The sand sticking is very harmful to steel castings. How to eliminate the effect is very important for foundry plants. Foundry grade Iron Chromite Sand could help to do the task.
For large castings of above 500 kilograms or heavier super large castings, the surface area and wall thickness of the castings are higher. When molten steel is poured, there gets an intense thermal impact of high-temperature molten steel on the surface of the shell.
When the molten steel is injected into the mold shell, the surface temperature of the mold shell can reach over 1400 degrees, and the molten steel and the molding sand will react chemically. The low-melting substance iron spinel, iron olivine, sodium dimetasilicate, etc. formed by the reaction will form crystals during the cooling and solidification process of the casting. When these crystals are similar to the crystal lattice on the surface of the casting, they will firmly stick to the casting. On the surface, chemical sticky sand is formed. This kind of chemical sticky sand is difficult to clean up. Thus, it will increase the cost and workload of post-processing. Some castings with thicker walls will also produce shrinkage holes or porosity defects.
The Advantages of Iron Chromite Sand including:
- high Cr2O3 purity above 46%
- low SiO2 content within 1%
- low dust and high cleanness
- high refractory temperature above 1900 degree
- low thermal expansion
- high thermal conductivity
- It can effectively avoid casting defects such as chemical sand sticking and shrinkage cavities and porosity.
By adopting iron chromite sand works for steel foundry as the surface sprinkling and the second layer sprinkling. It can eliminate sticking sand defects. Below shows why that occur:
- First of all, the wetting angle of the stainless steel molten steel and the chromite sand surface at 1500 degrees is 100 degrees, and the wetting angle of the No. 45 carbon steel molten steel with the chromite sand at 1357 degrees is about 95 degrees. The wetting angle in both above cases is greater than 90 degrees. Therefore, the iron chromite sand is not easily wetted by the high-temperature molten steel, the molten steel is hard to penetrate into the gaps of the sand particles. So it is not easy to form mechanical sand. Iron chromite sand has a good anti-alkaline slag effect and will not react with iron oxide, thereby avoiding the defects of chemical sand sticking.
- Secondly, the thermal conductivity and heat storage coefficient of chromite sand is relatively large (several times larger than that of silica sand). As a result, the cooling rate is fast, so that the metal on the surface of the casting is rapidly cooled and solidified.In the meantime, the low melting point generated during the casting of high-temperature molten metal liquid The object will also solidify rapidly with the rapid cooling of the metal.As the cooling rate is accelerated a lot, an amorphous glass phase is formed between the mold shell and the casting. The glass phase is easy to fall off the surface of the casting. Therefore, it is easy to clean the sand of the casting, and the surface of the casting after the sand cleaning is high, avoiding the defect of sticky sand on the surface.
- In addition, iron chromite sand has high thermal conductivity and heat storage coefficient. It chills the surface of high-temperature molten metal after casting. Its function is equivalent to external cold iron, which strengthens the sequential solidification of molten metal. Reduce the formation of shrinkage cavities and porosity. The chilling process refines the crystal particles of the metal, improves the mechanical properties of the metal, and improves the overall quality of the casting.
It is suitable for applications such as:
- Large-scale steel castings
- Thick-walled castings
- Local thick-walled castings
- Surface sand for small and medium-sized castings
- It can replace silica sand, improve the casting effect and reduce the defective rate. For some small castings, it can replace zircon sand to save costs without affecting the quality of the castings.
The iron chromite sand supplied by Haixu Abrasives comes from South Africa’s high-grade chromite ore. The production process includes washing, screening, magnetic separation, and other processing procedures. That will get very clean chromite sand with a chromium oxide content above 46% and a silicon content of less than 1% is obtained.