mill used to grind ores and other materials to 25 mesh or extremely fine powders, mainly used in the mineral processing industry, both in open or closed circuits. Ball milling is a grinding method that reduces the product into a controlled final grind and a uniform size, usually, the manganese, iron, steel balls or ceramic are used in the collision container. The ball milling process prepared by rod mill, sag mill (autogenous / semi autogenous grinding mill), jaw crusher, cone crusher, and other single or multistage crushing and screening. Ball mill manufacturer With more than 35 years of experience in grinding balls mill technology, JXSC design and produce heavy-duty scientific ball mill with long life minimum maintenance among industrial use, laboratory use. Besides, portable ball mills are designed for the mobile mineral processing plant. How much the ball mill, and how much invest a crushing plant? contact us today! Find more ball mill diagram at ball mill PDF ServiceBall mill design, Testing of the material, grinding circuit design, on site installation. The ball grinding mill machine usually coordinates with other rock crusher machines, like jaw crusher, cone crusher, get to know more details of rock crushers, ore grinders, contact us! sag mill vs ball mill, rod mill vs ball mill
How many types of ball mill 1. Based on the axial orientation a. Horizontal ball mill. It is the most common type supplied from ball mill manufacturers in China. Although the capacity, specification, and structure may vary from every supplier, they are basically shaped like a cylinder with a drum inside its chamber. As the name implies, it comes in a longer and thinner shape form that vertical ball mills. Most horizontal ball mills have timers that shut down automatically when the material is fully processed. b. Vertical ball mills are not very commonly used in industries owing to its capacity limitation and specific structure. Vertical roller mill comes in the form of an erect cylinder rather than a horizontal type like a detachable drum, that is the vertical grinding mill only produced base on custom requirements by vertical ball mill manufacturers. 2. Base on the loading capacity Ball mill manufacturers in China design different ball mill sizes to meet the customers from various sectors of the public administration, such as colleges and universities, metallurgical institutes, and mines. a. Industrial ball mills. They are applied in the manufacturing factories, where they need them to grind a huge amount of material into specific particles, and alway interlink with other equipment like feeder, vibrating screen. Such as ball mill for mining, ceramic industry, cement grinding. b. Planetary Ball Mills, small ball mill. They are intended for usage in the testing laboratory, usually come in the form of vertical structure, has a small chamber and small loading capacity. Ball mill for sale In all the ore mining beneficiation and concentrating processes, including gravity separation, chemical, froth flotation, the working principle is to prepare fine size ores by crushing and grinding often with rock crushers, rod mill, and ball mils for the subsequent treatment. Over a period of many years development, the fine grinding fineness have been reduced many times, and the ball mill machine has become the widest used grinding machine in various applications due to solid structure, and low operation cost. The ball miller machine is a tumbling mill that uses steel milling balls as the grinding media, applied in either primary grinding or secondary grinding applications. The feed can be dry or wet, as for dry materials process, the shell dustproof to minimize the dust pollution. Gear drive mill barrel tumbles iron or steel balls with the ore at a speed. Usually, the balls filling rate about 40%, the mill balls size are initially 3080 cm diameter but gradually wore away as the ore was ground. In general, ball mill grinder can be fed either wet or dry, the ball mill machine is classed by electric power rather than diameter and capacity. JXSC ball mill manufacturer has industrial ball mill and small ball mill for sale, power range 18.5-800KW. During the production process, the ball grinding machine may be called cement mill, limestone ball mill, sand mill, coal mill, pebble mill, rotary ball mill, wet grinding mill, etc. JXSC ball mills are designed for high capacity long service, good quality match Metso ball mill. Grinding media Grinding balls for mining usually adopt wet grinding ball mills, mostly manganese, steel, lead balls. Ceramic balls for ball mill often seen in the laboratory. Types of ball mill: wet grinding ball mill, dry grinding ball mill, horizontal ball mill, vibration mill, large ball mill, coal mill, stone mill grinder, tumbling ball mill, etc. The ball mill barrel is filled with powder and milling media, the powder can reduce the balls falling impact, but if the power too much that may cause balls to stick to the container side. Along with the rotational force, the crushing action mill the power, so, it is essential to ensure that there is enough space for media to tumble effectively. How does ball mill work The material fed into the drum through the hopper, motor drive cylinder rotates, causing grinding balls rises and falls follow the drum rotation direction, the grinding media be lifted to a certain height and then fall back into the cylinder and onto the material to be ground. The rotation speed is a key point related to the ball mill efficiency, rotation speed too great or too small, neither bring good grinding result. Based on experience, the rotat
ion is usually set between 4-20/minute, if the speed too great, may create centrifuge force thus the grinding balls stay with the mill perimeter and dont fall. In summary, it depends on the mill diameter, the larger the diameter, the slower the rotation (the suitable rotation speed adjusted before delivery). What is critical speed of ball mill? The critical speed of the ball mill is the speed at which the centrifugal force is equal to the gravity on the inner surface of the mill so that no ball falls from its position onto the mill shell. Ball mill machines usually operates at 65-75% of critical speed. What is the ball mill price? There are many factors affects the ball mill cost, for quicker quotations, kindly let me know the following basic information. (1) Application, what is the grinding material? (2) required capacity, feeding and discharge size (3) dry or wet grinding (4) single machine or complete processing plant, etc.
Our small-scale miners Ball Mills use horizontal rotating cylinders that contain the grinding media and the particles to be broken. The mass moves up the wall of the cylinder as it rotates and falls back into the toe of the mill when the force of gravity exceeds friction and centrifugal forces. Particles are broken in the toe of the mill when caught in the collisions between the grinding media themselves and the grinding media and the mill wall. In ball mills, the grinding media and particles acquire potential energy that becomes kinetic energy as the mass falls from the rotating shell. Ball mills are customarily divided into categories that are mainly defined by the size of the feed particles and the type of grinding media.
Intermediate and fine size reduction by grinding is frequently achieved in a ball mill in which the length of the cylindrical shell is usually 1 to 1.5 times the shell diameter. Ball mills of greater length are termed tube mills, and when hard pebbles rather than steel balls are used for the grinding media, the mills are known as pebble mills. In general, ball mills can be operated either wet or dry and are capable of producing products on the order of 100 um. This duty represents reduction ratios as great as 100.
The ball mill, an intermediate and fine-grinding device, is a tumbling drum with a 40% to 50% filling of balls. The material that is to be ground fills the voids between the balls. The tumbling balls capture the particles in ball/ball or ball/liner events and load them to the point of fracture. Very large tonnages can be ground with these devices because they are very effective material handling devices. The feed can be dry, with less than 3% moisture to minimize ball coating, or a slurry can be used containing 20% to 40% water by weight. Ball mills are employed in either primary or secondary grinding applications. In primary applications, they receive their feed from crushers, and in secondary applications, they receive their feed from rod mills, autogenous mills, or semi-autogenous mills. Regrind mills in mineral processing operations are usually ball mills, because the feed for these applications is typically quite fine. Ball mills are sometimes used in single-stage grinding, receiving crusher product. The circuits of these mills are often closed with classifiers at high-circulating loads.
All ball mills operate on the same principles. One of these principles is that the total weight of the charge in the mill-the sum of the weight of the grinding media, the weight of the material to be ground, and any water in the millis a function of the percentage of the volume of the mill it occupies.
