Blow Molding
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Improper PET pre-blow pressure and timing
Problem Phenomenon
Pearlescent whitening and uneven wall thickness coexist on the bottle body; after adjusting the pre-blow pressure and start timing, both types of defects improve simultaneously.
Cause Analysis
When the pre-blow pressure is too low or starts too late, the parison is not fully pre-formed before final blowing, and local areas are overstretched during final blowing; the pre-blow timing and pressure jointly determine the material distribution.
Solution
①Appropriately increase the pre-blow pressure; ②advance the pre-blow start timing; ③optimize the transition curve between pre-blow and final blow; ④verify the adjustment effect with wall thickness distribution.; after adjustment, take consecutive samples to verify the effect, and resume mass production only after confirming stability
Key Takeaway
Pre-blow is the core means of controlling wall thickness distribution and whitening; pressure and timing need to be adjusted in coordination, and changing a single item often trades one thing for another.; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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