David R. Roisum, Finishing Technologies, Inc.06.01.18
Last time we talked about the challenges of measuring bulk or thickness. Here we will talk about why bulk can be lost if the nonwoven is tender. Worse yet, any loss will be nonuniform. In short, the average nonwoven thickness will decrease and the variation of thickness will increase. The common operation that will likely do this, almost guaranteed to do this, is the winder.
What do we mean by tender? Scientists call behavior like this ‘creep.’ It is the slow, steady and permanent change in length (when in tension), width (when in tension due to necking) and/or bulk (when under Z-direction pressure). We will focus on pressure because that is the easiest to understand and may be the larger concern for many. The first thing we need to know is what the pressure is on each of the layers in the winding roll. While the exact numbers depend on the details, the trend is the same for all winders, run under all settings and for all nonwovens and in fact all materials of any kind. In short, pressure is guaranteed by the laws of winding physics. The only substantial difference in materials is that, for example, the pressures in a roll of newspaper, perhaps 50 psi, is
What do we mean by tender? Scientists call behavior like this ‘creep.’ It is the slow, steady and permanent change in length (when in tension), width (when in tension due to necking) and/or bulk (when under Z-direction pressure). We will focus on pressure because that is the easiest to understand and may be the larger concern for many. The first thing we need to know is what the pressure is on each of the layers in the winding roll. While the exact numbers depend on the details, the trend is the same for all winders, run under all settings and for all nonwovens and in fact all materials of any kind. In short, pressure is guaranteed by the laws of winding physics. The only substantial difference in materials is that, for example, the pressures in a roll of newspaper, perhaps 50 psi, is
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