how is a ball mill constructed

make a ball mill in 5 minutes : 4 steps - instructables

make a ball mill in 5 minutes : 4 steps - instructables

This is for all the pyro nuts that I came across on Instructables. This can be used to grind chemicals to a very fine grain or to polish rocks.Wiki says "A ball mill is a type of grinder used to grind materials into extremely fine powder for use in paints, pyrotechnics, and ceramics."Many instructables refer to United Nuclear Ball Mills. Their small ball mill cost between $70 and $80 dollars.For no more than $30 and in 5 minute you can build a ball mill of appreciable performance.Check out my other Instructables:MAKE A HIGH VOLTAGE SUPPLY IN 5 MINUTESHack The Spy Ear and Learn to Reverse Engineer a CircuitSuper Easy E-mail Encryption Using Gmail, Firefox and WindowsMake a Rechargeable Dual Voltage Power Supply for Electronic ProjectsMake a Voltage Controlled Resistor and Use ItSODA CAN HYDROGEN GENERATOR

You need 1. A rugged container (You can use PVC pipes or big plastic bottles) 2. An electric screwdriver (these are fairly cheap, I got mine for $10) 3. A bolt, a nut and maybe a washer. 4. Epoxy putty. 5. Steel or lead balls which in my case I substituted with screwdriver bits that I got for $3. 6. A vise clamp to hold down your ball mill.

This is the most important step. The joint holding the the container and electric screwdriver should be strong and able to hold the weight of the assembly. Put a little putty on the bolt first. Insert the bolt into the screwdriver's bit holder. Cover the whole joint with putty. The more putty the better the ball mill stays together.

Fill the container with the screwdriver bits or with steel balls or lead balls. Add the chemical you need to grind. Close the container and clamp the whole assembly to a table top. I use a popsicle stick to hold the screwdriver button down. I jam it between the clam vise and electric screwdriver (see video). But that depends on your electric screwdriver.

Im interested in this mill to dispose of mercury by combining it with sulphur to make mercury sulphide (HgS).A test report done in EU says an hours milling is best so there is no elemental mercury left.And the mercury sulphide is insoluble and is the same substance that mercury is found in the Earth which is cinnabar.

I may well be able to find a power drill at a resale shop, or buy an inexpensive one for the purpose. Any feedback on how well a power drill motor will hold up to being run for 24 hours continuously? I plan to make paper machie. I want to make a very fine paper pulp. While I doubt this is flammable, I would like to hear any comments on this as well. Who'd a thought flour was explosive?

If you want fine paper pulp, you may wish to consider using a blender. Ball mills are typically only needed for moderately-to-very hard materials that need to be crushed to effectively split them, and which might damage a blender if used in it.

Instead of using an electric screw driver, you could use a drill and a drill bit. Just putty the drill bit (preferably an old one) to the bolt inside the container. Seems like it would be a more powerful ball mill. But I'm definitely going to try this idea. Seems like it would be cool to make some gun powder. There's some simple step-by-step instructions on Wiki How if you guys need some instructions.

I would stay away from lead if you are making gun powder. That smoke that surrounds black powder ignition is not good for you. Fine particles of lead suspended in that smoke would be hell on your lungs etc.. i use a tumbler to get crud off of coins taken from the sea. Beach sand won't work well with water to do the job. But the sand at the oceans edge which is coarse makes a great scrubbing agent. Maybe some aquarium gravel would work to reduce some objects in size. Commercial media is often hell to work with.

hmm... methinks you should support the container. lead balls are heavy and (I'm assuming most people will want to make gunpowder with this so they'll have to use only lead balls) the current setup is going to make the screwdriver wear a lot, and the bottom of the container isn't going to last very long... I like this idea though, I haven't found a suitable motor to drive my ball mill, they're all either too weak or they're way too fast.

I know this is quite literally 10 years late, but for other hobbyists, try supporting it with a screw on the other side like the design pictured. The back end's screw can go through a piece of wood, brick etc. at the same level as the screw driver, creating a healthy amount of support, for a vitamin bottle filled with lead Potassium Nitrate, Sulfur and Carbon.

OR, you could just attach a bolt into the cap like he did for the bottom. Make a triangular piece of wood. Drill a hole for the bolt to fit through. And find some way to support the piece of wood? Seems like it would work to me, could even make your own cradle to support everything for that matter :P I'd never use something like this so have no need to make one, but that would be my advice :D

ball mills

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.

ball mills - an overview | sciencedirect topics

ball mills - an overview | sciencedirect topics

A ball mill is a type of grinder used to grind and blend bulk material into QDs/nanosize using different sized balls. The working principle is simple; impact and attrition size reduction take place as the ball drops from near the top of a rotating hollow cylindrical shell. The nanostructure size can be varied by varying the number and size of balls, the material used for the balls, the material used for the surface of the cylinder, the rotation speed, and the choice of material to be milled. Ball mills are commonly used for crushing and grinding the materials into an extremely fine form. The ball mill contains a hollow cylindrical shell that rotates about its axis. This cylinder is filled with balls that are made of stainless steel or rubber to the material contained in it. Ball mills are classified as attritor, horizontal, planetary, high energy, or shaker.

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.

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 the movement of particles within the mill and contact zones of colliding balls.

By the rotation of the mill body, due to friction between the mill wall and balls, the latter rise in the direction of rotation until a helix angle does not exceed the angle of repose, whereupon the balls roll down. Increasing the rotation rate leads to the growth of the centrifugal force and the helix angle increases, correspondingly, until the component of the weight strength of balls becomes larger than the centrifugal force. From this moment, the balls are beginning to fall down, describing certain parabolic curves during the fall (Fig. 2.10).

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 remain attached to the wall with the aid of centrifugal force is:

where Dm is the mill diameter in meters. The optimum rotational speed is usually set at 65%80% of the critical speed. These data are approximate and may not be valid for metal particles that tend to agglomerate by welding.

where db.max is the maximum size of the feed (mm), is the compression strength (MPa), E is the modulus of elasticity (MPa), b is the density of material of balls (kg/m3), and D is the inner diameter of the mill body (m).

The degree of filling the mill with balls also influences the 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 30%35% of its volume.

The productivity of ball mills depends on the drum diameter and the relation of drum diameter and length. The optimum ratio between length L and diameter D, L:D, is usually accepted in the range 1.561.64. The mill productivity also depends on many other factors, including the physical-chemical properties of the feed material, the filling of the mill by balls and their sizes, the armor surface shape, the speed of rotation, the milling fineness, and the timely moving off of the ground product.

where D is the drum diameter, L is the drum length, b.ap is the apparent density of the balls, is the degree of filling of the mill by balls, n is the revolutions per minute, and 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, that is, during the grinding of material. Therefore, it is most disadvantageous to use a ball mill at less than full capacity.

Milling time in tumbler mills is longer to accomplish the same level of blending achieved in the attrition or vibratory mill, but the overall productivity is substantially greater. Tumbler mills usually are used to pulverize or flake metals, using a grinding aid or lubricant to prevent cold welding agglomeration and to minimize oxidation [23].

Cylindrical Ball Mills differ usually in steel drum design (Fig. 2.11), which is lined inside by armor slabs that have dissimilar sizes and form a rough inside surface. Due to such juts, the impact force of falling balls is strengthened. The initial material is fed into the mill by a screw feeder located in a hollow trunnion; the ground product is discharged through the opposite hollow trunnion.

Cylindrical screen ball mills have a drum with spiral curved plates with longitudinal slits between them. The ground product passes into these slits and then through a cylindrical sieve and is discharged via the unloading funnel of the mill body.

Conical Ball Mills differ in mill body construction, which is composed of two cones and a short cylindrical part located between them (Fig. 2.12). Such a ball mill body is expedient because efficiency is appreciably increased. Peripheral velocity along the conical drum scales down in the direction from the cylindrical part to the discharge outlet; the helix angle of balls is decreased and, consequently, so is their kinetic energy. The size of the disintegrated particles also decreases as the discharge outlet is approached and the energy used decreases. In a conical mill, most big balls take up a position in the deeper, cylindrical part of the body; thus, the size of the balls scales down in the direction of the discharge outlet.

For emptying, the conical mill is installed with a slope from bearing to one. In wet grinding, emptying is realized by the decantation principle, that is, by means of unloading through one of two trunnions.

With dry grinding, these mills often work in a closed cycle. A scheme of the conical ball mill supplied with an air separator is shown in Fig. 2.13. Air is fed to the mill by means of a fan. Carried off by air currents, the product arrives at the air separator, from which the coarse particles are returned by gravity via a tube into the mill. The finished product is trapped in a cyclone while the air is returned in the fan.

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).

Modern ball mills consist of two chambers separated by a diaphragm. In the first chamber the steel-alloy balls (also described as charge balls or media) are about 90mm diameter. The mill liners are designed to lift the media as the mill rotates, so the comminution process in the first chamber is dominated by crushing. In the second chamber the ball diameters are of smaller diameter, between 60 and 15mm. In this chamber the lining is typically a classifying lining which sorts the media so that ball size reduces towards the discharge end of the mill. Here, comminution takes place in the rolling point-contact zone between each charge ball. An example of a two chamber ball mill is illustrated in Fig. 2.22.15

Much of the energy consumed by a ball mill generates heat. Water is injected into the second chamber of the mill to provide evaporative cooling. Air flow through the mill is one medium for cement transport but also removes water vapour and makes some contribution to cooling.

