Injection Molding
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PET bottle seal leakage
Problem Phenomenon
After the finished bottles are capped, the seal is not tight, with leakage when inverted or failure in vacuum decay testing, and they are frequently rejected on the filling line.
Cause Analysis
The dimensions of the bottle finish thread and sealing surface are out of tolerance, and white crystalline spots or flash on the bottle finish affect the fit; the bottle finish is formed in the injection stage, and subsequent processes cannot repair its dimensional deviation.
Solution
①Check the dimensional accuracy of the bottle finish thread and T value; ②reject preforms with bottle finish defects; ③inspect the wear of the bottle finish area of the injection mold; ④confirm the fit between the cap and the bottle finish.
Key Takeaway
Sealing performance is already determined in the preform injection stage; control of bottle finish dimensions and white spots is the key to leak prevention, and sampling inspection of cap-on sealing should be performed before filling.; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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