(1) During the formation stage of mold embryo, the transportation, melting, mixing and pumping of polymer in the extruder are the formation stage of mold embryo; At this stage, the main process parameters affecting the wall thickness distribution are:
① Molecular weight distribution and average molecular weight of the material;
② The temperature control system and screw speed of the blow molding machine, in which the temperature control system includes hopper temperature, barrel zone 1, zone 2, zone 3 and zone 4 temperature, flange temperature, and storage die zone 1, zone 2, zone 3 and zone 4 temperature.
(2) In the blanking stage of bottle blowing model embryo, the embryo is extruded from the gap between the die lip and the die core as the blanking stage. At this time, the two phenomena of mold embryo off mold expansion and mold embryo vertical extension affect the molding of mold embryo. The main process parameters affecting the wall thickness distribution are the die diameter and wall thickness control system of the blow molding machine. The control system includes axial wall thickness control system and circumferential wall thickness control system to adjust the gap between the die lip and the die core.
(3) In the stage of pre blowing of mold embryo, in order to avoid the contact and adhesion of the inner surface of mold embryo and improve the uniformity of product wall thickness, the mold embryo should be pre inflated. In the pre blowing stage of the embryo, air is sprayed from below the embryo into the embryo to protect the embryo and reduce its vertical extension. At this stage, the main process parameters affecting the wall thickness distribution are: pre blowing pressure and pre blowing time.
(4) In the stage of high-pressure blowing, the mold embryo is inflated under high pressure to make it close to the mold cavity to realize the plastic forming stage of the product. At this stage, what affects the product forming is the deformation of the mold embryo by high-pressure inflation and the contact deformation between the mold embryo and the mold cavity. The main process parameters affecting the wall thickness distribution are: material shrinkage; Blowing pressure and time; Mold material, structure, mold exhaust system and mold cooling system, such as cooling water channel distribution, cooling water inlet temperature, etc. Although there are many factors affecting the quality of blow molded products, when the production conditions and product requirements are determined, adjusting the blow molding process parameters can effectively improve the product quality. The optimized process parameters can improve production efficiency, reduce raw material consumption and optimize the comprehensive performance of products.
