Patent Application
20210102339
This application claims priority on Finnish application No. FI 20195843, filed Oct. 3, 2019, the disclosure of which is incorporated by reference herein.
Not applicable.
The present invention relates to a dryer fabric. The dryer fabric has a longitudinal direction and a cross direction and a first surface and a second surface. When the dryer fabric is in use the first surface is in contact with the material web to be processed, such as a paper or pulp web. The second surface of the dryer fabric faces towards machine parts, such as rolls of a paper machine. The dryer fabric forms an endless rotating loop when it is in use. The dryer fabric is mainly used in a dryer section of a paper or pulp making machine.
The dryer fabric extends in the longitudinal direction from a first end to a second end and in the cross direction from a first edge to a second edge. The dryer fabric comprises a weft comprising cross machine direction yarns, a double warp and a first seam-forming counterpart at the first end and a second seam-forming counterpart at the second end. The double warp comprises a first warp and a second warp. The first warp comprises first machine direction yarns and the second warp comprises second machine direction yarns. The yarns of the first warp are arranged above the yarns of the second warp on the first surface side in the thickness direction of the dryer fabric. The first warp comprises primary yarns whose breaking load is substantially stable within 15 days in conditions where RH=100%, T=125° C. and p=2.3 bar.
Further, the dryer fabric comprises a first seam-forming counterpart at the first end and a second seam-forming counterpart at the second end.
Monofilaments, which maintain their breaking load substantially stable in hydrolytic conditions, are usually quite expensive. The monofilaments may be made, for example, of polyphenylene sulfide. The raw material gives superior properties to the dryer fabric but has high costs. It is also substantially nonelastic.
An object of the present invention is to provide a dryer fabric so as to overcome the above problems. The object of the invention is achieved by a dryer fabric which has a first warp with primary yarns and secondary yarns arranged in such a manner that at least every second yarn of the first warp is a secondary yarn, the secondary yarns having a breaking load that is initially higher than the breaking load of the primary yarns but the breaking load of the secondary yarns decrease within 15 days in conditions where RH=100%, T=125° C. and p=2.3 bar.
An advantage of the dryer fabric is that the superior properties of the dryer fabric are mainly maintained while the fabric is much less expensive. Another advantage is that the fabric possesses more elasticity that enhances the performance of the dryer fabric e.g. during a web-break or during a high pressure washing.
The double warp comprises a first warp and a second warp. The first warp comprises first machine direction yarns and the second warp comprises second machine direction yarns. The yarns of the first warp and the yarns of the second warp are arranged above the yarns of the second warp on the first surface side in the thickness direction of the dryer fabric. The yarns of the first warp may be directly above the yarns of the second warp but alternatively the yarns of the first warp may be shifted in the cross-direction of the fabric in respect of the yarns of the second warp.
At the first end of the dryer fabric there is a first end region and at the second end there is a second end region. In order to form loops to the ends of the fabric the first machine direction yarns may be woven back in the end regions. The end segments of the second machine direction yarns may be removed so that free spaces are formed in the locations where the yarns have been removed. The end segments of the first machine direction yarns may be looped back onto themselves and woven back in the free spaces.
At the first edge of the dryer fabric there is a first edge zone extending in the machine direction and at the second edge there is a second edge zone extending in the machine direction. The edge zones have a certain width in the cross-machine direction.
According to one alternative, the first machine direction yarns, which form the first surface side of the fabric, comprise primary yarns and secondary yarns. The primary yarns and the secondary yarns are preferably monofilaments. The breaking load of the primary yarns is substantially stable within 15 days in conditions where RH=100%, T=125° C. and p=2.3 bar. Substantially stable means in this context that the breaking load decreases at the most five percent compared to the initial breaking load of the primary yarns. The breaking load of the secondary yarns is initially higher than the breaking load of the primary yarns but the breaking load of the secondary yarns decrease within 15 days in conditions where RH=100%, T=125° C. and p=2.3 bar. The breaking load of the secondary yarns decreases more than five percent compared to the initial breaking load of the secondary yarns.
