## building a ball mill for grinding chemicals

Ball mills are used in chemistry and in industry to grind hard solids to a very fine powder. They are very similar to rock tumblers. Basically, the idea is to rotate a container filled with heavy metal balls that crush the substance that you want to grind. Ball mills can be used to grind ceramic material, crystalline compounds, and even some metals.

Note: If you are clever, you can substitute most of these materials with other household items or things you may find in dumpsters. Also, the sizes used are just what I used in my mill and are here to give you a general idea.

Your final goal is to get a container rotating at about 50-100 rpm. If it goes too slowly, the balls will just roll in place- too fast and the centripetal force will be too strong and the balls will just roll along the sides of the container. What you want is the balls to reach the top of the container and then come crashing down.

First figure out what the speed of your motor runs. Most motors should have it labeled, but if it isn't you'll have to time it yourself. This can be done by hooking up the motor to two pulleys with known diameters and then by counting how many times the larger pulley rotates in one minute.

My motor runs at 1725 rpm and I attached a 1-3/4" (diameter) pulley to it. This pulley turns a belt which in turn rotates a 7.5" pulley. This corresponds to a reduction ratio of 1:7.5/1.75 or 1:4.25. This means that my larger pulley runs 4.25 times slower than the motor or at about 400 rpm. The axle that the larger pulley rotates has a diameter of 3/4" (including the rubber hose) and it rotates the 3.5" container. This additional reduction of 1:3.5/0.75 or 1:4.67 means that the container should theoretically rotate at 400/4.67 rpm or about 85 rpm. I measured a speed of 80 rpm- the slightly lower speed due to frictional losses.

## ball mill - an overview | sciencedirect topics

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.[44] 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. [4] 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 mills

In all ore dressing and milling Operations, including flotation, cyanidation, gravity concentration, and amalgamation, the Working Principle is to crush and grind, often with rob mill & ball mills, the ore in order to liberate the minerals. In the chemical and process industries, grinding is an important step in preparing raw materials for subsequent treatment.In present day practice, ore is reduced to a size many times finer than can be obtained with crushers. Over a period of many years various fine grinding machines have been developed and used, but the ball mill has become standard due to its simplicity and low operating cost.

A ball millefficiently operated performs a wide variety of services. In small milling plants, where simplicity is most essential, it is not economical to use more than single stage crushing, because the Steel-Head Ball or Rod Mill will take up to 2 feed and grind it to the desired fineness. In larger plants where several stages of coarse and fine crushing are used, it is customary to crush from 1/2 to as fine as 8 mesh.

Many grinding circuits necessitate regrinding of concentrates or middling products to extremely fine sizes to liberate the closely associated minerals from each other. In these cases, the feed to the ball mill may be from 10 to 100 mesh or even finer.

Where the finished product does not have to be uniform, a ball mill may be operated in open circuit, but where the finished product must be uniform it is essential that the grinding mill be used in closed circuit with a screen, if a coarse product is desired, and with a classifier if a fine product is required. In most cases it is desirable to operate the grinding mill in closed circuit with a screen or classifier as higher efficiency and capacity are obtained. Often a mill using steel rods as the grinding medium is recommended, where the product must have the minimum amount of fines (rods give a more nearly uniform product).

Often a problem requires some study to determine the economic fineness to which a product can or should be ground. In this case the 911Equipment Company offers its complete testing service so that accurate grinding mill size may be determined.

Until recently many operators have believed that one particular type of grinding mill had greater efficiency and resulting capacity than some other type. However, it is now commonly agreed and accepted that the work done by any ballmill depends directly upon the power input; the maximum power input into any ball or rod mill depends upon weight of grinding charge, mill speed, and liner design.

The apparent difference in capacities between grinding mills (listed as being the same size) is due to the fact that there is no uniform method of designating the size of a mill, for example: a 5 x 5 Ball Mill has a working diameter of 5 inside the liners and has 20 per cent more capacity than all other ball mills designated as 5 x 5 where the shell is 5 inside diameter and the working diameter is only 48 with the liners in place.

Ball-Rod Mills, based on 4 liners and capacity varying as 2.6 power of mill diameter, on the 5 size give 20 per cent increased capacity; on the 4 size, 25 per cent; and on the 3 size, 28 per cent. This fact should be carefully kept in mind when determining the capacity of a Steel- Head Ball-Rod Mill, as this unit can carry a greater ball or rod charge and has potentially higher capacity in a given size when the full ball or rod charge is carried.

A mill shorter in length may be used if the grinding problem indicates a definite power input. This allows the alternative of greater capacity at a later date or a considerable saving in first cost with a shorter mill, if reserve capacity is not desired. The capacities of Ball-Rod Mills are considerably higher than many other types because the diameters are measured inside the liners.

The correct grinding mill depends so much upon the particular ore being treated and the product desired, that a mill must have maximum flexibility in length, type of grinding medium, type of discharge, and speed.With the Ball-Rod Mill it is possible to build this unit in exact accordance with your requirements, as illustrated.

To best serve your needs, the Trunnion can be furnished with small (standard), medium, or large diameter opening for each type of discharge. The sketch shows diagrammatic arrangements of the four different types of discharge for each size of trunnion opening, and peripheral discharge is described later.

Ball-Rod Mills of the grate discharge type are made by adding the improved type of grates to a standard Ball-Rod Mill. These grates are bolted to the discharge head in much the same manner as the standard headliners.

The grates are of alloy steel and are cast integral with the lifter bars which are essential to the efficient operation of this type of ball or rod mill. These lifter bars have a similar action to a pump:i. e., in lifting the product so as to discharge quickly through the mill trunnion.

These Discharge Grates also incorporate as an integral part, a liner between the lifters and steel head of the ball mill to prevent wear of the mill head. By combining these parts into a single casting, repairs and maintenance are greatly simplified. The center of the grate discharge end of this mill is open to permit adding of balls or for adding water to the mill through the discharge end.

Instead of being constructed of bars cast into a frame, Grates are cast entire and have cored holes which widen toward the outside of the mill similar to the taper in grizzly bars. The grate type discharge is illustrated.

The peripheral discharge type of Ball-Rod Mill is a modification of the grate type, and is recommended where a free gravity discharge is desired. It is particularly applicable when production of too many fine particles is detrimental and a quick pass through the mill is desired, and for dry grinding.

The drawings show the arrangement of the peripheral discharge. The discharge consists of openings in the shell into which bushings with holes of the desired size are inserted. On the outside of the mill, flanges are used to attach a stationary discharge hopper to prevent pulp splash or too much dust.

The mill may be operated either as a peripheral discharge or a combination or peripheral and trunnion discharge unit, depending on the desired operating conditions. If at any time the peripheral discharge is undesirable, plugs inserted into the bushings will convert the mill to a trunnion discharge type mill.

Unless otherwise specified, a hard iron liner is furnished. This liner is made of the best grade white iron and is most serviceable for the smaller size mills where large balls are not used. Hard iron liners have a much lower first cost.

Electric steel, although more expensive than hard iron, has advantage of minimum breakage and allows final wear to thinner section. Steel liners are recommended when the mills are for export or where the source of liner replacement is at a considerable distance.

Molychrome steel has longer wearing qualities and greater strength than hard iron. Breakage is not so apt to occur during shipment, and any size ball can be charged into a mill equipped with molychrome liners.

Manganese liners for Ball-Rod Mills are the world famous AMSCO Brand, and are the best obtainable. The first cost is the highest, but in most cases the cost per ton of ore ground is the lowest. These liners contain 12 to 14% manganese.

The feed and discharge trunnions are provided with cast iron or white iron throat liners. As these parts are not subjected to impact and must only withstand abrasion, alloys are not commonly used but can be supplied.

Gears for Ball-Rod Mills drives are furnished as standard on the discharge end of the mill where they are out of the way of the classifier return, scoop feeder, or original feed. Due to convertible type construction the mills can be furnished with gears on the feed end. Gear drives are available in two alternative combinations, which are:

All pinions are properly bored, key-seated, and pressed onto the steel countershaft, which is oversize and properly keyseated for the pinion and drive pulleys or sheaves. The countershaft operates on high grade, heavy duty, nickel babbitt bearings.

Any type of drive can be furnished for Ball-Rod Mills in accordance with your requirements. Belt drives are available with pulleys either plain or equipped with friction clutch. Various V- Rope combinations can also be supplied.

