If the nozzle used is long, the melt is easy to cool during injection molding, and a lower temperature condensate will be generated at the front end of the nozzle. When the cavity is injected into the cavity, the cavity will be underfilled, and the other cavity will overflow due to overfilling. Especially when injecting gears of POM material (commonly known as “Sai Steel”), it is more difficult to fully fill, and the injection process is difficult to stabilize, especially the molds with latent and pin-point gates are the most obvious.
Therefore, the use of long nozzles should be avoided as far as possible during production. If you encounter frequent underfilling or it is difficult to fully fill under any pressure or acceleration, you should first check whether the machine uses a long nozzle. At the same time, when it is necessary to use slow injection to solve the defects of some products, it is impossible to use long nozzles. It is better not to use long nozzles for raw materials with poor fluidity (such as PC material), and PA and POM materials are not suitable for use because of the easy condensation of the melt.
However, in some cases, due to the mold structure, it is necessary to use long nozzles for injection molding. Therefore, if the above problems occur, the necessary remedial measures need to be taken. The following methods and measures will be helpful to improve the harm of long nozzles.
①Install a nozzle heating ring with a large heating power and a long enough size at the nozzle.
②The injection is carried out by moving the shooting table, that is, each time the injection is completed, the shooting table moves backward to avoid the nozzle and the mold contacting for a long time and dissipating too much heat. During the next cycle of injection, the shooting table moves forward and allows the nozzle Tighten the mold. However, it is worth noting that after using this method, the nozzle mouth will gradually become smaller due to repeated impacts over time, and it is easy to cause defects such as shrinkage or lack of material.
③ Avoid the nozzle being blown directly by the fan beside the machine and dissipating the heat too quickly.
④Modify the mold and increase the volume of the cold cavity of the mold (either length or diameter can be increased).
However, the above shortcomings of long nozzles can also occur with injection molding using too short nozzles, especially on large injection molding machines. The reason is the same as the long nozzle, but also because there is condensed melt in the nozzle. The common situation is that everything works normally in the day shift, but the problem occurs in the evening shift. The reason is that the temperature is low at night and the nozzle heat is dissipated too quickly. The solution is to increase the power of the nozzle heating ring.
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