The powder grinding technology of ball mill includes powder grinding craft and powder grinding equipment. The former is dominant and the latter is fundamental because the equipment needs to be driven by the craft and the craft is realized through the use of the equipment.
Ball mill plays a decisive role in the cement production process since the quality of the ball mill not only influences the quality of the cement, but directly relates to the economic benefits of the cement plant. Even in a modern cement plant, ball mill remains one of the mechanical machines ranking only second to rotary kiln which is partly because that the powder grinding work is an important production link in the cement production, the other aspect is because that ball mill has many features that can adapt to the modern cement production.
In some ore dressing plants, the crushing granularity is coarse and the processing ability of ball mill is low, thus influencing the system production capacity of the whole ore beneficiation plant. At the same time, the automatic degree of the system equipment is low and the power of the whole power grid is not high, so that energy conservancy and consumption reduction are even imperative.
The generally recognized fact that for economic reduction of any material, it is desirable to perform such reduction in steps or stages, removing that material which is sufficiently fine as soon as it is reduced and grinding it still finer in some device more adaptable to this finer reduction. It has been found that by so doing, the efficiency of the grinding machinery is increased, since material which is already finished and not removed interferes with the reduction of the coarser particles. This general principle is applied in the laboratory for the grinding of samples, where, after the material has been ground for a short time, it is screened for the purpose of removing the finished particles and the coarser material is then returned for further reduction.
Another application on a larger scale is the use of crushers or rolls in series with screens or trommels between them for removing finished or semi-finished material. It was with this idea in mind and with a realization that the machinery in use did not embody this working principle, that the Conical Mill was designed.
In the Hardinge Mills, due to the action of the cones, the coarse material on entering the machine gravitates to the point of largest diameter. Here it comes in contact with, and is broken by, the largest balls moving at the highest velocity and falling from the greatest height. As the particles are broken, they automatically work their way forward, being subjected to a gradually diminishing breaking and crushing effect as they decrease in size. The particles undergoing reduction reach the required degree of fineness and arrive at the discharge end of the mill at the same time. Thus it is seen that this automatic classification, both of the material being reduced and of the grinding mediums, as well as their height of fall, proportions the energy expended or exerted in crushing to the work required to be performed. In this way, we obtain an ideal step or stage reduction in a single machine, which is conducive to a maximum crushing effect for a minimum expenditure of power.
This classification of the material undergoing reduction, as well as of the grinding bodies, is illustrated in Figure 1, in which it is seen that in the largest diameter of the mill, the incoming feed is acted upon by the largest balls with the greatest superincumbent weight, the greatest height of fall, and the greatest peripheral speed. The grinding bodies and the crushing forces exerted are gradually reduced, as well as the size of the material undergoing reduction, as the discharge end is reached.
The Hardinge Conical Millbecause of its conical shapeoffsets one of the serious disadvantages found in the cylindrical, compartment type mill, i. e., unproportionate speeds for the different size balls.
The Hardinge Conical Ball Millbecause of its conical shapeoffsets one of the serious disadvantages found in the cylindrical, compartment type mill, i. e., unproportionate speeds for the different size balls.
In the Conical Mill, the largest balls being kept at the greatest diameter in the cone by centrifugal force, have greater height of fall and greater peripheral speed than the smaller balls which are found at the smallest diameter in the mill. Fig. 2 shows the decreasing peripheral speeds as the diameter of the cone decreases, and shows the various size balls as they are found in the mill.
It is not claimed that the Conical Mill absolutely adjusts the energy expended in crushing to the work to be performed, since in order to make it absolutely efficient, the design of the mill would have to be adjusted to the material and particular conditions attendant upon its reduction. This, of course, would be economically impracticable. However, the Hardinge Mill more nearly approximates this desired result than does any other type of crushing or grinding machine.
The Hardinge Conical Mill can be used in various combinations for the grinding of limestone and clay mixtures, coal and cement clinker. As a mill for preliminary grinding, it is equipped with balls of various sizes selected from an assortment running from 5-in. to 2-in. balls. It will grind material of 3-inch and finer sizes, and reduce this to a size suitable for feeding to the finishing mills of the same type as the preliminary mills, except that they are equipped with smaller balls.The Metallurgical Field has demonstrated the advantages to be obtained by quickly removing the finished material from the discharge end of the mill in order to increase the output. In accomplishing this, a certain amount of oversize material must be returned to the mill. Likewise in the Cement Industry, in two-stage grinding, it is desirable to utilize a separating screen in closed circuit with the preliminary mill. In addition to increasing the output, this permits definite control of the finished product, and as the separating screen will be ahead of the second stage, or finishing mill, it allows for close regulation of the entire operation and insures a uniform product of the desired fineness.The Hardinge Mill is adapted to the complete finishing of limestone mixtures, coal and cement clinker, in one operation. To accomplish this with a good output, it is advisable to crush the feed to 3/4, or preferably1/2 in size. This will allow the use of balls ranging from about 1 1/2 in diameter to 3/4, and will give a large output with extremely low use of power.
