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Size of feed affects capacity, but not always in the inverse proportion which might, at first thought appear to be logical. For example, suppose we were operating a medium-size hammermill on limestone, turning out a 10-mesh product. We know that this machine will handle more tonnage if we feed it with, say, 3-in. maximum size rock as compared with a feed of 10-in. or 12-in. maximum size-which accords with the "Logical" expectation. However, if we further reduce the feed size to, say ½ -in maximum, we find that our capacity will increase very little if at all; in fact it may actually decrease. This apparent anomaly is explained by the fact that the effect of impact upon a free body of material varies directly with the mass of the body; consequently the energy absorption, and hence the shattering effect, is much greater on the 3-in. piece than it is on the ½ -in. particle.
Because all these variables that we have noted have an influence upon the capacity of the hammermill, it is impossible to present a comprehensive tabulation of capacity ratings which can be relied upon for any and all materials. We can however do so for any one material, as we did for the Fairmount crusher. It is convenient and logical that this should be a medium limestone in this case also, because hammermills are applied extensively to crushing, and pulverizing, that kind of rock.
Table I gives approximate capacity ratings of the various sizes of Pulverators, on medium limestone, and for various grate bar spacings.
Unless the prospective hammermill user has operational data on which to predicate his selection of a new machine for some specific service, the safest procedure is to have his material tested, either in the field or in the laboratory, in a mill of the type he pro poses to install.
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