Roller mills are mills that use

cylindrical A cylinder () has traditionally been a Solid geometry, three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a Prism (geometry), prism with a circle as its base. A cylinder may ...

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

grain A grain is a small, hard, dry fruit (caryopsis) – with or without an attached husk, hull layer – harvested for human or animal consumption. A grain crop is a grain-producing plant. The two main types of commercial grain crops are cereals and ...

ore Ore is natural rock or sediment that contains one or more valuable minerals, typically including metals, concentrated above background levels, and that is economically viable to mine and process. The grade of ore refers to the concentration ...

gravel Gravel () is a loose aggregation of rock fragments. Gravel occurs naturally on Earth as a result of sedimentation, sedimentary and erosion, erosive geological processes; it is also produced in large quantities commercially as crushed stone. Gr ...

plastic Plastics are a wide range of synthetic polymers, synthetic or Semisynthesis, semisynthetic materials composed primarily of Polymer, polymers. Their defining characteristic, Plasticity (physics), plasticity, allows them to be Injection moulding ...

, 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 Wheat middlings, middlings. The term can refer to either the grinding mechanism or the building that holds it. Grist is grain that h ...

s. Roller mills for rock complement other types of mills, such as ball mills and hammermills, in such industries as the

mining Mining is the Resource extraction, extraction of valuable geological materials and minerals from the surface of the Earth. Mining is required to obtain most materials that cannot be grown through agriculture, agricultural processes, or feasib ...

and processing of ore and

construction aggregate Construction aggregate, or simply aggregate, is a broad category of coarse- to medium-grained particulate material used in construction. Traditionally, it includes natural materials such as sand, gravel, crushed stone. As with other types of ag ...

; cement milling; and

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

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 the 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. in a four-roller mill, 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. In this type of mill, 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 Steel is an alloy of iron and carbon that demonstrates improved mechanical properties compared to the pure form of iron. Due to steel's high Young's modulus, elastic modulus, Yield (engineering), yield strength, Fracture, fracture strength a ...

porcelain Porcelain (), also called china, is a ceramic material made by heating Industrial mineral, raw materials, generally including kaolinite, in a kiln to temperatures between . The greater strength and translucence of porcelain, relative to oth ...

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 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 The chemical industry comprises the companies and other organizations that develop and produce industrial, specialty and other chemicals. Central to the modern world economy, the chemical industry converts raw materials ( oil, natural gas, air, ...

Working principle

A motor or other prime mover 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 may refer to: Science and mathematics * Negative number * Minus sign (−), the mathematical symbol * Negative mass * Negative energy * Negative charge, one of the two types of electric charge * Negative (electrical polarity), ...

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

History

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

{{Reflist Grinding mills Mining equipment