Web tension in an accumulator and industry needs for the future
Abstract
A web is defined as a continuous strip of flexible material. Continuous web processes provide cost savings to manufacturers and converters. Converting processes use unwinds to provide a continuous supply of web material. Accumulators are often used for unwinds to allow a splice without stopping the web process. Accumulators are also used for winders to allow a roll transfer while the process continues to run. Webs are stored in wound rolls under stress and spend most of the time in storage before being converted into a final product. The combination of stress and time cause the web to have floppy edges, baggy lanes, and web camber. Accumulators must be capable of processing these non-ideal webs. Web tension is the most important parameter for any web process. Individual span tensions vary significantly within the accumulator during steady state operation. Individual spans undergo extreme tension differentials during the accumulator fill and feed process. Poor tension control within an accumulator can lead to waste and delay. Symptoms of poor tension control within the accumulator include web instability, web weave, wrinkling, and neck down. Failure modes include total web collapse and ultimately web breaks. Web tension collected from an accumulator will be presented. An emphasis will be given to the dynamic fill and feed operation of the accumulator. It will call attention to the challenges of proper accumulator design and control. A survey of industry needs for improved equipment and process capability will be offered. Fundamental research for web handling has been primarily limited to a single roller in an open span. There are several dozens of published papers that describe traction, air lubrication, and wrinkling. There have been a handful of papers that describe accumulators with little to no validation. Equipment builders have not improved their designs based on published papers. As a result, most accumulators are operated using a trial and error approach.
Citation
Michal, N. (2009, June). Web tension in an accumulator and industry needs for the future. Paper presented at the Tenth International Conference on Web Handling (IWEB), Stillwater, OK.