Size reduction equipment crushing rolls

Forces commonly used in food processes for particle size reduction are compressive, impact, attrition (or shear), and cutting forces. More than one force usually participates in the comminution operation in industrial size-reduction equipment. In particular, crushing rolls use mainly compressive forces, hammer mills are based on impact, disc mills cause particle attrition through shear force application, and rotary knife cutters use cutting forces. 

Crushing and Grinding. Some raw materials, such as hard clay and quartzite, must first be crushed to grains small enough for the grinding equipment. In general, a jaw, gyrotory, or roll cmsher is employed (see SIZE REDUCTION). 

Comminution, or particle size reduction of solids, is considerably different from that of the breakup of one liquid by dispersal as small droplets in another. Particle size reduction is generally achieved by one of four mechanisms (1) compression, (2) impact, (3) attrition and (4) cutting or shear. Equipment for particle size reduction or milling includes crushers (which operate by compression, e.g., crushing rolls), grinders (which operate principally by impact and attrition, although some compression may be involved, e.g.,... 

Figure 12.5. Jaw, roll, impact, and tumbling equipment for size reduction, (a) Blake-type jaw crusher operates at 200-300 strokes/min (Allis-Chalmers Co.), (b) Smooth roll crusher, for which operating data are in Table 12.8(b). (c) Swing hammer mill operating data in Table 12.7(a). (d) View of a conical ball mill, showing distributions of balls and material and crushing ranges data in Table 12.6(b) (Hardinge Co.), (e) Tube mill with three compartments, length to diameter ratio 3-5. (f) Rod miU in a cylindrical tumbler, L/D = 1.2-1.6 data in Table 12.6(d).

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