With the increasing requirements for casting quality and the increasingly stringent regulations on environmental protection and cleaner production, silica sand is not the most ideal raw sand for steel castings, which has become the consensus of many casting professionals. Seeking alternative materials for silica sand has become one of the important research topics in the casting industry. In recent years, the new molding material fused ceramic sand has developed rapidly, especially in the steel casting industry, many enterprises have applied fused ceramic sand.
Disadvantages of silica sand
At present, steel castings are mainly produced by resin sand, sodium silicate sand and other production processes, and the raw sand used is silica sand. Although silica sand is widely distributed and cheap, its disadvantages are also quite obvious.
(1) Poor thermal stability and high coefficient of thermal expansion. The phase transformation of silica sand at about 570 ℃ accompanied by large volume expansion is the root cause of "expansion defects" in castings.
(2) The chemical stability of silica sand at high temperature is not good, and it is easy to react with FeO to produce fusible iron olivine. In the production of large steel castings with thick wall, even the best coating can not solve the problem of serious sand sticking on the surface of castings.
(3) When the old sand is recycled, the silica sand is easy to be broken and the yield is low, and the dust generated by the breaking causes environmental pollution and harms the health of employees. It is difficult to deal with a large number of solid wastes.
Therefore, it is particularly urgent to develop new high-performance molding sand for the production of large steel castings.
Advantages of Fused ceramic sand compared with silica sand
Compared with ordinary silica sand, fused ceramic sand has the characteristics of high refractoriness, small angle coefficient and high regeneration recovery rate. It replaces silica sand for the production of large steel castings, it can not only reduce shrinkage porosity, shrinkage cavity, and eliminate casting defects such as sand sticking, improve the quality of castings, reduce the workload of casting cleaning, but also use nitrogen-containing resins and low-cost coatings, so as to reduce the production cost of castings.
In recent years, fused ceramic sand stands out because of its high refractoriness, small angle coefficient and high recycling rate. More and more foundries use it to replace silicon sand to produce steel castings.
The main advantages of fused ceramic sand are analyzed as follows:
(1) Refractoriness ≥ 1800 ℃, better adaptability under high temperature casting conditions such as stainless steel, which can effectively reduce the defect rate of sand sticking, sintering, veins and other defects of castings.
(2) The low thermal expansion rate can improve the dimensional accuracy of castings; The air permeability and surface accuracy of the casting can be effectively improved due to the low angle coefficient and round grain shape.
(3) The particle shape is similar to the spherical shape, with low crushing rate, recycling and regeneration rate of more than 98%, and the number of renewables is several times more than that of silica sand, showing a more superior recycling performance and greatly reducing the cost of industrial solid waste discharge and treatment of enterprises.
(4) In fact, ceramic foundry sand can be mixed with silica sand, which is not easy to cause segregation.
(5) When using ceramic foundry sand, the dust is greatly reduced, which is green and environmental protection.