The Second T in TNT

The TNT’s associated with the quality of winding are Tension, Nip Loading, and Torque2. Torque2 is the second T and is used when control of Tension and Nip Loading is not enough to produce a roll without defects. Each of the TNT’s contribute to the wound in tension in a wound roll. Tension requires a drive at the winder. This can be a center or surface drive. Nip loading is a surface function. It relies on controlled nip pressure. The nip roller may be driven or undriven.

Torque2 (as used in TNT) requires two drives. The first drive is used to establish web tension into the winder. The second drive is used to modify the wound in tension with torque2 control. At least one of the drives must be a surface drive. Zero or one center drive can be used.

Once the first drive establishes the web tension into the winder, a base wound in tension is produced. The units are N/m or PLI. The nip load then adds to the wound in tension. Finally, the Torque2 produced by the second drive adds to or subtracts from the wound in tension. That’s correct, a negative Torque2 can reduce the wound in tension. Torque2 is the only tool in the TNT toolbox that can either increase or decrease wound in tension.

A design strategy is required to use Torque2 effectively. Torque2 is often described in “%” or “% split”. Does anyone know what a 60%/40% split in Torque2 means? I suggest that each of the TNT’s be calibrated in N/m or PLI. Then the contributions of each of Tension, Nip Loading and Torque2 can be controlled independently and added to give an indication of the wound in tension. Advice from winding and process experts may be sought at this time.

Next, a drive control strategy is required to implement the design requirements. I mentioned that Tension and Torque2 could be controlled independently. This is not quite true. To maintain web tension (correct speed), the total torque of both drives must be summed to the correct value. If one drive provides more load, the other drive’s load must decrease or the web tension will vary. In general terms, one of the drives (surface drive) is used to hold speed with a speed regulator. The speed regulator will then automatically adjust the torque for that motor to regulate speed. The second motor can be given a torque2 reference. The more Torque2 the second motor provides, the less torque will be required from the first motor. This is oversimplified and you will need help from your drive designer.

We must also consider what happens during a speed change. An acceleration torque is required to change the speed of the winder. We expect that the wound in tension due to TNT should not vary when the speed is changed. Inertia compensation should be applied to the drives to accelerate the winder in such a way that Torque2 does not vary. Again, your drive designer will be required to control Torque2 during speed changes.