JNTU B.Tech II PRODUCTION TECHNOLOGY Previous Question Paper (October - 2020 - R18)

Moulding sand must possess specific characteristics to produce high-quality castings. The key properties include:

• Refractoriness: The ability of the sand to withstand high temperatures of molten metal without fusing or softening.
• Permeability: The porosity of the sand that allows gases and steam generated during pouring to escape through the mould walls, preventing defects like blowholes.
• Flowability: The capacity of the sand to behave like a fluid and pack into intricate patterns and corners of the mould under pressure.
• Cohesiveness (Bond Strength): The ability of sand particles to stick together, providing sufficient strength to maintain the mould shape against the pressure of molten metal.
• Adhesiveness: The ability of the sand to stick to the sides of the moulding box or flask.
• Collapsibility: The ability of the sand to yield during the contraction of the cooling metal, preventing hot tears or cracks in the casting.

Working Principle: Centrifugal casting involves pouring molten metal into a rotating mould. The mould is rotated at high speeds about its central axis, creating a strong centrifugal force that throws the molten metal against the inner walls of the mould. This force ensures the metal is distributed uniformly and forces out impurities and gases towards the center, resulting in a dense, fine-grained, and high-strength casting. The process does not require a core to create a central hole, as the internal diameter is determined by the amount of metal poured.

Applications: This method is primarily used for producing hollow, cylindrical, or symmetrical parts. Common applications include:

• Manufacturing of cast iron and steel pipes.
• Production of cylinder liners for internal combustion engines.
• Fabrication of high-pressure boiler tubes and bushings.
• Creation of large gear blanks and piston rings.
• Manufacturing of jet engine components where high structural integrity is required.