The ball mill is a key piece of equipment for grinding crushed materials, and it is widely used in production lines for powders such as cement, silicates, refractory material, fertilizer, glass ceramics, etc. as well as for ore dressing of ferrous and non ferrous metals. The ball mill can grind ores and other materials either wet or dry.
The drive sets the grinding drum into slow rotation, whereby the bed of grinding media is activated. Ball mills are usually operated at 75% of the critical speed. If the speed is slower, the balls roll in a cascading motion, whereas at higher speeds, the balls are lifted and impact back against the bed .
Critical Speed When the ball mill cylinder is rotated, there is no relative slip between the grinding medium and the cylinder wall, and it just starts to run in a state of rotation with the cylinder of the mill. This instantaneous speed of the mill is as follows: N0 mill working speed, r/min;
Critical Speed Of The Ball Mill Critical Speed Of A Ball Mill The critical speed of the mill amp c is defined as the speed at which a single ball will just remain against the wall for a full cycle At the top of the cycle 0 and Fc Fg 85 mp amp 2 cDm 2 mpg 86 amp c 2g Dm 12 87 The critical speed is usually expressed in terms of the number of revolutions per second Nc amp c 2 1 2 2g Dm 12...
The point where the mill becomes a centrifuge is called the Critical Speed, and ball mills usually operate at 65% to 75% of the critical speed. The critical speed is given by: nC = 42.29/d, where d is the internal diameter in metres. So a mill with diameter 5 metres will turn at around 14 rpm.
For a ball mill to work, critical speed must be achieved. Critical speed refers to the speed at which the enclosed balls begin to rotate along the inner walls of the ball mill. If a ball mill fails to reach critical speed, the balls will remain stationary at the bottom where they have little or no impact on the material.