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. Each crusher is designed to work with a certain maximum size of raw material, and often delivers its output to a screening machine which sorts and directs the product for further processing. Typically, crushing stages are followed by milling stages if the materials need to be further reduced.
Typical commonly used crushers:
· Jaw Crusher
Jaw Crusher can be used in mining, metallurgical industry, construction, road and railway building, chemistry, etc. 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. In the Blake or jaw crusher the moveable jaw is pivoted at top. The greatest amount of motion is at the bottom which means it has the little tendency to choke.
· Cone Crusher
Cone crushers are commonly used for secondary, tertiary and quaternary crushing duties. Cone crusher consists of an inverted cone (the bowl or concave) that sits over a conical head (refer to figure). The feed inlet is at the apex of the crusher; the crushing chamber (or cavity) tapers from the feed inlet to the product discharge outlet. The head is seated on a vertical shaft that is driven by spiral bevel gears connected to a counter shaft. This causes the head to move in an elliptical path around the main shaft; viewed in cross-section the crushing action is similar to that of a jaw crusher.
· Gyratory Crusher
Gyratory crushers are similar to cone crushers; they are frequently used in large-throughput primary crushing roles. Typically, they have larger capacities (up to 8000 tph) compared to jaw crushers (up to 1500 tph). Gyratory operate at a slower speed than cone crushers, typically in the range 85 to 105 rpm. They do not require feed mechanisms and are usually fed direct from the back of a dump truck. The available feed opening area of a gyratory crusher is approximately three times greater than that of a jaw crusher of a similar gape; the gyratory has a higher capacity. The most commonly-used type is a supported-shaft gyratory crusher; the main shaft is suspended from an overhead spider. The angle of the mantle is steeper than that used in a cone crusher and this causes gyratory crushers to have a smaller throw. This affects the flow of material and improves the particle shape as material is struck more frequently in the crusher cavity.