Fig. 6 shows a stamping mill very suitable for the crushing of bones, the illustration showing the mill open on the left side and closed on the right. It is furnished with 16 stamps, D, each stamp being provided with a cast-iron shoe. The stamps are lifted by means of a cam shaft in such a manner, that the height of fall of the outermost pairs of stamps is least and that of those in the centre greatest. Between the inner stamps is a sieve H with meshes of sufficient size to allow the largest pieces, which can be produced by granulation, to fall through.
Underneath the sieve is an Archimedean screw K for carrying off the pieces of bone passing through the sieve.
Fig. 7.
Fig. 8.
The base of the stamping mill consists of iron plates so arranged as to form steps, the plates lying towards the center of the mill constituting the lowest steps. Every two stamps standing alongside one another rest upon such a step. When the mill is set in motion, the bones reaching the stamping trough from the right and left fall upon the steps, and are crushed by the descending stamps.
As a rule, the bones to be stamped are not brought directly into the stamping trough, but are first passed through a crushing mill and the coarser pieces thus obtained are subjected to the action of the stamping mill.
Figs. 7 and 8 show a well-constructed bone crusher. It consists essentially of two cast-iron rollers A and B, furnished with case-hardened cutters. The bones are introduced through the hopper B, and the rolls set in motion by means of cog-wheels a and b. The bearings of the roll B run in a carriage which can be shifted by the lever-construction f i. The object of this contrivance is to allow of the roll B giving way in case a harder material than bones, for instance, a stone, passes between the rolls.