Stretch Blow Molding

What is the stretch blow molding process?

Stretch blow molding is a two stage process similar to injection blow molding. First, a test tube like preform parison (pictured above) is injection molded in-house, or the preform parison can be purchased from an outside vendor. The neck of the preforms is fully finished (with threads) but the diameter and length of the body are much smaller than the final product. The thermoplastic preform then undergoes a reheat process (usually via infrared heaters) and is stretched and blown against the mold. This process is sometimes referred to as “reheat and blow molding” process, RHB for short. Below is a step by step diagram of the stretch blow molding process:

 

1. The purchased preform is reheated and placed into the blow mold cavity.
   
2. Compressed air is injected into the preform via the core pin while the core pin pushes forward to stretch the preform further into the mold.
3. The blowing and stretching process continues until the core pin stops near the far end of the mold.
4. The thermoplastic solidifies to the shape of the mold (with a hollow center).
5. The mold opens and the finished product is ejected.