Solving the Rewinding Tension Control Puzzle: A Production Engineer's Story

[RDTHOMGT]

So, this problem is going to require some explaining..

I'm a Production Engineer who's recently started working at an adhesive tape converter/distributor and I've been working on an industrial rewinding machine for films, tapes, foams etc. The tapes I rewind range from 0.2mm - 3mm thickness, 1000mm - 1300mm in width, and up to 500M in length (diameter of each bulk roll being up to 800mm).

I'm familiar with the principles & equations of tension control:

• linear rate of tension decrease from unwinding bulk roll, and linear rate of tension increase as rewinding roll builds.
• The ideal tension is around 25% of material's tensile strength
• Tension = Torque/Radius
• Pounds per Linear Inch (PLI) = Total Tension (lbs) / Web Width (in)

The rewinder I'm working on was purchased abroad for a low price.

PROBLEMS:

1. Unfortunately, the TENSION CONTROLS for this machine are completely MANUAL.
2. The AMMETER reading dials are not accurately calibrated to the corresponding amps of the brake (at the unwind mandrel, this ammeter stops at 2A) and the induction motor (at the rewind mandrel, the ammeter stops at 2.4A).

I have consulted the manufacturer on both of these issues when I've attempted to accurately calculate the TORQUE of the brake/motor at any given setting. But they have only replied saying that the manual controls mean I have to work out optimal tension by "feel" on the roll's web. This wasn't good enough for me so I've made a tension control document to assist (see image). As it says, I've found the ammeter readings to the actual current of the brake/motor using an estimated ratio... But I have still only managed to use this document to record and calculate the tension settings, I have to initially do this by "feel" and observing of the web until I rewind the best roll possible. This is a very inefficient and rudimentary way of working this out.

I want to be able to use my document to find the best settings possible instead. Not just log down what the best settings are.

So I'm basically asking:
1. Does this format I have fall in line with the principles? Is this all correct to ensure the best control of the web?
2. What can I do to properly have a benchmark of settings that I can calculate BEFORE rewinding? Instead of rewinding to find the best settings?
3. Is there any attachable equipment/gauges/devices anyone knows of which can indicate web tension at any given setting?

As you can propably tell, this has been a strenuous task... The only other idea I have is to test a strip sample of each tape on a tensile tester at the workplace, to which I can then apply the principle (25% of tensile strength is optimal rewind tension) to at least have some idea on what will be ideal..

Thank you for reading, I hope someone can understand what I'm saying/assist with my problem!

 

[Lnewqban]

Welcome!
I have no experience with that.
Let’s page @jrmichler and @Baluncore

A quick Google search returned this:
https://www.pffc-online.com/news/15515-web-tension-control-fundamentals

 

[Baluncore]

3. Is there any attachable equipment/gauges/devices anyone knows of which can indicate web tension at any given setting?

It will depend on the orientation of the two spool shafts, and the path taken by the material, but if you fit load cells to measure the horizontal force component on the mounts of one spool, you could be reading tension in the material. The vertical force component will be confounded by the weight of the partial roll.

Another way would be to measure the torque on the motor mounts, but that will depend on the changing spool radius, which is the current problem.

What type of motors are used to drive the spools?

 

[jrmichler]

I strongly recommend that you get a copy of The Mechanics of Winding, by David R. Roisum. It's out of print, but Amazon has it as a used book. David Roisum also published the Mechanics of Web Handling and The Mechanics of Rollers. All three of those are highly recommended for a person in your situation. I have not read his more recent book, The Web Handling Handbook. If it has as much information on winding as his winding book, it might be a better book to buy.

Winding tension at 25% of tensile strength is a realistic upper limit for a manually controlled machine. Winding a good quality roll normally requires a tension profile, where the web tension is varied while the roll builds, although constant tension may work if your tape is stiff enough. The Roisum book on winding goes into why you need to do what in order to build quality rolls. The subject cannot be summarized in a forum post.

