Introduction to blow moulding process




Molding method

Different blow molding methods have different advantages in processing different products due to differences in raw materials, processing requirements, output and costs. The detailed blow molding process can refer to the literature. Here we introduce the characteristics of blow molding from a macro perspective.

Blow molding of hollow products includes three main methods: extrusion blow molding: mainly used for processing unsupported parisons; injection blow molding: mainly used for processing parisons supported by metal cores; stretch blow molding: including Extrusion-stretching-blow molding and injection-stretching-blow molding can process biaxially oriented products, greatly reducing production costs and improving product performance.

In addition, there are multi-layer blow molding, compression blow molding, dip coating blow molding, foam blow molding, three-dimensional blow molding and so on. But 75% of blow-molded products are extrusion blow molding, 24% are injection blow molding, and 1% are other blow moldings; 75% of all blow-molded products are biaxially stretched products. The advantages of extrusion blow molding are high production efficiency, low equipment cost, wide selection of molds and machinery, but the disadvantages are high rejection rate, poor recovery and utilization of waste, thickness control of products, limited dispersion of raw materials, and molding After that, trimming operations must be performed.

The advantage of injection blow molding is that there is no waste generated during the processing process, the wall thickness of the product and the dispersion of the material can be well controlled, the narrow neck product has high molding accuracy, the product surface is smooth, and small batch production can be economically carried out. The disadvantage is that the cost of molding equipment is high, and to a certain extent, it is only suitable for small blow-molded products. The process conditions of hollow blow molding require that the compressed air of the parison in the inflation mold must be clean. The injection blow molding air pressure is 0.55 ~ 1MPa; the extrusion blow molding pressure is 0.2l ~ 0.62MPa, and the stretch blow molding pressure often needs to be as high as 4MPa. In the solidification of plastics, low pressure makes the internal stress generated by the product low, and the stress dispersion is more uniform, and low stress can improve the tensile, impact, and bending properties of the product.

Blow-molded products include containers and industrial parts. The containers include: packaging containers, large-volume storage barrels/tanks, and collapsible containers. However, with the maturity of the blow molding process, there are more and more blow molded products of industrial parts, and the scope of application is also increasing. At present, containers account for about 80% of the market share, with an annual growth rate of about 4%; while industrial and structural products account for 20% of the total, with an annual growth rate of 12%. The increase in container consumption is due to the continuous expansion of the application range of twistable plastic containers. The increase in consumption of industrial products is mainly due to the improvement of new processing technologies, such as multi-layer parison extrusion, biaxial extrusion, and non-axial extrusion. Symmetrical blow molding, etc. Table 2 lists the applications and performance requirements of some blow molded products.
blow moulding process
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