Pre-coated sand casting process
Coated sand is the molding sand or core sand that is covered with a solid resin film before the surface of the sand grains are molded. There are two coating processes:
1. The cold method. The cold method is to use ethanol to dissolve the resin, and then add urotropine during the sand mixing process, so that both of them are coated on the surface of the sand grains, and finally the ethanol volatilizes, and the coated sand will be obtained;
2. Thermal method, the coated sand foundry will first preheat the sand to a certain temperature, then add the resin to melt it, then fully stir the resin to coat the surface of the sand, and finally add the urotropine aqueous solution and lubricant , Coated sand is obtained through cooling, crushing and screening. The general coated sand process is mainly used for casting steel castings and iron castings.
In fact, there are now three methods for preparing coated sand used by coated sand foundries. These three methods are cold coating, warm coating and thermal coating. Among them, the hot method is the most frequently used by manufacturers. Laminating, thermal laminating has the advantages of less numerical dosage and high production efficiency.
1. Cold laminating process, adding raw sand and thermosetting powdered phenolic resin to the sand mixer and mixing evenly, then adding an appropriate amount of solvent to continue mixing until the powdered resin is completely melted and adhered to the surface of the sand. After the solvent evaporates, it can be crushed and screened after the sand is produced. However, this method takes a long time to mix sand, consumes a lot of solvents, and the volatilized solvent gas is very easy to explode, which leads to very few uses of the cold coating process and almost no use.
2. Warm coating process. The warm coating process is relatively simple. It is to mix thermosetting liquid phenolic resin with 60-80℃ raw sand, mix for 2-3 minutes and then produce sand, then cool, crush and Sieving is enough.
3. Thermal laminating process. This thermal process is to first heat the raw sand to a certain temperature, and then put the resin, urotropine aqueous solution and calcium stearate into the raw sand, mix them evenly, and then cool them. , Crushed and sieved. Because of the difference in casting equipment and ratio, the mixing process is also different.
When the coated sand foundry stores the coated sand, they will put the coated sand in a well-sealed bag or container. It can be stored for about 0.5-1 years under dry conditions at room temperature less than or greater than 20°C. time. If the coated sand is stored for too long, it is more likely to have local agglomeration. If the agglomeration is not very serious, you can mash the agglomerated place and continue to use it after screening.
