Molds & Tooling
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Burn Marks and Trapped Air in PEEK
Problem Phenomenon
Black-brown burn marks appear at the flow ends or rib intersections of PEEK products, accompanied by yellowing and odor, at relatively fixed positions recurring from shot to shot.
Cause Analysis
When cavity venting is poor, compressed air heats up adiabatically under high-pressure filling, igniting or scorching the melt surface; PEEK has high filling pressure and fast speed, so the risk of trapped-air burning is higher than for ordinary plastics.
Solution
①Open or deepen vent grooves at the burn locations; ②Reduce the end-filling speed to give gas time to escape; ③Check whether the vent grooves are blocked by oil contamination; ④Use vacuum venting or porous steel if necessary.
Key Takeaway
Locating PEEK burn marks is locating the venting design defect; high-temperature materials are more sensitive to trapped air; vent groove depth must be specially designed according to PEEK viscosity — too deep will cause flash.
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