Impact mills, series SH, are secondary machines suitable for crushing very hard and abrasive materials. They are designed to produce aggregate having the shape coefficient (polyhedral) so the final product can have the mechanical properties required. These machines are equipped with an open type impeller, mounted on grease lubricated bearings that are protected by a series of labyrinth flanges. The hammers are fixed by means of a retainer bar and a locking wedge, which secure the hammers rigidly and make it possible to fit hammers either in manganese steel or chromium alloy. Protection plates, internal side armours made of manganese steel plates fixed using conical bolts, double impact walls with manganese steel bars complete the equipment. SH series mills are supplied complete with a hydraulic system to open the machine and adjust the lower impact walls.