Jaw Crusher Diagram
Rocks and stones are broken into smaller particles by at least one of the following actions: attrition, pressure or compression, impact, and shear. Most crushers apply two or more of these actions to the material they crush.
- Attrition is rubbing or grinding down by friction between material particles in the crushing chamber and between the material and the parts of the crusher (jaws, rolls, crusher heads, concaves plates, etc.). There is some of this action in all crushers. It is most effective with material that is friable, and not abrasive, that is, the material has a low silica content. Attrition is most beneficial when maximum fine material is wanted.
- Pressure or compression is a squeezing of rock between two surfaces. It is the principal means by which jaw and roll crushers accomplish their work. Crushing by compression is necessary when the material is hard, tough, and abrasive and a minimum of fines is required. It is not useful or recommended for crushing sticky materials.
- Impact is the sharp blow delivered by a hammer to the material. The hammermill and impact breaker are crushers that apply this action. Impact should be used to crush material that is not too abrasive (not much over 5% silica) and that contains a high percentage of soft stone. It also is recommended if more cubical particles are desired. Crushers designed to apply this action give well-graded products.
- Shear is an action found in gyratory and cone crushers which causes rock to break on a plane when the forces on each side of the plane act in opposite directions. It is used to reduce material, which is fairly soft and friable, when a minimum of fines is wanted. The material should not be too abrasive.
Crushers can be listed in the order of decreasing impact and increasing compression as follows: impact breaker; hammermill (high to low speed); rod mill (high speed); ball mill; single roll crusher; cone crusher; gyratory crusher; jaw crusher; and twin- or triple-roll crusher. All crushers deliver a strong impact blow or a compressive force to the rock, and attrition and shearing action, are found in every crusher.