Drying fabric for a papermaking machine

Abstract

A drying fabric for a papermaking machine, in particular for use in a drying section of a papermaking machine, is formed by longitudinal MD yarns (11) extending in the machine direction (MD), and by CMD yarns (12) extending in the cross machine direction (CMD) and substantially orthogonal to the MD yarns (11); both the MD yarns (11) and the CMD yarns (12) are flat yarns having flattened cross-section yarns with different dimensions in two mutually orthogonal directions, defining width and height, wherein the width is greater than the height.

Description

[0001] "DRYING FABRIC FOR A PAPERMAKING MACHINE"

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This Patent Appl ication claims priority from Italian Patent Application No . 102023000028260 filed on December 28 , 2023 , the entire disclosure of which is incorporated herein by reference .

[0004] TECHNICAL FIELD

[0005] The present invention relates to a drying fabric intended for use in a papermaking machine and in particular for drying a paper or paperboard web circulating in a drying section of a papermaking machine .

[0006] The fabric according to the present invention finds a preferred, but not exclusive , application in the field of paperboard manufacturing ( so-called "brown" sector ) .

[0007] CONTEXT

[0008] In general , a drying fabric of a papermaking machine , i . e . intended for use in a drying section of a papermaking machine , consists of warp yarns and weft yarns woven according to various patterns and extending respectively in the machine direction (MD yarns ) and in the cross machine direction ( CMD yarns ) , wherein the terms "machine direction" ( abbreviated "MD" ) and "cross machine direction" ( abbreviated "CMD" ) indicate respectively a direction aligned with the direction of advancement of the fabric in the papermaking machine , and a direction transverse ( orthogonal ) to the direction of advancement .

[0009] It is also understood, always in accordance with common use in the sector, that the surface of the fabric in contact with the paper material is the upper surface of the fabric ; and that the opposite surface facing the machine is the lower surface . This reference is also used to describe the vertical spatial arrangement of the yarns in the forming fabric .

[0010] In the drying sections of papermaking machines , the fabric used to support and transport the paper web (here and in the following the term "paper" is intended to include all types of paper and paperboard) must have a high flatness in order to allow a good support of the paper during drying, as well as an easy and ef fective cleaning of the fabric .

[0011] The fabric is normally made in flat form and then closed to form an endless web, during production or directly on the papermaking machine , j oining the two opposite ends of the fabric by means of a seam, commonly called a stitching .

[0012] Several methods for making the seam or stitching are known . For example , in one case , the ends of the fabric are provided with seaming loops , formed by folded MD yarns , which are then brought to interpenetrate so as to form a tubular passage through which a seaming cable ( or more than one ) is inserted . The seaming area, in addition to constituting the weakest part of the fabric and most subj ect to wear and deterioration in use , determines a discontinuity in the fabric that can imprint surface defects on the paper being formed and transported by the fabric .

[0013] It is therefore necessary to combine the characteristics of the fabric with those of the seam to obtain a fully ef fective and reliable fabric .

[0014] SUMMARY

[0015] It is an aim of the present invention to provide a drying fabric for a papermaking machine that is free from the drawbacks of the prior art , in particular being fully ef fective and reliable .

[0016] In particular, it is an aim of the invention to provide a drying fabric that provides , in the drying sections of the papermaking machine , an excellent support to the paper and allows an ef fective steam evaporation without marking the paper, as well as allowing an easy and ef ficient cleaning of the surface of the fabric .

[0017] The present invention therefore relates to a drying fabric for a papermaking machine as defined in essential terms in the appended claim 1 and, in its additional characters , in the dependent claims .

[0018] In essence , the drying fabric of the invention is formed by flat we ft yarns and by f lat warp yarns , where the weft yarns are wider than the warp yarns , having a width at least twice and preferably about 2 . 5 times greater than the warp yarns .

[0019] The fabric of the invention allows to provide excellent support to the paper without imprinting marks or other defects on the paper, as well as allowing an easy and ef ficient cleaning of the surface of the fabric .

[0020] When used, in particular, in a drying section, the fabric of the invention also ensures good steam evaporation .

[0021] BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Further features and advantages of the present invention will become clear from the description of the following non-limiting embodiments , with reference to the figures of the accompanying drawings , wherein :

[0023] - Figure 1 is a schematic top plan view of fabric in accordance with the invention;

[0024] - Figure 2 is a schematic cross-sectional view of the fabric of Figure 1 ;

[0025] - Figure 3 is an enlarged scale view with parts removed for clarity' s sake of a detail of the fabric of Figure 1 ;

[0026] - Figure 4 which is a partial schematic top plan view of a seaming area of the fabric in accordance with the invention;

[0027] - Figures 5-7 are schematic top plan views of the seaming area according to respective variants .

