The pet plastic bottle is disturbed by gas during the filling process, and some cavities or bubbles are often formed on the surface of the product. Now summarize the factors about the appearance of bubbles.
1. The speed is very fast, which makes the molten plastic decompose by large shearing and produces gas.
2. The local cooling of the product is very fast and the shrinkage is absolutely uneven. Especially when the wall thickness of the product is relatively large, the surface cooling speed is faster than that of the central part. During the cooling process, the plastic edge of the central part shrinks and expands to the outer surface, resulting in insufficient filling of the central part and forming vacuum bubbles.
3, the pressure and holding pressure is insufficient, so that the melt and cavity surface has not been close to, is not conducive to the discharge of air.
4. The back pressure is insufficient. The back pressure controls the speed of the screw back. When the back pressure is relatively small, the speed of the screw back will be fast, which is easy to produce insufficient feed. More air is brought in from the material, and it is too late to discharge from the feed port, resulting in a large number of bubbles.
The raw materials have moisture.
If the mold is trapped, the mold should be maintained or the exhaust tank should be added.
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