The most common is the mill ball mill grinding equipment , ball mill is the material to be broken, and then to smash the key equipment. It is widely used in cement, silicate products , new building materials, refractories , chemical fertilizer, black and non-ferrous metals and glass ceramics and other production industries of all kinds of ores and other grind-able materials dry or wet grinding. Ball mill for grinding various ores and other materials , dry and wet grinding methods are widely used in mineral processing , building materials and chemical industry can be divided into . According to different ways of discharge can be divided into lattice-type ball mill and overflow ball mill two kinds.

The so-called " stone " ( also known as the critical particle ) , generally refers to when the ball mill grinding, because the ore into the mill , the progression is less coarse , easily forming a lenient as grinding media in the mill , but as a ball mill grinding of mineral matter and can not be checked out of the hole row 30 ~ 50mm grain size nuggets . These nuggets ( stone ) gradually accumulate in the mill , mill occupies volume , resulting from the mill production decline , increased power consumption and generation units over crushed phenomenon .

Eliminate or prevent the accumulation of the stone mill can take the following methods:
1 , the use of self- mill - ball mill - crushing process , coming from the open mill grinding, cylinder sieve to drain the material leads, after crushing and ball mill grinding and screening products under the merger deal , which is called the ABC grinding process .
2 , the use of semi-autogenous grinding mill grinding , namely adding the filling rate of 5 % to 8 % of the large ball ( ball diameter 100 ~ 150mm) from the mill to supplement energy and grinding media as chunks " critical particle . "