Molds & Tooling
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PMMA Pin-Point Gate Flow Marks
Problem Phenomenon
Radial flow marks and haze spots appear at the pin-point gate of transparent products, eliminated after switching to a fan gate.
Cause Analysis
The pin-point gate has a small cross-section and extremely high shear rate; molecular chains tear as the melt passes through, producing silver streaks and flow marks; when the gate faces the optical surface directly, the defect is directly visible.; During on-site troubleshooting, verify item by item according to this mechanism to avoid blindly adjusting the machine based on experience alone.
Solution
①Prioritize fan gates for transparent parts to enlarge the feed cross-section; ②avoid direct melt entry through pin gates; ③reduce shear through the gate; ④locate the gate on a non-optical surface.; After adjustment, continuously sample to verify the effect, and resume mass production only after confirming stability.
Key Takeaway
Gate form has a direct influence on PMMA optical quality; fan gates with low shear and wide feeding are the recommended structure for high-transparency products.; After confirming effectiveness, fix the parameters and practices into the work instruction to prevent recurrence.
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