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The appearance of bubbles on the surface of Plastic Products refers to the small or string of pores that appear on the surface or inside of plastic products after they are formed, which may be obvious bubbles or undetectable dark bubbles.
1. Reason
(1) Die problems
l Poor or blocked mold exhaust system: the gas cannot be effectively discharged and formed into the melt.
l The gate cross-section area is too small or incorrect position: the gas is difficult to discharge, easy to form bubbles.
l Improper design of the flow channel: too long, too thin or have dead corners, affect the exhaust performance of the die.
(2) Raw material problems
l Excessive moisture content in the raw material or volatile components exceed the standard: after heating, a large amount of gas, mixed into the melt.
l Raw material particles are too small or particle size difference: in the process of feeding air.
(3) The molding operation problems
l The injection speed is too fast and the injection time is too short: the gas in the mold is too late to discharge, resulting in the residual gas in the melt.
l Insufficient cooling time: the plastic is not completely cured, and the internal gas is not completely discharged.
(4) Environmental problems
l Instable or insufficient pressure of Injection Molding Machine : the air cannot discharge the mold.
l Plastic properties: Some plastics are more likely to produce air bubbles in the injection molding process.
(5) Product problems
l The wall thickness of the product is large, and the outer surface speed is cooled faster than that of the central part. When cooling, the resin side of the central part shrinks and expands to the surface, so that the center part produces insufficient filling and vacuum bubbles.
(6) Gas problems
l Volatile gases produce air bubbles.
(7) Liquidity problems
l Bubbles caused by the poor mobility.
2. The Solution
(1) Die problems
l Optimize the exhaust system: ensure that the exhaust system of the mold is unimpeded and remove the gas in time.
l Adjust the gate design: increase the gate section area, to ensure the correct position, so that the gas is easily discharged.
l Improve the flow channel design: shorten and widen the narrow flow channels to avoid the existence of dead corners.
(2) Raw material problems
l Raw material pre-drying treatment: reduce the moisture content and volatile components in the raw materials.
l Control raw material particles: control the size of raw material particles, screen the fine materials, and reduce the chance of air mixing.
(3) The molding operation problems
l Adjust the injection speed and time: appropriately reduce the injection speed and increase the injection time to ensure adequate gas discharge.
l Control the cooling time: ensure that the plastic is fully cured and the internal gas is completely discharged.
(4) Environmental problems
l Check the performance of injection machine: ensure the injection machine pressure is stable and provide adequate injection pressure.
l Choose suitable plastic materials: according to the product requirements to choose the plastic materials with good bubble resistance performance.
(5) Product problems
l According to the wall thickness, determine the reasonable gate, pouring channel size. The general gate height should be 50%~60% of the wall thickness of the product.
l Until the pouring mouth is sealed, leave a certain supplementary injection material.
l The injection time should be slightly longer than the pouring mouth sealing time.
l Reduce the injection speed and increase the injection pressure,
l Materials with high molten viscosity grade are used.
(6) Gas problems
l Full pre-drying.
l Reduce the resin temperature and avoid producing decomposition gas.
l Liquidity problem
l Increase the temperature of resin and mold and improve the injection speed.
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June 18, 2024
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June 18, 2024
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