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November 03, 2006
Questions on misaligned edges of wound rolls:
Contributed by Tim Walker -
First rule of roll edge misalignment: Figure out if the web is shifting before it gets to the winding roll or if it enters the roll in the correct position and shifts later.
Q1: What causes one edge of a roll to be misaligned (but not the other edge)?
Q2: What causes roll edge misalignment only near core?
Q3: What causes misaligned roll edges as diameter increases?
Q4: What causes misaligned roll edges as speed increases?
A1: Anytime one side is aligned and the other side is not, it indicates the web width or tension is varying. When winding after slitting and one side if good, but one side is uneven, the top suspect is the slitting process. The web may be loose at the cutter causing the edge cut position to wander and width to vary or the slitting blade or knife assembly is wobbling.
If the winding alignment is controlled by a web guide, then one edge should always be well-aligned, but the other edge may wander due to width changes, tension and necking changes, or web wrinkling in the wound roll.
A2: I saw this recently on a differential winding shaft after slitting. This slitter used one of the newer differential winding shafts that have core stops to hold the core’s lateral position. However, due to core debris generation on these stops, the operators had moved them out a little, but this gave the core freedom to shift. At startup, the core shifted to one side over the first 100 feet of winding, causing a shifting of layers near the core. If you have severe shifting near the core, you likely have cinching (MD slippage) and telescoping.
A3: If you don’t use a winding nip (aka pack roller, lay-on roller, contact roller), then you may have slippage when the entrained air is greater than the product roughness. The lubricating air layer increases with roll diameter, so as some point, the air layer is too thick and the layers begin to shift.
A4: The same answer as #3, but now speed causes the increase in entrained air and lubrication.
Posted by Tim Walker at November 3, 2006 01:51 PM