Grinding is an energy intensive process and grinding more finely than necessary wastes energy. Cement consists of clinker, gypsum and other components mostly more easily ground than clinker. To minimise over-grinding modern ball mills are fitted with dynamic separators (otherwise described as classifiers or more simply as separators). The working principle is that cement is removed from the mill before over-grinding has taken place. The cement is then separated into a fine fraction, which meets finished product requirements, and a coarse fraction which is returned to mill inlet. Recirculation factor, that is, the ratio of mill throughput to fresh feed is up to three. Beyond this, efficiency gains are minimal.

For more than 50years vertical mills have been the mill of choice for grinding raw materials into raw meal. More recently they have become widely used for cement production. They have lower specific energy consumption than ball mills and the separator, as in raw mills, is integral with the mill body.

In the Loesche mill, Fig. 2.23,16 two pairs of rollers are used. In each pair the first, smaller diameter, roller stabilises the bed prior to grinding which takes place under the larger roller. Manufacturers use different technologies for bed stabilisation.

Comminution in ball mills and vertical mills differs fundamentally. In a ball mill, size reduction takes place by impact and attrition. In a vertical mill the bed of material is subject to such a high pressure that individual particles within the bed are fractured, even though the particles are very much smaller than the bed thickness.

Early issues with vertical mills, such as narrower PSD and modified cement hydration characteristics compared with ball mills, have been resolved. One modification has been to install a hot gas generator so the gas temperature is high enough to partially dehydrate the gypsum.

For many decades the two-compartment ball mill in closed circuit with a high-efficiency separator has been the mill of choice. In the last decade vertical mills have taken an increasing share of the cement milling market, not least because the specific power consumption of vertical mills is about 30% less than that of ball mills and for finely ground cement less still. The vertical mill has a proven track record in grinding blastfurnace slag, where it has the additional advantage of being a much more effective drier of wet feedstock than a ball mill.

The vertical mill is more complex but its installation is more compact. The relative installed capital costs tend to be site specific. Historically the installed cost has tended to be slightly higher for the vertical mill.

Special graph paper is used with lglg(1/R(x)) on the abscissa and lg(x) on the ordinate axes. The higher the value of n, the narrower the particle size distribution. The position parameter is the particle size with the highest mass density distribution, the peak of the mass density distribution curve.

Vertical mills tend to produce cement with a higher value of n. Values of n normally lie between 0.8 and 1.2, dependent particularly on cement fineness. The position parameter is, of course, lower for more finely ground cements.

Separator efficiency is defined as specific power consumption reduction of the mill open-to-closed-circuit with the actual separator, compared with specific power consumption reduction of the mill open-to-closed-circuit with an ideal separator.

As shown in Fig. 2.24, circulating factor is defined as mill mass flow, that is, fresh feed plus separator returns. The maximum power reduction arising from use of an ideal separator increases non-linearly with circulation factor and is dependent on Rf, normally based on residues in the interval 3245m. The value of the comminution index, W, is also a function of Rf. The finer the cement, the lower Rf and the greater the maximum power reduction. At C = 2 most of maximum power reduction is achieved, but beyond C = 3 there is very little further reduction.

Separator particle separation performance is assessed using the Tromp curve, a graph of percentage separator feed to rejects against particle size range. An example is shown in Fig. 2.25. Data required is the PSD of separator feed material and of rejects and finished product streams. The bypass and slope provide a measure of separator performance.

The particle size is plotted on a logarithmic scale on the ordinate axis. The percentage is plotted on the abscissa either on a linear (as shown here) or on a Gaussian scale. The advantage of using the Gaussian scale is that the two parts of the graph can be approximated by two straight lines.

The measurement of PSD of a sample of cement is carried out using laser-based methodologies. It requires a skilled operator to achieve consistent results. Agglomeration will vary dependent on whether grinding aid is used. Different laser analysis methods may not give the same results, so for comparative purposes the same method must be used.

The ball mill is a cylindrical drum (or cylindrical conical) turning around its horizontal axis. It is partially filled with grinding bodies: cast iron or steel balls, or even flint (silica) or porcelain bearings. Spaces between balls or bearings are occupied by the load to be milled.

Following drum rotation, balls or bearings rise by rolling along the cylindrical wall and descending again in a cascade or cataract from a certain height. The output is then milled between two grinding bodies.

Ball mills could operate dry or even process a water suspension (almost always for ores). Dry, it is fed through a chute or a screw through the units opening. In a wet path, a system of scoops that turn with the mill is used and it plunges into a stationary tank.

Mechanochemical synthesis involves high-energy milling techniques and is generally carried out under controlled atmospheres. Nanocomposite powders of oxide, nonoxide, and mixed oxide/nonoxide materials can be prepared using this method. The major drawbacks of this synthesis method are: (1) discrete nanoparticles in the finest size range cannot be prepared; and (2) contamination of the product by the milling media.

More or less any ceramic composite powder can be synthesized by mechanical mixing of the constituent phases. The main factors that determine the properties of the resultant nanocomposite products are the type of raw materials, purity, the particle size, size distribution, and degree of agglomeration. Maintaining purity of the powders is essential for avoiding the formation of a secondary phase during sintering. Wet ball or attrition milling techniques can be used for the synthesis of homogeneous powder mixture. Al2O3/SiC composites are widely prepared by this conventional powder mixing route by using ball milling [70]. However, the disadvantage in the milling step is that it may induce certain pollution derived from the milling media.

In this mechanical method of production of nanomaterials, which works on the principle of impact, the size reduction is achieved through the impact caused when the balls drop from the top of the chamber containing the source material.

A ball mill consists of a hollow cylindrical chamber (Fig. 6.2) which rotates about a horizontal axis, and the chamber is partially filled with small balls made of steel, tungsten carbide, zirconia, agate, alumina, or silicon nitride having diameter generally 10mm. The inner surface area of the chamber is lined with an abrasion-resistant material like manganese, steel, or rubber. The magnet, placed outside the chamber, provides the pulling force to the grinding material, and by changing the magnetic force, the milling energy can be varied as desired. The ball milling process is carried out for approximately 100150h to obtain uniform-sized fine powder. In high-energy ball milling, vacuum or a specific gaseous atmosphere is maintained inside the chamber. High-energy mills are classified into attrition ball mills, planetary ball mills, vibrating ball mills, and low-energy tumbling mills. In high-energy ball milling, formation of ceramic nano-reinforcement by in situ reaction is possible.

It is an inexpensive and easy process which enables industrial scale productivity. As grinding is done in a closed chamber, dust, or contamination from the surroundings is avoided. This technique can be used to prepare dry as well as wet nanopowders. Composition of the grinding material can be varied as desired. Even though this method has several advantages, there are some disadvantages. The major disadvantage is that the shape of the produced nanoparticles is not regular. Moreover, energy consumption is relatively high, which reduces the production efficiency. This technique is suitable for the fabrication of several nanocomposites, which include Co- and Cu-based nanomaterials, Ni-NiO nanocomposites, and nanocomposites of Ti,C [71].

Planetary ball mill was used to synthesize iron nanoparticles. The synthesized nanoparticles were subjected to the characterization studies by X-ray diffraction (XRD), and scanning electron microscopy (SEM) techniques using a SIEMENS-D5000 diffractometer and Hitachi S-4800. For the synthesis of iron nanoparticles, commercial iron powder having particles size of 10m was used. The iron powder was subjected to planetary ball milling for various period of time. The optimum time period for the synthesis of nanoparticles was observed to be 10h because after that time period, chances of contamination inclined and the particles size became almost constant so the powder was ball milled for 10h to synthesize nanoparticles [11]. Fig. 12 shows the SEM image of the iron nanoparticles.

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.

In spite of the traditional approaches used for gas-solid reaction at relatively high temperature, Calka etal.[58] and El-Eskandarany etal.[59] proposed a solid-state approach, the so-called reactive ball milling (RBM), used for preparations different families of meal nitrides and hydrides at ambient temperature. This mechanically induced gas-solid reaction can be successfully achieved, using either high- or low-energy ball-milling methods, as shown in Fig.9.5. However, high-energy ball mill is an efficient process for synthesizing nanocrystalline MgH2 powders using RBM technique, it may be difficult to scale up for matching the mass production required by industrial sector. Therefore, from a practical point of view, high-capacity low-energy milling, which can be easily scaled-up to produce large amount of MgH2 fine powders, may be more suitable for industrial mass production.

In both approaches but with different scale of time and milling efficiency, the starting Mg metal powders milled under hydrogen gas atmosphere are practicing to dramatic lattice imperfections such as twinning and dislocations. These defects are caused by plastics deformation coupled with shear and impact forces generated by the ball-milling media.[60] The powders are, therefore, disintegrated into smaller particles with large surface area, where very clean or fresh oxygen-free active surfaces of the powders are created. Moreover, these defects, which are intensively located at the grain boundaries, lead to separate micro-scaled Mg grains into finer grains capable to getter hydrogen by the first atomically clean surfaces to form MgH2 nanopowders.

Fig.9.5 illustrates common lab scale procedure for preparing MgH2 powders, starting from pure Mg powders, using RBM via (1) high-energy and (2) low-energy ball milling. The starting material can be Mg-rods, in which they are processed via sever plastic deformation,[61] using for example cold-rolling approach,[62] as illustrated in Fig.9.5. The heavily deformed Mg-rods obtained after certain cold rolling passes can be snipped into small chips and then ball-milled under hydrogen gas to produce MgH2 powders.[8]

Planetary ball mills are the most popular mills used in scientific research for synthesizing MgH2 nanopowders. In this type of mill, the ball-milling media have considerably high energy, because milling stock and balls come off the inner wall of the 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.

