Coated sand, the surface of the sand grains is shaped The molding sand or core sand is covered with a solid resin film. There are two coating processes: cold method and hot method: the cold method uses ethanol to dissolve the resin, and adds methenamine during the sand mixing process, so that the two coat the surface of the sand, and the ethanol evaporates to obtain coated sand; hot method Method: Preheat the sand to a certain temperature, add resin to melt it, stir to coat the surface of the sand with the resin, add methenamine aqueous solution and lubricant, cool, crush and screen to obtain coated sand. Used for steel castings and iron castings.
Calcium stearate is widely used in coated sand. It is usually used as a lubricant for coated sand and improves the flow of coated sand. Properties, caking, gas production, strength and thermal toughness are all affected.
1. Introduction to calcium stearate:
According to the supply of calcium stearate: calcium stearate is a white powder, insoluble in water, cold ethanol and ether, soluble in hot benzene, benzene and turpentine and other organic solvents, slightly soluble in hot Ethanol and ether. It decomposes slowly when heated to 400°C and is flammable. It decomposes into stearic acid and corresponding calcium salts when exposed to strong acid and is hygroscopic. Used as lubricant, sliding agent, heat stabilizer, release agent, accelerator, etc. in plastics, machinery, rubber, paint and ink and other industries.
2. The following is the specific role of calcium stearate in coated sand:
1. Calcium stearate can improve the fluidity and strength of coated sand
Calcium stearate is evenly distributed in the coated sand. At the core-making temperature, the resin and calcium stearate soften and melt, forming an interpenetrating network that increases the softness of the resin and increases the deflection of the shell, thus Leading to an increase in thermal toughness; the lubricating properties of calcium stearate improve the fluidity of the coated sand, increasing the compactness of the sand core, thus increasing the strength of the core.
2. Calcium stearate can increase the melting point of coated sand
The melting point of calcium stearate is 60-80 degrees higher than that of resin. The softening time of calcium stearate after heating is later than that of resin. The unmelted calcium stearate dispersed in the sand is within the desired range. Come to the skeleton role. During the softening period of the resin, it blocks the settlement of gravel, reducing the formation and expansion tendency of sand core voids; at the same time, it can also increase the melting point of coated sand.
3. Calcium stearate can improve the thermal cracking resistance of coated sand
Calcium stearate can also improve the thermal cracking resistance of coated sand. The main reason for thermal cracking of coated sand is thermal stress caused by thermal expansion. As the amount of calcium stearate increases, , the thermal cracking time is gradually delayed. The reason is that the melting point of calcium stearate is higher than that of resin. Its increase is beneficial to improving the thermoplasticity of the sand core, thereby relaxing the thermal stress of the sand core.
Although the amount of calcium stearate added to the coated sand is small, its effect is very large. It can prevent the caking of the coated sand and improve the fluidity. , Improve shelling resistance and demoulding properties.
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