DWH Technical Topic: Wrinkles during cutover

By Clarence Klassen, P. Eng.

Wrinkles are often created during turret winder indexes or cutovers. Wrinkles are often associated with changes in tension and misalignments. The cutover provides its share of tension variations and opportunities for alignment problems. I noticed this again this year while winding a stiff building product.

Tension variations can be expected when the laying roller lifts or makes contact with the web roll. Web length changes as the laying roller moves. Another source of tension disturbance is the entire turret index motion. The turret accelerates and decelerates and the web length increases during the index. The web may contact several other rollers during the index. The knife assembly probably makes contact with the web just before the cut. Another tension disturbance when the actual cut is made.

One problem with the tension variations is that the load cell for measuring the tension signal may not even see the correct tension. This is because the web is nipped and wrapped around so many new rollers. The load cell measures the tension right where it is located. Tension at the new core or where the knife cut takes place is not known. The tensioning can only be inferred from the wrinkles and by looking at how well the knife cuts.

Often the tension variations can be masked by putting the outgoing spindle drive into torque hold mode. If that is not enough, work with torque boost and tension boost at the appropriate stages of the index sequence. We expect a tension boost will be required for the entire time the layon roller is raised from the winding web roll. We expected a torque boost may be required just before the cut to provide extra tension for a clean cut.

If wrinkles due to misalignments are noticed, it may be necessary to realign the entire winder. The spindle alignment, layon roller alignment, and knife carriage alignment should be checked. Any auxiliary rollers which contact the web during the index should also be checked. The effect of misalignment may be reduced by reducing the time contact is made. Start the index as late as possible, and make motions as fast as possible to reduce the time wrinkles have to form. This is detailed work requiring timing to tenths or hundredths of a second. Good trending software is a must.

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