Material Drying
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Bubbles/voids appearing on the surface of random copolymer polypropylene injection molded products
Problem Phenomenon
Round or elliptical bubbles of varying 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-walled products.
Cause Analysis
(1) Insufficient raw '2079851475616104451; moisture vaporizes at high temperature to produce water vapor bubbles
(2) Injection speed is too fast; air in the cavity has no time to escape and is drawn into the melt
(3) Holding pressure is insufficient or holding time is too short; voids produced by shrinkage in thick-wall areas are not compensated
(4) Barrel temperature is too high (exceeding the 190-260°C upper limit); material thermal degradation produces gas
(5) The screw draws in air when retracting; insufficient back pressure leads to inadequate venting
Solution
(1) Fully dry the raw material; random copolymer polypropylene is dried at 60-80°C for 2-4h, with moisture content controlled below 0.02%
(2) Use multi-stage injection, slow-fast-slow, reducing injection speed at the beginning and end of filling to reduce gas entrainment
(3) Increase holding pressure to 80-120MPa and extend holding time to 15-25s to ensure full shrinkage compensation in thick walls
(4) Appropriately lower barrel temperature to a reasonable value within the 190-260°C range to avoid thermal degradation
(5) Increase back pressure to 5-10MPa to ensure full venting during screw preplasticizing
Key Takeaway
Bubbles and voids are mainly caused by moisture vaporization, gas entrainment or insufficient shrinkage compensation and need to be systematically solved from raw '2079851475616104451, injection process and holding pressure parameters.
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