[0028] DESCRIPTION OF EMBODIMENTS

[0029] In Figures 1 -3 , 1 denotes as a whole a drying fabric for a papermaking machine , i . e . a fabric intended to operate in a drying section of a papermaking machine for transporting and supporting a moving paper web during its drying . It is understood, however, that the fabric of the invention may be employed in other sections of the papermaking machine .

[0030] The fabric 1 is formed by MD yarns 11 , i . e . longitudinal warp yarns extending in the machine direction (MD) , and by CMD yarns 12 , i . e . transverse weft yarns , substantially orthogonal to the MD yarns and extending in the cross machine direction ( CMD) .

[0031] The fabric 1 has a repeating unit that is repeated both in the machine direction (warp ) and in the cross machine direction (weft ) . The repeating unit may be repeated several times , both in the machine direction and in the cross machine direction, to form a fabric 1 having the desired dimensions for use on the papermaking machine .

[0032] The fabric 1 is a single-layer fabric having a single fabric layer formed by a series of flat MD yarns 11 and a series of flat CMD yarns 12 woven orthogonal to each other based on the weaving sequence .

[0033] The MD yarns 11 and the CMD yarns 12 are woven with each other according to a repeated weaving pattern both in the machine direction and in the cross machine direction.

[0034] The weaving pattern can be of various type.

[0035] In the preferred embodiment shown, the fabric 1 has a plain weave structure with a ratio between MD yarns 11 and CMD yarns of 1:1.

[0036] It is understood that the fabric 1 may have a different weaving pattern.

[0037] In accordance with the invention, both the MD yarns 11 and the CMD yarns 12 are flat yarns. By flat yarn is meant a yarn having (under undeformed conditions) a flattened cross-section with different dimensions in two mutually orthogonal directions, defining width and height of the yarn, and having in particular a width greater than the height.

[0038] A flat yarn has two opposite major faces joined by two lateral sides, with rounded or chamfered edges; the maximum distance between the faces defines the height of the yarn, while the maximum distance between the sides defines the width .

[0039] The CMD yarns 12 (weft yarns) have a greater width than the MD yarns 11 (warp yarns) .

[0040] In particular, the CMD yarns 12 have a width L2 that is at least twice, preferably at least 2.5 times, the width LI of the MD yarns 11; preferably, the CMD yarns 12 have a width L2 that is between 2 and 3 times (extremes included) the width LI of the MD yarns 11. Preferably, the MD yarns 11 have height Hl between 0.25 mm and 0.40 mm and width LI between 0.58 mm and 0.70 mm; and the CMD yarns 12 have height H2 between 0.50 mm and 0.80 mm and width L2 between 1.50 mm and 1.80 mm.

[0041] For example, the MD yarns 11 have dimensions: 0.28 x 0.58 mm ; 0.30 x 0.60 mm ; 0.36 x 0.70 mm .

[0042] For example, the CMD 12 yarns have dimensions 0.52 x 1.60 mm ; 0.70 x 1.63 mm .

[0043] Preferably, both the MD yarns 11 and the CMD yarns 12 have a width at least twice the height.

[0044] A fabric 1 in accordance with the invention, having a plain weave structure and intended in particular for use as a drying fabric, may for example have the following characteristics :

[0045] TABLE 1

[0046] (*) warp yarns per cm x weft insertions per cm

[0047] The MD yarns 11 and the CMD yarns 12 can be made of any material suitable for the application, for example polyester, rayon, etc.

[0048] With reference also to Figure 4, the fabric 1 extends between two longitudinally opposite ends 21 having respective transverse edges 22 facing each other and joined by a seam 23 (stitching) to form an endless web.

[0049] The seam 23 comprises, at each end 21 of the fabric 1, a plurality of pairs of MD yarns Ila extending beyond a terminal CMD yarn 12a (last CMD yarn at the end) to form respective seaming loops 25 along the edge 22.

[0050] The seaming loops 25 projecting from the two facing edges 22 can be joined in various ways, for example by at least one stitching yarn passing through the seaming loops, and / or by at least one spiral.

