This invention relates to a papermaking fabric according to the preamble of claims 1 and 14 and also to a System of a paper machine and a papermaking fabric running between at least two rolls of the papermaking machine according to the preamble of claims 15.

Different papermaking fabrics, press felts, press belts, tension belts and transfer belts are used in a press section of a typical papermaking machine. These kinds of fabrics are subjected to high temperatures, pressures and pressure pulses, tensile loads and sudden impacts, not to mention different corrosive chemicals that cause wear in the fabric during its operational lifespan.

According to statistics, one press fabric will break daily, worldwide. Worn-down or otherwise damaged fabrics subjected to sudden impacts, or just simply exceeding a certain level of elongation are prone to break, either partially or completely, causing damage to machine equipment, not to mention potentially hazardous situations to personnel. Unplanned machine down-time caused by press fabric breaks, and repairing or replacing damaged equipment is costly, and maintaining an acceptable level of personnel safety within the press section can be difficult since these kinds of unexpected and sudden fabric breaks are not easily monitored or predicted. From prior art, it is known to use different reinforcement elements to enhance the durability of different papermachine fabrics. Mostly, these reinforcement elements are made of high-strength materials such as aramid or polyether ether ketone (PEEK), and organised into the fabric as a separate or extra layer either to protect the inner layers of the fabric from disintegration by heat and chemicals, or as yarns or fibres incorporated into an existing fabric layer or structure to give the structure more strength. US patent 6447648 B1 discloses a papermachine fabric, a press blanket with a woven base structure which is coated or impregnated with a polyurethane (PU) resin that includes short fibres aligned in the cross-machine direction. The fibres provide structural reinforcement in the PU to prevent it from collapsing from the pressure applied to the fabric in an extended nip press. The fibres can be for example carbon fibre, aramid (Kevlar) or ultra-high molecular weight polyethylene.

US patent 4229254 A discloses a press belt for a shoe press with a reinforcement structure having two plies of yarns extending in cross bias layers. The yarns of the reinforcing layers have sufficient strength and elastic modulus to resist tensions in the belt, and can be made of for example aramid.

US patent 5200260 A discloses a press felt for impulse drying with a woven base structure made of nylon monofilaments constituting top and bottom layers and a batt layer covering the top and bottom layers. The batt layer is made of PEEK or Kevlar, and its main function is to protect the base structure from heat to which the felt is subjected during pressing and impulse drying. US patent 4259394 A discloses a papermaking fabric with a base and a batt needled to one surface of the base. The base is formed with interwoven heat- infusible and heat-fusible core wrapped machine direction and cross-machine direction yarns. The infusible yarns can be aramid, fiberglass, metal etc. to provide dimensional stability to the fabric. The load-bearing reinforcement yarns have high strength and low shrinkage.

The main drawback of the solutions presented in the above-mentioned prior art is that manufacturing such fabrics is costly and complex. For example, adding separate reinforcement elements or fibres into the surface layer of a press felt does not necessarily improve the strength of the fabric as a whole. The kind of reinforcement structures disclosed in the prior art cannot be relied upon to carry the sudden impacts or sudden tensile loads to which the fabric is subjected to in break situations.

The purpose of the presented invention according to independent claim 1 and 14 is to provide a simple and trustworthy reinforced papermaking fabric. In particular, the purpose of the invention according to its preferred embodiment is to provide a papermaking fabric with a first load-carrying structure that bears the tensile load directed to the papermaking fabric in normal operation conditions, and in addition to that, a second load-carrying structure which is arranged to bear the substantial part of the tensile load directed to the papermaking fabric when the first load-carrying structure elongates over a predetermined level or altogether breaks. The tensile strength of the second load-carrying structure is higher than that of the first load-carrying structure. This way, the papermaking fabric will function normally as long as the operational conditions, i.e. the tensile load impacted on the fabric remains at a level acceptable and normal to a press section of a paper-machine. Only after the other parts of the fabric start to elongate too much or altogether break, does the second load-carrying structure start to carry the tensile load. Therefore only relatively small amounts of expensive reinforcement materials need to be used to reach an acceptable level of load-bearing capacity in the fabric as a whole.

