It describes the basic properties required in molding sand and sand core as under.
1) refractoriness. Refractoriness is defined as the ability of molding sand to withstand high temperatures without breaking down or fusing which facilitates to find sound solutions. It is a very important characteristic of sand molding. Refractoriness increase can only to a limited extent. Can refractoriness molding sand with a bad burn on to the casting surface and one can not get rid of surface solutions. The amount depends on the SiO2 refractoriness ie quartz material, and the shape and grain size of the particle. The higher the SiO2 content and the volumetric composition coarse grain the higher the refractoriness of the molding sand and core sand. Refractoriness is measured at the point sinter the sand rather than melting.
2) Permeability. It is also termed as the molding sand porosity to allow the escape of any air, gas or moisture present or generated in the mold when the molten metal is poured into it. All the gaseous generated during pouring and solidification process must escape becomes otherwise the faulty solutions. Permeability is a function of grain size, grain shape, and moisture and clay content in the sand molding. Size of ramming the sand directly affect the permeability of the mold. Mold permeability can be further increased by using rods loose vent
3) coherence. It is the property of molding sand by virtue of interacting particles and sand grains attract each other within the molding sand. Thus, the capacity of the molding sand gets enhanced binding to take to increase the green, dry and warm properties and core strength molding sand.
4) Green strength. The green sand after water mixed into it, must have sufficient strength and toughness to allow for and handle the model. So the sand grains must be adhesive, ie they must be able to attach themselves to another body. therefore, will and grain of sand is high adhesiveness cling to the side of the molding box. Also, have the grains of sand are the property called coherence ie the ability of sand grains to stick together. By virtue of this property, the pattern can be taken out of the mold without breaking the model and also the mold wall surfaces erosion does not occur during the flow of molten metal. The green strength also depends on the grain shape and size, amount and type of clay and moisture content.
5) Dry strength. Once the molten metal is poured into the mold, have the moisture in the layer of sand near the hot metal gets evaporated and the layer of dry sand sufficient strength to shape in order corrosion wall mold to avoid during the flow molten metal.
6) Flowability or plasticity. It is the ability to obtain the compacted sand and behave like a fluid. It will flow uniformly to all parts of a pattern when rammed and evenly distributed on the pressure ramming all around in all directions. Generally resist sand particles move around corners or projections. In general, increases flow capacity to reduce green strength, a reduction of grain size. Does the flow capacity as well as moisture and clay content.
7) adhesiveness. It is the property of molding sand stick to obtain or comply with such sticking foreign matter of sand molding to molding inner wall of the box.
8) collapsibility. After the molten metal gets the solidified mold,must be collapsible so free shrinkage occurs on the metal and this would naturally avoid the tearing or cracking of the metal contracting. In the absence of this property that the contraction of the metal barrier at the mold and thus results in tears and cracks in casting. This property is highly required in cores.
9) Miscellaneous properties. In addition to the above requirements, the molding sand should not comply with the resolution and should not react chemically with the metal. Moulding sand should be free and easily available. Should be reusable for economic reasons. Should its relatively low coefficients of expansion.