Question

The impurities in centrifugal casting are

• A. forced outside the surface
• B. collected in the centre of casting
• C. present in the middle section of casting
• D. do not entre into the casting

Hint:

Think of a salad spinner. The water (heavier) is thrown to the outside, while the lettuce leaves (lighter) stay more towards the inside. In centrifugal casting, the dense metal is thrown to the outside, and the lighter impurities are pushed to the inside (the center).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Centrifugal casting is a process where molten metal is poured into a rotating mold. The high-speed rotation generates a strong centrifugal force that pushes the molten metal against the inner walls of the mold. This force influences the distribution of the metal and any impurities within it.

Step 2: Detailed Explanation:
The principle of separation in centrifugal casting is based on density differences.

• The centrifugal force acts outwards from the center of rotation.

• Molten metal, being dense, is thrown with great force against the outer mold wall, where it solidifies.

• Impurities, such as slag, dross, and non-metallic inclusions, are generally less dense than the molten metal.

• Because they are lighter, these impurities are displaced by the heavier metal and are forced to float inwards, towards the center of rotation.

• As a result, the impurities segregate and become concentrated at the free inner surface of the casting (i.e., in the centre of a hollow cylindrical casting). This impure layer can then be machined away, leaving a sound, dense, and clean outer casting.
Therefore, the impurities are collected in the centre of the casting.

Step 3: Final Answer:
Due to the density difference, the less dense impurities are displaced by the heavier molten metal and accumulate at the inner radius, or the centre of the casting.