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These results might, at first glance, appear to be inconsistent in view of the fact that the maximum one-way dimension is established in each case by the respective open- and close-side positions, whereas the product analyses do not show similar percentages passing these respective opening sizes in the test screens. The apparent inconsistency clears itself up, however when we remember that the low-speed crusher, as well as the high-speed machine, dies its sizing on the close-side of its stroke. The governing point is the distance (above the discharge point) that the material can fall (once it has been broken to a none-way dimension less than the open-side setting) before the head can catch it again. In the high-speed crusher this points is quite close to the discharge opening; in the low-speed machine it is some distance above the opening, the amount depending upon the shape of the crusher chamber, as was made clear in our discussion of the preceding diagrams.
It is hardly practicable to rate the product of a high-speed, short-throw crusher at its open-side setting. In the case just noted, all of the product of the second crusher mentioned, except for an occasional flat spall, passes a square-opening test sieve equivalent to its open-side setting; in fact, at some combinations of setting and throw, the 100 percent point will be below the open-side setting. It is impossible to gauge a crusher product at, or near, the 100 percent passing point because a few flat spalls, more or less, in the sample will throw the analysis several points one way ore the other, giving results that are uncertain.
There is a very wide variation in the product delivered by different types of high-speed crushers at similar close-side settings. Short-throw crushers tend to give fairly consistent results, even on materials of divergent physical characteristics. The product of crushers with large throws, and lower eccentric speeds, will vary more widely, depending to a much greater extent upon the relative merits of crushers which are rated at their close-side settings, a check should be made to determine just what kind of product the crusher will deliver, with reference to any particular setting. |
