One personal computer combines web gauging & extrusion line control.

A new PC-based supervisory system that integrates line-wide process control and web-thickness gauging can simplify the task of meeting quality standards for high-specification products like flexible medical packaging.

Until recently, extrusion coating/laminating lines have generally had to rely on two separate systems to monitor the process and to gauge the final product. On some lines, the operator must individually adjust more than 10 control devices. Such heavy reliance on the operator for process control multiplies opportunities for error.

The latest development of the ConceptOne system from Measurex Systems Inc., Cupertino, Calif., now makes it possible for an operator to monitor and control both the process and the product using one PC-based system. "This is the new wave in web process control," says Dan Piroli, director, U.S. south. Measurex acquired the ConceptOne system when it bought Ohmart Corp.'s web-gauging business early last year. The PC supervisory control (reportedly the first such system from a gauging supplier) was first announced at NPE '94 in Chicago but has established a track record of field performance only in the past year and a half.

A HIT IN MEDICAL PACKAGING

One of the first five complete ConceptOne systems sold in the U.S. went to Rexam Medical Packaging, a custom processor in Mt. Holly, N.J., just a year ago. Measurex officials say Rexam today makes the most comprehensive use of the capabilities of the integrated system and thereby affords the best demonstration of its advantages.

Rexam was not satisfied with the results obtained with conventional dual monitoring systems. "If we apply too much coating, we're giving it away. If we apply too little, you get poor bonds with the material," says Ron Nowacki, director of manufacturing and engineering at Rexam's Mt. Holly plant. In just a single-layer coating operation, Rexam's line consists of 11 adjustable pieces of equipment. "Changeover of the line is the bottleneck," Nowacki says. Prior to installation of the supervisory system, each operator manually configured each controller on the line when setting up for a new product. That was time consuming and also increased the possibilities of error. Set-up is now accomplished by calling up recipes stored in the computer to ensure that all settings and tolerances for product and process are correct and repeatable. With the ConceptOne system, Rexam keeps the net coating thickness to [+ or -] 2% of target while running at line speeds up to 450-500 ft/min, which Nowacki says is better than the firm's prior performance.

In addition, he notes that typical stand-alone beta-gauge systems provide preset features and displays and are therefore inflexible to the changing needs of his process. As a custom processor, Rexam runs coated and laminated barrier films and film/foil combinations with anywhere from two to eight layers and thicknesses from 1.0 to 3.5 mm. Materials include PET, LDPE, HDPE, EMA, EVA, and ionomer. "In a 24-hour period we may change the line three times," says Nowacki.

WHAT'S 'UNDER THE HOOD'

The ConceptOne supervisory system runs on a 100-MHz Pentium processor with a 64 megabytes of RAM. It uses a multi-tasking OS/2 process-control software package called Paragon TNT, supplied by Intec Controls, Walpole, Mass. The ConceptOne gauging system operates as one task under the OS/2 operating system. The supervisory system, including PC, costs between $75,000 and $255,000, depending on configuration.

The Paragon supervisory software establishes bi-directional communication with each line controller (i.e., temperature, pressure, or drive controls) so that an operator can make setpoint changes either at the PC terminal or at the controller itself. The changes will appear on displays for both the supervisory system and the individual controller. The PC can quickly pull up displays of a line or an individual controller. The operator can switch back and forth between screens showing graphics of the process and screens that show gauging information. Moreover, the operator can store both process settings and product gauging data in a retrievable recipe form.

At Rexam, the system monitors 14 temperature controllers (six die zones, six barrel zones, an adapter zone, and a melt-temperature sensor). The line's drive-control system, manufactured by Amicon, Inc., Charlotte, N.C. includes three Klockner Moeller PLC's to control tension, roll diameter, and line speed of the fully automatic and computer-controlled unwind and rewind machines, made by WTI International, Rockford, Ill. At least 20 other discrete controls (from chill-water temperature and pressure to roll temperature, screw speed, extruder amps, laminator temperature, and corona-treater output) can be monitored through the supervisory system. Rexam plans to add automatic die control and other components of the line to the supervisory system in the future.

Rexam has a two-gauge system in place. One gauge monitors the pre-coated primary material, while the second measures the gross gauge of the final coated or laminated product. From the two readings the computer calculates net coating thickness.

The menu-driven software allows the processor to design a graph, chart, or report for any project.