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The Blow-and-Trim Process – Opportunities and Pitfalls

SpecialChem / Jul 10, 2007

Most PET bottles (soft drinks and water) we come across on super market shelves have a neck of 28 to 33 mm when measured on the outside of the thread beads (the so-called T-Dimension) while juice bottles usually feature a 43 mm neck. A bottle with a neck above 43 mm is considered a wide-mouth container. Several parameters change as neck sizes increase. When the neck is made in the traditional way on the injection machine fewer cavities fit into the machine frame and larger machines have to be used to get the same number of preforms when compared with narrow-neck ones. (Most machines can make necks up to 30 mm in the largest cavitation). Larger machines move slower, which adds a cycle time penalty to the process. This is true whether the preforms are made in the single or two-stage process. Single stage machines are preferred for wide-mouth applications because the preforms stay in the neck inserts where they are held tightly. As long as the injection clamp and the blow plate cylinder are large enough wide-mouth containers are relatively straightforward in this process.

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