
This defect, as our commenters below correctly state, is called ‘tin-canning.’ Unfortunately, many people also (incorrectly) use the word ‘tin-canning’ to refer to ‘corrugations’ while others call ‘tin-canning’ by the name ‘corrugations.’ Not to confuse the issue but the words ‘ridges’ are thrown about for these and other defects. This is why we have the Roll and Web Defect Terminology book, so that everyone knows what you are talking about. ‘Tin-canning’ is defined by a near-regular spacing of MD ridges, while ‘gage bands’ are irregularly spaced MD ridges, while a corrugation is an annular band in which the ridges inside are at a slight angle. There is nothing at all connecting these defects in terms of mechanics except that they are all made by or exacerbated by gage variations and that they are all tight defects. How they take their shape is an entirely different matter. Their remedies are also somewhat different beyond the obvious loosen the rolls by decreasing the TNT’s (decrease tension, nip and torque; increase speed).
This defect, as far as I know, is confined to wound rolls of thin film. (Though in principle it could happen to other materials because winding is determined directly by physical properties. The role of chemistry is quite minor here; chemistry merely influences physical properties.) Tin-canning is caused by constrained expansion. Specifically, web just under the surface wants to expand laterally due to its MD compression (caused by the hoop stress of winding physics). This web just under the surface can not expand laterally because it is held back by layers above. So instead of taking its extra width by going out, it does so by going up into repeated buckles. Those of you familiar with wrinkling can immediately recognize the near-uniform spacing of MD wrinkles as a fingerprint of expansion-induced buckling. So let’s get beyond the complex physics and dive into practical stuff that everyone should know and remember.
It is a tight defect as pointed out by the commenters, thus loosen using all of the TNT’s at your disposal. Katherine adds using a slip agent, which just might have a bit of truth to it. She also describes a similar appearance on the top of slender wound rolls that sag when supported by their ends. The buckling outcome is similar, but it got there not by winding tightness but rather by simple beam deflection. The difference is obvious; tin-canning goes all the way around the wound roll while the sag defect (this has no official name) shows up only on the top of the wound roll and then only in the middle.
What all of the commenters miss, as does most everyone else in the film and other industries is a more complete discussion of tightness. While winding (via the TNT’s of tightness + material properties) affects the average tightness, the distribution of tightness is determined solely by gage variations. Thus, merely leveling the gage will smooth out the tight and loose areas and thus reduce tin-canning in the high gage area without doing a thing with the winder. That is why you see the tin canning in this picture showing up at the 10%, 80% and 90% of the distance from the left edges. Those are the high gage areas. In fact, gage variation is usually much more responsible for tightness and looseness than is the winder itself. Thus leveling the gage will help this defect, as it also does for ridges and corrugations, but for entirely different reasons. Also, while oscillation would help enormously for ridges and corrugations, it will do next to nothing for tin-canning because the gage bands are too broad, much wider than ridge spacing. The exception is bubble oscillation where we are not limited in ‘stroke.’ The next defect will give you more practice in reading gage.
In short, the ‘tin-canning’ defect is recognizable by even spacing of ridges and is caused by constrained expansion. Wind looser, level the gage.
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