Application of magnesium olivine sand (powder) in the production of lost foam casting for high manganese steel parts

Table 2 Physical properties of magnesium olivine sand (powder)
Tab.2 Physical property of forsterite sand/powder

　　The data in Tables 1 and 2 show that magnesium olivine sand (powder) is alkaline, has strong resistance to alkaline slag, and has high refractoriness, which can withstand the erosion of high manganese steel molten metal. At the same time, it has a relatively low cost, and its application in lost foam casting of high manganese steel castings has shown superiority.

2 Magnesium olivine powder coating

　　With the development and application of the lost foam casting process, the position of coating technology in the entire process has become increasingly important. Coatings can improve the strength and rigidity of foam plastic patterns, prevent damage or deformation of patterns during sand filling vibration, prevent molten metal from penetrating into the sand or collapsing the mold, and ensure the smooth surface of castings. The quality of the coating and its cost directly affect the quality of the castings and the economic benefits of the products. After countless experiments, a relatively reasonable formulation method was selected, and the effect is very ideal. High manganese steel is an alkaline metal liquid, so a strongly alkaline coating needs to be formulated, with the ratio shown in Table 3.

Table 3 Ratio of magnesium olivine powder coating
Tab.3 Prescription of Coating in forsterite powder

Anhydrous sodium carbonate + bentonite mixed into the tank + CMC + milky glue stirred for 4 hours to discharge.
　　2.2 Coating process
　　无水碳酸钠+膨润土搅匀入罐+CMC+乳白胶搅拌4 h出料。
2.2　涂敷工艺
　　A method combining dipping and brushing is used to apply the coating. First, a large area is coated using the dipping method, followed by brushing in areas with poor coating. Then, it is smoothly placed in the drying room for baking, with a drying temperature of 45 to 50 ℃. After drying, a second coat is applied to ensure the coating thickness is within 1 to 2 mm. The first coat should be slightly thinner, while the second and third coats should have a suitable amount of foaming agent added to increase the permeability of the coating.
　　Coatings made from magnesium olivine powder have successfully produced magnetic liners (small 8 kg, wall thickness 8 mm), electric shovel teeth (130 kg), ball mill liners, grid plates, and more than a dozen other types, with some weighing over 300 kg. The surface of the castings is smooth, flat, and free of sand sticking.
3 Magnesium Olivine Sand Molding
　　Quartz sand is favored by many domestic foundries due to its low cost. Quartz sand is an acidic material, and its SiO₂Easily reacts chemically with MnO in alkaline high manganese steel molten metal, forming low melting point compounds, which can cause serious chemical sand sticking, affecting the surface finish of the castings, and in some cases, leading to the scrapping of castings. Therefore, using quartz sand as a molding material in the lost foam casting of high manganese steel is not suitable.
　　Magnesium olivine sand is an alkaline material, has high refractoriness, and is moderately priced, while also not producing silica dust pollution. Producing high manganese steel castings with magnesium olivine sand will not result in the above phenomena, significantly improving the surface finish of the castings, and 90% of the sand can be reused after pouring.
　　More than two years of production practice has proven that this magnesium olivine sand is a suitable molding material for producing high manganese steel parts.

Author Profile: Chen Shuying (1965-), female, from Yangling, Shaanxi, engineer, bachelor.
Chen Shuying (Mechanical and Electrical Repair Factory of Jinduicheng Molybdenum Industry Company, Huaxian, Shaanxi 714102)

References

[1] Ye Shengping, Luo Jirong, et al. New methods for testing the performance of lost foam casting coatings [J]. Casting Technology, 1999(1): 29-31
[2] Wu Xiaofeng, et al. Application of titanium slag sand (powder) in lost foam casting of high manganese steel parts [J]. Casting Technology, 1998(4): 15-17     

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