Dryer fabric with warp yarns of multiple materials

Abstract

A dryer fabric has a weft of cross machine direction yarns (6) and a first warp of first machine direction yarns (5) and a second warp of second machine direction yarns (9). The yarns of the first warp are arranged above the yarns of the second warp on a first surface (FS) side. The first warp has primary yarns (51) of PPS or PK yarns whose breaking load remains substantially stable within 15 days in conditions where RH=100%, T=125° C. and p=2.3 bar; and secondary yarns (52) of PET with breaking loads which substantially decrease under the same conditions. At least every second yarn of the first warp is a secondary yarn (52). The secondary yarns (52) may be two out of three or three out of four of the first machine direction yarns (5). PET reduces cost and adds elasticity to the dryer fabric.

Claims

1. A dryer fabric having a machine direction and a cross machine direction and a first surface for supporting a fiber web and a second surface for supporting the dryer fabric in a paper machine dryer section, the dryer fabric extending in the machine direction from a first end to a second end and in the cross machine direction from a first edge to a second edge, the dryer fabric comprising: a weft comprising cross machine direction yarns; a first warp comprising first machine direction yarns further comprising primary yarns and secondary yarns; a second warp comprising second machine direction yarns; wherein the yarns of the first warp form the first surface and are arranged above the yarns of the second warp in a thickness direction of the dryer fabric; wherein the first warp primary yarns have a breaking load which remains substantially stable after 15 days exposure to conditions of relative humidity of 100%, temperature of 125° C., and at a pressure of 2.3 bar; a first seam-forming counterpart at the first end and a second seam-forming counterpart at the second end; wherein in the first warp, the secondary yarns are arranged so that the secondary yarns are at least every second yarn of the first warp; and wherein the secondary yarns have a breaking load that is initially, before being subjected to heat and humidity, higher than the breaking load of the primary yarns but the breaking load of the secondary yarns is less than the breaking load of the primary yarns when exposed to 15 days in conditions of relative humidity of 100%, temperature of 125° C. and at a pressure of 2.3 bar; and wherein the first warp secondary yarns are arranged so at least one secondary yarn is between the primary yarns and at least every second yarn of the first warp is a secondary yarn, and wherein the secondary yarns have a breaking load that is initially higher than the breaking load of the primary yarns (51) but the breaking load of the secondary yarns (52) decrease within 15 days in conditions of relative humidity of 100%, temperature of 125° C. and at a pressure of 2.3 bar.

2. The dryer fabric of claim 1 wherein the primary yarns comprise polyphenylene sulfide (PPS) yarns.

3. The dryer fabric of claim 1 wherein the primary yarns consist of polyphenylene sulfide (PPS) yarns.

4. The dryer fabric of claim 1 wherein the primary yarns comprise polyketone (PK) yarns.

5. The dryer fabric of claim 1 wherein the primary yarns consist of polyketone (PK) yarns.

6. The dryer fabric of claim 1 wherein the secondary yarns comprise polyester (PET) yarns.

7. The dryer fabric of claim 1 wherein the secondary yarns consist of polyester (PET) yarns.

8. The dryer fabric of claim 1 wherein the first warp comprises alternately a primary yarn and a secondary yarn.

9. The dryer fabric of claim 1 wherein the first seam-forming counterpart and the second seam-forming counterpart comprise a locking spiral comprising individual loops, wherein said locking spirals intermeshed and together with a pin being capable of forming a seam.

10. The dryer fabric of claim 9 wherein the individual loop of the each locking spiral is arranged to bind the adjacent primary yarns and secondary yarns in such a manner that the primary yarn is on top of the secondary yarn on the first side of the dryer fabric.

11. The dryer fabric of claim 9 wherein the locking spiral is of polyether ether ketone (PEEK).

12. The dryer fabric of claim 7 wherein the polyester (PET) yarns comprise an anti-hydrolysis agent that is a carbodiimide compound.

