Method and apparatus for reduction of curling of paper in the drying section of a paper machine

Claim 3

The method of claim 1, further comprising applying said steam treatment at an end of the drying section.

Claim 4

The method of claim 1, further comprising applying said steam treatment in an area of said drying section where the dry solids content of the paper web is from about 80 to about 95 percent.

Claim 5

The method of claim 1, further comprising providing said drying section with groups of drying cylinders with single-wire draw, arranging said drying cylinders in an upper row, and arranging said suction roll or cylinder in a lower row, such that paper broke can be removed directly through open intermediate spaces located underneath said drying cylinders.

Claim 6

The method of claim 1, further comprising blowing air into spaces defined between the wire and said suction roll or cylinder.

Claim 7

A drying section of a paper machine, comprising at least one drying section group comprising a plurality of drying cylinders for drying a paper web having opposed bottom and top sides, said drying cylinders each having a heated surface, a drying wire running in a meandering fashion over said drying cylinders, said drying wire pressing the bottom side of the paper web against said heated surfaces of said drying cylinders, at least one steam box arranged in said drying group and comprising a counter-face which, together with a free face of the paper web, defines a contact-free steam-treatment gap in said drying group, said steam box extending substantially across an entire transverse width of the paper web, said steam box being positioned in a location after the bottom side of the web has separated from one of said heated surfaces of said drying cylinders and applying steam onto the bottom side of the web to raise the temperature of the bottom side of the web and control a moisture gradient in a direction of thickness of the paper web between the paper web sides substantially across an entire width of the paper web such that tensions that have been formed or that tend to be formed in the fiber mesh of the paper web are relaxed by means of heat and moisture in the area of their formation or substantially immediately thereafter, and said steam box applying steam to the paper web during the run of the paper web on a wire through the drying section the tendency of the paper web to curl is prevented in the run of the paper web through the drying section.

Claim 8

A drying section of a paper machine, comprising at least one drying section group comprising a plurality of drying cylinders for drying a paper web having opposed bottom and top sides, said drying cylinders each having a heated surface, a drying wire running in a meandering fashion over said drying cylinders, said drying wire pressing the bottom side of the paper web against said heated surfaces of said drying cylinders, at least one steam box arranged in said drying group and comprising a counter-face which, together with a free face of the paper web, defines a contact-free steam-treatment gap in said drying group, said steam box extending substantially across an entire transverse width of the paper web, said steam box being positioned in a location after the bottom side of the web has separated from one of said heated surfaces of said drying cylinders and applying steam onto the bottom side of the web to raise the temperature of the bottom side of the web and control a moisture gradient in a direction of thickness of the paper web between the paper web sides substantially across an entire width of the paper web such that tensions that have been formed or that tend to be formed in the fiber mesh of the paper web are relaxed by means of heat and moisture in the area of their formation or substantially immediately thereafter, and said steam box applying steam to the paper web during the run of the paper web on a wire through the drying section the tendency of the paper web to curl is prevented in the run of the paper web through the drying section.

Claim 9

The drying section of claim 6, wherein said steam box further comprises regulating means, said regulating means controlling the quantity of steam supplied by the steam box across the transverse width of the paper web.

Claim 10

The drying section of claim 7, wherein said steam box is arranged in an area of said drying section where the dry solids content of the paper web is from about 80 to about 95 percent, by weight.

Claim 11

The drying section of claim 6, wherein said drying group further comprises a plurality of wire guide rolls and/or leading cylinders over which the paper web runs, at least one of said wire guide rolls or leading cylinders being a suction-leading cylinder provided with negative pressure, said steam box being placed in an area of said drying section having a single-wire draw on a suction zone of said suction-leading cylinder, such that the negative pressure prevailing in interior spaces of said suction-leading cylinder supports the paper web and promotes the action of the steam on the paper.

Claim 12

The drying section of claim 9 which comprises at least two drying section groups, at least one guide roll located in a gap between said drying group sections for guiding the paper web, said steam box being fitted opposite said guide roll.

Claim 13

The drying section of claim 9, wherein said drying section group has a single-wire draw in which steam is applied to the paper web running on the wire, said drying cylinders being arranged in an upper row and said wire guide rolls and/or leading cylinders being arranged in a lower row below said drying cylinders.

Claim 14

The drying section of claim 11, wherein said drying section groups comprise a plurality of additional steam boxes fitted in connection with additional ones of said leading cylinders and/or said wire guide rolls.

Claim 15

The drying section of claim 9, wherein said suction-leading cylinder has an interior portion and an outer perforated and grooved mantle, whereby suction in the interior of said suction-leading cylinder is spread onto a circumference of said suction-leading cylinder to thereby promote penetration of steam into the paper web.

Claim 16

The drying section of claim 9, further comprising blow boxes for blowing air into spaces defined between said drying wire and said leading cylinders.

Claim 17

The drying section of claim 9, further comprising at least one inverted drying section group in which drying cylinders are arranged in a lower row and wire guide rolls and/or leading cylinders are arranged in a upper row above said drying cylinders, said at least one inverted drying section group being arranged adjacent to said at least one drying section group.

Claim 18

The drying section of claim 15, wherein the web is transferred from a wire in said at least one drying section group to a wire in said at least one inverted drying section group as a closed draw.

Claim 19

The drying section of claim 6, wherein said steam box is arranged in an area of said drying section where the dry solids content of the paper web is from about 70 to about 98 percent, by weight.

Claim 22

The method of claim 18, further comprising applying said steam treatment in an area of said drying section where the dry solids content of the paper web is from about 70 to about 98 percent.

Claim 23

The method of claim 18, further comprising applying said steam treatment in an area of said drying section where the dry solids content of the paper web is from about 80 to about 95 percent.

Claim 24

The method of claim 18, further comprising applying said steam treatment at an end of the drying section.

Claim 25

The method of claim 18, further comprising carrying the web on a wire around said drying cylinders and said suction rolls or cylinders such that the wire runs in a meandering fashion over said drying cylinders and said suction rolls or cylinders and blowing air into spaces defined between the wire and said suction rolls or cylinders.

Claim 26

The method of claim 18, further comprising arranging a first steam box to apply steam onto a first side of the web in the free draw and arranging a second steam box to apply steam onto an opposite side of the web in the free draw.