BallMill-Polysius 7-9m dia x 12-4m 3D model

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A Ball Mill crushes material by spinning a cylindrical container fitted with steel grinding balls, propelling the balls downward onto the material being crushed in a cyclical motion. Typically, the rotation speed of the mill ranges between 4 to 20 revolutions per minute, influenced primarily by the diameter of the mill itself. As the diameter increases, so does the time it takes for the mill to complete one full rotation. If the peripheral velocity becomes excessive, the mill starts behaving like a centrifuge, and the balls fail to return to their original position, instead staying at the outer edge of the mill. The point at which the mill transitions into a centrifuge-like state is known as the Critical Speed, with most ball mills operating within a range of 65% to 75% of this critical speed. Ball Mills are generally employed for grinding material measuring 1/4 inch or finer down to an extremely fine particle size of between 20 to 75 microns. To maximize efficiency in a ball mill, it must be run in a closed system where oversized particles are continuously cycled back into the mill for further reduction. Various classifiers such as screens, spiral classifiers, cyclones, and air classifiers are utilized to categorize the discharge from ball mills.