PETpla.net Insider 09 / 2017

BOTTLE MAKING 31 PET planet Insider Vol. 18 No. 09/17 www.petpla.net valves, allowing fine-tuning and reduc- ing dead-air volume. The same device that shuttles preforms in also takes the blown bottles out, either on stand- up or on air conveyors. Figure 3.7 This machine uses a cam- driven blow clamp and base insert mechanism controlled by a servo motor. Picture courtesy of Chumpower Machin- ery Corp. Machines of this type use servo motors to achieve proper synchronisa- tion between the continuously moving mandrels and the pick-up devices (see Fig. 3.8). Low energy consump- tion and minimal maintenance are resulting benefits. While the time between the end of oven section and the start of blowing is slightly differ- ent for each preform (the first preform may exit the oven section up to 3s before the last), the author has not found this to be of any consequence to the bottle wall distribution and has never had to use individual blow air control. Figure 3.8 Some of these machines use a gripper system that is very similar to that used on rotary machines. Picture courtesy of Kosme GmbH. The great advantage to these machines is that they deliver nearly identical quality to rotary machines at outputs ranging from 1,700 to 2,200 b/c/h (bottles/cavity/hour) but at a much reduced capital cost. Rotary machines are more expensive because of the costly distributor sys- tems that are in the centre of the blow wheel. The excellent quality of the linear continuous motion machines stems from the fact that all preforms receive the same heat and can be blown into bottles with identical wall thickness distribution. One caveat for owners of rotary machines may be that moulds of those will not fit into some linear machines. 3.5 Rotary machines Rotary machines are the stars of the blow-moulding world and produce most the world’s soft drinks and water bottles. This market segment con- sumes up to 80% of all PET converted into bottles, and the resulting income stream has enabled manufacturers to pour significant amounts of money into research and development efforts. This, in turn, has resulted in massive innovation intended to drive outputs up. Output is usually measured in bottles/cavity/hour and this number has increased from 800b/c/h in the 1990s to 2,200b/c/h today on some machines. Machines up to 40 cavities and with output of up to 80,000 b/h are on the market today. The enormous progress was possible by increasing mechanical speeds and fine-tuning process time. One major obstacle to running at the highest output rates is the thicker wall thickness in the base of a bottle that needs cooling time. Read- ers should note that published output numbers always refer to lightweight water bottles that feature completely stretched-out bases. Custom and carbonated soft drinks (CSD) bottles require longer process time and thus result in a reduced machine output. The oven sections of rotary machines are very similar to those of other machine types and each manufacturer has a particular design to effectively heat preforms and avoid undue temperature increase in the preform necks and at the connections of the infrared lamps (Fig. 3.9). This is discussed further in the section on oven design.