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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

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Answer: a [Reason:] 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

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Answer: c [Reason:] 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

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Answer: b [Reason:] 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

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Answer: a [Reason:] 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

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Answer: d [Reason:] In a stirred mill, a central paddle wheel or impellor armature stirs the media at speed from 100 to 1500 rpm.

6. What does colloid mill produces?
a) Emulsions and Solid dispersions
b) Wet and dry products
c) Coarse and fine particles
d) Broad particles

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Answer: a [Reason:] 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

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Answer: c [Reason:] 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

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Answer: d [Reason:] 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

View Answer

Answer: c [Reason:] 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

View Answer

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