Molding sand:
In the process of casting sand, molding sand (foundry sand) is used to create mould. On the bottom and banks of rivers and lakes, molding sand can be discovered. Because of natural forces such as wind, rain, water currents and heat, it is created by rock breakdown.
Main constituents of Molding sand:
Silica sand– Molding sand that contains 80 to 90 percent silicon oxide is the main component. In the process of casting sand, molding sand (foundry sand) is used to create mould. On the bottom and banks of rivers and lakes, molding sand can be discovered. Because of natural forces such as wind, rain, water currents and heat, it is created by rock breakdown.
Binder–The binder's aim is to deliver bonding action and strength. The binder is lowering the permeability. Clay is used as a binder for the most part. The content of clay ranges from 6% to 10%.
Water– Water enables plasticity and strength to create clay. The clay absorbs water to a certain limit. The extra water functions as a lubricant to make the sand more moldable, but it may reduce the strength.
Properties of molding sand:
Permeability (Porosity)–Sand is known as permeability or porosity to enable gasses, water and steam vapors to pass through it. The sand's permeability relies on the following variables.Sand grain size and grain shape. The round shape is more conducive to gas and steam vapor flight.
- Sand grain size and grain shape. The round shape is more conducive to gas and steam vapor flight.
- The content of moisture is greater, the permeability is less.
Adhesivity – Sand particles should stick specifically to the molding box to the other organs so that the sand mass can be correctly kept in the box and does not drop while moving the mold.
Cohesiveness– Particles of the sand should be able to stick together. When the mould is filled with molten metal, cohesion must be retained and it should not be washed away during pouring. Cohesivity relies on grain form and size. It also relies on binding material being distributed in the sand.
Plasticity– Plasticity is the material property of acquiring required shape under stress and retaining it after stress removal. In order to have a good feeling of mould pattern, sand should have excellent plasticity.
Green strength– Sand strength is called green strength in its moist phase. In its moist and dry condition, the sand should have sufficient power. The sand adjacent to metal dries when we pour the molten metal and it shouldn't erode.
Refractory–Sand's capacity to resist elevated heat without breaking or burning is called refractory. It is possible to improve the refractory by removing the impurities.
Chemical resistivity–The sand should not respond chemically with the molten metal to create mould for a long moment.
