Web201.44d – Bowed Roller Failure Modes – Crowding
***201.44d – Bowed Roller Failure Modes – Crowding
05 Slides Duration 03.43 v 15.08.27
201.44d.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 what happens when you crowd a bowed roller into a small space
201.44d.02 – Bowed Roller Mechanics
Yet another surefire way to cripple or kill a bowed roller is to crowd it too close to the upstream or downstream rollers. Understanding why this is requires understanding how the bowed roller works.
Recall from our Web101 class the mechanics of the bowed roller in bowed roller mode. The streamlines or paths of different segments of the web are defined largely by the normal entry law that was also covered in our class. These mechanics apply both to a full width web as well as a web slit into individual lanes.
201.44d.03 – Crowding the Upstream Roller
As we learned in our Web101 class, the ingoing section of the system is the ‘working’ section. Reducing that span length by crowding the upstream roller reduces the amount of expansive spreading work available.
201.44d.04 – Crowding the Downstream Roller
As we learned in our Web101 class, the web must adjust from an outward directed path as dictated by the normal entry law to a parallel entry to the downstream roller. If this is too crowded, two bad things might happen. First, you may have to decrease the bow magnitude and thus reduce the amount of spreading. Second, if you don’t and the path change is too abrupt, you can wrinkle. Yes, as we learned in class, you can easily make wrinkles via poor spreader application and this is just one of many ways.
201.44d.05 – How small is too small?
How much span length is needed is impractical to model. Thus we have to rely on not merely experience, but studied experience. Studied means literally going to school and reading the papers. Experience means seeing and recognizing failure modes under a wide set of circumstances.
The industry most at risk is the paper mills. Not so much because they are not studied or experienced, because they are, but because they have packaging challenges far greater than other industries. Because widths approach 10 meters, the L/W, or length to width ratios, are a crowded 0.1 compared to the more open 1.0 found in converting. So, I will give a very crude guideline just for paper mills. That is 1 foot is reckless, 1 yard is still risky except immediately after a coater where even that may not be nearly enough if hygroscopic expansion is high.
201.44d.06– Thank You
Thank you so very much for watching this module in my plant practical video clips. Stay tuned in the next clip where we will describe yet another bowed roller failure mode that is particularly troublesome with after slitter applications, namely poor curvature quality.