PVC is a heat-sensitive material, and its injection molding process is poor, because it is easy to decompose PVC by too high melting temperature or too long heating time, so controlling the melting temperature is the key to injection PVC products. The heat source of melting PVC raw materials comes from two aspects, that is, the shear heat of the plastic generated by the screw movement and the heating of the resistance wire on the outer wall of the barrel, which is mainly the shear heat of the screw movement, and the external heating of the barrel is mainly to provide 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 mutations as far as possible, and the thickness should not change much to prevent PVC degradation.
2. The die should have a drawing inclination of more than 10 degrees, and reserve 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 nozzle hole and larger than the diameter of the main channel, so that the PVC material does not flow into the mold cavity and the pressure can be balanced. Try to use a cut gate to prevent slag from flowing into the product and also to keep the temperature of the product from being cooled. The gate should be designed at the thickest wall of the product, and the width is sufficient, and the length is preferably between 6-8mm to make the PVC material flow smoothly. In order to support the pressure drop and easy release, the flow channel is preferably round, and the diameter is 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 ° C and 60 ° C.
5. The surface of the mold should be smooth and chrome-plated to prevent corrosion.
Due to the special performance of PVC, special PVC injection molding machine is selected for production, which should pay attention to the following points, Zhejiang Ceeto Mold Co.,Ltd. has over twenty years experiece in molding PVC plastic parts:
1. The screw length-diameter ratio should be 20:1, and the compression ratio should be between 1:1.6-1:1.2.
2. The screw and nozzle shall be made specifically for PVC and have a chrome-plated surface.
3. Injection pressure, speed, back pressure, temperature can be multi-level, precise control.
The following requirements should be noted in the preparation of raw materials: 1. It is necessary to avoid the deterioration of PVC raw materials caused by other plastics. Especially when injection molding other raw materials, it is necessary to clean the plastic in the barrel and screw before injection molding PVC products. (Clean screw and barrel with PE\PP\PS material)
2. Be sure to completely clean the PVC material before stopping, such as a long time stop, in order to prevent PVC corrosion of the machine, the use of cleaning materials to clean the screw and barrel.
3. When the PVC material is placed for more than 6 months, and the environment is high temperature and humidity, it should be dried at 60-80℃ for 2-5 hours before use.
Zhejiang Ceeto Mold Co.,Ltd.
