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

BACKGROUND OF THE INVENTION

1. Field of the Invention

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.

2. Description of the Related Art

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 cover in the interior of the roll cover, which second gastight cover forms an annular space with the outer roll cover. The annular space is sealed off in a gastight manner with respect to the interior of the inner cover.

DE 196 19 530 A1 discloses a drying group in a drying section of a machine for manufacturing a material web. The drying group includes a number of cylinders which, as viewed in the running direction of the material web, are heated and cooled alternately and around which the material web is guided in a meandering manner with a porous transport belt and with a metal belt. Here, the material web is arranged between the transport belt and the metal belt. The metal belt or the transport belt is pretensioned to a great extent, and the cylinders are assigned additional heating apparatuses which act on regions of the circumference, against which the material web bears with the transport belt and the metal belt.

Suction rolls for use in a drying section of a machine for manufacturing a fibrous web have been disclosed which have a uniform open surface, that is to say a surface which is provided with holes or other openings, over their width.

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.

What is needed in the art is a suction roll system including a suction roll, by way of which a fibrous web which is guided around it is held with a sufficient vacuum force.

SUMMARY OF THE INVENTION

The present invention provides a suction roll system including a suction roll of the type which is mentioned in the introduction, in that the circumferential surface is divided into more than two regions having different numbers of holes per unit area or in each case having holes with different diameters per unit area.

The circumferential surface of the roll therefore has, for example, at least three regions, there being a greater open surface in two regions than on the remaining circumferential surface of the roll. The higher open surface is produced either by the fact that the number of holes is greater in these two regions than in the other region, or by the fact that the holes in each case have a greater diameter than in the other region. Both measures (higher number of holes, holes with greater diameter) can also be combined in each case.

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.

There is advantageously provision for the circumferential surface to have strips which extend in the circumferential direction and have an increased number of holes per unit area in comparison with the regions between the strips of the circumferential surface, or have holes with greater diameters.

In another advantageous embodiment of the present invention, there is provision for the circumferential surface to have a strip which extends in a helical shape over it or a plurality of strips which extend in a helical shape over it, having an increased number of holes per unit area in comparison with the remaining region of the circumferential surface, or having holes with greater diameters.

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.

The strips preferably have a width of at least 70 mm, in particular from 100 mm to 1000 mm.

It is likewise advantageous if the strips are at a spacing from one another of at least 100 mm, in particular from 200 mm to 2000 mm. However, the spacings between the strips and their width can also be varied.

In a further embodiment of the present invention, the suction roll has groove-shaped depressions on its circumferential surface. Here, the depressions can have a depth of from 1 to 10 mm and a width of from 1 to 10 mm. The depressions are preferably at a spacing from one another of from 5 to 30 mm. Suction rolls having a great diameter are advantageously used; suction rolls having a diameter of at least 3 m are preferred.

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.

The suction roll is connected to a vacuum source via a rotary leadthrough in its shaft. In an alternative embodiment of the present invention, there is provision for the suction roll to have a vacuum applied to it via a suction box which bears sealingly against its circumferential surface.

The suction roll has an inner gastight cover, there being an annular vacuum space between the inner cover and the outer cover which has the holes.

In a further advantageous embodiment of the present invention, there is provision for the proportion of the surface which is occupied by the holes in the regions on the circumferential surface which have a lower number of holes or holes with a smaller diameter to be between 0.2 and 2.5%, in particular between 1 and 1.5%.

The proportion of the surface which is occupied by the holes is selected in such a way that these regions of strips which have a higher number of holes than the remaining regions of the circumferential surface are at least 1.5 times that of the surface which is occupied by holes in the remaining regions.

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.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a side view of a suction roll in a drying section, in conjunction with an impingement dryer;

FIG. 2 is a plan view of the cover of a suction roll having two regions which are arranged at its edges and have a higher number of holes per unit area;

FIG. 3 is a further plan view of the cover of a suction roll having transverse strips which have a higher number of holes per unit area than the remaining regions; and

FIGS. 4-5 are further plan views of the covers of suction rolls having diagonal or helical strips which have a higher number of holes per unit area than the remaining regions.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly to FIG. 1, there is shown a suction roll 1 is arranged behind a pressing section of a machine for producing a fibrous web 2, at the inlet of a drying section. A fibrous web 2 is guided over a first deflection roll 3 together with a dryer fabric, downward around the cover of the suction roll 1, and is guided further upward over a further deflection roll 4. A stabilizer 5 is positioned between the deflection rolls 3, 4 above the suction roll 1, which stabilizer 5 supplies the required vacuum, in order that the suction roll 1 can suck the fibrous web 2 onto its circumferential surface through the dryer fabric.

An impingement dryer 6 which covers substantially the outlet-side (as viewed in the web running direction) lower quadrant of the suction roll 1 and dries the fibrous web 2 is arranged on the underside of the suction roll 1.

