A ball mill is a special equipment intended for grinding hard materials. It can be ore or non-metallic minerals, building materials, etc. The crushing in them occurs with the help of solid spheres. Hence their name.
The main element of such equipment, as a ball mill, is a special drum of a generally cylindrical shape. Partially, its volume is filled with solid spheres. They can be made of steel, cast iron, aluminum, etc. Sometimes, instead of balls, grinding bodies of other shapes are used: cylindrical, square, etc. Even simple pebbles can be loaded into the drums of small mills. The torque to the working part of the mill is most often transmitted by an electric motor. The simplest models can be equipped with a conventional rotary knob.
In order to extend the life of the drums, when making mills, their walls are covered from the inside with special wear-resistant materials: hard alloys, manganese steels, surfacing materials.
All crushers of this variety have the feature that rocks and other solid materials are crushed in them to particles having an irregular fragment shape and a rough surface. Below is a diagram of a standard-type ball mill. As you can see, this type of equipment does not have a particularly complicated design.
Ball mill: the principle of operation
The grinding of hard materials inside the drum is due to the movement of the balls. The rocks can be shoveled to different grain sizes. The productivity of mills is not the same. The last parameter depends on the shape of the grinding bodies, the degree of filling of the drum and the speed of its rotation. In the process of the mill, two forces can act on the rocks: shock and abrasive. Actually the very process of fragmentation - the procedure for time is quite long. It can be continued using equipment such as a ball mill, from a couple of hours to several days.
The mills of this type can be classified according to the following features:
On the scope of use. Mills can be laboratory and industrial. The first variety is used for crushing a small amount of a solid, has small dimensions. Too high performance such equipment is not different. Industrial mills are designed for crushing a large number of rocks and are used most often for the manufacture of various kinds of building materials.
By type of construction. In factories and laboratories one or two-drum units can be used.
According to the working conditions. In this regard, the grinders are dry and wet grind. The first variety is usually used for making various kinds of building materials. Wet grinding mills are used mainly for crushing pre-crushed plastic and dispersed masses. Such equipment is usually installed in the shops of enterprises engaged in the manufacture of glass, ceramics and paint.
By the method of unloading. On this basis, grate and drain mills are distinguished. In the first case, unloading is forced. Such devices are considered more productive. In the drain mills, the finished pulp is discharged through the trunnion.
By the type of action. In this regard, we distinguish between continuous and periodic equipment.
Basic operating modes
Crushed hard materials in mills can be fine or coarse grains. In this case, the enterprises usually use two modes of operation: abrasion and shock. In the first case, powders with very fine grains are most often obtained. Shock mode is used to crush materials to large particles. The rock is scrubbed inside the mill at not too high speed of its rotation. In this case, the balls do not detach from the walls of the drum, but simply move relative to its surface and each other. At high speeds, they fly up and fall on the rock, creating a shock load.
For a ball mill to work at maximum capacity, a certain number of grinding elements must be present in the drum. If they are too small, the equipment will move to a sliding low-effective mode of processing the breed. The fact is that if the total weight of the balls is insufficient, they cease moving relative to each other, sliding along the walls of the drum with a single mass. This significantly reduces the area of their contact with the processed rock, and consequently, the productivity falls. The optimum weight of grinding elements is considered to be 1.7-1.9 kg per liter of drum volume.
Stamps of ball mills
Equipment of this type is produced by many companies today. Quite popular are, for example, the Retsch brand. The work of the ball mill of this manufacturer may be continuous as well. Also, such models are programmed during start-up. Technical characteristics of mills of this type are presented in the table below (for example Retsch PM 100).