DWH Technical Topic: Speed of the incoming core

By Clarence Klassen, P. Eng.

For turret winders, the speed of the incoming core can be very important for good tension control at the time of cutover. The core touches the web before the knife cut and may even have superior traction when the layon roller creates a nip.

The surface speed of the core should be at or slightly faster than the speed of the web. Steady core speed is easy to verify before threading the web. Start the line without the web. Then start each of the spindles with an empty core as though they were coming in for a cut. That is without tension control and with the correct core outside-diameter entered. The core speed can be verified with a hand tachometer and compared to the speed of the traction roller immediately upstream of the winder.

One problem with this method of measuring core speed is that it does not take into account the acceleration time and speed-regulator response of the spindle. Generally, the core must be accelerated very quickly in the middle of a turret index. Some drives are not responsive enough to get to a steady speed before contact with the web is made. A good check would be to trend the incoming web speed during an actual index to make sure the spindle is at speed when contact is made. Retuning or selecting a faster ramp rate may be in order.