Forces Applied in the Crushing Process

The size reduction process is expressed by the following transformation formula:

Ore to be reduced in size + Energy → Ore reduced in size + Sound + Heat

In the size reduction process;

• Torsion
• Compression or crushing
• Shear (cutting)
• Impact
• and collision forces are applied.

The crushing process is carried out with machines in which one or several of these forces are applied together.

In crusher machines, compression, impact and collision forces are commonly applied. Although there are no crushing machines that apply torsion and shear forces, these forces can occur during the crushing event.

In crushers where friction force is applied, the distance between the crushing hammers and the crusher-body screens is quite narrow. The ore is broken by the friction force that arises from the effect of impact and shear forces, and is removed from the system.

When ores are brittle, contain low silica, and a coarser product is aimed for as a result of crushing, crushers that work with shear force are used. Shear force is often applied together with impact and compression force.

For obtaining a coarse product from hard, abrasive, hard-to-break ore that does not contain sticky material, crushers that work with compression force are used. In these crushers, the ore is compressed between two surfaces, one or both of which are moving. Jaw crushers are the most common size reduction machines used to crush these types of ore. However, there are also jaw crushers in which, in addition to compression force, friction force is applied through the horizontal movement of the jaw. These types of crushers are not suitable for crushing abrasive ores.

For controlling the top size of brittle and non-abrasive ores after crushing, closed crushing circuits are set up. Most of the time, the first stage of crushing is done as an open circuit. After the first-stage crushing, running the pre-mill crushers in a closed circuit both makes grinding easier to manage and significantly lowers the size reduction cost.

The correct selection of crushers and crushing circuits carries particular importance, since it directly affects subsequent mineral processing operations, above all grinding. To increase the efficiency of crushing carried out in several stages, screens are used before the crusher so that ore of a suitable size is taken out of the circuit before entering the crusher, preventing it from being reduced unnecessarily. This process also increases the capacity of the crushing circuits. The amount of ore to be crushed, its properties and the intended use of the crushed product are the determining factors in the selection of crushers and crushing circuits.