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If the material to be crushed is of a slabby .nature-as, for example, a thinly stratified limestone or shale-the product of the jaw crusher is certain to contain slabs, some of which may be quite large, particularly so if some of the strata in the deposit are thinner than the discharge setting of the crusher. Nor is this tendency to slab in the crusher confined to stone of stratified formation. Some rocks of massive formation may contain parallel cleavage planes in certain sections of the deposit. Such material will slab in the crusher just the same as those rocks which were formed in definite layers, or beds.
The gyratory crusher by virtue of its annular discharge opening is an effective slab breaker. This faculty, coupled with the fact that its receiving openings are especially well suited for' admitting slabby feed, give it a very definite advantage over the jaw crusher in the handling of such material.
In the foregoing comparison of these two leading types of primary breakers we have endeavored to present the case for each of them in a fair and impartial manner. It would be difficult, and probably more than a little tedious for the reader, if we were to attempt a more definitive analysis 01' to set up fixed rules of procedure for selecting one 01' the other machine a process which is always fraught with pitfalls in such a broad and empirical branch of engineering as the processing of rocks and ores. Usually the matter of choice can quickly be narrowed down to a comparison of one size in each type.
These two machines may then be tabulated with respect to capital investment, capacity, power requirements, space requirements, and so forth; their receiving openings may be compared, as we have suggested, and all of the factors we have discussed in this section checked against the features and limitations of each machine to determine its ability, or inability, to fit into the plan. |