The power the mill draws is a function of the weight of the charge in the mill, the %of volumetric loading of the mill, the %of critical speed, which is the speed in RPM at which the outer layer of the charge in the mill will centrifuge.
For closed grinding circuits producing typical ball mill products, indirect and direct on-line measurements of the product size are available. The indirect means are those which assume that the product size is relatively constant when the feed condition to the classifying unit and the operating conditions in the classifying unit are constant. One example is maintaining a constant mass flow, pulp density and pressure in the feed to the cyclone classifier.
By using math modeling, it is possible to calculate the product size from measured cyclone classifier feed conditions and circuit operating data, thus establishing the effect on the particle size distribution in the product for changes in the variables.
Direct on-line means to measure either particle size or surface area are available for typical ball mill circuit products. These require the means to obtain representative or at least consistent samples from the grinding circuit product stream. These direct means and the calculated product particle size distributions can be used to:
Small variations in the feed size to ball mill circuits generally is not critical to the calculation of operating work index because they make a very small change in the 10F factor. Thus, a computer program can be developed to calculate operating work indices from on-line data with the feed size a constant and with the program designed to permit manually changing this value, as required to take into account changes in feed size resulting from such things as drawing down feed bins, crusher maintenance, work screen surfaces in the crushing plant, etc. which are generally known in advance, or can be established quickly. Developments underway for on-line measurement of particle size in coarser material which when completed will permit measuring the feed size used to calculate operating work indices.
recorded by a data logger, gives continuous means to report comminution circuit performance and evaluate in-plant testing. Changes in Wio indicated on data loggers alert operating and supervisory personnel that a change has occurred in either the ore or in circuit performance. If sufficient instrumentation is available, the cause for a problem can often be located from other recorded or logged data covering circuit and equipment operation, however, generally the problem calls for operator attention to be corrected.
Wio can be used to determine the efficiency of power utilization for the entire comminution section of a mill, and for the individual circuits making up the comminution section. The efficiency of a comminution circuit is determined by the following equation.
Wi is obtained by running the appropriate laboratory tests on a composite sample of circuit feed. Wio is calculated from plant operating data covering the period when the feed sample was taken. Since Wi from laboratory tests refers to specific conditions for accurate efficiency determinations, it is necessary to apply correction factors as discussed in The Tools of Power Power to Wio to put the laboratory and operating data on the same basis.
To-date, there is no known way to obtain standard work index data from on-line tests. Continuous measurement of comminution circuit efficiency is not possible and thus efficiency is not available for circuit control. Using laboratory data and operating data, efficiency can be determined for overall section and individual circuit for evaluation and reporting. Just monitoring Wio and correcting operating problems as they occur will improve the utilization of the power delivered to the comminution circuits.
Samples taken from the chips around blast hole drillings and from broken ore in the pit or mine for laboratory work index and other ore characteristic determinations before the ore is delivered to the mill, can be used to predict in advance comminution circuit performance. Test results can also be used for ore blending to obtain a more uniform feed, particularly to primary autogenous and semi-autogenous circuits.
We sell Small Ball Mills from 2 to 6 (600 mm X 1800 mm) in diameter and as long as 10 (3000 mm) in length. The mills are manufactured using a flanged mild steel shell, cast heads, overflow discharge, removable man door, spur type ring gear, pinion gear assembly with spherical roller bearings, replaceable roller bronze trunnion bearings, oil lubrication, replaceable trunnion liners with internal spirals, rubber liners and lifters, feed spout with wash port, discharge trommel with internal spiral, motor and gear reducer drive, direct coupled to pinion gear, gear guard and modular steel support frame. All ball mills always come withOSHA-type gear guard.
A PULP level sufficiently high to interpose a bed of pulp, partly to cushion the impact of the balls, permits a maximum crushing effect with a minimum wear of steel. The pulp level of theseSmall Ball Millscan be varied from discharging at the periphery to discharging at a point about halfway between the trunnion and the periphery.The mill shell is of welded plate steel with integral end flanges turned for perfect alignment, and the heads are semi-steel, with hand holes in the discharge end through which the diaphragm regulation is arranged with plugs.The trunnion bearings are babbitted, spherical, cast iron, and of ample size to insure low bearing pressure; while the shell and saddle are machined to gauge so that the shells are interchangeable.
Data based on:Wet grinding, single stage, closed circuit operation: feed:( one way dimension); Class III ore. All mills:free discharge, grated type, rapid pulp flow. N. B.for overflow type mills: capacity 80%power 83%. Dimensions :diameters inside shell without linerslengths working length shell between end liners.
The CIW is a Small Ball Mill thats belt driven, rigid bearing, wet grinding, trunnion or grate discharge type mill with friction clutch pulley and welded steel shell. The 7 and 8 foot diameter mills are of flange ring construction with cut gears while all other sizes have cast tooth gears. All these mills are standard with white iron bar wave type shell liners except the 8 foot diameter mill which is equipped with manganese steel liners. The horsepowers shown in the table are under running conditions so that high torque or wound rotor (slip ring) motors must be used. Manganese or alloy steel shell or head liners and grates can be supplied with all sizes of mills if required. Alloy steel shell liners are recommended where 4 or larger balls are used and particularly for the larger sized mills.
Small (Muleback Type) Ball Mill is built for muleback transportation in 30 and 3 diameters (inside liners). A 4 (Muleback Type) Ball Mill is of special design and will be carefully considered upon request. Mankinds search for valuable minerals often leads him far away from modern transportation facilities. The potential sources of gold, silver and strategic minerals are often found by the prospector, not close by our modern highways, but far back in the mountains and deserts all over the world. The Equipment Company has realized this fact, and therefore has designed a Ball Mill that can be transported to these faraway and relatively inaccessible properties, either by the age old muleback transportation system, or by the modern airplane. As a result these properties may now obtain a well-designed ball mill with the heaviest individual piece weighing only 350 pounds.
The prime factor considered in this design was to furnish equipment having a maximum strength with a minimum weight. For this reason, these mills are made of steel, giving a high tensile strength and light weight to the mills. The muleback design consists of the sturdy cast iron head construction on the 30 size and cast steel head construction on the larger sizes. The flanges on the heads are arranged to bolt to the rolled steel shell provided with flanged rings. When required, the total length of the shell may consist of several shell lengths flanged together to provide the desired mill length. Liners, bearings, gears and drives are similar to those standard on all Ball Mills.
This (Convertible) and Small Ball Mill is unique in design and is particularly adapted to small milling plants. The shell is cast in one piece with a flange for bolting to the head. In converting the mill from a 30x 18 to a 30x 36 unit with double the capacity, it is only necessary to secure a second cast shell (a duplicate of the first) and bolt it to the original section.
30 Convertible Ball Mills are furnished with scoop feeders with replaceable lips. Standard mills are furnished with liners to avoid replacement of the shell; however, themill can be obtained less liners. This ball mill is oftendriven by belts placed around the center, although gear drive units with cast gears can be furnished. A Spiral Screen can be attached to the discharge.
This mill may be used for batch or intermittent grinding, or mixing of dry or wet materials in the ore dressing industry, metallurgical, chemical, ceramic, or paint industries. The material is ground and mixed in one operation by rotating it together with balls, or pebbles in a hermetically sealed cylinder.
