PETpla.net Insider 04 / 2018

BOTTLE MAKING 28 PET planet Insider Vol. 19 No. 04/18 www.petpla.net Stretch Blow Molding, part 8 Machine details - Oven section 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 third edition under the Elsevier imprint. PETplanet Insider is publishing extracts from successive chapters in a series of articles. 4.1 Oven section The importance of a properly designed oven section cannot be overstated. This refers to both the overall layout and the design of the actual ovens. Ovens must:  impart the correct temperature profile into the bottle wall  give processors flexibility in heat- ing sections of the preform to the best temperature for even bottle wall thickness distribution  have large enough blowers to control heat buildup inside the ovens  protect the neck finish of preforms  cool the infrared lamps for maxi- mum life-span  cool the reflectors opposite the lamps  leave room for sufficient equilibra- tion time  be sized for the correct through- put at a given preform wall thick- ness. It is apparent from this list that oven design has attracted a great deal of engineering effort and modern achines feature excellent systems that are able to deliver lightweight bottles conforming to ever-increasing specifi- cations. Layout As previously mentioned preforms may travel through the oven system neck-up or neck-down. As long as heated air is efficiently vented out of the system both methods work well. Figure 4.1 Layout of infrared oven. Dia- gram courtesy of Krones AG. There are usually eight or nine infrared lamps spaced vertically at a distance of 15–19mm (5/8–3/4in). Close spacing is necessary in order that the corresponding sections of the preform can be heated exactly to the point where the best bottle wall thick- ness distribution is achieved. Older designs incorporated larger or twin lamps that did not offer processors enough flexibility and these systems are no longer being manufactured. Lamps should be adjustable hori- zontally. This allows the processor to move them closer into areas that need the most heat. This is usually the sec- tion immediately below the neck. This area requires more heat as it is adja- cent to the cooler (unheated) neck, and also because the shoulder of the bottle requires less material in most cases. Failure to heat up this section suffi- ciently results in a ring of thick material in the bottle that is both unsightly and leaves less material for the rest of the bottle where it is needed. Lamps are