GATE 2021 ME (ME1) – Question 46

Casting, Forming and Joining Processes · Casting: patterns, moulds, cores, solidification, riser and gating design, defects · 2 marks · Numerical answer

A true centrifugal casting operation needs to be performed horizontally to make copper tube sections with outer diameter of 250 mm and inner diameter of 230 mm. The value of acceleration due to gravity, $g=10$ m/s². If a G-factor (ratio of centrifugal force to weight) of 60 is used for casting the tube, the rotational speed required is _____ rpm (round off to the nearest integer).

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Correct answer: 662

Explanation

At the outer mould radius R=0.125 m, G-factor is $\omega^2R/g$. Thus $\omega=\sqrt{60(10)/0.125}=69.2820$ rad/s.

Convert to rpm: $N=60\omega/(2\pi)=661.5947$. **Answer: 662 rpm**. Inner diameter does not set the mould-wall centrifugal acceleration.