PVC parts injection

PVC is a heat sensitive material, and its injection molding process is poor. The reason is that too high melt temperature or too long heating time can easily decompose PVC. Therefore, controlling the melt temperature is the key to injection molding PVC products. The heat source for melting PVC raw materials comes from two aspects, namely, the shear heat of plastic generated by screw motion and the resistance wire heating of the outer wall of the barrel, which is mainly the shear heat of screw motion, and the outer heating of the barrel is mainly the heat source provided when the machine is started.

The following points should be paid attention to in product design and mold design:

1. The product shall not have sharp corners or sudden changes as far as possible, and the thickness shall not change much to prevent PVC degradation and deterioration.

2. The mold shall have a draft angle of more than 10 degrees and a shrinkage of about 0.5% shall be reserved.

3. Several points should be paid attention to in the runner design of the die

The injection port of the mold shall be slightly larger than the nozzle hole and larger than the diameter at the intersection of the main flow channel, so that the PVC material will not flow into the mold cavity and the pressure can be balanced.

Cut off gate shall be adopted as far as possible, so that the molten slag will not flow into the product and flow channel, and the temperature will be reduced and easy to form.

The gate shall be designed at the thickest wall of the product, with sufficient width and length of 6-8mm, so as to make the PVC material flow smoothly.

In order to feed the pressure drop and easy demoulding, the flow channel is preferably circular, and the diameter is 6-10mm according to the product size and weight.

4. The mold temperature shall be equipped with cooling water control device to make the mold temperature controllable between 30 ℃ and 60 ℃.

5. The surface of the mould shall be smooth and chrome plated for corrosion prevention.

Due to the special performance of PVC, special PVC injection molding machine is selected for production, and the following points should be paid attention to:

1. The length diameter ratio of screw shall be 20:1, and the compression ratio shall be between 1:1.6-1:1.2.

2. The screw and nozzle shall be specially made of PVC and the surface shall be chrome plated.

3. Injection pressure, speed, back pressure and temperature can be controlled in multiple levels and precision

Pay attention to the following requirements in raw material preparation:

1. The deterioration of PVC raw materials caused by other plastic PVC raw materials must be avoided. In particular, when other raw materials are injected, the plastic in the barrel and screw must be cleaned before injecting PVC products. (clean the screw and barrel with PE \ PP \ PS material)

2. Before shutdown, the PVC material must be completely cleaned. If it is shut down for a long time, in order to prevent PVC from corroding the machine, the screw and barrel shall be cleaned with cleaning material.

3. When the PVC material is placed for more than 6 months and the environment is high temperature and humid, it can be used only after drying at 60-80 ℃ for 2-5 hours before use.