The most economical drive to use up to 50 H. P., is a high starting torque motor connected to the pinion shaft by means of a flat or V-Rope drive. For larger size motors the wound rotor (slip ring) is recommended due to its low current requirement in starting up the ball mill.

Should you be operating your own power plant or have D. C. current, please specify so that there will be no confusion as to motor characteristics. If switches are to be supplied, exact voltage to be used should be given.

Even though many ores require fine grinding for maximum recovery, most ores liberate a large percentage of the minerals during the first pass through the grinding unit. Thus, if the free minerals can be immediately removed from the ball mill classifier circuit, there is little chance for overgrinding.

This is actually what has happened wherever Mineral Jigs or Unit Flotation Cells have been installed in the ball mill classifier circuit. With the installation of one or both of these machines between the ball mill and classifier, as high as 70 per cent of the free gold and sulphide minerals can be immediately removed, thus reducing grinding costs and improving over-all recovery. The advantage of this method lies in the fact that heavy and usually valuable minerals, which otherwise would be ground finer because of their faster settling in the classifier and consequent return to the grinding mill, are removed from the circuit as soon as freed. This applies particularly to gold and lead ores.

Ball-Rod Mills have heavy rolled steel plate shells which are arc welded inside and outside to the steel heads or to rolled steel flanges, depending upon the type of mill. The double welding not only gives increased structural strength, but eliminates any possibility of leakage.

Where a single or double flanged shell is used, the faces are accurately machined and drilled to template to insure perfect fit and alignment with the holes in the head. These flanges are machined with male and female joints which take the shearing stresses off the bolts.

The Ball-Rod Mill Heads are oversize in section, heavily ribbed and are cast from electric furnace steel which has a strength of approximately four times that of cast iron. The head and trunnion bearings are designed to support a mill with length double its diameter. This extra strength, besides eliminating the possibility of head breakage or other structural failure (either while in transit or while in service), imparts to Ball-Rod Mills a flexibility heretofore lacking in grinding mills. Also, for instance, if you have a 5 x 5 mill, you can add another 5 shell length and thus get double the original capacity; or any length required up to a maximum of 12 total length.

On Type A mills the steel heads are double welded to the rolled steel shell. On type B and other flanged type mills the heads are machined with male and female joints to match the shell flanges, thus taking the shearing stresses from the heavy machine bolts which connect the shell flanges to the heads.

The manhole cover is protected from wear by heavy liners. An extended lip is provided for loosening the door with a crow-bar, and lifting handles are also provided. The manhole door is furnished with suitable gaskets to prevent leakage.

The mill trunnions are carried on heavy babbitt bearings which provide ample surface to insure low bearing pressure. If at any time the normal length is doubled to obtain increased capacity, these large trunnion bearings will easily support the additional load. Trunnion bearings are of the rigid type, as the perfect alignment of the trunnion surface on Ball-Rod Mills eliminates any need for the more expensive self-aligning type of bearing.

The cap on the upper half of the trunnion bearing is provided with a shroud which extends over the drip flange of the trunnion and effectively prevents the entrance of dirt or grit. The bearing has a large space for wool waste and lubricant and this is easily accessible through a large opening which is covered to prevent dirt from getting into the bearing.Ball and socket bearings can be furnished.

Scoop Feeders for Ball-Rod Mills are made in various radius sizes. Standard scoops are made of cast iron and for the 3 size a 13 or 19 feeder is supplied, for the 4 size a 30 or 36, for the 5 a 36 or 42, and for the 6 a 42 or 48 feeder. Welded steel scoop feeders can, however, be supplied in any radius.

The correct size of feeder depends upon the size of the classifier, and the smallest feeder should be used which will permit gravity flow for closed circuit grinding between classifier and the ball or rod mill. All feeders are built with a removable wearing lip which can be easily replaced and are designed to give minimum scoop wear.

A combination drum and scoop feeder can be supplied if necessary. This feeder is made of heavy steel plate and strongly welded. These drum-scoop feeders are available in the same sizes as the cast iron feeders but can be built in any radius. Scoop liners can be furnished.

The trunnions on Ball-Rod Mills are flanged and carefully machined so that scoops are held in place by large machine bolts and not cap screws or stud bolts. The feed trunnion flange is machined with a shoulder for insuring a proper fit for the feed scoop, and the weight of the scoop is carried on this shoulder so that all strain is removed from the bolts which hold the scoop.

High carbon steel rods are recommended, hot rolled, hot sawed or sheared, to a length of 2 less than actual length of mill taken inside the liners. The initial rod charge is generally a mixture ranging from 1.5 to 3 in diameter. During operation, rod make-up is generally the maximum size. The weights per lineal foot of rods of various diameters are approximately: 1.5 to 6 lbs.; 2-10.7 lbs.; 2.5-16.7 lbs.; and 3-24 lbs.

Forged from the best high carbon manganese steel, they are of the finest quality which can be produced and give long, satisfactory service. Data on ball charges for Ball-Rod Mills are listed in Table 5. Further information regarding grinding balls is included in Table 6.

Rod Mills has a very define and narrow discharge product size range. Feeding a Rod Mill finer rocks will greatly impact its tonnage while not significantly affect its discharge product sizes. The 3.5 diameter rod of a mill, can only grind so fine.

Crushers are well understood by most. Rod and Ball Mills not so much however as their size reduction actions are hidden in the tube (mill). As for Rod Mills, the image above best expresses what is going on inside. As rocks is feed into the mill, they are crushed (pinched) by the weight of its 3.5 x 16 rods at one end while the smaller particles migrate towards the discharge end and get slightly abraded (as in a Ball Mill) on the way there.

We haveSmall Ball Mills for sale coming in at very good prices. These ball mills are relatively small, bearing mounted on a steel frame. All ball mills are sold with motor, gears, steel liners and optional grinding media charge/load.

Ball Mills or Rod Mills in a complete range of sizes up to 10 diameter x20 long, offer features of operation and convertibility to meet your exactneeds. They may be used for pulverizing and either wet or dry grindingsystems. Mills are available in both light-duty and heavy-duty constructionto meet your specific requirements.

All Mills feature electric cast steel heads and heavy rolled steelplate shells. Self-aligning main trunnion bearings on large mills are sealedand internally flood-lubricated. Replaceable mill trunnions. Pinion shaftbearings are self-aligning, roller bearing type, enclosed in dust-tightcarrier. Adjustable, single-unit soleplate under trunnion and drive pinionsfor perfect, permanent gear alignment.

Ball Mills can be supplied with either ceramic or rubber linings for wet or dry grinding, for continuous or batch type operation, in sizes from 15 x 21 to 8 x 12. High density ceramic linings of uniform hardness male possible thinner linings and greater and more effective grinding volume. Mills are shipped with liners installed.

Complete laboratory testing service, mill and air classifier engineering and proven equipment make possible a single source for your complete dry-grinding mill installation. Units available with air swept design and centrifugal classifiers or with elevators and mechanical type air classifiers. All sizes and capacities of units. Laboratory-size air classifier also available.

A special purpose batch mill designed especially for grinding and mixing involving acids and corrosive materials. No corners mean easy cleaning and choice of rubber or ceramic linings make it corrosion resistant. Shape of mill and ball segregation gives preferential grinding action for grinding and mixing of pigments and catalysts. Made in 2, 3 and 4 diameter grinding drums.

Nowadays grinding mills are almost extensively used for comminution of materials ranging from 5 mm to 40 mm (3/161 5/8) down to varying product sizes. They have vast applications within different branches of industry such as for example the ore dressing, cement, lime, porcelain and chemical industries and can be designed for continuous as well as batch grinding.

Ball mills can be used for coarse grinding as described for the rod mill. They will, however, in that application produce more fines and tramp oversize and will in any case necessitate installation of effective classification.If finer grinding is wanted two or three stage grinding is advisable as for instant primary rod mill with 75100 mm (34) rods, secondary ball mill with 2540 mm(11) balls and possibly tertiary ball mill with 20 mm () balls or cylpebs.To obtain a close size distribution in the fine range the specific surface of the grinding media should be as high as possible. Thus as small balls as possible should be used in each stage.

