Definitions

crumb-crusher

Crusher

[kruhsh]
A crusher is a machine designed to reduce large solid material objects into a smaller volume, or smaller pieces. Crushers may be used to reduce the size, or change the form, of waste materials so they can be more easily disposed of or recycled, or to reduce the size of a solid mix of raw materials (as in rock ore), so that pieces of different composition can be differentiated. Crushing is the process of transferring a force amplified by mechanical advantage through a material made of molecules that bond together more strongly, and resist deformation more, than those in the material being crushed do. Crushing devices hold material between two parallel or tangent solid surfaces, and apply sufficient force to bring the surfaces together to generate enough energy within the material being crushed so that its molecules separate from (fracturing), or change alignment in relation to (deformation), each other. The earliest crushers were hand-held stones, where the weight of the stone provided a boost to muscle power, used against a stone anvil. Querns and mortars are types of these crushing devices.

Description

In industry, a crusher is typically a machine which uses a metal surface to break or compress materials. Mining operations use crushers, commonly classified by the degree to which they fragment the starting material, with primary and secondary crushers handling coarse materials, and tertiary and quaternary crushers reducing ore particles to finer gradations. Typically, crushing stages are followed by milling stages if the materials needs to be further reduced. Crushers are used to reduce particle size enough so that the material can be processed into finer particles in a grinder. A typical circuit at a mine might consist of a crusher followed by a SAG mill followed by a ball mill. In this context, the SAG mill and ball mill are considered grinders rather than crushers.

Types of crushers

The following table describes typical uses of commonly used crushers:
Type Hardness Abrasion limit Moisture content Reduction ratio Main use
Jaw crushers Soft to very hard No limit Dry to slightly wet, not sticky 3/1 to 5/1 Quarried materials, sand & gravel
Gyratory crushers Soft to very hard Abrasive Dry to slightly wet, not sticky 4/1 to 7/1 Quarried materials
Cone crushers Medium hard to very hard Abrasive Dry or wet, not sticky 3/1 to 5/1 Sand & gravel
Horizontal shaft impactors Soft to medium hard Slightly abrasive Dry or wet, not sticky 10/1 to 25/1 Quarried materials, sand & gravel
Vertical shaft impactors (shoe and anvil) Medium hard to very hard Slightly abrasive Dry or wet, not sticky 6/1 to 8/1 Sand & gravel
Horizontal shaft impactors (autogenous) Soft to medium hard No limit Dry or wet, not sticky 2/1 to 5/1 Quarried materials, sand & gravel

By compaction method

Jaw crusher

A jaw or toggle crusher consists of a set of vertical jaws, one jaw being fixed and the other being moved back and forth relative to it by a cam or pitman mechanism. The jaws are farther apart at the top than at the bottom, forming a tapered chute so that the material is crushed progressively smaller and smaller as it travels downward until it is small enough to escape from the bottom opening. The movement of the jaw can be quite small, since complete crushing is not performed in one stroke.

The inertia required to crush the material is provided by a weighted flywheel that moves a shaft creating an eccentric motion that causes the closing of the gap.

Single and double toggle jaw crushers are constructed of heavy duty fabricated plate frames with reinforcing ribs throughout. The crushers components are of high strength design to accept high horsepower draw. Manganese steel is used for both fixed and movable jaw faces. Heavy flywheels allow crushing peaks on tough materials

Double Toggle jaw crushers may feature hydraulic toggle adjusting mechanisms.

Gyratory crusher

A gyratory crusher is similar in basic concept to a jaw crusher, consisting of a concave surface and a conical head; both surfaces are typically lined with manganese steel surfaces. The inner cone has a slight circular movement, but does not rotate; the movement is generated by an eccentric arrangement. As with the jaw crusher, material travels downward between the two surfaces being progressively crushed until it is small enough to fall out through the gap between the two surfaces.

As an example, a Fuller-Traylor gyratory crusher features throughputs to 12,000 TPH with installed powers to 1,300 HP.

Impact crushers

Impact crushers involve the use of impact rather than pressure to crush material. The material is contained within a cage, with openings on the bottom, end, or side of the desired size to allow pulverized material to escape. This type of crusher is usually used with soft and non-abrasive material such as coal, seeds, limestone, gypsum or soft metallic ores.

See also

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