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.
Thralls are player-allied NPCs in Conan Exiles. They can be captured and recruited by the player to be used as servants, either working at crafting stations, as companions following the player, or as lookouts guarding buildings.
It is possible to swim, but not to climb, or to use a two-handed weapon while dragging a Thrall. Using either options will unequip the bindings and drop the thrall where it was when performing said action. Gruel, or most food, must be placed inside the Wheel of Pain to act as "fuel". Thralls remain unconscious for 10 minutes inside any player's render range when not bound to any kind of bindings - longer when no player is in render range.
Beating an unconscious Thrall with a blunt weapon (Truncheon/Blunted Javelin) will wear down on the thin white bar above their health again. The Thrall will wake up when the white bar has fully recovered, so wearing it down regularly makes the thrall stay unconscious. Though it is worth noting that while the thrall is bound with any kind of binding, the white bar will temporarily stop recovering.
Thrall crafting time, or the speed at which thralls can be produced, is affected by the level of the thrall itself as well as the level of a Taskmaster assigned to the Wheel of Pain. The type of Wheel of Pain has no effect on crafting times; nor does Food type.
Fighters, Bearers, Archers and Performers can be placed anywhere that isn't within the claim radius of a different clan or which is prohibited by certain landmarks and zone as determined by the game (e.g. Unnamed City). This means a combat thrall can be placed within a base, or even out in the world. To deploy a combat thrall, move it to the hotbar and place it like any other building item.
Thralls can be useful for defending an area against weak, stupid, or disoriented opponents. They are particularly useful in defending a region against NPCs or against other players during a raid. On PvP servers, it is usually a bad idea to leave a combat thrall out in the open, or anywhere a passing enemy might snipe the thrall with their bow. They will still offer protection when placed inside a building structure.
Combat Thralls will attack other players that come within range, but only during raid times (e.g. 5 pm to 11 pm PST on official servers) (Building damage must be set as Thralls are considered buildings, other wise they won't attack players). This does not apply to Offical PvE/PvC-servers.
Combat thralls (Fighters, Archers, Bearers and Performers) are placed as level zero and can be leveled to 20 maximum. Experience is gained when your character or the thrall makes a kill and varies with the difficulty of the target. Please note experience is only gained when they are actively following you, not while on guard.
At each level gain, points are added to their attributes in a semi-random fashion. Additionally, at levels 10, 15 and 20, the thrall gains a random perk which adds (and sometimes subtracts) to those attributes. A complete list of the pool of perks can be seen at Follower Perks. Crafting thralls need no leveling; they are immediately ready to be placed into the appropriate equipment.
Some functions can be accessed remotely if you are not near the thrall you want to manipulate. The tab is called Followers and can be accessed from the Inventory page. Several columns of information are immediately available:
1. The ability to show or hide the follower on the map. It's an easy way to locate a lost thrall, by turning off all but the one in question and scouring the map for their icon. Should the follower not be at that location, a server restart may solve the issue. If the thrall's icon is not on the map, check the event log for anything that may have happened to them.
Newly placed thralls are relatively weak and require support from you and, if possible, good armor and weapons to survive. At higher levels, their ability to withstand damage increases and appropriate leveling areas may include the Jungle, Shattered Springs or the Unnamed City to increase experience. At high levels, their ability to withstand damage will exceed yours and make them fine tanks with agro control. Similarly, ranged-leveled thralls, appropriately placed, provide excellent defense for your base.
Thralls don't have to be fed, as they depend on a decay timer. If you do not log in in 15 days they will disappear as shown under Settings:Server Settings:Abandonment (private servers may be adjusted). They will consume preferred food in their inventory for healing when wounded.
Thralls can not die from hunger and will not lose any HP due to lack of food over any period of time. The foods shown in their inventory screen provide an increased chance to gain various stat points upon leveling; as well as a Strength buff, visible on their health bar. Usually visible during combat. You can also see their buff on the information screen.
At the top level, this is what you get when you long-press the interact key while targeting your thrall, leading to submenus that set behaviors. These controls persist through logout and server reset. Currently, there is no way to determine where those various controls are set, but we remain hopeful for a future release.
Several items on the wheel are self-evident, such as guard, follow or stop following, cancel. This section will delve into Behavior along with others. You may find the command Stop Following extremely versatile and useful. Break Bond will send the thrall to a peaceful valley, never to be seen again. Their equipment and inventory contents will appear in a loot bag where they stood.
Engagement has several key selections and can be fine-tuned for the situation. Thralls on guard will want different selections than those following. Thralls can be set to guard or attack and the ranges allow fine tuning.
The selections are situational but you can find a combination that fits your playstyle and vary it, or not, leaving it preset for any location or fight. There are a few things to stay aware of, though:
While more important on guard, this also affects a following companion. You really do not want your thrall to go running off and leave you partnerless. Similarly, running through the Unnamed City a thrall that runs off to attack something that is of no use to you is, well, useless. Play with the distances and find where you want each one for your playstyle.
With an active thrall, you have the option to long-press the interact key and control their immediate behavior. Caution is advised to avoid using this and the single press option in bushes or too close to keep from picking up greens or a rock instead of issuing a command.
Stop Following is one of the best adds to the follower system and adds a level of control in previously unavailable areas. You can command your thrall to Stop Following in almost any place. Simply command your thrall to Follow to return to the previous state.
Thralls have a variety of uses. Most can be visually identified from a distance by what they are holding, e.g. bow is an archer, sword and shield is a fighter. Thralls placed at a crafting station often provide unique or high-grade recipes. Subsequent additions of Crafting stations, such as the Fermentation Barrel and the Saddler's Worktable allow placement of some professions with their accompanied bonuses. Visit the various profession or thrall page to see which profession can be useful in a particular Crafting station. As an example:
All Tier 4 crafters now have a specialization as generally described below. Detailed information is on the profession page, accessed with the header link. For all crafters, expand your chosen profession.
Every crafting thrall profession has 4 different levels, or tiers, identified with a I, II, or III at the end of their name, with tier 4 thralls being uniquely named. The exceptions are priests (Priest, High Priest and Archpriest) and Taskmasters from Sepermeru (Journeyman, Apprentice, Master).
Archer and Fighter thralls will have more health and armor based on their tier. Damage is based on the weapon they use and their corresponding attribute, Accuracy or Strength. Note that with the December, 2019 update, Archers may have higher Strength than Accuracy; Fighters may have higher Accuracy than Strength.
The SMC Test is the most widely-used comminution test in the world for AG & SAG Mills, HPGRs and Crushers. It is used to design comminution plants, optimize circuit performance, forecast throughput, reduce CO2 emissions and cut energy costs.
The SMC Test uses either crushed rock pieces that are very closely sized ("crush and select" method), or particles that are cut to similar size from drill core using a diamond saw ("cut core" method). The latter approach is used when limited drill core sample is available. Almost any drill core size is suitable, even core that has been quartered (slivered).
The chosen rock particles are broken using a closely controlled range of impact energies on a JK Tech Drop Weight Tester (JKDWT). The high degree of control imposed on both the size of particles and the energies used to break them means that the test is largely free of the repeatability problems which plague tumbling mill rock characterisation tests.
The results from conducting the SMC Test are used to determine the drop-weight index (DWi) which is a measure of the strength of the rock as well as the comminution indices Mia, Mih and Mic. In conjunction with the Bond ball mill work index they can be used to accurately predict the overall specific energy requirements of circuits containing: AG and SAG mills, Ball mills, Rod mills, Crushers, High Pressure Grinding Rolls (HPGR).
The SMC Test also generates the JK rock breakage parameters A, b and ta as well as the JK crusher model's t10-Ecs matrix, all of which are generated as part of the standard report output from the test. These values can be used to simulate crushing and grinding circuits using JKTech's simulator JKSimMet.
