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Article | November 30, 1995
Single-stage is on stage at Coke plant
Coca-Cola Company's commitment to bringing consumers the packages they want has helped make this plant in Poland special. Integrated injection molding of PET preforms and stretch/blow molding of bottles was a first in the vast Coke empire.
Watch first buy later Though Radzymin was the first plant in the Coca-Cola system to install SIPA equipment Tilley says management was confident about the relatively untried machine because he and his colleagues had a chance to watch 40 or so of them producing bottles for the Italian water and soft drink producer San Benedetto. Also a rigorous qualification period using pilot molds produced solid results that met all Coca-Cola standards. "Being a first as it was I guess you could say that going with one-stage technology was a bit of a gamble" says Tilley. "But all along we felt fine about our decision. And now after nearly 15 months of operation we're very pleased. We've also installed three machines in Turkey one in the Ukraine and one in Hungary." In each of these cases bottle volumes are relatively small somewhere between 15 and 100 million bottles annually. "These are emerging markets where for a reasonable capital investment we could make our own bottles right from resin in locations where there is no local supplier of PET bottles or preforms" says Tilley. "All we do is import resin" he adds. "Also a factor in this equation are customs duties across borders which are fairly high. So though we pay duties on the resin we import they're lower than what we'd pay on either preforms or bottles." An added advantage is that the ECS 8000 can also be used to produce preforms that can be blown with reheat-and-blow equipment says Tilley. "What you can then do is set up a satellite plant with a blowing machine. You produce bottles in your main plant where the ECS 8000 is during that plant's nonfilling hours. Then you ship the preforms to your satellite. We'll soon be doing that in the Ukraine and in Romania." As for Radzymin here too the volumes are not enormous so single-stage production makes sense especially compared to buying bottles from a commercial blow molder. "It was very attractive from a cost-per-bottle perspective" says Tilley. "We estimated the single-stage system brought savings of seven cents per bottle compared to bottles brought in from an outside supplier including the depreciation on the capital investment involved." Linear system While most blow molding systems are typically rotary in nature the ECS 8000 has a linear orientation. Thanks to a special transport system the process moves forward in a straight line from extruder to preform molding to preform conditioning to bottle blowing to bottle ejection. And though the ECS 8000 has only one extruder it has two bottle forming lines one on each side of the machine. The relatively small footprint of the ECS 8000 is among its advantages. Fully enclosed in a "cabin" that provides some degree of sound-proofing and allows for better control over the atmospheric conditions in which bottle making unfolds the system is 13.5 m long and about 3.1 m wide (44.3' x 10.2'). PET pellets are first dried and dehumidified before feeding into the extruder. Its 125-mm (4.92") diameter and slow rotation allows plasticization of the PET at low pressure (approximately 1 psi). As it continuously rotates molten resin is pumped through a special manifold and hot runner system that fills four "booster units" each located at the back of one of the four preform molds (see drawing below). These boosters are similar in function to the "shooting pot" employed by Husky (Bolton Ontario Canada) in its high-output preform molding systems. In SIPA's case however there are four such pots instead of one. The boosters are filled one at a time. A hydraulic plunger in the booster retracts under pressure of the incoming melt and when it reaches a predetermined point a valve automatically shifts to redirect the melt flow to another booster unit. Then the hydraulic plunger strokes forward to inject the shot under constant pressure of 7 psi into the eight-cavity mold. Because the pressure is consistent and minimal degradation of the melt is minimal claims SIPA. Mold-filling velocity is also closely controlled. "Controlling the speed at which the melt enters the cavity is important because if you don't get the material into the cavity quickly you deprive part of it from getting its full chance to cool" says SIPA's Roberta Gualtieri. "The heat exchange will be different in the bottom of the preform than in the top." That she adds can cause unevenness or other defects in the finished bottle. In addition to controlling the pressure and speed at which the melt is injected the system keeps temperature at a consistent 270°c (518°F). Also the hot runners of the injection molds balance the flow of resin into the molds. All these controls-of speed pressure temperature and amount-are computer-based. The net result says Gualtieri are conditions that minimize stress on the material. That limits acetaldehyde formation in the preforms and reduces the likelihood of a finished bottle exhibiting stress cracks or other mechanical failures she adds. Minimizing AA levels is one area in which SIPA claims to have made great strides. In a paper delivered at Bev-Pak Americas '95 last April SIPA's Giorgio Masini showed a chart tracking AA levels from 1988 to 1994 in critical cavities of a preform for a 1.5-L mineral water bottle. "We have passed from 10 parts per million to 3.2" Masini told his audience. Transfer to transport system When injection is complete water is circulated through the molds to cool the preforms. Then the molds open and the 16 preforms from molds B1 and B2 are transferred by a reciprocating multi-grip robot to a transport system on one side of the machine. The 16 preforms from A1 and A2 enter an identical transport system on the opposite side again by means of a multi-grip robot. Preform temperature at this point is 105°c (221°F) though the neck is at 35°c (95°F). During transport preforms are kept in place by collars that grip them yet exert minimal pressure on the necks so as not to damage their perfectly round shape. Hanging in their collars from the intermittent-motion transport system the preforms pause momentarily in two conditioning stations that give them the optimal temperature profile for