Bowed roller quality can be measured in many ways. One is appropriately sized curvature (bow magnitude) that we cover in great detail in our Web101 class. (The last one this year in the US is Aug 22-23 in Patterson NJ, though you can take it anytime as video-on-demand). Another is a reasonably uniform curvature arc as we discuss here; perhaps the only time in the literature, internet or otherwise. Putting these two quality metrics together we would have a uniform spreading profile. In other words, the CD stress (unslit webs) or gaps (slit webs) would be consistent across the width. If the average curvature is too high and especially if the curvature uniformity quality is poor, we can have the tendency to wrinkle at local lanes instead of spread. The former is called ‘quarter-point’ spreading problems and the latter flat spots or kinks in the bow.
Web201.44e – Bowed Roller Failure Modes – Kinks in Curvature
***201.44e – Bowed Roller Failure Modes – Kinks in Curvature
05 Slides Duration 03.24 v 15.08.28
201.44e.01 – Title Slide
Welcome to web handling. My name is Dave Roisum. In this clip we continue our series on bowed roller failure modes by looking at the risks of a bowed roller arc that has kinks and flat spots in it curvature
201.44e.02 – Concerns
Only certain applications are very sensitive to the quality of curvature.
Before slitter spreaders are relatively tolerant, but not so when you slit the web into lanes that must be separated. Of course, the more lanes you have the more demanding is the system for curvature quality. You only have a limited total spreading power and you want that distributed as evenly as possible. Note, however, that gaps can not be even if the lanes are of different widths. Wide widths automatically make wide gaps and vice versa.
Also, while you might imagine a kink to be more trouble, it is in fact the flat spot that is the much greater concern because there is no local spreading there. Of course, for a given bow magnitude, if you have a high curvature kink there must be a corresponding low curvature flat spot.
201.44e.03 – After Slitter Applications
The practical concern is that tied up or stuck rolls is common in many industries, especially on two-drum winders or winders with a single shaft.
The practical problem is, however, that there are many totally different reasons that rolls could get tied up. This is where knowledge of web handling plus experience with spreaders plus clever detective work must all come together. Putting the right fix for the wrong problem may not be helpful. Increasing spreading power may not only not help, it can in some cases make the problem worse. In my web and winding classes we taught the necessary background to help troubleshoot this most troublesome problem.
201.44e.04 – Curvature Quality
The quality of curvature is an easy concept. It is merely how close the actual arc of the bowed roller axle matches the arc of a true circle.
Yet it is in practice, almost impossible to see kinks and flat spots that might disable or destroy spreading. Also, it is quite difficult to measure. So difficult, that when I worked for Beloit as a winder designer we had to develop and teach the bowed roller manufacturers how to check this so that our equipment performed as well as possible.
As a final observation, the issues we discussed here are also equally true for other spreaders and, most especially, bent pipe spreaders.
201.44e.05– Thank You
Thank you so very much for watching this module in my plant practical video clips. Stay tuned for the last clip in the series where we will just list a few final bowed roller failure modes.