GATE 2017 ME (ME2) – Question 62
A 120 mm wide, 8 mm thick strip passes between two 300 mm diameter rolls to become 7.2 mm thick, retaining its width. Exit speed is 30 m/min. With no front/back tension, uniform roll pressure 200 MPa and 100% mechanical efficiency, minimum total roll-drive power is ______ kW.
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Correct answer: 8.5 to 10.0
Explanation
Thickness reduction is0.8mm and roll radius is150mm. Projected contact length is√(RΔh)=√120=10.954mm. Roll force is200·120·10.954=262907N. Taking the resultant at half the contact length, each roll torque is F·L/2. Using roll peripheral speed approximately equal to exit speed0.5m/s gives total power F·L·v/R=**9.6kW**, within the official8.5–10.0kW range.