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 ?

Related Mcqs:

1. 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 ?

   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

2. Critical Speed (Nc) of a ball mill is given by (where R1 and R2 are radii of ball mill and the ball respectively) ?

   A. Nc = (1/4π). √(g/R1 – R2)
   B. Nc = (1/2π). √(g/R1 – R2)
   C. Nc = (1/π). √(g/R1 – R2)
   D. Nc = (1/2π). √(R1 – R2/g)

3. In a ball mill, the volume occupied by the balls (when the mill is stopped) is about _______________ percent of the volume of the mill?

   A. 35
   B. 50
   C. 70
   D. 85

4. Power required to drive a ball mill with a particular ball load is proportional to (where, D = diameter of ball mill.) ?

   A. D
   B. 1/D
   C. D2.5
   D. 1/D2.5

5. For achieving maximum capacity of the ball mill, the ball charge should be equal to about ______________ percent of the ball mill volume?

   A. 10
   B. 25
   C. 50
   D. 75

6. Critical speed of rotation, N (in rps – rotation per second) of a trammel is equal to (where, g = acceleration due to gravity = 9.81 m/sec2 and, r = radius of trammel, metre.) ?

   A. (1/2π). √(g/r)
   B. (1/π). √(g/r)
   C. ½ √(g/r)
   D. 2π. √(g/r)

7. The operating speed of a ball mill should be ______________ the critical speed?

   A. Less than
   B. Much more than
   C. At least equal to
   D. Slightly more than

8. ______________________ balls capable of grinding the feed in a ball mill gives the maximum efficiency ?

   A. Cast iron
   B. Minimum size
   C. Maximum size
   D. Elliptical

9. A _____________ mixer resembles a ball mill without balls?

   A. Banbury
   B. Pug mill
   C. Tumbling
   D. Pan

10. Theoretical capacity of crushing rolls in tons/hr is given by (where, V = peripheral velocity, m/sec. W = width of rolls, m Dr = distance between rolls ρ = density of material to be crushed, kg/m3 here, V =πND where, N = speed of the rolls in rotation per second (rps) D = diameter of rolls, m) ?

    A. 3.6 V.W.Dr.ρ
    B. 3.6 V.W. ρ
    C. 3.6 W.Dr.ρ
    D. 3.6 V.W.Dr/ρ