What are the high-gloss injection molded parts?
High-gloss injection molded parts products are indeed a more difficult for injection molding enterprises to cope with because they cannot hide external defects. Even the dust in the workshop can cause different degrees of defective products, such as trachoma, pockmark, staining, etc., so the environment is also affecting this product’s surface white mist.
From a visual point of view, high-gloss injection molded parts present a white shape, so it is not obvious when the white products, black high-gloss is the most obvious, the surrounding surface shows white spots, like cloud-like symptoms, here categorized as white fog.
Analysis of the causes of defects in high-gloss injection molded parts
Injection molding process, there is a certain gap between the plastic and plastic in the downstream stage. After the screw shear is brought into the barrel, in the screw shear process, the material will be physically changed internally.
From the glass state into a high elastic state, from the high elastic state, and then to the viscous flow state, the process of this change may only be between a few seconds – tens of seconds (depending on the size of the machine or product) in such a short period to transform a complex process, injection molding defects are then generated.
The gap between the plastic is compressed to the inside of the melt to produce gas. If the gas is not discharged to the outside of the barrel during plasticization, the presence of gas is wrapped into the melt is injected into the mold cavity. Whether the mold can be smoothly discharged depends on whether the exhaust of the mold is good, then the phenomenon of fogging trapped gas or burning.
A white mist is also a phenomenon of trapped gas. Many people engaged in injection molding technology mistakenly believe that only scorched is trapped gas, or trapped gas to open the exhaust tank, which is not scientific. Scorched because trapped gas is too serious, the gas is compressed at high pressure, the high-speed state can not be released to produce local combustion, burning temperature can instantly reach 600-800 ℃.
The solution of defective high-gloss injection molding parts
The solution of defective high-gloss injection molding parts in the injection mold
Exhaust is not entirely by the mold to solve, for PP material characteristics, the temperature range is very wide, its flow performance is superior, if the mold exhaust slot opens too large or incorrect location, cannot be correctly exhausted, but also easy to produce flying edge bad, so the correct exhaust is useful.
The solution of defective high-gloss injection molding parts in the injection mold processing
It is very effective to master the correct technique of tuning the machine in practice.
(1) Such as reducing the screw rotation speed can make the melt temperature uniform and the chance of entrained air be small. If the screw rotation speed is too fast, the chance of entrained air to more; melt by the screw shear force and frictional heat results in the uneven temperature of the melt and melt decomposition of gas.
(2) Improve the mold temperature, which can facilitate the high pressure and slow filling to win time. If the mold temperature is too low, the product surface is easy to freeze prematurely, and slow filling cannot be achieved, which may lead to a lack of glue.
(3) Reduce the injection speed. The faster the speed, the faster the gas compression, and the higher the temperature. The slower the speed, the slower the gas compression and the more conducive to gas discharge.
(4) Clamping force, the greater the clamping force, the worse the cavity surface exhaust effect. The smaller the clamping force, the better the cavity surface exhaust effect.
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