The cast iron shell which is bolted to the heads is made with an extra thick wall to give long wearing life. Two grate cleanout doors are provided on opposite sides of the shell by means of which the mill can be either gradually discharged and washed, while running, or easily and rapidly emptied and flushedout while shut down. Wash-water is introduced into the interior of the mill through a tapped opening in the trunnion. The mill may be lined with rubber, silex (buhrstone) or wood if desired.
The Hardinge Conical Ball Mill has been widely used with outstanding success in grinding many materials in a wide variety of fields. The conical mill operates on the principle of an ordinary ball mill with a certain amount of classification within the mill itself, due to its shape.
Sizes of conical mills are given in diameter of the cylindrical section in feet and the length of the cylindrical section in inches. Liners can be had of hard iron, manganese steel or Belgian Silex. Forged steel balls or Danish Flint Pebbles are used for the grinding media, depending upon the material being milled.
The Steel Head Ball-Rod Mill gives the ore dressing engineer a wide choice in grinding design so that he can easily secure a Ball-Rod Mill suited to his particular problem. The successful operation of any grinding unit is largely dependent on the method of removing the ground pulp. The Ball-Rod Mill is available with five types of discharge trunnions, each type obtainable in small, medium or large diameters. The types of discharge trunnions are:
The superiority of the Steel Head Ball-Rod Mill is due to the all steel construction. The trunnions are an integral part of the cast steel heads and are machined with the axis of the mill. The mill heads are assured against breakage due to the high tensile strength of cast steel as compared to that of the cast iron head found on the ordinary ball mill. Trunnion Bearings are made of high- grade nickel babbitt.
Steel Head Ball-Rod Mills can be converted intolarger capacity mills by bolting an additional shell lengthonto the flange of the original shell. This is possible because all Steel Head Ball or Rod Mills have bearings suitable for mills with length twice the diameter.
Head and shell liners for Steel Head Ball-Rod Mills are available in Decolloy (a chrome-nickel alloy), hard iron, electric steel, molychrome steel, and manganese steel. Drive gears are furnished either in cast tooth spur gear and pinion or cut tooth spur gear and pinion. The gears are furnished as standard on the discharge end of the mill, out of the way of the classifier return feed, but can be furnished at the mill feed end by request. Drives may be obtained according to the customers specifications.
Thats one characteristic of Traylor Ball Millsliked by ownersthey are built not only to do a first class job at low cost but to keep on doing it, year after year. Of course, that means we do not build as many mills as if they wore out quicklyor would we? but much as welike order, we value more the fine reputationTraylor Ball Mills have had for nearly threedecades.
Thats one characteristic of Traylor Ball Mills We dont aim to write specifications into thisliked by ownersthey are built not only to do advertisementlet it suffice to say that theresa first class job at low cost but to keep on do- a Traylor Ball Mills that will exactly fit anyanything it, year after year. Of course, that means requirement that anyone may have.
If this is true, there is significance in the factthat international Nicked and Climax Molybdenum, theworlds largest producers of two important steel alloys, areboth users of MARCY Mills exclusively. With international interest centered on increasingproduction of gold, it is even more significant that MARCYMills are the predominant choice of operators in everyimportants gold mining camp in the world.
Ball Mill. Intermediate and fine size reduction by grinding is frequently achieved in a ball mill in which the length of the cylindrical shell is usually 1 to 1.5 times the shell diameter. Ball mills of greater length are termed tube mills, and when hard pebbles rather than steel balls are used for the grinding media, the mills are known as pebble mills. In general, ball mills can be operated either wet or dry and are capable of producing products on the order of 100 pm. This duty represents reduction ratios as great as 100.
The ball mill, an intermediate and fine-grinding device, is a tumbling drum with a 40% to 50% filling of balls (usually steel or steel alloys). The material that is to be ground fills the voids between the balls. The tumbling balls capture the particles in ball/ball or ball/liner events and load them to the point of fracture. Very large tonnages can be ground with these devices because they are very effective material handling devices. The feed can be dry, with less than 3% moisture to minimize ball coating, or a slurry can be used containing 20% to 40% water by weight. Ball mills are employed in either primary or secondary grinding applications. In primary applications, they receive their feed from crushers, and in secondary applications, they receive their feed from rod mills, autogenous mills, or semiautogenous mills. Regrind mills in mineral processing operations are usually ball mills, because the feed for these applications is typically quite fine. Ball mills are sometimes used in single-stage grinding, receiving crusher product. The circuits of these mills are often closed with classifiers at high-circulating loads.
These loads maximize throughput at a desired product size. The characteristics of ball mills are summarized in the Table, which lists typical feed and product sizes. The size of the mill required to achieve a given task-that is, the diameter (D) inside the liners-can be calculated from the design relationships given. The design parameters must be specified.
The liner- and ball-wear equations are typically written in terms of an abrasion index (Bond 1963). The calculated liner and ball wear is expressed in kilograms per kilowatt-hour (kg/kWh), and when multiplied by the specific power (kWh/t), the wear rates are given in kilograms per ton of feed. The wear in dry ball mills is approximately one-tenth of that in wet ball mills because of the inhibition of corrosion. The efficiency of ball mills as measured relative to single-particle slow-compression loading is about 5%. Abrasion indices for five materials are also listed in the Table.
The L/D ratios of ball mills range from slightly less than 1:1 to something greater than 2:1. The tube and compartment ball mills commonly used in the cement industry have L/D ratios 2.75:1 or more. The fraction of critical speed that the mill turns depends on the application, and most mills operate at around 75% of critical speed. Increased speed generally means increased power, but as the simulations presented in Figure 3.26 show, it can also produce more wasted ball impacts on the liners above the toe. causing more wear and less breakage.
There are three principal forms of discharge mechanism. In the overflow ball mill, the ground product overflows through the discharge end trunnion. A diaphragm ball mill has a grate at thedischarge end. The product flows through the slots in the grate. Pulp lifters may be used to discharge the product through the trunnion, or peripheral ports may be used to discharge the product.
The majority of grinding balls are forged carbon or alloy steels. Generally, they are spherical, but other shapes have been used. The choice of the top (or recharge) ball size can be made using empirical equations developed by Bond or Azzaroni or by using special batch-grinding tests interpreted in the content of population balance models. The effect of changes in ball size on specific selection functions has been found to be different for different materials. A ball size-correction method can be used along with the specific selection function scale-up method to determine the best ball size. To do this, a set of ball size tests are performed in a batch mill from which the specific selection function dependence on ball size can be determined. Then, the mill capacities used to produce desired product size can be predicted by simulation using the kinetic parameter corresponding to the different ball sizes.
The mill liners used are constructed from cast alloy steels, wear-resistant cast irons, or polymer (rubber) and polymer metal combinations. The mill liner shapes often recommended in new mills are double-wave liners when balls less than 2.5 in. are used and single-wave liners when larger balls are used. Replaceable metal lifter bars are sometimes used. End liners are usually ribbed or employ replaceable lifters.
The typical mill-motor coupling is a pinion and gear. On larger mills two motors may be used, and in that arrangement two pinions drive one gear on the mill. Synchronous motors are well suited to the ball mill, because the power draw is almost constant. Induction, squirrel cage, and slip ring motors are also used. A high-speed motor running 600 to 1,000 rpm requires a speed reducer between the motor and pinion shaft. The gearless drive has been installed at a number of locations around the world.
