Mills grate-discharge

The holdup of material in a continuous mill determines the mean residence time, and thus the extent of grinding. Gupta et al. [International J. Mineral Processing, 8, 345-358 (Oct. 1981)] analyzed published e)merimental data on a 40 X 40-cm grate discharge laboratoiy mill, ana determined that holdup was represented by = (4.020 — 0.176 WT)F , (0.040 0.01237 WT)S, - (4.970 0.395 Wl), where... 

The screen or grating discharge for a hammer mill serves as an internal classifier, but its limited area does not permit effective usage when small apertures are required. A larger external screen may then be reqmred. 

FIGURE 6.16 Ball and rod mill discharge methods (a) trunnion overflow, (b) grate discharge, and (c) peripheral discharge. (From Meyers, R.A., Ed., Coal Handbook, Marcel Dekker, New York, 1981, p. 197.)... 

In the second type of mill (Fig. 20-28), a cyhndrical grating is provided beneath the rotor for product discharge. Some hammer crushers are symmetrically designed so that the direction of rotation can be reversed to distribute wear evenly on the hammer and breaker plates. When such a Pennsylvania nonreversible hammermill is used for reduction, material is broken first by impacl against hammers and then by rubbing action (attrition) against screen bars. Performance data of Pennsylvania reversible hammer mills are shown in Table 20-14. 

---