Comminution equipment

Rotor breakers Hammer mills Cage impactors 

Roll crushers and shredders (continuous) Tumbling media mills (batch and continuous) Ball mills Rod mills Autogneous 

FIGURE 4J2 Crushing and grinding equipment, (a) Jaw crusher, (b) gyratory crusher, (c) vibratory mill, (d) fluid shear mill, (e) pin mill, (f) fluid jet mill, (g) hammer mill, and (h) ball mill. Redrawn from various figures in Perry and Chilton [1], Lowrison [2], and VanCleef[3]. 

---

Table 10.12. Selection of comminution equipment (after Lowrison, 1974)...

Table 10.13. Selection of comminution equipment for various materials (after Marshall, 1974) Note Moh s scale of hardness is given in Table 10.12... 

Table 14.2 Laboratory homogenizers and comminution equipment supplied by Fritsch...

To use natural minerals it is necessary to grind them down to a desired particle size distribution. Grinding can be performed with the minerals dry or slurried in liquid. In most laboratories, this process is performed in a batch jar mill while on an industrial scale, continuous comminution equipment is used in conjunction with size classification equipment to recycle the coarse material. Figure 4.1 shows a typical comminution circuit with classification and recycle steps, as well as separation of the mineral from the conve3ring fluid. 

The strength of most materials is greater in compression than in tension. It is therefore unfortunate that technical difficulties prevent the direct application of tensile stresses. The compressive stresses commonly used in comminution equipment do not cause failure directly but generate by distortion sufficient tensile or shear stress to form a crack tip in a region away from the point of primary stress application. This is an inefficient but unavoidable mechanism. Impact and attrition are the other basic modes of stress application. The distinction between impact and compression is referred to later. Attrition, which is commonly employed, is difficult to classify but is probably primarily a shear mechanism. 

Table 10.14. Selection of Comminution Equipment for Various Materials (after Marshall, 1974)—Cont d... 

Table 3.2 Summary guide for application of comminution equipment covered in this chapter...

Breaking is the term applied to size operations on large material (say +75 mm) and crushing to particle size reduction below 75 mm the term grinding covers the size reduction of material to below about 6 mm. However, these terms are loosely employed. A general term for all equipment is size reduction equipment, and because the term comminution means size reduction, another general term for the equipment is comminution equipment. 

Comminution of the sample presents significant opportunity for contamination. Contamination of the sample from abrasion of the comminution equipment is fundamentally unavoidable, so efforts must be made to select the best possible equipment for each particular analytical task. Equipment is preferred in which the sample comes into contact only with surfaces fabricated from such high-purity plastics as polytetrafluoroethyl-ene (PTFE), since this permits the sample to be used without restriction for the determination of a large number of elements. Friability can be increased by deep-freezing or drying the sample prior to comminution. 

TYPES OF COMMINUTION EQUIPMENT 12.4.1 Factors Affecting Choice of Machine... 

An initial classification of comminution equipment can be made according to the stressing mechanisms employed, as follows. 

Table 12.2 Categorizing comminution equipment according to product size...

---