The breaking load of the yarns are tested by using speed of 100 mm/min in T=23° C. and RH=65%. Conditioning 24 hours in the same conditions precedes the test.
A device suitable for simulating hydrolytic conditions is an autoclave. Ageing in the autoclave shall be made in the same batch in order to get comparable results. Control samples shall also be in the same batch with the samples to be tested. A device suitable for testing the breaking load is e.g. Instron tensile strength tester. The same definitions, test methods and conditions mentioned above are also used in connection with the other alternatives described in this text
The primary and the secondary yarns are preferably flat monofilaments. The flat monofilaments mean in this context monofilaments that have a width that is greater than their thickness and the monofilaments have substantially planar upper and lower surfaces.
When taking a look at the cross-section of the dryer fabric the secondary yarns may have a lower profile on the first surface side in the thickness direction of the dryer fabric compared to the primary yarns. In other words, when the dryer fabric is in use the primary yarns 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 there are air gaps. In such a manner the less resistant secondary yarns are shielded from e.g. heat and wear.
The primary yarns may be polyphenylene sulfide (PPS) yarns, preferably monofilaments. The PPS yarns possess excellent heat and chemical resistance, high dimensional stability, low moisture absorption and high resistance to hydrolysis. The secondary yarns, preferably monofilaments, may be polyester (PET) yarns. The PET yarns possess restricted properties compared to the PPS yarns in many respects but they give extra elasticity to the dryer fabric. The PET yarns comprise polyethylene terephthalate. The PET yarns preferably comprise a chemical hydrolysis stabilizer for preventing degradation. The chemical hydrolysis stabilizer may be a carboimide compound, such as a cyclic carboimide compound, an aromatic polycarbodiimide, or a monomeric carbodiimide.
The cross-machine direction yarns may be made of the same material as the machine direction yarns.
According to another alternative the primary yarns may be polyketone (PK) yarns or yarns comprising polyketone. They are preferably monofilaments. The yarns comprising polyketone may comprise another polymer as a blend, or there may be a core/sheath structure. There may be a polyketone sheath and a core of another polymer. The secondary yarns may be polyester (PET) yarns, preferably monofilaments. The PET yarns possess restricted properties compared to the PK yarns in many respects, but they give extra elasticity to the dryer fabric. The PET yarns comprise polyethylene terephthalate. The PET yarns preferably comprise a chemical hydrolysis stabilizer for preventing degradation. The chemical hydrolysis stabilizer may be a carboimide compound, such as a cyclic carboimide compound, an aromatic polycarbodiimide, or a monomeric carbodiimide.
The first warp comprising first machine direction yarns, which are preferably monofilaments, may comprise alternately the primary yarns and secondary yarns but a primary yarn may also be e.g. every fourth yarn.
For example, the first warp comprising first machine direction yarns, which are preferably monofilaments, may comprise alternately the polyphenylene sulfide yarns or the polyketone yarns or yarns comprising polyketone, i.e. every other first machine direction yarn is a polyphenylene sulfide yarn or a polyketone yarn or a yarn comprising polyketone and every other first machine direction yarn is a polyester yarn. However, other proportions of the polyphenylene sulfide yarns or polyketone yarns or yarns comprising polyketone and polyester yarns are possible. For example, a polyphenylene sulfide yarn or a polyketone yarn or a yarn comprising polyketone may be e.g. every fourth yarn.
The cross-machine direction yarns may be made of the same material as the machine direction yarns.
The dryer fabric is due to be an endless loop in use. In order to form a seam, the first and second ends of the dryer fabric may be attached to each other by the loops which have been formed by looping back the first machine direction yarns, or the loops are utilized for fastening separate locking spirals in the both ends of the fabric. In both cases, the seam forming counterparts, i.e. the loops or the locking spirals, are fastened to each other in such a manner that individual loops of the first seam forming counterpart and individual loops of the second seam forming counterpart intermesh.
