What are the problems with high back pressure in plastic injection molding
Jul 25, 2021
What are the main injection process parameters of plastic injection processing technology? The flow of materials. Process changes in melt flow/shrinkage/hardening. The master at this stage must have perspective in order to see through the changes in the process of the melted material in the machine/mold. How to shrink? Where will stress occur after shrinking? How to transfer heat? Why is there internal pressure? What will happen? This ability is where this realm is higher than the previous realm. If the third area is from the outside to the inside and appears with fewer indicators on multiple indicators, then the area is from the inside to the outside, where the defect corresponds to the fishbone diagram without meaning, and the parameters become very simple. (William Shakespeare, Hamlet,) This state requires more understanding and practical foundation. When processing plastic molds, excessive back pressure may cause the following problems:
The melting pressure at the front of the barrel is too high, the material temperature is high, the viscosity decreases, the molten material flows back in the screw groove, the flow of water leakage between the barrel and the screw increases, and the plasticization efficiency (the amount of plasticizable material per unit time) decreases.
For plastics with low thermal stability (such as PVC, POM, etc.) or colorants, the temperature of the melt increases, and the heating time of the barrel increases, which leads to increased thermal decomposition or discoloration of the colorant, and the color/gloss of the product surface decreases. .
The back pressure is too high, the screws are back, the plastic recharging time is long beforehand, the cycle time increases, and the productivity decreases.
The back pressure is high and the pressure of the molten material is high. After injection, the nozzle is prone to melt drooling. When the adhesive is injected next time, the cold material in the nozzle runner will appear on the nozzle or product.
In the beer plastic process, the back pressure is too large, the nozzle leaks, the raw materials are wasted, and the heating ring near the inlet burns in many cases.
When processing plastic molds, excessive back pressure will increase the mechanical wear of the pre-plastic mechanism and the screw barrel.
