« Spiraling Tape Needed? | Main | Information overload? »
March 22, 2007
Is Center Surface Winding Overkill?
Someone wrote me this week to get a sanity check on when center-surface winding makes sense.
Definition: Center winders drive a roll from the core or center. Surface winders drive a roll a nipping roller in contact with the roll's outer surface. Center-surface winders do both, driving the roll from a combination of center and surface driving.
The inquiring party makes several good points / questions:
> Center-surface winding makes some sense for very slippery (low web side A to side B coefficient of friction) webs.
Yes, this is to avoid how much torque needs to be transmitted through the roll.
> The bottom line on wound roll tightness is the wound-on-tension and the profiling of the WOT versus the roll diameter (a.k.a. WOT and taper tension).
FYI, WOT is the tension of each layer as it is added to the winding roll) and is a function of applied center torque and winding nip load.
> A center winder with nip pressure control can achieve a large enough range of WOT to wind most everything.
Yes, I agree again. The paper industry (and other LARGE roll winders) use surface winders since torque is independent of roll diameter. Center winders can be limited if the core to final roll ratio is too high (a.k.a. the buildup ratio).
> Why do people 'need' the extra complication and cost of a center-surface winder?
I think of most center-surface winders as surface winders with center assist. Surface winders can have trouble getting the initial layers near a core tight enough and the center assist can help with this. If you want to wind an ultra-soft roll, say a nonwoven or tissue product, your surface winding can only go as soft as the nip load required to turn the core, core shaft, and bearings. If you have a center assist, you can go to lower nip loads and softer rolls.
> What does the addition of the last 'T' knob (in TNT) give you besides more variables to mess-up?
Yes, may people that buy surf-center winders never figure out what to do with them.
There has been some interesting work out of Oklahoma State's WHRC how different nip rollers change the tension induced from the nip roller, but it's still all about modeling a roll from a given WOT vs. diameter. I think there is work yet to be done on how WOT from tension and WOT from nip may magnify or de-magnify crossweb roll variations from crossweb caliper and roll diameter variations, but I haven't seen any good work to point anyone in the right direction.
Conclusion: Use winding technology appropriate to your application. Don't get more knobs if you don't need them.
-tjw
Posted by Tim Walker at March 22, 2007 12:35 PM
