What is hollow blow molding? What types are there?

　　(1) Hollow blow molding Hollow blow molding is an important method of thermoplastic molding. It is a plastic molding method that uses gas pressure to inflate a closed hot preform in a mold into a hollow product. Hollow blow molding is mainly used to produce plastic hollow packaging containers and industrial hollow parts.

　　(2) Types of Hollow Blow Molding

　　There are many types of hollow blow molding processes. According to the different preform molding processes, they can be generally divided into two categories: extrusion hollow blow molding and injection hollow blow molding; according to the different stretching conditions, they can also be divided into ordinary blow molding, stretch blow molding, and three-dimensional (3D) extrusion blow molding; according to the product structure, they can be divided into two categories: single-layer blow molding and multilayer blow molding.

　　(3) Characteristics of Various Hollow Blow Molding

　　① Extrusion hollow blow molding Extrusion hollow blow molding is a process in which thermoplastic plastic is melted and plasticized, and a preform is extruded through the die head of an extruder. Then, the preform is placed in a blow molding mold, and compressed air (or other medium) is introduced to inflate the preform. After cooling and shaping, the product is obtained. Extrusion hollow molding can also be divided into continuous extrusion hollow molding and intermittent extrusion hollow molding according to its discharge method. Continuous extrusion hollow molding refers to the extruder directly and continuously extruding the preform through the die head, mainly used for the production of hollow products with large output and small volume (no more than 8L capacity).

Intermittent extrusion hollow molding refers to the extruder intermittently extruding the preform directly or extruding the melt into a material reservoir. When the melt in the material reservoir meets the requirements, the preform is extruded through the die head nozzle, and after blow molding, cooling, and shaping, large-capacity hollow products can be obtained.

　　② Injection hollow blow molding Injection hollow blow molding is a molding method in which a molding machine injects melt into a mold to prepare a preform, and then the preform is placed in a blow molding mold while hot, and air is introduced to inflate the preform. Injection blow molded products generally do not require finishing, have less scrap, good uniformity of preform wall thickness, good product dimensional accuracy, especially bottle containers, high bottle mouth accuracy, and good surface finish of the products. However, when producing small batches, the product cost is high, and it is not suitable for molding products with overly complex shapes and structures.

　　③ Stretch blow molding Stretch blow molding is a molding method in which a pre-made preform is heated to an appropriate temperature below the melting point, placed in a blow molding mold, axially stretched using a stretching rod, and then blown and laterally stretched. Stretch blow molding can be divided into extrusion-stretch-blow molding and injection-stretch-blow molding according to different preform preparation methods. Extrusion-stretch-blow molding first melts and plasticizes the material through an extruder, extrudes the preform, and then heats the preform to the stretching temperature before axial stretching and blow molding.