n the field of injection molding, main runner sticking is a problem that cannot be ignored. It refers to the phenomenon where the main runner of the injection molded part fails to separate from the plastic mold during the ejection process. This phenomenon not only affects production efficiency but may also adversely affect product quality. So, what causes main runner sticking, and how can it be effectively eliminated?

The causes of main runner sticking are diverse, with the following being the main aspects:

Firstly, insufficient cooling time during the injection molding process is a common cause of main runner sticking. When the cooling time is too short, the main runner has not fully cooled and solidified, making it difficult to eject smoothly during mold opening. Therefore, adjusting the cooling time reasonably is an important measure to prevent main runner sticking.

Secondly, insufficient draft angle of the main runner is another factor leading to sticking. The main runner should have a certain draft angle to facilitate smooth ejection during mold opening. If the draft angle is insufficient, it should be appropriately increased to reduce the ejection resistance.

Furthermore, improper fitting dimensions between the main runner bushing and the nozzle of the injection mold can also cause leakage problems, leading to main runner sticking. Therefore, during mold design and manufacturing, it is necessary to ensure that the fitting dimensions between the main runner bushing and the nozzle are accurate to avoid leakage.

In addition, the surface roughness of the main runner and the presence of a cold slug well are also important factors affecting the ejection of the main runner. If the surface of the main runner is too rough and there is no cold slug well, it will increase the difficulty of ejection. Therefore, the surface roughness of the main runner should be improved, and a cold slug well should be reasonably set to reduce the ejection resistance.

Finally, a too low nozzle temperature of the injection molding machine can also cause main runner sticking. When the nozzle temperature is too low, the flowability of the plastic melt will be affected, thereby increasing the adhesion between the main runner and the mold. Therefore, the injection temperature should be appropriately increased to ensure that the plastic melt has good flowability.

In summary, the causes of main runner sticking in injection molding are diverse. However, by reasonably adjusting the cooling time, increasing the draft angle of the main runner, ensuring accurate fitting dimensions of the mold, improving the surface roughness of the main runner and setting a cold slug well, as well as increasing the injection temperature, we can effectively eliminate this problem and improve the production efficiency and product quality of injection molding.