The temperature change during the molding process of FRP is more complicated. Because plastic is a poor conductor of heat, the temperature difference between the center and the edge of the material is large at the beginning of molding, which will cause the curing and cross-linking reaction to not start at the same time in the inner and outer layers of the material.
On the premise of not damaging the strength and other performance indicators of the product, appropriately increasing the molding temperature is beneficial to shorten the molding cycle and improve the quality of the product.
If the molding temperature is too low, not only the melted material has high viscosity and poor fluidity, but also because the crosslinking reaction is difficult to proceed fully, the product strength is not high, the appearance is dull, and mold sticking and ejection deformation occur during demolding.
The molding temperature is the mold temperature specified during molding. This process parameter determines the heat transfer conditions of the mold to the material in the cavity, and has a decisive influence on the melting, flow and solidification of the material.
The surface layer material is cured earlier by heat to form a hard shell layer, while the later curing shrinkage of the inner layer material is limited by the outer hard shell layer, resulting in residual compressive stress in the surface layer of the molded product, and the inner layer is There is residual tensile stress, the existence of residual stress will cause the product to warp, crack and decrease the strength.
Therefore, taking measures to reduce the temperature difference between the inside and outside of the material in the mold cavity and eliminating uneven curing is one of the important conditions for obtaining high-quality products.
The SMC molding temperature depends on the exothermic peak temperature and curing rate of the curing system. Usually the temperature range with a slightly lower curing peak temperature is the curing temperature range, which is generally about 135～170℃ and determined by experiment; the curing rate is fast The temperature of the system is lower, and the temperature of the system with slow curing rate is higher.
When forming thin-walled products, take the upper limit of the temperature range, and forming thick-walled products can take the lower limit of the temperature range. However, when forming thin-walled products with a large depth, the lower limit of the temperature range should also be taken due to the long process to prevent material solidification during the flow process.
Post time: Apr-09-2021
