A ball mill called special equipment designed for grinding solid materials. These can be ore or non-metallic minerals, building materials, etc. Crushing in them occurs with the help of hard balls. Hence their name.
The main element of such equipment as a ball mill is a special drum of usually cylindrical shape. Partially its volume is filled with hard balls. They can be made of steel, cast iron, aluminum, etc. Sometimes grinding bodies and other shapes are used instead of balls: cylindrical, square, etc. Even simple pebbles can be loaded into the drums of small mills. Torque working body of the mill often transmits an electric motor. The simplest models can be equipped with a conventional rotation knob.
In order to extend the service life of the drums, in the manufacture of mills, their walls are coated on the inside with special wear-resistant materials: hard alloys, manganese steels, surfacing materials.
All crushers of this type have the peculiarity that rocks and other solid materials are crushed in them to particles having an irregular fragmentation shape and a rough surface. Below is a diagram of a standard mill ball mill. As you can see, this type of equipment has a not particularly complex structure.
Ball mill: principle of operation
Grinding of hard materials inside the drum is due to the movement of the balls. Rocks can be crushed to different sizes of grain. The performance of mills also varies. The last parameter depends on the shape of the grinding bodies, the degree of drum filling and the speed of its rotation. In the process of working the mill on the rocks can act two forces: shock and abrasive. Actually the crushing process itself is a rather time-consuming procedure. It can continue with the use of equipment such as a ball mill, maybe from a couple of hours to several days.
Mills of this type can be classified according to the following criteria:
By area of use. Mills are laboratory and industrial. The first type is used for crushing a small amount of solid matter, has small dimensions. Too high performance such equipment is no 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. At the enterprises and in laboratories devices with one or with two drums can be used.
According to the conditions of work. In this regard, there are mills, dry and wet grinding. The first type is usually used for the manufacture of various kinds of building materials. Wet grinding mills are mainly used for crushing pre-shredded plastic and dispersed masses. Such equipment is usually installed in the shops of enterprises engaged in the manufacture of glass, ceramics and paintwork materials.
By way of unloading. On this basis, lattice and drain mills are distinguished. In the first case, the unloading is forced. Such devices are considered more productive. In the drain mills, the finished pulp is discharged through a pin.
By type of action. In this regard, distinguished equipment of continuous and periodic action.
Main modes of operation
Solid materials can be ground in mills to fine or coarse grain. In this case, enterprises usually use two modes of operation: abrasion and impact. In the first case, powders with a very fine grain are most often obtained. Shock mode is used to crush materials to large particles. The rock inside the mill is abraded 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 to each other. At high speeds, they fly up and fall on the rock, creating a shock load.
In order for the ball mill to work with maximum performance, a certain number of grinding elements must be in the drum. If there are too few of them, the equipment will go into a rolling, inefficient mode of rock processing. The fact is that with insufficient overall weight of the balls, they cease to move relative to each other, sliding along the walls of the drum with a single mass. At the same time, the area of their contact with the treated rock is significantly reduced, and consequently, productivity decreases. The optimum weight of grinding elements is 1.7-1.9 kg per liter of drum volume.
Ball mill brands
Equipment of this type is produced today by many companies. Quite popular are, for example, devices brand Retsch. The work of the ball mill of this manufacturer may be including continuous. Also, such models are programmed during startup. Technical characteristics of mills of this type are presented in the table below (for example, Retsch PM 100).