Bubbles often occur at the seams or at the thicker parts of the plastic product.The product first cools the surface in the mold, while the exterior is cooled, the center is still hot, the center shrinks when cooled, and the plastic surface has been Cooled so that bubbles can only be formed by the shrinking of the interior itself.Many thick parts have no air bubbles at the time of die exit, but after a few tens of seconds there is air bubble in the center.
There are several situations of bubbles, the phenomenon is different for different reasons, are as follows:
Thicker products, the surface fat and muster, there are bubbles sawing section, the reason may be:
① injection speed is too fast, wrap the air, can not rule out the formation of bubbles.
② feeding too much or too little injection pressure is too high, it will produce this phenomenon, such as adjusting the feeding amount will improve this phenomenon.
③ cooling time is too short (especially thick-walled products), the solution can be used in the machine with cold water and cold mold cooling.
④ There is decomposition of black line in the product phenomenon, which is due to the formation of the temperature is too high.If the situation is not serious, you can lower the temperature, if the entire barrel decomposition, you must scrap clean.
⑥ mold into the gate is too small and poor exhaust, will also have this phenomenon.
Solid products are empty, and there is black phenomenon:
Solid product molding, the injection pressure is low, the injection speed to be slow, otherwise, the air under high pressure friction burnt was wrapped in products, so that products have black empty heir.
So appropriate to reduce the injection pressure and injection speed, voids will disappear.Also can check the amount of feed is too much, the appropriate reduction of some feeding amount to improve this phenomenon is also beneficial.
When the thickness of the product is different, there are small bubbles in the thick part of the product, or the black big bubble is wrapped in the extra thick product.
At the same time forming several different shapes of products, we must pay attention to the size of each gate to the weight of the product, otherwise, thick products prone to bubbles.
At the same time also pay attention to the mold exhaust, often left in the former mold products make the exhaust more difficult, it is easy to have the above phenomenon.May modify the mold or increase the dwell time and cooling time, to compensate for the lack of pressure on the thick section, which To improve this phenomenon is more important in the design of products, products should try to avoid having a thick part.