Let's take a brief look at the role of calcium stearate in coated sand. Coated sand, sand surface before modeling is covered with a layer of solid resin film sand or core sand. There are cold method and hot method two kinds of film coating process: cold method with ethanol to dissolve the resin, and in the sand mixing process to add urotropine, so that the two coated on the surface of the sand, ethanol volatilized, coated sand; The sand is preheated to a certain temperature by thermal method, and the resin is added to melt it. The resin is coated on the surface of the sand by stirring, and the water solution and lubricant are added to cool, break and screen the coated sand.
Used for steel casting, cast iron. Calcium stearate is a dry production process, the production process is energy-saving and pollution-free, the product purity is high, the free acid value is low, good lubrication. Calcium stearate is a white powder, insoluble in water, cold ethanol and ether, soluble in hot organic solvents such as benzene, benzene and turpentine, slightly soluble in hot ethanol and ether. When heated to 400 ℃ slowly decomposable, flammable, in strong acid decomposition into stearic acid and the corresponding calcium salt, hygroscopic. In plastics, machinery, rubber, paint ink and other industries as a lubricant, sliding agent, heat stabilizer, release agent.
Calcium stearate is widely used in the coated sand, usually as a lubricant of the coated sand, has an effect on the fluidity, caking, gas production, strength and thermal toughness of the coated sand. The following is the specific role of calcium stearate in coated sand:
1, calcium stearate can improve the fluidity and strength of the coated sand, calcium stearate evenly distributed in the coated sand, resin and calcium stearate softening and melting at the core temperature, forming a network through each other to increase the softness of the resin, increase the deflection of the shell, resulting in the increase of thermal toughness; The lubrication property of calcium stearate changes the fluidity of the coated sand and increases the compactness of the sand core, thus improving the strength of the core.
2. Calcium stearate can improve the melting point of the coated sand. The melting point of calcium stearate is 60-80 degrees higher than that of resin, and the softening time of calcium stearate after heating is later than that of resin. During the softening of resin, the sand settlement is blocked and the formation and expansion tendency of sand core voids are reduced. It can also improve the melting point of the coated sand.
3, calcium stearate can change the thermal cracking resistance of coated sand, calcium stearate can also change the thermal cracking resistance of coated sand, the thermal cracking of coated sand is mainly caused by thermal expansion and thermal stress, with the increase of calcium stearate dosage, 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 improve the thermoplasticity of the sand core and thus loosen the thermal stress of the sand core. Although the amount of calcium stearate in the coated sand is small, but the effect is very big, can prevent the coated sand caking, change the fluidity, change the anti-peeling and release property.