PETpla.net Insider 10 / 2017

BOTTLE MAKING 24 PET planet Insider Vol. 18 No. 10/17 www.petpla.net Stretch Blow Molding, part 7 Reheat Stretch Blow Moulding Machines by Ottmar Brandau Ottmar Brandau has newly revised his book “Stretch Blow Molding”, first published by hbmedia/ PETplanet Publisher, and now re-issued in a second edition under the Elsevier imprint. PETplanet Insider is publishing extracts from successive chapters in a series of articles. Differences between rotary machines of different manufacturers Differences between rotary machines include:  The orientation of the preforms in the ovens and blowing section  The number of cam-driven move- ments  The shape and location of the oven section  The way the blow moulds move  The way stretch rods are driven  The operator interface  Various process options Orientation of preforms and bottles In some machines, preforms travel neck down through the ovens, in others neck up. Neck-down orien- tation was thought to make it easier to protect the neck from the heat of the infrared lamps and was at one time the preferred method. However, advances in neck protection through more elaborate airflow systems have removed this obstacle, and two of the three most popular machines now use the neck-up position in their machines. This has eliminated turning of preforms and bottles and has thus simplified machine lay- outs, leading to gains in operational efficiency. Some manufacturers of linear machines have also adopted this preform transport method, which seems to have become the standard. From a process point of view, there is no difference in the orientation of the preform during blowing and there is slight advantage in the neck-up blow- ing position with pneumatically oper- ated stretch rods as they can move faster when they work with gravity, instead of against it. Movement actuation Most rotary machines have some movements driven by mechanical cams while using cylinders for other movements and vary in how these two methods of actuation are used. Cam-driven movements are more difficult to adjust but tend to be very stable without variations in speed or force. They also need little main- tenance for long periods of time. Cylinderdriven movements are more flexible and operators can easily adjust them from the control panel of the machine. However, they tend to show slight variations in movement behaviour and require more frequent maintenance. Servo-driven stretch rods are now in use by some manu- facturers offering consistent perfor- mance and ease of setup through the operator interface. Shape and location of oven section The trend over recent years has been to design machines that have U-shaped oven tracks. There are no ovens in the turnaround section, thus giving some extra equilibration time