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Design of contoured rollers for web spreading

Markum, R. E.
Good, J. K.
Contraction of a web in the cross width direction while running over rollers can be traced to runability problems and wound roll defects. These defects may include troughing, baggy lanes, wrinkles and registration difficulties on the machine and creases in the wound roll. Web spreading devices have long been used in industry to restore the moving web to a taught width. At IWEB 4, Swanson [1] presented cases for the effectiveness of ten such devices along with simple models to calculate their ability to spread the web. This presentation extends the previous work by looking at two devices, the parabolic and the "bow tie" shaped rollers, and presents the mathematical derivations used to calculate the spreading ability of each roller. In each case, equations will be presented that, given a reduction in web width, a roller profile may be designed to restore the web to its original width.