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Types of sand or Base sand


Types of Sand/Base Sand:
        The primary and basic material used for preparing moulds is sand, due to its high refractoriness
        Sand usually referred to as 'base sand‘
        Nearly 90 - 95 % of the total moulding sand is occupied by sand and the remaining is binder and additives.

Basic types of base sand are
ü  Silica Sand
ü  Chromite sand
ü  Zircon
ü  Olivine sand

1)SILICA SAND:
        Silica sand is essentially silicon dioxide (Si02) found in nature on the bottoms and banks of rivers, lakes and seashore
        Silica deposits tend to have varying degree of organic and contaminants like limestone, magnesia, soda and potash that must be removed prior to its use, otherwise which affects castings in numerous ways
        Silica sand is available in plenty, less expensive and possess favourable properties
        Thermal expansion leads to certain casting defects; the reason for which not being used in steel foundries
        However, silica sand when mixed with certain additives like wood flour, (corn flour), saw dust etc., defects can be eliminated
         These additives burn by the heat of the molten metal thereby creating voids that can accommodate the sand expansion
     
2) Chromite sand: this is African sand with cost being much higher compared to other sands
• Due to its superior thermal characteristics, it is generally used in steel foundries for both mould and core making .



3)Zircon or Zirconium silicate: this sand possesses most stable thermal properties of all the above sands. The choice for this type of sand arises when very high temperatures are encountered and refractoriness becomes a consideration.
• But the major disadvantage is that, zircon has trace elements of Uranium and Thorium which is hazardous in nature thereby restricting its use in foundries.

4)Olivine sand:  is typically used in non-ferrous foundries. With its thermal expansion about half of that of silica sand, makes it suitable for production steel castings .But the high cost restricts its wide use.


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