1. Plasticizing Stage
The stage of plasticization is the important process of melting material to the viscous flow which can be injected normally. The operating principle is: to ensure that the good physical properties of molding materials and have enough low viscosity for filling under the condition of the materials are plasticized at temperatures as low as possible, so that the production process has the maximum flexibility.
2.Injection Molding Stage
In view of the characteristics of hard PVC resin, we should pay attention to the following points during injection molding:
A、the process of injection barrel temperature control at 170 to 190 DEG C. When the barrel reaches the temperature, it should be accurately controlled by the temperature control system of injection molding machine.
B、In order to make the molten plastic (i.e. mixture tree powder, filler, lead salt stabilizer, calcium / zinc powder etc.) can be fully injected into the mold cavity, each speed uniform. General to multi segment injection speed control, the principle of slow start injection, with the forming area gradually increased and the segmental increasing injection rate, the product is free of cracks and obvious weld line as the basis, the injection speed can not be too high.
C、Back pressure should be controlled as much as possible within 1.0MPa when pre-plasticization, high back pressure will produce excessive shear force, so that the rigid PVC overheating decomposition. Meanwhile, multi-stage back pressure control should be adopted in the melting process.
D、Because of the high viscosity and thermal sensitivity of hard PVC, screw speed should be controlled. Under normal circumstances, if the screw diameter is smaller than 60mm,the speed is 50 to 70r/min, diameter bigger than 70mm, then the speed is 20-50r/min.
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