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THE HAMMERMILL IS the best known and by far the most widely used crushing device employing the impact principle of breaking stone.
Thus far we have described machines which' do a portion of their work by impact, but the only machine described in which this action plays an important role was the sledging roll type-particularly the Edison roll crusher-and in these machines impact is supplemented to a substantial degree by a positive and powerful sledging action by teeth which are rigidly attached to massive rolls. In the hammermill, impact is the predominating action although its scope varies in different designs of this machine, as will be seen.
HammerMill Description
The hammermill, fundamentally, is a simple mechanism. The "orthodox" machine comprises a box-like frame, or housing, a centrally disposed, horizontal-shaft rotating element (rotor) on which the hammers are mounted, and usually a set of circumferentially arranged grates in the lower part of the housing. The rotor consists of a shaft carried in bearings at either side of the housing, and the hammer center of multi-flange drum or spool shape. The flanges of this drum-like assembly are drilled near their outer edges for hinge pins to which the inner ends of the hammers or hammer arms are attached. The hammers themselves are made in a variety of styles and shapes. Sometimes the hammer arm and head are cast, or forged, integrally; in other designs as in the A-C Pulverator-the arms and hammer head are separate pieces.
The grates usually consist of a transversely arranged series of tapered, wear-resisting steel bars, which form a cage of circular cross section across the lower part of the housing just below the hammer path. The spacing of these steel bars varies quite widely, depending upon the size of product and upon the characteristics of the material to be crushed.
The spacing may be anything from % in. or slightly less, up to several inches, and in some machines may be dispensed with entirely for coarse products and closed-circuit operation.
Hammermills may be connected directly to the driving motor, or driven by a flat belt or V -belts. The two latter methods have one material advantage over the direct drive-they permit speed adjustments to achieve optimum performance for each particular set of conditions. Belts also afford a substantial cushioning effect between mill and motor when tramp iron or broken hammers throw heavy shock loads upon the driving apparatus.
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