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Reheat stretch blow machinery

PET Resin
Preform molding
Preform design
Preform Animation
Blow Molding
Bottle Design
Reheat stretch blow machinery
Single stage machinery
One stage vs. two stage machinery


These machines load completely cooled down preforms onto rotating mandrels, heat them up to blowing temperature through an oven section, allow a short period for equalization and then stretch and blow them into bottles.
There are linear and rotary machines. The linear machines have the oven and blow section in a line, sometimes a curved one for that. They are primarily used for smaller outputs.
The rotary machines always have the blow cavities on a carousel and might have the ovens in a linear or rotary fashion. Process parameters are often cam driven and the handling of preforms and bottles requires many mechanical components. Preforms and bottles are handled by the neck rings, which are common for water and soft drink bottles.
The oven section uses infrared heating lamps the wave length of which penetrates the PET and allows for even heating through the entire wall. Powerful fans keep the oven temperature low so that little convective heating takes place, which could cause process control problems.
Outputs are generally rated as number of bottles per cavity per hour. This number stayed for the longest time around 1,000 but has significantly increased over the last years. Sidel showed a machine at the K-Show 2001, that produced 2,000 bottles per cavity per hour! The bottle itself was remarkable too: a 26 g preform for a 1.5l bottle. Both SIG and Krones guarantee outputs around 1,800 bottles per hour per cavity.
Because the preform rotates in front of the ovens, circumferential conditioning proves to be difficult. Manufacturers have invented several methods of what is called “preferential heating”. These methods include blowing air at certain sections of the preform or holding the preform fixed in front of the oven for part of the way to achieve a temperature differential.
Another development is orienting the neck finish to the bottle. This feature is important for non-round closures that need to face in a certain direction to the bottle. Sensitive light sensors and servo drives are used to rotate the preform in the right position in the bottle mold.
Advantages of reheat stretch blow machines are:

  • high outputs
  • lower capital investment if preforms are purchased
  • optimal axial bottle conditioning leading to optimal bottles with respect to carbonation retention and other properties
  • easier mix-and-match between injection and blow cavities

Disadvantages are:

  • lower thermal efficiency since the molder has to pay to cool the preforms completely and then pay again to reheat them
  • preforms are frequently scratched during transport and storage
  • preforms without neck ring are difficult to handle

Manufacturers are: KHS Corpoplast, Krones, Magic, Mag Plastics, Siapi, SIDE, Sidel, SIPA, Urola, W. Amsler