13. The dryer fabric of claim 12 wherein the carbodiimide compound is selected from a group consisting of cyclic carbodiimide compound, an aromatic polycarbodiimide, and a monomeric carbodiimide.

14. The dryer fabric of claim 1 wherein the yarns of the first warp and the yarns of the second warp are monofilaments.

15. The dryer fabric of claim 1 wherein at the first edge there is a first edge zone and at the second edge there is a second edge zone, and the first warp comprises secondary yarns in such a manner that at least every second yarn of the first warp in at least one edge zone is a secondary yarn and the rest of the machine direction yarns of the first warp are secondary yarns.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, the invention will be described in more detail by means of preferred embodiments with reference to the accompanying drawings.

(2) FIG. 1 shows a schematic top plan view of a dryer fabric.

(3) FIG. 2 shows a schematic side elevational view of a dryer fabric of FIG. 1 with ends not connected.

(4) FIG. 3 shows a schematic side elevational view of a dryer fabric of FIG. 1 with ends connected.

(5) FIG. 4a shows a fragmentary schematic cross-sectional elevational view of a first embodiment of the dryer fabric of FIG. 1.

(6) FIG. 4b shows a fragmentary schematic cross-sectional elevational view of a second embodiment of the dryer fabric of FIG. 1.

(7) FIG. 5 shows a perspective view of a part of a dryer fabric.

(8) FIG. 6 shows another perspective view of a part of a dryer fabric.

(9) FIG. 7 shows a fragmentary schematic cross-sectional elevational view of the embodiment of the dryer fabric of FIG. 4a where the primary yarns of the first warp are thicker than the secondary yarns of the first warp.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(10) FIGS. 1 to 3 show schematic views of a dryer fabric 1. The dryer fabric has a longitudinal direction MD, a cross direction CMD, a first surface FS and a second surface SS. The dryer fabric 1 comprises a weave 2 and a seam forming counterparts 3, 4. The weave 2 comprises a first end FE, a second end SE, a first end region FR, a second end region SR, a first edge 7, a second edge 8, a first edge zone FZ and a second edge zone SZ.

(11) Besides the possible structures shown in other figures, one feasible structure is that every other machine direction yarn of the first warp in the first edge zone FZ, or every other machine direction yarn of the first warp in the second edge zone SZ may be a primary yarn and every other machine direction yarn may be a secondary yarn. It is also possible that both edge zones FZ, SZ have the above-mentioned structure. The primary yarn may be a polyphenylene sulfide (PPS) yarn, or a polyketone (PK) yarn. The secondary yarn may be a polyester (PET) yarn, or a polyketone (PK) yarn. The machine direction yarns of the first warp outside the edge zone(s) and the machine direction yarns of the second warp may be polyester (PET) yarns. The cross-machine direction yarns may be made of the same material as the machine direction yarns.

(12) In use the dryer fabric 1 forms an endless loop as shown in FIG. 3. The seam forming counterparts 3, 4 are joined together by a pin (not shown).

(13) FIGS. 4a and 4b are schematic views of possible arrangements of the first and the second warps of a dryer fabric 1 as cross-sections. When the dryer fabric is in use the first surface FS is in contact with the material web to be processed, such as a paper or pulp web. The second surface SS of the dryer fabric faces towards machine parts, such as rolls of a paper machine.

(14) The first warp 12 comprises primary yarns 51 and secondary yarns 52. The second warp 14 comprises yarns 9. In FIG. 4a the first warp comprises alternately a primary yarn 51 and a secondary yarn 52. In FIG. 4b every fourth first machine direction yarn is a primary yarn 51 and between two primary yarns 51 there are three secondary yarns 52.

(15) FIGS. 4a and 4b show the yarns 51, 52 of the first warp directly above the yarns 9 of the second warp. However, the yarns 51, 52 of the first warp may be at least partially offset in respect of the yarns of the second warp which means that at least part of the yarns 51, 51 of the first warp are shifted laterally in respect of the yarns 9 of the second warp. It is possible that all yarns 51, 52 of the first warp are offset in respect of the yarns 9 of the second warp.

