Web Tension & Guiding
idler roll and under the second carrier roll. As the tension of the web increases, the idler roll is pulled down and the load cell, which, through an electro-pneumatic signal, controls the roll stand’s brake pressure, senses the defl ection. The dancer roll method utilises an air loaded dancer roll that sends an impulse to a transducer that governs the roll stand’s brake pressure. In this design, the web is threaded around the dancer roll. As the web tension varies, the dancer roll is pulled out of its “dead center” position. The transducer senses this movement and the brake pressure is adjusted until the dancer roll moves back to its neutral position.
The proportional type tension control monitors the lineal footage of the web unwound and the number of revolutions of the roll at the unwind. The controller calculates the diameter of the roll and reduces the brake pressure at a rate relative to a preset tension at the core’s diameter. Another version of the proportional design uses the change in weight of the roll to vary the brake tension, maintaining constant tension as the roll gets smaller.
PROPORTIONAL TENSION CONTROL OPERATOR STATION.
Maintaining proper brake pressure for each roll is essential for precision sheeting. Well-designed installations use independent tension control systems for each web. In contrast, less expensive designs use one tension system to govern the brake pressure of all rolls. This “slave” design is less desirable because each roll has its own tension characteristics.
TROUBLESHOOTING WEB TENSION PROBLEMS
While too much brake pressure at the unwind will result in short sheets, conversely, too little brake pressure will cause wrinkles. Operators may have to experiment to fi nd the proper setting that works best.
Both the width of the roll and type of material have an infl uence on the amount of tension required. As a rule, requirements for paper vary from 0.25 PLI (pounds per linear inch) for 20 lb stock to 1 PLI for 80 lb stock. When sheeting board, the tension required ranges from 0.75 PLI for 0.008” thick board to 3 PLI for 0.030” thick board. Roll stands with automatic tension control can be
outfi tted with too many brake pads, which require little brake pressure. Low brake pressures are diffi cult to control. This problem can be solved by reducing the number of pads, or by using pads with a lower coeffi cient of friction. This arrangement requires higher air pressure and off ers greater control.
WEB GUIDANCE SYSTEMS
Web guidance systems evenly align webs as they feed into the cutter. These systems are recommended for poorly wound or telescoped rolls because they eliminate the need to take an edge trim.
Additionally, when slitting and sheeting multiple piles at high speeds, a web steering system can negate the need for the taking of side trim, thereby reducing waste.
In these high-speed sheeting applications, the most suitable system allows for the steering of the web after the unwind and prior to the web infeed of the sheeter. In this design, the web steering unit is separated from the roll stand and a series of rolls aligns the web. Web steering off ers greater responsiveness at higher speeds than other methods.
34
September 2025
www.convertermag.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46
