Quick Question Monday : What are PET Blow Molding Machines?

Single Stage Blow Molding Machine

While PET bottle development was proceeding in the US, a large manufacturer of injection molding machines in Japan, was leading a project to develop a machine to make biaxially oriented PP (polypropylene) containers. They recognized that the prototype machine could be used to produce the new PET bottles and, in December 1975, the One-stage ASB-150 injection stretch blow moulding machine for making the new biaxial oriented PET bottles was unveiled. All one-stage injection stretch blow moulding machines derived from this original Stretch Blow design are referred to as classic one-stage machines, as the concept has long since been extended into other PET developments. The classic one-stage machines design is extremely versatile in that the same basic machine design can be used to make a wide variety of bottles and jars in all shapes and sizes.

Two Stage Blow Molding Machine

In the early developments, performs were made by continuously extruding a PET tube. To make these prefroms, a perform manufacturing machine that took a continuously extruded PET tube, heated and closed one end, and then heated the other and formed a thread finish by blow moulding. This process had a faster output rate, at 12000 preforms per hour, than the early injection moulding routes of 8 and 16 cavity moulds. Being extruded, the performs could be multilayered with barrier materials. The system was overtaken by injection moulded performs as the cavitation increased to 32 and beyond. The quality of the injection moulded (IM) neck, adding for example vent slots, made the IM finish preferable. Moreover, IM technology is available from more than one company, giving customers greater technical and commercial choice. Two-stage technology machines with six blow moulds operating at around 4000 bottles per hour. Subsequent mould and cooling development increased the output to 6000 bottles per hour.

Two stage PET processing includes:

  • Making performs by Injection Molding
  • Blowing bottles by Stretch Blow Molding

Because it is more flexible than one step processing, it is widely accepted in Plastic packaging market. You may choose to make preforms only or blow bottles only if you want to do one of them specially.

Integrated Two Stage Blow Molding Machine

In Integrated Two Stage approach the performs were made by more conventional injection moulding routes (with the number of cavities optimized to match the required output) and then, while still hot, were carried to a separate blowing machine with the optimized number of blow moulds to suit the required output. This was the first ‘integrated ‘approach to PET bottle making. Equipment developers took the ‘single-stage’ approach. Here the equipment had the same number of injection cavities as blowing moulds. This was a more compact approach and proved ideal for small batch output with excellent glossy surfaces.

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