The hollow blow molding process is to place the semi-molten tube blank (parison) obtained by extrusion or injection molding in various shapes of molds, and blow compressed air into the tube blank to make it close to the mold. The molding method of hollow products is obtained by cooling and demoulding on the cavity wall. Its molding process includes the manufacture of plastic parisons and the blow molding of the parisons. This molding method can produce various packaging containers such as bottles, pots and barrels with different diameters and capacities, daily necessities and children's toys.

The plastic varieties used for hollow blow molding include polyethylene, polyvinyl chloride, polypropylene, polystyrene, linear polyester, polycarbonate, polyamide, cellulose acetate and polyacetal resin. Among them, the consumption of high-density polyethylene occupies the first place. It is widely used in the packaging of food, chemical and processing liquids. High molecular weight polyethylene is suitable for the manufacture of large fuel mash tanks and barrels. Because of its good transparency and air tightness, polyvinyl chloride is widely used in the packaging of cosmetics and detergents. With the development of non-toxic polyvinyl chloride resins and additives, as well as the development of stretch blow molding technology, the amount of polyvinyl chloride containers used in food packaging has increased rapidly, and has begun to be used in the packaging of beer and other beverages containing carbon dioxide gas . Linear polyester material is a new type of material that has entered the field of hollow blow molding in recent years. Because its products have the advantages of glossy appearance, excellent transparency, high mechanical strength and good preservation of items in the container, and no environmental pollution during waste incineration, it has developed rapidly in packaging bottles, especially It is widely used in pressure-resistant plastic food containers. Due to the improvement of resin modification and processing technology, the usage of polypropylene is also increasing year by year.

Blow molding can basically be divided into two categories: extrusion-blow molding and injection-blow molding. The main difference between the two is the preparation of the parison, and the subsequent blow molding process is basically the same. On the basis of these two molding methods, there are: extrusion-stretch-blow molding (referred to as extrusion-stretch-blow), injection-stretch-blow molding (referred to as injection-stretch-blow) and multi-layer imaging plastic etc.

Injection-blow molding (abbreviated as injection-blow) plastic bottle is a hollow product made of plastic with a bottom by injection molding, and then the parison is moved to a blow mold while hot. Note - Blown hollow containers have no flash, good dimensional stability, excellent bottle mouth and thread quality, pre-adjusted parison thickness, good gloss of products, saving raw materials. But note - blow molding is not suitable for the production of large and complex containers, and because two sets of injection and blow molding are required, the equipment investment is relatively large. Note - Blown hollow containers are mainly small bottles with a single shape, which can be produced from polyvinyl chloride, polyethylene, polypropylene and polystyrene, polyester, polyamide and other resins. Mainly used for packaging of medicine, food, cosmetics, etc.

(1), continuous extrusion inflation method. The sequence of continuous extrusion and blow molding of hollow plastic products: extrude the melted tube blank that has been mixed and plasticized uniformly from the extruder to a certain length - the product is moved from the inflation and cooling station to the melt tube with the molding die Below the billet → the billet tube material enters the forming mold → the mold is closed, and the tubular feed is cut off → the forming die is moved to the inflation and cooling position (the other forming die moves simultaneously to the bottom of the tube blank) → the mold is opened and the molded plastic product is demolded. The forming die moves reciprocatingly to exchange positions, so that the extrusion and blow molding of hollow plastic products can be carried out continuously. This production method has the advantages of simple equipment structure, low investment, and easy to master the production process and operation. At present, this method of producing hollow plastic products is widely used in small and medium-sized plastic products factories.

(2), transposition feeding extrusion inflation method. The production method of extruded and inflated hollow plastic products by transposition feeding is basically the same as that of continuous extrusion and inflation, except that the feeding method is controlled by the reversing valve (the forming mold is fixed), and the molten material is alternately supplied to the two forming molds, and then Inflation molded articles.

(3) Rotary disc continuous extrusion blowing method. The continuously extruded plasticized molten blank tubes are respectively supplied to a plurality of molding dies that rotate around the axis of the turntable. With the rotation of the turntable, the actions of clamping the mold, cutting the blank tube, inflating and cooling, and opening the mold to release the plastic product are completed.

In the extrusion and inflation molding of large-scale hollow plastic products, due to the large amount of materials used for one-time molding, the extruded molten material is first stored in a storage cavity during production, and when the amount of material is reached, the molten material is quickly pushed and melted. The material enters the product forming mold through the blank tube, and then blows and cools to form.