The Attention Of PVC In The Injection Molding
Typically, the injection process refers to the plasticizing stage and the injection molding stage. Whether the injection is proper or not affects the appearance, performance and so on of the final product. The following two stages of the plastic phase of the main points of attention to explain.
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 rigid 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 ℃. When the barrel reaches the temperature, the temperature control system by injection molding machine for accurate control.
B, in order to make the PVC compounds 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, pre molding, back pressure should be controlled as much as possible within 1.0MPa, 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 rigid PVC, screw speed should be controlled. Normally, if the screw diameter is small than 60mm, then the speed is 50 to 70r/min, diameter greater than 7omm, then the speed is 20 ~ 50r/min.
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