(16) FIG. 5 shows a perspective view of a part of a dryer fabric 1. The dryer fabric 1 comprises a weave 2 and seam forming counterparts 3, 4 (only counterpart 3 shown). The weave 2 comprises a first warp comprising first machine direction yarns 5, a second warp comprising second machine direction yarns 9 under the first warp and a weft comprising cross machine direction yarns 6.

(17) The seam forming counterparts 3, 4 are locking spirals. As one can see from FIG. 5, the locking spiral is flattened, i.e. the spiral has the shortest dimension in the thickness direction of the dryer fabric and the upper and the lower surface of the turn of the spiral is substantially planar.

(18) The first warp of the weave 2 comprises alternating primary monofilaments 51 and secondary monofilaments 52. The primary monofilament 51 is on top of the secondary monofilament 52 on the first surface side of the dryer fabric 1. A single turn 31 of the locking spiral binds itself to loops of the dryer fabric in such a manner that it binds itself to both the primary monofilament 51 and the secondary monofilament 52.

(19) The hydrolysis resistance of the above-mentioned dryer fabric 1 was tested when the primary monofilaments were polyphenylene sulfide monofilaments and the secondary monofilaments were polyester monofilaments. Also, two comparative dryer fabrics were tested. The first comparative fabric was a fabric consisting of PPS yarns. The second comparative fabric was a fabric consisting of PET yarns. The breaking loads of the tested fabrics were in the beginning of the test over 90 N. After 15 days in the hydrolytic conditions the breaking load of the second comparative fabric was collapsed under 10 N while the breaking load of the dryer fabric 1 of the invention was on the same 90 N level as the breaking load of a comparative fabric consisting of PPS yarns.

(20) Alternatively, the first warp of the weave 2 comprises alternating PK yarns 51 and PET yarns 52. The PK yarn 51 is on top of the PET yarn 52 on the first surface side of the dryer fabric 1. A single turn 31 of the locking spiral binds itself to loops of the dryer fabric in such a manner that it binds itself to both the PK yarn 51 and the PET yarn 52.

(21) FIG. 6 shows a perspective view of a part of a dryer fabric 1. The dryer fabric 1 comprises a weave 2 and seam forming counterparts 3, 4 (only counterpart 3 shown). The weave 2 comprises a first warp comprising first machine direction yarns 5, a second warp comprising second machine direction yarns 9 under the first warp and a weft comprising cross machine direction yarns 6.

(22) The seam forming counterparts 3, 4 are loops of the first machine direction yarns. The first warp of the weave 2 comprises alternating PPS yarns 51 and PET yarns 52. The PPS yarn 51 is on top of the PET yarn 52 on the first surface side of the dryer fabric.

(23) Alternatively, the first warp of the weave 2 comprises alternating PK yarns 51 and PET yarns 52. The PK yarn 51 is on top of the PET yarn 52 on the first surface side of the dryer fabric.

(24) FIG. 7 shows a schematic view of one possible arrangement of the first and the second warps of a dryer fabric 1 as a cross-section. The first warp comprises primary yarns 51 and secondary yarns 52. The second warp comprises yarns 9. The secondary yarns 52 may have a lower height in the thickness direction of the dryer fabric compared to the primary yarns 51. The secondary yarns 52 are on the same level with the primary yarns 51 on the second surface SS of the dryer fabric 1. In other words, when the dryer fabric is in use the primary yarns 51 make a direct contact to the web to be processed, such as a paper or pulp web, and between the web and the secondary yarns 52 on the first surface FS side there are air gaps 10. Thus, the secondary yarns 52 are shielded from e.g. heat and wear.

(25) It should be understood that substantially stable means: largely, mainly, materially, for the most part or to a large extent stable.

(26) It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.