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Article | May 31, 1995
Gleneagles springs for in-house stretch/blow molding
Scotland's Gleneagles Spring Waters shifts from buying PET bottles to stretch/blow molding them in-house from preforms. The change saves $600ꯠ/yr and provides a "family" image for its seven bottle sizes.
In-house solution "When we bought premade bottles we were limited to supplier availability so the bottles we sold looked like a hodge-podge of different shapes" laments John Hamilton managing director for Gleneagles Spring Waters a subsidiary of Allied-Lyons P.L.C. "We had disadvantages in terms of costs and control of quantity. We wanted to create a family look across our range of bottles and have the bottles resemble the quality image presented by glass" he adds. In '93 Gleneagles began to evaluate molding machinery in an effort to overcome these disadvantages. After visiting Krupp Corpoplast (Hamburg Germany) and working out its bottlemaking challenges with the machinery supplier Gleneagles placed an order for one of Krupp's new B 66 blow molding machines. Gleneagles uses a customized B 66. The original machine was rated at 6 bottles/hr on its six stations. By blowing preforms into warm molds and air-cooling blown bottles Gleneagles is able to produce as many as 7 bph (120/min) on its smallest bottle sizes. "Besides the superb service we receive there are two primary reasons we bought the Krupp machine" notes Hamilton. "One the machine is slightly smaller than competitive machines we evaluated for the same type of output. Two we were able to change over the equipment for different bottle sizes in anywhere between 50 minutes and an hour and 20 minutes. "The classic changeover time runs between five and eight hours so we enjoy a tremendous time and labor savings and an increase in our capacity. If we save four hours on a changeover that's roughly 24 extra bottles we can produce depending on the size we're running." On the materials side Hamilton wanted to stay with PET for its sharp clean image and blow-molding characteristics. "But we wanted to change to a consistent bottle shape and champagne base to create the appearance of glass" which U.K. consumers find desirable he says. United Kingdom-based Able Industries (Tenbury Wells Wor- cestershire) Continental PET (Corby Northants) Constar Intl. (Sherburn-In-Elmet North Yorkshire) and Johnson Controls (Mold Clwyd) all supply PET preforms. Multiple vendors are used for two primary reasons. First not every supplier can provide preforms for all of Gleneagles' bottle sizes. Second is availability. Having a backup supplier for each preform size is a must as Hamilton explains. "We've been trying to make certain we have an adequate future supply of PET resin. What has happened is that garment producers in the Far East have experienced shortages in cotton so they're converting to fiber. As a result PET for bottles is sometimes in short supply. By using multiple preform suppliers we have a backup source in the event of a PET shortage at one of our vendors." These suppliers add a green colorant to the batch to mold preforms for carbonated water offerings. On the Krupp machine "bottles for carbonated or spring water are blown the same way but they have slightly different preform weights and blow-molding characteristics" says Hamilton. "You have to increase the heat to transfer it through the green preform so those bottles are a little more expensive to produce. Also because the product in the green bottle is carbonated you need to put more plastic down in its base." Carbonated water bottles are also slightly taller than their spring water counterparts. Output meets demand Gleneagles receives preforms in lot quantities of 50 or more within rigid corrugated bins. A bin is emptied into an infeed hopper. An inclined slat conveyor carries preforms to an alignment device that places them neck-up to enter the machine's infeed rail. Grippers invert the preforms which makes it easier to evacuate dust and also helps to eliminate neck stress from rising warm air when the preform is preheated. Transport mandrels carry the preforms throughout the stre-tch/blow-molding process which continues from a loading/unloading wheel through a transfer wheel and into a heating wheel. Mandrels move around the wheel once turning on their own axis to ensure the preforms receive even heat distribution. Temperatures vary based on the preform but are usually in the 160° to 170° C range. Preform size determines spacing of the heating units as well as the speed at which the mandrels on the heating wheel revolve. As the wheel revolves each mandrel with its preform transfers onto one of the six mold cavities on the rotating blowing wheel. The molds close and a stretch rod rises up through the open preform neck finish initiating axial stretching. Before the axial dimension is stretched completely compressed air is blown into the preform to press the PET material radially against the mold walls to form the bottle shape. The neck is held within a closed insert to protect it from deformation. The preform is blown against a warm mold in what Krupp refers to as a "thermo-relax mode." Gleneagles' Hamilton says "The advantage to blowing into warm molds is that we can raise the speed to more than 7 units per hour on smaller bottles. We can run at this speed because we can release finished bottles more quickly." Stretch rods retract from the six bottles mold halves unlock and open. The mandrel carrying the bottle is taken out of the mold by a transfer wheel and passed to a loading/unloading wheel where a mechanical take-off device removes the bottle. An inverting wheel then uses a suction cup to invert the container 180°. "Right after the bottle comes out of the mold its base is hit with cold air to help stabilize the material and prevent it from reverting back to the original round preform base shape" explains Hamilton rather than the distinctive champagne-style base. "If bottles reverted to their original base shape they wouldn't stand upright in the conveyor during the filling process." Air conveyors transfer post-cooled bottles by their necks to the "cleanroom-equivalent" filling area. Empty transport mandrels circle back to reload themselves with preforms for the next cycle. The B 66 runs three shifts/day seven days/week keeping two filling lines busy. Operators are well-trained to take advantage of the machine's modular design easily exchangeable product-dependent parts special locks and self-adjusting mold halves to speed changeovers. More than bells and whistles these equipment features help Gleneagles feed its ever-expanding global pipeline.
Until last spring Gleneagles Spring Waters Blackford Perthshire Scotland had purchased polyethylene terephthalate bottles that it filled with its line of natural spring and carbonated waters (see p. 53). A year ago the company brought bottle production in-house when it began to stretch/blow mold bottles from preforms it buys. Among the refreshing results of the switch are: * Savings of $600/yr based on the company's 1995 sales forecast of 20 million units. * Savings of $350 from not having to build an 18-sq-ft warehouse which would have been necessary to hold sufficient quantities of bottles to meet forecast sales. * Consistent appearance. Instead of settling for a variety of bottles based on availability from vendors in-house molding produces bottles with a consistent "family" appearance. * Enhanced bottle control. Bottles can be subject to transit damage. And when they do arrive they can include dust dirt corrugated or paperboard particulatesthat aren't up to Gleneagles' meticulous standards.
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