I recommend that you not try to calibrate everything. Instead, start winding product. Find what happens if the tension is too high, and what happens if the tension is too low. Use halfway between as the suggested tension. That tension will be different for each product code. Do this for a range of products (stiff, stretchy, soft, hard), then correlate to tensile strength, stiffness, and hardness. You should be able to derive an empirical relationship to winding variables.

You can buy tension measuring rolls to measure web tension. Here's a good place to start looking: https://dfe.com/applications/web-tension-control/. I think that's the manufacturer of the last web tension roll that I bought. You will also need strain gauge signal conditioners and readout instrumentation.

But first, BUY THE BOOK.

 

[Baluncore]

But first, BUY THE BOOK.

His books sound great, but are very scarce.
https://www.bookfinder.com/search/?author=David+R.+Roisum

 

[jrmichler]

They really are excellent books. Very readable and lots of good information. The intended readers are people exactly like the OP. There is a lot more to winding than pulling a web onto a roll with some back tension.

His three books, "The Mechanics of...", had a lot of overlap. The total material in all three was about 1.5 times the length of anyone of those books. The Amazon description of The Web Handling Handbook sounds like it replaces and expands on the three earlier books.

 

[RDTHOMGT]

What type of motors are used to drive the spools?

The motor at the rewind shaft is a three phase induction: 4KW, 8.8A, 380V, PF = 0.81
and at the unwind mandrel is a magnetic brake: 480W, 2.4A, (calculated 200V from this)

His books sound great, but are very scarce.
https://www.bookfinder.com/search/?author=David+R.+Roisum

Thank you for all the useful information and resources provided! I've got one of David R. Roisum's books (only sample pages) from The Mechanics of series, unfortunately it's unlikely my company would purchase the whole book but I'll still look into this.

I strongly recommend that you get a copy of The Mechanics of Winding, by David R. Roisum. It's out of print, but Amazon has it as a used book. David Roisum also published the Mechanics of Web Handling and The Mechanics of Rollers. All three of those are highly recommended for a person in your situation. I have not read his more recent book, The Web Handling Handbook. If it has as much information on winding as his winding book, it might be a better book to buy.

Winding tension at 25% of tensile strength is a realistic upper limit for a manually controlled machine. Winding a good quality roll normally requires a tension profile, where the web tension is varied while the roll builds, although constant tension may work if your tape is stiff enough. The Roisum book on winding goes into why you need to do what in order to build quality rolls. The subject cannot be summarized in a forum post.

I recommend that you not try to calibrate everything. Instead, start winding product. Find what happens if the tension is too high, and what happens if the tension is too low. Use halfway between as the suggested tension. That tension will be different for each product code. Do this for a range of products (stiff, stretchy, soft, hard), then correlate to tensile strength, stiffness, and hardness. You should be able to derive an empirical relationship to winding variables.

You can buy tension measuring rolls to measure web tension. Here's a good place to start looking: https://dfe.com/applications/web-tension-control/. I think that's the manufacturer of the last web tension roll that I bought. You will also need strain gauge signal conditioners and readout instrumentation.

But first, BUY THE BOOK.

I was going to see what equipment I can use to generate some readings of tension for a wide range of materials that we run through the machine. This is a good framework to go from, much appreciated thank you.

Thank you all for the prompt responses, sorry I couldn't get back sooner but you've helped me more than I could've asked for.

 

[Dilwyn Jones]

I just came across your query in a search today. David Roisum, Tim Walker and I recently wrote The Web Handling Handbook, which is probably the most comprehensive book around. You can buy a copy at most big online booksellers, amazon, google etc and also from DesTech, the publishers, at https://www.destechpub.com/product/web-handling-handbook/. If you've already bought a copy - thank you!
Dilwyn Jones

 

[berkeman]

Dilwyn

Thanks for the update, Dilwyn. It's great to have you at PF.