In the typical experimental procedure, a certain amount of the Mg (usually in the range between 3 and 10g based on the vials volume) is balanced inside an inert gas atmosphere (argon or helium) in a glove box and sealed together with certain number of balls (e.g., 2050 hardened steel balls) into a hardened steel vial (Fig.9.5A and B), using, for example, a gas-temperature-monitoring system (GST). With the GST system, it becomes possible to monitor the progress of the gas-solid reaction taking place during the RBM process, as shown in Fig.9.5C and D. The temperature and pressure changes in the system during milling can be also used to realize the completion of the reaction and the expected end product during the different stages of milling (Fig.9.5D). The ball-to-powder weight ratio is usually selected to be in the range between 10:1 and 50:1. The vial is then evacuated to the level of 103bar before introducing H2 gas to fill the vial with a pressure of 550bar (Fig.9.5B). The milling process is started by mounting the vial on a high-energy ball mill operated at ambient temperature (Fig.9.5C).

Tumbling mill is cylindrical shell (Fig.9.6AC) that rotates about a horizontal axis (Fig.9.6D). Hydrogen gas is pressurized into the vial (Fig.9.6C) together with Mg powders and ball-milling media, using ball-to-powder weight ratio in the range between 30:1 and 100:1. Mg powder particles meet the abrasive and impacting force (Fig.9.6E), which reduce the particle size and create fresh-powder surfaces (Fig.9.6F) ready to react with hydrogen milling atmosphere.

Figure 9.6. Photographs taken from KISR-EBRC/NAM Lab, Kuwait, show (A) the vial and milling media (balls) and (B) the setup performed to charge the vial with 50bar of hydrogen gas. The photograph in (C) presents the complete setup of GST (supplied by Evico-magnetic, Germany) system prior to start the RBM experiment for preparing of MgH2 powders, using Planetary Ball Mill P400 (provided by Retsch, Germany). GST system allows us to monitor the progress of RBM process, as indexed by temperature and pressure versus milling time (D).

The useful kinetic energy in tumbling mill can be applied to the Mg powder particles (Fig.9.7E) by the following means: (1) collision between the balls and the powders; (2) pressure loading of powders pinned between milling media or between the milling media and the liner; (3) impact of the falling milling media; (4) shear and abrasion caused by dragging of particles between moving milling media; and (5) shock-wave transmitted through crop load by falling milling media. One advantage of this type of mill is that large amount of the powders (100500g or more based on the mill capacity) can be fabricated for each milling run. Thus, it is suitable for pilot and/or industrial scale of MgH2 production. In addition, low-energy ball mill produces homogeneous and uniform powders when compared with the high-energy ball mill. Furthermore, such tumbling mills are cheaper than high-energy mills and operated simply with low-maintenance requirements. However, this kind of low-energy mill requires long-term milling time (more than 300h) to complete the gas-solid reaction and to obtain nanocrystalline MgH2 powders.

Figure 9.7. Photos taken from KISR-EBRC/NAM Lab, Kuwait, display setup of a lab-scale roller mill (1000m in volume) showing (A) the milling tools including the balls (milling media and vial), (B) charging Mg powders in the vial inside inert gas atmosphere glove box, (C) evacuation setup and pressurizing hydrogen gas in the vial, and (D) ball milling processed, using a roller mill. Schematic presentations show the ball positions and movement inside the vial of a tumbler mall mill at a dynamic mode is shown in (E), where a typical ball-powder-ball collusion for a low energy tumbling ball mill is presented in (F).

construction of ball mill/ ball mill structure | henan deya machinery co., ltd

construction of ball mill/ ball mill structure | henan deya machinery co., ltd

Structurally, each ball mill consists of a horizontal cylindrical shell, provided with renewable wearing liners and a charge of grinding medium. The drum is supported so as to rotate on its axis on hollow trunnions attached to the end walls (attached figure 1 ball mill). The diameter of the mill determines the pressure that can be exerted by the medium on the ore particles and, in general, the larger the feed size the larger needs to be the mill diameter. The length of the mill, in conjunction with the diameter, determines the volume, and hence the capacity of the mill.

The feed material is usually fed to the mill continuously through one end trunnion, the ground product leaving via the other trunnion, although in certain applications the product may leave the mill through a number of ports spaced around the periphery of the shell. All types of mill can be used for wet or dry grinding by modification of feed and discharge equipment.

Mill shells are designed to sustain impact and heavy loading, and are constructed from rolled mild steel plates, buttwelded together. Holes are drilled to take the bolts for holding the liners. Normally one or two access manholes are provided. For attachment of the trunnion heads, heavy flanges of fabricated or cast steel are usually welded or bolted to the ends of the plate shells, planed with parallel faces which are grooved to receive a corresponding spigot on the head, and drilled for bolting to the head.

The mill ends, or trunnion heads, may be of nodular or grey cast iron for diameters less than about 1 m. Larger heads are constructed from cast steel, which is relatively light, and can be welded. The heads are fibbed for reinforcement and may be flat, slightly conical, or dished. They are machined and drilled to fit shell flanges(attached figure 2 tube mill end and trunnion). figure 2 Tube mill end and trunnion Trunnions and bearings The trunnions are made from cast iron or steel and are spigoted and bolted to the end plates, although in small mills they may be integral with the end plates. They are highly polished to reduce bearing friction. Most trunnion bearings are rigid highgrade iron castings with 120-180 degree lining of white metal in the bearing area, surrounded by a fabricated mild steel housing, which is bolted into the concrete foundations (attached figure 3 oil-lubricated trunnion bearing). figure 3 oil-lubricated trunnion bearing The bearings in smaller mills may be grease lubricated, but oil lubrication is favoured in large mills, via motor-driven oil pumps. The effectiveness of normal lubrication protection is reduced when the mill is shut down for any length of time, and many mills are fitted with manually operated hydraulic starting lubricators, which force oil between the trunnion and trunnion bearing, preventing friction damage to the beating surface, on starting, by re-establishing the protecting film of oil (attached figure 4 Hydraulic starting lubricator). figure 4 Hydraulic starting lubricator Some manufacturers install large roller bearings, which can withstand higher forces than plain metal bearings (attached figure 5 Trunnion with roller-type bearings ). Trunnion with roller-type bearings Drive Ball mills are most commonly rotated by a pinion meshing with a girth ring bolted to one end of the machine. The pinion shaft is driven from the prime mover through vee-belts, in small mills of less than about 180 kW. For larger mills the shaft is coupled directly to the output shaft of a slow-speed synchronous motor, or to the output shaft of a motor-driven helical or double helical gear reducer. In some mills thyristors and DC motors are used to give variable speed control. Very large mills driven by girth gears require two to four pinions, and complex load sharing systems must be incorporated. Large ball mills can be rotated by a central trunnion drive, which has the advantage of requiting no expensive ring gear, the drive being from one or two motors, with the inclusion of two-or three-speed gearing. The larger the mill, the greater are the stresses between the shells and heads and the trunnions and heads. In the early 1970s, maintenance problems related to the application of gear and pinion and large speed reducer drives on dry grinding cement mills of long length drove operators to seek an alternative drive design. As a result, a number of gearless drive (ring motor) cement mills were installed and the technology became relatively common in the European cement industry. Liners The internal working faces of mills consist of renewable liners, which must withstand impact, be wear-resistant, and promote the most favourable motion of the charge. Rod mill ends have plain fiat liners, slightly coned to encourage the selfcentring and straight-line action of rods. They are made usually from manganese or chromemolybdenum steels, having high impact strength. Ball-mill ends usually have ribs to lift the charge with the mill rotation. These prevent excessive slipping and increase liner life. They can be made from white cast iron, alloyed with nickel (Ni-hard), other wear-resistant materials, and rubber. Trunnion liners are designed for each application and can be conical, plain, with advancing or retarding spirals. They are manufactured from hard cast iron or cast alloy steel, a rubber lining often being bonded to the inner surface for increased life. Shell liners have an endless variety of lifter shapes. Smooth linings result in much abrasion, and hence a fine grind, but with associated high metal wear. The liners are therefore generally shaped to provide lifting action and to add impact and crushing, the most common shapes being wave, Lorain, stepped, and shiplap (attached figure 6 ball mill shell liners). The liners are attached to the mill shell and ends by forged steel countersunk liner bolts. figure 6 ball mill shell liners Rod mill liners are also generally of alloyed steel or cast iron, and of the wave type, although Nihard step liners may be used with rods up to 4 cm in diameter. Lorain liners are extensively used for coarse grinding in rod and ball mills, and consist of high carbon rolled steel plates held in place by manganese or hard alloy steel lifter bars. Ball mill liners may be made of hard cast iron when balls of up to 5 cm in diameter are used, but otherwise cast manganese steel, cast chromium steel, or Ni-hard are used. Ball Mill liners are a major cost in mill operation, and efforts to prolong liner life are constantly being made. There are at least ten wear-resistant alloys used for ball-mill linings, the more abrasion-resistant alloys containing large amounts of chromium, molybdenum, and nickel being the most expensive. However, with steadily increasing labour costs for replacing liners, the trend is towards selecting liners which have the best service life regardless of cost. Rubber liners and lifters have supplanted steel in some operations, and have been found to be longer lasting, easier and faster to install, and their use results in a significant reduction of noise level. However, increased medium consumption has been reported using rubber liners rather than Ni-hard liners. Rubber lining may also have drawbacks in processes requiring the addition of flotation reagents directly into the mill, or temperatures exceeding 80. They are also thicker than their steel counterparts, which reduces mill capacity, a particularly important factor in small mills. There are also important differences in design aspects between steel and rubber linings. The engineering advantage of rubber is that, at relatively low impact forces, it will yield, resuming its shape when the forces are removed. However, if the forces are too powerful, or the speed of the material hitting the rubber is too high, the wear rate is dramatic. In primary grinding applications, with severe grinding forces, the wear rate of rubber inhibits its use. Even though the wear cost per tonne of ore may be similar to that of the more expensive steel lining, the more frequent interruptions for maintenance often make it uneconomical. The advantage of steel is its great hardness, and steel-capped liners have been developed which combine the best qualities of rubber and steel. These consist of rubber lifter bars with steel inserts embedded in the face, the steel providing the wear resistance and the rubber backing cushioning the impacts. A concept which has found some application for ball mills is the angular spiral lining. The circular cross-section of a conventional mill is changed to a square cross-section with rounded corners by the addition of rubber-lined, flanged frames, which are offset to spiral in a direction opposite to the mill rotation. Double wave liner plates are fitted to these frames, and a sequential lifting of the charge down the length of the mill results, which increases the grinding ball to pulp mixing through axial motion of the grinding charge, along with the normal cascading motion. Substantial increases in throughput, along with reductions in energy and grinding medium consumptions, have been reported. To avoid the rapid wear of rubber liners, a new patented technology for a magnetic metal liner has been developed by China Metallurgical Mining Corp. The magnets keep the lining in contact with the steel shell and the end plates without using bolts, while the ball scats in the charge and magnetic minerals are attracted to the liner to form a 30-40mm protective layer, which is continuously renewed as it wears. Over 10 years the magnetic metal liner has been used in more than 300 full-scale ball mills at over 100 mine sites in China. For example, one set of the magnetic metal liner was installed in a 3.2m (D) x 4.5 m (L) secondary ball mill (60mm ball charge) at Waitoushan concentrator of Benxi Iron and Steel Corp. in 1992. Over nine years, 2.6 Mt of iron ore were ground at zero additional liner cost and zero maintenance of the liners. The magnetic metal liner has also found applications in large ball mills, such as the 5.5 m (D) x 8.8 m (L) mills installed at Diaojuntai concentrator in Qidashan Iron Ore Mines. Another advantage of the magnetic metal liner is that as the liners are thinner and lighter than conventional manganese steel, the effective mill volume is larger, and the mill weight is reduced. An 11.3% decrease in mill power draw at the same operational conditions has been realised in a 2.7m (D) x 3.6m (L) ball mill by using the magnetic metal liner. Mill feeders Spout feeder The type of feeding arrangement used on the mill depends on whether the grinding is done in open or closed circuit and whether it is done wet or dry. The size and rate of feed are also important. Dry mills are usually fed by some sort of vibratory feeder. Three types of feeder are in use in wet-grinding mills. The simplest form is the spout feeder (attached figure 7 Spout feeder), consisting of a cylindrical or elliptical chute supported independently of the mill, and projecting directly into the trunnion liner. Material is fed by gravity through the spout to feed the mills. They are often used for feeding rod mills operating in open circuit or mills in closed circuit with hydrocyclone classifiers. figure 7 Spout feeder Drum feeders Drum feeders (attached figure 8 Drum feeder on ball mill) may be used as an alternative to a spout feeder when headroom is limited. The entire mill feed enters the drum via a chute or spout and an internal spiral carries it into the trunnion liner. The drum also provides a convenient method of adding grinding balls to a mill. figure 8 Drum feeder on ball mill Combination drum-scoop feeders These (attached figure 9 Drum-scoop feeder) are generally used for wet grinding in closed circuit with a spiral or rake classifier. New material is fed directly into the drum, while the scoop picks up the classifier sands for regrinding. Either a single or a double scoop can be used, the latter providing an increased feed rate and more uniform flow of material into the mill; the counter-balancing effect of the double-scoop design serves to smooth out power fluctuation and it is normally incorporated in large-diameter mills. Scoop feeders are sometimes used in place of the drum-scoop combination when mill feed is in the fine-size range. figure 9 Drum-scoop feeder

