Blow moulding, also called hollow blow moulding, is a rapidly developing plastic processing method. The tubular plastic parison obtained by extrusion or injection molding of the thermoplastic resin is placed in a split mold while it is hot (or heated to a softened state). After the mold is closed, compressed air is injected into the parison to blow the plastic parison It expands and clings to the inner wall of the mold, and after cooling and demolding, various hollow products are obtained. The manufacturing process of blown film is very similar in principle to blow molding of hollow products, but it does not use molds. From the perspective of plastic processing technology classification, the molding process of blown film is usually included in extrusion. The blow molding process was used to produce low-density polyethylene vials during the Second World War. In the late 1950s, with the birth of high-density polyethylene and the development of blow molding machines, blow molding technology has been widely used. The volume of the hollow container can reach thousands of liters, and some production has adopted computer control. Plastics suitable for blow molding include polyethylene, polyvinyl chloride, polypropylene, polyester, etc. The resulting hollow containers are widely used as industrial packaging containers.
According to the production method of the parison, blow molding can be divided into extrusion blow molding and injection blow molding, and the newly developed multi-layer blow molding and stretch blow molding.
