After the injection molding of the modified plastic products , the defects of small volume or string of pores will be formed inside. The main reason for the bubbles generated by the modified plastic products is that the gas enters the donor and is cooled and formed along with the melt. The reason for the dark bubble is that when the plastic part is cooled and solidified, the cooling speed is different inside and outside the plastic part, the outer part is slow inside, the outer layer is solidified first, and the inner melt is cooled and shrunk, which is a vacuum hole inside the modified plastic product. Form a dark bubble.
There are many reasons for the formation of bubbles in modified plastic products, such as too low injection pressure, too fast, too short time and cycle, too much or too little feed, insufficient pressure retention, uneven cooling or insufficient cooling, and temperature And improper control of the mold temperature will cause bubbles in the modified plastic products. The specific reasons are analyzed as follows:
When controlling the mold temperature and the melt temperature, it should be noted that the temperature should not be too high, otherwise it will cause the melt to depolymerize and decompose, generate a large amount of gas or excessive shrinkage, forming bubbles or shrinkage holes; if the temperature is too low, it will cause the filling pressure. Insufficient, the inside of the modified plastic part is prone to voids and bubbles.
Under normal circumstances, the melt temperature should be controlled slightly lower, and the mold temperature should be controlled slightly higher. Under such process conditions, it is not easy to generate a large amount of gas, and it is not easy to generate shrinkage cavities. When controlling the temperature of the barrel, the temperature of the feed section should not be too high, otherwise it will cause backflow and return bubbles.
If the exhaust system of the mold is clogged, the gas will be mixed into the melt, causing bubbles to be generated. For this, the exhaust system of the mold should be carefully checked to clear the blocked passage.
If the flow is too long, too thin, or there is a dead angle in the flow path, the mold will be poorly exhausted. In this case, the narrow flow path should be shortened and widened, and there should be no dead corners in the flow path.
If the particle size of the raw material is too small, the difference in particle size is large, so that too much air is mixed in the feeding process, the chance of gas entering the melt is increased, and bubbles are easily generated. For this, the raw material particles should be controlled and the fine material should be sieved out.
If the moisture content of the raw materials is too high, or the volatile components exceed the standard, they will generate a large amount of gas after being subjected to humans, which will add an extra burden to the exhaust system of the mold. If they are not discharged in time, they will be mixed into the melt to form bubbles. Therefore, these materials should be pre-dried.
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