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How to do Blow Molding

It draws on the long-established glass container blowing process. Blow molding originated in the 1930s. It was not until 1979 that blow molding entered the stage of widespread application. Blow molding is one of the third most commonly used plastic molding methods, and it is also a rapidly developing plastic molding method. Blow molding of hollow products includes three main methods: extrusion blow molding, mainly for unsupported parison processing; injection blow molding, mainly for parison processing supported by metal cores; stretch blow molding, including extrusion blow molding.

Out-stretch-blow molding, injection-stretch-blow molding two methods, can process biaxially oriented products. In addition, there are multi-layer blow mold, but 75% of blow molding products are extrusion blow molding, 24% are injection blow molding, and 1% are other blow molding. The advantages of extrusion blow molding are high production efficiency, low equipment cost, and a wide selection of molds and machinery; the disadvantages are high scrap rate, waste recycling, poor utilization, product thickness control, and limited raw material dispersibility. Trimming must be done afterwards.

The hollow container is prepared by extrusion blow molding by first extruding the tubular parison into between the two open molds. When the parison reaches a predetermined length, the mold is closed, the parison is cut, and the upper and bottom of the parison are closed. Compressed air is introduced into the center of the blank or the needle inserted into the parison, and the parison is inflated to make it close to the cavity wall. After cooling, the mold is opened and the product is released.

The film prepared by extrusion blow molding is extruded into a thin-walled tube with a constant cross-section through an annular gap die, and at the same time, compressed air is introduced from the center of the mandrel to inflate it. Under the action, it is gradually extended and shaped; after Z, it is led to the winding device, and rolled into a double-folded plastic film.