The injection molding process points of PVC are as follows:
Due to the existence of chloride ions, PVC materials will slightly absorb water, so they must be dried at 75-90 ℃ for about 1.5-2.5h before production.
(2) Melting temperature
Melting temperature is one of the most important processing parameters in PVC processing. If the proper temperature is not set, the material may decompose. PVC is an amorphous polymer with no definite melting point. Generally, it will melt when heated to 120-145 ℃, but hydrogen chloride smoke will be released at 150 ℃, and a large amount of HCl will be released when heated to 180 ℃. Because it will release toxic gas during injection molding, a large amount of heat stabilizer is required before processing. The adjustable range of injection temperature is very narrow. In the injection molding process, the common temperature is between 140 and 160 ℃; Sometimes the temperature can reach 190 ℃, but the injection time should be kept within 20min, otherwise the material will be seriously decomposed. As the injection temperature of the material is close to the decomposition temperature, the temperature should be kept as low as possible and the injection cycle should be as short as possible during the injection, so as to reduce the time that the material remains in the barrel.
Material temperature parameters - Phase I: 160-170 ℃, Phase II: 160-165 ℃, Phase III: 140-150 ℃. Due to its poor thermal stability, PVC will release hydrogen chloride (HCl) if it is heated in the barrel for too long, which will cause the plastic to become yellow or black spots on the product surface. In addition, HCl will corrode the cavity, so it is necessary to clean the dead corners of the mold cavity and the head frequently.
(3) Plastic mold temperature
Keep the temperature of the plastic mold as low as possible, shorten the injection cycle, and reduce the deformation of small and thin plastic parts.
(4) Runner and rubber port
PVC has poor fluidity, so the plastic mold gate and runner should be as large, short and thick as possible to minimize the pressure loss and fill the mold cavity as soon as possible. In a word, high pressure and low temperature are more suitable.
(5) Other reasons
The injection pressure can reach 150MPa; The pressure can be maintained up to 100MPa. Injection speed: The appropriate injection speed must be used to avoid material decomposition.
PVC, ABS, PE, PC, PP, EPS and other plastic extrusion profiles and various injection molded parts.