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In the Pulverator, a cross-sectional view of which is shown in Fig. 1, the process is, in one important respect, a reversal of that just described. The material enters the machine on the up-running side of the rotor, where it is struck by the hammers as they start their sweep across the upper part of the housing. The top of the crushing chamber is lined with a series of breaker plates whose impact faces are involute with respect to the hammer circle, so that material hurled by the hammers impinges squarely against these surfaces regardless of the striking point.
The action in this impact zone is a succession of violent blows, first from hammer-to-material and then from material-to-breaker plate, and so on through the several stages of the involute series. As contrasted to the type previously described, most of the work in this crusher is done in the breaker-plate zone; the grates function chiefly as a scalping grizzly, and the clearance between hammers and grates is relatively large. A certain amount of impact breaking does take place between hammers and grates, but this is secondary to the work done against the involute plates. On friable material this machine will deliver a medium fine (%. in. to % in.) product with some, or even a11, of the grates removed.
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