PRINCIPAL INGREDIENTS OF MOULDING SANDS :
The principal ingredients of moulding sands are given below :
(1) Silica sand grains
(2) Clay
(3) Moisture
(4) Miscellaneous materials
>> SILICA SAND GRAINS :
Silica in the form of granular quartz, itself a sand, is the chief constituent of moulding sands.silica sand contains from 80% to 90% silicon dioxide and is characterized by a high softening temperature and thermal stability.it is a product of the breaking up of quartz rocks or the decomposition of granite, which is composed of quartz and feldspar.
>> CLAY :
Clay is defined as those particles of sand ( under 20 microns in diameter ) that fails to settle at a rate of 25mm per minute, when suspended in water. Clay consists of two ingredients : FINE SILT and TRUE CLAY. Fine silt is the sort of foreign matter or mineral deposit and has no bonding power. It is the true clay which imparts the necessary bonding strength to the mould sand, so that the mould does not lose its shape after rimming. Most moulding sands for different grades of work contain 5% to 20% clay.
>> MOISTURE :
Moisture in requisite amount, furnished the bonding action of clay. When water is added to clay, it penetrates the mixture and forms a microfilm which coats the surface of flake-shaped clay particles. The bonding quality of clay depends of the maximum thickness of water film it can maintain. The bonding action is considered best if the water added is the exact quantity required to form the film. The water should be between 2% to 8% .
>> MISCELLANEOUS MATERIALS :
Miscellaneous materials that are found, in addition to silica and clay in moulding sand are oxide of iron, limestone, magnesia, soda, and potash. The impurities should be below 2% .
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