Ore grade is considered to be the main determining factor of the viability and profitability of developing an ore deposit. However, when facing declining ore grades or increased mining complexity, the costs associated with energy usage of comminution plants become increasingly important. The SMC Test's world-leading technology can provide your mining company with an "Energy Grade", giving you insight into your potential plant's energy consumption and equipment sizes and hence its impact on capital and operating costs both vital for determining the financial viability of the project. In existing operations the Energy Grade gives you the ability to benchmark performance across your global operations and identify opportunities for production capacity improvements and/or energy savings.
The range of mill sizes and versatile applications allow SAG milling to be accomplished with fewer lines than conventional set-ups. This, in turn, contributes to lower capital and maintenance costs for a SAG mill circuit.
SAG milling extends itself to many applications due to the range of mill sizes available. Theycan accomplish the same size reduction work as two or three stages of crushing and screening, a rod mill and some or all of the work done by a ball mill.
The Metso Outotec Qdx4TM mill drive provides the next step in the evolution of change in mill drive architecture, while allowing the system to be built with components that are within current manufacturing capabilities. We are essentially providing up to twice the power transmission of a conventional dual pinion drive.
Metso Outotec Premier horizontal grinding mills are customized and optimized grinding solutions built on advanced simulation tools and unmatched expertise. A Metso Outotec Premier horizontal grinding mill is able to meet any projects needs, even if it means creating something novel and unseen before.
Metso Outotec Select horizontal grinding mills are a pre-engineered range of class-leading horizontal grinding mills that were selected by utilizing our industry leading experience and expertise. With developing a pre-engineered package, this eliminates a lot of the time and costs usually spent in the engineering and selection stages.
Mill Sizing:After laboratory and pilot plant testing confirm the feasibility of autogenous or semi-autogenous grinding, it can be used to establish the exact grinding circuit and mill size. In the pilot plant tests, the tare power of the pilot plant mills should be determined before and after each test run. The tare power should be for the empty mill. To give the same bearing pressures as a loaded mill, weights can be bolted to the shell in a pattern to give a balanced rotation. The tare power should be deducted from the total mill power drawn when grinding at full loads so that the net power can be established and net power per ton calculated.
Experience to date in using net power per ton data from pilot plant tests indicates that production mills will require close to the same net power per ton as the pilot plant mill. To date, the Bond Work Index has not been used to determine the power required for grinding in a autogenous mill because there are factors other than Work Index (grindability) which influence mill performance. There has not been any correlation between Work Indices calculated from operating data for autogenous mills with grindability test results. Operating Work Indices have varied from slightly less than to more than twice the Work Indices obtained from grindability tests.
The net power determined from pilot plant work is increased to cover mechanical losses in the mill trunnion bearings, in the gear and pinion and in the pinionshaft bearings to obtain the power per ton at the mill pinionshaft. From this the total power required is determined and the mill or mills that will draw the required power are selected. A typical calculation is given in the following example:
Based upon the pilot plant test results, the volumetric loading for the mill can be determined. Normally, autogenous and semi-autogenous mills are selected for a 30% volumetric loading; however, with soft ore, and conglomerates it is not always possible to build up a 30% loading. This will show up in the operation of the pilot plant test mill.
Data collected to date shows that it is usually not possible to extrapolate power draw and capacity direct from small, pilot plant size mills to production size mills. Allis-Chalmers has a proprietary equation, adapted from the kilowatt hours per ton of balls (Kwb) equation for calculating ball mill power published by Bond, to determine the power which an autogenous mill or semi-autogenous mill will draw under specified conditions or ore specific gravity, pulp density in mill, mill speed and volumetric loading.
The ore in Example I has a specific gravity of 3.4. The computer data input sheet Figure 2 shows the set of data given to the computer to finalize the mill sizing. Figure 3a and 3b gives the results of the computer calculation. The mill power at the pinionshaft for a 30% volume charge is the sum of:
In the above example the power was calculated for a 30% volume. However, with the same sheets the power can be determined for any volumetric loading from 15% to 35%. The computer program can also be used to calculate power for larger or smaller volumetric loadings of balls.
Mill power draft is a function of the diameter to the 2.3 exponent and is directly proportional to mill length. The early history of autogenous mills in the United States and Canada has featured mills of large diameter and short length. Primary autogenous and semi-autogenous mills in Sweden and South Africa have much larger length to diameter ratios than mills in the United States and Canada. At Bolidens Aitik plant in Sweden, the primary mills are 20 feet in diameter by 34 feet long. Some of the mills purchased recently for installation in the U.S. and Canada are trending toward larger mill length to mill diameter ratios. Experience in the next few years, hopefully, will begin to answer some of the questions on the effect of mill length to diameter ratios in production sized mills.
Once the feasibility for either autogenous or semi-autogenous primary grinding and the total grinding circuit established, and required power and mill size determined, the mill design for the circuit selected can be established.
Defining the charge weight and height for fully autogenous grinding mill requires allowance for the ore specific gravity (and its variations) and accounting for the water content and the fine ore which will fill the interstitial spaces between the large ore pieces. This charge weight is usually calculated for the percent filling determined from the performance of the pilot plant tests and by the design of the feed end of the mill. Generally some user-specified safety factor is provided above the normal operating conditions such as actually designing for a 35% volume rather than 30%.
The pulp density in the mill is normally greater than that of the mill discharge due to an assumed differential flow rate of solids and water through the mill. Generally, a pulp density of 75% solids is used for the fines and water filling the interstitial space in the media portion of the ore charge.
The net charge density changes at each incremental change in total charge volume. Consider for example, a 30% total charge of ore with a 3.4 specific gravity, a 6% ball charge at 290 lbs. per cubic foot, and 75% slurry solids in the mill. The following illustrates the calculation of the net charge density:
It can easily be seen that at 29% or any other charge the net charge density will change. This variation lends itself to computer calculation with the increments as finite as desired. Figures 4a and b show how the total charge density varies with a comparable ore at 6% ball charge and various total mill charges.
Experience to date has indicated that the ball charges used in semi-autogenous grinding have generally been most effective in the range of 6% to 10% of the mill volume including the void spaces between the balls, i.e. ball charge volume based upon 290 lbs. per cubic foot.
A mill greater than 26 diameter and rated greater than approximately 4,000 horsepower will most likely have conical ends. The ore charge contained within the conical ends of course must also be considered in calculating the total charge weight. Figures 3a and b, and 4a and b show a typical print-out of mill cylinder and cone charge weight for an autogenous and semi-autogenous mill. The total charge weight is the sum of cylinder and conical charge weights.
The total charge weight, as calculated in this step of the design process, will have a direct input in the calculation of head and shell stresses, the selection of the trunnion bearing sizes and, of course, influences mill power draft. The importance of this step, although seemingly fundamental and simple, cannot be underestimated.
If the mill operating horsepower is defined as net at the shell, then the appropriate losses for trunnion bearings, pinionshaft bearings, and gearing must be accounted for to compute the power at the pinionshaft: the power point upon which both gear sets and speed reducers are rated. See Example I.
The losses in hydrodynamically lubricated trunnion bearings are generally no more than 1%. Even this is a very liberal amount. Modern designed, well lubricated, properly aligned ring gears and pinions can normally be assumed to be at least 98.5% efficient. Experience has shown that the losses for properly lubricated, anti-friction type, spherical roller type pinionshaft bearings can well be included within the 98.5% efficiency of the main gear and pinions. These result in the 1.025 multiplier used in Example I.
For fully autogenous grinding the mill drives are usually selected with a rating so that the drive is slightly oversized, to allow for variations in ore specific gravity and charge level. For example, if the ore is quite uniform and normal operation is expected to be 30% charge, a drive is selected at, perhaps, a 35% charge. Drive componentssuch as gearing, reducer, and couplingsshould be rated with the motor horsepower capability, including its service factor.
