PETpla.net Insider 03 / 2021

INSPECTION 45 PETplanet Insider Vol. 22 No. 03/21 www.petpla.net directed to turn on during blowing. The process was running too hot, and the preform temperature was higher than necessary to produce the ideal stretch and orientation of the PET molecules. “In general, when making PET bottles, the colder you can make the process, the better,” explains Choate. “The goal in blowing is to get the very best orientation of the PET, both vertically and hori- zontally. This gives the best container strength.” It’s true that high heat makes the PET more pliable and easier to stretch, but all stretching is not equal, he points out. Cold forces the molecules to align better vertically and horizontally. Reduc- ing the preform temperature specified in the recipe by a few degrees will produce better overall resin distribution and better strength and rigidity, a critical attribute for shelf life. Gas permeation through the walls and resistance to volume expan- sion also improve with the proper orien- tation of molecules in a colder blow. In all, the PPOG engineers reduced the number of lamps that turned on in the oven by 15, from 69 from the original recipe to 54 in the revised one. They also lowered the preform temperature setpoint by four degrees. With these two changes, the bottle volume expan- sion went down to the most desirable rate of 12 to 13 per cent, from 40 per cent prior to the engagement, “a vast improvement,” DiZinno notes. Addition- ally, while it wasn’t a goal at the outset, the significant reduction in the blow- moulder operating temperature gener- ated approximately $20,000 in annual energy savings. Adressing the variables While the preform temperature inside the blowmoulder was the chief cause of non-conforming bottles for the German drinks maker, in other cases the PPOG engineers often connect the dots back to a processor’s preform supply. In fact, one of the most common challenges to optimum blowmoulder performance is the lack of consistency in preforms. Given that blowmoulding is a process where uniformity is key to stability, preform variations can produce out-of-spec bottles that seriously disrupt downstream production. Especially with today’s ultra-high line speeds, just a few minutes of downtime can cause a processor to lose thousands of dollars in sellable goods. Preform variations have multiple root causes. Without strict inventory control, they can age in storage and absorb moisture, or batches can become mixed. Preform age is a major source of variation. Further up the supply chain, preform manufacturers might switch to a different resin composition or use differ- ent injection moulding machines to fill a single customer order. “Self-manufactur- ers aren’t always tuned in to the subtle differences in product from their suppli- ers, and those differences can impact the entire filling line,” DiZinno comments. As an example, he cites one plant that was having trouble with non- conforming bottles. There were mul- tiple issues with poor bottle handling due to the preform variability causing unplanned stops, and jams in the filler, labeller, and bundler. After investigat- ing, DiZinno found that the plant was receiving preforms made from two different resins on 10 different injec- tion machines at five different facilities within the organisation. “The operators were making a single bottle design on a dedicated blowmoulder, but they needed 33 different recipes to accommodate the different preforms. There was so much variability in their process, they tried to compensate by fine-tuning a recipe for each different combination,” he relates. “The plethora of recipes just multiplies the opportunities for errors, and in the end, the bottles were never ideal.” To help plant personnel under- stand what was happening, DiZinno called up a production history chart on the Process Pilot screen to illustrate in granular detail how the thickness of the bottle sidewall jumped for 25 minutes when correlated with a specific preform batch. He explained how to interpret the data, showing operators how to use that detailed insight into thickness distribution to learn how to make better perform- ing bottles. After assisting the customer with optimising its process and engag- ing Process Pilot, the plant was able to handle all its preform sources with a single recipe. Lightweight and rPET That knowledge will be of increasing value as sustainability continues to grow in importance and brand owners embark on lightweighting and rPET initiatives. While global water brand owners have already made dramatic strides in reduc- ing bottle weights, CSD applications are just beginning to see weight reduction initiatives, Choate reports. Similarly, the commitment from major beverage producers to increase the use of rPET poses additional manufacturing chal- lenges. “When you use recycled resin, the material in the preform is inconsistent, and the bottle becomes increasingly diffi- cult to make,” DiZinno remarks. “Opera- tors typically don’t have the experience to deal with the issues that can occur.” Because Agr is not affiliated with any specific blowmoulder manufacturer, the engineers can provide whole-plant assis- tance even in facilities where multiple blowmoulder brands are running. The PPOG engineers utilising Process Pilot have achieved a gamut of improvements that range from faster blowmoulder start- ups, shorter changeovers, less operator involvement, rapid jam recovery, and reduced scrap to improved bottle qual- ity, lower material consumption, better performance in transit, enhanced shelf appeal, and fewer consumer complaints. “There will always be a bit of an art to manufacturing preforms and containers,” DiZinno observes. “Our engineers help operators develop a balanced, centered process that allows continuous operation without slowdowns or jamming despite changes like an increase in temperature or the amount of rPET in the preforms. It’s a matter of finding the right recipe for the plant, based on the unique environ- ment. It’s very custom work,” he con- cludes. www.agrintl.com One of the most common challenges to optimum blowmoulder performance is the lack of consistency in preforms.