Types of Molding sand in Casting Process
Natural sand with moisture
Not suitable for large castings
This sand is used directly next to the surface of the pattern and comes into contact with the molten metal when the mould is poured.
As a result, it is subjected to the severest conditions and must possess, therefore, high strength and refractoriness. This sand also provides a smoother casting surface and should be of fine texture. It is made of silica sand and clay, and some additives without the addition of used sand.
Facing sand is always used to make dry sand moulds while system sand is frequently used for green sand molding.
This sand is used to prevent adhering of two halves of mould surfaces in each molding box when they are separated. Thus, to ensure good parting, the mould surface (at contact of cope and Drag) should be treated with parting sand or some other parting material.
It is also sprinkled or applied on the pattern surface (before the molding sand is put over it) to avoid its sticking and permit its easy withdrawal from the mould. The parting sand is fine dry sand.
This is the sand which is used to back up the facing sand and to fill the whole volume of the flask. Old, repeatedly used molding sand is mainly employed for this purpose.
The core sand mainly consists of silica sand and an organic binder, with very little, if any, clay content. The presence of clay in core sand reduces its permeability and collapsibility. The core sand may contain small percentages of other constituents also, to enhance its properties.
50 % of clay and dried hard and using for large castings