For semi-autogenous grinding the drive is usually selected for both a higher total charge and a higher ball charge than normally expected. In order to be assured of fully utilizing the mills total capacity capability. When selecting the drive for a mill that is being designed for both autogenous and semi-autogenous grinding (keeping in mind power and capacity requirements). It is necessary to specify the exact conditions under which the drive is selected. The exact ratio of drive rating to mill power is often a function of operators preference. Therefore, we will not lay down any hard rules at this time.
The user of the mill or his engineering consultant will normally have to make a detailed power system study in order to determine the maximum motor size which can be started across the line at any one time. In addition, any inrush limitations must be determined since both of these factors will have a direct effect on the drive design.
The application of autogenous and semi-autogenous grinding circuits in recent years has contributed toward substantial savings in capital and operating costs compared to conventional circuits, particularly for large scale copper and molybdenum operations.
The decision as to how much grinding testwork is required is more complex for autogenous or semi-autogenous (collectively read ASAG for economy) grinding than for conventional grinding. Firstly, conventional crushing and grinding circuits can be designed confidently on the basis of small-scale batch or locked-cycle tests requiring only 35 kg sample per test. Secondly, ASAG circuits can be designed using various methods each of which carries an element of risk commensurate with the experience, of the engineers involved and the amount of sample tested.
The Bond Work Index is the generally accepted parameter for gauging specific energy requirements in conventional crushing and grinding. The results are highly reliable if these tests are conducted on representative samples, usually of drill core, and follow the prescribed Bond method and test equipment.
Analysis of Bond Work Index test results for crushing, rod milling and ball milling will indicate uniformity or otherwise of breakage characteristics in different size ranges. Very often one is much higher (or lower) than the others and such variations can govern the power distribution between primary and secondary stages of grinding. Also, these observations will give an indication of the potential existence of a critical size relative to autogenous or semi-autogenous grinding.
It is considered that the determination of power requirement for an ASAG mill requires the same understanding of breakage characteristics and Bond Work Index developed for conventional grinding in testing particular ore samples. In addition, however, it is necessary to know how competent run-of-mine or primary crushed ore is in the coarser sizes and in what is generally termed the critical size range (75,000 to 13,000 microns) when operating in the presence of a reduced ball charge (up to 12% by volume) or when grinding autogenously.
The most critical parameter governing ESAG is the 80 percent passing size of the primary circuit product, PSAG. In using this formula, lower values of ESAG can be expected for coarser product sizings and these in turn depend upon ball loading and the production of natural fines. The usual relationships found in testing competent ores, i.e. those in which breakage is predominantly across grain boundaries.
With reference to the power distribution between primary and secondary grinding stages, higher power efficiencies can be obtained with a coarser primary product sent to ball milling. There are some exceptions, but generally industrial practice has been to utilize secondary ball milling capacity to the fullest and, if necessary, install more. Ball milling capacity can be justified if the incremental decrease in specific power consumption for the primary mill, for example between 500 and 1000 microns for primary mill circuit product.
It is important therefore that a metallurgical engineers judgement should be obtained in such circumstances, which is independent from any given by mill manufacturers, regarding the power required for a particular operation. The design of the test program, the nature of the samples tested, and the interpretation of the results should benefit from such independent expertise.
The principal factor governing the cost of a test program is the length of time required to achieve stable conditions under which the circuit can be sampled. Until recently, several days of operation with periodic checks of load level and successive sample campaigns were required to ensure confidence in results. The application of load cells to the support frame of the test mill has in most cases considerably reduced the time taken to achieve stability. Use of this tool will enable three or four test conditions to be investigated during a 24 hour period. Exceptions are usually very hard ores for which critical sizes have to be crushed and recycled..
For single-stage circuits in which the primary mill is operated autogenously, test parameters to be investigated are feed rates, specific power consumption and, if necessary, the effect of pebble crushing in varying quantities on feed rate and specific power consumption (kWh/tonne) to produce a final product siting. Where the primary mill is semi-autogenous, the principal variables are ball charge volume and ball size distribution.
The Escalante Project (750 mtpd) was designed following two stages of study. Firstly, a comparison of capital and operating costs was conducted based on empirical scale-up from Bond Work Index data. Product for cyanidation was set at 80% passing 44 microns and various drill core sections were tested for grindabllity.
Current operational results show that the SAG mill is operating at 5% ball charge level by volume and is delivering a K80 800 micron product as predicted. Power drawn at the pinion is 448 kW, 13.617 kWh/tonne (SAG mill) and 570 kW, 17.325 kWh/tonne (ball mill) when processing 32.9 mtph, for a total of 30.942 kWh/tonne or 14.6% above the conventional estimate. A ball charge volume which is lower than those tested has been selected in order to minimize wear. Obviously, the SAG mill is consuming more and the ball mill less power than was predicted by the empirical method, but the overall total is 99.5% of the predicted total.
The Hemlo gold project of Teck-Corona (1000 mtpd) provides an example of mill sizing using the empirical calculation method alone. The situation facing Teck-Corona was their inability to obtain samples for batch or continuous testing. Underground access was not possible in sufficient time to provide bulk samples. A tight construction schedule dictated that engineering proceed on the basis of information obtainable only from drill core. This meant that Bond Work Indices had to be used for mill sizing which was reviewed with mill manufacturers and other consultants.
The SAG mill was sized with 746 kW to give a 25% contingency for power swings on the calculated power. The ball mill was sized at 1120 kW. Total installed power for comminution exceeded that required for conventional grinding by a factor of 1.163 (including secondary crushing).
The power split between primary and secondary grinding stages in a two-stage circuit is a function of PSAG for maximum power efficiency. Since ball milling involves a more efficient transmission of energy for comminution compared to autogenous or semi-autogenous grinding, the selection of PSAG for ball mill feed is made at the point where it begins to cost less to grind by ball milling than it does to produce a finer product by primary grinding.
It is very difficult to provide an appropriate response to your question. The aspects of the arrangement of the comminution phases are complex and depend on the numerous factors as follows: ore hardness and size distribution and aimed size reduction ratios. Apparently, secondary crushing before the SAG diminishes the grinding power consumption but, the high participation of the fine particles will deteriorate the grinding efficiency and the power consumption will be higher. In addition, the fine particles will be recirculated and the result will be the power consumption increase. I met, during my operational and consulting experience the both comminution arrangements, but the selection of optimal scenarios was based on the study of the experimental and/or operational data. The study of the screening circuit is another required action. I met a situation that required the separation of the fine size fraction before the grinding, in order to increase the SAG efficiency. Sorry, I cannot provide you a general law of the arrangement of the comminution phases. The knowledge of the aspects mentioned above is required.
I suppose you have a dry comminution concept. Please do not forget the HPGRs. I combined the crushers, SAGs and HPGRs, but unfortunately, I do not know your required grinding size. In addition, please think to the crushers maintenance cost that can be higher than SAG maintenance cost. It is a very interesting project and its results can be surprising under incidence of efficiency and cost criteria. I met some similar situations. I and can mention Canada, Kazakhstan and Mauritania. The required production capacity is another important aspect.
I think you're very correctly identified the difficulty of the question. I agree with you that there is no single answer. Some experts believe that the secondary crushing effectively used for hard ore, crushing critical size effectively for soft ore.
This question nevertheless remains very important to today's time. Now the maximum capacity of SAG mills reached to 5000 t/h or 35-37 million t/y. But unfortunately (or fortunately) this maximum achieved by pre-crushing.
There is no definite rule for crushing circuits for any ore and depends on characteristics of material in the deposit. The first option should be AGM...which can be done with primary crushing followed by AGM as practiced in Kudremukh. For SAG, may be two stages crushing followed by SAG better option. However, the right crushing circuit can be decided only after initial test work including competency test of ore of particular size as grinding media.
