# Food Processing Unit Operations Questions and Answers – Size Reduction – Grinding Equipments

This set of Food Processing Unit Operations Multiple Choice Questions & Answers (MCQs) focuses on “Size Reduction – Grinding Equipments”.

1. Identify this size reduction equipment?

a) Rolling compression mill
b) Burr mill
c) Jaw crusher
d) Hammer mill

Explanation: The working principle of the jaw crushers is motorized by a diesel or gas motor, the jaw crusher brakes materials in a crushing chamber. The materials are pushed inside the chamber from the top opening and when crushed they are released through the bottom opening.

2. What is other name for attrition mill?
a) Rolling compression mill
b) Burr mill
c) Jaw crusher
d) Hammer mill

Explanation: It is also known as burr mill. Grains are rubbed between the grooved flat faces of rotating circular disks where one plate is stationary and fixed with the body of the mill while the other one is rotating disk. Material is fed between the plates and is reduced by crushing and shear.

3. Which of the following forces acts in ball mill?
a) Gravitational force
b) Centrifugal force
c) Gravitational and centrifugal forces
d) Does not depend on any force

Explanation: In ball mills, product is released by the gravitational pull and drop to the bottom and the centrifugal force keeps the ball in contact with the mill wall. Due to centrifugal force, if the speed of rotation of mill is faster, the balls are carried to more distance therefore critical speed is required for rotational speed at which centrifuging occurs.

4. Which of the following statements about reduction ratio of crusherare correct?
Statement 1: It depends on the feed size of the equipment.
Statement 2: It is used in determining the mechanism of crusher.
a) True, False
b) True, True
c) False, True
d) False, False

Explanation: The Reduction Ratio is defined as the ratio of the feed size to the product size in any crushing operation. It is very useful in determining mechanism of crusher and type of size reduction.

5. What is the working principle of ball mill?
a) Impact and attrition
b) Compression and attrition
c) Shear and compression
d) Tear and impact

Explanation: Ball mill works on the principle of impact and attrition. Size reduction is done by impact as the balls drop from near the top of the shell. A ball mill consists of a hollow cylindrical shell rotating about its axis.
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6. What is the working principle of triple roller mill?
a) Impact
b) Compression
c) Shear
d) Tear

Explanation: A triple roll mill is a machine that uses shear force which is created by three horizontally positioned rolls rotating in the opposite directions and also with different speeds relative to each other. This is done in order to refine, mix, disperse and homogenize viscous materials.

7. Which of the following machine is not used for fine grinding?
a) Jaw crushers
b) Ball mill
c) Hammer mill
d) Attrition mill

Explanation: Ball mill, Hammer mill and attrition mill are used for fine grinding whereas the jaw crushers, crusher rolls and gyratory crushers are used for coarse grinding.

8. What is the working principle of hammer mill?
a) Impact
b) Compression
c) Shear
d) Tear

Explanation: A hammer mill is a mill which is used to shred or crush larger material into smaller pieces by the repeated blows of little hammers. It creates impact force.

9. Which of the following forces acts in attrition mill?
a) Impact and crush
b) Compression and impact
c) Shear and crush
d) Tear and impact

Explanation: It is also known as burr mill. Grains are rubbed between the grooved flat faces of rotating circular disks where one plate is stationary and fixed with the body of the mill while the other one is rotating disk. Material is fed between the plates and is reduced by crushing and shear.

10. Are gyratory crusher and cone crusher same?
a) True
b) False

Explanation: Gyratory crushers are for primary crushing. Cone crushers are used for secondary or tertiary crushing for making a cubical product for feeding to process equipment.

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