Norman G. Clark - Precise tension control is vital to any web- or strip-fed operation. The product - whether paper, plastics, metal strip, rubber sheet or wire - must be fed under tension, processed under tension and wound up again under tension.
Factors such as poorly wound rolls, elasticity, roll diameter change and irregularities in web thickness cause significant variations in web tension. Some applications require taper tension on windup. Winding begins at relatively high tension, with a gradual reduction, or tapering, in tension as the roll builds in diameter.
At the very least, your tension control system must compensate for the change in roll diameter. For precise control and high line speeds, it must also be capable of measuring and controlling tension within very close tolerances.
Nexen systems are available to control variable speed motors and pneumatic and electric brakes and clutches.
Sensor Based Tension Control
Nexen's load cell based tension control system senses tension in a web and compares it to a set point, or desired tension level and automatically adjusts air pressure to a pneumatic clutch or brake to maintain appropriate web tension.
The load cell based system can also control electric clutches and brakes. The load cell based systems also can be used with variable speed drives to maintain proper tension in internal tension zones or at the windup stand.
- Control accuracy of 1-2 percent - highest of any web control systems
- Ideal for use with brakes, drives and clutches
- Simple to operate - set the tension level and let the controller do the rest
- Allows remote computer to determine the tension and set points for each job
Open Loop Tension Control
The open loop tension control system electronically measures or estimates the diameter of the unwind or windup roll, directly or by extrapolation of related variables.
An open loop system modulates a brake to control unwind tension, or a clutch or variable speed drive for windup applications. Accuracy is typically about 8-10 percent.
Dancer Position Control
Dancer position control is ideal for egg-shaped rolls and other unusual roll configurations, as well as in applications involving multiple start/stop procedures. In a dancer system, web tension is created by the load placer on the dancer arm.
The dancer arm is free to rotate about its pivot point to maintain this tension at its loaded value. The controller reads the position of the dancer arm and regulates the brake or clutch to maintain the arm in a constant position.
Nexen dancer controls are compatible with numerous pivot point sensors and potentiometers, and feature and adjustable dead band for more stable tuning.
Due to the engineering expertise required for installation, dancer rolls and arms are generally not recommended for retrofit applications. However, dancer position controls on existing dancer rolls often are easily replaceable.
Controlled alignment is absolutely essential in providing a quality roll, and reducing scrap and waste. Nireco Web Guiding systems provide better alignment for the enhance quality that the customer demands. Web guiding is the technique of correctly aligning a continuous strip of material with the process to be performed upon it..
The strip of material or web can be paper, plastic, paperboard, rubber, metal, textile, non-woven, or any other product that is normally processed in a continuous strip. As these materials are unwound and fed into a machine, they must be properly aligned with the process to be performed on them. There are three basic techniques of web guiding:
Unwind Guiding - This technique is performed by sensing the web as it enters the machine. The sensor is mounted as part of the main machine frame
Roll Steering Guiding - This method of web guiding is normally used in mid-process for minor corrections as a web passes through several processes within a machine
Wind-Up Roll Stand Guiding - This technique is the reverse of unwind stand web guiding. In wind up stand guiding, the web position is sensed by a sensor mounted as part of the moveable wind-up roll stand.