GATE 2026 PI – Question 46
A 200 mm wide, 23 mm thick strip must be rolled to 20 mm in one pass with 200 mm diameter rolls. Available lubricants P,Q,R,S have friction coefficients 0.05,0.1,0.2,0.25. Width remains constant. Which ONE OR MORE lubricants permit the required draft?
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Correct answer: (C) R; (D) S
Explanation
Maximum draft is approximately $\Delta h_{max}=\mu^2R$. Here R = 100 mm and required draft is 3 mm, so $\mu\ge\sqrt{3/100}\approx0.1732$. Coefficients 0.2 and 0.25 satisfy this, whereas 0.05 and 0.1 do not. **R,S: C,D**.