A roller mill is a milling machine that gently and gradually reduces material to a smaller size. There are one or two pair of chilled cast iron rolls inside the machine. These rolls are lying parallel and are supported at each end by roller bearings. The back roll is in a fixed position and the front roll is movable to adjust the roll clearance. This allows the rolls to almost touch one another to give a gap of up to 20mm between them.
Material is pulled by the corrugations into the area where the two rolls meet.
The work done by the rolls on these particles will depend on the speed of the rolls, the differential speed or the difference in the speed of each roll, the type of flutes, the number of flutes, the amount of pressure holding the rolls together and the amount of space between the rolls.
The final product size is usually cracked, granulated, ground, bruised or flaked. Cracking will only cut the product into two or three pieces, while granulating may cut the product into ten to twenty pieces. Grinding may grind the product as fine as flour. Bruising will slightly damage the grain and flaking produces flakes.
Roller Mills produce a higher quality product at a lower cost, better appearance and more uniform texture than any other process for reducing a medium size particle.
Roller mills are energy efficient.
The rolls come in contact with the material just once. The material passes between the rolls and the reduction is immediate.