The principal field of rod mill usage is the preparation of products in the 5 mm0.4 mm (4 mesh to 35 mesh) range. It may sometimes be recommended also for finer grinding. Within these limits a rod mill is usually superior to and more efficient than a ball mill. The basic principle for rod grinding is reduction by line contact between rods extending the full length of the mill, resulting in selective grinding carried out on the largest particle sizes. This results in a minimum production of extreme fines or slimes and more effective grinding work as compared with a ball mill. One stage rod mill grinding is therefore suitable for preparation of feed to gravimetric ore dressing methods, certain flotation processes with slime problems and magnetic cobbing. Rod mills are frequently used as primary mills to produce suitable feed to the second grinding stage. Rod mills have usually a length/diameter ratio of at least 1.4.

Tube mills are in principle to be considered as ball mills, the basic difference being that the length/diameter ratio is greater (35). They are commonly used for surface cleaning or scrubbing action and fine grinding in open circuit.

In some cases it is suitable to use screened fractions of the material as grinding media. Such mills are usually called pebble mills, but the working principle is the same as for ball mills. As the power input is approximately directly proportional to the volume weight of the grinding media, the power input for pebble mills is correspondingly smaller than for a ball mill.

A dry process requires usually dry grinding. If the feed is wet and sticky, it is often necessary to lower the moisture content below 1 %. Grinding in front of wet processes can be done wet or dry. In dry grinding the energy consumption is higher, but the wear of linings and charge is less than for wet grinding, especially when treating highly abrasive and corrosive material. When comparing the economy of wet and dry grinding, the different costs for the entire process must be considered.

An increase in the mill speed will give a directly proportional increase in mill power but there seems to be a square proportional increase in the wear. Rod mills generally operate within the range of 6075 % of critical speed in order to avoid excessive wear and tangled rods. Ball and pebble mills are usually operated at 7085 % of critical speed. For dry grinding the speed is usually somewhat lower.

The mill lining can be made of rubber or different types of steel (manganese or Ni-hard) with liner types according to the customers requirements. For special applications we can also supply porcelain, basalt and other linings.

The mill power is approximately directly proportional to the charge volume within the normal range. When calculating a mill 40 % charge volume is generally used. In pebble and ball mills quite often charge volumes close to 50 % are used. In a pebble mill the pebble consumption ranges from 315 % and the charge has to be controlled automatically to maintain uniform power consumption.

In all cases the net energy consumption per ton (kWh/ton) must be known either from previous experience or laboratory tests before mill size can be determined. The required mill net power P kW ( = ton/hX kWh/ton) is obtained from

Trunnions of S.G. iron or steel castings with machined flange and bearing seat incl. device for dismantling the bearings. For smaller mills the heads and trunnions are sometimes made in grey cast iron.

The mills can be used either for dry or wet, rod or ball grinding. By using a separate attachment the discharge end can be changed so that the mills can be used for peripheral instead of overflow discharge.

## effect of ball and feed particle size distribution on the milling efficiency of a ball mill: an attainable region approach - sciencedirect

In this article, alternative forms of optimizing the milling efficiency of a laboratory scale ball mill by varying the grinding media size distribution and the feed material particle size distribution were investigated. Silica ore was used as the test material. The experimental parameters that were kept constant in this investigation was the grinding media filling, powder filling and the mill rotational speed. The data obtained from these batch tests was then analyzed using a model free technique called the Attainable Region method. This analysis technique showed that the required product fineness is a function of grinding media and feed material size distributions. It was also observed from the experimental results that in order to increase the milling efficiency of a ball mill, towards optimum production of material in the desired size class, there is a need to correlate the ball size and the feed size distributions.

## used ball mills | ball mills for sale | phoenix equipment

Why buy a brand new ball mill when we have high-quality used and refurbished ball mills for sale? Well-made industrial equipment from top manufacturers maintain their value and save your company or industry substantially.

Ball mills are a fundamental part of the manufacturing industry in the USA as well as around the world. Ball mills crush material into various sizes and extract resources from mined materials. Pebble mills are a type of ball mill and are also used to reduce the size of hard materials, down to 1 micron or less.

Because of their fairly simple design, ball mills and pebble mills are less likely to need costly repairs (unlike other crushing or extraction equipment) making them an attractive option for businesses on a budget.

Unused 24 x 41 Polysius EGL Ball Mill. Steel Lined. Twin 7MW Electric Motor Drives, 14MW/11kV Power Supply Unit. Twin Combiflex Fixed Speed Gear Drive. Auxiliary Drive Motors, Lubrication Unit Fixed Bearing and Lubrication Unit Floating Bearing, Frozen Charge Protection System, Vibration Sensors for COMBIFLEX, Dam Ring, Permanent installed Centrifuge for Fixed Bearing, Closed Circuit Chiller Unit, Insurance and Commissioning Spares, Special Tools. Qty 2 Available.

Used 11.5' diameter X 17' long ball mill. Manufactured by KVS (Kennedy Van Saun). 1000 HP open winding synchronous motor. Features trommel discharge and feed tank. Refurbished in 2013, which included installation of new oil jacking system, oil lube system for Babbitt bearings, new titanium steel water jet-machined discharge grates, and motor refurbishment. Set of new babbit bearings available. Previously operated as a closed circuit dry mill with grinding capacity of 40 metric tons per hour with output fineness of >80% passing 200 mesh. Motor operating speed of 15.8 RPM charged with approximately 78 tons of 1", 2" and 3" steel balls. Last used at a phosphate processing facility and in good condition.

Used 8' x 10' Epworth 200 HP jacketed steel ball mill, approximately 8' diameter x 10' long, jacketed chamber, gear and pinion driven with approximately 200 motor drive, on stands, Serial# K-0845.

Used 175HP Hosokawa Alpine Super Orion Continuous Ball mill. Model 195/495 CLKE. Alumina Oxide lined. 195 cm (76")inner diameter x 495 cm (194") long drum, periphery dry discharge with adjustable discharge openings, enclosed discharge housing, direct driven thru gearbox. 175HP 460 volt motor with VFD motor controller. Serial# C1198474. Built 2012.

Used 6' x 8' Paul Abbe jacketed 100 HP steel ball mill, approximately 6' diameter x 8' long, jacketed chamber, gear and pinion driven with approximately 100 motor drive, on stands.

Unused 5' diameter X 6' long Steel Lined Ball Mill, manufactured by Patterson Industries, Type D, non-jacketed, with AR400 steel liners. Includes 30 HP, 3 phase, 60 Hz, 230-460 V, 1725 RPM motor. Mill drive is integrally coupled to horizontal parallel shafted helical gear reducer. Continuous type, with product feeding through spiral inlet trunnion and exiting through the discharge end trunnion. Features cylinder manway access door for cleaning. Internal volume measures approximately 839 USG (112 CF). Mill shell is lined with (24) 1/4" thick liner plates, each head lined with (8) 3/8" thick pie-shaped liner plates. Mounted on stand with approximately 66" clearance between the mill cylinder and floor. Mills were intended for use in glass particle size reduction but were never installed. Manufactured in 2019, units are still in factory plastic wrap and in new condition. (Qty - 2 available)

Used 5 ft. dia. x 6 ft. (Approx 120 Cu.Ft) Patterson Pebble Mill. Alumina brick lining. On stand with 20 HP motor and gear reduced drive with brake. Bull gear and pinion. Babbit bearings. Door is polyurethane and has a drain with plug.

Used 4' x 5' (345 Gallon Total/210 Gallon Working) Ball Mill. Mfg Steveco. Steel Lining. Jacketed. 20 HP (460V/60Hz/3ph) Gear Reduced heavy duty drive on high stands. Solid door and discharge door.

Used Paul O. Abbe One Piece Ceramic Ball Mill, Model JM-300. Non-Jacketed chamber approximate 24.8" diameter x 39.5" long. Vessel volume 300 liter (79 gallons). Approximate 5" charge and discharge port with cover. Driven by a 3 HP, 3/60/208-230/460 volt 1760 rpm motor with a shaft mounted Sumitomo Model 203E-25 reducer. Approximate 32 rpm drum speed. Includes a control panel with an ABB drive. Mounted on a common carbon steel frame legs. Serial # 0830032JM. Built 2008.

Used 28 Gallon Paul O. Abbe Ceramic Jar / Ball Mill. Approximate 3.7 Cubic Feet. Approximate 20" diameter x 20" straight side. Includes motor and cage. Mounted on a carbon steel frame with safety cage.