In one-stage grinding, in order to achieve the best results, it is recommended that a considerable oversize be run from the mill and the product be obtained through a separating screen, or air separator. See Figures 3, 4 and 5 for several different arrangements.
Hardinge Mills are built in several standard sizes (see Figures 6 and 7). A complete stock of linings and repair parts is carried at all times so that deliveries can be promptly made.For dry grinding, the Conical Mill, 6-ft. in diameter and over, is made of a plate steel shell, with cast steel trunnions. Trunnions are machined on the inside faces of their joints together with the plates before being riveted to the cones, insuring a perfect fit and producing a cylindrical truss of great strength. All rivet holes are drilled in trunnion castings, countersunk and rivets flattened on the inside of the mill, making a smooth surface for the lining.
When completely assembled and riveted, the drum is swung in a lathe, centered, the trunnions turned and polished, and the supports for the gear machined. This method of construction and the care exercised in the plate work assure a true alignment of trunnions and gears, as well as a machine which is perfectly balanced, with the consequent advantages of smooth, even-running and minimum power consumption. All seams and joints in the shell are thoroughly caulked andtested before shipment. Gears are ample in size and are made of steel, with cutor cast teeth, as desired.
Mills furnished for wet grinding may be supplied with cast iron trunnions, cones, gears and gear rings. The absence of heat in mills used on this class of work permits the use of less expensive material.
The feeder supplied for coarse, dry feed is of the plunger type, which is positive in action. Where the feed is 1J/2 inches or smaller, it is practical to use a screw feeder with cast steel or cast iron flights.
For wet grinding, the feeder is simple and takes no extra machinery for its operation. A patent reversible scoop feeder or a conical feeder may be used. Under certain conditions, a combination scoop and conical feeder may be used to advantage.
The Conical Ball Mill is lined with Titanite metal plates which are heldin place by heavy chrome steel bars and heavy taper head bolts. The design of the bars and bolts allows for considerable wear on the bars without affecting the bolts. The construction of the lining, as indicated by the illustration, prevents the slipping of balls, thereby increasing the efficiency of the mill and reducing the wear on both lining and balls.
The charge for balls furnished with the mill varies with the size of feed and product desired. The larger sized balls are made of forged steel. For sizes of 2 in. and smaller, cast iron balls of a special mixture are recommended, as they are more uniform in size and material and less subject to fracture.
Hardinge Mills may be used for grinding limestone or raw material mixtures used in the manufacture of Portland Cement, cement clinker and coal, either as preliminary or finishing machines, or as units to complete the grinding in one operation. The size of the plant determines in a large measure the best way to utilize the machine. In a large plant, it is recommended that the mills be installed in two stages with a screen between the two sets of mills to insure a uniform product for the finishing mills. Used in this way, as indicated on the diagram or flow sheet, one mill or battery of mills would perform the heavy grinding, say, from feed which would pass through a 1.5 ring, delivering the product to a separating screen. From this separating screen, the finished material would pass immediately to conveyor lines running to cement storage; the material which has passed through the 20-mesh screen, would go to one or more finishing mills for final grinding; and the oversize or rejected material would be returned to the preliminary mill for further grinding as indicated on the flow sheet. This insures the greatest possible production and the lowest cost of operation.
For grinding in one-stage operation, it is advisable to reduce the feed by rolls or crushers so that it will pass a %-in. ring. This permits the use of much smaller balls. In order to get the greatest possible production from a Conical Mill in a one-stage operation, it is recommended that a separating screen be used in closed circuit with the mill. (Air separators may be used instead of screen if desirable.) From this screen, the finished material will pass directly to the cement storage, and the oversize will be returned to the feed end of the mill for further grinding.
The results from one-stage grinding do not show quite the same efficiency as from two-stage operation, but it is often desirable, particularly in small plants, to complete the grinding in one or two mills in order to take advantage of the greater efficiency which is obtainable by the use of larger units. The results obtained in exhaustive tests made within the past two years in grinding an unusually hard clinker, taken with the extensive experience of the Hardinge Company in the grinding of many kinds of ores and industrial material, permit a close approximation of results that may be expected in the grinding of cement clinker.
These capacities are furnished as a guide for the selection of sizes of mills that will meet the desired requirements, and are not to be considered as absolutely correct on account of the various degrees of hardness of cement clinker. It may, however, be expected that Hardinge Mills will grind approximately the amount of material indicated, and in many cases the capacities will greatly exceed these figures.
The cost of grinding with Hardinge Mills is remarkably low. It has been found, by comparing the operation of Conical Mills with cylindrical tube mills in the grinding of ore and limestone, that with the same ball load in both types of mills, the cylindrical mill will consume about 60 per cent, more power for the same work as will the Conical Mill. Likewise, in comparison with a cylindrical tube mill, taking approximately the same power for operation, the Conical Mill will have a capacity greatly in excess of the tube mill, with a consequent lower cost of operation. It has been definitely determined that the wear on the lining plates and balls per ton of material ground, is much less in the Conical than in the cylindrical ball and tube mills.
