Extrusion & Post
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PMMA Gate Stress Whitening
Problem Phenomenon
Radial whitening zones appear around the product gate, and whitening decreases after annealing.
Cause Analysis
Shear stress and holding pressure stress concentrate in the gate area, and highly oriented molecular chains freeze to form stress whitening; whitening is more severe with small gates and high holding pressure.; During on-site troubleshooting, verify item by item according to this mechanism to avoid blindly adjusting the machine based on experience alone.
Solution
①Enlarge the gate to reduce shear; ②optimize the holding pressure profile to reduce pressure; ③raise mold temperature; ④annealing treatment to eliminate stress.; After adjustment, continuously sample to verify the effect, and resume mass production only after confirming stability.
Key Takeaway
Gate whitening is a sign of local stress overload; matched adjustment of gate and holding pressure combined with annealing can restore transparent appearance.; After confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence.
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