Core is a sand body specially prepared in a core box and it is used to form a cavity/hole/recess or projection in a casting for different purposes. As core is surrounded by liquid metal from all the sides, it has to have better characteristics than the moulds. Better raw sand and binder are used for the purpose. The main characteristics of core are highly permeable, highly refractory, hard, and high collapsible. Various types of cores are shown in Figure 20.18.
Figure 20.18 Types of Cores
Horizontal Core: Horizontal core is used to provide a hole in the casting from one end to other end and lies axially horizontal. Both the ends of core are supported in the mould. Generally, it is located at parting line but its location depends on shape. In the case of uniform core, it is located at parting line.
Vertical Core: This is similar to horizontal core but lies axially vertical. It is supported by core prints in drag and cope. It is slightly tapered and its major part lies in drag.
Balanced Core: This is just like a cantilever. Its one end is supported in mould and the other end is free. It is used to produce a blind hole in a casting.
Hanging Core: Hanging core is supported only at the tope in the cope and there is no support at the bottom. The whole portion of the core lies in the cavity in the drag of the mould. It is also known as cover core since it acts as a cover for the cavity.
Drop Core: A drop core is required when hole is not in line with the parting surface but must be formed at lower level. Its one side remains flush with the inner surface of the mould and back is provided with enough taper for its location.
Kiss Core: Kiss core is held vertically in the mould. It is not supported by the core print. It is held vertically due to pressure of the cope and drag part of the mould.
Core Print: Core print is a sand body, which is used to give support to the core.
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