Polyvinyl chloride injection molding process

PVC is a heat-sensitive material, its injection molding process is poor, the reason is that too high a melt temperature or too long a heat time can easily make PVC decomposition, so controlling the melting temperature is the key to injection molding PVC products. The heat source of melting PVC raw material comes from two aspects namely the sheer heat of the plastic generated by the screw movement and the resistance wire heating of the outer wall of the barrel, while mainly the sheer heat of the screw movement, the outer heating of the barrel mainly provides the heat source when the machine starts.



Product design and mold design should pay attention to the following points.

1. the product should not have sharp corners or abrupt changes as far as possible, and the thickness should strive to vary little to prevent the degradation of PVC.

2. The mold should have more than 10 degrees of mold slope and allow for about 0.5% shrinkage.

3. The flow channel design of the mold should pay attention to several points

The injection port of the mold should be slightly larger than the injection nozzle hole, and larger than the diameter of the main flow channel intersection so that the PVC material flows into the mold cavity without stagnation and the pressure can be balanced.

The gate should be cut off as much as possible so that the slag will not flow into the product and the temperature in the scopolamine runner will be lowered and it will be easier to mold.

The gate should be designed at the thickest wall of the product with enough width, preferably between 6-8mm in length, to make the PVC material flow smoothly.

In order to feed the pressure drop and easy to take off the mold, the runner should preferably be round, and the diameter should be chosen between 6-10mm according to the size and weight of the product.

4. the mold temperature should have a cooling water control device so that the mold temperature can be controlled between 30 ℃ ~ 60 ℃.

5. The surface of the mold should be smooth and chrome plated to prevent corrosion.

Because of the special properties of PVC, so the production of a special PVC injection molding machine is selected, of which the following points should be noted.

1. the screw L/D ratio should be 20:1 is better, and the compression ratio is between 1:1.6 and 1:1.2.

2. the screw and nozzle should be specially made for PVC with a chrome-plated surface.

3. Injection pressure, speed, back pressure, and temperature can be multi-stage and precision-controlled.

The following requirements should be noted in the preparation of raw materials.

1. must avoid having other plastic PVC raw materials in, causing deterioration of PVC raw materials. Especially when injection molding over other raw materials, must first clean the barrel and screw inside the plastic, in order to inject PVC products. (Use PE\\\PP\\\PS material to clean the screw and barrel)

2. Before stopping the machine, make sure to clean the PVC material completely. If you stop the machine for a long time, to prevent PVC from corroding the machine, you should clean the screw and barrel with cleaning material.

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