If the Crushers and SAG are not able to ensure the aimed hourly production, I have the doubts concerning the FAG grinding scenario. Please do not forget Wi = 12 kWh/t. The ore is not very hard, but it is not soft. I think, the audit of the comminution plant, including the screening, is the right way to the comminution plant optimization. Our opinions are a general character; we do not know the flowsheet and the responses of the grinding and screening equipment to the size change. We do not know the recirculation degree of the screens. Under these conditions, I think, we are not able to provide the appropriate solution. As previously mentioned, the Novoi ore characteristics are very important. The simulation and the model of the process are, in fact, the final step of the project development. My opinion is based on the experience acquired from direct operation of the different comminution plants (soft and hard ores, dry and wet process), including the Crushers, FAG, SAG, HPRG, RMs and fine grinding including BMs, Vertimills and ISA Mills. I worked in favor to Kudremukh, I think in 2000 or 2001, if my memory is OK, but the ore are maybe very different of Novoi ore. In the mining industry is not recommended to accept the use of the general laws. Even in the case of the same ore, because of its quality variation (daily, weekly), the process efficiency and the product quality can significantly vary. The stability (STD) of the process efficiency and product quality is a required target associated to the production capacity. Really, we can discuss and provide our opinions but without to effectively provide the right way necessary to the problem solving.
In addition to my previous comment: My opinion, is not possible to indicate an appropriate/right way, without to know the operational people opinions. The operators experience and well process knowledge is the most valuable information. Please note, the Novoi Plant operation did not start yesterday. Thanks.
The question is not "what is better? it is "what does the ore want to do?". The case of a SAG mill followed by scats (oversize in mill discharge) crushing is usually used to reduce the oversize material by crushing because a) there is not enough competent coarse material in the SAG mill to do this at the required rate or b) there is a hard component in the mill feed which is resistant to breakage by the operating conditions in the mill. Pre-crushing part of the SAG feed on the other hand is a means of increasing mill throughput by reducing the coarse lump breakage energy required in the mill by reducing the quantity of coarse material which has to be broken by impact with balls or coarse ore lumps. You need to review the grinding characterisation data for the Novoi ore(s) and operating practices to determine which approach will achieve your objective. Simulations will be helpful if properly interpreted.
To select the "best" circuit in your case I would need to review your operational grinding data and/or grinding characterisation testwork results you have for the ore in question. There is no general "best" grinding circuit, only the best circuit for a particular set of ore breakage characteristics.
We can go on making general statements about the alternative circuits but it would be much more productive if you define the circuit, e.g. single stage SAG, SAG/ball, what performance you expect of the circuit and of course what are the ore's grinding characteristics.
A pebble crusher is the way to go for a greenfields project. SAG mill grates generally limit pebble extraction rates to around 25%, so you can't expect a throughput increase of more than 5-10% depending on the ore. To pebble crush, you need to port the grate. This removes any fine media, so achieving a fine grind size in a single stage becomes difficult.
Full secondary crushing is not recommended as these circuits are unstable and grind-outs (i.e liner damage) can occur frequently without experienced operators. You typically need a pebble crusher anyway because you fill the mill up with critical size material and constipate the mill! Not a good option.
Partial secondary crush circuits allow a stable load to develop and protect the liners. This is a good option for brownfields expansion targeting ~50% throughput increase. Partial secondary crushing also typically increases power efficiency.
If the ore is really hard, you might just have to bite the bullet and go three stage crush ball mill. Remember, pebble crushing and secondary crushing will coarsen the transfer size and may overload the secondary mill.
If you have identified that the ore is suitable for SAG milling go ahead and select a suitable SAG/Ball Mill combination (without pebble crushing if characterisation indicates it is not required). This will give you a cost effective, easy to operate circuit. You will need to recirculate trommel/screen oversize from the SAG mill so in the layout make provision for a pebble crusher installation in the conveying arrangement. If the ore changes and pebble crushing is required it will be relatively easy to install the pebble crusher. If the ore remains unchanged you can get another 5-10% more throughput by including a pebble crusher.
If after installation of the basic SAG/Ball Mill circuit you want a significant increase in throughput (>10%) you can consider pre-crushing part of the SAG mill feed. Since you already have a pebble conveying system in place, with or without a pebble crusher installed, it will be possible to install a pre-crushing circuit without hindering the operation of the grinding circuit.
If you feel there is a need to install pre-crushing for a green field grinding circuit, it suggests you are SAG mill limited (because of ore hardness), in which case an HPGR/Ball Mill circuit should be considered.
Yes, 5-10 years ago SAG mills was designed with pebble crusher, however over the last 5 years in some plant pebble crusher was replaced by secondary crusher. Unstable work of secondary crushing doesn't take a place in practice. Use of the equipment makes 90... 92%.
When you load large pieces in a mill, you spend is useless the electric power: large pieces rotate in a mill, but crushing doesn't happen. Large pieces occupy mill volume, and it was possible to give to ball. Kinetic energy of a ball is 2.5 times more, than at large pieces of ore.
Your opinion is entirely right. Your ore is not very hard, but it is hard. That is right, is not recommended to increase the feed size, hopping in an increase of kinetic energy of ore particle. In the case of the hard ore (I met this situation in the case of the hard magnetite) the size reducing is preponderantly carried out by abrasion and not by ore fracture. Under these conditions you are obliged to increase the ball size and, finally to spend the power. I do not know the required size of the final product, after the grinding but, I am sure, you will obtain a particular size distribution and oversize flow rate will be higher. Another negative aspect generated by the feed size increase will be the over charge of the SAG, the increase of the unit power consumption etc. Based on the experimental and operational results, you can find an optimal point of SAG operation, including the feed size, power consumption, ball consumption and production capacity, excepting the size of the ground product. Taking account of this aspect, logically, you will need a second reducing phase. Sure, you think to the crushing but you can find other more economic variants, as HPGRs. Here is the key of my right response. I do not know your operational parameters (flow rate, SAG characteristics, required size distribution of the ground ore etc.). Under these conditions, I am not able to provide my opinion. You know, the crusher power consumption is lower than SAG power consumption, but maintenance cost of the crushers are higher. HPGRs seem to be the best. They accept max. 50 mm feed size, the maintenance costs are lower than the crushers and the power consumption is not very high in comparison with the crusher power requirement. Really, this equipment seems to be OK, after the SAG, but without knowledge of your existing comminution circuit and required operational parameters, I am not able to provide you the best connection of the secondary grinding circuit. You have a big advantage in comparison with you. You know very well your flowsheet and the daily operational experience is available and known. Our opinions are the suppositions only. We try to the find the right way without to know it. In conclusion, I agree with your opinion, to add a secondary grinding/crushing size after the SAG, without be able to specify you the equipment type and its connection with the SAG circuit. You will be obliged to review the screens. Thank you and my colleagues for your and their time.
Pre-crushing feed to the SAG mill may also increase the SAG Mill POWER consumption. Others have played with pre-crushing down to 50 mm but what is the point? You may as well replace the SAG mill with a large Ball Mill. HPGR is now developed to the point that it is actually being considered as a replacement for SAG technology. Something to think about. HPGR has many advantages over the SAG, starting with capital cost and power costs as well as maintenance. The way I see it anyhow.
Yes High pressure is now considered as replacement to a SAG mill. In 2008 I reported (Comminution 08) to need the feed size reducing to 40-50mm. To me asked a question: if the feed size is 40mm, why a SAG mill is better from the High pressure? I answered "may be".
DISCLAIMER: Material presented on the 911METALLURGIST.COM FORUMS is intended for information purposes only and does not constitute advice. The 911METALLURGIST.COM and 911METALLURGY CORP tries to provide content that is true and accurate as of the date of writing; however, we give no assurance or warranty regarding the accuracy, timeliness, or applicability of any of the contents. Visitors to the 911METALLURGIST.COM website should not act upon the websites content or information without first seeking appropriate professional advice. 911METALLURGY CORP accepts no responsibility for and excludes all liability in connection with browsing this website, use of information or downloading any materials from it, including but not limited to any liability for errors, inaccuracies, omissions, or misleading statements. The information at this website might include opinions or views which, unless expressly stated otherwise, are not necessarily those of the 911METALLURGIST.COM or 911METALLURGY CORP or any associated company or any person in relation to whom they would have any liability or responsibility.
