Gas injection moulding

A particularly distinguishing feature compared to conventional injection moulding processes is the the creation of a permanent hollow area in the interior after the melt has been injected into the mould. This is possible with the use of an inert compressed gas (nitrogen). In principle there are two different processes: the inflating process (standard- GIT) and the blow-out process (secondary cavity process) or blow-back process. In the standard GIT process the mould is firstly partly filled with the melt and then "inflated" with the aid of the gas. In this way the final shape of the item is created. The gas pressure in the interior of the piece to be moulded pushes the melt onto the outer walls of the mould and in this way the hollow area in the centre is created. In the blow-out or blow-back process the cavity is at first filled completely with the melt which is subsequently "blown out" again. The blown-out melt runs into an overflow cavity which is attached to the mould or is blown back into the injection cylinder. The process to be used is determined primarily by the form of the piece to be moulded. Furthermore the patent situation has to be taken into account when deciding on what process to use.