Tissue paper machine comprising an extended nip press forming a transfer nip with variable linear load

Abstract

The present invention relates to a tissue paper machine (100) comprising - a forming section (101), - a drying section (102) comprising a Yankee dryer (20) and a non-dewatering transfer nip formed (TN) between the Yankee dryer (20) and a press assembly (30) for transferring the paper web (W) from the structured fabric (10) to the Yankee dryer (20), - a structured fabric (10), wherein the transfer nip (TN) is an extended press nip, the press assembly (30) comprising a press shoe (31) and an actuator (60) configured to operate the press shoe (31) to form the transfer nip (TN), and wherein the actuator (60) is configured to generate a desired linear load in the transfer nip (TN) by operating the press shoe (31) to extend into the transfer nip (TN) with a desired pressure and to change the linear load during operation of the tissue paper machine (100).

Description

[0001] TISSUE PAPER MACHINE COMPRISING AN EXTENDED NIP PRESS FORMING A TRANSFER NIP WITH VARIABLE LINEAR LOAD

[0002] TECHNICAL FIELD

[0003] The present invention relates to a tissue paper machine having a drying section with a transfer nip for transferring a paper web from a structured fabric to a Yankee dryer.

[0004] BACKGROUND

[0005] When manufacturing tissue paper, a paper web is formed in a forming section and is then then dried in a drying section where the paper web is transferred from a structured fabric to a final drying step on a Yankee dryer. The transfer to the Yankee dryer takes place by a transfer nip traditionally formed between the Yankee dryer and a transfer roll.

[0006] To achieve an efficient transfer from the fabric to the Yankee dryer, the paper web should ideally transfer in a transfer point that acts like a line across the machine where the entire sheet width is transferred instantly. To achieve this, a small transfer roll must be used and it is the diameter of the transfer roll and the Yankee dryer in combination with the transfer roll cover thickness, cover hardness and potential grooves in the cover that sets a nip profile for the nip at a certain linear load. For the ideal transfer, the transfer roll is pressed against the Yankee dryer at a very high pressure that causes deformation of the cover on the transfer roll or even of the transfer roll itself. Also, any imperfections such as thickness variations in the structured fabric, wear to the transfer roll or coating build-up on the Yankee dryer changes the nip profile so that the transfer is rendered less efficient. To compensate for this, the amount of coating applied to the Yankee is often increased to ensure that the paper web is transferred even if the nip profile varies. Additional coating is costly, however, and there is also a risk of damage to the paper web if the nip profile is not as intended. Another drawback associated with such transfer nips is that the set nip profile cannot be altered to accommodate change in paper grade or moisture content of the paper web. There is therefore a need for improvements to the transfer nip from the structured fabric to the Yankee dryer in tissue paper machines.

[0007] SUMMARY

[0008] The object of the present invention is to eliminate or at least to minimize the problems discussed above. This is achieved by a tissue paper machine according to the appended independent claims.

[0009] The tissue paper machine of the present invention comprises a forming section for forming a paper web, a drying section for drying the paper web, and a structured fabric for transporting the paper web. Also, the drying section comprises a Yankee dryer and a non-dewatering transfer nip formed between the Yankee dryer and a press assembly for transferring the paper web from the structured fabric to the Yankee dryer, wherein the transfer nip is an extended press nip and the press assembly comprises a press shoe and an actuator configured to operate the press shoe for extending a working surface on a first side of the press shoe towards the Yankee dryer to form the transfer nip. Also, the actuator is configured to cause a desired linear load in the transfer nip by operating the press shoe with a desired pressure. Furthermore, the actuator is configured to change the linear load in the transfer nip during operation of the tissue paper machine by changing the pressure with which the press shoe is extended into the transfer nip.

[0010] By using an extended press nip as the transfer nip, the nip profile can be set as desired to achieve an efficient transfer from the structured fabric to the Yankee dryer without the linear load in the transfer nip causing damage or excessive wear as is typically the case when using a prior art transfer roll. Also, due to the interaction of the actuator with the press shoe, the pressure and thereby also the linear load in the nip can be changed as desired, such as when switching the tissue paper machine to manufacturing tissue paper of a different paper grade or when parameters such as moisture content of the paper web at the transfer nip changes. Thereby, an efficient transfer can be achieved without requiring adding excessive coating to the Yankee dryer or using excessive pressure from a transfer roll. Also, by providing the extended nip press the nip itself can be shorter than with conventional transfer rolls, which also improves the transfer. Furthermore, due to the actuator operating the press shoe with the desired pressure to cause the desired linear load in the transfer nip, control of the nip profile is greatly enhanced compared to prior art solutions where the transfer nip is achieved by a transfer roll. This is highly advantageous in enabling an ideal transfer of the paper web to the Yankee dryer.

