# Mechanical Operations Questions and Answers – Size Reduction Equipments

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This set of Mechanical Operations Multiple Choice Questions & Answers (MCQs) focuses on “Size Reduction Equipments”.

1. For crushing rolls, α is_____
a) Angle of bend
b) Angle of Nip
c) Angle of stamp
d) Angle of Camp

Explanation: Angle of nip is the angle formed by the tangents to the roll faces at the point of contact with the particle to be crushed.

2. What is α for average conditions?
a) 0.961
b) 160
c) 170
d) 200

Explanation: For average conditions the angle of nip α is 160 i.e. cos α = 0.961.

3. How can be the angle of nip calculated?
a) r+d/r+R
b) R+r/r+d
c) D/r+d
d) R/r+d

Explanation: The angle of nip i.e. cos α = r+d/r+R, where R and r are the radius of feed particle and the roll and d is the diameter of largest possible product.
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4. Calculate α. If radius of feed and roll are 100 mm and 500 mm respectively and largest particle is 5 mm?
a) 41.1
b) 32.75
c) 16
d) 20

Explanation: As Cos α = r+d/r+R = 500+5/100+500 = 0.841 = arcos (0.841) = 32.750.

5. Which of the following works on the principle of shearing?
a) Ball mill
b) Roll crusher
c) Toothed crusher
d) Rod mill

Explanation: The toothed crusher works on the principle of the shearing, while all other mentioned work on the principle of compression.

6. The feed size of a toothed crusher ranges from ____
a) 20 inches
b) 10 inches
c) 30 inches
d) 40 inches

Explanation: The feed size of a toothed crusher ranges from 20 inches, while product size ranges from 50 to 200 mm.

7. Which of the following works on the principle of impact?
a) Ball mill
b) Roll crusher
c) Jaw crusher
d) Gyratory Mill

Explanation: The ball mill works on the principle of impact, it consists of the horizontal cylinder lined with steel or high carbon plates.

8. The shell diameter ranges from ____
a) 1 to 2.5 m
b) 3 to 4.25 m
c) 2 to 3 m
d) 5 to 10 m

Explanation: The shell diameter ranges from 3 to 4.25 m and while the balls diameter varies from 1 inch to 5 inches in the diameter.

9. The feed size of a ball mill ranges from _____
a) 50 mm
b) 100 mm
c) 200 mm
d) 300 mm

Explanation: The feed size of a ball mill ranges from 50 mm, while the product size ranges from 100 to 200 mesh screen.

10. As the rate of feed increases, the size reduction ____
a) Increases
b) Remains constant
c) Equals
d) Decreases

Explanation: With high rate of feed, less size reduction is done since the material is retained in the mill for shorter time.

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