Sometimes the processed injection molded products will shrink and sag. What is going on? What are the causes of these situations? plastic injection profiles supplier to share with you:
Machine side
The nozzle hole is too large to cause the melt to reflow and shrink. If it is too small, the resistance is insufficient and the shrinkage occurs.
Flashing will also cause shrinkage due to insufficient clamping force. Check the clamping system for problems.
If the amount of plasticization is insufficient, a machine with a large amount of plasticization should be selected to check whether the screw and the barrel are worn.
2. Mould aspect
Custom plastic injection should make the wall thickness uniform and ensure consistent shrinkage.
The cooling and heating system of the mold must ensure that the temperature of each part is consistent.
The gating system must ensure unobstructed flow, and the resistance must not be too large. For example, the size of the main flow channel, the runner, and the gate should be appropriate, the smoothness must be sufficient, and the transition area must be arc-shaped.
For thin parts, the temperature should be increased to ensure smooth materials, and for thick-walled parts, the mold temperature should be reduced.
The gate should be opened symmetrically, and it should be opened in the thick-walled part of the part as much as possible, and the volume of the cold well should be increased.
Plastic Injection Profiles
3. Plastics
Crystalline plastics shrink more strongly than non-crystalline plastics. When processing, increase the amount of material appropriately, or add a nucleating agent to the plastic to accelerate crystallization and reduce shrinkage.
4. Processing
The barrel temperature is too high, and the volume changes greatly, especially the temperature of the front furnace. For plastics with poor fluidity, the temperature should be appropriately raised to ensure smoothness.
The injection pressure, speed, and back pressure are too low, and the injection time is too short, so that the shrinkage pressure, speed, and back pressure are too large and the time is too short to cause shrinkage.
The feeding amount means that the injection pressure is consumed when the cushion is too large, and when it is too small, the feeding amount is insufficient.
For parts that do not require accuracy, after the injection pressure is maintained, the outer layer is basically condensed and hardened, and the sandwich part is still soft and can be ejected. Release the mold early to allow it to cool slowly in air or hot water. The shrinkage depression is gentle and less noticeable without affecting use.
The shrinkage problems of plastic injection profiles (surface shrinkage and internal shrinkage) are all defects caused by insufficient melt glue replenishment when the thicker parts are cooled. We often encounter situations that increase the pressure, increase the water inlet, and extend the injection time, and the shrinkage problem cannot be solved.
Among the commonly used raw materials, the shrinkage problem of the PC material is the most difficult to solve due to the fast cooling rate, and the shrinkage and shrinkage problems of the PP material are also more difficult to handle.
