TABLE OF CONTENTS The characteristic feature of gas injection moulding technology is the filling of a form with two different materials. Plastic materials form the first component. The second component consists of a gas, generally nitrogen (N 2). The two components do not mix. All standard injection moulding machines which are equipped with a device for introducing gas are suitable for the GIT process. The injection of the gas may be performed by a machine nozzle or by a separate injection module in the mould.
The process sequence begins with the injection of the first component ?the plastic. A dose of approximately 70% 20% of the volume of the cavity is proportioned and injected.
Shortly before the conclusion of the injection phase, the gas injection phase begins. The brief overlapping of injection and gas injection phases is intended to prevent a speed break of the melt front and the switch over marking which is related to this. The location for introduction of the gas is best in areas with large melt accumulations. The gas fills the cavity and forces the melt forward. Design specific cavities in the moulded part are the result.
Once the cavity is completely filled, the gas-holding pressure phase begins. This pressure phase is applied until the part is dimensionally stable (maximum gas pressure is 400 bar). Gas pressure during this time is constant throughout the entire canal. Because of the relatively low gas pressure, there are...
