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ROLL CRUSHERS of the sledging type have a crushing action unlike that of any of the machines thus far described. Moreover, the actions of the single- and double-roll forms of this type are dissimilar, at least in the relative importance of impact and sledging action. Both types employ a combination of these two actions but in a reversed order of efficacy.
Inasmuch as a sledging blow transfers a large part of its force by impact, it may seem anomalous to attempt to differentiate these two terms; nevertheless there is a convenient distinction between them as they apply to the action of crushing machines. Impact crushing is customarily taken to mean the breaking of a piece of material by a sharp blow, delivered with sufficient force to shatter the piece while it is in a free position, i.e., not restricted from moving away from the blow other than by its own inertia. Sledging, while the blow may be just as violent as the impact blow, is a stroke delivered against the material while it is prevented from moving away from the applied force by reason of being in contact with an opposing crushing surface, either fixed or moving.
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