1. Field of the Invention
The present invention relates to a vacuum guide roll apparatus and method for guiding a web between an upstream dryer and a downstream dryer of a dryer section. More particularly, the present invention relates to a vacuum guide roll in which the vacuum is supplied via a housing rather than through a support journal.
2. Information Disclosure Statement
Although much of the water is removed from a formed web during passage of the web through a press section, further water must be removed from the web in order to provide a paper web having the requisite printing characteristics and the like.
A dryer section typically includes a plurality of heated dryer drums, or dryers, around which the web to be dried is trained. Various dryer section arrangements have been proposed and it has been found desirable to continuously support the web on one or more dryer felts during transit through the dryer section.
More particularly, the TOTAL BELRUN system provides such web support from press section to calendar. TOTAL BELRUN is a registered trademark of Beloit Corporation. The TOTAL BELRUN system includes dryer drums and vacuum guide rolls disposed between adjacent drums such that the web is brought into intimate contact with the external surface of each dryer drum. By the aforementioned arrangement, the greatest thermal transfer between the dryers and the web is obtained. The web supported by a dryer felt extends around a vacuum guide roll such that the dryer felt is sandwiched between the web and the roll. By the application of vacuum to the guide rolls, any tendency for the web to sag relative to the felt during transit around the guide roll is inhibited.
Furthermore, particularly when the guide roll is disposed in close proximity to the adjacent dryers, the tendency for the web to flutter between a dryer and adjacent guide roll is minimized.
Additionally, by the aforementioned arrangement, the web is effectively restrained during transit through the dryer section so that shrinkage of the web is inhibited.
In the prior art arrangements, particularly with dryer arrangements including an open draw or unsupported span of the web between dryers, such tendency to shrink causes cockling of the resultant web.
In order to provide the necessary relatively high vacuum to guide rolls in order to inhibit the aforementioned problem of cockling, various proposals have been set forth as exemplified by co-pending patent application Ser. No. 07/014,569 to Beloit Corporation. U.S. Ser. No. 07/014,569 teaches incorporating vacuum seals in a guide roll and the like.
In order to simplify the aforementioned arrangement while providing the necessary vacuum level, the present invention includes a perforate shell for applying a vacuum along the cross-machine direction of the web.
Although vacuum guide rolls have been known, such vacuum has been achieved by means of passages defined by the support journals, these passages being connected to a source of partial vacuum. However, the provision of channels, or passageways, through the support journals of a guide roll of necessity require the provision of relatively massive journal bearings.
The present invention seeks to overcome the need for such massive bearings by the provision of a stationary housing disposed adjacent to one end of a perforate roll shell. The housing is connected to a source of partial vacuum. The housing is sealed relative to an adjacent rotatable shaft and roll shell so that vacuum can be pulled through the perforate shell via the housing.
Therefore, it is a primary objective of the present invention to provide a vacuum guide roll apparatus that overcomes the aforementioned inadequacies of the prior art devices and which makes a considerable contribution to the dryer section art.
Another object of the present invention is the provision of a vacuum guide roll apparatus which includes a housing disposed coaxially relative to a perforate roll shell and adjacent to one support shaft rigidly secured to the shell. The housing is connected to a source of partial vacuum and is sealed relative to the shaft and the roll shell so that air is drawn through the perforate shell and the housing for urging the web towards the roll shell.
Another object of the present invention is the provision of a vacuum guide roll which includes a first and second shaft disposed respectively adjacent to a first and second end of a roll shell and rigidly secured thereto so that the vacuum guide roll does not include a continuous center shaft.
Another object of the present invention is the provision of a vacuum guide roll having a housing and a further housing disposed respectively adjacent to a first and second shaft of the roll shell, the arrangement being such that the edges of the web are held against shrinkage thereby preventing cockle and curl of the web.
Other objects and advantages of the present invention will be apparent to those skilled in the art by a consideration of the detailed description contained hereinafter taken in conjunction with the annexed drawings.