stretch blowing. "One thing we learned as Coca-Cola developed its PET contour bottles is that for this more complex shape the conditioning stations require infrared ovens with special reflector lamps. This lets us profile the preform temperature more precisely" says Gualtieri. These IR ovens are not needed at Radzymin however since the 2- and 2.5-L bottles blown on the SIPA line are straight-walled. But according to CCA's Tilley they can be retrofitted. Next the preforms still held by their collars enter the blow molding stations. When the molds close the preforms are stretched vertically by hydraulically operated rods. They're blown radially at the same time in two sequential stages by low-pressure compressed air (around 145 psi) and then high-pressure compressed air (360 to 580 psi). The bottle base is formed by a base mold whose movement is synchronized with sidewall molds. Because the machine has parallel operating sides fed by the same extruder yet each fully independent of the other it's possible to produce two different sizes of bottles at the same time one on each side. Or preforms can be produced on one side and bottles on the other. At Radzymin however blown bottles are produced on both sides. When the molds open the transport system conveys the finished containers to an unloading station. It takes bottles out of the transport system and into an air conveyor system where the bottles are suspended by their neck rings. Next is a converging point where bottles blown from one SIPA machine merge with those blown by the other onto a single air conveyor. Rinser/filler/capper From the molder bottles are conveyed directly to the filling line. Ideally says Tilley a palletizer would be in place to accumulate blown bottles in case the filling line goes down; there is simply no room for one. But a 40-min buffer is available thanks to a spiral accumulation conveyor system from Neu-Transf'air (Marcq En Baroeul France). It also helps says Tilley that the SIPA systems can be slowed to 50% of their regular capacity with no loss in bottle quality and no need for restarting. At the head of the filling line is a monoblock rinser/filler/capper supplied by Sasib Corp. (Richmond VA). The 80-valve system discharges bottles to a Trine roll-fed straight-through labeler from CMS Gilbreth Packaging Systems (Trevose PA). It cuts the label material takes it by vacuum drum over the glue station then applies the label. A Kisters (Kleve Germany) tray packer packs eight bottles per tray and applies shrink film before a heat tunnel shrinks the film down tight. An automated palletizer and stretch wrapper both from Sasib complete the line. As with any in-line blowing and filling arrangement the two halves of the operation are fully dependent on each other. Should bottle-making go down filling stops too and vice versa. But according to Tilley that has not been a problem. Radzymin plant manager Bernhard Fisher agrees. "We installed the SIPA equipment in May of 1994" says Fisher. "It was September before the line was shut down for any real length of time. We ran around the clock that summer. It's now been some 16 months we've been running the line and we're very happy with it." Tilley believes today's modern controls have a lot to do with that. "It used to be that blowing bottles was made out to be a black art of some kind" says Tilley. "But with modern PLC controls changes are made at the touch of a button. Heating cooling pressure-they're all controlled automatically." These sophisticated yet user-friendly capabilities will help CCA expand in regions east of Poland. "Eastern Europe and the former USSR have tremendous potential" says Tilley. "In the franchise area of CCA-Europe there are 250 million people." It appears a lot of those people will soon be quaffing Coke.
The Coca-Cola Co. has been producing carbonated soft drinks in Poland since 1972. Like its peers in the Polish market Coke has relied on returnable containers for most of that time glass for the most part and in the last year or two polyethylene terephthalate as well. But in 1993 a brand new plant was built outside Warsaw in a town called Radzymin and when it opened Polish consumers got their first real taste of Coke Sprite and Fanta in nonrefillable cans and PET bottles. "Our philosophy is that consumers want both refillable and nonrefillable containers" says Nick Tilley technical director of Coca-Cola Amatil (CCA) the Australian-based franchise bottler that bought The Coca-Cola Co.'s Polish operations early in 1995. "If they want both our aim is to give them both." In the 8-sq-m (86-sq-ft) Radzymin plant the centerpiece of packaging technology is a line dedicated to 2- and 2.5-LPET bottles. The bottles are made and then filled in-line. The bottle-making portion of the operation represents a first for Coca-Cola franchise bottlers: injection molding of preforms and stretch blow molding of bottles on single-stage equipment from SIPA S.p.A. Based in Vittorio Veneto Italy SIPA has U.S. offices in Mt. Laurel NJ. At Radzymin two SIPA model ECS 8000 systems each equipped with 32 injection molding cavities and 16 blow molding cavities supply bottles to a filling line running at 200 bottles/min. Both 2- and 2.5-L bottles are produced. The installation of this line however reflects no particular CCA bias toward single-stage bottle-making systems. In fact in the same plant is an even newer in-line bottle blowing and filling line dedicated to 1-L PET bottles that uses the two-stage reheat-and-blow approach (see sidebar p. 35). The way CCA management sees it each new project has its own unique set of requirements. These are not only technical in nature but cultural geographical and political as well. Under such circumstances says Tilley "There is no one best thing to do." In other words there's a place for single-stage blowing and a place for reheat/blow technology. "But I do think" he adds "that it's very healthy for the industry to have someone like SIPA make an entry and a strong entry into a field that was largely dominated by two-stage technology for many years." Tilley formerly worked for The Coca-Cola Co. and played an integral role in assembling the Radzymin plant. He became a part of CCA in March of this year but he says the links between the Atlanta-based business and "anchor bottlers" like CCA are strong. "We try to view the business as a single enterprise if you like" he notes.
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