Silica sand has always been the main raw sand used in foundry industry all over the world.
At present, the foundry industry worldwide consumes no less than 60million tons of raw sand every year, of which silica sand accounts for more than 97%. Among the silica sands, the amount of natural granular sedimentary sand is the largest, and the amount of artificial silica sand made of broken quartzite is very small. The most desirable feature of silica sand is that it is abundant in reserves and cheap and easy to obtain, which is unmatched by any other mineral sand. In addition, it also has some characteristics that can adapt to the casting conditions, such as:
It has enough high refractoriness to withstand the pouring temperature of most casting alloys. The particles are hard and can withstand the pounding and compression during molding and the impact and friction during old sand regeneration. It still has enough strength to maintain its shape near its melting point.
However, silica sand also has many disadvantages, mainly including:
Poor thermal stability, phase transformation at about 570 ℃, accompanied by large volume expansion, is the root cause of various "expansion defects" in castings, and is also the main factor affecting the dimensional accuracy and surface roughness of castings.
At high temperature, the chemical stability is not good, and it is easy to produce fusible iron olivine with FeO, resulting in sand sticking on the surface of the casting. The dust generated by crushing is prone to silicosis.
Nowadays, with the increasing requirements for the quality of castings and the increasingly stringent regulations on environmental protection and cleaner production, silica sand is not the ideal raw sand, which has become the consensus of many foundry men. Seeking the substitute material of silica sand has become one of the important research topics in the current foundry industry, and all industries attach great importance to it.
At present, the non-siliceous sand used in the foundry industry mainly includes forsterite sand, zirconium sand and chromite sand.
Zirconium sand has a variety of characteristics suitable for casting raw sand, and is an ideal molding material. However, the reserves of zirconium sand in the world are small, mainly produced in Australia and South Africa, and the high price restricts its application in casting production, which is only widely used in investment casting.
Forsterite sand and chromite are abundant and cheaper than zirconium sand, but both are made from crushed ore, with poor grain shape and much more expensive than silica sand. At present, they are only used for some steel castings. Another way to seek substitute for silica sand is to develop manufactured granular materials. The research and development work in this area has been carried out for more than 40 years, and has gradually entered the practical application stage in the past 10 years, and has shown good results in the foundry industry in various countries.