When there is just 15 minutes between blowing and filling a PET bottle, consistent container quality is imperative. Defects can cause serious and costly disruptions that ripple across the processing plant.
When the PET containers are two disparate types--standard beverage bottles and wide mouth jars-being fabricated on the same machine, the complexity of the blowmolding process intensifies.
These challenges, at the co-located facilities of an internationally known food processor and Graham Packaging Co. L.P., a leading custom blow-molded plastic container manufacturer, are being met with the help of Agr International's Process Pilot® Automated Blowmolder Control system, along with the OptiCheckT vision-based inspection and measurement system.
Installed in the blowmolder, the Process Pilot uses a combination of powerful software and high accuracy sensors to proactively manage material distribution throughout the container. Downstream, the OptiCheck ensures that all output meets specifications before entering the filling line.
The containers Graham makes for the food processor have different finish diameters: a 43mm finish for the bottles, and from 63mm to 83mm for the jars. The mission to produce both types on a single Sidel blowmolder with a spindle diameter of 43mm at first appeared impossible, but the container manufacturer has developed an economical approach that adapts to each format.
Graham's innovative response is the deployment of its proprietary blow-trim technology. In the blow-trim process, custom molds inserted inside the blowmolder shape the wide-mouth jars out of 43mm diameter preforms. Instead of using the threads of the original preform, the mold forms a new set of jar threads at a point along the preform side wall. In a secondary process, the portion of the jar above the newly blown threads--the moil, or excess area--is cut off by a trimmer downstream and recycled.
According to David Piccioli, Director, Global PET Technology Development for the York, Pa.-headquartered Graham, the blow-trim process is more challenging than traditional reheat stretch blowmolding. "It is much more difficult to control the blown finish," he notes.
The difficulty lies in attaining the right material distribution in the body and thickness in the thread region, a task for which the Process Pilot is ideally suited. Its thickness gauge sensors precisely measure 16 different points on the side wall, around the perimeter of the bottle. Sophisticated algorithms analyze minute changes in material distribution. If there are any deviations from specifications, the Process Pilot automatically corrects the corresponding area of the blowmolder. Working in conjunction with the blowmolder controls, the system can simultaneously adjust multiple settings--lamps, blow pressure, and timing, for example-to maintain tight process control parameters with minimal operator intervention.
Because jar finish is so critical to protect product integrity, the containers go through one final inspection step before being conveyed through the wall to the filling plant. Graham personnel view the Agr OptiCheck, a compact inspection and measurement system, as their "last line of defense." The OptiCheck's finish gauging module uses a proprietary configuration of multiple cameras, LED-based backlighting, and high-speed imaging to measure critical container dimensions inline to an accuracy of 0.002 inches. The system's image analysis algorithms accurately identify flaws and blemishes, such as whiskers left from trimming, rejecting jars that could pose seal surface-related problems.
The cost-effective blow-trim approach offers multiple benefits for the container manufacturer and its customer. Fabricating the wide-mouth jars from standard preforms eliminates the need for special handling equipment and a dedicated blowmolder with larger spindles. The jar line is able to run at normal production speeds, in synch with the filling line, making the customized containers very competitive. Automated management of material distribution overcomes many potential container issues, whether relating to operator inexperience, preform variability, or environmental influences. Controlling the blowmolding process to a level of unmatched precision assures that every jar and bottle can be sealed flawlessly to protect the integrity of its contents.
In the 12 months following the installation of the Process Pilot, the bottle plant experienced a 52.7 percent improvement in waste reduction. Looking at all the benefits, including enhanced productivity and the savings in raw material due to consistent output, the payback period for the new system was less than one year. The operation has seen a big improvement in Cpks and PPKs since the Process Pilot and OptiCheck were installed on the blow-trim line, observes Graham Plant Manager Don Waud, who concludes, "Our productivity and customer satisfaction have increased, and we don't run our jar line without them."
