Precautions in Polyurethane Rigid Foam Casting
The catalysts for casting foam molding are mainly amine catalysts. Delayed amine catalysts can be used to prolong the whitening time to meet the filling requirements of the mold. This type of catalyst can improve the fluidity of the raw material system, but does not affect its curability. Isocyanate The index is slightly greater than 100, such as 105. In the process of pouring and foaming, the raw material temperature and the ambient temperature directly affect the quality of the foamed plastic products. The ambient temperature is preferably 20-30 °C, and the raw material temperature can be controlled at 20-30 °C or slightly higher Some. It is difficult to obtain high-quality products if the temperature is too high or too low. For large-scale products such as ships and vehicles, it is difficult to control the ambient temperature by on-site casting.
The requirements for the mold are reasonable structure, easy disassembly and assembly, light weight, certain pressure resistance, and a good finish on the inner surface. At the same time, according to the size and different shapes of the mold, drill multiple rows in suitable positions. Stoma. The material for making the mold is generally aluminum alloy, and sometimes steel mold is used. The temperature of the mold directly affects the speed of reaction heat removal. The mold temperature is low, the foaming ratio is small, the product density is high, and the skin is thick; high mold temperature On the contrary. In order to make high-quality foamed plastic products, the mold temperature is generally controlled in the range of 40-50 °C. When the material temperature and mold temperature are low, the chemical reaction proceeds slowly, and the foam curing time is long; the temperature is high, the curing time is short. . When foaming is injected into the mold, the mold and the product should be cured in a higher temperature environment before demoulding, so that the chemical reaction can be completed. If demoulding is premature, the curing will be insufficient and the foam will be deformed. Raw materials The variety and the shape and size of the parts are different, and the required curing time and temperature are also different. Generally, the molded foam needs to be cured in the mold for 10 minutes before it can be demolded. Due to the short mixing time, the mixing efficiency is a factor to be paid attention to. Manual pouring and foaming , The stirrer should have sufficient power and rotation speed. The mixing is uniform, the foam cells are fine and uniform, and the quality is good; the mixing is not good, the cells are thick and uneven, and even the chemical composition does not meet the formula requirements in a local area. Greatly affect the quality of the product.