If the seam is made by the loops of the machine direction yarns a pin is inserted in a channel which has been formed by the intermeshing loops. If the seam is made by the locking spirals a pin is inserted in a channel, which has been formed by the intermeshing turns of the locking spirals. The locking spiral may be of polyether ether ketone (PEEK). The form of the locking spiral may be flattened, i.e. the spiral has a shorter 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.
When the primary yarns and the secondary yarns alternate and the primary yarn is on top of the secondary yarn on the first side of the dryer fabric a turn of the locking spiral binds itself to loops of the dryer fabric in such a manner that it binds itself to both a primary yarn and a secondary yarn. The uppermost yarn is highly resistant to hydrolysis and the monofilament under the uppermost yarn backs up the durability of the joint between the weave and the locking spiral.
When the polyphenylene sulfide yarns or polyketone yarns or yarns comprising polyketone and the polyester yarns alternate and the PPS or PK yarn is on top of the PET yarn on the first surface side of the dryer fabric a turn of the locking spiral binds itself to loops of the dryer fabric in such a manner that it binds itself to both a PPS yarn or a PK yarn and a PET yarn. The uppermost PPS yarn or PK yarn is highly resistant to hydrolysis and the PET yarn under the highly resistant yarn backs up the durability of the joint between the weave and the locking spiral.
Another alternative to make a dryer fabric is to use two different high performance yarns, i.e. the first warp of the dryer fabric comprises primary yarns whose breaking load and elongation at break are substantially stable within 15 days in conditions where RH=100%, T=125° C. and p=2.3 bar, and the first warp of the dryer fabric comprises secondary yarns whose breaking load and elongation at break are substantially stable within 15 days in conditions where RH=100%, T=125° C. and p=2.3 bar in such a manner that the primary yarns are different from the secondary yarns. The above-mentioned conditions may be arranged in an autoclave. After the treatment in the autoclave the monofilaments are tested.
The primary yarns may be, for example, polyphenylene sulfide (PPS) yarns and the secondary yarns may be, for example, polyketone yarns (PK). The primary and secondary yarns are preferably monofilaments. The first warp comprising first machine direction yarns may comprise alternately the PPS and the PK yarns, i.e. every other first machine direction yarn is a PPS yarn and every other first machine direction yarn is a PK yarn. However, other proportions of the PPS and PK yarns are possible. For example, a PPS yarn may be e.g. every fourth yarn.
The second warp may comprise polyester (PET) yarns. They preferably comprise a chemical hydrolysis stabilizer for preventing degradation. The chemical hydrolysis stabilizer may be a carboimide compound, such as a cyclic carboimide compound, an aromatic polycarbodiimide, or a monomeric carbodiimide. One possible structure of the dryer fabric is described below.
The cross-machine direction yarns may be made of the same material as the machine direction yarns.
If the seam is made by the loops of the machine direction yarns a pin is inserted in a channel which has been formed by the intermeshing loops. If the seam is made by the locking spirals a pin is inserted in a channel, which has been formed by the intermeshing turns of the locking spirals. The locking spiral may be of polyether ether ketone (PEEK). The form of the locking spiral may be flattened, i.e. the spiral has a shorter 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.
Still another alternative is to form the first warp of the dryer fabric from polyketone yarns (PK), i.e. the first warp of the dryer fabric comprises yarns of polyketone whose breaking load is substantially stable within 15 days in conditions where RH=100%, T=125° C. and p=2.3 bar. The second warp may comprise polyester (PET) yarns. The yarns of the first and second warps are preferably monofilaments. They preferably comprise a chemical hydrolysis stabilizer for preventing degradation. The chemical hydrolysis stabilizer may be a carboimide compound, such as a cyclic carboimide compound, an aromatic polycarbodiimide, or a monomeric carbodiimide.
The cross-machine direction yarns may be made of the same material as the machine direction yarns.
If the seam is made by the loops of the machine direction yarns a pin is inserted in a channel which has been formed by the intermeshing loops. If the seam is made by the locking spirals a pin is inserted in a channel, which has been formed by the intermeshing turns of the locking spirals. The locking spiral may be of polyether ether ketone (PEEK). The form of the locking spiral may be flattened, i.e. the spiral has a shorter 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.