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Rod mills were developed as a logical substitute for the rolls crusher when larger tonnages had to be handled, on a continuous basis. Today, with even larger tonnages to process, the trend is to install larger equipment, automate the plant and develop the highest availability possible, in order to cut costs. The rod mills, because of design limitations in size and speed, are not able to meet these new requirements.
One of the primary reasons for investigating alternate flowsheets is the desire to reduce cost. Two flowsheets have been developed to compare capital and operating costs for a taconite plant with 4.5 million long tons per year concentrate production capacity at an assumed concentration ratio of 3:1.
The first flowsheet is a conventional circuit in which - tertiary crusher product is fed to a rod mill drawing 4.6 Kwhr/Ton and producing an 80% -10 mesh product. At this stage 40% of the rod mill product is rejected in cobber magnetic separators as tailings. The cobber concentrate is ground in two ball mills in closed circuit with rougher, magnetic separators and cyclones. The calculated.ball mill power consumption is 13.8 Kwhr/Ton of crude. The cyclone overflow is deslimed, and upgraded in finisher magnetic separators.
Diameter to Length Ratio in Mills Rod mill L/D ratio is about 1.4:1. Pilot scale tests suggest that this should be revised to about 2:1 in the case of primary ball mills. This will off-set the effect of the random action of the balls and produce a smaller circulating-load.
The estimated savings is 10.5 cents per ton of crude which is a conservative figure. This, comparison takes into account only the most important aspects of the concentrator costs as a first approximation. It does not include pumping costs, maintenance costs and operating labor costs but all of these, would favor the proposed new circuit thus making the cost differential even more marked. Relative mill availability has not been considered in this cost evaluation, but it can also represent a considerable saving. The ball mill availability ranges between 94-96% whereas that of the rod mill ranges between 92-94% particularly because of stoppages for rod charging.
Capital costs were, developed for the two plants based on a location on the Iron Range. Support facilities, feed preparation or product handling were assumed to be essentially the same for both plants. These include ore crushing and stockpiling, maintenance shops, offices, water supply, tailings, disposal, etc., and were not made a part of this comparison. The saving of six million dollars, or 27% of scope considered, was to be expected.
In a tumbling type of mill, the size reduction can result from direct crushing, from shearing or abrasion between the particles in the feed, between the particles in the feed and the mill media or between the particles and the mill lining and thus is a complicated process. The precise mode of transfer of energy to the crushing surfaces cannot be simply presented.
For hard ores the influence of ball size is less pronounced and larger balls have little effect on grinding efficiency. Also from a simple graphical analysis of the zone of operation idea it follows that the radius of the zone varies as the square root of the particle diameter. Other things being equal, there is increased tendency for preferential grinding of the larger particles. As would be expected, the grinding of coarse feed with small balls did not result in effective grinding of the coarse particles in the feed but only produced considerable amounts of fines.
Hello: I would like to start a new discussion. When HPGR should be used instead of SAGs in a grinding circuit. What are the technical advantages, sensitivity to feed distribution, hardness of ore, efficiency etc? What are the trade-offs between SAG vs HPGR grinding technologies?
HPGRs are suitable for comminution circuits that deal with ores qualified as "competent". I like to leave the term hardness out of this analysis so I recommend not using the Bond Mill work index as an indicator to decide whether to use HPGRs in a circuit or not.
Everyone in the industry is trying to have the simplest circuit possible that will deliver the lowest CAPEX and OPEX possible while allowing to reach design capacity but in case of competent ores there is no alternative other than adding "crushing power". With technology available today you will be forced to have about 3 stages of crushing before feeding a ball mill if your ore is a competent ore. HPGR is a machine that plays a role in tertiary crushing, receiving top sizes of about 45 mm and delivering product sizes of around 4 mm (this is achieved by using a classification circuit together with the HPGRs). I have seen HPGRs in circuits dealing with throughput of about 1,500 t/h of fresh feed, so you can safely assume that HPGR can be used in a wide variety of tonnages up to the limits I mention. In one place the circuit I have seen working has 3-4 HPGRs to process about 4,800 t/h. May be an easiest way to show when HPGRs are needed in a circuit is to look at those projects where a SAG mill circuit didn't reach design capacity. If I remember well ALL of the SAG circuits dealing with competent ores have been forced to add either pebble crushers or secondary crushers to reach design capacity. This situation has transformed some SAG mills into an unusual hybrid mill which looks like a SAG but that is fed with a particle size close to the typical critical size that forms inside a SAG mill, i.e particle sizes in the range of 45 mm. The critical size generated in a SAG mill when dealing with competent ores is such that these pebbles are very hard to crush and impossible to grind down in a reasonable amount of time in a regular tumbling mill. The 45 mm competent ore produced in a crusher has internal fractures that make it suitable to feed a SAG mill where these rocks are easily reduced to final SAG product.
In discussion with about this topic some time ago I asked him a similar question. He suggested the following high level guidance when thinking about the selection of equipment to treat particular ore strengths.
Above 200 use a scrubber Above 60 use AG milling Above 40 use SAG milling Above 25 use HPGR AxB very rarely goes below 25. For AG and HPRC analysis the SMC test and DWi is very important." Mike may care to clarify further?
I recommend thinking on HPGR for AxB below 40. At AxB values between 37 and 40 there may still be a trade-off between conventional SAG and HPGR circuits. Under 37 I would be very careful to have a SAG circuit in my design. In this case a secondary crusher or pebble crusher (together with big SAG grate openings) is almost a must have.
HPGR may not be the right machine for less competent ore, especially when the ore has clays. So far it looks like that there are certain ore types that require too much energy to have them ground down in a conventional SAG-Ball Mill circuit. This is the case where HPGR circuits come handy. When the ore is competent there are less fractures available so the ore gets its size reduction mainly through abrasion. You will understand that trying to abrade a 6 inches rock down to 2.5 inches may take lots of time and hence the rock just spins around the SAG mill. If you want to reach design capacity then you need more SAG mills which just take you down the path of energy waste.
For less competent ore the conventional circuit is still the best choice due to lower CAPEX. HPGR circuits needs that more real state is made available as an ore classifying system needs to be in place. This system requires the construction of conveyor belt systems which enlarge the size of a circuit.
I think, the SAG/FAG cannot simply be compared with HPGR, taking account of their very different grinding process requirements and results, even the process is dry. As an example, if you expect to grind an ore from 200 mm size to 1 mm size, the use of the HPGR instead SAG/FAG requires the addition of 12 crushing phases, consequently the FAG/SAG cannot be replaced by HPGR only. If we add the screening, handling and feeding equipment CAPEX and OPEX, the comparison work will be more complex. The complexity degree of this comparison will be higher if the process water is available, due to the significant benefits of the wet screening vs. dry screening. Another aspect, with a major impact on the screening efficiency, is the different particle forms resulted from the SAG and HPRG processes. In conclusion, the optimal grinding circuit and its equipment requires a complex study of the technical and financial aspects. Taking into consideration the different recommended utilization areas of SAG and HPGR, their limited comparison is not possible to be correctly developed.