Hardinge Mills require a minimum amount of attention in operation and maintenance, and, due to the low consumption of power per barrel of clinker, the cost of grinding is remarkably low. Clinker ground in Hardinge Mills with a maintenance cost at present prices should not exceed one-half cent per barrel, and on a conservative estimate, the complete cost of grinding on a five-year basis, during which time the first cost of equipment may be entirely absorbed, should favor the Hardinge Mill by at least 50 per cent, over any other machine or combination of machines presently used in the cement industry.
The Engineering Staff of the Company has had extensive and varied experience in the grinding of materials used in the manufacture of Portland Cement and various other industrial products, as well as the reduction of practically all types of ore. Their knowledge of the many problems incident to this work is at the disposal of those desiring information regarding the application of the Hardinge Mills to their individual requirements. In order that we may make an intelligent recommendation of the size and type of Conical Mill most adaptable, it is necessary that we have the following information:
Pulverized Coal Vertical Mill, also known asCoal Pulverizer,is widely used in coal industry, cement industry, chemical industry, electric power industry, and other industry which is the large-scale material grinding and superfine grinding processing. It is the ideal milling industry assembly equipment of crushing, grinding, drying, classification and conveying, being used for pulverized coal preparation can meet the industry fineness national standards.
As a kind of widely used energy, environmental protection and efficient of coal will make a great contribution to the realization of low carbon targets. The combustion efficiency of pulverized coal is closely related to its fineness, the more appropriate the fineness of pulverized coal, the more quickly it burns, the less the incomplete combustion loss, and the higher combustion efficiency. Therefore the use of high performance grinding equipment can greatly improve the utilization of coal thermal energy in coal processing.
In the process of pulverized coal production, the main motor drives the grinding disc through the speed reducer to rotate, while the hot air enters into the vertical mill body from the air inlet. The raw coal goes down to the center of the grinding disc through the feeding tube, and the disc rotating at a constant speed disperses the raw coal evenly by the centrifugal force to form a material bed with a certain thickness, at the same time raw coal is rolled and crushed by a number of grinding rollers. Under the driving by a continuous centrifugal force, the raw coal move to the grinding disc edge. When the powder leaving the grinding disc meets the hot gas entering the mill the air ring and ascends. The powder get into the separator through the middle shell, during which process the coal powder and the hot gas are fully heat exchanged and moisture is rapidly evaporated. The separator controls finished product granularity from the vertical mill outlet, and the particles larger than the specified size are separated and returned to the grinding disc. The pulverized coal meeting with the requirements of the fineness enter into dust collector and the finished product gets into the finished product warehouse.
2 Assembly equipment of crushing, grinding, classification and drying, the compact equipment layout, the simplification of technological process and saving infrastructure investment with construction area and building space is small more than 30% than the ball mill system.
Pulverized coal vertical mill has obvious advantages in grinding efficiency, energy consumption, environmental protection and other aspects, and its application in the field of coal grinding will become more and more popular. ZK is a professional pulverized coal vertical mill manufacturer, and we can provide high-quality products and intimate service. Welcome to visit our plant.
The ball mill accepts the SAG or AG mill product. Ball mills give a controlled final grind and produce flotation feed of a uniform size. Ball mills tumble iron or steel balls with the ore. The balls are initially 510 cm diameter but gradually wear away as grinding of the ore proceeds. The feed to ball mills (dry basis) is typically 75 vol.-% ore and 25% steel.
The ball mill is operated in closed circuit with a particle-size measurement device and size-control cyclones. The cyclones send correct-size material on to flotation and direct oversize material back to the ball mill for further grinding.
Grinding elements in ball mills travel at different velocities. Therefore, collision force, direction and kinetic energy between two or more elements vary greatly within the ball charge. Frictional wear or rubbing forces act on the particles, as well as collision energy. These forces are derived from the rotational motion of the balls and movement of particles within the mill and contact zones of colliding balls.
By rotation of the mill body, due to friction between mill wall and balls, the latter rise in the direction of rotation till a helix angle does not exceed the angle of repose, whereupon, the balls roll down. Increasing of rotation rate leads to growth of the centrifugal force and the helix angle increases, correspondingly, till the component of weight strength of balls become larger than the centrifugal force. From this moment the balls are beginning to fall down, describing during falling certain parabolic curves (Figure 2.7). With the further increase of rotation rate, the centrifugal force may become so large that balls will turn together with the mill body without falling down. The critical speed n (rpm) when the balls are attached to the wall due to centrifugation:
where Dm is the mill diameter in meters. The optimum rotational speed is usually set at 6580% of the critical speed. These data are approximate and may not be valid for metal particles that tend to agglomerate by welding.
The degree of filling the mill with balls also influences productivity of the mill and milling efficiency. With excessive filling, the rising balls collide with falling ones. Generally, filling the mill by balls must not exceed 3035% of its volume.
