Main parameters of the mill
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(1) Mill productivity. There are many factors that affect mill productivity, such as the type, size and speed of the mill, the nature of the material being milled, the nature, size, shape and filling rate of the grinding media, the classification efficiency during closed-circuit grinding, the feed size and Discharge fineness, operating conditions, etc. Therefore, it is very difficult to theoretically determine the productivity of the mill. It is generally determined by specific tests and simulation methods, and the results obtained are approximate, and some actual data are used for checking. Therefore, some productivity calculation methods in textbooks and design manuals are not listed here, and the range of productivity is only listed in the mill technical performance table in various mill selection examples.
(2) Mill speed. The working speed of the cylinder of the mill is generally 30~14r/min, and the rotation speed of the cylinder is low, and vice versa. The ratio of the working speed of the mill barrel to its critical speed is called the transfer rate, which is generally 76%~88%.
(3) Filling rate and loading amount of medium in the mill. When the mill is in operation, the percentage of the area occupied by the medium on the cross section of the cylinder and the area of ​​the cross section is referred to as the filling rate of the mill. Through calculation, the filling rate of different types of mills at different speeds can be obtained. In actual work, the filling rate of wet lattice ball mill is generally 40%~50%, and the filling rate of overflow ball mill or rod mill is generally 35%~40%, dry lattice type mill and tube mill The filling rate is generally 25% to 35%.
After the filling rate of the mill is known, the amount of the medium loaded can be calculated from the effective volume of the mill and the bulk density of the medium. The media loading of the different mills is listed in the mill technical performance table in the mill selection example. In the self-grinding machine , generally no medium is loaded, but in order to improve the grinding efficiency, a small number of steel balls are often added, and the ball loading amount is about 4% to 10% of the effective volume of the self-grinding machine.
(4) Mill power. Mills of different types and sizes are actually equipped with a motor of appropriate power from the manufacturer. The motor itself consumes about 10% of its power, and the mechanical friction loss consumes about 10% to 15%. The useful power used to move the grinding media and material to produce crushing and grinding is about 75%.
Generally, the actual required power is derived from the experimental data obtained by a small test mill under various specific grinding conditions. This is called the analogy method, and its calculation formula is:
Where, N, D, L - calculate the power of the mill, the inner diameter and length of the cylinder; N c , D c , L c - the power of the test mill, the inner diameter and length of the cylinder; y - the ordinary mill y = 2.5, self-grinding machine y = 2.5-2.6.