Within the crushing circuit, a primary crusher reduces material down to a size that can be conveyed and fed to the secondary crushing circuit. The two most common primary crushers used for coarse run-of-mine material are the jaw and gyratory crushers. These primary crushers break rock through compressive forces created by a hard moving surface forcing and squeezing the rocks towards a hard stationary surface.
A Jaw Crusher reduces large rocks by dropping them into a flat “V” shaped space created between a fixed surface and a movable surface. The compression is created by forcing the rock against the stationary plate. The opening at the bottom of the jaw plates is the crusher product size gap. The rocks remain in the jaws until it is small enough to pass through this adjustable gap at the bottom of the jaws.
In a gyratory crusher, a round moving crushing surface is located within a round hard shell which serves as the stationary surface. The crushing action is created by the closing the gap between the hard crushing surface attached to the spindle and the concave liners (fixed) mounted on the main frame of the crusher. The gap is opened and closed by an eccentric drive on the bottom of the spindle that causes the central vertical spindle to gyrate.