The trunnions are made from cast iron or steel and are spigoted and bolted to the end plates, although in small mills they may be integral with the end plates. They are highly polished to reduce bearing friction. Most trunnion bearings are rigid highgrade iron castings with 120-180 degree lining of white metal in the bearing area, surrounded by a fabricated mild steel housing, which is bolted into the concrete foundations (attached figure 3 oil-lubricated trunnion bearing). figure 3 oil-lubricated trunnion bearing The bearings in smaller mills may be grease lubricated, but oil lubrication is favoured in large mills, via motor-driven oil pumps. The effectiveness of normal lubrication protection is reduced when the mill is shut down for any length of time, and many mills are fitted with manually operated hydraulic starting lubricators, which force oil between the trunnion and trunnion bearing, preventing friction damage to the beating surface, on starting, by re-establishing the protecting film of oil (attached figure 4 Hydraulic starting lubricator). figure 4 Hydraulic starting lubricator Some manufacturers install large roller bearings, which can withstand higher forces than plain metal bearings (attached figure 5 Trunnion with roller-type bearings ). Trunnion with roller-type bearings Drive Ball mills are most commonly rotated by a pinion meshing with a girth ring bolted to one end of the machine. The pinion shaft is driven from the prime mover through vee-belts, in small mills of less than about 180 kW. For larger mills the shaft is coupled directly to the output shaft of a slow-speed synchronous motor, or to the output shaft of a motor-driven helical or double helical gear reducer. In some mills thyristors and DC motors are used to give variable speed control. Very large mills driven by girth gears require two to four pinions, and complex load sharing systems must be incorporated. Large ball mills can be rotated by a central trunnion drive, which has the advantage of requiting no expensive ring gear, the drive being from one or two motors, with the inclusion of two-or three-speed gearing. The larger the mill, the greater are the stresses between the shells and heads and the trunnions and heads. In the early 1970s, maintenance problems related to the application of gear and pinion and large speed reducer drives on dry grinding cement mills of long length drove operators to seek an alternative drive design. As a result, a number of gearless drive (ring motor) cement mills were installed and the technology became relatively common in the European cement industry. Liners The internal working faces of mills consist of renewable liners, which must withstand impact, be wear-resistant, and promote the most favourable motion of the charge. Rod mill ends have plain fiat liners, slightly coned to encourage the selfcentring and straight-line action of rods. They are made usually from manganese or chromemolybdenum steels, having high impact strength. Ball-mill ends usually have ribs to lift the charge with the mill rotation. These prevent excessive slipping and increase liner life. They can be made from white cast iron, alloyed with nickel (Ni-hard), other wear-resistant materials, and rubber. Trunnion liners are designed for each application and can be conical, plain, with advancing or retarding spirals. They are manufactured from hard cast iron or cast alloy steel, a rubber lining often being bonded to the inner surface for increased life. Shell liners have an endless variety of lifter shapes. Smooth linings result in much abrasion, and hence a fine grind, but with associated high metal wear. The liners are therefore generally shaped to provide lifting action and to add impact and crushing, the most common shapes being wave, Lorain, stepped, and shiplap (attached figure 6 ball mill shell liners). The liners are attached to the mill shell and ends by forged steel countersunk liner bolts. figure 6 ball mill shell liners Rod mill liners are also generally of alloyed steel or cast iron, and of the wave type, although Nihard step liners may be used with rods up to 4 cm in diameter. Lorain liners are extensively used for coarse grinding in rod and ball mills, and consist of high carbon rolled steel plates held in place by manganese or hard alloy steel lifter bars. Ball mill liners may be made of hard cast iron when balls of up to 5 cm in diameter are used, but otherwise cast manganese steel, cast chromium steel, or Ni-hard are used. Ball Mill liners are a major cost in mill operation, and efforts to prolong liner life are constantly being made. There are at least ten wear-resistant alloys used for ball-mill linings, the more abrasion-resistant alloys containing large amounts of chromium, molybdenum, and nickel being the most expensive. However, with steadily increasing labour costs for replacing liners, the trend is towards selecting liners which have the best service life regardless of cost. Rubber liners and lifters have supplanted steel in some operations, and have been found to be longer lasting, easier and faster to install, and their use results in a significant reduction of noise level. However, increased medium consumption has been reported using rubber liners rather than Ni-hard liners. Rubber lining may also have drawbacks in processes requiring the addition of flotation reagents directly into the mill, or temperatures exceeding 80. They are also thicker than their steel counterparts, which reduces mill capacity, a particularly important factor in small mills. There are also important differences in design aspects between steel and rubber linings. The engineering advantage of rubber is that, at relatively low impact forces, it will yield, resuming its shape when the forces are removed. However, if the forces are too powerful, or the speed of the material hitting the rubber is too high, the wear rate is dramatic. In primary grinding applications, with severe grinding forces, the wear rate of rubber inhibits its use. Even though the wear cost per tonne of ore may be similar to that of the more expensive steel lining, the more frequent interruptions for maintenance often make it uneconomical. The advantage of steel is its great hardness, and steel-capped liners have been developed which combine the best qualities of rubber and steel. These consist of rubber lifter bars with steel inserts embedded in the face, the steel providing the wear resistance and the rubber backing cushioning the impacts. A concept which has found some application for ball mills is the angular spiral lining. The circular cross-section of a conventional mill is changed to a square cross-section with rounded corners by the addition of rubber-lined, flanged frames, which are offset to spiral in a direction opposite to the mill rotation. Double wave liner plates are fitted to these frames, and a sequential lifting of the charge down the length of the mill results, which increases the grinding ball to pulp mixing through axial motion of the grinding charge, along with the normal cascading motion. Substantial increases in throughput, along with reductions in energy and grinding medium consumptions, have been reported. To avoid the rapid wear of rubber liners, a new patented technology for a magnetic metal liner has been developed by China Metallurgical Mining Corp. The magnets keep the lining in contact with the steel shell and the end plates without using bolts, while the ball scats in the charge and magnetic minerals are attracted to the liner to form a 30-40mm protective layer, which is continuously renewed as it wears. Over 10 years the magnetic metal liner has been used in more than 300 full-scale ball mills at over 100 mine sites in China. For example, one set of the magnetic metal liner was installed in a 3.2m (D) x 4.5 m (L) secondary ball mill (60mm ball charge) at Waitoushan concentrator of Benxi Iron and Steel Corp. in 1992. Over nine years, 2.6 Mt of iron ore were ground at zero additional liner cost and zero maintenance of the liners. The magnetic metal liner has also found applications in large ball mills, such as the 5.5 m (D) x 8.8 m (L) mills installed at Diaojuntai concentrator in Qidashan Iron Ore Mines. Another advantage of the magnetic metal liner is that as the liners are thinner and lighter than conventional manganese steel, the effective mill volume is larger, and the mill weight is reduced. An 11.3% decrease in mill power draw at the same operational conditions has been realised in a 2.7m (D) x 3.6m (L) ball mill by using the magnetic metal liner. Mill feeders Spout feeder The type of feeding arrangement used on the mill depends on whether the grinding is done in open or closed circuit and whether it is done wet or dry. The size and rate of feed are also important. Dry mills are usually fed by some sort of vibratory feeder. Three types of feeder are in use in wet-grinding mills. The simplest form is the spout feeder (attached figure 7 Spout feeder), consisting of a cylindrical or elliptical chute supported independently of the mill, and projecting directly into the trunnion liner. Material is fed by gravity through the spout to feed the mills. They are often used for feeding rod mills operating in open circuit or mills in closed circuit with hydrocyclone classifiers. figure 7 Spout feeder Drum feeders Drum feeders (attached figure 8 Drum feeder on ball mill) may be used as an alternative to a spout feeder when headroom is limited. The entire mill feed enters the drum via a chute or spout and an internal spiral carries it into the trunnion liner. The drum also provides a convenient method of adding grinding balls to a mill. figure 8 Drum feeder on ball mill Combination drum-scoop feeders These (attached figure 9 Drum-scoop feeder) are generally used for wet grinding in closed circuit with a spiral or rake classifier. New material is fed directly into the drum, while the scoop picks up the classifier sands for regrinding. Either a single or a double scoop can be used, the latter providing an increased feed rate and more uniform flow of material into the mill; the counter-balancing effect of the double-scoop design serves to smooth out power fluctuation and it is normally incorporated in large-diameter mills. Scoop feeders are sometimes used in place of the drum-scoop combination when mill feed is in the fine-size range. figure 9 Drum-scoop feeder

