Although stretch blow molding produces a variety of products, it is best known for the production of PET bottles used for juices, sports drinks, water, and similar products. First introduced in the early part of the 1970s thanks to advanced materials and techniques, it is now what manufactures prefer among the different types of blow molding for making bottles for carbonated beverages.
The primary benefit of using this molding process is that it can stretch a preform in both the axial and hoop direction. With the biaxial stretching of materials, tensile strength increases, as does clarity, drop impact, barrier properties, and top load. Also, the weight of the container decreases by as much as 15 percent compared to using one of the other types of blow molding processes.
There are two categories: single-stage and two-stage. For the single-stage, an extruder injects a parison into the preform mold where the plastic material cools rapidly to form the preform. Once reheated and placed into the bottle mold, the now-softened parison stretches to roughly 50 percent of its original length. At that point, compressed air gets blown into the parison, expanding it to the bottle mold. After the bottle cools, the mold opens and the finished product ejects.
The two-stage process is like the single-stage process with the exception that it works with an already made preform. Also, instead of using one blow molding machine for plastics as in the case of the single-stage process, the two-stage process relies on two machines – one to mold the preforms and one for blowing and ejection. With this blow method, manufacturers can either make or buy the preforms. A huge advantage of the two-stage process is that it can handle high-volume production runs, thereby lowering overall cost.
Regardless of the category, there are many unique applications for stretch blow molding. As mentioned, one application is the manufacturing of bottles used for beverages. However, manufacturers use this same process to make bottles that hold household cleaners, plastic food containers, health and oral hygiene products, agricultural containers, bathroom and toiletry products, and much more. With such a broad reach, it is easy to see why this method of blow molding is in such high demand.
For the highest-quality equipment, including stretch and extrusion blow molding among many others, you can always count on PET All Manufacturing, Inc. Providing services to customers in North America and Europe, we would love the opportunity to work with you regarding your needs. Call or visit us online today.