Blow forming is a forming method in which an extruded or injection-molded parison is placed in a mold, inflated by compressed air to adhere closely to the cavity walls, and then cooled and demolded to obtain a hollow product. This forming method can produce various packaging containers such as bottles, pots, barrels, as well as daily necessities and children's toys. Blow forming mainly refers to hollow blow forming, which is a method of forming hollow products by using gas pressure to inflate a molten parison enclosed in a mold. It is the third most commonly used plastic processing method and also a rapidly developing plastic forming method. The molds used in blow forming are only female molds (concave molds). Compared with injection forming, the equipment costs are lower, the adaptability is stronger, it has good forming performance (such as low stress), and can form products with complex undulating curves (shapes).
All materials with a melt index of 0.04 ~ 1.12 are relatively excellent hollow blow forming materials, such as polyethylene, polyvinyl chloride, polypropylene, polystyrene, thermoplastic polyester, polycarbonate, polyamide, cellulose acetate, and polyoxymethylene resin, among which polyethylene is used the most.
The blow forming process includes three basic steps: parison forming, inflation forming, and product cooling. First, the plastic is processed into a parison (injection or extrusion), then the high-temperature parison is placed in the blow mold. Compressed air is injected into the parison, inflating it to adhere closely to the cavity walls, maintaining the inflation pressure until the part cools and sets, and then deforming to obtain the hollow plastic part.
Blow forming is a plastic processing technology involving the following main steps: Firstly, melt and plasticize the plastic raw material in an extruder or injection forming machine to form a viscous fluid melt. Next, use the extruder head and die or injection mold to form the melt into a tube or parison. Then, place the high-temperature parison into the blow mold, close the mold while clamping the parison. Subsequently, an auxiliary air compressor injects compressed air into the parison, inflating it to closely adhere to the mold cavity walls, maintaining the inflation pressure until the plastic part cools and sets. Finally, open the mold to take out the product, and conduct necessary post-processing such as trimming flash, printing, and labeling. Blow forming has the advantages of a wide range of product sizes, complex shapes, and high production efficiency, and is widely used in packaging, containers, toys, automobiles, and other fields.
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