Many people know that trapped gas is caused by poor exhaust of the mold during the injection process, which is only one of the reasons. In fact, there is another important reason that can cause severe gas traps in injection molded parts, which is caused by the phenomenon of melt “ back pack ” during filling.
The so-called “back-packing” phenomenon refers to the phenomenon that when the filling resistance of a certain position of the mold is relatively large on both sides, when the melt is filled into this place, the phenomenon of fast melt flow on both sides and slow flow of the intermediate melt occur. When the melts on both sides that flow faster meet in front, the air that has not been exhausted in the middle will inevitably be enclosed, thus forming trapped air. This trapped gas caused by the melt surrounding the air is commonly referred to as the ‘back pack’ trapped gas. The greater the difference between the resistance on both sides and the resistance in the middle, the worse the sleepiness is, and the harder it is to solve
The aforementioned common trapped gas caused by poor exhaust of the mold is generally divided into two cases: one is the trapped gas that can be solved by adding a vent groove and a vent needle, for example, next to the mold clamping line The trapped gas formed can be solved by adding an exhaust slot; the other is that trapped gas that cannot be removed by adding an exhaust system is called a “dead spot” trapped gas.
The trapped air caused by the two reasons of ‘dead end’ and ‘back-packing’ are two important reasons for the difficulty of trapping the trapped air. It has always been a problem in injection molding production. Tuning techniques for these two types of sleepiness are possible.
In addition, the problem of trapped gas caused by multiple gates can be solved by simply blocking a gate or rearranging the gate position, which is relatively simple.
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