Now comes container forming (6), the heart of glasscontainer production, where the gob is manipulated and/or blown into its final form. Different forming techniques are used to make different types of container: blow-and-blow is primarily used for bottles, while press-and-blow is mainly used for jars.
Both processes comprise a ‘blank side’, in which the gob is formed into a partially completed form known as a ‘parison’ and a ‘blow side’, where the final shape is achieved. The container starts off upside down and is gripped by the ‘neck ring’, which allows the parison to be inverted as it moves from the blank side to the blow side.
In the blow-and-blow process, the sheared gob is blown downwards to form the ‘finish’ (outer surface) – this is called the ‘settle blow’. A ‘counter blow’ from below the gob then creates the cavity within the container. Finally, the parison is then inverted and blown into the ‘blow mould’ to form the final shape.
In the press-and-blow process, the parison is formed by a metal plunger, which presses the molten glass out to fill the blank mould. The parison is inverted and then blown out as in blow-and-blow.
Production lines for glass containers typically feature more than one container-forming unit, or section. Emhart Glass is well known for developing the individual section machine, or IS machine, which allows each section to be maintained independently of the others. Modern IS machines comprise as many as 12 sections.
As well as producing one container at a time (known as single-gob production) they can work with multiple gobs to make two, three or four containers simultaneously (referred to as double-gob, triple-gob and quad-gob production respectively).