Material Drying
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CMC injection thick wall bubbles
Problem Phenomenon
Dense bubbles of 0.1-0.5mm appear inside the CMC injection thick-walled product, concentrated in the center of the wall thickness
Cause Analysis
The holding pressure is insufficient <40MPa or the holding pressure time is short and the center of the thick wall is not compacted; the raw material contains moisture; the injection speed is too fast and air is entrapped; the mold venting is poor
Solution
1) Increase the holding pressure to 60-80MPa; 2) Extend the holding pressure time to fully compact the thick wall; 3) Fully dry the raw material to a moisture content <0.02%; 4) Add vent grooves or vent pins to the mold; 5) Gradually decelerate the injection to avoid air entrapment
Key Takeaway
Thick wall bubbles are caused by a combination of insufficient holding pressure, moisture and poor venting
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