Core sand

Core sand:-
The core sand should contain grains, binders and additives.
Sand- The silica sand without clay is used as a core sand material. Coarse silica is used in steel foundries where as fine silica is used for cast iron and non ferrous alloys.
Binders:- The normal binders used are organic in nature, because this will burnt away by the heat of molten metal and make the core collapsible during cooling. The binders generally used are linseed oil, core oil, resins, dextrin, molasses etc. Core oils are the mixture of linseed, soy, fish, petroleum oils and coal tar.
Types of cores:-
Two types:-
(a) Green sand core:- This is obtained by the pattern itself during moulding. Green sand has low strength, so is not suitable for deep holes.
(b) Dry sand core:- This is made with special core sands in separate core box, baked & placed in mould. Different types of dry sand cores are
-Unbalanced core -cover core -drop core
-balanced core -vertical core
Core prints:-
Core prints are used to position the core securely and correctly in mould cavity. It should take care of the weight of the core and upward metallostatic pressure of molten metal.