Sometimes because the flow channel is too long, the melt at the forefront is cooled too much, which leads to injection moldings with radial lines and shock lines, and the performance of PC materials in this regard is particularly prominent, followed by transparent PVC.
This is why sometimes the melt temperature has risen so high that the injection molded parts have not eliminated the ridges or shock lines.
At this time, if the two ends of the flow channel are extended by a few centimeters, the low-temperature melt that has been cooled at the front can flow into the extended cross flow channel, and will not flow into the cavity, and the defects will be very good. Improvement. I believe this method will also improve other plastics, and the improvement of PC and PVC materials will be more obvious.
The reason for loosening (reverse) cannot be used after injection of PC material. After the injection is completed, the loosening (reverse) is opened, the screw moves backward, and the air will be drawn into the nozzle and mixed with the high-temperature PC material. Because the PC material is easy to absorb moisture, a small amount of moisture in the air can cause the injection molding to produce silver wire grain.
In a similar situation, the transparent PVC melt cannot be reversed. Because transparent PVC is very easy to scorch, it will cause a chemical reaction immediately when it encounters air, resulting in yellow spots in injection molded parts, and even many black spots.
Therefore, when injecting PC material or transparent PVC material, do not reverse the cable after injection. If the backpressure needs to be increased due to the process and the nozzle is drooling, it can only be poured a little bit to eliminate the drooling. No more, never allow air to enter the nozzle.
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