Points for attention of the hottest PVC injection

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Points for attention in PVC injection molding process

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 injecting PVC products. The heat source for melting PVC raw materials comes from two aspects, namely, the shear heat of plastic produced by screw motion and the resistance wire heating of the outer wall of the barrel, which is mainly the shear heat of screw reaction in terms of strength. The outer heating of the barrel is mainly to provide heat source when the machine is started

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

1 Try not to have sharp corners or sudden changes in the product, and strive to have little change in thickness to prevent PVC degradation and deterioration

2. The mold should have a draft angle of more than 10 degrees, with about 0.5% shrinkage reserved

3. Several points should be paid attention to in the design of the flow channel of the mold

the injection port of the mold should 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 flows into the mold cavity without retention and the pressure can be balanced

try to use the cutting gate, so that the slag will not flow into the product and the temperature in the flow channel will be reduced, and it is easy to form

the gate should 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 runner should preferably be circular, and the diameter should be 6-10mm according to the size and weight of the product

4. The mold temperature should have a cooling water control device of 0.15 ~ 0.17, so that the mold temperature can be controlled between 30 ℃ ~60 ℃

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

due to the special performance of PVC angular strength testing machine except for many operations and processes in use, special PVC injection molding machine is selected for production, which is mainly reflected in the "cold winter and hot summer". The following points should be paid attention to:

1 The length diameter ratio of screw should be 20:1, and the compression ratio should be 1:1.: 1.2

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

3. The injection pressure, speed, back pressure and temperature can be precisely controlled in multiple stages

the following requirements should be paid attention to in the preparation of raw materials:

1 It is necessary to avoid the deterioration of PVC raw materials caused by other plastic PVC raw materials. In particular, when injecting other raw materials, the plastic in the barrel and screw must be cleaned before injecting PVC products. (use peppps material to clean the screw and barrel)

2 Before shutdown, the PVC material must be completely cleaned. If the machine is shut down for a long time, in order to prevent PVC from corroding the machine, the screw and barrel should 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 being dried at ℃ for hours before use

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