Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A) : In attrition mill, overfeeding lowers the grinder performance.
Reason (R) : The fineness of grinding in attrition mill is controlled by the type of plates and the gap between them.
In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

Remember that overfeeding affects the feed rate and throughput balance of a mill, whereas plate configuration and gap settings control the particle size of the processed material.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
An attrition mill (disc mill) reduces the size of materials through a combination of cutting, shearing, and crushing actions between two closely spaced plates.
One plate is typically stationary while the other rotates, or both plates rotate in opposite directions.

Step 2: Detailed Explanation:
Let us analyze the assertion and reason statements individually:
Assertion (A): Overfeeding occurs when the raw material is introduced into the milling chamber faster than the plates can process and discharge it.
This clogs the gap between the plates, increases friction and operating temperatures, and strains the motor.
As a result, the grinding efficiency decreases, the motor may stall, and the output quality degrades, making the assertion true.
Reason (R): The primary adjustments that determine the final particle size (fineness) of the ground product are the surface texture (or pattern) of the plates and the width of the gap between them.
A narrower gap produces finer material, while different plate patterns are designed for specific crops.
Thus, the reason statement is technically true.
However, the reason does not explain why overfeeding reduces grinder performance.
Overfeeding reduces performance due to material accumulation, clogging, and motor overload, which is independent of the plate gap setting.
Therefore, both statements are true, but the reason is not the correct explanation of the assertion.

Step 3: Final Answer:
Both (A) and (R) are true but (R) is NOT the correct explanation of (A).