Why must South African chromite sand used in casting?
The ore series products mainly include South African foundry grade, chemical grade, refractory grade, metallurgical grade chrome ore, Indian refractory and metallurgical grade chrome ore, Philippine chrome ore and other ore products from many countries. Among them, South African foundry grade chrome ore sells well in more than 20 provinces and cities nationwide, and has won wide acclaim from industry insiders. Let Xiaobian give you a detailed introduction to why chromite sand is popular.
Application of Chromite Sand in Foundry
Chromite sand belongs to chromium spinel, the main mineral composition is FeO·Cr2O3, and 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) Chromium ore has a good effect of resisting alkaline slag, and does not react with iron oxide, etc.; therefore, in practical applications, chrome ore can avoid thermochemical sticking of sand;
(2) During the casting process of molten metal, the chrome 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 larger than that of silica sand, which can improve the cooling rate of castings. Therefore, chrome ore can play the role of external cold iron in practical applications;
(4) The most harmful impurity in chromium ore is carbonate (CaCO3·MgCO3), which decomposes CO2 when it is in contact with high-temperature metal, which is easy to cause pores in castings; 900°C—950°C high temperature roasting to decompose the carbonate.
(5) Influence of particle size of chromium ore on its refractoriness The particle size of chromium ore can significantly affect its refractoriness. In the past, it was believed that too coarse particle size would reduce the surface finish of the casting, but 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.
Generally, the suitable particle size of the sand mold used in the modeling of large steel castings is 40/70 mesh, and the particle size of the sand used for medium and small parts is 50/100 mesh. There are also some special cases such as: some small water pump industries, considering economic factors, replace zircon sand with chrome ore. The chrome ore purchased by these factories is required to be very fine, requiring 70/140 mesh, or even 100/200 mesh, and so on.