Used 30 gallon Paul O. Abbe Jar Mill. Porcelain jar 21" diameter x 18" straight side. Driven by 1hp, 1/60/115/230 volt, 1740 rpm motor thru a reducer, ratio 9.3 to 1. Inlet & outlet with cover and clamp. Mounted on carbon steel legs with a discharge housing. Serial#84876

Used 25 Gallon Norton Chemical Process Products Jar Mill. Porcelain jar 20" diameter x 20" straight side. Driven by 1hp, 3/60/230/460 volt, 1730 rpm motor thru a reducer, no ratio. Inlet & outlet with cover and clamp. Mounted on carbon steel legs with a discharge housing. Serial# AV-83104.

Used 35.30 Gallon Paul O. Abbe Jar Mill. Model 5A Porcelain jar 22" diameter x 20" straight side. Driven by 1hp, 3/60/230/460 volt, 1745 rpm motor thru a reducer, ratio 25 to 1. Inlet & outlet with cover and clamp. Mounted on carbon steel legs with a discharge housing. Serial#A41563.

Unused 24 x 41 Polysius EGL Ball Mill. Steel Lined. Twin 7MW Electric Motor Drives, 14MW/11kV Power Supply Unit. Twin Combiflex Fixed Speed Gear Drive. Auxiliary Drive Motors, Lubrication Unit Fixed Bearing and Lubrication Unit Floating Bearing, Frozen Charge Protection System, Vibration Sensors for COMBIFLEX, Dam Ring, Permanent installed Centrifuge for Fixed Bearing, Closed Circuit Chiller Unit, Insurance and Commissioning Spares, Special Tools. Qty 2 Available.

Used 11.5' diameter X 17' long ball mill. Manufactured by KVS (Kennedy Van Saun). 1000 HP open winding synchronous motor. Features trommel discharge and feed tank. Refurbished in 2013, which included installation of new oil jacking system, oil lube system for Babbitt bearings, new titanium steel water jet-machined discharge grates, and motor refurbishment. Set of new babbit bearings available. Previously operated as a closed circuit dry mill with grinding capacity of 40 metric tons per hour with output fineness of >80% passing 200 mesh. Motor operating speed of 15.8 RPM charged with approximately 78 tons of 1", 2" and 3" steel balls. Last used at a phosphate processing facility and in good condition.

Used 8' x 10' Epworth 200 HP jacketed steel ball mill, approximately 8' diameter x 10' long, jacketed chamber, gear and pinion driven with approximately 200 motor drive, on stands, Serial# K-0845.

Used 175HP Hosokawa Alpine Super Orion Continuous Ball mill. Model 195/495 CLKE. Alumina Oxide lined. 195 cm (76")inner diameter x 495 cm (194") long drum, periphery dry discharge with adjustable discharge openings, enclosed discharge housing, direct driven thru gearbox. 175HP 460 volt motor with VFD motor controller. Serial# C1198474. Built 2012.

Used 6' x 8' Paul Abbe jacketed 100 HP steel ball mill, approximately 6' diameter x 8' long, jacketed chamber, gear and pinion driven with approximately 100 motor drive, on stands.

Unused 5' diameter X 6' long Steel Lined Ball Mill, manufactured by Patterson Industries, Type D, non-jacketed, with AR400 steel liners. Includes 30 HP, 3 phase, 60 Hz, 230-460 V, 1725 RPM motor. Mill drive is integrally coupled to horizontal parallel shafted helical gear reducer. Continuous type, with product feeding through spiral inlet trunnion and exiting through the discharge end trunnion. Features cylinder manway access door for cleaning. Internal volume measures approximately 839 USG (112 CF). Mill shell is lined with (24) 1/4" thick liner plates, each head lined with (8) 3/8" thick pie-shaped liner plates. Mounted on stand with approximately 66" clearance between the mill cylinder and floor. Mills were intended for use in glass particle size reduction but were never installed. Manufactured in 2019, units are still in factory plastic wrap and in new condition. (Qty - 2 available)

Used 5 ft. dia. x 6 ft. (Approx 120 Cu.Ft) Patterson Pebble Mill. Alumina brick lining. On stand with 20 HP motor and gear reduced drive with brake. Bull gear and pinion. Babbit bearings. Door is polyurethane and has a drain with plug.

Used 4' x 5' (345 Gallon Total/210 Gallon Working) Ball Mill. Mfg Steveco. Steel Lining. Jacketed. 20 HP (460V/60Hz/3ph) Gear Reduced heavy duty drive on high stands. Solid door and discharge door.

Used Paul O. Abbe One Piece Ceramic Ball Mill, Model JM-300. Non-Jacketed chamber approximate 24.8" diameter x 39.5" long. Vessel volume 300 liter (79 gallons). Approximate 5" charge and discharge port with cover. Driven by a 3 HP, 3/60/208-230/460 volt 1760 rpm motor with a shaft mounted Sumitomo Model 203E-25 reducer. Approximate 32 rpm drum speed. Includes a control panel with an ABB drive. Mounted on a common carbon steel frame legs. Serial # 0830032JM. Built 2008.

Used 28 Gallon Paul O. Abbe Ceramic Jar / Ball Mill. Approximate 3.7 Cubic Feet. Approximate 20" diameter x 20" straight side. Includes motor and cage. Mounted on a carbon steel frame with safety cage.

Used 30 gallon Paul O. Abbe Jar Mill. Porcelain jar 21" diameter x 18" straight side. Driven by 1hp, 1/60/115/230 volt, 1740 rpm motor thru a reducer, ratio 9.3 to 1. Inlet & outlet with cover and clamp. Mounted on carbon steel legs with a discharge housing. Serial#84876

Used 25 Gallon Norton Chemical Process Products Jar Mill. Porcelain jar 20" diameter x 20" straight side. Driven by 1hp, 3/60/230/460 volt, 1730 rpm motor thru a reducer, no ratio. Inlet & outlet with cover and clamp. Mounted on carbon steel legs with a discharge housing. Serial# AV-83104.

Used 35.30 Gallon Paul O. Abbe Jar Mill. Model 5A Porcelain jar 22" diameter x 20" straight side. Driven by 1hp, 3/60/230/460 volt, 1745 rpm motor thru a reducer, ratio 25 to 1. Inlet & outlet with cover and clamp. Mounted on carbon steel legs with a discharge housing. Serial#A41563.

Ball mills are used in a wide-range of industrial applications: cement processing, paint dyes and pigmentation processing, coal and ore processing, chemical processing and pyrotechnics, and many others.

Whether you are in the market for a used ball mill for your business or you have a pre-owned ball mill youd like to sell, USA-based Phoenix Equipment can help. Contact us today to learn more about what Phoenix can do for you.

Phoenix Equipment buys and sells used chemical process equipment and plants for relocation. Our industry focus includes process plants and machinery in the chemical, petrochemical, fertilizer, refining, gas processing, power generation, pharmaceutical and food manufacturing industries. We have extensive experience acquiring processing plants and process lines that require the execution of complex dismantlement, demolition and decommissioning projects. Based in Red Bank, New Jersey, USA, we have team members located in China, India, Germany and relationships throughout the world.

Why Use Phoenix for Your Plant Dismantling & Plant Relocation Needs A Common Plant Liquidation Scenario Your company has made the tough decision to close a plant. This plant was running for years, and the company paid a lot to have it built, paid everyones salaries, and maintained or even modernized all of the production assets over the plants life but the plant needs to be sold off for one reason or another. Your company has called upon you to recover as much dollar as you can to help keep the organization alive, and better yet, healthy, in what is a constant battle in the marketplace. Youve either: Have spent months, maybe even years trying to find a buyer that would operate the plant in place, without any success, while the plants assets lose value every passing day. Or, you cant sell it to another company, as you are one of the few suppliers of the product the plant makes, and you dont want to create a competitor, or improve a competitors position. Or, the plant is on leased propert

Hydrogenation: Major Applications Hydrogenation is a billion-dollar industry. Hydrogenating means to add hydrogen to something. According to Haldor Topsoe, hydrogenation comprises 48% of total hydrogen consumption, 44% of which is for hydrocracking and hydrotreating in refineries , and 4% for hydrogenation of unsaturated hydrocarbons (including hardening of edible oil) and of aromatics, hydrogenation of aldehydes and ketones (for instance oxo-products), and hydrogenation of nitrobezene (for manufacture of aniline). Hydrocracking & Hydrotreating Industrially, hydrotreating and hydrocracking are performed in down flow trickle bed reactors, where the gas and the liquid feed are sent concurrently through a fixed bed plug flow reactor. Although the flow pattern in the reactor can be reasonably approximated, the observed kinetics in such a trickle bed reactor are quite often affected by minor unplanned oscillations in the flow. How the gas and liquid collide and mix together affects the end prod

