Application of chromite sand in foundry

Chromite sand belongs to the chromium spinel group. The main mineral composition is FEO•CR2O3. The actual mineral is composed of a mixture of various spinels. The density of chromite sand is 4—4.8g/cm3, the Mohs hardness is 5.5—6, and the refractoriness is >1900°C. The main properties of chrome ore (1) Chrome ore has a good effect of resisting alkaline slag, and does not react with iron oxide; therefore, in practical applications, chrome ore can avoid thermochemical sand sticking; (2) In molten metal During the 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 chromium ore is several times greater than that of silica sand, which can increase the cooling rate of castings. Therefore, chromium ore It can play the role of external cold iron in practical applications; (4) The most harmful magazine in chrome ore is carbonate (CACO3•MgCO3), which decomposes CO2 when it comes in contact with high-temperature metals, which is easy to cause porosity in castings ; Normally, the chromium ore containing carbonate is roasted at a high temperature of 900°C-950°C to decompose the carbonate. (5) The influence of the particle size of chrome ore on its refractoriness The particle size of chrome ore can significantly affect its refractoriness. In the past, it was believed that too coarse particle size would reduce the surface finish of castings. However, the surface of sand molds and cores made of chrome ore are usually sprayed with a certain thickness of paint, so that the surface finish of the castings is hardly affected. Generally, the suitable size of the sand mold used for large-scale steel casting is 40/70 mesh, and the size of the sand used for medium and small parts is 50/100 mesh. There are also special circumstances such as: some small water pump industries, considering economic factors, use chromium ore instead of zirconium sand. The chromium ore purchased by these factories is required to be very fine, requiring 70/140 mesh, or even 100/200 mesh, and so on. The application object of chrome ore is mainly large-scale low-carbon steel castings. Steel castings such as Dalian Heavy Industry and Erzhong are often more than tens of tons. Such large steel castings are most suitable for the use of chrome ore as the molding material. Generally, chrome ore is required. The particle size is 40/70 mesh, or even coarser. However, in the past ten years, small castings in the automobile engine industry have also used a large number of chrome ore moldings. This is mainly due to the high refractoriness of chrome ore, which can result in smooth and high-quality castings.