JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B. Tech II MANUFACTURING PROCESS Previous Question Paper (September/October - 2023 - R16)

A pattern is a replica of the object to be cast, used to create a cavity in the molding sand. The following are four common types of patterns used in foundry practice:

• Solid (Single-Piece) Pattern: The simplest type, consisting of a single piece without any joints or loose parts. It is used for large, simple castings where the mold is relatively shallow.
• Split Pattern: Consists of two or more parts that are joined together using dowel pins. This type is used when the shape of the casting is complex, making it difficult to withdraw a single-piece pattern from the mold.
• Match Plate Pattern: In this type, the cope and drag portions of a split pattern are mounted on opposite sides of a metal or wooden plate. This facilitates high-speed production in machine molding.
• Sweep Pattern: Used for generating large circular or symmetrical shapes (like gears or wheels) by rotating a shaped wooden board (the sweep) around a central vertical axis in the molding sand.

Moulding sand is the primary material used in sand casting to create the mould cavity. To ensure the production of high-quality castings, the sand must possess specific physical and chemical properties:

• Refractoriness: The ability of the sand to withstand high molten metal temperatures without fusing or softening. High refractoriness prevents the sand from sticking to the casting surface, ensuring a smooth finish.
• Permeability: The porosity of the sand that allows gases, steam, and air generated during pouring to escape through the mould. If permeability is low, trapped gases cause defects like blowholes or porosity in the casting.
• Cohesiveness (Bond Strength): The ability of sand particles to stick together. This is essential for the mould to retain its shape and withstand the pressure exerted by the molten metal.
• Flowability: The capacity of the sand to behave like a fluid and fill the intricate details of the pattern when rammed. High flowability ensures uniform density throughout the mould.
• Collapsibility: The ability of the mould to break down easily after the metal has solidified and cooled. This allows the casting to shrink freely, preventing hot tears or cracks caused by residual mould stress.
• Adhesiveness: The property that allows the sand to stick to the surfaces of the moulding box and other objects, ensuring the mould remains intact during handling.