This set of Basic Mechanical Operations Questions and Answers focuses on “Intermediate and Fine Crushers”.
1. The ball mill can be best used for which kind of feed?
a) Wet and Dry
b) Coarse and Fine
c) Rocks and Bricks
d) Any kind of feed
Explanation: The ball mill can be used wet or dry grinding facilities the removal of the product, this is the best feed that can be utilized with ball mill.
2. What is the ratio of length to diameter of tube mill?
c) Both 3 and 4:1
Explanation: The tube mill is similar to ball mill in the construction and operation and the ratio of length to diameter is 3 or 4:1.
3. Which of the following forces act on the tumbling mill?
a) Tangential force
b) Centrifugal force
c) Circular force
d) Gravitational force
Explanation: Centrifugal forces keeps the ball in contact with the ball mill and with each other during the upward movement.
4. Which of the following is true, when operating speed is less than critical speed?
a) No grinding
b) Effective grinding
c) Best grinding
d) Bold grinding
Explanation: The speed at which the centrifuging occurs is called as the critical speed and little or no grinding tales place during this phase.
5. What is the angle of nip for ball mill?
a) 4π2n2 (R-d)/g
b) 4π2n2 (R+d)/g
c) 4π2n2 (R-r)/g
d) 4π2n2 (R-n)/g
Explanation: The angle of nip for a ball mill cos α is defined as 4π2n2 (R-r)/g, Where n is the speed of the rotation of the ball mill.
6. At critical speed, α = 0 and cos α = 1, what is critical speed?
a) n = nc
b) 2π = nc
c) g = nc
d) gn= nc
Explanation: The critical speed is given when the n i.e. the natural number of revolutions becomes the critical point and critical speed nc.
Explanation: The equation represents critical speed where, g is the gravitational constant and R and r are the radius of ball and the ball mill.
8. What is percentage of tumbling mill speed?
a) 80 to 100%
b) 65 to 80%
c) 50 to 90%
d) 10 to 50%
Explanation: Tumbling mill runs at 65 and 80 percent of the critical speed, with lower values for wet grinding as well as dry tumbling.
9. Which of the following uses shearing action?
a) Buhrstone mill
b) Tumbling mill
c) Rod mill
d) Ball mill
Explanation: Size reduction take place by the shearing action, it consists two heavy horizontal wheels placed over one and another.
10. What is the feed size for a buhrstone mill?
a) Size of peat
b) Size of rock
c) Size of grain
d) Any size
Explanation: The buhrstone mill has a feed size of a grain, while the product ranges from 200 to 400 mesh and is mainly used for making flour.
Sanfoundry Global Education & Learning Series – Mechanical Operations.
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