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August 09, 2005
Winding Tension Answers? Not 'Exactly'.
In response to my August 5 on differential winding, a couple of blog readers commented with specific questions. Case 1: A reader asked for the 'exact data of rewind tension' required for a series of products and listed 5 different webs (plus two mysterious laminates called 3 Ply and 2 Ply), listing only the thickness of one web, one maximum width, and one maximum speed. Case 2: A second reader asks if there is a system to differentially wind to 60-in. OD for a specified range of steel and aluminum webs.
How do I reply to these well-intentioned inquiries? I have problems on three levels.
1. There is a great deal of missing information?
2. Even with near perfect information, is it possible to provide 'exact data on rewind tension'?
3. Is answering this type of specific question the purpose of convertingblog.com?
Lets go through each one of these a little bit...
1. There is a great deal of missing information?
For Case 1, missing key information includes: What is the core diameter? What is the maximum roll size? What are the web thicknesses? What is the product friction? Are the products coated? What is the core properties and geometry? What is the product surface roughness? Do the products or coatings have viscoelastic properties? For the laminates, what are the 2 and 3 Plys, both material properties and thickness?
Given the high speeds, 450 m/min (1500 fpm), this product will likely need a winding nip to prevent air lubrication and shifted layers.
For Case 2, there is no core diameter, so we can't determine the torque range. If the cores are 3" diameter, the diameter range is 20:1. For a pneumatically controlled system that runs from 4 to 80 psi, this diameter range will eat up the entire torque range, so the system can only run at one tension (if constant tension is desired).
For Case 2, I have another concern. These large rolls of steel or aluminum will be quite heavy. The friction that develops from roll weight is often overlooked in differential winding. In the September 2003 issue of Paper, Film, Foil Converter magazine, I reviewed this concept. Click here to read it.
2. Even with near perfect information, is it possible to provide 'exact data on rewind tension'?
Determining the best winding conditions can start with an educated guess, but in the end winding experiments to explore different initial tension, final tension, and tension taper profiles are always required. Unless your product has a wide winding process window, you'll need to complete a series of experiments to get to what is best for your product.
What is the educated guess? I'd start with your web handling tension. What is your web handling tension? It is likely around 1 pound per inch of width. It is usually 10-20% of the break or yield point of your material. For many papers and films, tension are typically between 0.5 and 1.0 lbs per inch, per mil of thickness. Winding tensions may start above this and remain constant, taper linearly, or taper along a constant torque function. Winding is a "graduate level topic" in the web handling and converting world. It is extremely difficult to come out with "the answer" even with what may seem like complete information.
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3. Is answering this type of specific question the purpose of convertingblog.com?
Convertingblog.com is not intended as an avenue to provide specific technical advice to individual converters. More directly, convertingblog.com is not intended to be 'free advice from Tim'.
My goal is sharing these posts is to educate the converting industry and hopefully persuade others to contribute similarly. (Of course, I also view my work here as one of several marketing effort for my consulting business.) In the Blog Use section, it states 'Maxcess International allows for the posting of comments on converting industry topics to foster communication between members of the converting community'.
For more on differential winding, I wrote three articles for PFFC from Nov. 2002 to Jan. 2003.
Part 1
Part 2
Part 3
Posted by Tim Walker at August 9, 2005 02:29 PM
Comments
Do converters know what their running waste is? In my mind running waste is a combination of trim waste and tree waste. Trim waste being defined as that part of the roll that is cut-off before it goes to a secondary process like a sheeter. Tree waste being defined as those sheets that the operator or the operators helper pulls from the line and dumped in a waste container. How do they track it? Manually or automatically? If they can track it and know how much waste is being created, Do they know how much, on average, waste is costing them or what percentage or average dollar amount waste makes up their COST OF GOODS SOLD?
Thank you.
John Needham
PaperSoft, Inc.
Posted by: John at August 16, 2005 12:56 PM
On your August 5 on differential winding you wrote If your (tension) need is outside the 0.3-3.0 lbs/in range, you may find it difficult to get a differential shaft to fit your product.
Regarding Tony question, aluminium .015-.060 tension need is about 3 lbs/in, per mil of thickness, or even more (isn't it?). It means 3x60mil=180 lbs/in, completely outside the 0.3-3.0 lbs/in range. If .060 mm instead of .060 in, it means 60 micron/25.4=2.36mil, then 3x2.36=7.08 lbs/in which still outside the 0.3-3.0 lbs/in range?.
Posted by: Francisco at September 6, 2005 06:46 AM
On your August 5 on differential winding you wrote If your need is outside the 0.3-3.0 lbs/in range, you may find it difficult to get a differential shaft to fit your product.
Regarding Tony question, aluminium .015-.060 tension need is about 3 lbs/in, per mil of thickness, or even more (isn't it?). It means 3x60mil=180 lbs/in, completely outside the 0.3-3.0 lbs/in range. If .060 mm instead of .060 in, it means 60 micron/25.4=2.36mil, then 3x2.36=7.08 lbs/in which still outside the 0.3-3.0 lbs/in range?.
Posted by: Francisco at September 6, 2005 06:48 AM
Coated aluminum is prone to form wrinkles at the beginning of the coil winding (first wraps around the core). Does differential winding give a smoother winding start than lock-bar winding which help to eliminate those first wraps wrinkles?
Thank you.
Francisco
Posted by: Francisco at September 6, 2005 07:00 AM
Reply to aluminum tension needs.
First, I'd say my aluminum slitting and rewinding experience is limited, but from what I know, it is not wound at the high tensions you are calculating.
Rolls are wound with enough tension to create layer to layer pressure and transmit the winding torque needed for centering winding or unwinding. I've used a similar rule for polyesters, recommending tensions at 0.5-1.0 lbs/in/mils of thickness. This is appropriate for 0.1-3.0 mil product, but I also say that this doesn't continue indefinitely. Above 0.003" thick, the polyester web get enough stiffness than more tension isn't needed. Yes, tension should be high enough to make sure the rolls aren't too loose, but 0.020" polyester isn't wound at 10-20 lbs/in.
Another point, even though I said differential winding is usually in the 0.3-3.0 lbs/in range, I'm sure systems can be designed for more tension. The lateral loading systems, such as on many Dusenbury slitters, can be cranked up and up as long as you instally larger side loading air cylinders and can figure how to dissipate the heat generated.
tjw
Posted by: tim walker at October 10, 2005 01:52 PM
It would be interesting to know what tension is used for aluminum .015-.060 at Tony location.
FC.
Posted by: Francisco at October 12, 2005 03:48 PM
