The main properties of chrome ore
(1) Chromium ore has a good anti-alkaline slag effect and does not react with iron oxide; therefore, in practical applications, chrome ore can avoid thermochemical sticking of sand;
(2) During the molten metal casting process, the chromium ore itself undergoes solid-phase sintering, which prevents the penetration of molten metal, thereby preventing mechanical sand sticking;
(3) The thermal conductivity of chrome ore is several times greater than that of silica sand, which can increase the cooling rate of castings. Therefore, chrome ore can play the role of an external cooling iron in practical applications;
(4) The most harmful impurity in chrome ore is carbonate (CaCO 3 ·MgCO 3 ), which decomposes into CO 2 when in contact with high-temperature metals, which easily causes pores in castings; usually, chrome ore containing carbonate Calcined at a high temperature of 900°C-950°C to decompose the carbonate in it.
(5) The particle size of chrome ore affects its refractoriness. The particle size of chrome ore can significantly affect its refractoriness. In the past, it was believed that if the grain size was too coarse, the surface finish of the casting would be reduced. However, the surface of the sand mold and sand core made of chrome ore is usually sprayed with a certain thickness of paint, so that the surface finish of the casting is hardly affected.
Application of Chromite Sand in Foundry
Foundry grade chrome ore composition indicators: quality requirements: in line with technical standards JB/T6984-1993, the specific requirements are as follows
Particle size: 20-40 mesh; 20-70 mesh; 20-80 mesh; 20-100 mesh; 40-70 mesh; 50-100 mesh; 70-140 mesh; 220 mesh; Used as raw material for drainage sand, casting, ceramics, glass and refractory materials, etc.
Generally, the suitable grain size of the sand mold used in the molding of large steel castings is 40-70 mesh, and the sand grain size of the sand used for medium and small castings is 50-100 mesh. There are also some special cases such as: some small water pump industries, considering economic factors, use chrome ore sand instead of zircon sand. The chrome ore sand purchased by these factories is required to be very fine, requiring 70-140 mesh, or even 100-200 mesh, etc.
The application object of chrome ore is mainly large-scale low-carbon steel castings. The steel castings of Dalian Heavy Industry Co., Ltd. are often more than tens of tons. Such large steel castings are most suitable to use chrome ore as the molding material. Generally, the particle size of chrome ore is required to be 40-70 mesh, or even thicker. However, in the past ten years, a large number of small castings in the automotive engine industry have also used chrome ore sand molding. This is mainly because of the high refractoriness of chrome ore sand, which can produce smooth and high-quality castings.