[0011] In some embodiments, the press shoe comprises a metal and the actuator is configured to operate the press shoe by displacing the press shoe towards the Yankee dryer such that the working surface is pressed into the nip. This enables precise control over the nip profile since a metal press shoe deforms only slightly when subjected to high pressure. Also, wear on the press shoe can be kept very low which enables a long lifetime.

[0012] In other embodiments, the press shoe comprises a polymer and also comprises at least one internal pressure chamber, and the actuator is further configured to operate the press shoe by supplying a pressurized fluid into said at least one internal pressure chamber so that the press shoe is expanded to extend the working surface towards the Yankee dryer to form the transfer nip. Using a flexible polymer press shoe also enables a precise control over the nip profile when taking deformation of the working surface into account, while at the same time extending the lifetime of components of the paper machine subjected to pressure by the press shoe in the transfer nip, such as the structured fabric itself.

[0013] Suitably, the tissue paper machine comprises a control unit and at least one input device, wherein the control unit is configured to receive input from the at least one input device, to determine a desired change of pressure and / or linear load in the transfer nip and to operate the actuator to apply this change. Thereby, the linear load in the transfer nip can be changed based on input received in the control unit and this enables a dynamic adjustment of the linear load during operation. At least one input device suitably comprises a sensor or detector for determining at least one wear parameter of the tissue paper machine. By basing the change of linear load on wear parameters, the lifetime of components of the tissue paper machine can be extended, thereby decreasing the need of repair or replacement.

[0014] Also, at least one input device suitably comprises a sensor or detector for determining at least one runnability parameter of the tissue paper machine. By basing the change of linear load on runnability parameters, operation of the tissue paper machine is improved and the risk of faults such as web breakage is reduced.

[0015] Also, at least one input device suitably comprises a sensor or detector for determining at least one property of finished tissue paper produced by the tissue paper machine. Thereby, quality of the finished tissue paper can be assessed, and the operation of the extended nip press be adapted to increase or maintain the quality.

[0016] The at least one input device suitably comprises a user interface for receiving a manual input with at least one wear parameter, runnability parameter or property of finished tissue paper. Thereby, manual input may also be added to allow for changing the linear load also based on information that is difficult to assess using sensors or detectors in the tissue paper machine itself.

[0017] Many additional benefits and advantages of the present invention will be readily understood by the skilled person in view of the detailed description below.

[0018] DRAWINGS

[0019] The invention will now be described in more detail with reference to the appended drawings, wherein

[0020] The invention will now be described in more detail with reference to the appended drawings, wherein Fig. 1 discloses schematically a paper machine according to the invention;

[0021] Fig. 2 discloses a schematic cross-sectional view from the side of an extended nip press forming a transfer nip with a Yankee dryer according to a the invention;

[0022] Fig. 3 discloses a schematic cross-sectional view from the side of the extended nip press and the Yankee dryer of Fig. 2 in a rest position where the transfer nip is not active;

[0023] Fig. 4a discloses a schematic cross-sectional view from the side of the extended nip press and the Yankee dryer in a rest position according to a first embodiment of the invention;

[0024] Fig. 4b discloses a schematic cross-sectional view from the side of the extended nip press and the Yankee dryer in an active position according to a first embodiment of the invention;

[0025] Fig. 5a discloses a schematic cross-sectional view from the side of the extended nip press and the Yankee dryer in a rest position according to a second embodiment of the invention;

[0026] Fig. 5b discloses a schematic cross-sectional view from the side of the extended nip press and the Yankee dryer in an active position according to a second embodiment of the invention;

[0027] Fig. 6a discloses a schematic cross-sectional view from the side of the extended nip press and the Yankee dryer in a rest position according to a third embodiment of the invention;

[0028] Fig. 6b discloses a schematic cross-sectional view from the side of the extended nip press and the Yankee dryer in an active position according to a third embodiment of the invention;

[0029] Fig. 7 discloses an experiment comparing the transfer nip of the invention with a prior art transfer nip; and Fig. 8 discloses schematically the actuator of the extended nip press together with the control unit and input devices.

[0030] All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the respective embodiments, whereas other parts may be omitted or merely suggested. