Methods and apparatus for prescribing web tracking in processing equipment
Methods and apparatus to reduce or eliminate misalignment, wrinkles, and creases in coated web product. A relationship between web outgassing pressure and surface roughness of the web and web transporting rollers is developed. This relationship allows for the control over the web outgassing pressure. The ability to adjust the web tension pressure, as well as the selection of web transporting rollers with prescribed surface characteristics, allows an operator to control the degree to which the web floats over or tracks the web transporting roller. A controller, in response to pressure and tension sensors, can also provide dynamic, closed-loop control of the entire system.
1. A method for selecting a web transporting roller for a desired degree of floating or tracking of a web thereover, the web transporting roller having an actual average surface roughness, the method comprising the steps of:
providing a web;
computing a web outgassing molecular density based on at least one of web geometry, geometry of a plurality of candidate web transporting rollers, and a maximum web tension pressure;
computing an average surface roughness of each of the candidate web transporting rollers based at least in part on the web outgassing molecular density; and
selecting at least one web transporting roller, from among the plurality of candidate web transporting rollers, based on the actual average surface roughness in relation to the computed average surface roughness to achieve the desired degree of floating or tracking of a web over the selected web transporting roller.
2. The method of claim 1 wherein the actual average surface roughness is less than the computed average surface roughness.
3. The method of claim 1 wherein the actual average surface roughness is substantially equal to the computed average surface roughness.
4. The method of claim 1 wherein the actual average surface roughness is greater than the computed average surface roughness.