The bearings in smaller mills may be grease lubricated, but oil lubrication is favoured in large mills, via motor-driven oil pumps. The effectiveness of normal lubrication protection is reduced when the mill is shut down for any length of time, and many mills are fitted with manually operated hydraulic starting lubricators, which force oil between the trunnion and trunnion bearing, preventing friction damage to the beating surface, on starting, by re-establishing the protecting film of oil (attached figure 4 Hydraulic starting lubricator). figure 4 Hydraulic starting lubricator Some manufacturers install large roller bearings, which can withstand higher forces than plain metal bearings (attached figure 5 Trunnion with roller-type bearings ). Trunnion with roller-type bearings Drive Ball mills are most commonly rotated by a pinion meshing with a girth ring bolted to one end of the machine. The pinion shaft is driven from the prime mover through vee-belts, in small mills of less than about 180 kW. For larger mills the shaft is coupled directly to the output shaft of a slow-speed synchronous motor, or to the output shaft of a motor-driven helical or double helical gear reducer. In some mills thyristors and DC motors are used to give variable speed control. Very large mills driven by girth gears require two to four pinions, and complex load sharing systems must be incorporated. Large ball mills can be rotated by a central trunnion drive, which has the advantage of requiting no expensive ring gear, the drive being from one or two motors, with the inclusion of two-or three-speed gearing. The larger the mill, the greater are the stresses between the shells and heads and the trunnions and heads. In the early 1970s, maintenance problems related to the application of gear and pinion and large speed reducer drives on dry grinding cement mills of long length drove operators to seek an alternative drive design. As a result, a number of gearless drive (ring motor) cement mills were installed and the technology became relatively common in the European cement industry. Liners The internal working faces of mills consist of renewable liners, which must withstand impact, be wear-resistant, and promote the most favourable motion of the charge. Rod mill ends have plain fiat liners, slightly coned to encourage the selfcentring and straight-line action of rods. They are made usually from manganese or chromemolybdenum steels, having high impact strength. Ball-mill ends usually have ribs to lift the charge with the mill rotation. These prevent excessive slipping and increase liner life. They can be made from white cast iron, alloyed with nickel (Ni-hard), other wear-resistant materials, and rubber. Trunnion liners are designed for each application and can be conical, plain, with advancing or retarding spirals. They are manufactured from hard cast iron or cast alloy steel, a rubber lining often being bonded to the inner surface for increased life. Shell liners have an endless variety of lifter shapes. Smooth linings result in much abrasion, and hence a fine grind, but with associated high metal wear. The liners are therefore generally shaped to provide lifting action and to add impact and crushing, the most common shapes being wave, Lorain, stepped, and shiplap (attached figure 6 ball mill shell liners). The liners are attached to the mill shell and ends by forged steel countersunk liner bolts. figure 6 ball mill shell liners Rod mill liners are also generally of alloyed steel or cast iron, and of the wave type, although Nihard step liners may be used with rods up to 4 cm in diameter. Lorain liners are extensively used for coarse grinding in rod and ball mills, and consist of high carbon rolled steel plates held in place by manganese or hard alloy steel lifter bars. Ball mill liners may be made of hard cast iron when balls of up to 5 cm in diameter are used, but otherwise cast manganese steel, cast chromium steel, or Ni-hard are used. Ball Mill liners are a major cost in mill operation, and efforts to prolong liner life are constantly being made. There are at least ten wear-resistant alloys used for ball-mill linings, the more abrasion-resistant alloys containing large amounts of chromium, molybdenum, and nickel being the most expensive. However, with steadily increasing labour costs for replacing liners, the trend is towards selecting liners which have the best service life regardless of cost. Rubber liners and lifters have supplanted steel in some operations, and have been found to be longer lasting, easier and faster to install, and their use results in a significant reduction of noise level. However, increased medium consumption has been reported using rubber liners rather than Ni-hard liners. Rubber lining may also have drawbacks in processes requiring the addition of flotation reagents directly into the mill, or temperatures exceeding 80. They are also thicker than their steel counterparts, which reduces mill capacity, a particularly important factor in small mills. There are also important differences in design aspects between steel and rubber linings. The engineering advantage of rubber is that, at relatively low impact forces, it will yield, resuming its shape when the forces are removed. However, if the forces are too powerful, or the speed of the material hitting the rubber is too high, the wear rate is dramatic. In primary grinding applications, with severe grinding forces, the wear rate of rubber inhibits its use. Even though the wear cost per tonne of ore may be similar to that of the more expensive steel lining, the more frequent interruptions for maintenance often make it uneconomical. The advantage of steel is its great hardness, and steel-capped liners have been developed which combine the best qualities of rubber and steel. These consist of rubber lifter bars with steel inserts embedded in the face, the steel providing the wear resistance and the rubber backing cushioning the impacts. A concept which has found some application for ball mills is the angular spiral lining. The circular cross-section of a conventional mill is changed to a square cross-section with rounded corners by the addition of rubber-lined, flanged frames, which are offset to spiral in a direction opposite to the mill rotation. Double wave liner plates are fitted to these frames, and a sequential lifting of the charge down the length of the mill results, which increases the grinding ball to pulp mixing through axial motion of the grinding charge, along with the normal cascading motion. Substantial increases in throughput, along with reductions in energy and grinding medium consumptions, have been reported. To avoid the rapid wear of rubber liners, a new patented technology for a magnetic metal liner has been developed by China Metallurgical Mining Corp. The magnets keep the lining in contact with the steel shell and the end plates without using bolts, while the ball scats in the charge and magnetic minerals are attracted to the liner to form a 30-40mm protective layer, which is continuously renewed as it wears. Over 10 years the magnetic metal liner has been used in more than 300 full-scale ball mills at over 100 mine sites in China. For example, one set of the magnetic metal liner was installed in a 3.2m (D) x 4.5 m (L) secondary ball mill (60mm ball charge) at Waitoushan concentrator of Benxi Iron and Steel Corp. in 1992. Over nine years, 2.6 Mt of iron ore were ground at zero additional liner cost and zero maintenance of the liners. The magnetic metal liner has also found applications in large ball mills, such as the 5.5 m (D) x 8.8 m (L) mills installed at Diaojuntai concentrator in Qidashan Iron Ore Mines. Another advantage of the magnetic metal liner is that as the liners are thinner and lighter than conventional manganese steel, the effective mill volume is larger, and the mill weight is reduced. An 11.3% decrease in mill power draw at the same operational conditions has been realised in a 2.7m (D) x 3.6m (L) ball mill by using the magnetic metal liner. Mill feeders Spout feeder The type of feeding arrangement used on the mill depends on whether the grinding is done in open or closed circuit and whether it is done wet or dry. The size and rate of feed are also important. Dry mills are usually fed by some sort of vibratory feeder. Three types of feeder are in use in wet-grinding mills. The simplest form is the spout feeder (attached figure 7 Spout feeder), consisting of a cylindrical or elliptical chute supported independently of the mill, and projecting directly into the trunnion liner. Material is fed by gravity through the spout to feed the mills. They are often used for feeding rod mills operating in open circuit or mills in closed circuit with hydrocyclone classifiers. figure 7 Spout feeder Drum feeders Drum feeders (attached figure 8 Drum feeder on ball mill) may be used as an alternative to a spout feeder when headroom is limited. The entire mill feed enters the drum via a chute or spout and an internal spiral carries it into the trunnion liner. The drum also provides a convenient method of adding grinding balls to a mill. figure 8 Drum feeder on ball mill Combination drum-scoop feeders These (attached figure 9 Drum-scoop feeder) are generally used for wet grinding in closed circuit with a spiral or rake classifier. New material is fed directly into the drum, while the scoop picks up the classifier sands for regrinding. Either a single or a double scoop can be used, the latter providing an increased feed rate and more uniform flow of material into the mill; the counter-balancing effect of the double-scoop design serves to smooth out power fluctuation and it is normally incorporated in large-diameter mills. Scoop feeders are sometimes used in place of the drum-scoop combination when mill feed is in the fine-size range. figure 9 Drum-scoop feeder

