Polyvinyl chloride (PVC) is an amorphous plastic. Its main uses are as follows:
Mainly used for the production of hose, hard pipe, soft board, hard board, wire, toys, shoes, artificial leather, floor, window frame.
Its main properties are as follows:
1, refractory self-extinguishing, poor thermal stability.
2, PVC soluble in cyclohexanone, tetrahydrofuran, dichloroethane. Spray oil with a soft glue to open the oil (including cyclohexanone).
3. Hard PVC has high mechanical strength, excellent electrical performance, strong resistance to acid halogen, good chemical stability and low softening point.
4, by adding plasticizer to make the material soft hardness range (60.0.8-100.0.8), hard PVC, soft PVC (about 40% plasticizer).
Polyvinyl chloride (PVC) molding process is as follows:
1. Adding ABS to soft PVC can improve toughness, hardness and mechanical strength.
2. In order to prevent cold material from blocking the gate or flowing into the mold cavity, large cold material hole should be designed to accumulate cold material.
3, the injection speed should not be too fast, so as to avoid the temperature rise caused by the intense friction of the molten material through the gate, and easy to produce shrinkage marks.
4, the mold temperature as low as possible (30-45℃ or so), in order to shorten the molding cycle and prevent plastic parts out of the mold deformation. (If necessary, the mold should be set).
5. In view of easy decomposition and poor fluidity, the mold runner and gate should be thick, short and thick to reduce pressure loss and fill the cavity as soon as possible. Various types of inlet, flow passage size 0.16.0-0.110.0mm, exhaust groove size 0.05-0.07mmx1.5mmx6.0mm gate size 0.7-1.0TX2t.
6, molding cylinder for a long time heat decomposition of vinyl chloride monomer and HCL (degradation), corrosion of the cavity, so should often clean the cavity and the head of the internal dead Angle. In addition, the surface of the cavity is often plated with hard chromium or nitriding to resist corrosion.
7, soft PVC shrinkage rate is larger (1.0%-5.0%), often take 2.0% (2.5%). Hard PVC shrinkage rate is small (0.2%-0.6%). PVC polar molecules easy water absorption, molding before drying, drying temperature 85-95℃. For 2 HRS. Commonly used internal mould S136H (due to the decomposition of corrosive gas HCL from PVC in beer molding)
8, because PVC molding processing temperature is close to the decomposition temperature, so the barrel temperature should be strictly controlled, as far as possible with low molding temperature, but also as far as possible to shorten the molding cycle, in order to reduce the residence time of molten material in the barrel. Temperature parameters: front barrel temperature 160-170℃, middle barrel temperature 160-165℃, rear barrel temperature 140-150℃.