Smooth-roll crushers

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).

Roll crushers are available as smooth or toothed rolls. Figure 12.6(b) is an example of a smooth-roll crusher and Table 12.10(b) presents data for a double tooth-roll crusher for coal. For smooth rolls, the feed size is hmited by the angle of nip, which depends on surface conditions but it is approximately 16 degrees. Table 12.10(c) contains additional operating data for roll crushers. The relation between the diameters of the roll d, and feed df and the gap do between the rolls is given by... 

Crushers are slow-speed machines for coarse reduction of large quantities of solids. The main types are jaw crushers, gyratory crushers, smooth-roll crushers, and toothed-roU crushers. The first three operate by compression and can break large lumps of very hard materials, as in the primary and secondary reduction of rocks and ores. Toothed-roll crushers tear the feed apart as well as crushing it they handle softer feeds like coal, bone, and soft shale. 

SMOOTH-ROLL CRUSHERS. Two heavy smooth-faced metal rolls turning on parallel horizontal axes are the working elements of the smooth-roll crusher illustrated in Fig. 29.4. Particles of feed caught between the rolls are broken in compression and drop out below. The rolls turn toward each other at the same speed. They have relatively narrow faces and are large in diameter so that they can nip moderately large lumps. Typical rolls are 6(X) mm (24 in.) in diameter with a 300-mm (12-in.) face to 2000 mm (78 in.) in diameter with a 914-mm (36-in.)... 

Roll crushers. In Fig. 14.5-3b a typical smooth roll crusher is shown. The rolls are rotated toward each other at the same or different speeds. Wear of the rolls is a serious problem. The reduction ratio varies from about 4 1 to 2.5 1. Single rolls are often used, rotating against a fixed surface, and corrugated and toothed rolls are also used. Many food products that are not hard materials, such as flour, soybeans, and starch, are ground on rolls. 

Roll Crushers. Traditional roU emshers effect size reduction by cmshing single particles between two counterrotating roUs hence they are emshed between the two surfaces. The roUs can either be smooth or profiled to aid feeding of coarser materials. Figure 6 shows a particle of diameter x being reduced between two roUs of diameter D. For smooth roUs D/x > 17 is usually selected, whereas for profiled roUs this can be varied to D/x < 10. The feed size-to-gap width ratio is essentially limited to approximately 4. 

Roll crushers are made either smooth or with teeth. A 24 in. toothed roll can accept lumps 14 in. dia. Smooth roiis effect reduction ratios up to about 4. Speeds are 50-900 rpm. Capacity is about 25% of the maximum corresponding to a continuous ribbon of materiai passing through the roiis. 

These tertiary crushers employ smooth or toothed heavy-duty impact and abrasion-resistant steel-rimmed rolls. The rolls are mounted inline in a horizontal manner and turn toward each other at equal speeds to create a nip into which a friable feed material is introduced (Fig. 4). Heavy-duty compression springs with automatic reset are used to dampen crushing shock and to protect the crusher from tramp iron and oversize material. An adjustable screw that adjusts spring tension changes the crusher opening. A flywheel is used to even out pulses and economize on power consumption. These crushers have a theoretical maximum reduction ratio of 4 1 and will only crush materials to about 10 mesh. Roll crushers produce a controlled product size distribution without a lot of fines. The narrow particle size distribution is achieved by controlling a combination of variables including roll speed, gap measure, differential speed, feed rate, and roll surface. 

Jaw crusher feed diameter 0.1 to 1.5 m reduction ratio 5 1 to 10 1 capacity 1 to 300 kg/s Mohs hardness <9 (reduction by compression). Gyratory crusher feed diameter 0.75 to 1.5 m reduction ratio 5 1 to 10 1, usually 8 1 capacity 140 to 1,000 kg/s Mohs hardness <9. More suitable for slabby feeds than jaw crusher (reduction by compression). Roll crusher feed diameter 1 cm reduction ratio 5 1 to 10 1 capacity 0.3 to 20 kg/s Mohs hardness <7.5. Suitable for softer, friable, and nonabrasive materials. OK for wet and sticky materials. Cone crusher and short head cone feed diameter <25 cm reduction ratio 5 1 to 10 1, usually 7 1 capacity 5 to 300 kg/s Mohs hardness <8. Usually secondary or tertiary crusher. Impact crusher pulverizers, shredders, or smooth roll feed diameter 1 cm with a reduction ratio of 7 1 to 10 1 capacity 0.3 to 50 kg/s. Mills, hammer, feed diameter 10 mm, reduction ratio 10 1 to 50 1, capacity 0.01 to 5 kg/s Mohs hardness <4.5. Maximum fines feed not hard or abrasive. Mills, ball, and rod feed diameter 0.5 mm with a reduction ratio of 10 1 to 50 1 Mohs hardness <9. Mills, autogenous, semiautogenous feed diameter 200 mm, reduction ratio 10 1 to 50 1 capacity 0.1 to 100 kg/s Mohs hardness <6. Mills, fluid energy feed diameter 50 pm reduction ratio 10 1 to 50 1 capacity <2 kg/s Mohs hardness <4.5. 

Rolls crushers consist of two counter-rotating rolls, one of which is fixed and the other is spring-loaded. They draw feed material into a nip point , where it is crushed (Fig. 5.5). The rolls may be smooth, or profiled, which helps to draw the rock through the crusher and to reduce the slabbiness of the crushed product. Reduction ratios of only 4 1 are achievable, but the production of fines is low. The head-room requirement is lower than for impactors, but the capital cost is higher. 

Impact crusher pulverizers, shredders or smooth roll feed diameter 1 cm with a reduction ratio of 7 1 to 10 1 capacity 0.3 to 50 kg/s. 

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