According to a further embodiment of the invention, the second load-carrying structure is incorporated into the base structure and/or into any other layer of the papermaking fabric and the second load-carrying structure comprises second machine direction yarns. The advantage of these kind of embodiments is that the reinforcement material of the second load-carrying structure can be for example woven into a textile base structure at the same time as it is manufactured, enabling cost savings.

According to a further embodiment of the invention, the second machine direction yarns are arranged with an even or an uneven spacing into the papermaking fabric, and the second machine direction yarns can substitute at least some of the first machine direction yarns of the base structure. For example, every 7 ^th to 15 ^th first machine direction yarn can be substituted with a second machine direction yarn acting as reinforcement, or preferably, every 10 ^th yarn. This way, depending on the use or application of the fabric, only a minimal amount of expensive reinforcement material needs to be used, further reduces the manufacturing costs of the fabric while ensuring its functionality.

According to yet another embodiment of the invention at least some of the second machine direction yarns are twisted around at least some of the first machine direction yarns. This is a very elegant way to make it possible, that the second load-carrying structure has some kind of way reserve in it and so does not carry the stress in the fabric, during normal operation. Does not carry the stress does not mean in every case, that the second carry-load structure does not carry any part of the stress. But if there is a part of stress being carried of the second load-carrying structure during normal operation of the fabric, it is small against the part carried by the first carrying load structure until a predetermined level of elongation or stress is reached. Even if a fraction of the fabric normally is very rapid, it usually takes a few seconds until the fabric tears from at least one initial break point or site to the whole, that is the full width. In a preferred embodiment of the present invention, it is therefore provided that the extension of the still non load-carrying yarns of the second structure force required is increased. This is to be achieved through the provision of preferably high coefficients of friction between the yarns of the second structure and the surrounding environment. It is preferred that here friction coefficients of greater 0.59, preferably greater than 0.69, more preferably greater than 0.75 are provided but always less than 0.95. In this way the velocity of fraction can be reduced. At particularly high friction coefficients an emergency running property of several minutes can be achieved by this. At least during this period, the yarns of the second structure are stronger than those of the first structure. The aforementioned friction coefficients can be reconstructed in a so-called yarn pull-out test.

In some paper machines known in the art there are edge detection devices installed. This device navigates the tension in the fabric over the web width by tilting a roll. So a straight running of the fabric could be ensured. Now if a fabric very slowly breaks from one side to the other, the acting stresses in it distributed on the remaining part, and could lead to a malfunction that could worsen the effects of subsequent fracture. Therefore, it may be on the contrary to the previously mentioned preferred embodiment, in other cases of advantage that the friction between the yarns of the second structure and the surrounding environment is less than 0.59, preferably less than 0.45 or even more preferably less than 0.35.

To achieve another kind of damping effect, without the effect that the second load-carrying structure hinders the surrounding environment, for example the first load-carrying structure, in its natural elongations, it could also be provided that the yarns have an internal damping effect on when they are, especially suddenly, stretched, for example like a spring.

According to yet another embodiment of the invention, the second load-carrying structure can be incorporated into a non-woven layer or batt layer of the papermaking fabric, so the batt layer can protect the second load-carrying structure from the worst wear caused by heat, chemicals or pressure during the papermaking process.

According to a further embodiment of the invention, the second load-carrying structure can also be arranged into the papermaking fabric as an additional layer comprising second machine direction yarns arranged on top of a base structure, making the manufacturing of the papermaking fabric yet simpler. According to a further embodiment of the invention, the second machine direction yarns of the second load-carrying structure or layer can be arranged in a meandering or zigzag pattern. This way the second load-carrying structure is so constructed as to allow for the normal elongation during operational life of a papermaking fabric without starting to carry the tensile load unnecessarily before a break situation is actually at hand. In a preferred embodiment of the invention, the second load-carrying structure is arranged so that its overall length is greater than the standard elongation of the specific fabric in which the second load-carrying structure is arranged.

According to a further embodiment of the invention, the fabric, especially the second load-carrying structure produces a, preferable optical or chemical or electrical or chemo-electricial or electro-magnetic signal or field when the elongation or mechanical stress in the second load-carrying structure reaches a predetermined level. This can improve security in the area of the fabrics. Also it makes the installation of a user or machine side initiated security action especially easy.