Thermoplastics A Focus on Polyethylene & Polypropylene Thermoplastics are a class of polymers, that with the application of heat, can be softened and melted, and can be processed either in the heat-softened state (e.g. by thermoforming) or in the liquid state (e.g. by extrusion and injection molding). Over 70% of the plastics used in the world are thermoplastics, and the two most commonly used thermoplastics are both olefins, compound made up of hydrogen and carbon that contains one or more pairs of carbon atoms linked by a double bond. These two olefins are polyethylene and polypropylene. Polyethylene Polyethylene is a tough, light, flexible synthetic resin made by polymerizing ethylene, chiefly used for plastic bags, food containers, and other packaging. It may be of low density or high density depending upon the process used in its manufacturing. It is resistant to moisture and most of the chemicals. It can be heat sealed and is flexible at room temperature (and low temperature), and in additional to its material properties,

## grinding mills

Common types of grinding millsinclude Ball Mills and Rod Mills. This includes all rotating mills with heavy grinding media loads. This article focuses on ball and rod mills excluding SAG and AG mills. Although their concepts are very similar, they are not discussed here.

As the mill revolves, lifters assist in picking up the grinding charge and elevate it to an angle at which gravity overcomes friction and centrifugal force. The charge then cascades downward, effectively grinding particles of material within the mill by continuous, repeated impact and attrition action.

Grinding Mill speed is one of the factors affecting the character of the cascading charge. As shown in the illustrations, the lower the percentage of critical speed, the smoother the flow of balls from top of charge to bottom. Higher percentage of critical speed is used for impact grinding of large feed. Lower percentage of critical speed is used for attrition grinding when a fine product is desired. The graph belowwill be helpful in determining percentage of critical speed when internal mill diameter and RPMare known. A Grinding Mill is a revolving cylinder loaded to approximately one-half its volume with steel rods, balls or pebbles.

Grinding mills reduce particle size by impact, rolling and sliding. Of the many types in use, the cylindrical mill, which employs a cascading mass of balls or rods, is universally used for the size reduction of hard, moderate to highly abrasive materials, such as minerals, ores, stone, and chemicals. ,

A cylindrical mill, when operating under uniform conditions, will produce a uniform product. Wear on grinding surfaces has little effect on capacity or product size. Very little maintenance is required with these mills, downtime being a negligible factor in their operation. For continuity of operation, the cylindrical mill has no equal.

Grinding mills of this type will give you dependable, trouble-free operation year after year, with planned periods of stoppage for renewal of parts. Initial cost is distributed over a long operating period. Many grinding mills are still in service after more than 40 years of almost continuous operation. Ton for ton of material handled, the cylindrical type mill has proved to be the most economical investment for reducing moderate to extremely abrasive materials.

911Metallurgist sourcesmanufacturers of all the proven mill designs in a small range of sizes your assurance of getting the most suitable mill for your purpose. Best grinding efficiency and economy can be obtained only when the type and size of your mill is matched with your grinding job. Mills can also be furnished with modifications to suit any special application.

The choice between wet or dry grinding is dependent upon the use of the product or the subsequent process. It is imperative to dry grind many materials because of physical or chemical changes which occur if water or a solution are added. Wet grinding with water (or with a concentrated solution of the soluble salts being ground) is generally preferred, because of the overall economies of this operation.

Another factor in choosing a grinding mill is the consideration of the feed size introduced into the mill, and the product required from the mill or mill circuit. This can be best illustrated by comparing two prevailing and diametrically opposite grinds.

In the manufacture of standard cement by grinding cement clinker, the clinker is reduced from 1 or finer down to a specific surface of 1750 sq cm per gram. This area can be produced by an open or closed circuit grind. The specific area method (which indicates the square centimeters of surface exposed per gram of material ground) is a most satisfactory method of determining whether a cement product will meet an accepted standard.

In a typical cement plant employing closed circuit grinding, 1750 surface can be obtained with a finish grind of between 93 and 96% passing 200 mesh. This arearequirement means that fines are not only desirable but necessary, and that a size analysis must show a distribution of material from approximately 80 microns down to less than one micron.

When grinding ore prior to concentration, on the other hand, the grind is determined by the degree of reduction necessary to unlock the valuable mineral from the gangue. This gangue is undesirable and must be separated from the desired material. For example, the full-size illustration above shows a piece of coarse-grained magnetite. The grind necessary to unlock the magnetite is about 14 mesh. At this grind, almost every individual crystal of iron oxideis freed from associated gangue and the ground material is ready for magnetic concentration.

Actually then, the ideal grind would be to reduce this ore down to 14 mesh particlesnot finer, for any expenditure of energy to reduce this ore beyond the unlocking mesh size is wasted. Such a grind is impossible, but any grinding circuit should be controlled so as to minimize overgrinding. Some fine material is produced, but it is tolerated rather than desired.

The product resulting from the reduction of a number of particles is dependent on two distinct shapes of grinding mediathe rod and the ball. Here the term ball is used to cover the entire range of grinding media which is spherical in shape, or roughly so.

The principle of grinding action, rods as compared to balls, can be best understood by making a comparison of their contact with adjacent rods or balls. Rods making up a grinding charge are nearly parallel and tend to meet adjacent rods in line contact. Rods tend to bear only on the largest particles, thereby expending most of their crushing force on the over-size and allowing the fine particles a freer passage between the rods without being ground to objectionable fineness. Balls, on the other hand, meet adjacent balls in point contact and particles of material at these points are ground to a very fine state.

Concavex grinding medium is an improved type of ball grinding media which offers more surface area per unit of weight, and has found extensive use in the grinding of cement clinker. The advantage of Concavex medium is its ability to increase mill capacity because of its interlocking shape and increased density per cubic foot of grinding charge. Surface areas for Concavex grinding media are given later.

Ball mills are built in Overflow and Diaphragm types. In the Overflow mill the material is discharged by new feed moving into the mill and displacing a mixture of solids and water being ground within the mill. The diaphragm arrangement in a ball mill is a positive means of pumping pulp or dry material out of the mill. The gradient is steeper than in an Overflow type mill. A Diaphragm ball mill has a higher capacity and requires more power than an Overflow ball mill of equal ball charge.

The Overflow rod mill is applied to wet grinding. The Center Peripheral Discharge rod mill is also used for wet grinding but produces a coarser product than the overflow type. Either the End or Center Peripheral discharge rod mill can be used for wet or dry grinding. Whatever the type, the rod mill is used to produce a coarse product, whereas the ball mill is used to produce a finer product.

Should a ball mill grind be required, the relationship of the length to the diameter of the mill is important. Feed and product screen analyses, and the type of circuit (openor closed), dictate the proper diameter to length ratio of a mill.

The type of mill for a particular grind and the circuit in which it is to be used must be considered simultaneously. Circuits are divided into two broad classifications, open and closed. In open circuit, the material is fed into the mill at a rate calculated to produce the correct finished product in one pass through the mill. This circuit has been popular in the cement and chemical industries, although the present trend is toward closed circuit installations. The closed circuit is generally employed in the mineral dressing industry.

In the closed circuit the material is discharged from the mill into a classifying device. The classifier separates and (1) returns the oversize material to the mill for further grinding, (2) delivers the fine material as finished product of that circuit. Material returning to the mill is called circulating load, and the ratio of this material to new feed may vary from a few percent to 600 percent or more.

Several types of separators are used in closed circuit grinding. Vibrating screens with screen cloth as fine as 28 mesh are used to produce a mesh product from either wet or dry grinding circuits. Fine wet grinding circuits employa classifier to separate a product varying from 10 to 325 mesh. Fine dry grinding circuits employ an air separator for products of 65 mesh and finer.

In open circuit grinding the feed rate must be low enough to permit a longer retention time per particle within the mill. This assures that each particle of the incoming feed, however large, will be broken down to product size. As a result, many particles in the product are ground to sub-sieve size. In ore dressing, these fine particles are usually undesirable, and the additional power required to produce them is a wasted expenditure. However, sub-sieve size particles are sometimes desirable, where the properties of the finished material require it. Finished cement and pottery glaze are examples of products requiring fines in the micron sizes.

