Due to its long chain structure and the flexibility of molecular chain, generally, when the polymer is placed at a certain temperature, from the action of external force, the formation and recombination of macromolecules undergo a series of intermediate states to the equilibrium state suitable for external force, which is a relaxation process, and its deformation changes with time.

Because the relaxation time t * of the polymer is very short near the high elastic state or viscous flow temperature, if the deformation time T1 > > t * during molding, it can be obtained from formula (3). When the external force action time t = T1: the high elastic deformation recovers after the external force is released. The formation of injection blow molding parison is to mold the parison on on a metal pipe by injection molding method. One end of the pipe is filled with compressed air, and the pipe wall at the other end is provided with micropores. The parison of injection molding is usually taken out after cooling, reheated above Tg before blow molding, quickly moved into the mold, and blown with compressed air. The parison expands, separates from the metal pipe and adheres to the mold wall for molding and cooling.

Once the injection mold blank is formed, it is still in the plastic state, and the mold is opened; Enter the second stage of molding, that is, quickly send the mandrel together with the parison to the blow molding mold, open the compressed air valve, blow the compressed air through the mandrel to make the parison still in the molten state expand to the shape of the mold cavity, open the mold after cooling in the mold and take out the products.

Vacuum bubble is generally that the product is not compacted, the product shrinks and the volume becomes smaller in the cooling process, and the outer surface of the product has been cooled and solidified. So there will be air pockets inside the thick meat. Hollow blow molding (also known as blow Bai molding) is a method of forming hollow products by Du blowing the hot-melt parison closed in the mold with the help of gas pressure.

It is the third commonly used plastic processing method, and it is also a rapidly developing plastic molding method. Blow molding in Zhongpeng mold design explanation, the commonly used blow molding mold is only female mold (female mold). Compared with injection molding, the equipment cost is low and the adaptability is strong