Non-contact vacuum box and method of operation

摘要

A vacuum box (38) is provided with recesses (86, 88, 90, 92) on the inner surfaces (74, 76) of its front and/or back walls (40, 42) along at least two of its interior corners (78, 80, 82, 84); so that, the pressures on opposite sides of the incoming and outgoing spans (64i, 64o) of the web (50) are substantially equalized at discrete locations along the lengths of the spans, whereby differential pressure applied to the central curved loop (64) between the spans causes the incoming and outgoing spans to remain substantially out of contact with the side walls (40, 42). The side walls (44, 46) may be provided with chamfers (154, 156) at the interior corners or bores (158; 166-172) and ports (160-164; 174-180) to facilitate equalization of the pressure to facilitate equalizing the pressure on opposite sides of webs having a transverse curl toward a centerline of the box. The box may include web keepers (102) to retain the web during thread-up and a removable, sound insulated closure (130). A method of operating such a vacuum box is taught.