What is the critical rotation speed in revolutions per second, for a ball mill of 1.2 m diameter charged with 70 mm dia balls ?
Correct answer: D. 0.66
- A. 0.5
- B. 1.0
- C. 2.76
- D. 0.66
Explanation
The critical speed is calculated from the effective radius to the ball centre: N_c = [g/(4π²(R-r))]¹ᐟ². With a 1.2 m mill and 70 mm balls, this gives about 0.66 revolutions per second.
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