IS Process for Container Glass Forming
The IS process has now universally replaced almost all others. It is not certain whether ‘IS’ denotes its inventors, Ingle and Smith, or its main characteristic which is independent synchronized units with a synchronized gob distribution system to each section (i.e. Individual Section). IS machines can comprise several sections and 10 & 12 section or 16 to 20 section tandem machines are now common.
The machine can operate on the blow and blow or press and blow principle and double gob production, i.e. delivery of two gobs of glass at the same time is common. Triple and quadruple gob machines are also increasingly used. The machine is currently capable of producing more than 600 containers per minute.
Most bottles and jars are now made automatically by one of the two methods shown below.
The Blow and Blow Method
Molten ‘gobs’ of glass are delivered into a mould known as a ‘blank’ or parison mould. A puff of compressed air blows the glass down into the base of the mould to form the neck or ‘finish’ part of the bottle or jar. A second blast of compressed air is then applied through the already formed neck of the container to form the ‘parison’ of pre-form for the bottle against the walls of the parison mould cavity.
The thick walled parison is then transferred to the final mould during which time the surface of the glass ‘reheats’ and softens again enough to allow the final container shape to be fully formed against the walls of the final mould cavity by the application of either compressed air or vacuum. The container is then removed and transferred to an annealing oven (lehr) where it is reheated to remove the stresses produced during forming and then cooled under carefully controlled conditions.
The Press and Blow Method
Molten ‘gobs’ of glass are delivered into the parison mould and a plunger is used to press the glass into the parison shape. The final mould stage of the process is the same as that described for the Blow and Blow Process. Due to the first stage pressing process the glass distribution overall is better controlled.
Narrow Neck Press and Blow (NNPB)
Narrow neck press and blow is in fact equal to the press and blow process. Due to improved plunger material, which is now capable to withstand the high temperatures, it became possible to make those plunger thinner and therefore capable to penetrate the narrow necks of the bottle’s parison. Because parison pressing provides better glass distribution equality, thus better wall thickness equality, NNPB was one of the major process improvements in recent bottle production leading to potential weight reductions.