Roller mills use cylindrical rollers to grind all sorts of materials rather than crushing them or grinding them between stones such as in a traditional grains mill. Roller mills are usually used for industrial grain milling (Agriculture) and for grinding gravel into smaller rocks or pulverizing them. The roller mill is a relatively new kind of large scale power mill which is designed specially to solve the problems of low capacity and high consumption of industry mills. It is a necessary equipment for the high production of mineral powder in the non-metal mine industry and large scale powder making in many other industries. The product size is adjustable in the range of 0-2.8mm.
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To produce refined (‘white’) wheat flour,[1] grain is usually tempered, i.e. moisture added to the grain, before milling, to optimize milling efficiency. This softens the starchy "endosperm" portion of the wheat kernel, which will be separated out in the milling process to produce what is known to consumers as "white flour”. The addition of moisture also toughens the bran and ultimately reduces the energy input required to shatter the kernel, while at the same time avoiding the shattering of bran and germ particles to be separated out in this milling process by "sieving" or sifting.
The endosperm portion of the kernel makes up about 80% of the volume and is desirable because the products produced by this white flour are often considered to have milder flavor, smoother texture, and, in the case of bread, greater volume. The balance of the kernel is composed of the bran and the germ which tend to be coarser. With the invention of the roller milling system in the late 19th century, the bran and the germ were able to be removed, dramatically improving the appeal of baked products to the public.
The moistened grain is first passed through the series of break rollers, then sieved to separate out the fine particles that make up white flour. The balance are intermediate particles of endosperm (otherwise known as product "middling" or "farina") and coarse particles of bran and germ. The middling then makes multiple passes through the reduction rolls, and is again sieved after each pass to maximize extraction of white flour from the endosperm, while removing coarser bran and germ particles.
To produce "whole wheat" flour, 100% of the bran and germ must be reintroduced to the white flour that the Roller Milling system was originally designed to separate it from. Therefore, these elements are first ground on another mill (usually a pin mill). These finer bran and germ fractions are then reintroduced to the endosperm ("white flour") to produce whole wheat flour made of 100% of the kernel of wheat.
In the 19th century roller mills were adapted to grist mills before replacing them. The mill used either steel or porcelain rollers.[2]
Other mill systems include:
While working, motor drives the hanger of the grinding roller to rotate through V pulley and centre bearing. The roller, which is hung by bearing and pendulum shaft, will roll along the inner circle of the roll ring while the hanger is rotating. A dust removal blower will generate negative pressure at the inlet and outlet of the grinder to prevent dust and radiating the heat in the machine.