Effect of Feed Gradation on Crusher Performance

If the feed to any gyratory or jaw crusher consisted entirely of cubes or spheres of a size that woul

d just barely enter the crushing chamber, the crusher could not be expected to produce anything like its normal rated capacity because the upper part of the crusher could not shatter the large pieces enough to keep the rest of the crushing chamber busy. Such a condition is of course nev

er met with in actual practice. We occasionally encounter special applications where the crusher is called upon to handle pieces which are all of the same size, but in such a case the machine is chosen with a large enough receiving opening to permit the pieces to fall at least a short distance into the crushing chamber before they are nipped.  Even so, the crusher is not apt to perform up to its rated capacity on such a feed – unless the receiving opening is quite large with respect to the feed size.

By far the greater number of crusher applications involve feeds which are either graded (a mixture or large, medium, and small particles), or sized to a top a dimension well within the effective receiving-opening dimension of the crusher. Primary crusher feeds usually fall under the “grated” category, and reduction crusher feeds under the “sized”. Grated feeds may or may not have the undersize removed, depending upon the nature of the operation and of the material. Sized for reduction crushers is generally a screened feed which has definite maximum and minimum limits.

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