1. Pre-crushing- three crusher MP-2500(Metso) for crushing from 300mm to 50mm. Two working and once in reserve. 2. Primary grinding- once SAG mill with size 42ft x 24ft, power motor 28MW. F80-50mm, p80- 2mm. 3. Secondary grinding- two Ball mills with size 31ft x 45ft, power motor 28MW (each). F80- 2mm, P80 - 250microns. 4. Thirty grinding- once Ball mill (analogically). F80- 350microns, P80- 150microns. 5. Capacity of flowsheet - 10 000t/h. 6. Bond index for ball mill- 12.7 KW/t. 7. Power consumption of flowsheet - 10KW/t.
So far we have clarified that HPGR doesn't replace s SAG mill and hence these two machines can't be compared. We need to compare the HPGR circuits against the SAG-crush-Ball mill and against the Crush--Ball mill circuits
A always with equipment differences "there are horses for courses" - an analogy I would like to propose is that HPGR is like a race horse, not too good in variable circumstances in the same race, no hills, no uneven ground and a fixed handicap as the main challenge to performance. All this being correct, it is the fastest horse available option to get from point A to point B.
Now a SAG, could be seen as, a pack horse, a rodeo quarter horse, show jumper and all those other equine functions that require flexibility. One clear example is the ability to change it into a large ball mill (seems quite common these days) with increased charge and higher dependence of a P80 particle reduction. Drawing a even longer bow, you tend to shoot a race horse, should it break a leg....and spend serious money to replace it....
An interesting question. Published data shows HPGR capex is typically 15% to 30% higher than a comparable SABC circuit for the hardest ores. HPGR though provides opex reductions. I am curious to see if the opex reductions have actually panned out? Any experience out there on this?
Cerro Verde actual data shows that the HPGR circuit energy consumption was 3 kWh/t less than the SAG/Ball mill circuit that was considered in the trade off studies. The initial trade off studies were expecting to have 4.2 kWH/t of less energy consumption.
HPGR may be after 5...10 years. Why? SAG mill drinks water more them HPGR. Water consumption of SAG nearly 1.0 m3/t (with thickener), HPGR have less 0.1m3/h (without thickener). After 5...10 years the capacity plant will be 70...100 Mt/y may be more. Where to look 100 million tons water? May be after 5 years will be new favorite horse. For example - microwave grinder (Pegasus).
I would recommend to see if the horse would do the work he is expected to do. You may choose a cheaper horse that may look strong but if he won't walk at the pace you want THEN you may not arrive to the cash flow town you expect.
The decision needs to include a risk analysis. My suggestion is to look at the rock "competency" or look at the axb. If axb is low I would recommend to NOT believe in the SAG design output and add some extra percentage of power needed, lets say 20% or 30% more. The reason for this is that SAG modeling tools available have the tendency to make the wrong predictions when SAG circuits deal with competent ore.
However, things are changing with SAG throughputs regularly achieving higher than rated flows and better P80 expectations. At the risk of not trying to promote our work, as these forums are not for this at all. Our work these days is actually blending ball sizes and grades to optimize the process. This is not usual as most ball makers would not be able to blend say a 5" ball with a 3" ball in a high impact SAG environment without killing the 3" media either partly or totally. This now can be done without media carnage - plus the media retains its spherical shape throughout its deployment. Take a look at this scenario - you can actually have your cake and eat it too. I believe I am keeping within the scope of the question as it does give a SAG scenario that is not possible with HPGR that has no media to play with. We calculate impact energy in relation to ball size ensuring that targeted throughputs are met - then using the grinding surface adjustability of blending we can target the grind closely as well. The question that I would like to put forward to this forum is; As SAG can have this little spoken about flexibility, how can HPGR ever hope to match this?
size of balls in SAG: 6 inch size of balls in Ball Mill: 3 inch (50%) 2 in (50%) load of balls in SAG: 14% load of balls in Ball mills: 32% f80 to SAG: 152 mm (6 inches) SAG P80: 2 inch Circuit p80: 274 microns SAG speed : 10 RPM
This scenario for the SAG mill is taken from a design criteria. P80 for the SAG is 2 inch (this p80 considers SAG discharge only). If we consider the SAG screen and pebble crusher then SAG CIRCUIT p80 = 7mm.
This one is not a design that I have encountered before which is interesting as competent 150mm SAG media can only be made by a very, very limited list of suppliers. We have theoretically designed 200mm media as an exercise targeting almost 60 as an average volumetric hardness. We may look at the modeling for a size blend which may also include a percentage of 140mm media as well for that finer P80. !2.8m SAG is also an odd one. First thought, apart from the above, is a P80 of 50mm (2") when say 15mm/20mm could be achievable even at that bond work index of 20kWt/h. as a direct mill grate discharge prior pebble crushing.
Frankly, I would really like to have a close look at this ourselves if it ever got passed the design stage. The Ball mills are a great size as well and probably very capable of better than the 274um noted as the final grind or BM discharge. A blended media size with compatible ball grades would also be interesting to run through our modeling. Totally, very interesting sets of equipment to fine tune.
I have seen a design for a similar ore who has 4 HPGRs (5,600 kw each) and 4 cone crushers (933kw each) in the secondary crusher area. It has a 60x113 primary crusher and 3 ball mills (17,000 kw each). This circuit process between 110-120 ktpd
I'm not looking to get advice on designing a new circuit but to only add facts (numbers from actual operations) to this discussion to try help Tony with his question I appreciate your passion and help with the exchange of information. Knowledge is the only thing we will leave in this world long after we are gone.
As a media supplier, I am happy to concede applications where HPGR is indeed the front runner in equipment selection. HPGR will be the better performer when you have a very consistent ore body as that machine can be specifically set up to maximize the greater ore quantities. It is when the ore body feed to processing has a wide range of ore variations that fast processing adjustment and flexibility is demanded. Then SAG takes the lead.
Higher energy-efficiency than SAG milling Finer product than cone crushing Similar transfer size to SAG milling Reduced work index of product Improved minerals liberation Reduced over-grinding and sliming Smaller footprint (m/kW) Improved delivery times Shorter installation times More rapid plant ramp-up Easier plant debottlenecking Disadvantages: Plant complexity, larger overall footprint: Closed circuit secondary and HPGR Crushers & screens Conveyors, bins & feeders Dust control Tramp metal management Capital costs: Capex differential = (ore competency-1) Capex differential = (plant capacity-1) 100,000 tpd 10% 20,000 tpd 30%Show less
1. Capacity of flowsheet - 3600t/h. This is few for SAG mill with size 12.8 meters of diameter and 7.4 meters of light (even with 20 Bond Index). 2. The work power consumption of SAG is 20,24 MW. Nearly 80% (16.3 MW) consumed to crushing large rocks from 350mm ( F80=152mm) to 56mm. Specific power consumption will be 4.3 kW/t. May be this work make in secondary crushers ( 0.7kW/t)? 3. The work power consumption of ball mills is 21.2 MW (each) and capacity of each mill is 1800 t/h. This is too few.