In one embodiment of the present invention, the suction roll 1 (FIG. 2) has at the edges of its circumferential surface 7, in each case regions 8, 9, an increased number of holes or openings per unit area in comparison with a region 10 in the center between the regions 8, 9, through which holes or openings air is sucked out of the interior of the suction roll 1. In particular, this embodiment of the present invention is suitable for threading a feed strip of the fibrous web 2, the feed strip being held reliably over one of the regions 8, 9, because a greater suction force acts in these regions 8, 9 than in the region 10 in the center of the suction roll 1.

In a further embodiment of the present invention (FIG. 3), the suction roll 1 has transverse strips 11 which extend at equal spacings over its entire width, regions 12 having in each case a lower number of holes per unit area being arranged between the transverse strips 11.

In a further alternative embodiment of the present invention (FIG. 4), the suction roll has a single helically extending strip 13 on its circumferential surface 7 with an increased number of holes in comparison with a region 14 next to the strip 13.

As an alternative, there can also be a plurality of diagonally extending strips 15, 16, 17 (FIG. 5) with an increased number of holes in comparison with the regions 18, 19, 20, 21 between them.

While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.

Claims

1. A suction roll system in a drying section of a machine for manufacturing a fibrous web, said suction roll system comprising a suction roll including an outer circumferential surface including a plurality of holes for attracting the fibrous web by suction, said circumferential surface divided into more than two regions having one of a different number of said holes per unit area and having said holes with different diameters per unit area, said circumferential surface having one of a plurality of strips which extends in a circumferential direction, at least one strip which extends in a helical shape over said circumferential surface, and a plurality of strips which extends one of substantially in a direction of a longitudinal axis of said suction roll and diagonally, said plurality of strips one of having an increased number of said plurality of holes per unit area in comparison with said plurality of regions between said plurality of strips and having said plurality of holes with greater diameters.

2. The suction roll system of claim 1, wherein said circumferential surface includes a plurality of end-side edges and a central region, at least one of said plurality of end-side edges including one of said plurality of regions one of having an increased number of said plurality of holes per unit area in comparison with a number of said plurality of holes per unit area in said central region and having said plurality of holes with greater diameters.

3. The suction roll system of claim 1, wherein each of said plurality of strips has a width of at least 70 mm.

4. The suction roll system of claim 1, wherein each of said plurality of strips has a width from 100 mm to 1000 mm.

5. The suction roll system of claim 1, wherein each of said plurality of strips is at a spacing from one another of at least 100 mm.

6. The suction roll system of claim 1, wherein each of said plurality of strips is at a spacing from one another of more than 200 mm.

7. The suction roll system of claim 1, wherein said circumferential surface includes a plurality of groove-shaped depressions.

8. The suction roll system of claim 7, wherein each of said plurality of depressions has a depth of from 1 to 10 mm.

9. The suction roll system of claim 7, wherein each of said plurality of depressions has a width between 1 and 10 mm.

10. The suction roll system of claim 7, wherein each of said plurality of depressions is at a spacing from one another of from 5 to 30 mm.

11. The suction roll system of claim 1, wherein said suction roll has a diameter of at least 3 m.

12. The suction roll system of claim 1, further comprising a dryer fabric and an impingement dryer, wherein said suction roll is wrapped around by said dryer fabric and the fibrous web lying on said dryer fabric, said impingement dryer being set against said suction roll in order to dry the fibrous web.

13. The suction roll system of claim 1, further comprising a vacuum source, wherein said suction roll includes a rotary leadthrough and a shaft, said suction roll being connected to said vacuum source via said rotary leadthrough in said shaft.

14. The suction roll system of claim 1, further comprising a suction box which applies a vacuum to said suction roll and which bears sealingly against said circumferential surface.

15. The suction roll system of claim 1, wherein said suction roll comprises an inner gastight cover and an outer cover, said outer cover including said plurality of holes, said inner gastight cover and said outer cover defining an annular vacuum space therebetween.

16. The suction roll system of claim 1, wherein a proportion of said circumferential surface which is occupied by said plurality of holes in said plurality of regions on said circumferential surface which have one of a lower number of said plurality of holes and said plurality of holes with a smaller diameter is between 0.2 and 2.5%.

17. The suction roll system of claim 1, wherein a proportion of said circumferential surface which is occupied by said plurality of holes in said plurality of regions on said circumferential surface which have one of a lower number of said plurality of holes and said plurality of holes with a smaller diameter is between 1 and 1.5%.

18. The suction roll system of claim 1, wherein a proportion of said circumferential surface which is occupied by said plurality of holes of one of said plurality of regions and said plurality of strips which have a higher number of said plurality of holes than remaining said plurality of regions of said circumferential surface is at least 1.5 times that of said circumferential surface which is occupied by said plurality of holes in remaining said plurality of regions.