Three options for injection molding machines

Fixed feeding: the nozzle is always stuck into the mold before and after pre molding, and the injection seat does not move.
Front feeding: the nozzle carries out pre molding feeding against the die. After the pre molding is completed, the injection seat retreats and the nozzle leaves the die. The purpose of this method is to use the injection hole of the mold to help the nozzle during pre molding to avoid the melt flowing out of the nozzle when the back pressure is high. After pre molding, the heat transfer caused by long-time contact between the nozzle and the mold can be avoided, affecting the relative stability of their respective temperatures.—Embossed carrier tape

Post feeding: after the injection, the injection seat retreats, the nozzle leaves the mold, and then the injection seat advances after the pre molding. This action is suitable for processing plastics with particularly narrow molding temperature. Due to the short contact time between the nozzle and the mold, the loss of heat and the solidification of molten material in the nozzle hole are avoided. After the injection is completed and the cooling timer is timed, the pre molding action starts.—Embossed carrier tape
The screw rotates to melt and squeeze the plastic in front of the screw head. Due to the role of the check valve played by the check ring at the front end of the screw, molten plastic accumulates at the front end of the barrel and forces the screw backward. When the screw retreats to the predetermined position (this position is determined by the travel switch to control the backward distance of the screw and realize quantitative feeding), the pre molding stops and the screw stops rotating. Then, the reverse shrinkage action is followed, that is, the screw makes a small amount of axial retreat. —Embossed carrier tape

This action can relieve the pressure of the molten material gathered at the nozzle and overcome the problem caused by the imbalance of internal and external pressure of the barrel “Salivation” phenomenon. If it is not necessary to shrink back, the shrink back stop switch shall be adjusted to the appropriate position so that the shrink back stop switch can be pressed at the same time when the pre molding stop switch is pressed.
When the screw moves backward to press the stop switch, the backward retraction stops. Then the injection seat began to retreat. When the injection seat retreats to press the stop switch, the injection seat stops retreating. If fixed feeding mode is adopted, pay attention to adjust the position of travel switch. Generally, fixed feeding mode is adopted in production to save the advance and retreat * operation time of injection seat and speed up the production cycle.—-Embossed carrier tape