Q&A: Collecting Process Tension Data Over Time

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Recently DFE had the opportunity to work with an internationally known wire and cable manufacturer providing tension control for an insulation extrusion line. The machine in question applied a foam insulation to a single center conductor which would later be covered with a braided shield to form coaxial cable.

The process in question was a line used to apply insulation to the center conductor of coaxial cable. It consisted of a wire supply fed to an infeed capstan with multiple wraps, from the capstan the wire is fed to an idler and then through an extrusion die for application of the foam insulation. From the die the product is fed to a cooling trough, and then around a pull capstan (again multiple wraps) and to the winder.

The customer’s problems were two, maintaining consistent coating through the extrusion die and not allowing the product to come in contact with the sides of the trough that was used for the cooling. The coated product, if allowed to contact the sides of the “box”, would be damaged and the insulation would be inconsistent if tension through the die was not held exactly.

Our approach was to install a ribbon filament transducer with a large diameter wheel between the infeed capstan and the extrusion die, set the infeed capstan as the master drive with a slow speed ramp (10 seconds 0 to full speed) and install a SW 16D micro controller in speed follow tension trim mode to control the pull capstan at the end of the line.

The major problem with the application was the tremendous inertia of the capstan drums on the infeed and pull capstans, which caused tremendous tension swings. This was overcome by slowing the master drive acceleration rate, taking a speed signal from the motor of this capstan, and feeding it to the pull capstan. The pull capstan was configured for a 0.1 second accel/deccel rate allowing it to maintain the same speed as the infeed. The tension signal was set to trim the speed signal by 10% and the controller was able to maintain satisfactory control for the entire range of speeds
and materials. When the speed pot was set to maximum (1200 FPM) and the start button was pressed, the line would accelerate from 0 to max speed with no appreciable variation in tension as viewed on the tension meter.

The final outcome was a major reduction in scrap and a much more consistent product.

-- Glyn Green
Technical Support Manager
techsupport@dfe.com
July 1998