Also seen in some web manufacturing but much more commonly in web converting is to ask for a range of widths. While some request only a 20% width range capabilities, a few will be running a 2:1 width range. The tension issues we described above certainly apply. Additionally, we have to tell the drive what width we are running so that a correct tension (tension load per unit width of web) can be run. This makes the operators life slightly simpler as they only have to vary tension for grade (thickness, width etc) but NOT width because the drive/PLC does that compensation.
With properly designed web handling components, the web will run equally well to the front, centered or to the back. This even includes spreaders. (Consider the spreaders used after slitting a web into separate lanes. Most lanes are running ‘off center’ anyway.) Thus, we often keep the back side fixed, especially on winders, to make setups quicker and easier.
A more severe challenge comes from precision processes (as opposed to web handling). A good example to consider would be nipped calender rolls. Here you need to run centered otherwise the resulting deflection is asymmetric and the load would be uneven. Also, calender rolls wear. Thus the rule that you can go narrower without too many issues, but you must consider regrinding the very first time you increase width. If you don’t, the wider product will be running up on the less worn ridge of the roller(s) and carry a very intense nip there. These are just a couple of issues with only one converting process. There are many others that are no less sensitive to product width changes.
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