Especially during high-speed injection, the gas inside the mold is too late to be discharged, resulting in too much gas remaining in the melt. Therefore, we should appropriately reduce the injection speed. However, if the speed drops too much and the injection pressure is too low, it is difficult to exhaust the gas in the melt. And then bubbles, dents and undershot will probably occur. Therefore, you should be especially careful when adjusting the injection speed and pressure.

In addition, we can avoid bubbles and vacuum bubbles by adjusting the injection and holding time, improving the cooling conditions, controlling the amount of feed and other methods. If the cooling conditions of the plastic parts are poor, the plastic parts can be immediately put into hot water after demoulding, so that the internal and external cooling rate tends to be the same. 

When controlling the mold temperature and melt temperature, the temperature can’t be too high. Otherwise it will cause the melt to depolymerize and decompose, generate a lot of gas or shrink excessively, and form bubbles or shrinkage holes. If the temperature is too low, the filling pressure will be insufficient, and the plastic parts are prone to voids and bubbles.

In general, the melt temperature should be controlled slightly lower, while the mold temperature slightly higher. Under such process conditions, it is not easy to produce a large amount of gas and shrinkage holes. When controlling the barrel temperature, the temperature of the feeding section shouldn’t be too high. Otherwise it will cause backflow of material and then bubbles.