Qiming Machinery is the leading manganese steel, chromium steel, alloy steel, and heat-resisting steel manufacturer in China. We manufacture replacement wear part castings for impact, abrasion, and high heat applications in mining, crushing, grinding, and shredding, for industrial clients worldwide. No matter which wear parts you are interested in, send us the drawings or sample products, you will get the best products and professional suggestions. Know more+
Qiming Machinery manufactures shredder wear parts, crusher wear parts, mill liners, TIC inserts wear parts, apron feeder pans, and other industries wear parts for ore and aggregate crushers, metal and waste shredders, coal-fired power plants, cement industry, and custom application.
Qiming Machinery manufactures AG mill liner, SAG mill liner, ball mill liner, roll mill liner, and other types of mill liners for all popular brands. Material includes Cr-Mo, manganese, chrome, Ni-hard, and other steel.
Our steel casting foundry services include manganese steel casting, chromium steel casting, alloy steel casting, and carbon steel casting. Casting products of our steel casting foundry span across many industries. On the other hand, customized materials also can be manufactured after checked with our professional engineers.
Qiming Machinery manufactures ASTM A128 standard manganese steel wear parts over 12,000 tons per year, which products include cone crusher liners, jaw crusher liners, mill liner, apron feeder pans, hammer mill hammer, and other wear parts.
Qiming Machinery manufactures ASTM A532M standard chromium steel wear parts over 4,000 tons per year, which products include impact crusher blow bars, impact plates, feed tube, VSI wear parts, mill liners, distributor plate, and other wear parts.
As an alloy steel casting foundry, Qiming Machinery specialized in manufacturing low-alloy steel and high-alloy steel parts. Material includes Cr-Mo alloy steel, 30CrNiMo alloy steel, heat-resistant alloy steel. Products include alloy mill liners, alloy hammer, heat-resistant liners
Qiming Machinery has had cooperation with casting foundries to offer carbon steel (ZG250-700, ZG20SiMn, G20Mn5, ASTM A148, ASTM A488, ASTM A781, ASTM A802) wear parts, which include cone crusher shell, jaw crusher flywheel, pitman, adjustment ring, and other parts.
We have a customer from Australia, who runs MVP450 cone crusher to crush hard stone. However, the original wear parts just can work for around 7 days. This customer wants to prolong this mantle and concave span life. After visiting our foundry, this customer wants us to manufacture TIC insert MVP450 mantle and concave to
Qiming Machinery is a professional cone crusher liner manufacture in China. We had exported more than 12,000 tons of cone crusher liners for our customers. Recently, we get a trail order from Serbia to test our Mn18Cr2 HP300 cone crusher mantle and concave. About the feedback, please check the following communication message: T The messages
We have a Philippines customer who has four crushing lines to crush hard stone. There are 1 set HPT300 crushing lines, 1 set PEW760 crushing line, 1 set HP200 crushing line, and 1 set HP300 crushing line. They had tested many foundries crusher wear parts, however, no products have a long working life. From April
Qiming Machinery is the leading manganese steel, chromium steel, alloy steel, and heat-resisting steel manufacturer in China. We manufacture crusher wear parts, shredder wear parts, mill liners, apron feeder pans, and other wear parts for customers.
The cone crusherwas designed primarily with a view to achieving top performance in the field of fine-reduction crushing. It has also been adapted to what is designated simply as fine crushing, which extends into a range below that ordinarily defined by the term fine-reduction. Although the eccentric speeds of the various sizes of this type are not quite so high as the speeds used for the Newhouse crusher, the Hydro-cone crusher definitely rates as a high-speed machine, its product comparing quite closely to that of the former type, for equal close-side settings.Probably the outstanding feature of the. Hydrocone crusher is the hydraulic support, from which its name is derived and which is clearly shown in the sectional view. This device makes it possible to adjust the crusher to any desired setting within its range in a matter of seconds;adjustments may be made while the crusher is running, although the feed must be shut off before operating the adjusting pump. An accumulator in the hydraulic system provides protection against tramp iron or packing.
Cone crushers are used in AG and SAG grinding circuits to increase tonnage by effectively dealing with any pebble (critical size) build-up problem. Normally, heavy-duty short-head crushers are employed to crush pebbles. Power and crusher cavity level are the key variables for monitoring and controlling the crusher operation. Crusher product size is adjusted by changing the closed side setting.
On the left is a diagram of the Hydro-cone crushing chamber. A comparison of this chamber with those previously discussed is interesting. It will be noted that the choke-point has been raised far above the discharge level, in fact, to a point not far below the nip-point for the recommended maximum one-way feed dimension. By virtue of the decided flare of the head, and the corresponding flare of the top shell bore, the line-of-mean-diameters slopes sharply away from the crusher centerline. For some, distance above the discharge point the angle between head and concave is very acute; in fact, at the open-side position of the head, this zone is almost parallel. For recommended operating conditions, i.e., for safe combinations of throw and setting, and with screened feed, this type of crushing chamber does not approach anything like a choke or near-choke condition. For the combination shown in the diagram the ratio of volume reduction is almost 1:1 from zone 0-1 to zone 2-3 at the choke-point; consequently, if the crusher is given a screened feed (as all fine-reduction crushers should be) the reduction in voids by the time the choke-point is reached cannot very well reach serious proportions. The diagram shows the standard chamber. With screened feed, these crushers will operate at closed-side discharge settings equal to the throw of the head at the discharge point (usually spoken of as eccentric-throw.)
The level in the crusher feed pocket is an important variable since it can indicate whether the feed is building up. A build-up could lead to a plugin the feed chute, a spill through the skirting on the crusher feed, or a crusher plug. None of these are desirable.
In a normal feed situation, the level in the crusher cavity is kept fairly low, just enough to ensure that there is sufficient feed to keep the crusher working, but if the feed has to be suspended suddenly because of impending plugging, the crush-out wont take too long (10 seconds or less). Normal feed is usually used in standard crushers where the feed particle size is quite large, say greater than 65 mm.
Choke feed is when the crusher cavity is kept full, without spilling out through the skirting. Choke feeding is usually used in short-head crushers where the feed particle is smaller than that for a standard crusher.
This crusher is a modification of the standard machine, developed for fine-crushing duty. Mechanically, the machine is the same in every respect as the standard crusher of the same type, but for each developed size of machine a special top shell and the concave ring has been designed, with reduced receiving opening, reduced angularity between head and concave, and, consequently, superior characteristics at the finer settings. Medium crushing chambers may be operated at close-side settings of one-half the eccentric-throw, on screened feed; hence capacities at the finer settings are better than those of the standard type. Fine crushing chambers operate at one-fourth the eccentric throw. Inasmuch as the maximum feed size is smaller in the case of the fine chamber, the ratios of reduction are approximately the same for both machines.
There are two main types of cone crushers: standard and shorthead. They differ by the shape of the cavity. The standard crusher cavity is wider to accommodate larger feed-size material. The short head crusher is designed to crush finer material and to produce a finer product.
The closest approach between the mantle and the bowl liner is called the closed side setting. This is usually specified by the metallurgist to give the desired crusher product discharge size. It can be checked by running the crusher empty, hanging a lead plug into the crusher bowl, and then removing it to measure the gap. The gap is adjusted by rotating the bowl. Some crushers are equipped with a hydraulic jack mechanism on the crushing head assembly instead of having a bowl adjustment ring. The head can be raised or lowered to meet the operators needs. It can be very helpful in operation and process control.
