Actual operating speed of a ball mill may vary from 65 to 80% of the critical speed. Which of the following duties would require the ball mill to be operated at maximum percentage of critical speed ?
Correct answer: D. Dry grinding of large particles in un-baffed mills
- A. Wet grinding in low viscous suspension
- B. Wet grinding in high viscous suspension
- C. Dry grinding of large particles (upto 1.25 cms)
- D. Dry grinding of large particles in un-baffed mills
Explanation
Dry grinding of large particles in an unbaffled mill needs a higher speed so the balls are lifted sufficiently before falling and causing impact breakage. Viscous wet suspensions generally require lower speeds because of the increased drag on the mill contents.
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