Ball-mill liners

FIG. 20-32 Typ es of ball-mill liners (a) combination liner [McTavish, Mining Engineering, 42, 11, 1249-1251 (1990) Exton Industries, Inc.] (h) all-rubber liner [MoUer and Brough, Mining Engineering, 41, 8, 849-853 (1989) Skega Ltd.]. 

Grinding-media wear in phosphate ball-mill grinding systems ranges from 5 to g/Mg (0.05 to 0.20 Ib/ton) ground ball-mill liners show an average consumrtion of 2.5 to 100 Mg (0.01 to 0.05 Ib/ton) ground. 

Cast irons of various sorts are often used for structural parts of large mills such as large ball mills and jaw curshers, while product contact parts such as ball-mill liners and cone crusher mantels are made from... 

Alumina produced by the Bayer process is precipitated and then calcined [Krawczyk, Ceramic Forum International, 67(7-8), 342-8 (1990)]. Aggregates are typically 20 to 70 [Lm, and have to be reduced. The standard product is typically made in continuous dry ball or vibra-toiy mills to give a product d o size of 3-7 [Lm, 98 percent finer than 45 [Lm. The mills are lined with wear-resistant alumina blocks, and balls or cylinders are used with an alumina content of 80-92 percent. The products containing up to 96 percent AI9O3 are used for bricks, kiln furniture, grinding balls and liners, high voltage insulators, catalyst carriers, etc. 

The white cast irons and their low alloys have good abrasion resistance properties [2,3]. White cast irons are used for grinding balls, segments for mill liners and slurry pumps. In the ceramic industry they are used for muller tyres and augers in the pulp and paper industry for attrition mill plates and chip feeders and in the paint industry for balls for grinding pigments. 

Ball mills. Ball charge is 315/ton. Price includes liner, motor, drive, and guard. 

Some of these are variable or under the control of the operator others are fixed, once the mill is running. Maximum mill efficiency is obtained when the greatest number of tons of ore is ground to the desired fineness in the shortest time, with the expenditure of a minimum amount of power and with the least wear on balls and liners. It is determined largely by the right combination of the factors above listed. 

These mills employ attrition and impact to grind the product by tumbling in cylindrical mills partly filled with grinding media. The media can be round metal balls or nonmetallic pebbles that are 1/2 in. or larger in size. Ball mills for grinding hard materials are usually lined with heavy-duty steel alloy liners. Some ball mills employ internal baffles to prevent slippage of the grinding media over the internal shell surface. 

Cleary PW. (2001). Charge behaviour and power consumption in ball mills sensitivity to mill operating conditions, liner geometry and charge composition. Int J Miner Process, 63, 79-114. 

It is important to cut down maintenance costs and periods of outage to replace liners. Many mines open their mills once a month for maintenance and to replace the worn liners. The grinding medium is steel rods in the case of rod mills and steel balls in the case of ball mills. As the cylinder or tumbler rotates, the heavy rods and balls are lifted by the ribs of the liners. The rods and balls fall by gravity after a certain angle of rotation is reached. The impact in turn fiactures and grinds the rocks into smaller stones. 

When designing components of pumps subject to torsion and bending loads, such as shaft sleeves and pump casings, it is important to appreciate that the harder the material, the narrower the limit on strain or elongation. A range of elongation of 0.5% to 1.5% is a minimum for bowls, mantle liners, pump-wetted parts, ball mill grates, and components... 

Liner wear increases with the size, hardness, and sharpness of feed more than with ball size. The hardness of manganese steel corresponds to softer types of ore, while Nihard is about the same as magnetite [Moore et al.. International J. of Mineral Proce.s.sing, 22, 313-343 (1983)]. Quartz and pyrite are considerablv harder than any metals used. Rubber, being resihent, is less affected by ore hardness, and therefore has the advantage with harder ores. Low-charge volume below 35 percent results in increased wear since the liners are not protected bv a covering of ore. Several studies indicate that wear increases at least proportional to the square of mill speed in percent of critical. 

---