With the rapid development of economy, China has a lot of large engineering project construction, so it requires a lot of steel, which increases the vigorous mining of iron ore. This will need a lot of mineral processing machinery and equipment, and ball mill is a good equipment at this stage, which is the most popular devices. Therefore, ball mill has the very good market prospect.

The main task of a small ball mill is grinding raw material. However the rotating speed of the ball mill directly determines the moving state of the grinding media and the grinding effect in the cylinder.

When the ball mill rotates at a low speed, the ball of mill ball raised at a low height, the ball will roll down from the top of the ball charge because of its own gravity and presents a cascading state, at which time the impact force of the ball is very small but the grinding effect is evident. However, the ore is mainly ground by grinding and the grinding efficiency is not high.

When the ball mill rotates at a high speed, the ball will be lifted highly. After the ball is lifted to a certain height, it will separate from the barrel and falls along a parabolic trajectory in throwing working state. The ball will gain a great impact at the drop point. The ore is mainly ground by the impact, and the grinding efficiency is high.

When the rotating speed of the ball mill exceeds a certain limit ( speed is very high ), the ball will rotate with the cylinder to rotate without falling in centrifugal running state. The ball will not gain any impact which means no grinding efficiency.

The control of the rotating speed of a ball mill not only relates to the grinding effect, but also relates to the service life of a ball mill. For example, nowadays the ball mill is designed and manufactured below the critical speed. If it rotates at the critical speed or supercritical speed movement, firstly, it will lost its grinding performance because of the centrifugal force; secondly, the high speed rotating will cause mechanical vibration and abrasion, the service life of the equipment is greatly reduced. At the same time the grinding effect of the internal ball mill damages, discharging thickens and it also increases the graded load, so that products are not up to the qualified size requirements. So it is more important of controlling the rotating speed of a ball mill.

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