Size reduction equipment hammer mill

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. 

It has been argued that hammer mills constitute the most efficient comminution machines available for different size reduction purposes. Their relations of reduction are, therefore, considered among the top within the range of size reduction equipment. The object of this experiment is to study the factors affecting the performance of a hammer mill using the reduction ratio obtained as criteria. 

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 crusting ranges data in Table 12.6(b) (Hardinge Co.). (e) Tube mill with three compartments, length to diameter ratio 3-5. (f) Rod mill in a cylindrical tumbler, LID = 1.2-1.6 data in Table 12.6(d).

The particle size reduction tests for various selected biomass types have been executed in the pilot installation of CIEMAT. A flow diagram of the installation is shown in Figure 1. Basically, the equipment consists of two hammer mills connected in series, the first one has a nominal power of 11 kW and is used for pre-grinding (emshing). The second hammer mill has a nominal power of 15 kW and is used for refining the pre-ground biomass. 

Although the term shredders is sometimes used as a general term to include the equipment that causes size reduction of solid waste, it fits best to the equipment that uses mainly shear force to reduce the size of the materials. In such a sense, hammer mills are sometimes included in the category of shredders, as, in addition to impact force, materials are also subjected to shear force for their size reduction, in case that they are also equipped with stationary knives fixed at the wall. In this chapter, shredders are considered only the equipment that use shear... 

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