# Mechanical Operations Questions and Answers – Ball Mill

This set of Mechanical Operations Multiple Choice Questions & Answers (MCQs) focuses on “Ball Mill”.

1. What is the average particle size of ultra-fine grinders?
a) 1 to 20 µm
b) 4 to 10 µm
c) 5 to 200 µm
d) 50 to 100 µm

Explanation: The particle averaging 1 to 2 µm in size with substantially all particles through a standard 325 mesh screen.

2. Which of the following uses impact and attrition?
a) Ball mill
b) Tumbling mill
c) Ultra-fine grinders
d) Hammer mill

Explanation: Grinding takes place due to impact and attrition, it consists set of swing hammers, rotor, classifier wheels and fan wheels.

3. What is the feed size for a Ultra-Fine grinder?
a) > 34 inches
b) < 34 inches
c) > 12 inches
d) < 12 inches

Explanation: The feed size of ultra-fine grinder is less than 34 inches and the product sizes between 1 to 20 micro meter passing through 100 mesh.

4. The fluid energy mill involves __________
a) Pressure
b) Temperature
c) Fluid
d) Density

Explanation: The fluid energy mill usually uses compressed air and super-heated steam admitted at a pressure of 7 atm through nozzles.

5. At what speed stirred mill operates?
a) 50 to 500 rpm
b) 5 to 10 rpm
c) 10 to 500 rpm
d) 100 to 1500 rpm

Explanation: In a stirred mill, a central paddle wheel or impellor armature stirs the media at speed from 100 to 1500 rpm.
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6. What does colloid mill produces?
a) Emulsions and Solid dispersions
b) Wet and dry products
c) Coarse and fine particles

Explanation: Colloidal suspensions, emulsions and solid dispersions are produced by means of colloid mills or dispersions mills.

7. The clearance between rotor and stator is ______
a) 5 to 10 mm
b) 1 to 2.5 mm
c) 0 to 1.25 mm
d) 5 to 15 mm

Explanation: The mill consists of a flat rotor and stator, the clearance between the rotor and stator is generally 1 to 1.25 mm.

8. The power consumption of colloid mill is _______
a) Very low
b) Optimum
c) Critical
d) Very high

Explanation: The power consumption is very high and the material should therefore be ground as fine as possible before it is fed to mill.

9. The speed of a rotary knife cutter is ___
a) 100 to 500 rev/min
b) 200 to 900 rev/min
c) 400 to 600 rev/min
d) 50 to 60 rev/min

Explanation: A rotary knife cutter contains a horizontal rotor turning at 200 to 900 revolutions per minute, which is cylindrical chamber.

10. ______ indicates the impact of resistance.
a) Toughness
b) Rigidity
c) Brittleness
d) Fatigue

Explanation: Toughness indicates the impact of resistance. It is the inverse of friability and brittleness, it is also a deciding factor for commutation.

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