Is a higher chromium content always better for foundry-grade chromite sand?
For foundry – grade chromite sand, a higher chromium content is not always better. The appropriate chromium content should be determined according to specific casting requirements. The following is a detailed analysis:
- Advantages of higher chromium content
- Enhanced refractoriness and chemical stability: Chromium oxide (Cr2O3) is a key component of chromite sand. A higher Cr2O3 content means higher refractoriness. In the casting of large – scale steel castings, high – chromium – content chromite sand is not easy to react with molten steel and its oxides at high temperatures, which can effectively prevent chemical sand – sticking, ensuring the surface finish of castings and meeting the strict requirements of high – end castings for sand performance.
- Stronger anti – sand – sticking ability: Chromite sand with a high chromium content has good solid – phase sintering characteristics. During the pouring process, solid – phase sintering can close the gaps between particles. In addition, chromite sand is not wetted by molten steel, and its high – temperature thermal conductivity is about 4 times that of zircon sand, with good chilling properties. These factors can jointly prevent the penetration of molten steel into the coating, improving the sand’s ability to resist mechanical penetration and sand – sticking.
- Disadvantages of excessive chromium content
- Increased cost: Natural chromite sand usually contains a certain amount of chromium. To increase the chromium content, processes such as magnetic separation and flotation are required. If an extremely high chromium content is required, the complexity and energy consumption of the purification process will increase significantly, leading to a multiple – fold increase in the purchase price of the sand, which is not cost – effective for some ordinary castings.
- Unnecessary performance surplus: For some ordinary cast steel and cast iron parts with lower pouring temperatures (1300 – 1500°C), as long as the chromium content of chromite sand can meet the basic requirements (such as 35% – 45%), it can already meet the needs of preventing sand – sticking and ensuring casting quality. There is no need to pursue a very high chromium content, because excessive chromium content will not bring obvious performance improvements in this case, but will only cause a waste of resources.