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 produced by the screw motion and the resistance wire heating of the outer wall of the barrel, which is mainly the shear heat of the screw motion. The external heating of the barrel is mainly the heat source provided when the machine is started.
PVC used to be the world's largest general-purpose plastic with a wide range of applications, mainly PVC pipes and fittings.
The following points shall be noted in product design and mold design:
1. The product shall not have sharp corners or abrupt changes as far as possible, and the thickness shall not change much to prevent the degradation of PVC.
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 design of the flow channel of the mold
A. The injection port of the mold shall be slightly larger than the nozzle hole and larger than the diameter of the intersection of the main flow channel, so that the PVC material does not flow into the mold cavity and the pressure can be balanced.
B. Cut off gate shall be used as much as possible to prevent molten slag from flowing into the product and the temperature in the runner from decreasing and make it easy to form.
C. The gate shall be designed at the thickest wall of the product with sufficient width and length of 6-8mm to make the PVC material flow smoothly.
D. In order to support the pressure drop and easy demoulding, the flow channel should be round, and the diameter should be 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 mold shall be smooth and clean, and chrome plating shall be used to prevent corrosion.
Post time: Aug-12-2022