Core:
Cores are pieces that are placed into casting moulds to form internal cavities of the casting. Cores can be made from metal or chemically bonded sand. It is inserted into the mould cavity prior to pouring. The molten metal flows and solidifies between the mould cavity and the core to form the casting's external and internal surfaces. Shaken out after finished casting is produced.
Essential Qualities of a Core:
The cores are subjected to severe thermal and mechanical effects than the mould. Because, they surrounded on all sides by molten metal. They must possess some special requirements which are as follows:
• A good core must have sufficient strength and hardness to retain its shape and to resist during the pouring of liquid metal.
• Sufficient permeability is also necessary for the escape of gases generated during the casting process.
• Cores should be highly refractory to resist cracking on contact with high temperature molten metal.
• A core should be capable of collapsing shortly after solidification.
Advantages of a Core:
• To provide internal holes and cavities.
• Intricate castings can be produced.
• Core may be used as part of mould.
• Improves strength of mould surface.
• Used as part of gating system.
Types of Core:
According to state of core the cores can be classified into;
• Green sand cores: These are prepared by green sand.
• Dry sand cores: These are prepared by synthetic sand and baked in oven
• Oil sand cores.
• Loam sand cores.
According to the position of the core in the mould;
• Horizontal core.
• Vertical core.
• Balanced core.
• Cover core
• Hanging core
• Wing core.
Horizontal Core:
The Core is cylindrical in form and is positioned horizontally at the parting line of the mould.
The ends of the core rests in the seats provided by the core prints on the pattern.
Vertical Core:
Usually top and bottom of the core provided with taper.
The taper in top is larger than bottom side, so that it does not damage the mould.
Balanced Core:
It is suitable to castings which have an opening on one side. This core is similar to horizontal core and is supported at one end only. Its extends horizontally in the mould. One side core print only available in the mould.
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