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Terminology
Title: 17. Bird Swing
Bird Swing or Bird Cage, also called Telephone Line, is a glass thread that hangs across the internal wall of a bottle,
close to the Gob Settle Wave level, almost at right angle to the parting seam line.
It is a very critical bottle defect.
It usually happens to DG, TG or QG process, after Counter Blow and before Final Blow, having two-opposite points in Parison cavity,
close to Gob Settle Line level, touching one another, due to the deforming of Parison shape, folded halfway during Invert or
compressed by external air during Blow Mould Close, or a combination of both.
It may happen when the mould cooling or machine timing are unstable, after mould parts are replaced.
Bird Swing may appear in other part of bottle, such as at the heel or neck zone. There could be 2 or more lines associated.
