What are the different types of Molding Sand?
Molding sands can also be classified into various types according to their use are backing sand, core sand, dry sand, facing sand, green sand, loam sand, parting sand, system sand.
1.Backing sand or floor 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. Backing sand is sometimes called black sand because old, repeatedly used molding sand is black in color due to the addition of coal dust and burning on coming in contact with the molten metal.
2. Core sand
Core sand is used for making cores and it is sometimes also known as oil sand. Core sand 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. Pitch or flours and water may also be used in large cores for the sake of the economy.
3. Dry sand
Greensand that has been dried or baked in a suitable oven after making mold and cores is called dry sand. It possesses more strength, rigidity, and thermal stability. Dry sand is mainly used for larger castings. Mold prepared in this sand is known as dry sand molds.
4. Facing sand:
Facing sand forms the face of the mold. It is next to the surface of the pattern and it comes into contact with molten metal when the mold is poured. The initial coating around the pattern and hence for mold surface is given by facing sand. Facing sand has high strength refractoriness. Facing sand is made of silica sand and clay, without the use of already used sand. Different forms of carbon are used in facing sand to prevent the metal from burning into the sand. A facing sand mixture for green sand of cast iron may consist of 25% fresh and specially prepared and 5% sea-coal. They are sometimes mixed with 6-15 times as much fine molding sand to make facings. The layer of facing sand in a mold usually ranges between 20-30 mm. From 10 to 15% of the whole amount of molding sand is the facing sand.
5. 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% 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. Greensand is damp when squeezed in the hand and it retains the shape and the impression to give to it under pressure. Molds prepared by this sand are not requiring backing and hence are known as green sand molds. Greensand is easily available and it possesses low cost. Greensand is commonly employed for the production of ferrous and non-ferrous castings.
6. Loam sand
Loam sand is a mixture of sand and clay with water to a thin plastic paste. Loam sand possesses high clay as much as 30-50% and 18% of water. Patterns are not used for loam molding and shape is given to mold by sweeps. Loam sand is particularly employed for loam molding used for large grey iron castings.
7. 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 to the parting surface the cope and drag to separate without clinging. Parting sand is clean clay-free silica sand that serves the same purpose as parting dust.
