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Roll the film.

Plastic bags are everywhere. They hold our new stuff when we carry it home. They catch our old stuff when we throw it out. They are produced on blown film extrusion lines. In this process, extruders melt plastic pellets in a heated barrel and feed the hot plastic into a die. As the plastic exits the die, it is cooled by forced air and travels up a tall cooling tower in the form of a bubble. At the top of the tower, the film tube is collapsed and fed back down to large rollers in the plant floor. Temperature control throughout the process is crucial to maximizing line speed and maintaining the right gauge of film.

Pliant Corp., a producer of bags, or flexible packaging, needed to upgrade the temperature controllers on two of its blown film lines in its South Deerfield, Mass., plant. The analog controllers on the original equipment were obsolete, according to maintenance and engineering manager Mike Johannig. The plant was keeping the controllers operating with spare parts. "If something were to fail, our production lines would have been down," he said. The original controllers were cumbersome to use, often requiring operators to scroll through several menus to get to desired information. Troubleshooting the process with the old controllers was difficult; operators would be tipped off to a temperature production problem by observing subtle changes in the bubble's frost line, the point where the polymer changes from liquid back to solid.

Johannig had three requirements in mind when be shopped for a new controller: ease of use, the ability to automatically change temperature settings on the line when switching to new resin grades, and the ability to log and store data. Working with FM Keefe Co., a distributor of industrial heating and control equipment based in Springfield, Mass., Pliant chose the PPC-2000, a multiloop digital controller designed for extrusion lines, supplied by Watlow Electric Manufacturing Co. of St. Louis. The controller's software provides centralized data logging, graphing, auto-tuning, recipe management, and alarm capability.

FM Keefe used AutoCAD to design graphical representations on the control screens of the heat zones--or sections of the extruder and die equipped with heater bands and cooling fans--for each blown-film line, according to George Holman Jr., the company's application engineer who handled the installation. The graphical representations of each of the approximately 30 heat zones on each line are color-coded to indicate whether the temperature of the equipment is within or outside desired limits.

Using the control's touch screen, the operator can adjust for a new resin grade; the control automatically changes temperature settings on the line. Now data is collected in Johannig's office, providing a history of a run. Johannig added that he could also control machine settings from his office computer.

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Title Annotation:Instrumentation And Control; Pliant Corp upgrading the temperature controllers
Comment:Roll the film.(Instrumentation And Control)(Pliant Corp upgrading the temperature controllers)
Author:Degaspari, John
Publication:Mechanical Engineering-CIME
Geographic Code:1USA
Date:Oct 1, 2004
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