New PET Reheat Machines Offer Higher Outputs, Faster Changeovers

Output rates of 1.5 liter bottles are 1350/hr for the Tetra Plast LX-1 single-cavity unit, 3000 bottles/hr for the LX-2 two-cavity model, and 7200/hr for the LX-6 six-cavity machine, says Dan Gehling, business manager. The LX-1 produces bottles from 250 cc to 6 liters, the LX-2 can make 250-cc to 3L sizes, and the LX-6 can produce from 500 cc to 2L.

A new nameplate

Based in Sweden, Tetra Pak is one of the five largest packaging companies in the world, specializing in coated-paperboard for drink boxes, dairy cartons, and other liquid-food packages. In 1994, the firm acquired Dynaplast, a Swiss maker of reheat stretch-blow machines. Since then, Tetra Pak has expanded in plastics packaging by developing an aseptic filler system for PET bottles, buying or building four factories that supply PET preforms, and establishing operations making HDPE bottles and PET-bottle closures--all outside North America. About a year ago, the firm came out with the new PET machinery line. Over 20 units have been sold, including a handful in North America.

The LX series has preform ovens with a separate heating lane for each blow-mold cavity. The four-phase heating system comprises the preheating area, a long stabilization section, a temperature profiling area, and a final stabilization section. Eight lamps in each heating section can be moved up/down or in/out individually or as a bank. A special ninth lamp can be positioned for more intense heating in a particular area, or it can be raised above the other lamps if the preform is especially tall.

LX machines use servo-electric drives to rotate the preform, move preforms into the molds, and then to eject and transport the bottles. Most important are the servo-driven stretch rods linked to the proportional preblowing pressure valve. The servo motor makes rod action programmable and repeatable, says Gehling. "Servo drive on the stretch-rod allows the rate of stretching to be controlled and reproduced, unlike a pneumatic cylinder, which drives the stretch rod to the top of the mold at its maximum speed when the valve opens. We can control acceleration, deceleration, and stroke length," he explains. Such control allows production of bottles with improved topload and burst strengths, he adds.

When changing bottle size, the stretch-rod operating profile is adjusted with a few keystrokes or by calling up a recipe. Process settings and preform or bottle specifications are checked automatically by the system to ensure they are correct. The higher level of control also permits changing the blowing and stretching parameters on the fly during production. A servo valve for the preblowing step also permits more control over bottle formation.

Quick-change artist

Tool-less removal of preform neck-ring holders, simple adjustment of infeed and outfeed rails, and quick-change molds and heating lamps all facilitate fast changeovers. Preform and mold changes on the two-cavity unit take a total of 45-60 min, versus 1.5-3 hr for a competing machine. The LX-6 can be changed over in 2-3 hr, compared with 4-8 hr for comparable machines.