The mill productivity also depends on many other factors: physical-chemical properties of feed material, filling of the mill by balls and their sizes, armor surface shape, speed of rotation, milling fineness and timely moving off of ground product.
where b.ap is the apparent density of the balls; l is the degree of filling of the mill by balls; n is revolutions per minute; 1, and 2 are coefficients of efficiency of electric engine and drive, respectively.
A feature of ball mills is their high specific energy consumption; a mill filled with balls, working idle, consumes approximately as much energy as at full-scale capacity, i.e. during grinding of material. Therefore, it is most disadvantageous to use a ball mill at less than full capacity.
The ball mill is a tumbling mill that uses steel balls as the grinding media. The length of the cylindrical shell is usually 11.5 times the shell diameter (Figure 8.11). The feed can be dry, with less than 3% moisture to minimize ball coating, or slurry containing 2040% water by weight. Ball mills are employed in either primary or secondary grinding applications. In primary applications, they receive their feed from crushers, and in secondary applications, they receive their feed from rod mills, AG mills, or SAG mills.
Ball mills are filled up to 40% with steel balls (with 3080mm diameter), which effectively grind the ore. The material that is to be ground fills the voids between the balls. The tumbling balls capture the particles in ball/ball or ball/liner events and load them to the point of fracture.
When hard pebbles rather than steel balls are used for the grinding media, the mills are known as pebble mills. As mentioned earlier, pebble mills are widely used in the North American taconite iron ore operations. Since the weight of pebbles per unit volume is 3555% of that of steel balls, and as the power input is directly proportional to the volume weight of the grinding medium, the power input and capacity of pebble mills are correspondingly lower. Thus, in a given grinding circuit, for a certain feed rate, a pebble mill would be much larger than a ball mill, with correspondingly a higher capital cost. However, the increase in capital cost is justified economically by a reduction in operating cost attributed to the elimination of steel grinding media.
In general, ball mills can be operated either wet or dry and are capable of producing products in the order of 100m. This represents reduction ratios of as great as 100. Very large tonnages can be ground with these ball mills because they are very effective material handling devices. Ball mills are rated by power rather than capacity. Today, the largest ball mill in operation is 8.53m diameter and 13.41m long with a corresponding motor power of 22MW (Toromocho, private communications).
Planetary ball mills. A planetary ball mill consists of at least one grinding jar, which is arranged eccentrically on a so-called sun wheel. The direction of movement of the sun wheel is opposite to that of the grinding jars according to a fixed ratio. The grinding balls in the grinding jars are subjected to superimposed rotational movements. The jars are moved around their own axis and, in the opposite direction, around the axis of the sun wheel at uniform speed and uniform rotation ratios. The result is that the superimposition of the centrifugal forces changes constantly (Coriolis motion). The grinding balls describe a semicircular movement, separate from the inside wall, and collide with the opposite surface at high impact energy. The difference in speeds produces an interaction between frictional and impact forces, which releases high dynamic energies. The interplay between these forces produces the high and very effective degree of size reduction of the planetary ball mill. Planetary ball mills are smaller than common ball mills, and are mainly used in laboratories for grinding sample material down to very small sizes.
Vibration mill. Twin- and three-tube vibrating mills are driven by an unbalanced drive. The entire filling of the grinding cylinders, which comprises the grinding media and the feed material, constantly receives impulses from the circular vibrations in the body of the mill. The grinding action itself is produced by the rotation of the grinding media in the opposite direction to the driving rotation and by continuous head-on collisions of the grinding media. The residence time of the material contained in the grinding cylinders is determined by the quantity of the flowing material. The residence time can also be influenced by using damming devices. The sample passes through the grinding cylinders in a helical curve and slides down from the inflow to the outflow. The high degree of fineness achieved is the result of this long grinding procedure. Continuous feeding is carried out by vibrating feeders, rotary valves, or conveyor screws. The product is subsequently conveyed either pneumatically or mechanically. They are basically used to homogenize food and feed.
CryoGrinder. As small samples (100 mg or <20 ml) are difficult to recover from a standard mortar and pestle, the CryoGrinder serves as an alternative. The CryoGrinder is a miniature mortar shaped as a small well and a tightly fitting pestle. The CryoGrinder is prechilled, then samples are added to the well and ground by a handheld cordless screwdriver. The homogenization and collection of the sample is highly efficient. In environmental analysis, this system is used when very small samples are available, such as small organisms or organs (brains, hepatopancreas, etc.).
The vibratory ball mill is another kind of high-energy ball mill that is used mainly for preparing amorphous alloys. The vials capacities in the vibratory mills are smaller (about 10 ml in volume) compared to the previous types of mills. In this mill, the charge of the powder and milling tools are agitated in three perpendicular directions (Fig. 1.6) at very high speed, as high as 1200 rpm.
Another type of the vibratory ball mill, which is used at the van der Waals-Zeeman Laboratory, consists of a stainless steel vial with a hardened steel bottom, and a single hardened steel ball of 6 cm in diameter (Fig. 1.7).
