The injection hole of the mold is used to resist the nozzle during pre-molding to prevent the melt from flowing out of the nozzle when the back pressure is high. After pre-molding, it can prevent the nozzle and the mold from contacting for a long time to generate heat transfer and affect the relative stability of their respective temperatures.
Post-feeding: After the injection is completed, the injection seat moves back, the nozzle leaves the mold and then preforms, and then the injection seat moves forward after the preformation. This action is suitable for processing plastics with a particularly narrow molding temperature. Due to the short contact time between the nozzle and the mold, the loss of heat and the solidification of the melt in the nozzle hole are avoided.
After the injection is over and the cooling timer finishes, the pre-plastic action starts. The screw rotates to melt and squeeze the plastic to the front of the screw head. Due to the role of the check valve at the front end of the screw, the molten plastic accumulates at the front end of the barrel, which forces the screw back.
When the screw retreats to a predetermined position (this position is determined by the travel switch, which controls the retreat distance of the screw to achieve quantitative feeding), the pre-plasticizing stops and the screw stops rotating. This is followed by a retraction action, which means that the screw makes a slight axial retreat. This action can relieve the pressure of the melt gathered at the nozzle and overcome the “salivation” caused by the imbalance of the pressure inside and outside the barrel. phenomenon.
If there is no need to retract, the retract stop switch should be adjusted to the appropriate position, so that the same time the pre-plastic stop switch is pressed, the back stop switch is also pressed. When the screw retreats to the stop switch, the retraction stops. Then the shooter began to retreat. When the shooter retreats to the stop switch, the shooter stops retreating. If a fixed feeding method is used, attention should be paid to adjusting the position of the travel switch.