Roller mills are

mills Mills is the plural form of mill, but may also refer to: As a name * Mills (surname), a common family name of English or Gaelic origin * Mills (given name) *Mills, a fictional British secret agent in a trilogy by writer Manning O'Brine Places Uni ...

that use cylindrical rollers, either in opposing pairs or against flat plates, to crush or grind various materials, such as grain,

ore Ore is natural rock or sediment that contains one or more valuable minerals, typically containing metals, that can be mined, treated and sold at a profit.Encyclopædia Britannica. "Ore". Encyclopædia Britannica Online. Retrieved 7 Apr ...

, gravel,

plastic Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptab ...

, and others. Roller grain mills are an alternative to traditional millstone arrangements in

gristmill A gristmill (also: grist mill, corn mill, flour mill, feed mill or feedmill) grinds cereal grain into flour and middlings. The term can refer to either the grinding mechanism or the building that holds it. Grist is grain that has been separat ...

s. Roller mills for rock complement other types of mills, such as ball mills and

hammermill A hammer mill is a mill whose purpose is to shred or crush aggregate material into smaller pieces by the repeated blows of little hammers. These machines have numerous industrial applications, including: * Ethanol plants (grains) * A farm mach ...

s, in such industries as the

mining Mining is the extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. The exploitation of these deposits for raw material is based on the economic ...

and processing of ore and construction aggregate;

cement mill A cement mill (or finish mill in North American usage) is the equipment used to grind the hard, nodular clinker from the cement kiln into the fine grey powder that is cement. Most cement is currently ground in ball mills and also vertical rolle ...

ing; and

recycling Recycling is the process of converting waste materials into new materials and objects. The recovery of energy from waste materials is often included in this concept. The recyclability of a material depends on its ability to reacquire the p ...

Types

Two-roller mills Two-roller mills are the simplest variety, in which the material is crushed between two rollers before it continues on to its final destination. The spacing between these two rollers can be adjusted by the operator. Thinner spacing usually leads to that material being crushed into smaller pieces. Four-roller mills Four-roller mills have two sets of rollers. When using a four-roller mill to mill grain, the grain first goes through rollers with a rather wide gap, which separates the seed from the husk without much damage to the husk, but leaves large grits. Flour is sieved out of the cracked grain, and then the coarse grist and husks are sent through the second set of rollers, which further crush the grist without damaging the crusts. Similarly, there are three-roller mills, in which one of the rollers is used twice. Five- and six-roller mills Six-roller mills have three sets of rollers. When using this type of mill on grain, the first set of rollers crush the whole kernel, and its output is divided three ways: Flour immediately is sent out the mill, grits without a husk proceed to the last roller, and husk, possibly still containing parts of the seed, go to the second set of rollers. From the second roller flour is directly output, as are husks and any possible seed still in them, and the husk-free grits are channeled into the last roller. Five-roller mills are six-roller mills in which one of the rollers performs double duty.

Gristmill conversion

In the 19th century roller mills were adapted to grist mills before replacing them. The mill used either steel or

porcelain Porcelain () is a ceramic material made by heating substances, generally including materials such as kaolinite, in a kiln to temperatures between . The strength and translucence of porcelain, relative to other types of pottery, arises main ...

rollers. Between the years 1865 and 1872, the Hungarian milling industry upgraded and expanded the use of stone mills combined with roller mills in a process known as Hungarian high milling. Hungarian hard wheat so milled was claimed as integral to the "First in the world" success of the Vienna Bakery of the 1867 Paris Exposition.

Other applications

*Specialized for the high production of superfine pyrophyllite powder making in

glass fiber Glass fiber ( or glass fibre) is a material consisting of numerous extremely fine fibers of glass. Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fiber was only made possible with the inventio ...

industry *Specialized for the high production of gangue powder making in coal industry *Specialized for the high production of various of chemical raw material powder making in the chemical industry.

Working principle

A motor or other

prime mover Prime mover may refer to: Philosophy *Unmoved mover, a concept in Aristotle's writings Engineering * Prime mover (engine), motor, a machine that converts various other forms of energy (chemical, electrical, fluid pressure/flow, etc) into energy ...

drives the hanger of the grinding roller to rotate through a V pulley and center bearing. The roller, which is hung by a 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 Negative pressure may refer to: * Negative value of a pressure variable * Negative room pressure, a ventilation technique used to avoid contaminating outside areas * Negative pressure ventilator, also known as an iron lung * Negative-pressure wou ...

at the inlet and outlet of the grinder to prevent dust and radiating the heat in the machine.

History

Sugar rolling mills first appeared in the

Mughal Empire The Mughal Empire was an early-modern empire that controlled much of South Asia between the 16th and 19th centuries. Quote: "Although the first two Timurid emperors and many of their noblemen were recent migrants to the subcontinent, the d ...

, using the principle of rollers as well as worm gearing, by the 17th century. The Indian roller mills used the principle of rollers as well as

worm gear A worm drive is a gear arrangement in which a worm (which is a gear in the form of a screw) meshes with a worm wheel (which is similar in appearance to a spur gear). The two elements are also called the worm screw and worm gear. The terminol ...

ing.

Irfan Habib Irfan Habib (born August 10, 1931) is an Indian historian of ancient and medieval India, following the methodology of Marxist historiography in his contributions to economic history. He identifies as a Marxist and is well known for his strong ...

(2011)
''Economic History of Medieval India, 1200-1500'', page 53
Pearson Education Modern era roller mills were re-invented by the Hungarian engineer András Mechwart in 1874, then quickly spread to other parts of Europe and Americas.

References