The mill is evacuated during milling to a pressure of 106 Torr, in order to avoid reactions with a gas atmosphere. Subsequently, this mill is suitable for mechanical alloying of some special systems that are highly reactive with the surrounding atmosphere, such as rare earth elements.
A ball mill is a relatively simple apparatus in which the motion of the reactor, or of a part of it, induces a series of collisions of balls with each other and with the reactor walls (Suryanarayana, 2001). At each collision, a fraction of the powder inside the reactor is trapped between the colliding surfaces of the milling tools and submitted to a mechanical load at relatively high strain rates (Suryanarayana, 2001). This load generates a local nonhydrostatic mechanical stress at every point of contact between any pair of powder particles. The specific features of the deformation processes induced by these stresses depend on the intensity of the mechanical stresses themselves, on the details of the powder particle arrangement, that is on the topology of the contact network, and on the physical and chemical properties of powders (Martin et al., 2003; Delogu, 2008a). At the end of any given collision event, the powder that has been trapped is remixed with the powder that has not undergone this process. Correspondingly, at any instant in the mechanical processing, the whole powder charge includes fractions of powder that have undergone a different number of collisions.
The individual reactive processes at the perturbed interface between metallic elements are expected to occur on timescales that are, at most, comparable with the collision duration (Hammerberg et al., 1998; Urakaev and Boldyrev, 2000; Lund and Schuh, 2003; Delogu and Cocco, 2005a,b). Therefore, unless the ball mill is characterized by unusually high rates of powder mixing and frequency of collisions, reactive events initiated by local deformation processes at a given collision are not affected by a successive collision. Indeed, the time interval between successive collisions is significantly longer than the time period required by local structural perturbations for full relaxation (Hammerberg et al., 1998; Urakaev and Boldyrev, 2000; Lund and Schuh, 2003; Delogu and Cocco, 2005a,b).
These few considerations suffice to point out the two fundamental features of powder processing by ball milling, which in turn govern the MA processes in ball mills. First, mechanical processing by ball milling is a discrete processing method. Second, it has statistical character. All of this has important consequences for the study of the kinetics of MA processes. The fact that local deformation events are connected to individual collisions suggests that absolute time is not an appropriate reference quantity to describe mechanically induced phase transformations. Such a description should rather be made as a function of the number of collisions (Delogu et al., 2004). A satisfactory description of the MA kinetics must also account for the intrinsic statistical character of powder processing by ball milling. The amount of powder trapped in any given collision, at the end of collision is indeed substantially remixed with the other powder in the reactor. It follows that the same amount, or a fraction of it, could at least in principle be trapped again in the successive collision.
This is undoubtedly a difficult aspect to take into account in a mathematical description of MA kinetics. There are at least two extreme cases to consider. On the one hand, it could be assumed that the powder trapped in a given collision cannot be trapped in the successive one. On the other, it could be assumed that powder mixing is ideal and that the amount of powder trapped at a given collision has the same probability of being processed in the successive collision. Both these cases allow the development of a mathematical model able to describe the relationship between apparent kinetics and individual collision events. However, the latter assumption seems to be more reliable than the former one, at least for commercial mills characterized by relatively complex displacement in the reactor (Manai et al., 2001, 2004).
A further obvious condition for the successful development of a mathematical description of MA processes is the one related to the uniformity of collision regimes. More specifically, it is highly desirable that the powders trapped at impact always experience the same conditions. This requires the control of the ball dynamics inside the reactor, which can be approximately obtained by using a single milling ball and an amount of powder large enough to assure inelastic impact conditions (Manai et al., 2001, 2004; Delogu et al., 2004). In fact, the use of a single milling ball avoids impacts between balls, which have a remarkable disordering effect on the ball dynamics, whereas inelastic impact conditions permit the establishment of regular and periodic ball dynamics (Manai et al., 2001, 2004; Delogu et al., 2004).
All of the above assumptions and observations represent the basis and guidelines for the development of the mathematical model briefly outlined in the following. It has been successfully applied to the case of a Spex Mixer/ Mill mod. 8000, but the same approach can, in principle, be used for other ball mills.
The Planetary ball mills are the most popular mills used in MM, MA, and MD scientific researches for synthesizing almost all of the materials presented in Figure 1.1. In this type of mill, the milling media have considerably high energy, because milling stock and balls come off the inner wall of the vial (milling bowl or vial) and the effective centrifugal force reaches up to 20 times gravitational acceleration.
The centrifugal forces caused by the rotation of the supporting disc and autonomous turning of the vial act on the milling charge (balls and powders). Since the turning directions of the supporting disc and the vial are opposite, the centrifugal forces alternately are synchronized and opposite. Therefore, the milling media and the charged powders alternatively roll on the inner wall of the vial, and are lifted and thrown off across the bowl at high speed, as schematically presented in Figure 2.17.
However, there are some companies in the world who manufacture and sell number of planetary-type ball mills; Fritsch GmbH (www.fritsch-milling.com) and Retsch (http://www.retsch.com) are considered to be the oldest and principal companies in this area.
