Why Gas Assisted Molding?

GAM is increasingly successful in providing molders and end users substantial benefit - both technical and economic  - compared with conventional injection molding. To find out more about how GAM has revolutionised the plastics industry click here.

Gas Assisted Molding Process Methods

There are 3 alternative methods of applying internal gas molding, all of which use nitrogen gas as a medium for applying pressure to molten plastic in the mold - nitrgoen gas is used as it is chemically inert and therefore does not react with the molten plastic.

The three methods are detailed below:

      1. Short Shot - the basic and original method consisting of first injecting a controlled volume, "short shot", of plastic to part fill the mold cavity. Gas is then injected into the plastic in order to fill the cavity with plastic and internal continuous "bubbles" of gas. The gas is then controlled to apply pressure to the plastic as it cools and solidifies.

      2. Full Shot or Nearly Full Shot - these methods comprise of filling completely or nearly filling the mold cavity with plastic before injecting gas into the plastic to complete filling of the mold cavity. This enables the application of packing pressure to the plastic and to compensate for the volumatric shrinkage of the plastic as it cools and solidifies.

      3.  "Plastic Outflow" Methods - include allowing plastic to flow out of the product cavity into outflow or overflow cavities through connecting  channels in order to extend the penetration of gas in the plastic. The basic principal of out flowing material has been used casting and molding processes for many years.

All molding methods use the nitrogen gas as a medium for applying pressure to the plastic in order to improve the product surface finishes and to eliminate sink marks. Also the plastic is not subject to lamina flow whilst cooling, resulting in much reduced molded-in- stress, which otherwise can cause molding distortion of the product.

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