Published on the Packaging World Web site
| December 31, 1994
Empty-bottle handling is no picnic
The lightest of the PET bottles filled on Pepsi's new line weighs just 27.5 g. Controlling these empty containers at high speeds is difficult to say the least.
"This is a very new bottle" says Pepsi-Cola Co.'s Winston-Salem plant manager Matthew Bucherati in describing the 20-oz PET Fast Break bottle. "We're still learning how to handle it." Nowhere are the lessons more critical than in the area of empty-bottle handling especially depalletizing and single-filing. Simplimatic Engineering (Lynchburg VA) supplied the equipment that performs both tasks as well as the air conveying system that follows.(For a look at how the bottles are filled see Packaging World December '94 p. 18.) The photos included here reflect the fact that on the day Packaging World toured Pepsi's Winston-Salem plant 2-L bottles of Mountain Dew were in production. The 20-oz Fast Break bottle is handled by the same equipment in just the same way. The scary part doesn't really begin until after a layer of bottles has been swept from its pallet onto the mass conveyor belt. Between here and the point at which the bottle neck is in the firm grasp of the air conveying system every single bottle is a free agent capable of tipping over if given the slightest excuse. One big help is matte-top conveying. It's smoother than chain-link conveyors so the opportunities for a bottle to get hung up on a protruding or slightly uneven link are eliminated. Split the flow in half Dividing the initial mass of bottles into two separate mass flows is also critical. "The device does not exist that can single-file these small bottles from one large mass at these kinds of speeds" says Bucherati. "So we divide into two mass streams before we attempt to single file. Once we have two separate single files we combine them into one." While the bottles are moving forward in a mass they're mutually supportive which in itself contributes a certain measure of stability. But to minimize friction along the perimeter the guide rails are lined with hundreds of revolving beads. As a result the bottles that touch the guide rails are in contact with a moving surface that helps them along rather than hindering them. This lets bottles flow more smoothly and reduces the likelihood of one tipping over. The matte-top conveyors accomplish the task of single-filing because each section runs increasingly faster than the section that precedes it. This causes the mass of bottles to be elongated and individual bottles to be pulled apart from their mass alignment. Once they begin behaving more like individual units rather than parts of a mass it's much easier to get them into a single file. The final stages of single filing are accomplished in a pressureless combining system. That is rather than use rails on both sides to more or less squeeze the flow of bottles down to a single file the fragile bottles are gently encouraged to align themselves along a single rail. Vacuum assist plays an important role too as ducts are constantly pulling air through the matt-top conveyor. This downward pressure helps to stabilize the bottle in an upright position. Old concept new application According to Simplimatic's Scott Jamison pressureless combining has been used in the past for glass bottles when too much friction during single-filing might abrade an expensive applied ceramic label. "But with glass you're looking at a whole different set of problems and generally they're much easier to resolve" says Jamison. "The system we developed for Pepsi is practically a prototype." One built-in complication inherent in the fast-paced world of one-piece PET bottles is that each bottle supplier has its own unique bottle base profile. The precise configuration of that base is an all-important factor in getting the bottle to stay upright with any kind of consistency on a fast-moving conveyor. Other variables have surfaced as well some of them quite unexpectedly says Jamison. "We're discovering that atmospheric conditions like humidity or sometimes the age of the bottle can play a role in how we handle the bottle. If it's humid we may have to slow the bottle down or adjust the force of the vacuum in a specific area. Even the color green or clear can make a difference in how the bottle handles. They have two different surface tensions one stickier than the other. So we may be running smoothly with Pepsi in a clear Fast Break bottle but then when we switch to Mountain Dew in green we discover we have to make all kinds of adjustments. There's just a lot of unknowns when it comes to one-piece PET bottles right now." Some of the problems experienced early on have been addressed by subtle modifications to the mold in which the bottles are stretch/blow molded by Constar Intl. (Atlanta GA). Tweaking bottle and line "Just as we've been tweaking the line we've been perfecting the bottle too" says Bucherati. "We want it to have an esthetically pleasing shape while being as operationally runnable as possible." Some of the changes are barely discernible. For instance an increase of 20 thousandths of an inch in the size of the areas where Fast Break bottles touch each other above and below the recessed label panel produced what Bucherati calls a "night and day difference" in stability. In spite of all these variables in each of two lanes the bottles are eventually aligned in a single file and are conveyed forward to a transfer point where their neck rings rest on the supporting guide rails of the air conveying system. From this point they hang suspended pushed by air. Downline a two-to-one combiner constantly monitors availability of bottles in each of the two lanes and through a gate switch it sends bottles down toward the rinser from one lane or the other. Though Bucherati and his colleagues in Winston-Salem are candid about just how difficult it is to fill this new breed of small one-piece PET bottles they also know they have no choice but to get good at it fast. "The small PET bottles are preferred by consumers because they're light unbreakable recyclable and resealable in a way that even an aluminum can is not" says Bucherati. It's clearly one of those shifts in beverage packaging that should continue gaining momentum for some time to come. What choice does a beverage marketer have but to get used to it?