Processes

INJECTION STRETCH BLOW MOLDING

Nathanial Wyeth, inventor/ engineer at DuPont, introduced the first plastic PET bottle able to hold carbonated drinks in 1973. An experiment in his home refridgerator showed that the plastic at the time was not rigid enough to hold the expansive gases in a carbonated drink. He knew that he needed a stronger construction of the bottle to hold the gases. Wyeth developed a method of aligning the molecules with a biaxial orientation, on two axis instead of just one. He developed the preform and the extrusion technique which produced a final product that was light, safe, clear, and resilient.

Whether using single or two stage processes, there are four phases to the process:
Injection, conditioning, Stretching and blowing, Discharge.

1. Injection – PET resin is heated to its molten state. The resin is injected through the hot runner into the injection cavity where the perform is made. The perform resembles a test tube. It contains all the plastic to create the bottle. The neck finish and it’s threads have been formed at this point.
2. Conditioning. The preform is warmed or cooled in targeted locations to prepare it for stretch blow molding.
3. Stretching and Blowing: Once the preform has been conditioned, it is moved to the stretch blow molding stage. Here the perform is biaxially stretched using a pneumatic stretch rod and high pressure air create the container.
4. Eject: Once the container is formed, the mold opens and the container is ejected for down stream quality inspection and further processing.

In a two stage process performs and blow molds are made in separate machines. The performs are made in a stand alone injection molding machine. They are then transferred to a reheat and stretch blow machine. Preforms can also be stored for future use or transferred to other stretch blow molding locations.

reheat and blow machine