Shear shredders

Rotational speeds are very low, in most cases ranging between 50 and 200 RPM. The low-speed hydraulic motors develop very high torques on the shafts, providing considerable shearing power to the cutting discs. This power makes shear shredders effective in difificult-to-cut materials. This equipment has been used to shred materials such as metals, truck and car tires, wood, pallets, bulky objects, and electrical and electronic devices, for example, in relatively coarse particle size. On the contrary, they are not capable of shredding materials into fine size (less than 10 mm). The main advantage of shear shredders is that... 

Figure 4 (a) Rotor shear shredder, (b) Details of the cutting disks. (From Ref. 5.)... 

The second type of tire chipper is the replaceable cutter tire shredder. This is a low-speed shear shredder specifically designed for tires. The principle cutting feature is shown in Hgure 6.6. Note the addition of star-shaped feed rolls that force the individual tires, one at a tinK, into the cutting zone. As the tires are fed into the cutting zone, the cutters engage them with a true shearing action. 

For brittle materials, shear force is restricted to hammer mills, acting along with impact and attrition, as well as to toothed crushing rolls. The prerequisite for successful size reduction of particles is the existence of macro- or microstructure weaknesses (e.g., layered structure, schistosity) or differences in the characteristics of adjacent minerals (e.g., hardness, friability). Contrary to rocks and minerals, shear force is widely applied in soUd waste size reduction, as most of its constituents are soft, nonbrittle, plastic, and ductile, and, consequently, shear forces are effective. The various forms of shredders use shear force to reduce the size of solid waste constituents. 

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... 

Apply shear or frictional stresses (tumbling mass, mixing tools, special accessories (e.g. shredders, baffles)... 

There are basically two types of tire shredding equipment in conunercial use, the solid cutter shredder and the replaceable cutter tire shredder [18,19]. Both of these machines shear a whole tire to produce a chip with a fixed size in one dimension, but to control the oth chip dimension, additicmal passes through the chipper may be required. 

Figure 6.5. Schematic of solid cutter shredder shearing blades...

The two main disadvantages of the solid cuttm shredder are that it was not specifically designed for tires and thus tends to tear the tire rather than shear or cut it. and sectmdly the sharpness of the cutter edge tends to deteriorate rapidly. This can be overcome with the use of harder steels however they are more costly. 

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