1. What is a ball mill
A ball mill is a type of grinder used to grind or blend materials for use in mineral dressing processes, paints, pyrotechnics, ceramics, cement, etc. It works on the principle of impact and attrition: size reduction is done by impact as the balls drop from near the top of the shell.
The final stages of comminution are performed in tumbling mills using steel balls as the grinding medium and so designated “ball mills.” In the mineral dressing plant, only the grate ball mill and overflow ball mill are widely used. Click here to know more about ball mill machine.
2. Working principle
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. 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.
3. Structures of ball mill
1. Drum 2. Flange 4. Screw 5. Manhole 7. Quill shaft end cover 8. Combination drum-scoop feeder 9. End cover liner 10. Bearing inner sleeve 11 Dust Cover 12 Quill shaft end cover 13 Grate liners 16 Central liners
-The ball mill drum 1 is rolled and welded by steel plates with thickness about 18-36 mm, there are welded casting steel flanges 2 at both ends of it, the end cover 7 and 12 are connected to the flanges, both of which must be precisely machined and matched, because the quill shafts are welded on the end covers which bear the weight of the mill. There is a manhole 5 on the drum for maintenance and liner replacement.
-The drum is equipped with liners, which are made of manganese steel, chromium steel, wear-resistant cast iron or rubber and other materials, of which high manganese steel is widely used, the use of rubber liner is still in the trial stage. The liner plate is about 50-130 mm thick, with a gap of 10-14 mm between the drum shell, with plywood, asbestos pad, or plastic sheet or rubber laid in it, used to slow down the impact of the steel ball on the drum. The liner plate 3 is fixed to the drum shell with screws 4, with rubber rings and metal washers under the nuts to prevent the slurry from leaking out.