Used Converting Machinery

Control system integrates PLCs and PACs

As food and beverage manufacturers adapt to meet changing consumer demands for freshness and convenience, they rely on packaging suppliers to deliver cartons and containers comprised of a variety of materials and in a range of shapes and sizes. Evergreen Packaging (www.evergreenpackaging.com) works with many manufacturers to develop fiber-based packaging for everything from juice and candy to specialty products such as liquid eggs and fabric softener.

At its Olmsted Falls, Ohio, plant, Evergreen produces milk cartons from rolls of paperboard supplied by one of its paper mills. The plant uses eight sealers and converting machines to fold, print, die cut and seal the cardboard cartons (Figure 1). The high-speed converting operation produces cartons ranging in volume from four ounces to one-half gallon, with an average output capacity of approximately 400,000 cartons per hour.

After a converting machine prints the words and images on the paperboard, the same machine scores the paperboard along what will be the edges of the milk carton, where the box will fold later. A die lowers and stamps out a flat, scored and printed piece called a blank.

The blanks are loaded into a sealer, which takes the blank and folds it laterally into an overlapping side seam. The seam is heated and squeezed. The sealed and folded blanks are then loaded into corrugated cartons and shipped to the dairy. The dairy uses specialized machinery to transform the blanks into open containers, where they’re filled and top-sealed.

Over the years, Evergreen machines have used a mix of control technologies from different suppliers. Most recently, the machines consisted of outdated drives, relay logic and PLCs running on proprietary software, which was making them increasingly difficult to operate, maintain and support. To make changes to the machines, engineers had to perform complex reprogramming for each new control function.

Access to reliable support also was a growing concern as the company was finding it increasingly difficult to find engineers with the knowledge and skills needed to support the older, diverse technologies. In addition, limited diagnostic capabilities made troubleshooting an ongoing challenge.

Another area of complexity centered on the extensive amount of wiring required with the existing control system design, which complicated maintenance and repair, and multiplied the potential points of failure.

“Some of our machines had 15 e-stop buttons wired in series, which produced a troubleshooting nightmare,” says Richard Stewart, senior project engineer, Evergreen Packaging. “Even a simple problem, such as a failed sensor, could be extremely difficult to identify and locate, putting the entire operation at risk for incurring substantial downtime losses.

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