Stretchblow

Stretchblow, more commonly referred to as stretch blow molding, is a plastics manufacturing process used to form hollow plastic parts, especially bottles and containers. The term usually denotes the two-stage variant in which a polymer is first formed into a close-ended preform and then blown into a final shape, with biaxial stretching invoked to orient the polymer and improve performance. A related one-step variant combines injection and blowing in a single machine.

In the two-stage process, a thermoplastic such as polyethylene terephthalate (PET) is first injection molded into a preform that has a standardized finish for neck opening. The preform is then heated to a temperature suitable for stretching and blown within a bottle-shaped mold. A stretch rod applies axial elongation before high-pressure air expands the preform to conform to the mold, producing enhanced strength and clarity due to molecular orientation.

Materials commonly used include PET, with PETG and other polymers used in specialized applications. One-step stretch blow molding adapts the process for inline production, potentially reducing cycle times for high-volume beverage applications.

Advantages of stretchblow molding include improved mechanical strength, gas and moisture barrier properties, and the ability to produce lightweight, high-clarity containers. Limitations involve higher equipment costs, material and process control requirements, and longer cycle times compared with some alternative molding methods.

Applications are dominated by beverage bottles, but the technique is also used for cosmetic and household containers, pharmaceuticals, and other hollow articles.