WHAT IS SAND MOULDING PROCESS? FEW KINDS OF MOULDING SAND'S

Molding which is prepared with sand is know Sand Molds or Temporary Molds as they Broken when we remove the casting.The major production of casting is in Sand Molds.About 4 to 5 Tons of molding sand may be required to produce 1 ton of castings.The most commonly used for making all types of molds irrespective of whether they are used for producing castings of ferrous or non-ferrous metals.Most sand casting operations are used silica sand.And the sand which is used to manufacture a mould for casting process is held by mixture of water and clay.A typical mixture by volume could be 89% Sand,4% Water and 7% Clay.

Molding sands can also be classified according to their use into number of varieties which are described below.





1. Green sand: 
Green sand is also known as tempered or natural sand which is a just prepared mixture of silica sand with 18 to 30 percent clay, having moisture content from 6 to 8%. The clay and water furnish the bond for green sand. It is fine, soft, light, and porous.



2. Dry sand: 
Green sand that has been dried or baked in suitable oven after the making mold and cores, is called dry sand. It possesses more strength, rigidity and thermal stability.

3. Loam sand: 
Loam is mixture of sand and clay with water to a thin plastic paste. Loam sand possesses high clay as much as 30-50% and 18% water.

4. Facing sand: 
Facing sand is just prepared and forms the face of the mould. It is directly next to the surface of the pattern and it comes into contact molten metal when the mould is poured. Initial coating around the pattern and hence for mold surface is given by this sand. This sand is subjected severest conditions and must possess, therefore, high strength refractoriness.

5. Backing sand: 
Backing sand or floor sand is used to back up the facing sand and is used to fill the whole volume of the molding flask.

6. Parting sand: 
Parting sand without binder and moisture is used to keep the green sand not to stick to the pattern and also to allow the sand on the parting surface the cope and drag to separate without clinging



7. Core sand: 
Core sand is used for making cores and it is sometimes also known as oil sand. This is highly rich silica sand mixed with oil binders such as core oil which composed of linseed oil, resin, light mineral oil and other bind materials.

Characteristic of Molding Sand :-

1. Molding Sand are refractory in nature and can withstand temperature of metal being poured without fusing. 
2. The molding sand do not chemically react with molten metal.
3. The sand have high degree of permeability and thus allow gases formed during pouring to escape.
4. These strength, permeability and hardness of the sand mix can be varied by changing the structure of sand.