Compression molding temperature control mainly refers to the control of molding temperature, heating rate, molding curing temperature and holding time.
In the compression molding process, temperature, pressure and duration under pressure are important process parameters, and they have their own functions and mutual constraints. High temperature is conducive to shortening the molding cycle and improving the physical and mechanical properties of the product. However, if the temperature is too high, the fluidity of the melt will be reduced to fill the mold cavity, or the surface layer will solidify prematurely and affect the discharge of moisture and volatiles. Decrease the surface quality of the product, and undesirable phenomena such as product expansion and cracking may occur during mold opening. On the contrary, if the molding temperature is too low, the curing time is prolonged, and the cross-linking reaction is not perfect, which will also affect the quality of the product. It will also cause problems such as gray surface of the product, mold sticking and decreased mechanical properties.
Mold loading temperature: refers to the temperature of the compression mold when the material is put into the mold cavity. When it is difficult to install a mold for a complex or large molded product, the temperature of the mold should be lower, and the mold can be controlled at room temperature. Increasing the mold assembly temperature can shorten the production cycle and improve production efficiency. The molding temperature depends on the type of material. For example, the molding temperature of the magnesium phenolic premixed molding compound is the molding curing temperature, not at room temperature.
Heating rate: It also depends on the material variety. For example, the heating rate of 616# phenolic premixed molding material is 1-20℃/min. The speed of the temperature rise is closely related to the speed of the resin curing reaction. If the temperature rises too fast, it is easy to cause uneven curing of the resin and affect product quality.
Curing temperature: The resin will release or absorb a certain amount of heat during the curing process. The degree of resin polycondensation reaction can be judged according to the heat release to determine the curing temperature. Under normal circumstances, first determine a relatively large temperature range, and then select a reasonable curing temperature through testing.
Molding heat preservation time: Molding heat preservation time refers to the time of heat preservation under the molding pressure and molding temperature. The main function of this stage is to completely cure the product and eliminate internal stress. The length of the molding holding time depends on the type of material, the level of molding temperature and the structural size and performance of the product. Cooling: There are two cooling methods: natural cooling and forced cooling. In slow molding, after the heat preservation, the temperature must be gradually reduced under a certain pressure, and the mold can be demolded when the mold temperature drops below 60°C.
The control of curing molding temperature and holding time also depends on the type of material. Appropriately increasing the molding temperature can shorten the production cycle and help stabilize the quality of the product. However, the temperature is too high, which affects the fluidity of the material, makes it difficult to fill the material, and causes waste. If the temperature is too low and the product holding time is insufficient, the defect of incomplete curing will occur. In order to fully cure the product and eliminate the curing internal stress, it needs to be kept warm for a period of time.
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