[0051] In the embodiment of Figure 4, the seaming loops 25 are woven with each other and joined by a stitching yarn 26 passing through the seaming loops 25.

[0052] The fabric 1 has a seaming ratio, defined as the ratio between the number of pairs of MD yarns Ila forming seaming loops 25 and the number of pairs of MD yarns 11 that do not form seaming loops, between 1:1 and 4:1.

[0053] In general, the seaming loops 25 are spaced apart by a single pair of MD yarns 11 that do not form seaming loops.

[0054] In the example of Figure 4, the fabric 1 has a seaming ratio of 2:1, i.e. there are two pairs of adjacent and consecutive yarns Ila (in the cross machine direction) interspersed by a pair of MD yarns 11 that do not form seaming loops.

[0055] In the example of Figure 5, the fabric 1 has a seaming ratio of 3:1, i.e. there are three pairs of adjacent and consecutive yarns Ila (in the cross machine direction) interspersed by a pair of MD yarns 11 that do not form seaming loops.

[0056] In the example of Figure 6, the fabric 1 has a seaming ratio of 4:1, i.e. there are four pairs of adjacent and consecutive yarns Ila (in the cross machine direction) interspersed by a pair of MD yarns 11 that do not form seaming loops.

[0057] In the embodiment of Figure 7, all pairs of adjacent MD yarns 11 form respective seaming loops 25, which are woven, at each end 21, with a spiral 27 extending along the edge 22. The two spirals 27 are in turn joined by a connecting yarn 28 passing through the spirals 27.

[0058] Finally, it is understood that further modifications and variants may be made to the papermaking fabric described and shown herein that do not fall outside the scope of the appended claims.

Claims

CLAIMS1. A drying fabric (1) for a papermaking machine, in particular for drying a paper or paperboard web circulating in a drying section of a papermaking machine, formed by longitudinal MD yarns (11) extending in the machine direction (MD) , and by CMD yarns (12) extending in the cross machine direction (CMD) and substantially orthogonal to the MD yarns (11) ; wherein both the MD yarns (11) and the CMD yarns (12) are flat yarns having flattened cross-section with different dimensions in two mutually orthogonal directions, defining width and height, wherein the width is greater than the height; characterized in that the CMD yarns (12) have greater width than the MD yarns (11) .

2. The fabric according to claim 1, wherein the fabric (1) is a single-layer fabric having a single fabric layer formed by a series of flat MD yarns (11) and a series of flat CMD yarns (12) woven orthogonal to each other.

3. The fabric according to claim 1 or 2, wherein the fabric (1) has a plain weave structure with a ratio between MD yarns (11) and CMD yarns (12) of 1:1.

4. The fabric according to any one of the preceding claims, wherein the CMD yarns (12) have a width that is at least twice, preferably at least 2.5 times, the width of the MD yarns (11) .

5. The fabric according to any one of the precedingclaims, wherein the CMD yarns (12) have a width that is between 2 and 3 times, extremes included, the width of the MD yarns (11) .

6. The fabric according to any one of the preceding claims, wherein the MD yarns (11) have height between 0.25 mm and 0.40 mm and width between 0.58 mm and 0.70 mm; and the CMD yarns (12) have height between 0.50 mm and 0.80 mm and width between 1.50 mm and 1.80 mm.

7. The fabric according to any one of the preceding claims, wherein the MD yarns (11) have dimensions ranging between 0.28 x 0.58 mm and 0.36 x 0.70 mm.

8. The fabric according to any one of the preceding claims, wherein the CMD yarns (12) have dimensions ranging between 0.52 x 1.60 mm and 0.70 x 1.63 mm.

9. The fabric according to any one of the preceding claims, wherein both the MD yarns (11) and the CMD yarns (12) have width at least twice the height.

10. The fabric according to any one of the preceding claims, wherein the fabric (1) extends between two longitudinally opposite transverse edges (22) facing each other and joined by a seam (23) to form an endless web; and wherein the seam (23) comprises, on each edge (22) , a plurality of seaming loops (25) formed by at least some pairs of MD yarns (Ila) and joined by at least one stitching yarn (26) passing through the seaming loops (25) , and / or by atleast one spiral (27) engaging the seaming loops (25) .

11. The fabric according to claim 10, wherein the fabric (1) has a seaming ratio, defined as the ratio between the number of pairs of MD yarns (Ila) forming seaming loops (25) and the number of pairs of MD yarns (11) that do not form seaming loops, between 1:1 and 4:1.

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