Fast changeover and overall versatility were foremost in mind when Pepsi designed its high-speed line for hard-to-handle one-piece PET bottles in four different sizes. Machine redundancy, computerization, and modular construction all contribute significantly.
Sleek lightweight and easy to grip thanks to a slightly recessed label panel Pepsi's new 20-oz Fast Break plastic bottle is everything consumers could want (see PW July '94 p. 2). But all the things that make it so easy to handle by the consumer are the very factors that make it such a challenging bottle to fill. "Like any one-piece plastic bottle it's not an easy container to handle" says Matthew Bucherati plant manager at the Winston-Salem NC plant that was the first Pepsi-Cola Co. facility to fill the polyethylene terephthalate bottle. For starters it has no base cup to lend it stability and it weighs a mere 27.5 g. Further complicating things is the recessed label panel. "We don't have the entire side of the bottle as a contact point for bottle-to-bottle stability" says Bucherati. "All we have are two small contact points above and below the label panel." As if that weren't challenging enough when Bucherati and colleagues designed the high-speed line on which the new bottle was to be filled they had to make sure it would also accept three other PET bottle sizes: 12-oz 16-oz and 2-L. That meant quick and efficient changeover was all-important. "It wasn't just the Fast Break bottle that drove the design of the line" says Bucherati. "Other bottles and even packages of the future entered into it. Flexibility was critical so we had to ask ourselves 'If we need change parts what exactly are they? Or how do we avoid change parts altogether?'" Redundancy helps In some cases redundancy was the answer like the installation of two continuous-motion case packers even though one was capable of handling the line's top speeds. "It lets us continue to run one package size at the same time we're reconfiguring the case packer for another size" says Bucherati. Computers contribute too. "At the touch of a button on a screen the guide rails on entire conveyor systems reconfigure themselves to a new package size with no change parts or mechanical adjustments by operators at all" says Bucherati. Conveyor speeds are automatically adjusted too faster for a smaller bottle slower for a larger. Modular construction plays a role as well particularly on the case packers. The modules that handle the different bottle shapes mount on the machines' frames and the modules are interchangeable. "We move modules around from line to line not only for flexibility now but for future needs as we add more new packages or move packages from line to line" says Bucherati. The idea behind all these touches was to get down to where package changeover time is in the range of 10 to 15 minutes instead of several hours. Thus on a given day Line 1 may run three different packages. This represents a significant departure from the past both for this plant and for the soft drink industry. "We used to schedule a line for a 20-ounce day or a one-liter day and in that one package we might run as many as seven different flavors" says Bucherati. "But as we get package changeover down from hours to minutes suddenly we have a greater variety of options as we develop our production schedules. We're not locked into changing flavors we can change packages if we want to. That also allows us to make larger batches of product and not have to flush out the filler as often for flavor changes." The bottom line says Bucherati is that now there is a choice. Whatever is the most efficient way to meet current sales needs without carrying excess inventory that's the way a line can be scheduled. As for throughput it varies from size to size. Also it's still improving since the line has only been in commercial production since May. Bucherati isn't saying just how fast it runs other than to say it's designed to be among the fastest PET bottling lines around. Depalletizing and single-filing of the flimsy bottles is challenging to say the least (see story in next month's issue of Packaging World). But once bottles are single filed they're air-conveyed from their overhead position down to floor level and a rinser supplied by Simplimatic Engineering (Lynchburg VA). The bottles are air conveyed into the rinser and then controlled by side grippers as they move through the rinsing operation. When they emerge they return to air conveying and are blown into the filler room. Filling is performed by a 108-valve rotary unit removed from another line in the plant and rebuilt for Line 1. Adjacent to it is a rebuilt capper that applies 28-mm screw-cap closures with breakaway tamper evident bands. The speed at which the filler runs is automatically and constantly modulated according to information it receives from the line's control system. This consists of two Allen-Bradley 56 programmable logic controllers one governing the empty-bottle side of the line the other controlling the filled-bottle side. Each of these PLCs receives a constant flow of information describing line conditions from an assortment of Model 25 PLCs also from Allen-Bradley (Milwaukee WI) located up and down the line. The end result is a system that constantly analyzes incoming data and "decides" through programming logic what any given machine should do. Keep the filler running "The whole idea is to keep the filler running steadily" says Bucherati. "That way there's much less wear on brakes bearings and gears." Filled bottles exit the filling/capping room and are warmed to prevent condensation. "It's true we're putting these bottles in plastic shells which aren't affected by condensation the way corrugated shippers would be" says Bucherati. "But if we didn't warm the bottles after filling and thus allowed condensation to form the moisture dripping onto the warehouse floor would be a huge mess." Once past a large accumulation table the bottles are automatically assembled into discrete groups of 50 or 100 depending on bottle size. This greatly reduces back pressure on the bottles and with a one-piece PET back pressure has got to be minimized or bottles can be damaged. Now bottles proceed down one of two paths. If 2-L bottles are being filled they're conveyed directly to one of two side-by-side continuous-motion packers from Hartness (Greenville SC). It gently lowers them into plastic reusable shells eight per shell. However when the smaller sizes are in production the bottles are conveyed first through a carrier applicator. It applies photodegradable polyethylene tear tab carriers to six packs. Then the six packs move to one of the continuous-motion Hartness packers to be loaded into a plastic shell. In keeping with the overall objective of automating wherever possible Pepsi's engineers worked with Nigrelli Systems (Kiel WI) to develop a semi-automatic shell handling system that greatly simplifies shell handling for both packers. In most lines these are removed from pallets and fed singly onto the conveyor that carries them into the packer. Pepsi's system eliminates much of the repetitive motion involved in such a system. Pallets filled with returned shells are brought by forklift to the Nigrelli unit. There an operator lifts a stack of 10 shells and places them on the machine's conveyor infeed. The stacks are conveyed into the denesting station. As needed shells are fed individually onto a conveyor leading first to a washer and then to one of the Hartness continuous-motion packers. Fewer actions required "Without this system if we're running 50 shells per minute the operator has to perform 50 actions to get those 50 shells onto the conveyor" says Bucherati. "This way he only performs five actions per minute. And he's free to help in other areas nearby." As many as 20 stacks of shells can be placed on the Nigrelli system at a time. Filled shells leave the continuous-motion packers and are conveyed back up to the same overhead level at which the empty-bottle handling system operates. Following automatic palletizing the final piece of equipment in the line is a stretch wrapper from Lantech (Louisville KY). "It's the Lanwrapper model which has the wrapping head that moves around a stationary pallet" says Bucherati. "When handling plastic bottles in plastic shells you face some real stability issues so the last thing you want to do once you've stacked them on a pallet is to spin them like a top while applying stretch wrap." Bucherati says the thing that most amazes him as he looks at his plant today is its expanded capability. Until this spring he filled 16-oz glass 20-oz glass and 2-L PET on two lines. He now runs no glass and instead of three packages on two lines he now runs 10 on two lines. So much for the days of the dedicated bottling line. "Flexibility in package type is more important than ever in today's bottling lines" says Bucherati. "You build it in though as you do you also build in greater and greater complexity." Learning to live with that complexity and turning it into an advantage was the challenge that Bucherati and his people were faced with. By all appearances the challenge has been met.