The gyratory crusher comprises a lined inverted conical crushing chamber within which 'gyrates' an upright conical crushing member, the shaft and cone, protected by a liner called the 'mantle'. The shaft does not rotate but 'gyrates' or 'precesses' compressing material as it moves towards the wall of the chamber and at the same time releasing material at the diametrically opposite point so that crushed rock can descend through the chamber towards the discharge. The frequency of this action is between 100 and 200 cycles per minute and the movement or throw between 20 and 50mm. The crushers are usually designated by the width of the feed opening and the diameter of the head. The 'gyratory' action can be created in several ways including: (i) a vertical shaft running in upper and lower eccentric bushings supported by thrust bearings or hydraulic means and (ii) the most common, a shaft located by an upper fixed bearing within the spider and supported hydraulically, actuated by an eccentric bushing at the lower point.
The principal advantage of the gyratory crusher is the much greater unit capacity for any given 'gape' or maximum lump size assuming that this capacity can be fully utilized to justify the substantially greater capital cost. The reduction ratio is 4:1 to 6 : 1 and the machine is suitable for all hard, abrasive rocks but not for soft, porous material that may compact in the chamber.
Gyratory crushers are sometimes employed at the secondary stage, where cone crushers might be more usual, owing to their ability to accept larger lump sizes.