Improvement of web spacing characteristics by two types of guide rollers
Abstract
In the manufacturing fields of plastic sheet, paper, magnetic tape, thin metal plate, photographic film etc., the web transporting systems supported by guide rollers are often used. In such systems, it is of cardinal importance to control the web spacing between the traveling web and guide rollers. For example, when the guide roller is used as turn bar in the commercial web offset press or used as dryer in the coating processes of web, it is sometimes needed to keep sufficient air film thickness between web and roller for avoiding the web defects due to surface roughness, stain and lack of uniforming. On the other hand, when the guide roller is used as drag roller, it is desirable to remove the entrained air between web and roller for keeping enough level of traction. In this paper, two types of guide rollers are presented to improve the web spacing characteristics, one of which is hybrid type hollow porous roller for keeping the sufficient web spacing, and the other is grooved type roller for removing the entrained air. In the hybrid type hollow porous roller, the pressurized air is added to the lubrication air flow between web and roller from inside the roller. Then, the web spacing characteristics are improved by the hybrid effects of hydrodynamic pressure due to web movements and hydrostatic pressure due to pressurized added air through the roller. The relations between web spacing and web traveling velocity are measured under various supply pressures. Moreover, the relations between web spacing and web tension are examined. The contactless optical sensor, which can measure the variation of the quantities of reflected light from the back surface of web according to the variation of web spacing, is used to obtain the web spacing under various conditions. In the grooved rollers, the method for the estimation of web spacing by using the concept of equivalent spacing between web and roller is presented, and the web spacing is measured by the same experimental apparatus used in the case of hollow porous roller. From the calculated and measured results obtained, the effectiveness of two types of guide rollers on the web spacing is clarified.
Citation
Hashimoto, H. (1999, June). Improvement of web spacing characteristics by two types of guide rollers. Paper presented at the Fifth International Conference on Web Handling (IWEB), Stillwater, OK.