Closed-Loop Bottle Control Saves Truckloads of PET for Blow Molder

For Mexican beverage producer GEPP, automatic control of the stretch-blow molding machine based on in-line bottle wall-thickness measurement has saved literally tons of PET resin every day. Line 1 at GEPP’s Hermosillo plant has trimmed the weight of its 2L low-carbonation PET bottle from 52 to 46 g. Given operating speeds of 24,000 bottles/hr, the 6-g (11.5%) reduction is saving the company approximately 7 tons of resin in each 48-hr production run. This impressive saving has been accomplished despite challenging environmental conditions at the plant, where temperature swings 40° F or more throughout the day. As noted by Jesús López, GEPP corporate technical manager, “You don’t want to put the same amount of heat on a 90° preform as a 70° preform.

Successful lightweighting demands strict adherence to the material-distribution recipe developed for the bottle type. That is a lot harder to do when working with less material, says López. GEPP’s success is attributed to the Process Pilot system from Agr International. Located in the blow molder takeout area, the Pilot’s sensors measure the thickness of each bottle at 12.5-mm intervals along the sidewall. Agr’s control algorithms instantaneously analyze the measurements and compare them to the recipe. If necessary, the Pilot adjusts the appropriate machine function—for example, tweaking the preblow setting or lamp temperature.

In addition to the bottom-line impact of lower material consumption, the Agr system has enabled GEPP, the exclusive bottler of PepsiCo beverages in Mexico, to speed changeovers among six different bottles blown on Line 1 in sizes from 600 ml to 3L. It used to take an average of 1.5 hr to replace the molds on the 16-station blow molder and then another 30 min for process verification and quality checks. Now, with Process Pilot, the machine produces good bottles on startup, with no need for sampling and tweaking, making each changeover 25% faster and saving 6000 bottles of startup scrap. Likewise, when jams occur, “Pilot brings the process back to baseline two to three times faster,” López says. What’s more, improved bottle consistency with Process Pilot produces fewer disruptions in downstream labeling, capping and shrink-wrapping.

López hopes to install Process Pilot on Hermosillo’s second blowing line and to establish the plant as the model and training site for all GEPP’s 25 PET bottle operations.