Web201.43b – Taper – More Nonsense
***201.43b – Taper – More Nonsense
05 Slides Duration 04.33 v 15.08.06
201.43b.01 – Title Slide
Welcome to web handling. My name is Dave Roisum. In the last clip we showed how the great majority of all winding defects are totally insensitive to taper. Attention to taper in those cases is distracting at best. In this clip we lament on more of the nonsense of taper.
201.43b.02 – Mixed Units
Mixing units is one of the most fundamental sins an engineer can make. Yet, this is exactly what the builders have done when they mix tension with percent taper tension. The units of tension are kN/m in the metric system and Lb/in in the US system. Taper is unitless.
However, to put this in more of a layman’s perspective, consider a speed limit sign as you enter the city limits from a highway. The sign didn’t say slow down 36.3%. It said, quite sensible, 35 mph.
201.43b.03 – (Calculation) Confusion of Ending Tension
Tension is a fundamental web and winding control parameter. Here we will illustrate the immense complication of answering a simple and useful question. “At what tension does my roll finish at?”
First, we must find out from the builder’s instruction manual or the builder himself whether the taper takes place starting at zero diameter or core diameter. Similarly, we need to know if the taper is calculated through the finish diameter of the current roll or the design diameter of the machine. We assume here the most common of starting at zero diameter and tapering to the design diameter of the machine.
Then, the calculation is relatively straightforward using the method of equivalent triangles. Given the assumptions above, the answer is 1.28, I think. Alternatively, the operator could use trigonometry if they felt more comfortable with that technique.
Because this is an impossible calculation for an operator they will not be able to translate their learnings from one product to another whose only change is merely finish diameter. The only thing they can try is, trial and error.
This is also a total pain in the !!!! for electrical engineers to troubleshoot as well as for any of your favorite QA techniques such as ISO or Six Sigma.
201.43b.04 – Constant Tension, Constant Torque or Hyperbolic
There has been decades long debate on what the best shape of the taper curve is. Is it constant tension, constant torque or hyperbolic? All of this without even identifying the problem they were trying to solve.
It is absurd to think one shape is best for all.
It is absurd to think that the ideal shape for any particular defect, as yet unspecified, would be so convenient as to be one of these most easily programmed curves.
Why not a -30 to +70 degree portion of a cosine curve? That, in fact, is close to the near optimum shape for the rider roll curve on a two-drum winder. Come to my winding class and find out why.
Why not a 0 to 70 degree portion of a cosine curve? That, in fact, is close to the optimum shape for Type 1 Telescoping. Come to my winding class and find out why.
201.43b.05 – Questions
How we got to this point of using taper is only of historical and cultural interest; it really has little to do with what the wound roll would care about. It is simply that before the age of the computer, taper was the easiest thing for electrical engineers to do. Now we know better. In the next clip I will show a much much better alternative to taper. In the next clip I will show a much much simpler alternative to taper; namely; the two point method.