PVC material because of cheap, born to have anti-inflammatory properties, tough and strong, good chemical resistance, shrinkage ratio of 0.2 to 0.6%, the product in electrical appliances, machinery, building, daily necessities, toys, packaging applications increasingly widespread, according to the characteristics of PVC material, analysis product injection molding process is as follows:
1, the characteristics of PVC material
PVC thermal stability, molding temperature and decomposition temperature is close to, poor liquidity, easy to form bad appearance defects, PVC material poor heat resistance, burning, acid gases and most easily corrosion mold, processing additive plasticizer increased its liquidity, generally use doping, its strength, good electrical insulation, drug resistance.
2, mould and gate design
To shorten the injection molding cycle, the shorter the sprue, the better, a transverse to the garden, shoot tip of minimum 6 mm diameter, conical, an internal Angle into five degrees, best to add cold slug well, bad cold slug well can prevent melt semisolid material into the cavity, which will affect the surface modification of materials and products such as strength. Draft Angle to between 0.50 to 10, to ensure that the cavity you have plenty of exhaust device, commonly used vent size 0.03 0.05 mm deep, 6 mm wide, or each thimble peripheral clearance of 0.03-0.03 mm. Mould application is made of stainless steel or hard chromium plating.
3, PVC molding process
PVC is heat-sensitive plastic, shear excessive can cause overheating or decomposition, and quickly spread, because one of the decomposition (such as acid or HCI) will produce catalysis, lead to process further decomposition, acid erodes metal, into depression, and can make the metal protective layer spalling, caused by rust, more harmful to the human body
4, injection speed:
Injection speed slower, or excessive shear will make the material degradation, using UPVC production extremely smooth and thick wall products, multi-stage injection speed should be adopted, if there is a beige stripe to radiate from the gate, it indicates that the feed speed is too fast.
5, back pressure：the surface of the common value is 5 bar, increasing back pressure to mixed color and exhaust, but should back pressure is lower, the better.
6, downtime: as the PVC thermal stability is low, so the downtime of flash is very important, put the barrel clean, without leaving any PVC, can use other overheat high stability and resistance of PVC thermoplastic, or (for example, PMMA, PP, LDPE, GPPS), avoid by all means within the same barrel mixed POMT UPVC, otherwise it will cause a strong chemical reaction, cause serious damage to the machine.
7, mixing proportion: shuikou material mixing ratio is 20%, most otherwise it will affect the products quality.
9, typical products: UPVC drainage pipe main purpose is to create, or the computers and TV shell, filter water pressure tank, copy machine shell, and gas meter shell, transparent bubble of printing presses, style, and various electronic components, etc.