In a closed circuit operation no effort is made to produce all the reduction during a single pass through the mill. Instead, every effort is made to remove a particle from the circuit as soon as it reaches the required product size. Quite often one of the largest particles of the feed, partiallyreduced, will be discharged, separated and returned to the mill several times before being completely reduced to the desired size.

Open circuits are particularly useful where simplicity of the layout may be a determining factor . . . where a product containing ultra-fines is preferred or where the material does not lend itself to handling in any classifying device.

All foregoing references to open and closed circuits apply to the ball mill. Because of the action of its grinding media, many rod mills are operated in open circuit, especially when preparing feed for ball mills. The rod mill, due to the character of its parallel grinding surfaces, simulates a slotted screen. The screening effect in the mill tends to retard the larger particles until reduced. Smaller particles slip through spaces between rods and are discharged without appreciable reduction.

Due to many variables, grinding is considered an art, not a science. A number of factors which affect grinding capacity are so variable that considerable engineering experience is required for a judicious selection of the propermill and circuit for a given operation.

Some operators prefer the high speed mill, others will consider only grinding mills operating at low speeds. Grinding mill speed, it should be noted, is not absolute, not a definite rpm, but relative to a quantity called critical speed.

The critical speed of a mill is defined as the lowest rpm necessary to centrifuge an infinitely small particle next to the shell lining within the mill. By equation: where CS=Critical speed in rpm. D=Internal diameter of mill inside the shell lining, in feet.

Allis-Chalmers recognizes these, as well as other factors influencing HPrequirements, and has developed an equation for calculating mill HP. This equation, as applied to dry grinding diaphragm ball mills, is as follows:

HP=HP per ft of mill length. W=Weight of grinding charge and material per ft of mill length. C=Distance in feet from center of mill to the center of gravity of the grinding media. a=Dynamic angle of repose of grinding charges, usually 43 for dry grinding slow speed ball mill, 51 for normal ball mill speeds.

The dynamic angle of repose, a, is impossible to determine, and is calculated from the equation by substitution of all other factors. Once determined for a set of conditions, angle a can be substituted in the formula for any horsepower calculation. The horsepower so obtained is sufficient to cover fractional losses in the bearings and drive.

From quantity (W) of the equation, it is obvious that the mill horsepower is proportional to the apparent density of the grinding media. Also, mill horsepower is proportional to the angle of repose of the grinding media. Thats why Concavex grinding media increases a mills horsepower. Concavex media has a slightly greater apparent density. Because of its shape, it interlocks more than balls, resulting in a higher angle of repose.

The equation shown in the graph below will be helpful in determining the percent charge in specific mills, knowing Q (see Fig. 4). A definite charge percent and weight can be calculated for a desired value of Q, or the distance below the mill centerline (Q-D).

One of the oldest; and most reliable methods of determining the horsepower-hours required per unit of grinding capacity is to get comparable information from an existing operation which is grinding a similar material to the same grind.

To select a mill size by this method, it is therefore essential to have laboratory grindability results on a large number of commercially ground materials and to have this grinding data in considerable detail.

We havetabulated results of grindability tests covering a wide variety of materials and product specifications of commercially ground materials. These test results are a reliable guide in relating the grinding characteristics ofyour material to a material that is being ground in an existing operation.

Weemploy two methods of determining a materials resistance to grinding. One is made by grinding to a specific mesh size. The grindability index, G, is expressed as grams produced with a definite percentage of circulating load.

The other method is applicable to materials ground inthe cement and chemical industries, where no specific meshsize may be required, but a definite surface area must beproduced. Essentially, this test simulates an open circuitby grinding the sample in a ball mill until 85 percent passes20 mesh. The ball mill product is further ground in a jarmill until 92 percent passes 200 mesh. Index I is derivedfrom the product screen analvsis plot of the ball mill test:

Occasionally a test is requested on a material for which field data does not exist. The grindability test is still useful, but it is recommended that a verifying pilot plant test be made when a large operation is planned.

In recent years, rod mills have found increasing use in preparing ball mill feed. The rod mill is exceptionally well suited to handle coarse feed and to control the top size of the product. Rod mill products are generally coarser than those produced in a ball mill. Because of these characteristics, the rod mill has also found wide acceptance by manufacturers of fine concrete aggregates, where rigid state or federal specifications must be met.

Rod mills are also used extensively in the grinding of chemicals, coke, limestone, slag, etc. It has been a general practice to build rod mills in lengths of 10 to 12 feet. This permits the use of rods of sufficient length to perform screening action, retarding the passage of oversize particles through the mill until reduced to product size and finer.

Where a finely divided product must not be adulterated by iron, the pebble mill is the logical choice. These mills are lined with a non-metallic material such as porcelain or stone, and employ flint or stone grinding bodies. Thus, iron contamination caused by grinding is kept to a minimum. This is an important consideration in the glass sand, scouring powder, talc, and ceramic industries.

Since pebble grinding bodies have a density of about one-third that of metallic media, these mills are of lighter construction and require only about one-third the horsepower of a ball mill of equal size. Capacity is approximately one-third that of a ball mill.

A Ballpeb mill is a secondary ball mill having either one or two compartments. This mill is specifically designed for operation in series with a Preliminator mill, or as a finish grinding mill with small size feed. Ballpeb mills will produce a finished product from relatively fine feed in open or closed circuit. The Ballpeb mill will take the product of a Preliminator mill and produce finished kiln feed, finished cement, mine dust, sized calcined coke, etc.These mills are equipped with thinner shell liners and employ smaller size grinding media than Preliminator mills.

Ball mills originally were used to grind approximately 2 in. material to pass 10 to 80 mesh screens. Present day practice is to use a feed of about 1/2 in. or finer. Product size has become increasingly finer and no actual grind limit is indicated.

The principal field for ball mill grinding has been the metalliferous ores and the more abrasive minerals. Because of the mills inherent characteristics of simple operation and low maintenance, it is gaining acceptance for grinding materials formerly ground in other types of mills.

Ball mills used in the mining industry are invariably short, the length being roughly equal to the diameter. When close circuited with a classifier, the short length of the mill and the high circulating load allows a short retention time with minimum overgrinding.

Preliminator mills are widely used in the cement industry for the reduction of cement raw materials and clinker. It is also used for the reduction of abrasives, refractories, limestone for mine dust, etc.

These mills can handle 1 in. feed. To grind this large feed efficiently, Preliminator mills are provided with thick shell liners and employ large balls as grinding media. Length is generally equal to or somewhat greater than the diameter.

The Compeb mill is a type of ball mill designed to incorporate the Preliminator and Ballpeb mills in one relatively long shell. The initial or primary grinding compartment is lined with thick liners and carries large balls to accomplish the coarse grind. This primary compartment is followed by one or more secondary compartments which are provided with thinner lining and smaller grinding bodies. In the secondary compartments the product of the primary compartment is further reduced. Thus, the Compeb mill offers complete grinding from coarse feed to finished product in a single mill, either closed or open circuit.

Ourgrinding mill shells are fabricated of rolled steel plate of a thickness sufficient to insure against distortion or failure in operation. Shells are of all-welded construction, welded one plate to a circle. Welding is done by an automatic welding process which assures full penetration and an even flow of weld rod for uniform strength. Comparable results are difficult to attain by hand welding methods.

Todays millhas unsurpassed facilities and personnel for the precision rolling of mill shells of consistently uniform diameter. Shells of true circular shape result in more uniform load on bearings, gears, drives, and permit better shell liner fit.

Grinding mill shells up to 26 feet in length are rolled from structural steel plate having approximately 55,000 psi tensile strength. Shells longer than 26 feet are rolled from carbon-silicon flange quality steel plate having approximately 60,000 psi tensile strength.

Flanges for mill shells are fabricated of rolled steel bars. Shells are welded integral to flanges, which are not machined until the entire welding operation on the shell, including the attachment of the manhole frames, has been completed. This machining operation (see illustration) assures that flange faces will be true with one another and that all parts will be in alignment.

When the nominal mill length exceeds twice the diameter, the entire mill is stress-relieved as a unit, prior to machining the flanges. Heat treatment relieves the residual stresses caused by rolling and welding . . . assures low bending stresses on long mills.Holes for shell liner bolts on all mills are drilled, not punched.