Fritsch produces different types of planetary ball mills with different capacities and rotation speeds. Perhaps, Fritsch Pulverisette P5 (Figure 2.18(a)) and Fritsch Pulverisette P6 (Figure 2.18(b)) are the most popular models of Fritsch planetary ball mills. A variety of vials and balls made of different materials with different capacities, starting from 80ml up to 500ml, are available for the Fritsch Pulverisette planetary ball mills; these include tempered steel, stainless steel, tungsten carbide, agate, sintered corundum, silicon nitride, and zirconium oxide. Figure 2.19 presents 80ml-tempered steel vial (a) and 500ml-agate vials (b) together with their milling media that are made of the same materials.
Figure 2.18. Photographs of Fritsch planetary-type high-energy ball mill of (a) Pulverisette P5 and (b) Pulverisette P6. The equipment is housed in the Nanotechnology Laboratory, Energy and Building Research Center (EBRC), Kuwait Institute for Scientific Research (KISR).
Figure 2.19. Photographs of the vials used for Fritsch planetary ball mills with capacity of (a) 80ml and (b) 500ml. The vials and the balls shown in (a) and (b) are made of tempered steel agate materials, respectively (Nanotechnology Laboratory, Energy and Building Research Center (EBRC), Kuwait Institute for Scientific Research (KISR)).
More recently and in year 2011, Fritsch GmbH (http://www.fritsch-milling.com) introduced a new high-speed and versatile planetary ball mill called Planetary Micro Mill PULVERISETTE 7 (Figure 2.20). The company claims this new ball mill will be helpful to enable extreme high-energy ball milling at rotational speed reaching to 1,100rpm. This allows the new mill to achieve sensational centrifugal accelerations up to 95 times Earth gravity. They also mentioned that the energy application resulted from this new machine is about 150% greater than the classic planetary mills. Accordingly, it is expected that this new milling machine will enable the researchers to get their milled powders in short ball-milling time with fine powder particle sizes that can reach to be less than 1m in diameter. The vials available for this new type of mill have sizes of 20, 45, and 80ml. Both the vials and balls can be made of the same materials, which are used in the manufacture of large vials used for the classic Fritsch planetary ball mills, as shown in the previous text.
Retsch has also produced a number of capable high-energy planetary ball mills with different capacities (http://www.retsch.com/products/milling/planetary-ball-mills/); namely Planetary Ball Mill PM 100 (Figure 2.21(a)), Planetary Ball Mill PM 100 CM, Planetary Ball Mill PM 200, and Planetary Ball Mill PM 400 (Figure 2.21(b)). Like Fritsch, Retsch offers high-quality ball-milling vials with different capacities (12, 25, 50, 50, 125, 250, and 500ml) and balls of different diameters (540mm), as exemplified in Figure 2.22. These milling tools can be made of hardened steel as well as other different materials such as carbides, nitrides, and oxides.
Figure 2.21. Photographs of Retsch planetary-type high-energy ball mill of (a) PM 100 and (b) PM 400. The equipment is housed in the Nanotechnology Laboratory, Energy and Building Research Center (EBRC), Kuwait Institute for Scientific Research (KISR).
Figure 2.22. Photographs of the vials used for Retsch planetary ball mills with capacity of (a) 80ml, (b) 250ml, and (c) 500ml. The vials and the balls shown are made of tempered steel (Nanotechnology Laboratory, Energy and Building Research Center (EBRC), Kuwait Institute for Scientific Research (KISR)).
Both Fritsch and Retsch companies have offered special types of vials that allow monitoring and measure the gas pressure and temperature inside the vial during the high-energy planetary ball-milling process. Moreover, these vials allow milling the powders under inert (e.g., argon or helium) or reactive gas (e.g., hydrogen or nitrogen) with a maximum gas pressure of 500kPa (5bar). It is worth mentioning here that such a development made on the vials design allows the users and researchers to monitor the progress tackled during the MA and MD processes by following up the phase transformations and heat realizing upon RBM, where the interaction of the gas used with the freshly created surfaces of the powders during milling (adsorption, absorption, desorption, and decomposition) can be monitored. Furthermore, the data of the temperature and pressure driven upon using this system is very helpful when the ball mills are used for the formation of stable (e.g., intermetallic compounds) and metastable (e.g., amorphous and nanocrystalline materials) phases. In addition, measuring the vial temperature during blank (without samples) high-energy ball mill can be used as an indication to realize the effects of friction, impact, and conversion processes.
More recently, Evico-magnetics (www.evico-magnetics.de) has manufactured an extraordinary high-pressure milling vial with gas-temperature-monitoring (GTM) system. Likewise both system produced by Fritsch and Retsch, the developed system produced by Evico-magnetics, allowing RBM but at very high gas pressure that can reach to 15,000kPa (150bar). In addition, it allows in situ monitoring of temperature and of pressure by incorporating GTM. The vials, which can be used with any planetary mills, are made of hardened steel with capacity up to 220ml. The manufacturer offers also two-channel system for simultaneous use of two milling vials.
