The GATE Grind

GATE 2024 MT – Question 46

Manufacturing Processes · Metal forming · 2 marks · Multiple choice

For slab rolling, assess the assertion [a] and reason [r].

[a]: Grooves parallel to the roll axes are made on roll surfaces to achieve large thickness reduction in a short time.

[r]: If $\mu$ is roll–slab friction coefficient and $\alpha$ the bite angle between the entrance plane and roll centerline, unaided entry is possible only if $\mu<\tan\alpha$.

  1. Both [a] and [r] are true, and [r] is the correct reason of [a].
  2. Both [a] and [r] are true, but [r] is the not the correct reason of [a].
  3. Both [a] and [r] are false.
  4. [a] is true, but [r] is false.

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Show answer and explanation

Correct answer: (D) [a] is true, but [r] is false.

Explanation

Roll grooves increase grip, enabling larger reductions and making the assertion true.

Unaided biting requires μ≥tanα; the stated μ<tanα reverses that inequality.

Therefore the assertion is true but the reason false: **D**.