Allis-Chalmers grinding mill heads are cast of iron or steel and bolted to the shell flange with through bolts. These bolts are relieved of shear stress by a machined male and female joint between head and shell flange. All ball, rod and Preliminator mills, as well as the shorter Ballpeb and Compeb mills, have conical heads. The longer Ballpeb and Compeb mills have starfish heads (see illustration) which offer extra body and strength by means of a pattern of external braces.

Whether of conical or starfish design, all heads and trunnions are cast integral. This makes the task of maintaining alignment of the mill much simpler than on mills where head and trunnion are two separate pieces. Trunnions are machined true with head fit. Thus, when the head is attached to the shell flange, the trunnion is concentric with the true horizontal axis of the mill.

The sturdy construction of these trunnion bearings assures more than adequate support for the revolving mass of the grinding mill. Bearings are designed with sufficiently low bearing pressure to assure long bearing life and trouble-free operation.

The use of babbitted bearing and the ball and socket design are two important features of thesetrunnion bearings. Experience has shown that there is less possibility of scouring the trunnion with babbitt than with any other material. The ball and socket design corrects for minor misalignment during mill erection

Weoffers large mills with oil lubricated trunnion bearings and small mills with grease bearings. Grease lubricated bearings have a large space within the bearing cap for grease. Oil lubricated bearings are lubricated with a positive internal oiling system or, if desired, an external system.

The cross-sections on the opposite page show the mechanism of the oil and grease lubricated bearings. In the oil type, an arm extends radially from the trunnion. A cup fixed to the outer end of this arm fills with oil from the reservoir, when the mill rotates, and is brought up and discharged onto the distributing pan, providing flood lubrication to the trunnion.

Experience has proved this an effective means to lubricate the bearing. Sufficient oil in the reservoir assures proper lubrication. The piston ring seal is an effective way of sealing the bearing from dirt while retaining the oil. Economy conscious operators are aware of the lower coefficient of friction attainable with oil lubrication.

A most important adjunct of the oil lubricated bearing is the manually operated high pressure pump used to float the mill before starting. Large, heavy mills lock when idle for long periods. This occurs when the idle load of the mill squeezes the oil out from between the trunnion and trunnion bearing. Floating the mill provides an oil film between metal parts, reduces friction before starting, and eliminates the high bearing wear incident to dry starting. A floated mill also reduces the high inrush of starting current an important advantage often overlooked when considering the merits of various grinding mills. If grease lubricated bearings are used, a mill can be floated by using a manually operated grease pump. Although this is optional equipment, the resultant advantages under starting conditions are the same.

Allis-Chalmers mills are provided with steel sole plates under the trunnion bearings. All mills have adjustable sole plates for lateral movement of the mill. On direct connected mills the sole plate at the gear end is extended for bolting to the steel pinionshaft sole plate.

Todaysgrinding mills are equipped with a new, improved 20 true involute cut tooth spur gear with short addendum gear and long addendum pinion. This design assures overlap of tooth contact by as much as 40 percent. The pinion teeth roll evenly on gear teeth, resulting in smooth, even transmission of power from pinion to gear. Comparative results have proved the 20 involute gear a most suitable gear for smooth mill operation and long gear life.

Gears for 3, 4 and 5 ft diameter mills are made of high quality cast iron with cut teeth; gears for the larger mills are made of either cast or welded steel, with cut teeth. The teeth are cut to a true form and then subjected to a thorough inspection of spacing and profile. The resultant uniformity of teeth assures long service.

The millsmain drive pinions are fabricated of forged steel and the teeth are carefully cut to assure smooth mating action with the main gear. Pinions meshing with steel gears are hardened to prolong their life.

Main gears are reversible and split in halves to permit easy removal and reversal. All main gears on direct driven dry grinding mills are manufactured with an extended flange on both sides of the teeth to provide a seat for the oil and dust seal which is a part of the gear guard and lubrication housing.

Theserod and ball mills may be equipped with either herringbone or single helical gears. These are not recommended for Preliminator, Ballpeb or Compeb mills because the heat generated during dry grinding results in expansion problems.

Direct drive spur pinions are mounted on a short reversible stub pinionshaft which permits reversing the pinion without removing the pinion from the shaft. The pinionshaft is keyseated for both spur pinion and coupling. For mills equipped with Texrope drive, pinionshafts are keyseated for pinion and Texrope sheave.

In all mill sizes, the pinionshafts are mounted in antifriction (roller) bearings which are considered superior to the babbitted sleeve type for these reasons: (1) Roller type bearings offer a decreased coefficient of friction. (2) Since the wear on an anti-friction bearing is negligible, the alignment of gear and pinion is maintained. (3) Antifriction bearings require minimum lubrication and provide excellent seals for keeping dust and dirt out of the bearing.

Wet grinding mills of 6 ft diameter and larger are fitted with semi-enclosed safety type guard. Preliminator, Ballpeb, Compeb, and dry grinding ball and rod mills have gear and pinion totally enclosed in a 360 steel plate lubrication housing.

The lubrication housing protects the gear and pinion from outside dust and dirt, materially lengthening the life of the gears by preventing unnecessary wear from abrasive dust. The housing is supplied with a heavy, long-life felt seal which bears against the extended flange of the gear and thus effectively seals the gearing from dirt.

The gear housing for Preliminator, Ballpeb and Compeb mills is provided with a plastic impregnated laminated fabric oiling pinion which is located in an oil reservoir in the bottom of the housing. This lubricating pinion mates with the main gear and, when the mill is rotating, transfers oil to the gear teeth which in turn lubricate the drive pinion.

For grinding mills of 250 hp or less, the Texrope V-belt drive has proven to be most satisfactory. Actually, the Texrope drive may be supplied for mills larger than 250 hp but the arrangement is usually undesirable because of the outboard bearing required by the motor and the large size of the driven sheave.

The Texrope drive employs a driven sheave mounted between the outboard bearing and one of the bearings adjacent to the pinion. The driving sheave is mounted directly on the motor shaft. Such a drive is flexible and economical both in initial cost and in maintenance, repair and replacement. A wound rotor motor is recommended for use with a Texrope drive.

This type of drive is used to permit the use of high speed motors or to meet special space requirements. Speed reducer drives offer a highly efficient and economical means of stepping down motor speeds. The speed reducer may be located either alongside or at the end of the mill.

With either the direct connected or speed reducer drive, the gear is aligned with the pinion by means of a set screw adjustment on the main bearing sole plates. This adjustment can be made without disturbing the alignment of the motor and pinionshaft. Weoffer several possible drives in its direct connected series. A mill can be provided with a low speed synchronous motor having torques of approximately 40% starting, 30% pull-in and 175% pull-out for use with a magnetic clutch. A magnetic clutch drive may involve a close coupled unit with two pinionshaft bearings and combination clutch-coupling (Drive 1), or four bearings with a clutch and flexible coupling (Drive 2). The use of a magnetic clutch permits the use of a reduced voltage starter to reduce the starting kva which would result when a full voltage starter is employed.

The most compact direct drive, where electrical conditions permit its use, is the direct connection of a high torque synchronous motor (approximately 160% starting, 140% pull-in and 225% pull-out) to the pinionshaft through a flexible coupling (Drive 3). When plant design makes it essential to locate the motor at a distance from the mill, the drive arrangement may be as shown in Drive 4 or 5.

In addition to the drives described above, weoffer the synchronous-induction motor, which is wound so as to permit the use of a reduced voltage starter. This motor starts its operation as a wound rotor motor but reverts to a synchronous motor after it picks up speed and comes into step. This permits use of a synchronous motor with low starting current inrush and without magnetic clutch. This arrangement is used where a magnetic clutch is not desired and where electrical transmission line characteristics do not permit high starting kva.

Grinding mills for the mining, cement and rock products industries may he furnished with or with-out mill feeders, as desired. Feed chutes can he any one of several types which convey the material into the mill. None of the feeders described here weigh or proportion materials fed to the mill. Weighing or proportioning feeders can he purchased from several manufacturers and many operators feel that a feeder which controls and records the feed rate is well worth the additional cost.

This type handles dry, dusty feed and is no .longer in general use. Screw feeders can be designed to feed material into the mill and, at the same time, effectively seal the trunnion opening. This is essential for grinding some materials in a controlled atmosphere, other than air. Screw feeders have individual motor drives.

