Web Tension & Guiding
Tension control & web guidance
By Nicholas D. Datson, sales manager, Maxson Automatic I
n a modern sheeting operation, web conditioning systems will often include tension control and web guidance arrangements. When used in conjunction with a close tolerance drive, these systems provide the basis for a precision sheet. By maintaining the correct amount of brake pressure at each unwind station and smooth web flow into the cutter, sheeting operations can improve accuracy and reduce waste. This article will explore some tension control systems and web steering for optimising sheeter efficiency.
TENSION CONTROL SYSTEMS Web tension plays a major role in sheet length accuracy. Too much roll stand brake pressure creates web slippage in the cutter’s draw roll section. If brake pressure is not reduced as the roll’s diameter decreases, slippage occurs, resulting in short sheets. In contrast, insufficient brake pressure will cause the sheeter to pull wrinkles in the web. When sheeting at speeds beyond 300 fpm (90 mpm), an Operator may not have the reaction time necessary to reduce brake
pressure as the roll rapidly unwinds. This inability to compensate quickly can have an impact on sheet length accuracy, usually resulting in short sheets. Therefore, for high-speed sheeting, automatic systems are recommended to maintain constant tension as the roll unwinds. Load cell, dancer roll, and proportional type systems are available to maintain constant tension.
In the load cell design, an idler roll is mounted on a tension sensing device. The idler roll is located between two web carrier rolls. The web is threaded under the first carrier roll, over the 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 deflection.
The dancer roll method utilizes 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 centre” 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.
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 find the proper setting that works best.
Both the width of the roll and type of material have an influence 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 outfitted with too many brake pads, which require little brake pressure. Low brake pressures are difficult to control. This problem can be solved by reducing the number of pads, or by using pads with a lower coefficient of friction. This arrangement requires higher air pressure and offers greater control.
WEB GUIDANCE SYSTEMS
Web guidance systems evenly align webs as they feed ito 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 offers greater responsiveness at higher speeds than other methods.
28
September 2026
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