The Symons Cone Crusher has come into almost universal use during the last few years for the final stage of crushing. It is a development of the secondary gyratory crusher, which is merely a small gyratory crusher designed to break the product of the primary machine down to about 1-in. size; but the main shaft of a cone crusher instead of being suspended from a spider is supported on a large socket bearing situated immediately under the crushing head and protected from grit and dust by a sealing assembly, this bearing taking the whole of the crushing load.
Fig. 8 gives a sectional view of the machine. The main shaft is carried in a long gear-driven eccentric, the rotation of which causes the gyration of the head in the usual way, but the center of gyration is at the apex of the crushing head instead of in the spider. At the top of the bowl, therefore, the lumps of ore entering the crushing zone are cracked by short powerful strokes; but at the bottom the head has a much longer but less powerful stroke, enabling the ore in the finishing stages to be rapidly crushed and quickly discharged without any tendency to choke, a condition which reduces over crushing to a minimum. This, together with the curved shape of the bowl, accounts for the large reduction ratio possible with this type of machine and makes it superior to other secondary crushers and coarse rolls.
It will be seen that the head and the bowl are parallel at the lower part of the crushing zone. The parallel space is deep enough, in conjunction with the speed of gyration, to ensure that no piece of ore can pass through it without being struck two or three times by the head before it falls clear. It follows that, unlike the jaw and gyratory crushers, the size of the product is determined by the distance apart of the bottom edges of the head and bowl in the position when they are closest together.
Coarse buttress threads on the outer circumference of the bowl fit into corresponding threads on the inner side of the adjusting ring, which is held down to the mainframe by a circle of long heavy springs, flexible enough to allow the whole assembly to rise should tramp iron or other uncrushable material enters the crushing zone. By means of a windlass and chain, the bowl can be rotated in the threads that support it in the adjusting ring while the machine is running, thus enabling the bowl liner to be adjusted for wear or the size of the product to be changed without stopping. The cone crusher is usually set to give a 3/8-in. or -in. product when discharging to ball mills.
Table 9 gives particulars of the different sizes of crushers. The capacity figures are based on material weighing 100 lb. per cubic foot and must be increased in direct proportions for heavier ores. It will be noted that each size of machine has two ranges of capacity; this is due to the fact that it can be fitted with a coarse or a fine crushing bowl according to the duty that is required of it. With either one, the range of reduction is greater than is economically possible with any other type of dry crushing machine.
A possible disadvantage of the cone crusher is that as a rule it cannot be choke-fed, but must be given an even feed of ore if it is to do efficient work. Should circumstances call for the installation of a machine that can be run if necessary with the ore piled up over the top of the head, a secondary gyratory crusher of the suspended shaft type will be required. The Traylor Reduction Crusher Type TZ, which is constructed on the principles of an ordinary gyratory crusher, but is fitted with a curved bowl liner similar to that of the Symons Cone Crusher, is designed to meet the case. Although the suspension of the shaft restricts the movement of the head to a smaller circle of gyration than that of the cone crusher, the ratio of reduction is still large enough to enable it to crush the product of the primary breaker to -in. size (-in. for the large machines), and it fulfills the condition that it can be choke-fed. Owing to the smaller movement of the head, however, the capacity for a given range is much less than that of the equivalent size of cone crusher, and the latter is therefore preferred when choke-feeding can be avoided.
The Symons Shorthead Cone Crusher, which is constructed on the same general principles as the larger machine, is designed to follow the latter, taking its product at 1-in. and reducing it to about -in. size. The strains imposed on the crushing members, however, would be very heavy if the machine were run with the discharge opening set to -in. or less. It is usual, therefore, to crush in closed circuit with a screen, the discharge opening of the bowl being set to 5/8 or in. Thus a circulating load is built up and a certain amount of choke-crushing takes place, but the method actually gives greater efficiency with a finer product than can be obtained in an open circuit, whatever the discharge setting of the bowl in the latter case.
In ordinary crushing practice, the grinding section is supplied with -in. or 3/8-in. material direct from Symons Cone Crushers. But the demand is for a finer feed and it seems likely that the Shorthead Cone Crusher will satisfy this demand to the exclusion of fine crushing rolls.
Symons Cone Crushers have been used extensively for secondary crushing in metallic, non-metallic, rock products, and industrial operations. The Symons Cone was developed to give large capacity, fine crushing. The combination of high speed and wide travel of the cone results in a series of rapid, hammer-like blows on the material as it passes through the crushing cavity and permits the free flow of material through the cavity.
Reduction in size of any particle, with each impact of the head, is regulated by the opening between the head and bowl at that point. A threaded arrangement of the bowl affords a quick and easy method for changing the size of the product or to compensate for wear. This adjustment can be made while the crusher is operating. A parallel zone between the lower portion of the crushing members assures uniform sizing.
Frame, adjustment ring, and cone are made of cast steel; gears are made of specially treated steel and have cut teeth; all bearings are bronze; mantle and bowl liners are manganese steel. The head and shaft can be removed as a unit, and other parts such as the eccentric and thrust bearings can easily be lifted out after the head is removed. The countershaft assembly can also be removed as a complete unit.
The circle of heavy coil springs, which holds the bowl and adjustment ring down firmly onto the frame, provides automatic protection against damage due to tramp iron. These springs compress, allowing the bowl to rise the full movement of the head until non-crushable material passes through. The springs then automatically return to their normal position.
Symons Cone Crushers are made in Standard and Short Head types. They are of the same general construction but differ in the shape of the crushing cavity. The Standard cone is used for intermediate crushing. The Short Head cone is used for finer crushing. It has a steeper angle of the head, a shorter crushing cavity, and greater movement of the head at the top of the crushing cavity.
If you observe the illustrations you will notice that the center line of the main shaft is at an angle to the center line of the crusher. The center of the main shaft bisects the center line of the crusher at the opening of the crushing chamber. As the MANTLE revolves that point is the pivot point of the mantle. This means that both the top and the bottom of the crusher mantle have a circular gyrating motion.
Tramp iron had long been a source of worry to those engaged in fine crushing.Here is what one operator had to say.Shutdowns were frequent, costs were uncertain because of enforced delays due to excessive breakage. Plugged machines had to be freed continually with a torch tocut out frozen and wedged-in tramp iron.The cone crusher overcame these troubles,helped reduce and stabilize costs. The bestevidence of this statement is the universalacceptance of the cone as the outstandingcrusher in its field.
While tramp iron is not recommended as a regular diet for a Cone Crusher, its construction is such that damage will not result should any ordinary noncrushable material get into the crushing cavity. The band of heavy coil springs encircling the frame allows the bowl to lift from its seat with each movement of the head until Such non-crushable object passes off into the discharge. The tramp iron shown in the accompanying illustration passed the protective devices installed for its removal and would have resulted in expensive repairs and long shutdown periods for any crusher except the Symons Cone.
Cone crushers can have two types of heads, standard and short head types. The principle difference between the two is in the shape (size and volume) of the crushing cavities and feed plate arrangements. Standard head cone crushers have cavities that are designed to take a primary crushed feed ranging up to 300mm generating product sizes around 20mm to 40mm. For finer products, short head cone crushers are normally used. They have a steeper angle of the head and a more parallel crushing cavity than the standard machines. Due to the more compact chamber volume and shorter working crushing length, the much needed higher crushing forces/power can be imparted to the smaller-sized material being fed to the crusher. Cavities for the short head machine are designed to produce a crushed product ranging from 5mm to 20mm in a closed circuit.
At the discharge end of the cone crusher is a parallel crushing section, where all material passing through must receive at least one impact. This ensures that all particles, which pass through the cone crusher, will have a maximum size, in at least one dimension, no larger than the set of the crusher. For this reason, the set of a cone crusher can be specified as the minimum discharge opening, being commonly known as the closed side setting (CSS).
