Gas Assist Injection Molding

Nitrogen is an inert, dry, non-toxic, odorless gas. Its ability to contact melts at high temperatures without introducing oxidation or splay makes it an ideal candidate for GAIM. In GAIM applications purity of the nitrogen gas required for clean part production varies based on the polymer type and additive package. Nitrogen purity levels typically range from 95 - 99.995%. Oxidation at melt temperature is the phenomenon often dictating nitrogen purity requirements.

Linde offers the complete nitrogen GAIM package. Our specially trained Application Engineers will consult with you to design a turnkey operation best suited for your situation. Linde supplies cylinder gas to get you started and continues to work with you as you grow. As your GAIM use increases, we can assist in the evaluation of on-site nitrogen generation and/or a bulk liquid nitrogen installation.

In GAIM, conventional injection molding techniques are utilized in combination with the introduction of gaseous nitrogen. The material is melted and injected into a cavity mold using a standard injection molding press. As the melt begins to solidify the area in contact with the mold walls will harden first. At this point nitrogen gas is injected into the melt pressurizing it from the inside out. This internal pressure of the gas pushes the molten material to the extremities of the cavity. The gaseous nitrogen will always follow the path of least resistance. Once the material sustains an adequate cure, the nitrogen is vented, the mold is opened, and the part is ejected.

In conventional injection molding the rule of thumb was that the polymer melt was designed to flow from a thick section to a thin section in a part. GAIM allows part and tool designers to think a little different. With the addition of nitrogen gas to a hot melt, polymer flow can go from thin to thick sections. This allows for greater design freedom and reduction of multiple part assemblies.
Another significant advantage to GAIM is the ability to reduce warpage and distortion by abolishing molded in stress. The nitrogen gas is used to reinforce ribbed parts eliminating sink marks and surface blemishes. Nitrogen aids with uniform pressure distribution throughout the mold resulting in better packing and a more aesthetically pleasing part.

With the use of the internal pressure provided by the nitrogen gas the outer force needed to hold the part in its shape can be lowered. This provides a condition for larger parts to be produced with less tonnage on smaller machines. This will reduce the molders capital investment when purchasing new equipment.

Diminishing wall thickness and resin consumption will decrease the cure time needed for part production. Curing is the act in which polymer melts harden and hold shape. With GAIM, less polymer is needed which leads to faster cooling and lower cycle times, allowing the machines to increase part output. Nitrogen gas displaces some of the volume that is normally filled by resin. This results in a savings of polymer feedstock.

For pressure requirements over 300 bar, an additional booster operated with very low energy consumption can be used.
Main advantages of the system are:

• Very low energy requirements due to cost-effective liquid compression
• The DESY® 300/100 pumps exactly the quantity of nitrogen which is required by the user, even when strong fluctuations in demand occur
• Unchangingly high quality of the injection moulded parts because of the very pure and oil-free nitrogen