Mark, i understand that you want blending difference ball size for increasing capacity of mill and reducing P80? We investigated at this and head follow result. You are right about killing small balls by large balls. Ball of 4' are will killing the 1.5' ball. Therefore blend 4' & 1.5' is impossible. If use the 2'ball the lifetime of it will be short. If use only 4' so after 20...25 days the balls size curve is will be consist 80% less 3.2' (with permanent adding necessary 4' balls) and 15...20% less 1.5'. This curve will be permanently. If blending 4' with 2.5' the grade of 1.5' will be more 20%. Is it need? I think for SAG mill the load ball size will be one size. For reducing P80 this work must do Ball mill (secondary grinding) with small balls. We are load only 2.5' and this ball killed 1' ball. For more reducing P80 necessary use thirty grinding with Ball mill or Vertimill with load of 1.0'...1.5'ball etc.
However, some good up to date news for you! We have the ability to make even 5" with 3" in a blend that works in harmony - without breakage concerns. As a SAG guy you will appreciate this as a new set of options. This plan was first started in ball mills we tune, in an actual trial account, this was a start-up seasoned charge in a single stage mill where we had several sizes - the top being a 133mm and the smallest being 80mm. Commissioning was quicker and the results were very good.
I do think blending ball sizes with compatible media grades is the future and a flexibility that HPGR cannot match. At this time we are carefully planning a shift in the final grind by using a 2.8: ration of 115mm: 90mm. This should move 76% of passing 200mesh to over 80%. I would welcome your comments on this as well.
You will be amazed to see people making decisions based on CAPEX only and based on what they are used to do. If they have been operating with a SAG circuit they will have the tendency to continue doing this. The real evaluation comes from developing a trade-off where the following needs to be considered CAPEX and OPEX Revenues (coming from Metallurgical performance as Kshirasagara points out) Risks of project construction (for example, is the new site far from roads infrastructure? this puts a limitation on machine sizes sometimes) Availability of financing Investors expectations in regards to the time they will have their capital back and start making earnings. Start-up Risks (learning curve of the operators) Social Risks (dust generation for example)
I studied all comments related SAG vs. HPGR. In addition, I remarked the change of flowsheet production capacity, from 10000 t/h to 36004000 t/h. I strongly recommend you, in accordance with Juans opinion, to select the following comminution steps: 1) Crushing, from 300 to 40 mm; 2) HPGRs from F80 40 mm to P80 2 mm in closed circuit with dry screening 2 mm; 3) The under screening -2 mm will be submitted to the wet screening 0.25 mm opening; the size fractions +0.25 mm will be sent to the secondary BM and the under screening to tertiary grinding; 4) Secondary BM grinding, F80 2 mm, P80 0.25 mm; 5) Tertiary BM grinding, F80 0.25 mm, P80 0.150 mm.
Taking account of your lower production capacity, you can think to replace the two BMG phases by one VM grinding step only, able to ensure a very efficient grinding from F80 2 mm to P80 0.150 mm under very, very efficient technical and financial conditions. You can look at METSO VM 3000 or new METSO VM 5000. You can develop the VM grinding tests with METSO (USA, PA) on 60 kg ore sample and the cost of the test is about US$6000. Based on the test result you can quantify the accurate number of VMs required by your ore and production capacity. The VM is a very profitable grinding equipment, under incidence of the OPEX and even the CAPEX. Based on my rough estimate, you need 1416 VMs for your flowsheet of 3600 tph. If you need further information concerning the VMs and their high grinding efficiency, please contact me. It will my pleasure to introduce you to METSO people, USA, PA, in order to develop the VM grinding test.
Unit Eq Power Total Power Supplied kW kW MP-2500(Metso) 2 1,864 3,728 SAG mill 1 28,000 28,000 Ball mills 2 28,000 56,000 Thirty grinding- Ball mill 1 42,973 42,973 Total (kW) 130,701 Specific Energy (kwh/t) 13.07
Certainly, there will be some saving on power consumption when HPGR is used as against a SAG Mill. However, there are other factors that do affect the decision, as well. For example, abrasiveness of the ore.
We have just completed DFS for a large Zinc Mine with beneficiation plant. Carried out a trade-off between SAG Mill and HPGR. Simply because of high abrasiveness of the ore (Index = 65) the saving on power got set-off by higher consumption of wear components (Crusher Liners & Screen panels) and requirement of additional O&M staff.
Make decision on commercial recovery and grade not on equipment based. Finally it is the operator and owner who is benefited and not equipment vendor. After SAG if metallurgy fails then what to do. Who will answer, vendor or operator? Today many industries are facing serious problems in this subject. Test both particles produced form SAG and HPGR and do cost benefit analysis and then take decision. It is the final Cost of concentrate produced, quality, and quantity that will give you confidence in buying equipment. Please don t forget metallurgy part.
Please do not take offence to these remarks, as it is not meant to be so, the circuit you have mapped seems quite viable BUT an alternate SAG circuit proposal (as you see it) will make it less of an "only" alternative. VM's are also interesting to look at, as they do seem very efficient. A single stage BM we have been fine tuning has F80: 75mm and P80+: passing 200mesh and does it easily. Much better than 2mm to 150um in a single step.
You can select your flowsheet based on BM use but, as I mentioned, it is recommendable to replace the SAG equipment (F80 50 mm; P80 2 mm) by HPGRs keeping the same feed and product sizes 50 mm and 2 mm). It is your choice but, taking account of your new throughput (4000 t/h), you can look at another flowsheet variant, significantly more efficient (lower OPEX) and characterized by reduced CAPEX than comminution scenario SAG + 2 BM stages. I suggest you to consider the following grinding circuit:
1. Primary HPRG F80 50 mm, P80 3 mm, in closed circuit with dry screening 3 mm opening (3 mm instead 2 mm in order to increase the dry screening efficiency); 2. Secondary grinding, using the Metso Vertimill 3000 (F80 3 mm and P80 250 m, the last being your required final product size).
1. The Metso VMT is characterized by lower power consumption than BM (up to 35 % less power) and lower grinding media consumption than BM (up to 53% less media consumption); 2. The operation of your secondary and tertiary BMs is not situated on the optimal size range of the product size (BM optimal product size 15000900 M) in comparison with Metso VTM optimal operating range, of 100040 m; You need the final size 250 m; 3. The CAPEX and OPEX of the fine grinding circuit will be considerably reduced (screens, feeders, pipes etc.).
In order to develop this flowsheet and accurately assess the CAPEX and OPEX, you need to proceed to HPRG laboratory and, in addition, the semi-pilot tests. The VTM tests will be developed with METSO, on the ground sample resulted from HPRG semi-pilot test (3 mm size) in order to check the VTM response to the size distribution obtained from HPRG process (tests). If you need further information please do not hesitate to contact me.
1. The VMs replace 4 BM units (2 secondary and 2 tertiary) based on your assessment; The BM CAPEX are higher than 10...14 VM (about US$10 M each); The accurate VM number can be quantified based on the stirred mill test results; In addition, you will reduce the CAPEX and OPEX required by BM size classification Equipment;
I do not try to convict you to use the VMs (same situation HPGR instead SAG), but your SAG and BM grinding circuit is an old grinding concept. The final flowsheet, as I mentioned, is your choice. As an example, I would agree to use the SAG if the size reduction ratio, in one step would be 100 or higher. In addition, I kept in my mind your remark concerning the water consumption, but the minimal information package, that you provided, does not allow to select the optimal grinding circuit.
The interesting thing is that savings in maintenance manpower, steel balls and energy largely pay to have more VTMs. The payback of the extra capex is about 40 months, which is paid by the operational savings.