Using different ball mills as examples, it has been shown that, on the basis of the theory of glancing collision of rigid bodies, the theoretical calculation of tPT conditions and the kinetics of mechanochemical processes are possible for the reactors that are intended to perform different physicochemical processes during mechanical treatment of solids. According to the calculations, the physicochemical effect of mechanochemical reactors is due to short-time impulses of pressure (P = ~ 10101011 dyn cm2) with shift, and temperature T(x, t). The highest temperature impulse T ~ 103 K are caused by the dry friction phenomenon.
Typical spatial and time parameters of the impactfriction interaction of the particles with a size R ~ 104 cm are as follows: localization region, x ~ 106 cm; time, t ~ 108 s. On the basis of the obtained theoretical results, the effect of short-time contact fusion of particles treated in various comminuting devices can play a key role in the mechanism of activation and chemical reactions for wide range of mechanochemical processes. This role involves several aspects, that is, the very fact of contact fusion transforms the solid phase process onto another qualitative level, judging from the mass transfer coefficients. The spatial and time characteristics of the fused zone are such that quenching of non-equilibrium defects and intermediate products of chemical reactions occurs; solidification of the fused zone near the contact point results in the formation of a nanocrystal or nanoamor- phous state. The calculation models considered above and the kinetic equations obtained using them allow quantitative ab initio estimates of rate constants to be performed for any specific processes of mechanical activation and chemical transformation of the substances in ball mills.
There are two classes of ball mills: planetary and mixer (also called swing) mill. The terms high-speed vibration milling (HSVM), high-speed ball milling (HSBM), and planetary ball mill (PBM) are often used. The commercial apparatus are PBMs Fritsch P-5 and Fritsch Pulverisettes 6 and 7 classic line, the Retsch shaker (or mixer) mills ZM1, MM200, MM400, AS200, the Spex 8000, 6750 freezer/mill SPEX CertiPrep, and the SWH-0.4 vibrational ball mill. In some instances temperature controlled apparatus were used (58MI1); freezer/mills were used in some rare cases (13MOP1824).
The balls are made of stainless steel, agate (SiO2), zirconium oxide (ZrO2), or silicon nitride (Si3N). The use of stainless steel will contaminate the samples with steel particles and this is a problem both for solid-state NMR and for drug purity.
However, there are many types of ball mills (see Chapter 2 for more details), such as drum ball mills, jet ball mills, bead-mills, roller ball mills, vibration ball mills, and planetary ball mills, they can be grouped or classified into two types according to their rotation speed, as follows: (i) high-energy ball mills and (ii) low-energy ball mills. Table 3.1 presents characteristics and comparison between three types of ball mills (attritors, vibratory mills, planetary ball mills and roller mills) that are intensively used on MA, MD, and MM techniques.
In fact, choosing the right ball mill depends on the objectives of the process and the sort of materials (hard, brittle, ductile, etc.) that will be subjecting to the ball-milling process. For example, the characteristics and properties of those ball mills used for reduction in the particle size of the starting materials via top-down approach, or so-called mechanical milling (MM process), or for mechanically induced solid-state mixing for fabrications of composite and nanocomposite powders may differ widely from those mills used for achieving mechanically induced solid-state reaction (MISSR) between the starting reactant materials of elemental powders (MA process), or for tackling dramatic phase transformation changes on the structure of the starting materials (MD). Most of the ball mills in the market can be employed for different purposes and for preparing of wide range of new materials.
Martinez-Sanchez et al.  have pointed out that employing of high-energy ball mills not only contaminates the milled amorphous powders with significant volume fractions of impurities that come from milling media that move at high velocity, but it also affects the stability and crystallization properties of the formed amorphous phase. They have proved that the properties of the formed amorphous phase (Mo53Ni47) powder depends on the type of the ball-mill equipment (SPEX 8000D Mixer/Mill and Zoz Simoloter mill) used in their important investigations. This was indicated by the high contamination content of oxygen on the amorphous powders prepared by SPEX 8000D Mixer/Mill, when compared with the corresponding amorphous powders prepared by Zoz Simoloter mill. Accordingly, they have attributed the poor stabilities, indexed by the crystallization temperature of the amorphous phase formed by SPEX 8000D Mixer/Mill to the presence of foreign matter (impurities).
Ball Mill The ball mill has been around for eons. There are many shapes and sizes and types. There is a single enclosed drum-type where material is placed in the drum along with a charge of grinding media. These can be in various shapes, and typically they are balls. There is a whole science in the size of the starting material versus the ball size, shape material of construction and charge percentage of grinding media. All of these variables affect particle size, shape, and grinding efficiency. This type of grinding is very good for abrasive materials to prevent contamination. The grinding media as well as the interior surfaces of the mill can be lined with abrasion resistant materials suited to the material being ground. In some cases, it can even be the material being ground. However, the batch type system is not a very efficient means of grinding. There is a variety of ball mill that is a continuous process versus a batch process. It has an external classifier which returns the oversized material to the ball mill for further milling. This system is much more efficient in the grinding ability, but it is much more difficult to line the entire system with wear parts to grind an abrasive material.
