Difficulty: Easy
Correct Answer: Castings produced by centrifugal casting have an open, coarse-grained structure.
Explanation:
Introduction / Context:
Different casting processes suit different alloys and quality requirements. Correctly pairing process and material is essential. This question tests recognition of standard pairings and the typical microstructure from centrifugal casting.
Given Data / Assumptions:
Concept / Approach:
Hot-chamber machines immerse the shot sleeve in molten metal and are suitable for low-melting, non-corrosive alloys (zinc, tin, lead). Cold-chamber machines ladle metal into a separate shot sleeve and are used for higher-melting or more aggressive alloys (aluminium, some magnesium, copper-base). Centrifugal casting produces dense, fine, and relatively sound structures at the outer periphery due to high centrifugal pressure; porosity segregates toward the inner surface and can be machined away. Therefore, calling centrifugal castings “open, coarse-grained” is wrong.
Step-by-Step Solution:
Validate (a): matches low-melting alloys → correct.Validate (b): matches higher-melting alloys → correct.Check (c): contradicts known densification in centrifugal casting → this is the wrong statement.Hence, choose option (c) as the incorrect one.
Verification / Alternative check:
Metallographic sections of centrifugally cast pipes show fine-grained, dense outer layers with directional solidification; defects concentrate near the bore.
Why Other Options Are Wrong:
“All of the above” cannot be correct because one statement is demonstrably false.
“None of the above” is also incorrect for the same reason.
Common Pitfalls:
Confusing semi-solid casting with die casting selection; assuming magnesium always requires hot-chamber—many Mg alloys are run in cold-chamber due to reactivity.
Final Answer:
Castings produced by centrifugal casting have an open, coarse-grained structure.
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