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Practice application and design of concave rollers

Walker, T. J.
A concave roller is an effective and inexpensive wrinkle-preventing roller design. By definition, a concave roller (a.k.a. a reverse-crowned roller) is a roller with a larger diameter at the edges than at its center. But a definition is not an engineering specification. What is the right amount of diameter variation? What is the best way to shift from large to small diameter? This paper will present a simple, logical approach to specifying a concave roller's profile tailored to roller and web properties.
Beyond a concave roller's anti-wrinkle effects, they also have a lesser known web-to-roller traction benefit. Most air lubrication and traction models only consider cylindrical rollers. Concave rollers induce crossweb tension variations, creating crossweb differences in air lubrication and web-roller coefficient of traction. By combining concave roller tensioning with air lubrication and traction models, this paper will show how a concave roller will maintain good traction and better control under higher lubricating layers than a cylindrical roller of the same surface roughness or texture.