Size reduction equipment rollers mills

Crushers and Roller Mills. In this equipment group, stress is applied by either cmshing single particles or a bed of particles between two sohd surfaces. In general, most machines are used for coarse and medium-size reduction, with the exception of the high pressure roUer mill which can achieve extremely fine particle distributions. 

Open-circuit grinding occurs when no attempt is made to return the oversize material to the mill for further size reduction. Closed-circuit grinding employs a means whereby only material smaller than a specified size appears in the product. A less precise mode of operation employs an air stream through the equipment at such a rate that only the appropriately fine material is withdrawn and the rest remains until it is crushed to size. Ball mills sometimes are operated in this fashion, and also the ring-roller mill of Figure 12.5(a). For closer size control, all of the crushed material is withdrawn as it is formed and classified externally into product and recycle. The other examples of Figure 12.5 illustrate several such schemes. 

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