After the material has slid down a short distance, the larger lumps or masses of the material are crushed into smaller masses by the impact created when these lumps are caught between the crushing head wall and the inner wall of the mantle jacket, as the head approaches a portion of the mantle wall.
When the head retracts after having delivered the impact, the material continues to slip down and spread out on the flaring wall of the head along a course bounded by the adjacent head and mantle walls, until another impact is delivered by the head. After each succeeding impact the crushed material becomes smaller and slides along and spreads out into an area of the tapered cavity having a smaller spacing between its walls.
The final size of the crushed product is determined by the spacing between the walls at the lower end of the crushing cavity, when the head is in its position closest to the mantle.
The size of the crushed product can be regulated by raising or lowering the mantle by means of the sprocket nuts, thereby increasing or decreasing the cross section of the crushing cavity.