Metal Casting and Welding Questions and Answers

Answer: D

The shrinkage allowance is provided to compensate for the contraction of the metal as it cools from the pouring temperature to the room temperature. The pattern is made larger than the casting by this amount. The draft allowance is a taper given for easy removal of the pattern, the machining allowance is extra material for finishing, and the distortion allowance is for warping in casting, so only the shrinkage allowance fits.

The allowance depends on the metal, about 1 percent for cast iron and about 2 percent for steel, and pattern makers use a shrink rule to build it in.

Answer: D

It is the shake allowance.

Before a pattern is lifted out of the sand, it is rapped or shaken so that it loosens, which slightly enlarges the mould cavity. The shake (rapping) allowance compensates for that enlargement; because it acts the opposite way to the other allowances, the pattern is made slightly smaller to allow for it.

The finishing (machining) allowance provides extra metal for machining, the shrinkage allowance makes up for contraction on cooling, and the distortion allowance counteracts warping of irregular castings. None of them is about withdrawing the pattern.