Air bubbles often occur at the last seams of plastic products or at thicker parts of the product. The surface of the product is first cooled in the model. When the appearance has cooled, the center part is still hot. The central part shrinks as it cools, and the plastic surface has cooled, so it can only shrink by itself to form air bubbles. Many thick parts have no bubbles when they are ejected, but after tens of seconds, bubbles appear in the center.
There are several cases of bubbles, with different phenomena and different reasons, as described below:
Thicker products, the surface is fat and swollen, and there are air bubbles at the saw section. The reasons may be:
① The injection speed is too fast, which can trap the air and cannot be eliminated, and air bubbles are formed.
② Too much or too little feeding amount and too high injection pressure will also cause this phenomenon. If the feeding amount is adjusted appropriately, this phenomenon will be improved.
③ The cooling time is too short (especially for thick-walled products), the solution can be cooled with cold water and cold pressing molds outside the machine.
④ There is a phenomenon of decomposition of black lines in the product, which is caused by excessive temperature. If the situation is not serious, you can lower the temperature appropriately. If the entire barrel is decomposed, you must disassemble the car to clean it.
⑤ The mold inlet is too small and the exhaust is poor, this phenomenon can also occur.
Solid products have holes and blackness. When solid products are molded, the injection pressure should be low and the injection speed should be slow. Otherwise, the air will be trapped in the product through friction and scorch under high pressure, so that the product has black voids. . Therefore, if the injection pressure and injection speed are appropriately reduced, the cavity phenomenon will disappear. You can also check whether the amount of feed is too much, and appropriately reducing some of the feed is also beneficial to improve this phenomenon.
When the thickness of the plastic product is different, there are small bubbles in the thicker part of the product, or a large black bubble bag in the thick part of the product. When molding several products with different shapes at the same time, you must pay attention to the size of each gate to be equal to the weight Otherwise, thick products are prone to air bubbles.
At the same time, we should also pay attention to the exhaust of the mold. The products that are often left on the front mold make exhausting more difficult. This phenomenon is easy to occur. This phenomenon can be improved by modifying the mold or increasing the dwell time and cooling time to make up for the lack of thick section pressure. More importantly, when designing products, try to avoid special thick parts of the products.