Why do gas trails occur in injection molding?

Gas marks are a common and problematic situation in injection molding. They appear as tree-like, wavy scratches on the surface of plastic parts around the injection molding hole, significantly affecting the appearance and quality of the product.

To solve this problem, Dongguan Yize Mould Co., Ltd. offers professional recommendations. Firstly, they advise increasing the temperature of the mold and nozzle, which improves the plastic flowability. In addition, accelerating injection molding speed, filling speed, and increasing injection pressure, holding pressure and mold filling time can also effectively reduce the appearance of gas traces.

Second, the design of the pour hole is critical. They recommend installing an electric heating device in the pour hole to increase its temperature, allowing for a smoother flow of plastic through the hole. In addition, increasing the area of the pour hole and channel, as well as making the cross-section of the hole and channel circular in shape, also helps to reduce the formation of gas trails.

The mold design cannot neglect the machining of the bottom of the vent and the tail of the channel. They suggest making larger cooling holes at these two locations to help move gas and heat out of the mold. At the same time, special care must be taken in the size and location of the cooling holes to ensure that they work best and do not adversely affect the product.

In addition, when the melt flows from a narrow cross-section to a wider cavity cross-section or when the flow path in the mold is narrow and has poor smoothness, this can lead to persistent seepage, causing wavy flow marks on the surface of the plastic part. In such cases, they recommend reducing or controlling the injection rate accordingly to ensure smooth filling of the mold with plastic.

Finally, VOCs can also cause cloudy, wavy gas trails on the surface of plastic parts, especially when using polymers such as ABS. To avoid this problem, they suggest lowering the cylinder temperature, improving mold vents, lowering the raw material temperature and fill rate, and trying to increase the cross-section of the fill port to minimize gas formation and accumulation.