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No DlSCUSSION of primary crusher selection would be complete without a comparison of the two leading types: the standard gyratory and the Blake jaw crusher. Although their fields of application overlap to a considerable degree (at least in the realm of primary crushing) there is no real conflict between these two machines; one supplements the other and, between them they very effectively cover an imposingly large proportion of the entire field of primary crushing applications. This does not mean that other types, such as the sledging rolls, for example, are not better suited for certain applications; but there are very few primary crushing jobs to which the gyratory or jaw, or both of them cannot be applied with .at least a fair degree of satisfaction.
Either of the two types can be built to handle the hardest and toughest rock or ore that can be economically mined or quarried. The jaw crusher, because of its box-frame construction, and simple toggle mechanism, is especially well adapted to extra heavy design for the crushing of extremely tough materials: in this respect it holds some advantage over the gyratory type, because the extra strength necessary for such work can be built into it at less cost than is required for the gyratory with its more complex shell castings. However, cases where extreme brute strength enters into the selection problem are relatively rare, either type can be used for the great
majority of materials encountered in crushing practice, either in standard form or in reinforced design. Strengthening of these machines for extra-heavy duty follows certain well established practices which have been proven to be necessary or desirable. Usually it is a matter of selecting stronger metals, or adding weight in the frame, or both; seldom is it necessary to change the proportions of the working mechanism.
In most cases selection of one type or the other can be made on the basis of performance characteristics, receiving openings, space requirements, and so forth, without regard to relative strength of design. In choosing between the two for any specific application it is helpful to have a list of the salient features of each type, in a form that will permit quick and easy comparison. The following lists emphasize the favorable characteristics of each machine.
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