It is possible that the above-mentioned alternatives become materialized only in either of the edge zones and the rest of the machine direction yarns of the first warp may be secondary yarns. The above-mentioned alternatives may also become materialized in both edge zones and the machine direction yarns between the edge zones may be secondary yarns. The width of the first edge zone and the width of the second edge zone may be at the highest 500 mm, preferably at the highest 300 mm and more preferably at the highest 150 mm as from the respective edge of the dryer fabric. For example, every other machine direction yarn in the edge zone(s) may be a primary yarn and every other machine direction yarn may be a secondary yarn. 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.
All yarns or monofilaments described above in the different alternatives may comprise auxiliary components besides the polymer, such as fillers or the like. The same applies to the locking spirals.
The dryer fabric may have many alternative structures. For example, the dryer fabric may have a structure described below. The structure may be applied to every alternative described above.
The dryer fabric comprises a double warp, i.e. there are two warps one above the other. A first warp comprises first machine direction yarns and a second warp comprises second machine direction yarns. The yarns of the first warp are arranged above the yarns of the second warp. The first machine direction yarns of the first warp and the second machine direction yarns of the second warp may be flat yarns.
The yarns 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 of the first warp are shifted laterally in respect of the yarns of the second warp. However, it is possible that all yarns of the first warp are offset in respect of the yarns of the second warp. The warp cover of each warp is preferably from 75 to 95%.
The dryer fabric comprises a weft which comprises cross-machine direction yarns. The cross-machine direction yarns of the weft may be round yarns, i.e. their cross section is a circle, or they may be oval yarns, i.e. their cross section is oval. The cross-machine direction yarns are usually monofilaments.
The yarns of the first warp and the yarns of the weft bind themselves to each other according to a first predetermined pattern, and the yarns of the second warp and the yarns of the weft bind themselves to each other according to a second predetermined pattern.
The dryer fabric may have a granular texture on the first side of the dryer fabric. In other words, there are a lot of contact points on the first surface of the industrial textile but less contact area. The granular texture is achieved by short yarn floats. For example, the first predetermined pattern may be formed in such a manner that the yarns of the first warp and the yarns of the weft bind to each other so that the yarns of the first warp repeatedly pass over two yarns of the weft and under two yarns of the weft. The yarns of the first warp next to each other are arranged in such a manner that when a coincidentally selected warp yarn is under the weft yarns the warp yarn next to the coincidentally selected warp yarn is above the weft yarns. This results in the granular texture on the first surface, i.e. the surface of the textile looks like being covered by grains.
The second predetermined pattern may be formed in such a manner that the yarns of the second warp and the yarns of the weft bind to each other so that the yarns of the second warp repeatedly pass above one weft yarn and under three weft yarns. The yarns of the second warp next to each other are arranged in such a manner that when a coincidentally selected warp yarn is above the weft yarn the warp yarn next to the coincidentally selected warp yarn is above the second weft yarn as from the weft yarn above which the coincidentally selected warp yarn is, i.e. the weft yarn that is the second from the weft yarn above which the coincidentally selected warp yarn is. The weft yarn over which the yarn of the second warp passes is the second weft yarn over which the yarn of the first warp passes.
The structure of the dryer fabric is not limited to the above-mentioned bind or cross-sections of yarns. The description of the structure is only one example of how to manufacture the weave of the dryer fabric.
In the following, the invention will be described in more detail by means of preferred embodiments with reference to the accompanying drawings.
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.
In use the dryer fabric 1 forms an endless loop as shown in
The first warp 12 comprises primary yarns 51 and secondary yarns 52. The second warp 14 comprises yarns 9. In
The seam forming counterparts 3, 4 are locking spirals. As one can see from
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.
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.
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.
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.
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.
It should be understood that substantially stable means: largely, mainly, materially, for the most part or to a large extent stable.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20195843 | Oct 2019 | FI | national |
