Fig. 1.
[Fig. 1] represents a breaker (made by the Badische Maschinenfabrik, Durlach), suitable for the rough crushing of clayey materials supplied in large lumps. It can, however, also crush shale, lime, chalk, as well as hard, sticky masses which would clog up a stone-breaker.
The material fed into this breaker is gripped at once by the powerful projecting teeth, which are connected together by sharp-edged ridges, and is crushed in such a way that it can be easily reduced still further by a succeeding pair of smooth rollers.
Fig. 2.
The granulator ([Fig. 2]), made by the same firm, is an example of a machine for crushing harder materials. It is similar in construction to a stone-breaker, but differs in the movement of the jaws, and combines the properties of breaker and grinder, inasmuch as it tears the material as well as crushes it. The figure shows the machine adapted for direct electric drive. If necessary, these granulators can be fitted with classifying jig screens.
Stamps.—Stamps or stamping-mills have been used from prehistoric times, and were probably employed for reducing hard materials long before the introduction of grinding-mills. The underlying principle of the stamping-mill is very simple. The material to be reduced is placed in a trough or mortar, and the ram or head, which is of considerable weight, is raised by a mechanical device and then allowed to fall freely, from a certain height, on to the material underneath, which it crushes. The heavier the head and the greater the height of fall, the greater the effect produced. As a rule, a large number of stamps are mounted together, and in such a way that half of them are being lifted while the other half are falling. Either a separate mortar or trough is arranged under each stamp, or else the whole drop into a common trough charged with the material under treatment. Sometimes a lateral movement is imparted to the material in the trough, so as to bring it under the action of all the stamps in succession.
Although the construction of stamping-mills in general appears simple, various modifications are employed for different purposes.
As a rule, a single passage through a stamping-mill is not sufficient to reduce the material completely to the desired fineness, the first product always containing large and coarse fragments of various sizes, as well as fine powder.
If the latter were left in with the larger pieces for the second stamping it would impede the work, and the stamping-mill should therefore be provided with means for classifying the material discharged from the trough, to separate the fine from the coarse and grade the latter into sizes. This is usually effected by means of a grading-screen.