Hollow blow molding (also known as blow molding) is the method of forming hollow products with the help of gas pressure to make the hot melt parison closed in the mold blowing, is the third most commonly used plastics processing methods, but also a faster development of a plastics molding method. Blow molding with only negative mold (concave mold), compared with injection molding, equipment cost is lower, more adaptable, can be molded with good performance (such as low stress), can be molded with complex undulating curve (shape) of the product.
Blow molding originated in the 1830s. It was not until after 1979 that blow molding entered into widespread use. At this stage, blow molding grade plastics include: polyolefins, engineering plastics and elastomers; blow molded products applications involving automobiles, office equipment, household appliances, medical care, etc.; hourly production of 60,000 bottles can also manufacture large blow molded parts (pieces weighing up to 180kg), multi-layer blow molding technology has been a greater development;
blow molding equipment has been used microcomputer, solid-state electronic closed-loop control system, computer CAE/CAM technology has also been used in the blow molding industry.
Blow molding equipment has adopted microcomputer, solid-state electronic closed-loop control system, computer CAE/CAM technology is also increasingly mature; and blow molding machinery is more specialized, more characteristics.
Here are the characteristics of blow molding from a macro point of view. Blow molding of hollow products include three main methods: extrusion blow molding: mainly used for unsupported billet processing; injection blow molding: mainly used for billet processing supported by the metal core; stretch blow molding: including extrusion a stretch a blow molding, injection a stretch a blow molding two methods, can be processed biaxially oriented products, greatly reducing the cost of production and improve the performance of products. In addition, there are multi-layer blow molding, compression blow molding, dip coating blow molding, foam blow molding, three-dimensional blow molding. However, 75% of the blow molded products with extrusion blow molding, 24% with injection blow molding, 1% with other blow molding; in all the blow molded products, 75% belong to the two-way stretch products. The advantages of extrusion blow molding is high production efficiency, low equipment costs, a wide range of choice of molds and machinery, the disadvantage is the high rate of scrap, waste recycling, poor utilization, product thickness control, the dispersion of raw materials is limited, the molding must be trimmed after the operation. The advantages of injection blow molding is no waste generated during processing, can well control the wall thickness of the product and the dispersion of the material, fine-necked products with high molding accuracy, the product surface is smooth and clean, and can be economically small batch production. The disadvantage is the high cost of molding equipment, and to a certain extent only suitable for small blow molding products.