Here are facts about the conecrusher known as Hydrocone. This line of hydraulically adjusted gyratory crushers was developed in smaller sizes some fifteen years ago by Allis-Chalmers to meet a demand for improved secondary or tertiary crushing units. The line is now expanded to include sizes up to 84-in. diameter cones.
This modern crusher is the result of many years of experience in building all types of crushing equipment, when the first gyratory or cone crusher, the Gates, was put into operation. Overall these years AC has followed a continuing policy of improvement in crusher engineering, changes in design being based on operating experience of crushers in actual operation.
The Hydrocone cone crusher is the logical outgrowth, a crusher having a means of rapidly changing product size or compensating for wear on the crushing surfaces a crusher which produces a better, more cubical product than any comparable crusher and a crusher so designed that it can be operated and maintained with a minimum of expense.
The most important fact about the Hydrocone crusher is its hydraulic principle of operation. Hydraulic control makes possible quick, accurate product size adjustments fast unloading of the crushing chamber in case of power failure or other emergency protection against tramp iron or other uncrushable materials in the crushing chamber. Another important fact about this crusher is its simplicity of design and operation. The accompanying sketch shows the simplicity of the Hydrocone crushers principle of operation. The main shaft assembly, including the crushing cone, is supported on a hydraulic jack. When oil is pumped into or out of the jack the mainshaft assembly is raised or lowered, changing the crusher setting.
Since the crushing cone is supported on a hydraulic jack, its position with respect to the concave ring, and therefore the crusher setting, can be controlled by the amount of oil in the hydraulic jack.
Speed-Set control raises or lowers the crushing shaft assembly hydraulically, and permits quick adjustment to produce precise product specifications without stopping the crusher. Speed-Set control also provides a convenient way to compensate for wear on crushing surfaces.
On Hydrocone crushers in sizes up to 48-in., the Speed-Set device is a hand-driven gear pump; on the larger sizes a motor-driven gear pump operated by push-button. On all sizes the setting can be changed in a matter of minutes by one man without additional equipment, reducing downtime materially.
Protection against tramp iron or other uncrushable materials is afforded by an accumulator in the hydraulic system. This consists of a neoprene rubber oil-resistant bladder inside a steel shell. This bladder is inflated with nitrogen to a predetermined pressure higher than the average pressures encountered during normal crushing.
Ordinarily, the Automatic Reset remains inoperative, but if steel or some other foreign material should enter the crushing chamber, the oil pressure in the hydraulic jack will exceed the gas pressure in the accumulator. The bladder will then compress, allowing the oil to enter the steel shell. This permits the crushing cone to lower and discharge the uncrushable material without damage to the crusher.
After the crushing chamber is freed of the foreign material, the gas pressure in the accumulator will again exceed the oil pressure in the hydraulic system. Oil is then expelled from the accumulator shell and the crushing cone is returned to its original operating setting automatically.
A Hydrocone crusher will produce a cubical product with excellent size distribution and a minimum of flats and slivers. This is especially important in the crushed stone industry where a cubical stone is required to meet rigid product specifications. It is also of considerable significance in the mining industry where the elimination of large amounts of tramp oversize reduces circulating loads or makes open circuit crushing possible.
The reason why the Hydrocone crusher will produce such a uniform, cubical product is that it has a small eccentric throw with respect to the crusher setting. This means a smaller effective ratio of reduction during each crushing stroke, and therefore, the production of fewer fines and slivers. Likewise, a small eccentric throw means a small open side setting, which results in a smaller top size of the product. A large percentage of the product from a Hydrocone crusher will be of a size equal to or finer than the close side setting.
For fine crushing, or in installations where the feed to the crusher is irregular, the use of a wobble plate feeder is recommended. This feeder is installed in place of the spider cap and affords a means of controlling the feed to the crusher, as well as a means of distributing the feed evenly around the crushing chamber.
Essentially, the feeder consists of a plate that is oscillated by a shaft extending down into the crushers main shaft. The motion of the main shaft oscillates or wobbles the feeder plate. The plate is supported on a rubber mounting which permits its motion and, at the same time, positively seals the top of the spider bearing against the entry of dust. Maintenance is reduced by the use of self-lubricating bushings between the feeder plate shaft and the crusher main shaft.
Hydrocone crushers are mounted on rubber machinery mountings in order to reduce installation costs and make it possible to locate these machines on the upper floors of crushing plants. These mountings operate without maintenance, absorb the gyrating motion of the crusher, thereby eliminating the need for massive foundations. Rubber mountings also prolong the life of the eccentric bearing, since this bearing is not subjected to the severe pounding encountered when rigid mountings are used.
The exclusion of dust and dirt from the internal mechanism of the crusher is of extreme importance from a maintenance standpoint. To accomplish this, Hydrocone crushers are equipped with one of the most effective dust seals yet devised.
This seal consists of a self-lubricating, graphite impregnated plastic ring which is supported from the head center in such a way that it is free to rotate, or gyrate, independently of the head center.
The plastic ring surrounds the dust collar with only a very slight clearance between the two parts. With the plastic ring being free to move as it is, it accommodates the rotation, gyration, and vertical movement of the main shaft assembly, maintaining the seal around the dust collar at all times. Because of its lightweight and self-lubricating characteristics, wear on the plastic ring is negligible.
The ease with which any wearing part can be replaced is of the utmost importance to any crusher operator. With this in mind, the Hydrocone crusher has been designed so that any part can be replaced by disturbing only a minimum number of other parts.
For example, the Mantalloy crushing surfaces are exposed by simply removing the top shell from the crusher. This can be done easily by removing the nuts from the studs at the top and bottom shell joint. The eccentric and hydraulic support mechanisms are serviced from underneath the crusher without disturbing any of the feeding arrangements, or the upper part of the crusher.
Efficient lubrication of all wearing parts is one of the reasons why crushing costs are low with the Hydrocone crusher. On most sizes, lubrication is divided into three distinct systems, each functioning independently.
This bearing, whether of the ball and socket type as on the smaller sizes, or of the hourglass design (as shown) found on the larger Hydrocone crushers, is pool lubricated. On the 51, 60 and 84-inch sizes, provision is made for introducing the lubricant from outside the top shell through the spider arm. On the smaller crushers, oil is introduced through an oil inlet in the spider cap. On all sizes, oil is retained in the bearing by a garter-type oil seal located in the base of the spider bearing.
All Hydrocone crushers are provided with a compact external lubrication system consisting of an oil storage tank, an independently motor-driven oil pump, a pressure-type oil filter, and a condenser-type cooler.
Cool, clean oil is pumped into the crusher from the conditioning tank, lubricating first the three-piece step bearing assembly. The oil then travels up the inner surface of the eccentric, lubricating the eccentric bearing and main shaft.
At the top of the eccentric, the oil is split into two paths. Part of the oil flow passes through ports in the eccentric and down its outer surface, lubricating the bronze bottom shell bushing, driving gears and wearing ring. On the 48-in. and smaller crushers, the balance of the oil overflows the eccentric and returns over the gears to the bottom of the crusher where it flows by gravity back into the conditioning tank. On the 51-in. and larger Hydrocone crushers, any oil which overflows the top of the eccentric is returned directly to the conditioning system without coming into contact with the gears.
On all but the 36 and 48-in. Hydrocone crushers, the countershaft bearings are of the anti-friction type with separate pool lubrication. Both ends of the countershaft bearing housing are sealed by garter spring-type oil seals to prevent dirt or other contaminants from entering the system.
Rather than use one eccentric throw under all operating conditions, Hydrocone crushers are designed to operate most efficiently with a predetermined ratio of eccentric throw to the crusher setting. By operating with an eccentric throw specifically selected for a given application, the most desirable crushing conditions are attained the most economical use of Mantalloy crushing surfaces reduced crusher maintenance a more cubical product.
The eccentric throw is controlled by a replaceable bronze sleeve in the cast steel eccentric. This sleeve, being a wearing part, can be renewed readily in the field. Also, should operating conditions change, the throw or motion of the crushing head can be changed accordingly.