The spout feeder is the simplest of all feeders. It consists of a cylindrical spout or chute lined with either steel wearing plates or rubber lining. Spout feeders are used where the feed, plus the circulating load, if any, has sufficient elevation to be spouted directly through this feeder into the trunnion opening of the mill. Generally, the spout feeder can be used wherever a drum feeder is used. It has the advantage of permitting a constant flow of feed, resulting in higher capacity through the feeder. Most operators prefer the spout feeder because of its simple and inexpensive maintenance.

In closed circuit grinding, scoop feeders return classifier sands to the mill for regrinding. They may also be used to take initial feed and may be of either single or double scoop construction. The illustration above shows the double scoop type. The opening in the center is used to charge balls into the mill. Scoops are provided with replaceable wearing tips.

The drum feeder is the logical substitute for a spout feeder if the bin storage lacks sufficient headroom to spout the material successfully.This feeder consists of a steel plate drum or housing, a spiral made of high quality cast iron and suitable liner plates for the housing. If the material being ground is corrosive, the feeder may be constructed of stainless steel throughout.

The overflow mill, used for wet grinding, is the simplest of the three basic mill designs. Pulp in overflow mills is discharged by displacement, the new feed to the mill displacing an equal volume of ground pulp.

Since there is no appreciable pulp gradient within the mill, all the grinding media is surrounded by pulp to be ground. This cushioning by the pulp tends to reduce wear of grinding media and liners. The cost of metallic balls, rods and liners has risen steadily in the past decade and many operators have chosen the overflow mill to reduce their operating costs. Furthermore, the overflow mill does not have a diaphragm, component parts of which are more complex, expensive and short-lived than the comparable end liner in an overflow mill.

The capacity of the overflow mill is not as high as a diaphragm mill with the .same size grinding chamber. Power requirements per ton of material ground are substantially the same for either type mill.

Overflow mills have proven mot popular as secondary mills in a two-stage circuit, as employed in the mining industry. There are some operators who prefer the overflow mill for single stage closed circuit grinding of large feed.

The peripheral discharge, as used in a rod mill, is a means of establishing a gradient within the mill without the use of a low-level diaphragm. This cannot be done in a ball mill unless a special division head is used.

Occasionally, a multi-compartment mill is used with peripheral discharge openings following either the first or second compartments. A plain division head is used to retain the charge of balls or Concavex grinding media. Material is discharged and classified, the oversize returning to the (original) feed end of the mill and the fines being fed through the opposite end of the mill for further grinding.

The discharge end of this mill is fitted with a diaphragm, i.e. a perforated steel plate placed approximately 6 in. from the discharge head. Lifters between this perforated plate and the mill head elevate the ground material and drop it on a discharge cone (see illustration) which directs the material into the trunnion and out of the mill.

The function of the diaphragm is to retain the grinding media and allow free passage of the wet pulp or dry material through the perforations. On starting, the pumping action of the diaphragm lifters establishes a gradient within the mill. For grinding dry materials a steep gradient is essential to move the material through the mill. In wet grinding this gradient results in a short retention time per particle, with the advantage of less overgrinding.

Diaphragm mills have been designed with twovariations, Low-Level and Intermediate Level types. In the first, the diaphragm sections are perforated down to the periphery of the mill, which establishes the maximum gradient within the mill. The Intermediate Level diaphragm mill establishes a gradient which is less steep by maintaining a pool of pulp at the discharge end. Diaphragm perforations are held to within 10 to 18 in. (depending on the mill diameter) of the periphery. Size for size, the Intermediate Level mill offers a capacity greater than the Overflow mill and less than the Low-Level diaphragm mill.

Use of the diaphragm is almost universal with ball mills in the cement and rock products industries because of the many dry grinding operations in this field. It is optional on ball mills in the mining industry, but not recommended for rod mills. Diaphragms are standard equipment for Preliminator, Ballpeb and Compeb mills.

Division heads are used in Compeb mills to divide the mill into two or three compartments . . . and in long Ballpeb mills to divide it into two compartments.Plain division heads are made in both dry and wet types. The dry type have screen plates on the feed side and solid wearing plates on the discharge side. Material in the first compartment cannot flush through into the second compartment, but must be picked up by wings between the screen and the solid side and discharged into a center cone which funnels the partially ground material into the succeeding compartment.

Grinding in small plants, as in larger installations, has proven to be the most costly of all unit operations from both capital and operating standpoints. Therefore, grinding deserves the most scrutiny of all operations during the design procedure.

A recent survey by a major grinding mill manufacturer reveals that more than 80 autogenous or semi-autogenous mills having between 100 and 1,000 connected horsepower have been sold during the last twenty years. Obviously, this type of grinding approach cannot be arbitrarily excluded from consideration in a small installation.

This configuration has proven in the past to be a most reliable system due to the fact that rod mills are not particularly susceptible to variations in feed size. However, the necessity to procure grinding rods may limit the usefulness of this approach in certain locations.

This configuration is employed when it is desired to produce a final ground product having a very high pulp density. This situation can be useful for various types of leaching circuits but does not normally apply to flotation concentrators.

Single stage ball milling has proven to be very popular in recent years. Both overflow and diaphragm (grate) ball mills have been used as single stage grinding units. If the feed to such a system can be top size limited, for example by the use of closed circuit crushing, this type of installation can prove to be the most efficient from both the capital and operating standpoint.

Occasionally, the liberation requirement for an ore requires very fine primary grinding. Usually, the most expeditious way to accomplish this objective is by double stage ball milling. Both mills are usually operated in closed circuit with separate classifiers.

In smaller plants, grinding mill drives should be as simple as possible. The drive train usually recommended consists of a slow speed motor which drives the mill pinion through an air clutch. This slow speed motor system tends to be slightly more expensive than the alternate drive train consisting of a high speed motor and speed reducer but the ease of maintenance and the simplicity of the slow speed system offset the additional cost.

The mill feed belt should be equipped with a weightometer having cumulative and instantaneous tonnage indicators visible both locally and in the control room. In recent years, load cell weightometers have proven to be very reliable and are relatively simple to calibrate. The digital readouts supplied with load cell weightometers have proven to be rugged and reliable.

The mill dilution water stream should be visible and its control valve should be readily accessable. A simple water proportioning valve is sometimes recommended to give semiautomatic regulation to mill dilution water.

Mill sizing for most grinding installations is usually arrived at through calculations involving required throughput, ore work index estimates, and feed and product size-distribution requirements. This information is then tempered with experience to arrive at actual mill size recommendations. In the case of small concentrators located in remote areas, the method and route of delivery to the plant site must also be considered. There are cases on record where mill diameter has been dictated by railroad tunnel dimensions and mill length by the presence of severe switchbacks and small bridges over precipitous canyons.

Ball mills should be equipped with trommels constructed of punched plate or screen cloth and are usually fabricated with a reverse internal spiral. The trash rejected by the trommel is normally collected in a forklift box.

Ball charging should be arranged for the convenience of the operator. In remote areas, grinding balls are usually received in welded 55 gallon drums each of which weighs between 500 and 600 kilograms. Suitable handling equipment for grinding media must be supplied by the design engineer. It should be noted that the ability to assemble a graded ball charge at the mill site prior to startup may not be possible. An initial properly-graded ball charge should be purchased from capital funds and included in the grinding area unit cost.

Rubber liners represent a significant cost saving for smaller installations. This type of liner, although possibly contributing to somewhat less efficient power utilization, is very simple to install with unskilled personnel as contrasted to conventional cast metal liners.

The necessity for regrinding is usually determined by laboratory or pilot-scale test work. If a project is to be designed from bench scale work only it is prudent to include a regrind mill in the circuit even though laboratory work does not indicate the necessity for this unit operation. Regrind mills are difficult to size since work index data are not generally available. Therefore, the design engineer should be generous when sizing a regrinding installation.

There is a tendency to employ spent grinding media from the primary grinding installation as media for the regrind mill. It is much better to use small-diameter properly-sized grinding media for regrinding since the utilization of spent media tends to reduce efficiency.

Regrind mills tend to be rather difficult to reline since they are usually of small diameter. Rubber regrind mill liners are an obvious solution and have found application in many installations. Of course, the rubber composition employed must be compatible with the flotation reagents associated with the regrind mill feed.

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