8.8.10 Injection Stretch Blow Molding PET tends to perform much better if it is biaxially oriented. Normal bottles have uniaxial orientation as they are stretched radially (horizontally) when the bottle is blown. To get biaxial orientation, we need to also stretch in a perpendicular direction (vertically). Notice in the picture below that the parison is much shorter than the finished bottle. That is the key to getting biaxial orientation and the process that does this is injection stretch blow molding. 8.8.9 Injection Blow Molding Injection blow molding is a two-step process. Often, the steps are located in different plants which may be adjacent to each other or separated by hundreds of miles. The first step uses the injection molding process to manufacture a preform. The preform is a plastic tube, similar to a test tube, with a complete bottle finish. The injection molding process manufactures the threads and other parts of the finish to closer tolerances than is possible with the extrusion blow molding process. This is important when the finished bottle will be used for
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