Because of the large choice of eccentric throws available and the variety of crushing chambers that may be obtained a Hydrocone crusher may be selected that will fulfill the requirements of almost any secondary or tertiary crushing operation.
They may be used in the crushed stone industries to produce a premium cubical product in the mining industries to produce a grinding mill feed having a minimum of oversize, thereby reducing circulating loads and making open circuit crushing possible. The Hydrocone crusher is used in the cement industry to reduce cement clinker prior to finish grinding.
One of three general types of crushing chambers can be furnished for any size Hydrocone crusher to suit your specific needs. The selection of the proper chamber for a given application is dependent upon the feed size, the tonnage to be handled and the product desired. A crusher already in use can be readily converted to meet changing requirements, making this machine highly flexible in operation.
The Coarse crushing chamber affords the maximum feed opening for a given size crusher. Crushers fitted with a Coarse chamber can be choke fed, provided that product size material in the feed is removed.
The Coarse chamber has a relatively short parallel zone and is designed to be operated at a close side setting equal to or greater than the eccentric throw. For example, a crusher with a 3/8-in. the eccentric throw should be operated at a 3/8-in. (or more) close side setting, and therefore a -in. open side setting. Optimum capacity and product will result when operated under these conditions, as well as most economical wear on the mantalloy crushing surfaces.
One way dimension (slot size) of the feed to a crusher fitted with a Coarse chamber should not exceed two-thirds to 70 percent of the feed opening. The maximum feed size to an 848 Hydrocone crusher would therefore be about 5-in. one way dimension.
The use of a wobble plate feeder, furnished as optional equipment, is recommended if the feed size is relatively large, if the crusher is to be operated in closed circuit, or if the feed to the crusher is irregular.
If the Hydrocone crusher is operated with a Coarse crushing chamber, the product will average about 60% passing a square mesh testing sieve equal to the close side setting of the crusher. On certain materials which break very slabby, this percentage will be somewhat lower, and on cubically breaking material the percentage will be somewhat higher. As an average, approximately 90% of the product will pass a square mesh testing sieve corresponding to the open side setting, although this percentage frequently runs higher.
The Intermediate crushing chamber has a feed opening somewhat less than a coarse crushing chamber, but because of its longer parallel zone, is designed to be operated at a close side setting equal to or greater than half the eccentric throw. For example, with a -in. eccentric throw, the minimum close side setting would be 3/8-in.
Crushers fitted with this type of chamber can be choke fed, provided that product size material in the feed be removed ahead of the crusher. The one-way dimension or slot size of the feed to a crusher should not exceed approximately half the receiving opening. A 436 Hydrocone crusher with a 5/8-in. the eccentric throw could be operated at 5/16-in. close side setting and feed size should not exceed 2-in. one-way dimension.
The wobble plate feeder, although not required under most circumstances, is recommended if the feed is irregular, or if the crusher is operated as a re-crusher, at a relatively close setting, or in a closed circuit.
Because of the longer parallel zone in this crushing chamber, a somewhat greater percentage of the product will pass a square mesh testing sieve equal to the close side setting. This will usually average about 65 to 70%, with this percentage varying, depending on the material being crushed. Very frequently, 100% of the product will pass a square mesh testing sieve equal to the open side setting of the crusher.
The Fine crushing chamber has the longest parallel zone and therefore the smallest feed opening for any given size crusher. It can be operated at ratios of eccentric throw to close side setting of up to 4 to 1. With a -in. throw, for example, a 236 Hydro-cone crusher could be operated at 3/16-in. on the close side.
Because of their design, crushers with Fine crushing chambers cannot be choke fed but must be equipped with the wobble plate feeder. The maximum one-way dimension of the feed approaches the crusher feed opening. A 348 Hydrocone crusher can be fed with material up to 3-in. one-way dimension.
The Fine crushing chamber will give the highest percentage passing the close side setting of any of the chambers discussed here. The product will average approximately 75% passing a square mesh testing sieve equal to the close side setting. Because of the long parallel zone, the top size of the product will be only slightly larger than the close side setting of the crusher.
In addition to the three general types of crushing chambers described here, special chambers can be designed to meet varying operating requirements, giving the crusher even greater flexibility than can be obtained with these three main types.
For example, a special concave ring can be used in a 636 Hydro-cone crusher which will reduce the feed opening to 5 inches and permits a two to one ratio of eccentric throw to close side setting. Thus, the crusher can be furnished to fit the exact requirements of any application.
The following capacity table gives a complete range of all Hydrocone cone crusher capacities with varying crushing chambers and eccentric throws. This table shows the minimum recommended setting for any given eccentric throw, the recommended maximum one-way (slot size) dimension of the feed, and the maximum recommended horsepower for any eccentric throw.
Capacities given are based on crushing dry feed from which the product size material has been removed. The material must readily enter the feed opening and be evenly distributed around the crushing chamber. The table is based on material weighing 100 lb per cubic foot crushed. Any variation from this must be accounted for.
The curves on the following page can be used to approximate the screen analysis of the product from any given Hydrocone crusher. These curves are only approximations since the actual screen analysis of the product of a Hydrocone crusher will depend upon the nature of the material being crushed, the feed size and a number of other considerations which could not be taken into account in these curves. Within these limits, the curves should give fairly accurate estimates.
Note that the Coarse crushing chamber is represented as giving a product of which 60 percent will pass the close side setting, the Intermediate chamber 67 percent and the Fine chamber 75 percent passing the close side setting. These percentages are the averages of a large number of tests and some variations from these must be expected. If material breaks slabby the percentage with a coarse crushing chamber may be as low as 50 percent; if it breaks very cubically it might be as high as 70 percent, or even higher.
These curves have been prepared so that they can be used for any crushing chamber. To estimate the product of any Hydrocone crusher, it is necessary to know the type of crushing chamber used (Coarse, Intermediate or Fine), the close side setting and the eccentric throw.
If the crusher is a 636 Hydrocone crusher with a 3/8-in. throw and a 3/8-in. close side setting, the approximate screen analysis would be the curve that would pass through the 3/8-in. horizontal line and the vertical line representing the close side setting for the Coarse crushing chamber, which is the 60 percent passing line. If no curve passes through the precise point of intersection between the horizontal and vertical lines, an approximate curve can be sketched in which parallels the other curves. The same procedure can be used for approximating the products from any other crushing chamber.
Barite..170 Basalt.100 Cement Clinker.95 Coal..40-60 Coke.23-32 Glass..95 Granite100 Gravel.100 Gypsum..85 Iron Ore.125-150 Limestone..95-100 Magnesite.100 Perlite..95 Porphyry.100 Quartz..95 Sandstone..85 Slag..80 Taconite125 Talc..95 Trap Rock100
We canprovide testing to solve the most difficult crushing problems. Laboratory equipment makes it possible to measure the crushing strengths and characteristics of rock or ore samples accurately, and this data is used in the selection of a crusher of proper size and type.
Impact and batch tests are frequently sufficient to indicate the type and size crusher that will be the most economical for a particular application. However, batch testing is often followed by pilot plant tests to provide additional information about large-scale operations, or to observe rock or ore reduction under actual plant operating conditions.
Pilot plant tests duplicate a continuous crushing operation provide a practical demonstration of the commercial potential of the process on a pilot scale. Such tests are useful because they may disclose factors that affect the full-scale operation, favorably or otherwise, but which remain hidden in tests on limited samples.
All Laboratory tests are guided by modern scientific knowledge of crushing fundamentals and by ourinvaluable backlog of experience in engineering and building all types of crushing equipment for any crushing application.
In addition to the facilities for crushing tests, the Laboratory maintains complete batch and pilot mill facilities for use in investigating an entire process. Tests in grinding, sizing, concentrating, thickening, filtering, drying, and pyro- processing can be made.Get in Touch with Mechanic