Ball mill grinding is one method of crushing ore to an appropriate size fraction.Specifically, ore is put into a large receptacle (a drum) and then it rotates slowly around.Inside the receptacle, there are balls, usually made of metal, that as the ore is rotated around the revolving drum the ore is crushed as the balls rise and fall.The drum has a slight tilt to it, from one end to the other so that the ore slowly works its way to discharging end.The trick or art to all of this is to rotate the drum at a distinct rpm and the balls are harder than the ore so as to efficiently crush the continuous stream of ore to the desired size at the discharge end.
The ball mill is a key piece of equipment for grinding crushed materials, and it is widely used in production lines for powders such as cement, silicates, refractory material, fertilizer, glass ceramics, etc. as well as for ore dressing of both ferrous and non-ferrous metals. The ball mill can grind various ores and other materials either wet or dry. There are two kinds of ball mill, grate type and overfall type due to different ways of discharging material. There are many types of grinding media suitable for use in a ball mill, each material having its own specific properties and advantages. Key properties of grinding media are size, density, hardness, and composition.
The grinding chamber can also be filled with an inertshield gasthat does not react with the material being ground, to prevent oxidation or explosive reactions that could occur with ambient air inside the mill.
Overflow ball mill is a kind ofball grinding millwhich works in wet water state. It belongs to a type of wet ball mill and is a very common grinding equipment in the concentrator. Ball grinding mills are classified according to the discharge methods and can be divided into overflow ball mill and grate ball mill. Unlike the grate ball mill, the overflow type ball mill has a simple structure, and the discharge method is based on the gravity flow of the slurry to discharge the ore.
The product size of the overflow discharge ball mill is generally less than 0.2mm, which is suitable for concentrate re-grinding operation and can be used as one-stage grinding or two-stage grinding operation to obtain fine qualified products.
The slow transmission system is added to the wet overflow ball mill. When the ball mill is started, the low-speed slow-speed transmission system operates first, and the high-speed main motor transmission system operates later. This not only saves energy consumption but also reduces the impact on the overflow type ball mill barrel and power grid system.
The main part of the overflow discharge ball mill is a barrel with a smaller diameter and larger length, which is supported by rolling bearing and rotates slowly by transmission mechanism. The material is fed from the feeding end of the barrel, and the material is crushed in the barrel due to the impact of the steel ball and the ore itself.
The diameter of the hollow shaft at the discharge end of the wet overflow ball mill is slightly larger than that at the feed end, resulting in a certain inclination angle of the pulp in the mill towards the discharge end. Due to the continuous feeding of materials, the pressure makes the materials in the barrel move from the feeding end to the discharging end.
When the height of the slurry surface is higher than the lowest generatrix of the inner diameter of the discharge port, the slurry overflows out of the overflow discharge ball mill. This is a non forced high-level ore discharge with sufficient grinding and good grinding effect. The hollow shaft at the discharge end of the overflow type ball mill has reverse spiral blades, which can return the overflowing steel balls and coarse ore blocks to the mill.
As a ball mills supplier with 22 years of experience in the grinding industry, we can provide customers with types of ball mill, vertical mill, rod mill and AG/SAG mill for grinding in a variety of industries and materials.
Ball mill is a major equipment in the production of power plants, cement plants, mines, chemical industry, metallurgy and other industries, the liner is one of the components of the mill, the main role is to protect the cylinder, the cylinder from the grinding body and Material direct impact and friction, help to improve the mill grinding efficiency, increase production and reduce metal consumption. As the liner in the harsh conditions of long-term conditions, maintenance and replacement of considerable volume, not only requires human, material and financial resources, but also a direct impact on productivity.
Ball mill liner plays a major role in protecting the inner wall of the anchor windlass. Different shapes of the ball mill lining plate can improve the grinding effect of the ball mill and improve the working efficiency of the ball mill. 1, flat ball mill liner, the surface smooth, suitable for installation in the fine grinding warehouse. 2, the pressure of the type of ball mill liner, suitable for coarse grinding warehouse, for low speed ball mill. 3, ladder-type ball mill liner, ladder liner is better than the pressure liner, suitable for installation in the coarse grinding warehouse. 4, small corrugated liner crest and pitch are small, suitable for fine grinding and coal mill. 5, end cover liner installed in the grinding head cover or cylinder cover to protect the end cover from wear and tear. 6, ring groove liner in the lining of the T surface for casting a circular groove, after installation to form a circular groove, suitable for multi-warehouse grinding of the first and second positions, dry, wet grinding Machine can be. 7, grading liner, grinding mill for the ideal state should be large particles of material with a large diameter grinding body to impact and crush, that is, in the direction of the mill feed with large diameter grinding body, with the material The direction of the material to the gradual reduction of the grinding body should be sequentially reduced.
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