Suction roll in a machine for producing a fibrous web

Abstract

The present invention provides a suction roll system in a drying section of a machine for manufacturing a fibrous web, the suction roll system including a suction roll having an outer circumferential surface. The circumferential surface defines holes configured for attracting the fibrous web by suction and includes regions, more than two of the regions including the holes, at least two of the regions relative to one another having different numbers of the holes per unit area or having the holes with different diameters per unit area. The circumferential surface has strips which extend in a circumferential direction, at least one strip which extends in a helical shape over the circumferential surface, or strips which extend either substantially in a direction of a longitudinal axis of the suction roll or diagonally relative to the longitudinal axis. The regions include the strips. The strips have an increased number of the holes per unit area in comparison with the remaining regions between the strips or have the holes with greater diameters in comparison with the remaining regions.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This is a continuation of PCT application No. PCT / EP2005 / 051308, entitled “SUCTION ROLL IN A MACHINE FOR PRODUCING A FIBROUS WEB”, filed Mar. 22, 2005.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The invention relates to a suction roll system in a drying section of a machine for manufacturing a paper, cardboard, tissue or other fibrous web, including a suction roll which has holes in its outer circumferential surface for attracting the fibrous web by suction. [0004] 2. Description of the Related Art [0005] DE 100 47 369 A1 describes a drying cylinder for drying a material web which serves, in particular, for guiding and holding a paper web which has a drying gas applied to it. The drying cylinder has a cover, over which the material web is guided during operation of the roll, in a manner which wraps partially around the roll in the process. There are gas passage openings in the cover. There is a second gastight co...

AI Technical Summary

Benefits of technology

[0012] In one advantageous embodiment of the present invention, there is provision for the circumferential surface of the suction roll to have, on at least one of its end-side edges, a region having an increased number of holes, in comparison with the number of holes per unit area in the central region of the circumferential surface, or having holes with greater diameters. It is precisely this embodiment of the suction roll which is particularly suitable for the transfer of a narrow transfer strip, the width of which corresponds approximately to the width of the edge-side region having the increased number of holes, with the result that the transfer strip is attracted reliably by suction during the transfer process, without high vacuum losses being produced at the same time as a result of excessively large openings in the remaining surface of the cover of the suction roll, which surface is not yet covered by the fibrous web.

[0015] It is also advantageous if the suction roll has strips which extend substantially in the direction of the longitudinal axis of the suction roll or are diagonal and have an increased number of holes per unit area in comparison with the regions between the strips, or have holes with greater diameters.

[0019] It proves advantageous if the suction roll is wrapped around by a dryer fabric and a fibrous web which lies on the dryer fabric, an impingement dryer being set against the suction roll in order to drive the fibrous web.

[0024] Overall, the advantages of the invention consist in the fact that the suction roll has a plurality of regions over its width or its circumference, in which the boundary air between the paper of the fibrous web and the fabric or the roll can be removed rapidly on account of the great open surface and therefore the web as a whole can be held and transferred reliably over the web width.

Problems solved by technology

Suction rolls of this type have the disadvantage that the boundary air layer which is formed between the paper web and the roll or the fabric which rests on it is not removed rapidly enough when a paper web is transferred over its full web width.

Difficulties can also occur during the transfer of paper webs.

If, as an alternative, the proportion of the open surface area to the overall surface area of the circumferential surface of the suction roll were increased, the air amounts to be removed by suction would be too great.

Images