Measurement of web feed rates in rubber covered nip roller applications and the impact on wrinkle formation

Abstract

Nip rollers are used extensively in web handling processes; however, rubber-covered rollers have the unwanted and often unpredictable characteristic of unknown surface speed owing to coupling between circumferential and radial strains within the nip. When nip rollers are used to transport continuous webs, this behavior can lead to speed or feed rate variation between the nip roller and the web line in the process direction. Further, variations in feed rate across the width of the web due to roller deflection or other widthwise variations can lead to corrugations and wrinkles. In this paper, a measurement method is described and demonstrated for accurately measuring nip roller feed rates. Data is presented for asymmetrical nip systems consisting of a rubber-covered nip roller loaded against a metal roller. Results are shown for a conventional nip roller covering and a second nip roller covering engineered with the ability to control nip roller feed rate while retaining desirable nip pressure characteristics. Results from a troughing and wrinkling study using two pairs of end-loaded symmetric nip rollers of each design are also presented. These results are used to compare and contrast the performance of nip rollers systems where differences in nip roller feed rate significantly alters system behavior.