Material Drying
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Bubbles/voids on the surface of homopolymer polypropylene injection products
Problem Phenomenon
Round or elliptical bubbles of various sizes appear inside or on the surface of the product, with visible bulges or depressions on the surface.
Bubbles not only affect appearance, but also significantly reduce product density and mechanical strength, especially severe in thick-wall products.
Cause Analysis
(1) Insufficient raw '2079851475616104451; moisture vaporizes at high temperature producing water vapor bubbles
(2) Injection speed too fast; air in the cavity has no time to escape and is drawn into the melt
(3) Insufficient holding pressure or holding time too short; voids from shrinkage in thick-wall areas not compensated
(4) Barrel temperature too high (exceeding the 200-280°C upper limit); material thermal degradation produces gas
(5) Air drawn in during screw retraction feeding; insufficient back pressure causes inadequate venting
Solution
(1) Fully dry raw material; homopolymer polypropylene dried at 60-80°C for 2-4h, moisture content controlled below 0.02%
(2) Adopt multi-stage injection, slow first then fast then slow; reduce injection speed at the beginning and end of mold filling to reduce gas entrainment
(3) Increase holding pressure to 80-120MPa, extend holding time to 15-25s, ensure sufficient shrinkage compensation in thick walls
(4) Appropriately reduce barrel temperature to a reasonable value within the 200-280°C range, avoid thermal degradation
(5) Increase back pressure to 5-10MPa, ensure sufficient venting during screw pre-plasticizing
Key Takeaway
Bubbles and voids are mainly caused by moisture vaporization, gas entrainment, or insufficient shrinkage compensation; they need to be systematically solved from raw '2079851475616104451, injection process, and holding pressure parameters.
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