According to yet another preferred embodiment of the invention, the second load-carrying structure has a longitudinal tensile strength of over 100 kN/m, more preferably over 150 kN/m, and most preferably over 200 kN/m, in order for the second load-carrying structure to withstand the sudden tensile loads or impulses directed to the papermaking fabric during a break situation.

Accoding to a further embodiment of the invention, the second load-carrying structure is made of aramid (for example Kevlar), ultra-high molecular weight polyethylene (commercial name Spectra), melt spun liquid chrystal polymer (commercial name Vectran), fibres containing carbon nanotubes, PEEK or similar high-strength material suitable for use in the corrosive environment of a paper machine. According to a preferred embodiment of the invention, the papermaking fabric is a press felt or a press belt or a similar water-removing fabric to be used in the press section of a paper machine. In everyday press section operations, a press fabric would be changed when it fails to deliver the expected dewatering performance and keep up the efficiency of the papermachine.

Advantageously is also provided that at least portions of the second structure consisting of materials which is inert means stable and unreactive with respect to the potentially used paper chemistry. In these materials, it may be in particular UHMW-PE or HPPE and with respect to their chemical and mechanical properties closely related materials. This variant of the present invention can be used with all other terms referred to in this document.

Due to a press fabric bursting during the running of a paper machine, severe damages can be caused. When a burst or otherwise damaged fabric can be kept "on the roll", on its proper placement within the press section, there will be enough time to shut down the paper machine without damages caused by an uncontrollable bursting felt. By incorporating a second load-carrying or reinforcing element into a press fabric, the fabric would withstand the tensile load caused by the burst without breaking altogether and resulting in a situation where the fabric or pieces of the fabric would get loose of its proper placement in the press section in an out-of-control manner. The fabric would stay on the paper machine, and therefore costly and potentially dangerous fabric breaks can be avoided, thus increasing the operational time of the press section and reducing the costs caused by maintenance and replacement work.

Furthermore the invention relates to a papermaking fabric comprising a spiral fabric as first load-carrying structure bearing the substantial part of the tensile load directed to the papermaking fabric; and a second load-carrying structure.

In the sense of the present invention, this fabric is ch a ra cte ri sed i n t h at the second load-carrying structure is arranged to bear the substantial part of the tensile load directed to the papermaking fabric when the first load- carrying structure elongates over a predetermined level or breaks; and that the tensile strength of the second load-carrying structure is higher than that of the first load-carrying structure.

The advantages of a spiral linked fabric with a second load-carrying structure like this are comparable to the features and advantages said already in relationship with the fabric comprising a woven structure.

It is understood that such a spiral fabric is needled preferably also with one or more layers, and in particular provided with a batt or felt layer. Preferred the second load-carrying structure is arranged than in one of the additional layers.

Because a spiral-linked fabric always starts to break at one side of the fabric, it is an effective protection when unwinding is prevented, preferably by a change of material. In particular the change of material, which means that in the context of the present invention, therefore, the change between the first and the second load-carrying structure is oriented toward the lateral edge of the fabric. For this, the material forming the spiral also may be partially covered. In another embodiment the second load-carrying structure is integrated in the pintles between the spirals.

Furthermore the invention relates to a system of a paper machine and a papermaking fabric running between at least two rolls of the papermaking machine, wherein the papermaking machine has at least one sensor to observe at least one property of the papermaking fabric.

In the sense of the present invention, this system is characterised in that the papermaking fabric is a fabric according to any of the claims 1 to 14 and the sensor monitors a mechanical stress or an elongation in the first and/or the second load-carrying structure or a, preferable optical, signal or chemical or electrical or chemo-electricial or electro-magnetic, signal or field of the second load-carrying structure.

In this case it is very easy to slow down the running speed of the papermaking machine before an accident could happen. So any damage can be prevented. Machine side sensors could be anywhere. Most preferable the signals of the tension roll are coupled with an automatic system to reduce the running speed or stop the machine, when a predetermined tension, stress or elongation is reached.

A detailed description of the invention is given in the following, with reference to figures 1 -5.