OPEX for Vertimil may reach values that are 18% lower than for BM circuits Now some equipment manufacturers will help to pay the initial capex to receive a payment every month for 4 years or so. I would rather have more machines to operate to have lower OPEX for the mine of the life
I agree, but our assumptions have a general character only. The sensitivity analysis of the grinding circuit (NPV and IRR) can provide the accurate response to the question VM or BM? In principle, in the case of the size reduction from 2 mm to 0.25 mm (2 stages BM), one stage VM seems to be the better variant. The 4500 Metso VM can successfully use.
SAG, HPRG, BM, VM and other industrial grinders are one generation - mechanism of energy passing are same. Primary energy from electricity net pass to motor, it pass energy to gearbox, then to drum, from it to ball, and only these acts energy (balls kinetic energy) passed to address - to rock or particle ore. If the primary energy is 100%, gearbox consumption will be 10%, consumption drum rotating 35%, to lifting balls, ore and water 55%, consumption to heating of drum, balls, ore, water, grinder "music"& "dance" 15%, to grinding rock or particle ore...no? This is very "effectively", ok?
This generation is use kinetic energy by contact. The main problem is in comminution, other problem is residence time. At present time, i think, is necessary determine the concepts for new generation? In my opinion the new grinder mast be follow: 1. The energy passing to ore particle, will be without contact. For example by microwave, ultrasonic, pneumatic energy etc. 2. The manufacturing material of grinder, will be non-metallic (polymer, ceramic or carbon). 3. The residence time, will be less 1 minute. 4. Needless of water. 5. The grinding and separating of ore particles, will be in one time with one stage (one machine). 6. Installation of grinder will be self-mobile (may be fly). 7. Energy feed will be autonomy (plasma generator with buttery).
I appreciate your efforts and understand them. Your project is a big investment. As Juan and others mentioned, the right way of your work is the preliminary technical and financial study of the both variants of the comminution circuit as follows:
If the Variant B will be more profitable, I suggest you to develop the HPRG laboratory and pilot tests with the HPGR supplier (i.e. Thyssen Krupp Polysius), on 1.52 t crushed ore 300 mm size. The objective of the tests is the complete qualification of the response of your ore to the HPRG process. FYI information, the cost of the VM and HPRG tests are not expensive (VM test on 6070 kg sample, of 3 mm size about US$6000; HPRG test (laboratory and pilot, in closed circuit, about US$25000). For additional data and test development, you can contact your regional representative of the suppliers of HPGRs and VMs (Metso). Please carefully study and select the optimal screening concepts and equipment, under incidence of CAPEX and OPEX, in addition to technical criteria.
I have always wanted someone with this ability (I do not have it) to look at a hypothetical case, I say this as we are travelling down this road now and it would be wonderful if anyone could be able to calculate the possible efficiency outcome. SAG/BM circuit. SAG using 5" media with several pebble ports (4") discharging smaller media for magnetic separation and media captured is being reloaded into the BM. BM has 3" media. Now the hard part. The media retains its spherical shape throughout deployment in both SAG and BM - repeating that all media remains round throughout deployment. Small spherical ball populations grow in the BM promoting a better grind, SAG balls are not retained below say 3.5" leaving more space for new ore. The question: If the above was fully achieved, what would be the "estimated" improvement in efficiencies? I have no evidence (data) to quantify the media saving or the additional room for more ore. I also do not have an estimate of savings due to media remaining round and not losing shape. I do have one (and only one) reference for this - unused media additions to BM were reduced by 25% as this is the estimated media additions won from used round SAG media. Our aim was always to reduce costs and increase efficiencies in existing SAG/BM circuits. The HPGR and VM alternative does read well - and calculating this new efficiencies in comparison with the SAG/BM best operating scenario is probably relevant? Any thoughts or questions would be most welcome.
The technical and financial comparison BM vs. VM, based on grinding test results, is not a problem. The comparison SAG vs. HPRG is more complex and requires the good knowledge of the entire grinding circuit and its phases, including the material classification and its handling. The experimental checking of the compatibility with the ore with HPRG process is obligatory. As an example, please look at the Juan remark related to the clay content. In 2011 - 2012, I developed a similar preliminary economic assessment (PEA) for our project Roche Bay Magnetite Deposit, Nunavut Canada. Based on the RB ore characteristics, production capacity and study and test results, I selected the final scenario: Primary Crushing (from 1000 mm to 175 mm); Wet FAG/SAG (from 175 mm to 1.6 mm) followed by VM grinding (from 1.6 mm to 30 m).
The selection of the FAG/SAG as a primary grinding phase has been the result of the study of the efficiency of entire flowsheet, including magnetic separation and sulfide flotation. In spite of the higher profitability of the HPRG in comparison with FAG/SAG, the major financial impact of the efficiency of the wet ore classification and magnetic separation, on the global process efficiency, has been the final criterion of the selection of the FAG/SAG variant.
After you unload -50mm balls summary size in sag will be: 125...100mm 50%, 100...50mm 50%. All balls in sag will be have spherical shape. Unloading balls in ball mill after one day will be spherical too.
Usual SAG consumption milling mid hardness ores (say WI 16) can expect 300-400gr per tonne of ore milled. Harder ores and media breakage a take these numbers well over the KG per tonne consumption. We have seen (first hand) in access of 3kg/mt, due to unnecessary media breakage due to incorrect media grade/size selection.
Collectively all of us have the task to look closely in comparing new designs in equipment, meanwhile we also have the task to "optimize" existing equipment. Strict SAG operation does not include grinding only crack the ore and discharge with only short transitional time in the primary mill. However, now we are all seeing higher ball charges and ore levels in these primary mills. Targeting a smaller size particle (P80) is the reasoning most likely for this? Taking some work from the secondary mill(s) for an improvement in the final grind follows that same logic. Round media in the SAG mill in such cases then makes sense as round media in traditional SAG operation is no great gain (as no grinding is planned). Your percentages for media size seasoned charge distribution is similar to our own, but with pebble porting those smaller sizes should have been mostly discharged. SAG discharge being roughly classified by a screen to BM and oversize then magnetic separation and then to cyclone classification with overflow to the BM and underflow back to the SAG. Keep an acceptance of media retaining its shape throughout deployment and read further. BM operation using size/grade media blend to target the final grind - if the BM is at high efficiency then either throughput or grind can be adjusted with media selection - but not both. Recent site visits that we have had enabled both throughput and grind to be enhanced as efficiencies were low. Sorry to write these long comments about SAG/BM circuits but the point is that many circuits can be improved greatly and so may be a more accurate circuit to compare with the HPGR/VM alternative. The best thing that I see (please correct me if I am wrong), with HPGR/VM scenario is that there is far less chance of getting such a circuit operating incorrectly - simplicity is its greatest gift?
An HPGR has less things to look at, compared to a SAG or Ball mill, when trying to optimize its performance. The residence time is really short in this machine and it is really easy to take a sample to see what the outcome of a change was.
In contrast, when you change the grind media distribution in a SAG or Ball Mill you need to wait a much larger period of time until you see the final result. By that time the ore may be different, liners may be at different state of their useful life, you may have new operators, etc.
We should be ready to agree on some items that we, as a group, can accept as valid. 1. HPGR - VM is more energy efficient PROVIDED that the ore body remains very consistent. 2. HPGR - VM requires a lower skill set for operation. 3. HPGR - VM will trend out instantly if adjustments (rebuild) are required.
