Grinding critical speed

The critical speed is the speed at which the grinding media cease to cascade owing to the centrifugal force imparted by the rotating vessel. The critical speed can be estimated by employing the following relationship (Lantz, 1990) ... 

Figure 123. Power Change During Grinding Period for Batch Grinding with Various Ball Sizes. Charge, 50 lb 14/20-mesh Dolomite. Pulp Consistency 60 Percent, Critical Speed 50 Percent.

Figure 125. Comparison of Wet and Dry Batch Grinding of Chert at 50 Percent Critical Speed. Wet Grinding at 60 Percent Pulp Consistency.

Calculate the critical speed of a mill 28 in. in diameter. What is the significance of critical speed in grinding operations ... 

A ball mill having an inside diameter of 12 ft and an inside length of 14 ft is to be used to grind a copper ore. Measurement shows that the distance between the top of the mill and the leveled surface of the ball charge is 6.35 ft. What is the weight of balls in the mill What is the critical speed of the mill (the speed at which the centrifugal force on a ball in contact with the mill wall at the top of its path equals the force due to gravity) At what percent of critical speed should the mill operate ... 

A larger mill reaches its critical speed at a slower revolution rate than a smaller mill. Ball mills are operated at from 60 to 85% of the critical speed. Over this range, the output increases with the speed however, the lower speeds are for finer grinding. An empiric rule for the optimum speed of a ball mill is... 

Ball mills are better suited than rod mills to fine grinding. The charge is of equal weights of 1.5, 2 and 3-in. balls for the finest grinding. The volume occupied by the balls is 50% of the mill volume. Rotation is 70-80% of critical speed. Ball mills have a length-to-diameter ratio of 1-1.5. 

Critical and Operating Speed. In operation, the balls in the mill are carried up in contact with each other and with the walls until the centrifugal force is overcome by the centripetal force. The critical speed of a ball mill is the speed in rpm above which the grinding media will centrifuge and all milling effectively stops. 

The operating speed of ball mills is usually 55-75% of the critical speed. Operating close to drastically reduces the effectiveness of the grinding action. 

Tumbling mills run at 65 to 80 percent of the critical speed, with the lower values for wet grinding in viscous suspensions. ... 

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