Reduction roller mill

In the food processing industry, a large number of food products are subjected to size reduction. Roller mills are used to. grind wheat and rye to flour and corn. Soybeans are rolled, pressed, and ground to produce oil and flour. Hammer mills are often used to produce potato flour, tapioca, and other flours. Sugar is ground to a finer product. 

What are the main differences between break and reduction roller mills in terms of equipment design and operation ... 

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. 

Flour and Feed Meal The roller mill is the traditional machine for grinding wheat and lye into high-grade flour. A typical mill used for this purpose is fitted with two pairs of rolls, capable of making two separate reductions. After each reduction the product is taken to a bolting machine or classifier to separate the fine flour, the coarse produc t being returned for further reduction. Feed is supphed at the top, where a vibratoiy shaker spreads it out in a thin stream across the full width of the rolls. 

In a flour mill the Farinograph is used as a control instrument since the water absorption of flour can be increased or reduced by adjusting the mill, to deliver more or less starch damage. If the water absorption is too low, the pressure on the reduction rollers of the mill will be increased, thereby increasing the starch damage. Similarly, if the water absorption and hence the starch damage is too high the pressure must be... 

In industrial and laboratory settings the subdivision process more commonly involves the comminution of large particles or aggregates into smaller sizes, either dry with subsequent dispersion (size reduction to the order of a few pm) or directly in a slurry (size reduction to as small as a few tenths of pm). Examples of comminution machines include agitator ball mills, colloid mills, cutting mills, disk mills, homogenizers, jet mills, mechanical impact mills, ring-roller mills, and roll crushers. 

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. 

Fig. 5.61 Agglomerates produced during the grinding of limestone and cement clinker in a roller mill with a high reduction ratio.

One measure for the fineness, the intensity of stressing, and the unintentional formation of agglomerates is the so called reduction ratio, that is, the quotient of maximum feed particle size and gap between the rollers. Fig. 5.61 depicts typical agglomerates produced in a roller mill with a high reduction ratio. Since the fine material is immediately compacted, almost all free valences at the newly created surfaces participate in recombination bonding. Consequently, the formation of agglomerates in roller mills can be only avoided if a smaller reduction ratio is chosen or by applying friction between the rollers. 

Ring-Roller Mill A machine for the comminution, or size reduction, of minerals. Such machines crush the input material between a stationary ring and vertical rollers revolving inside the ring. Particle sizes of as low as about 30 fim can be produced. 

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