Figure 1 presents a machine direction cross-cut of a papermaking fabric according to the invention

Figure 2 presents another embodiment of the papermaking fabric according to the invention, in a machine direction cross-cut Figure 3 presents a third embodiment of the papermaking fabric according to the invention, in a machine direction cross-cut

Figures 4a, b present a detail of the second load carrying structure arranged into the base structure of the papermaking fabric according to the invention

Figures 5a, b present another detail of the second load-carrying structure arranged in or on top of the base structure in a special pattern Figure 6 presents another embodiment of the papermaking fabric according to the invention, with a spiral link base structure Figure 7 presents a system of a paper machine and a papermaking fabric running between at least two rolls of the papermaking machine The following reference numbers are used in connection with the figures:

1 papermaking fabric

2 base structure

21 first machine direction yarns

22 cross-machine direction yarns

3 first load-carrying structure

4 second load-carrying structure

41 , 42 second machine direction yarns

5 second load-carrying structure layer as an additional layer

6 non-woven layer(s)

7 surface layer(s)

8 pintle

9 system of a paper machine and a papermaking fabric

10 roll, tension roll

1 1 sensor

12 roll

Figure 1 shows an embodiment of the papermaking fabric (1 ) according to the invention. The fabric comprises a base structure (2) having first machine direction yarns (21 ). The base structure (2) may also include cross-machine direction yarns (22), that together with the first machine direction yarns (21 ) form a woven textile, for example in a linen/plain weave, or any other suitable weave pattern. In this case, the base structure (2) acts as a first load-carrying structure (3). Into the first load-carrying structure (3), a second load-carrying structure (4) is arranged in order to have a papermaking fabric (1 ) capable of withstanding higher tensile loads or sudden impacts than what the papermaking fabric (1 ) would withstand in normal operational conditions, thus enabling the fabric (1 ) to stay on its proper place in the press section in the case of a burst situation, instead of behaving in an out-of-control and dangerous manner, as a standard press fabric without any reinforcing elements would.

The papermaking fabric (1 ) can further include any number of other functional or structural layers, such as non-woven layers (6) or surface layers (7). The non-woven layer (6) can be for example a batt, foam or coating layer. The surface layer (7) can be for example coating or a combination of coating and non-woven layer.

In the embodiment presented in figure 1 , the second load-carrying structure (4) is in fact incorporated into the base structure (2) in such a manner as to replace or substitute a number of first machine direction yarns (21 ). As can be seen from figures 4a and 4b, the first machine direction yarns (21 ) can be substituted by second machine direction yarns (41 ) making up the second load-carrying structure (4) in any suitable manner, for example by replacing every 7 ^th first machine direction yarn of the base structure weave pattern, or replacing a pair of adjacent first machine direction yarns (21 ) with a pair of second machine direction yarns (42). In certain cases, it can be preferable to substitute also some of the cross-directional yarns (22) of the base structure (2) with similar second cross-directional yarns.

In further preferred embodiments, the second load-carrying structure (4) can be incorporated into the papermaking fabric (1 ) as a separate, additional layer (5), as shown in figures 2 and 3. This additional layer (5) can for example be arranged on top of the first load-carrying structure (3) or the base structure (2), as shown in figure 2, or it can be arranged between two non-woven layers (6), as shown in figure 3. Also other positions within the papermaking fabric layer structure are naturally possible. The second load-carrying layer (4) or additional layer (5) can be added on the base structure (2) for example after heat-setting the base structure, before a possible non-woven layer (6) is needled in place. Figures 5a and 5b show how the second machine direction yarns (41 , 42) of the second load-carrying structure (4) can be arranged to account for the normal wear elongation of a papermaking fabric (1 ). The second machine direction yarns (41 , 42) can be arranged to meander in z-direction of the papermaking fabric (1 ) so that the overall length of the second machine direction yarns (41 , 42) becomes somewhat greater that that of the rest of the papermaking fabric (1 ). This kind of pattern is especially advantageous when the second load- carrying structure (4) or the second machine direction yarns (41 , 42) of the second load-carrying structure (4) are incorporated into the base structure (2) of the papermaking fabric (1 ).

