WEB WISE: What’s behind the real problems caused by air entrainment?

Alex Nevels

Air entrainment is real, and it can cause real problems, but only in certain circumstances. When and where and what are the salient questions. Let us begin with the “what” of the mechanics.

As seen in Figure 1, air “sticks” to both the web and the roll(er). During run, air is pushed or entrained between the web and roll(er). This is part of the answer to the “what” question. While this boundary layer of air is quite small – far less than the thickness of a human hair – web handlers learn time and time again that small numbers don’t mean small effects. If the web is separated from the roller even just a bit, traction will be reduced and, with enough speed, can be totally lost. So, loss of traction on both driven and undriven rollers alike is one possible risk. Loss of traction, obviously, means loss of function for some rollers, guides, spreaders and other elements.

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