Some manufacturers install large roller bearings, which can withstand higher forces than plain metal bearings (attached figure 5 Trunnion with roller-type bearings ). Trunnion with roller-type bearings Drive Ball mills are most commonly rotated by a pinion meshing with a girth ring bolted to one end of the machine. The pinion shaft is driven from the prime mover through vee-belts, in small mills of less than about 180 kW. For larger mills the shaft is coupled directly to the output shaft of a slow-speed synchronous motor, or to the output shaft of a motor-driven helical or double helical gear reducer. In some mills thyristors and DC motors are used to give variable speed control. Very large mills driven by girth gears require two to four pinions, and complex load sharing systems must be incorporated. Large ball mills can be rotated by a central trunnion drive, which has the advantage of requiting no expensive ring gear, the drive being from one or two motors, with the inclusion of two-or three-speed gearing. The larger the mill, the greater are the stresses between the shells and heads and the trunnions and heads. In the early 1970s, maintenance problems related to the application of gear and pinion and large speed reducer drives on dry grinding cement mills of long length drove operators to seek an alternative drive design. As a result, a number of gearless drive (ring motor) cement mills were installed and the technology became relatively common in the European cement industry. Liners The internal working faces of mills consist of renewable liners, which must withstand impact, be wear-resistant, and promote the most favourable motion of the charge. Rod mill ends have plain fiat liners, slightly coned to encourage the selfcentring and straight-line action of rods. They are made usually from manganese or chromemolybdenum steels, having high impact strength. Ball-mill ends usually have ribs to lift the charge with the mill rotation. These prevent excessive slipping and increase liner life. They can be made from white cast iron, alloyed with nickel (Ni-hard), other wear-resistant materials, and rubber. Trunnion liners are designed for each application and can be conical, plain, with advancing or retarding spirals. They are manufactured from hard cast iron or cast alloy steel, a rubber lining often being bonded to the inner surface for increased life. Shell liners have an endless variety of lifter shapes. Smooth linings result in much abrasion, and hence a fine grind, but with associated high metal wear. The liners are therefore generally shaped to provide lifting action and to add impact and crushing, the most common shapes being wave, Lorain, stepped, and shiplap (attached figure 6 ball mill shell liners). The liners are attached to the mill shell and ends by forged steel countersunk liner bolts. figure 6 ball mill shell liners Rod mill liners are also generally of alloyed steel or cast iron, and of the wave type, although Nihard step liners may be used with rods up to 4 cm in diameter. Lorain liners are extensively used for coarse grinding in rod and ball mills, and consist of high carbon rolled steel plates held in place by manganese or hard alloy steel lifter bars. Ball mill liners may be made of hard cast iron when balls of up to 5 cm in diameter are used, but otherwise cast manganese steel, cast chromium steel, or Ni-hard are used. Ball Mill liners are a major cost in mill operation, and efforts to prolong liner life are constantly being made. There are at least ten wear-resistant alloys used for ball-mill linings, the more abrasion-resistant alloys containing large amounts of chromium, molybdenum, and nickel being the most expensive. However, with steadily increasing labour costs for replacing liners, the trend is towards selecting liners which have the best service life regardless of cost. Rubber liners and lifters have supplanted steel in some operations, and have been found to be longer lasting, easier and faster to install, and their use results in a significant reduction of noise level. However, increased medium consumption has been reported using rubber liners rather than Ni-hard liners. Rubber lining may also have drawbacks in processes requiring the addition of flotation reagents directly into the mill, or temperatures exceeding 80. They are also thicker than their steel counterparts, which reduces mill capacity, a particularly important factor in small mills. There are also important differences in design aspects between steel and rubber linings. The engineering advantage of rubber is that, at relatively low impact forces, it will yield, resuming its shape when the forces are removed. However, if the forces are too powerful, or the speed of the material hitting the rubber is too high, the wear rate is dramatic. In primary grinding applications, with severe grinding forces, the wear rate of rubber inhibits its use. Even though the wear cost per tonne of ore may be similar to that of the more expensive steel lining, the more frequent interruptions for maintenance often make it uneconomical. The advantage of steel is its great hardness, and steel-capped liners have been developed which combine the best qualities of rubber and steel. These consist of rubber lifter bars with steel inserts embedded in the face, the steel providing the wear resistance and the rubber backing cushioning the impacts. A concept which has found some application for ball mills is the angular spiral lining. The circular cross-section of a conventional mill is changed to a square cross-section with rounded corners by the addition of rubber-lined, flanged frames, which are offset to spiral in a direction opposite to the mill rotation. Double wave liner plates are fitted to these frames, and a sequential lifting of the charge down the length of the mill results, which increases the grinding ball to pulp mixing through axial motion of the grinding charge, along with the normal cascading motion. Substantial increases in throughput, along with reductions in energy and grinding medium consumptions, have been reported. To avoid the rapid wear of rubber liners, a new patented technology for a magnetic metal liner has been developed by China Metallurgical Mining Corp. The magnets keep the lining in contact with the steel shell and the end plates without using bolts, while the ball scats in the charge and magnetic minerals are attracted to the liner to form a 30-40mm protective layer, which is continuously renewed as it wears. Over 10 years the magnetic metal liner has been used in more than 300 full-scale ball mills at over 100 mine sites in China. For example, one set of the magnetic metal liner was installed in a 3.2m (D) x 4.5 m (L) secondary ball mill (60mm ball charge) at Waitoushan concentrator of Benxi Iron and Steel Corp. in 1992. Over nine years, 2.6 Mt of iron ore were ground at zero additional liner cost and zero maintenance of the liners. The magnetic metal liner has also found applications in large ball mills, such as the 5.5 m (D) x 8.8 m (L) mills installed at Diaojuntai concentrator in Qidashan Iron Ore Mines. Another advantage of the magnetic metal liner is that as the liners are thinner and lighter than conventional manganese steel, the effective mill volume is larger, and the mill weight is reduced. An 11.3% decrease in mill power draw at the same operational conditions has been realised in a 2.7m (D) x 3.6m (L) ball mill by using the magnetic metal liner. Mill feeders Spout feeder The type of feeding arrangement used on the mill depends on whether the grinding is done in open or closed circuit and whether it is done wet or dry. The size and rate of feed are also important. Dry mills are usually fed by some sort of vibratory feeder. Three types of feeder are in use in wet-grinding mills. The simplest form is the spout feeder (attached figure 7 Spout feeder), consisting of a cylindrical or elliptical chute supported independently of the mill, and projecting directly into the trunnion liner. Material is fed by gravity through the spout to feed the mills. They are often used for feeding rod mills operating in open circuit or mills in closed circuit with hydrocyclone classifiers. figure 7 Spout feeder Drum feeders Drum feeders (attached figure 8 Drum feeder on ball mill) may be used as an alternative to a spout feeder when headroom is limited. The entire mill feed enters the drum via a chute or spout and an internal spiral carries it into the trunnion liner. The drum also provides a convenient method of adding grinding balls to a mill. figure 8 Drum feeder on ball mill Combination drum-scoop feeders These (attached figure 9 Drum-scoop feeder) are generally used for wet grinding in closed circuit with a spiral or rake classifier. New material is fed directly into the drum, while the scoop picks up the classifier sands for regrinding. Either a single or a double scoop can be used, the latter providing an increased feed rate and more uniform flow of material into the mill; the counter-balancing effect of the double-scoop design serves to smooth out power fluctuation and it is normally incorporated in large-diameter mills. Scoop feeders are sometimes used in place of the drum-scoop combination when mill feed is in the fine-size range. figure 9 Drum-scoop feeder

Ball mills are most commonly rotated by a pinion meshing with a girth ring bolted to one end of the machine. The pinion shaft is driven from the prime mover through vee-belts, in small mills of less than about 180 kW. For larger mills the shaft is coupled directly to the output shaft of a slow-speed synchronous motor, or to the output shaft of a motor-driven helical or double helical gear reducer. In some mills thyristors and DC motors are used to give variable speed control. Very large mills driven by girth gears require two to four pinions, and complex load sharing systems must be incorporated.

Large ball mills can be rotated by a central trunnion drive, which has the advantage of requiting no expensive ring gear, the drive being from one or two motors, with the inclusion of two-or three-speed gearing.