In another preferred embodiment, the second machine direction yarns (41 , 42) are arranged into a zig-zag pattern as shown in figure 5b. While the essential direction of the second machine direction yarns is still in machine direction, the yarns are arranged to make small bends, curves or angles on the longitudinal surface of the layer on which they are arranged. Also this way, the length of the second machine direction yarns (41 , 42) and the second load-carrying structure (4) becomes greater than the length of the overall papermaking fabric (1 ), thus enabling the fabric (1 ) to function and respond to normal elongation during use without having the second load-carrying structure (4) engaging in load-carrying before the papermaking fabric (1 ) is subjected to break-inducing tensile loads or impulses. In an advantageous embodiment, the second load-carrying structure is arranged so that its overall length is greater than the standard elongation of the specific fabric in which the second load-carrying structure is arranged.

In order for the second load-carrying structure (4) to function as desired, it should be designed to have a longitudinal tensile strength of over 100 kN/m, more preferably over 150 kN/m, and most preferably over 200 kN/m, depending on the design and functionality of the press fabric in question.

Figure 6 shows another embodiment of the papermaking fabric (1 ) according to the invention. The fabric comprises a spiral-linked base structure (2). In this case, the base structure (2) acts as a first load-carrying structure (3). Into the first load-carrying structure (3), a second load-carrying structure (4) is arranged in order to have a papermaking fabric (1 ) capable of withstanding higher tensile loads or sudden impacts than what the papermaking fabric (1 ) would withstand in normal operational conditions, thus enabling the fabric (1 ) to stay on its proper place in the press section in the case of a burst situation, instead of behaving in an out-of-control and dangerous manner, as a standard press fabric without any reinforcing elements would. The papermaking fabric (1 ) can - in accordance with the embodiments of woven fabrics - further include any number of other functional or structural layers, such as non-woven layers (6) or surface layers. The non-woven layer (6) can be for example a batt, foam or coating layer. The in this figure not shown surface layer can be for example coating or a combination of coating and non-woven layer.

In the embodiment presented in figure 6, the second load-carrying structure (4) is in fact integrated in the yarns of the first load-carrying structure. In deed it could be the same yarn, as shown in Figure 6a, because a spiral-linked fabric always starts to break at one side of the fabric. So it is an effective protection when unwinding is prevented by a change of material. In particular the change of material, which means that in the context of the present invention, therefore, the change between the first and the second load-carrying structure is oriented toward the lateral edge of the fabric. For this, the material forming the spiral also may be partially covered.

Preferred the second load-carrying structure is arranged similar to the embodiments described with the figures 2, 3 or 5b.

Suitable materials for the second load-carrying structure (4) are heat-resistant and high-strength synthetic aramid fibres, for example Kevlar or Nomex; ultrahigh molecular weight polyethylene (UHMWPE), for example Spectra; melt spun liquid crystal polymer known commercially as Vectran; fibres containing carbon nanotubes; or polyether ether ketone (PEEK). Any other, similarly high- strength and resistant material can also be used to as the material for the second load-carrying structure (4). To avoid damages in consequence of a chemical attach it is preferred to choose materials like UHMW-PE or HPPE.

A papermaking fabric (1 ) as presented above can be used in any suitable position in a paper machine. Preferably the fabric (1 ) is used as a press felt, press belt, tension belt or a transfer belt in connection with the press section of a paper machine.

Figure 7 presents a system 9 of a paper machine and a papermaking fabric 1 running between at least two rolls 10, 12 of the papermaking machine, wherein the papermaking machine has at least one sensor 1 1 to observe at least one property of the papermaking fabric 1 . The papermaking fabric 1 is a fabric according to any of the claims 1 to 14 and the sensor 1 1 monitors a mechanical stress or an elongation in the first and/or the second load-carrying structure or a preferable optical, signal or chemical or electrical or chemo-electrical or electromagnetic, signal or field of the second load-carrying structure. One sensor 1 1 may be integrated in the roll 10. The roll 10 then is a so called tension roll, which is able to measure the tension in the web. Preferable the tension roll 10 is also moveable to expand the fabric and may also be angulary adjustable in its orientation.