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Tension Control #7
What is taper tension? When do I need it?
By
John Campbell
Nexen Group

To read other articles in this series click on the installment number below
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This is a continuing, in-depth article covering Web Tension Control. We will cover many principals of Web Tension Control over several continuing installments.

This is installment number 7. We recommend reading installment number 1 through 6 before continuing. Click above to got to the other installments. This is a continuing, in-depth article covering Web Tension Control. We will cover many principals of Web Tension Control over several continuing installments.

This is installment number 7. We recommend reading installment number 1,2,3,4,5 and 6 before continuing. Click here to go to installment number 1, Click here to go to installment number 2, Click here to go to installment number 3, Click here to go to installment number 4, Click here to go to installment number 5, Click here to go to installment number 6 (Cecily - insert this sentence as hypertext linked to #1,2,3,4 and 5).

Taper Tension We often have inquiries from people who wish to purchase a tension control system with "taper tension". Many times these people do not really want true taper tension. They wish to have a system that will decrease the braking torque on an unwind stand or increase the driving torque on a winding stand as the roll diameter changes. This will not yield taper tension, it will provide constant tension (which is what is needed in most cases). This is a common mistake of confusing taper tension with varying torque to maintain constant tension. True taper tension is used to wind goods on a roll starting with a relatively high tension and gradually "tapering" off to a lower tension as the roll builds in diameter. The purpose of this technique is to decrease the internal pressures in the roll, which are caused by tension in the outer wraps. The internal pressures can cause telescoping of the wound roll, starring of the roll, or crushed cores. Normally these problems occur when the surface texture of the web is very smooth which allows the web to move freely upon itself. Clay coated papers and cellophane are two products, which are particularly prone to these problems. The lower torque requirement at the OD of the roll can also result in a lower horsepower requirement for the winder drive. This is a very rare benefit of taper tension, and I don't recommend it as the drive will be marginally sized if it requires taper tension to make it work. That is not a good way to size a drive, as it does not leave any room for future growth in the product line or processing tensions. Most tension controllers have some form of built in taper tension capacity. Reverse taper is used when the output decreases as the roll diameter increases, as is the case when speed controlling a winder drive. Reverse taper is also used when attempting to run taper tension on a surface winder on a single tension zone machine. In this type of machine the winder drums control the speed of the machine, and the unwind brake controls the web tension. In order to have taper tension on this type of machine the unwind must be reverse tapered, that is, the highest tension is produced when the roll is large; tapering to a lower tension as the roll size decreases. This will theoretically produce a hard core, tapering to a softer OD, on the wound roll. I say theoretically, because this method is not as positive as the others in giving predictable results due to the nipping action of the roller against the surface winding drum. It is better t

han nothing, and really the only option you have with a single zone machine. Well there you have it! Short of the actual physical formulae to determine the predictable out comes, that is all there is to taper tension. Remember the next time you are considering taper tension: Do you really want taper tension, or just varying torque or speed to maintain a constant tension? Taper tension is not a cure all - but it does provide a valuable solution to certain winding problems.

Next month we will continue our look tension control, so stay tuned! About the author:

My name is John Campbell and I have been involved in the field of industrial brakes and clutches for over 25 years, with Nexen Group Inc. and its predecessor, Horton Industrial Products. The last 20 years have been almost exclusively with tension control applications of clutches and brakes, and also the control packages that are used to perform these control functions. I have also had the honor since 1997, to address the CEMA (Converting Equipment Manufacturer's Association) Slitting and Winding Seminars on the field of tension controls. To contact CEMA for details of their programs and seminars visit their website www.cema-converting.org

To read other articles in this series click on the installment number below
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