A cement mill is an installation used to grind the clinker component of concrete. Clinker is a hard, nodular material produced by sintering aluminosilicate and limestone in a cement kiln. There are several cement mill types which are able to grind clinker of which the ball mill is the most common.
Ball mills are highly effective grinding systems which subject the raw material to relatively low heat and pressure levels. They consist of large diameter, rotating cylinders or drums driven by electric motors. The drum is partially filled with high-chromium steel balls or, occasionally, cubes. These roll around freely inside the cylinder when it is rotated. This rolling action crushes clinker by impact and then grinds it finely due to friction between the balls.
Cement clinker is usually ground using a ball mill. This is essentially a large rotating drum containing grinding media - normally steel balls. As the drum rotates, the motion of the balls crushes the clinker. The drum rotates approximately once every couple of seconds.
The drum is generally divided into two or three chambers, with different size grinding media. As the clinker particles are ground down, smaller media are more efficient at reducing the particle size still further.Gypsum is interground with the clinker in order to control the setting properties of the cement. Clinker grinding uses a lot of energy and the cement becomes hot - this can result in the gypsum becoming dehydrated, with potentially undesirable results.