The larger the mill, the greater are the stresses between the shells and heads and the trunnions and heads. In the early 1970s, maintenance problems related to the application of gear and pinion and large speed reducer drives on dry grinding cement mills of long length drove operators to seek an alternative drive design. As a result, a number of gearless drive (ring motor) cement mills were installed and the technology became relatively common in the European cement industry.

The internal working faces of mills consist of renewable liners, which must withstand impact, be wear-resistant, and promote the most favourable motion of the charge. Rod mill ends have plain fiat liners, slightly coned to encourage the selfcentring and straight-line action of rods. They are made usually from manganese or chromemolybdenum steels, having high impact strength. Ball-mill ends usually have ribs to lift the charge with the mill rotation. These prevent excessive slipping and increase liner life. They can be made from white cast iron, alloyed with nickel (Ni-hard), other wear-resistant materials, and rubber. Trunnion liners are designed for each application and can be conical, plain, with advancing or retarding spirals. They are manufactured from hard cast iron or cast alloy steel, a rubber lining often being bonded to the inner surface for increased life. Shell liners have an endless variety of lifter shapes. Smooth linings result in much abrasion, and hence a fine grind, but with associated high metal wear. The liners are therefore generally shaped to provide lifting action and to add impact and crushing, the most common shapes being wave, Lorain, stepped, and shiplap (attached figure 6 ball mill shell liners). The liners are attached to the mill shell and ends by forged steel countersunk liner bolts. figure 6 ball mill shell liners Rod mill liners are also generally of alloyed steel or cast iron, and of the wave type, although Nihard step liners may be used with rods up to 4 cm in diameter. Lorain liners are extensively used for coarse grinding in rod and ball mills, and consist of high carbon rolled steel plates held in place by manganese or hard alloy steel lifter bars. Ball mill liners may be made of hard cast iron when balls of up to 5 cm in diameter are used, but otherwise cast manganese steel, cast chromium steel, or Ni-hard are used. Ball Mill liners are a major cost in mill operation, and efforts to prolong liner life are constantly being made. There are at least ten wear-resistant alloys used for ball-mill linings, the more abrasion-resistant alloys containing large amounts of chromium, molybdenum, and nickel being the most expensive. However, with steadily increasing labour costs for replacing liners, the trend is towards selecting liners which have the best service life regardless of cost. Rubber liners and lifters have supplanted steel in some operations, and have been found to be longer lasting, easier and faster to install, and their use results in a significant reduction of noise level. However, increased medium consumption has been reported using rubber liners rather than Ni-hard liners. Rubber lining may also have drawbacks in processes requiring the addition of flotation reagents directly into the mill, or temperatures exceeding 80. They are also thicker than their steel counterparts, which reduces mill capacity, a particularly important factor in small mills. There are also important differences in design aspects between steel and rubber linings. The engineering advantage of rubber is that, at relatively low impact forces, it will yield, resuming its shape when the forces are removed. However, if the forces are too powerful, or the speed of the material hitting the rubber is too high, the wear rate is dramatic. In primary grinding applications, with severe grinding forces, the wear rate of rubber inhibits its use. Even though the wear cost per tonne of ore may be similar to that of the more expensive steel lining, the more frequent interruptions for maintenance often make it uneconomical. The advantage of steel is its great hardness, and steel-capped liners have been developed which combine the best qualities of rubber and steel. These consist of rubber lifter bars with steel inserts embedded in the face, the steel providing the wear resistance and the rubber backing cushioning the impacts. A concept which has found some application for ball mills is the angular spiral lining. The circular cross-section of a conventional mill is changed to a square cross-section with rounded corners by the addition of rubber-lined, flanged frames, which are offset to spiral in a direction opposite to the mill rotation. Double wave liner plates are fitted to these frames, and a sequential lifting of the charge down the length of the mill results, which increases the grinding ball to pulp mixing through axial motion of the grinding charge, along with the normal cascading motion. Substantial increases in throughput, along with reductions in energy and grinding medium consumptions, have been reported. To avoid the rapid wear of rubber liners, a new patented technology for a magnetic metal liner has been developed by China Metallurgical Mining Corp. The magnets keep the lining in contact with the steel shell and the end plates without using bolts, while the ball scats in the charge and magnetic minerals are attracted to the liner to form a 30-40mm protective layer, which is continuously renewed as it wears. Over 10 years the magnetic metal liner has been used in more than 300 full-scale ball mills at over 100 mine sites in China. For example, one set of the magnetic metal liner was installed in a 3.2m (D) x 4.5 m (L) secondary ball mill (60mm ball charge) at Waitoushan concentrator of Benxi Iron and Steel Corp. in 1992. Over nine years, 2.6 Mt of iron ore were ground at zero additional liner cost and zero maintenance of the liners. The magnetic metal liner has also found applications in large ball mills, such as the 5.5 m (D) x 8.8 m (L) mills installed at Diaojuntai concentrator in Qidashan Iron Ore Mines. Another advantage of the magnetic metal liner is that as the liners are thinner and lighter than conventional manganese steel, the effective mill volume is larger, and the mill weight is reduced. An 11.3% decrease in mill power draw at the same operational conditions has been realised in a 2.7m (D) x 3.6m (L) ball mill by using the magnetic metal liner. Mill feeders Spout feeder The type of feeding arrangement used on the mill depends on whether the grinding is done in open or closed circuit and whether it is done wet or dry. The size and rate of feed are also important. Dry mills are usually fed by some sort of vibratory feeder. Three types of feeder are in use in wet-grinding mills. The simplest form is the spout feeder (attached figure 7 Spout feeder), consisting of a cylindrical or elliptical chute supported independently of the mill, and projecting directly into the trunnion liner. Material is fed by gravity through the spout to feed the mills. They are often used for feeding rod mills operating in open circuit or mills in closed circuit with hydrocyclone classifiers. figure 7 Spout feeder Drum feeders Drum feeders (attached figure 8 Drum feeder on ball mill) may be used as an alternative to a spout feeder when headroom is limited. The entire mill feed enters the drum via a chute or spout and an internal spiral carries it into the trunnion liner. The drum also provides a convenient method of adding grinding balls to a mill. figure 8 Drum feeder on ball mill Combination drum-scoop feeders These (attached figure 9 Drum-scoop feeder) are generally used for wet grinding in closed circuit with a spiral or rake classifier. New material is fed directly into the drum, while the scoop picks up the classifier sands for regrinding. Either a single or a double scoop can be used, the latter providing an increased feed rate and more uniform flow of material into the mill; the counter-balancing effect of the double-scoop design serves to smooth out power fluctuation and it is normally incorporated in large-diameter mills. Scoop feeders are sometimes used in place of the drum-scoop combination when mill feed is in the fine-size range. figure 9 Drum-scoop feeder

Rod mill liners are also generally of alloyed steel or cast iron, and of the wave type, although Nihard step liners may be used with rods up to 4 cm in diameter. Lorain liners are extensively used for coarse grinding in rod and ball mills, and consist of high carbon rolled steel plates held in place by manganese or hard alloy steel lifter bars. Ball mill liners may be made of hard cast iron when balls of up to 5 cm in diameter are used, but otherwise cast manganese steel, cast chromium steel, or Ni-hard are used.

Ball Mill liners are a major cost in mill operation, and efforts to prolong liner life are constantly being made. There are at least ten wear-resistant alloys used for ball-mill linings, the more abrasion-resistant alloys containing large amounts of chromium, molybdenum, and nickel being the most expensive. However, with steadily increasing labour costs for replacing liners, the trend is towards selecting liners which have the best service life regardless of cost.

Rubber liners and lifters have supplanted steel in some operations, and have been found to be longer lasting, easier and faster to install, and their use results in a significant reduction of noise level. However, increased medium consumption has been reported using rubber liners rather than Ni-hard liners. Rubber lining may also have drawbacks in processes requiring the addition of flotation reagents directly into the mill, or temperatures exceeding 80. They are also thicker than their steel counterparts, which reduces mill capacity, a particularly important factor in small mills. There are also important differences in design aspects between steel and rubber linings.

The engineering advantage of rubber is that, at relatively low impact forces, it will yield, resuming its shape when the forces are removed. However, if the forces are too powerful, or the speed of the material hitting the rubber is too high, the wear rate is dramatic. In primary grinding applications, with severe grinding forces, the wear rate of rubber inhibits its use. Even though the wear cost per tonne of ore may be similar to that of the more expensive steel lining, the more frequent interruptions for maintenance often make it uneconomical. The advantage of steel is its great hardness, and steel-capped liners have been developed which combine the best qualities of rubber and steel. These consist of rubber lifter bars with steel inserts embedded in the face, the steel providing the wear resistance and the rubber backing cushioning the impacts.

A concept which has found some application for ball mills is the angular spiral lining. The circular cross-section of a conventional mill is changed to a square cross-section with rounded corners by the addition of rubber-lined, flanged frames, which are offset to spiral in a direction opposite to the mill rotation. Double wave liner plates are fitted to these frames, and a sequential lifting of the charge down the length of the mill results, which increases the grinding ball to pulp mixing through axial motion of the grinding charge, along with the normal cascading motion. Substantial increases in throughput, along with reductions in energy and grinding medium consumptions, have been reported.

To avoid the rapid wear of rubber liners, a new patented technology for a magnetic metal liner has been developed by China Metallurgical Mining Corp. The magnets keep the lining in contact with the steel shell and the end plates without using bolts, while the ball scats in the charge and magnetic minerals are attracted to the liner to form a 30-40mm protective layer, which is continuously renewed as it wears. Over 10 years the magnetic metal liner has been used in more than 300 full-scale ball mills at over 100 mine sites in China. For example, one set of the magnetic metal liner was installed in a 3.2m (D) x 4.5 m (L) secondary ball mill (60mm ball charge) at Waitoushan concentrator of Benxi Iron and Steel Corp. in 1992. Over nine years, 2.6 Mt of iron ore were ground at zero additional liner cost and zero maintenance of the liners. The magnetic metal liner has also found applications in large ball mills, such as the 5.5 m (D) x 8.8 m (L) mills installed at Diaojuntai concentrator in Qidashan Iron Ore Mines.

