Depending on the purity and other ingredients are present, sand is classified into (i) Natural sand. (ii) synthetic sand, (iii) sand loam.
(i) Natural sand: natural sand is used directly for molding and 5-20% of clay as binding material. It needs 5-8% for mixing water before making the mold. Natural sand is quite wide working range of moisture and are able to retain the moisture content for long. The main disadvantage is that it is less refractory compared with synthetic sand. There are many natural sand molding weak properties. The sand is restored by small amounts of a binding material such as bentonite to improve their properties and are called semi-synthetic sand mix.
(II) synthetic Sands: synthetic sand consists of silica sand with or without clay, binder or moisture. It is a combined sand ie sand made by various constituents. Sand formulations made more certain desired properties possessed by natural sand. The sand is better casting properties such as permeability and refractoriness and is ideal for casting non-ferrous and ferrous materials. The symptoms can be controlled by mixing different ingredients. Synthetic sand used for making heavy castings.
(III) Loam Sand: sand loam has many ingredients, such as fine particles of sand, finely ground refractories, clay, graphite and fiber reinforced. In many cases, the material can be clay the order of 50% or more. When mixed with water, the mixture of materials such as mortar and consistency to be hard after drying. Large molds for casting made of brick framework lined with sand loam and dried. Sweeping etc used for making large castings like big bells by using sand loam.
Refractory sand grains: sand grain size and shape have a significant effect on the properties of molding sand. The unique surface rough idea of the amount needed for molding sand binder.