Tension for pre-cutter tow is a crucial part of the fiber cutting process. The consistency of cut length and quality depends upon it. The process of cutting manmade fiber into staple involves a radial blade tow cutter, in which a reel is fitted with razor blades that face outward. As the reel rotates, the tow wraps around the blades and the inner wraps are pressed against and through the blades by a fixed presser wheel.
The tension that’s applied to incoming tow keeps the tow secured against the blades. If the tension is too high, it will cause the tow to slip as the reel turns. The excessive tension on longer cut lengths can create enough force on the razor blades to sever the tow. Conversely, when there is insufficient tension, it creates a loose wrapping around the reel, which causes loose tow to accumulate in front of the presser wheel. As a result, the excess tow folds over and the subsequent three layers of tow must be cut. When that occurs, the folded tow often breaks blades and will always create cut-length problems.
Methods of Tension Control
One method of tension control in tow cutter systems involves threading the tow through a ladder of polished bars, which creates tension as the tow enters the cutter. As the tow moves through the bars, final tension increases. However, with ladder bars, the tension is multiplied as it moves passes through the bars. As a result, this method is the least preferred way to control pre-cutter tension.
Fiber production of less critical products using low-tension processes often choose the two-roll stand as their method for supplying tension. It’s an economical solution for those types of processes. The two-roll stand can adjust tension by controlling the compression force between two rubber rolls that grip the tow. Adjusting the compressing pressure modifies the rolling resistance of the rolls. These stands always add tension, there isn’t feedback of downstream tension. So, tension is lost when the cutter stops.
For precise control of cut-length, consistent tow tension is critical. As increased throughput on tow cutters is demanded, higher tensions are required to maintain uniform cut-length. Very short cut-length applications also require controlled higher tensions. Regulating tension stands are required to meet those needs. As a result, the only method that delivers consistent tension is a stand that measures and regulates the final tension of the tow.
In these types of tension stands, the tow is grasped by a nip roll assembly. A tension roll, or dancer system, detects the level of tension in the tow as it’s pulled by the cutter. There is a brake or motor connected to the nip roll that is adjusted electronically to control the tow band tension.
Tension stands that use a brake system to control and regulate tension provide consistent tension control and simplicity. They operate best when the infeed tension is just a small fraction of the tension that’s required at the cutter. These stands allow for accurate tension control independent of speed, and they maintain tension even when the cutter is stopped.
When supply tension is higher than the required tension at the cutter, a motor driven regulating tension stand must be used. In this type of stand, the motor powers the tension stand when supply tensions are high, and it changes to function as a brake when that force is needed. The motor can be coupled electrically with the cutter motor. The coupling allows tension stand motor to share excess energy with the cutter motor, which can provide energy savings. However, the two motors must be compatible.
Improve Tow Cutter Efficiency with a DM&E Tension Stand
After more than four decades in the industry, DM&E has supplied tow cutter equipment to fiber producers all over the world. Our machines are used to process nearly every synthetic fiber available today. As tension control is so essential to the efficiency of the tow cutter process, tension stands are a critical part of the system. DM&E offers our fiber producing clients several options for tension control to optimize their production beyond what stand-alone cutters can do.