Another advantage of the magnetic metal liner is that as the liners are thinner and lighter than conventional manganese steel, the effective mill volume is larger, and the mill weight is reduced. An 11.3% decrease in mill power draw at the same operational conditions has been realised in a 2.7m (D) x 3.6m (L) ball mill by using the magnetic metal liner.

The type of feeding arrangement used on the mill depends on whether the grinding is done in open or closed circuit and whether it is done wet or dry. The size and rate of feed are also important. Dry mills are usually fed by some sort of vibratory feeder. Three types of feeder are in use in wet-grinding mills. The simplest form is the spout feeder (attached figure 7 Spout feeder), consisting of a cylindrical or elliptical chute supported independently of the mill, and projecting directly into the trunnion liner. Material is fed by gravity through the spout to feed the mills. They are often used for feeding rod mills operating in open circuit or mills in closed circuit with hydrocyclone classifiers. figure 7 Spout feeder Drum feeders Drum feeders (attached figure 8 Drum feeder on ball mill) may be used as an alternative to a spout feeder when headroom is limited. The entire mill feed enters the drum via a chute or spout and an internal spiral carries it into the trunnion liner. The drum also provides a convenient method of adding grinding balls to a mill. figure 8 Drum feeder on ball mill Combination drum-scoop feeders These (attached figure 9 Drum-scoop feeder) are generally used for wet grinding in closed circuit with a spiral or rake classifier. New material is fed directly into the drum, while the scoop picks up the classifier sands for regrinding. Either a single or a double scoop can be used, the latter providing an increased feed rate and more uniform flow of material into the mill; the counter-balancing effect of the double-scoop design serves to smooth out power fluctuation and it is normally incorporated in large-diameter mills. Scoop feeders are sometimes used in place of the drum-scoop combination when mill feed is in the fine-size range. figure 9 Drum-scoop feeder

Drum feeders (attached figure 8 Drum feeder on ball mill) may be used as an alternative to a spout feeder when headroom is limited. The entire mill feed enters the drum via a chute or spout and an internal spiral carries it into the trunnion liner. The drum also provides a convenient method of adding grinding balls to a mill. figure 8 Drum feeder on ball mill Combination drum-scoop feeders These (attached figure 9 Drum-scoop feeder) are generally used for wet grinding in closed circuit with a spiral or rake classifier. New material is fed directly into the drum, while the scoop picks up the classifier sands for regrinding. Either a single or a double scoop can be used, the latter providing an increased feed rate and more uniform flow of material into the mill; the counter-balancing effect of the double-scoop design serves to smooth out power fluctuation and it is normally incorporated in large-diameter mills. Scoop feeders are sometimes used in place of the drum-scoop combination when mill feed is in the fine-size range. figure 9 Drum-scoop feeder

These (attached figure 9 Drum-scoop feeder) are generally used for wet grinding in closed circuit with a spiral or rake classifier. New material is fed directly into the drum, while the scoop picks up the classifier sands for regrinding. Either a single or a double scoop can be used, the latter providing an increased feed rate and more uniform flow of material into the mill; the counter-balancing effect of the double-scoop design serves to smooth out power fluctuation and it is normally incorporated in large-diameter mills. Scoop feeders are sometimes used in place of the drum-scoop combination when mill feed is in the fine-size range. figure 9 Drum-scoop feeder

ball mill: operating principles, components, uses, advantages and

ball mill: operating principles, components, uses, advantages and

A ball mill also known as pebble mill or tumbling mill is a milling machine that consists of a hallow cylinder containing balls; mounted on a metallic frame such that it can be rotated along its longitudinal axis. The balls which could be of different diameter occupy 30 50 % of the mill volume and its size depends on the feed and mill size. The large balls tend to break down the coarse feed materials and the smaller balls help to form fine product by reducing void spaces between the balls. Ball mills grind material by impact and attrition.

Several types of ball mills exist. They differ to an extent in their operating principle. They also differ in their maximum capacity of the milling vessel, ranging from 0.010 liters for planetary ball mills, mixer mills, or vibration ball mills to several 100 liters for horizontal rolling ball mills.

Im grateful for the information about using a ball mill for pharmaceutical products as it produces very fine powder. My friend is working for a pharmaceutical company and this is a good article to share with her. Its good to know that ball mills are suitable for milling toxic materials since they can be used in a completely enclosed for. Thanks for the tips!

the operating principle of the ball mill

the operating principle of the ball mill

The operating principle of the ball mill consists of following steps. In a continuously operating ball mill, feed material fed through the central hole one of the caps into the drum and moves therealong, being exposed by grinding media. The material grinding occurs during impact falling grinding balls and abrasion the particles between the balls. Then, discharge of ground material performed through the central hole in the discharge cap or through the grid (mills with center unloading the milled product and mills with unloading the milled product through the grid).

In filling mill by grinding balls on 40 50% and non-smooth liner, the outer layers slip is virtually absent, but the sliding of the inner layers one on another observed in various modes of operation mill. In a monolayer filling mill by grinding media, they rotate around their axis parallel to the drum axis of rotation. Grinding media are not subjected to a circular motion by a smooth lining, even at high speeds. In a multilayer filling mill by grinding media, depending on the rotational speed, there is possible one of the following modes the grinding media motion:

Cascade mode motion of grinding balls carried out at low drum speed. At start-up of a mill, the grinding material rotated by a certain angle and grinding balls start to move by closed path. The curved surface of natural slope is close to the plane inclined at some angle to the horizontal. This angle is equal to a limit angle of rotation. In this mode, the ground material remains in this position, but the grinding balls continuously circulate, rise on circular trajectory and cascade roll to the reference point. There is a zone or core in the central trajectory of the grinding material. This zone is inactive. In cascade mode grinding occurs as a result of crushing and abrasive actions by grinding balls. This mode used in the ball mill with a central discharge.

Waterfall mode motion of grinding media in the mill carried out by the drum rotation speed, ensures the transfer all of the grinding balls layers from a circular to a parabolic trajectory. In this mode, grinding balls rise on circular trajectory and at certain points deviate from it and make a free flight by a parabolic curve.

Weight of grinding balls should be sufficient to grind the largest pieces of crushed material. For efficient operation of ball mills necessary to observe the right balance between balls size and feed material size. If the feed material contains many large lumps and grinding balls cant crush them, it leads to a gradual accumulation them between the balls. As a result, mill suspends own operation. In these cases, need to reduce the size of crushed material or increase the size of the balls. By increasing the grinding balls size, decreases the mill working surface and reduced mill productivity. It is important to follow the degree of drum filling by grinding balls, because with a large filling rising grinding balls collide with falling balls.

Established impact of design mills and lining forms on their productivity. Mills operating with low pulp level, have better productivity than mills with high pulp level. Particularly, productivity of mills with unloading the milled product through the grid approximately 15% higher productivity mills with center unloading the milled product. Productivity mills with smooth lining less than productivity mills with ribbed liner. Mill productivity also depends on other factors: number of the drum rotations, the grinding fineness, humidity and size of the crushed material, timely removal the finished product.

Ball mills characterized by high energy consumption. When the mill idles, the energy consumption is approximately equal to the energy consumption with full mill capacity. Therefore, the work of the mill with partial load conditions is unprofitable. Energy consumption for ball mills is a function of many factors: the physical properties of the ground material its specific gravity and hardness; the degree of drum filling by grinding balls; the number of drum rotations, etc. Ball mills have low efficiency no more than 15%. Energy is mainly consumed on the wear of grinding balls and mill housing, friction; heating the material etc.

The advantages of ball mill there are large unit capacity, achievement degree of fineness corresponding to a specific surface of 5000 cm2 / g, simple construction, high reliability and well designed scientific justification.

The disadvantages of ball mills include their considerable metal consumption and deterioration grinding media, as well as a lot of noise. Most of the energy useless lost during ball mill operation, leading to low it efficiency. But even a significant specific energy consumption for grinding material compensates beneficial effect by using mill. This does not exclude a search energy saving solutions for milling, and this handled by experts from around the world.

how to make a ball mill: 12 steps (with pictures) - wikihow

how to make a ball mill: 12 steps (with pictures) - wikihow

This article was co-authored by our trained team of editors and researchers who validated it for accuracy and comprehensiveness. wikiHow's Content Management Team carefully monitors the work from our editorial staff to ensure that each article is backed by trusted research and meets our high quality standards. This article has been viewed 29,198 times. Learn more...

Ball mills are a special instrument used to break up hard solids into a fine powder. They are similar to rock tumblers in that the instrument is a rotating container filled with heavy balls to grind the substance into powder. Ceramic material, crystalline compounds, and even some metals can be ground up using a ball mill. Using a motor, container, belt, caster wheels, and some basic building supplies, you can make your own ball mill.[1] X Research source

To make a ball mill, start by building a wooden platform and attaching a motor underneath it. Then, cut a slit into the wooden platform for the belt to pass through and attach casters to the platform for the container to sit on. Next, thread the belt through the slit and position the container so the belt is pulled tight. Finish by connecting the motor to the power supply, and filling the cylinder with metal balls and the substance you want to grind. For tips on how to operate your ball mill, read on! Did this summary help you?YesNo

Related Equipments