Laboratory and pilot HPRG tests, the last in closed circuit, aiming to qualify the response of your ore to the HPRG process; The tests will be developed on 1.21.5 t crushed ore, 50 mm size; I suggest you to select the P80 3 mm size instead 2 mm (HPRG process) in order to increase the dry screening efficiency, consequently, in order to reduce the screening CAPEX and OPEX and HPGR throughput; VM test on 60...70 kg ore, F80 3mm, necessary to the accurate quantification of the VM number/units; It is preferable, in order to reproduce the commercial operating conditions, to submit to VM test a sample resulted from the HPRG pilot test.
If you need the rough CAPEX and power consumptions required by the 6 options mentioned above, please contact me. For the current phase of your project (probably Preliminary Economic assessment or Scoping Study), the accuracy degree of my estimate is higher than the accuracy degree of your study. The VM tests will give you the very accurate VM number and power consumption. For the development of the tests, you can contact the METSO (VM) and Thyssen Krupp Polysius regional representative, or contact me in order to introduce you to METSO and TKP concerned people.
Selection -- Type of grinding system---- i. For very hard ores SAG mill. For soft ores and all FLOTATION TECHNOLOGY use HPGR. ii. Before taking decision consult Experts in Mineral processing for FLOTATION. iii. Do compare results of metallurgy for both. ivDo cost benefit analysis. v. Develop operator knowledge in controlling OPERATING PARAMETERS as per design, not as per fancy ideas given by many. Redesign if you fail to get results.( from the company who has supplied equipment.) vi. Many times ore characteristics changes as you go deep in the mine, or change location.
For all problems we have solutions. Clays in ore is 1st washed to -2mm, and +2mm. +2mm in INDIA will dry so fast that it will have hardly 6% moisture. You are giving examples of site specific. Yes you are correct if this ore is in cold countries at <10 C or where it is difficult to dry naturally. It will add to cost for drying +2 mm. 2.Let us not get confused with this subject. For some it is good for some it is not---This is based on situation, temperature, nature of ore, Flotation problems, Leaching problems, etc. 3.Anyone who want to use please do tests, and calculate cost benefit analysis form all points of view 100% then decide. It is only to know and gain more knowledge and each ones experience. Good to learn all have given reasonably good suggestions. All suggestions are very valuable and thought provoking. 4. We had very good time to learn many new concepts, practical solutions. We need not stop at one point and use age old technologies. New technologies are equally good. Let us learn how best we can make use of them. 5.Our priority is Mineral conservation, recovery, yield, simple operation, cost after installation. 6.Today Metals have become so costly that CAPEX and OPEX can be absorbed in profit.
TIGHTEST control of ore particle size throughout the "pit to product" flow sheet is agreed by all of us, as paramount. After looking at this forum contributor list, and their credentials, we can take this as 100% incontrovertible fact.
We have also discussed how that this can be done best - right on topic. Contributors have generously shared detailed firsthand information and also references to clarify points made. This has been invaluable to us all, it has certainly improved my own knowledge for one.
Agreed that this is a generalization, BUT we have, I think, given project designers a great "starting point" for initial assessment of equipment selection. The exercise has been totally worth the effort and we should all be pleased of the exchange. I do hope a balanced paper can be drafted on this very question, as it does have universal benefit.
Adaptation of HPGR as fourth stage size reducer for high clay and bit over critical moisture content feed ore is difficult because of the increase in force of cohesion for adhered fine particles on roll. This may spoil the plant reliability and operator's confidence. The same seems to be addressed by pre-screening for fines reduction, pre washing to reduce sticky adhered fine clays then dry and etc. HPGR consumes less energy for the same duty condition because
a. It works on breaking the particle to particle cleavages. The surface coatings took place at the time of ore body evolution in metamorphism may not damage to the greater extent as it happens in case of SAG - Ball mill combination. This activity may be desired or less desired for some onward separation process based on surface coatings. HPGR generates narrow band PSD particles. b. The SAG- Ball mill combination works on impacting and attrition action and the particles residence time increases with its size and density combination. This will generate slimes of high density valuable mineral particle, which is undesired activity and consumes unrequired energy. The hydro cyclones in efficiency will also add up and increase in close circuits grinding operation.
Size reduction is a liberation process which needs to be designed or focussed to felicitate more on wards separation process results. Off course selected combination essentially needs to strengthen plant reliability and economy.
The HPGR has earned a place in front end processing by being the best cost option for particle resizing, if the ore body has fixed and reliable characteristics - even I accept this and we are a ball supplier! I am content however, that the SAG mill still has greater utility in its flexibility to handle a wide range, or changing feed ore characteristic.
In the early releases there was too much expectation in HPGR ability to handle some great variations in an particular ore bodies. Careful planning of what goes in HPGR gives you the fixed and reliably fixed discharge result. I think Boddington (Australia) is happy with current results over the other option of 3 X 40' SAG mills, this will be one to research for sure.
New technologies generally take years to get traction with mining companies but once they do get something good they learn to use it well. It always needs a senior operations person to champion the cause before there is "traction". Then that is just step #1....
We have had some new developed products accepted by large mining houses and not by the smaller ones and vice versa....so it just depends on the company people to embrace new things or to even get them to consider....I have found the copper guys to be more interested in exploring things lately...(probably something to do with USD3/Pd?).
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Ore ball mill sometimes called ore grinding mill, is generally used in mineral processing concentrator, processing materials include iron ore, copper ore, gold ore, molybdenum ore and all kinds of nonferrous metal ore. The core function of the ore ball mill is to grind the materials, and also to separate and screen different mineral materials, and to separate the tailings, which is very important to improve the quality of the selected mineral materials.
The ore ball mill designed by our company, which is represented by gold ore ball mill and iron ore ball mill, is manufactured with high-quality materials and advanced technology. They have the characteristics of high efficiency, energy-saving, green environmental protection, simple operation, stable operation, and low failure rate, and have a good reputation in the industry.
The crushing ratio of the ore grinding mill is very large, and it is easy to adjust the fineness of the grinding product. The ore grinding mill has strong sealing performance and can be operated under negative pressure. It is widely used in chemical industry, metallurgy, new building materials and other fields.
We offer different types of ore ball mills for customers to choose from. There are energy-saving ore ball mill, dry and wet ball mill,wet grate ball mill, andwet overflow ball mill. Customers can choose to purchase according to material conditions.
Mineral processing is the most important link in the entire production process of mineral products. It is a process of separating useful minerals from useless minerals (usually called gangue) or harmful minerals in a mineral raw material by physical or chemical methods, or a process of separating multiple useful minerals The process is called mineral processing, also known as ore processing.
The first step in the ore processing is to select the useful minerals. In order to select useful minerals from ore, the ore must be crushed first. Sometimes, in order to meet the requirements of subsequent operations on the particle size of materials, it is necessary to add a certain ore grinding operation in the process.
The preparation before beneficiation is usually carried out in two stages: crushing screening operation and mineral classification operation. Crusher and ore ball mill are the main equipment in these two stages.
As a ball mills supplier with 22 years of experience in the grinding industry, we can provide customers with types of ball mill, vertical mill, rod mill and AG/SAG mill for grinding in a variety of industries and materials.Get in Touch with Mechanic