Extrusion & Post
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Abnormal PET polarized light stress lines
Problem Phenomenon
Under a polarizing microscope, the bottle body shows irregular colored stress streaks, the corresponding areas have uneven stretch orientation, and mechanical properties fluctuate.
Cause Analysis
Improper stretching timing during bottle blowing or uneven preform temperature makes the molecular chain orientation degree spatially inconsistent; residual stress differences appear as interference fringes under polarized light.; during on-site troubleshooting, verify item by item according to this mechanism, and avoid blindly adjusting the machine based only on experience
Solution
①Establish a standard stress pattern map under the polarizing microscope; ②optimize the stretch rod speed and blowing timing; ③balance the preform temperature distribution; ④adjust the heating zones for abnormal areas.
Key Takeaway
Polarized light inspection can see through the orientation and stress distribution of the bottle body; after establishing the baseline pattern of qualified products, abnormal stress lines can serve as a directional guide for process adjustment.; after confirming effectiveness, solidify the parameters and practices into the work instruction to prevent recurrence
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