Core and its Characteristics

Explain core and its characteristics.

Core and its Characteristics

Sometimes a casting is to be made either hollow or with few holes, cavities or pockets in it. This makes the casting quite difficult to mold. Use of cores simplifies this problem. Cores are made from special core sands. The contours of a core are exactly similar to the cavities, pockets or holes it is supposed to provide in the casting. Cores eliminate much of machining of the castings and give strength to the mold.

The core is made in a core box. For molding a straight two-flanged pipe, core and core box arc shown in Figure. A core print forms a seat in the mold and is used to support and locate the core at desired position.

A core should have the following characteristics:

(a) Permeability

A core is supposed to be mere permeable than a mold and for this reason, sand with large grains is preferred for core making. Vents are also provided in core for giving easy escape to the gases that get generated during casting.

(b) Collapsibility

A core should be capable of collapsing shortly after the molten metal has solidified around the core. This property can be encouraged by using oil binding materials. Collapsibility provides freeness in the contraction of metal.

(c) Thermal Stability

According to the service conditions to which a core is subjected, core sand should be highly refractory otherwise defects like rough surface, and metal penetration may occur. Some suitable blacking should be applied On core before setting it in a mold.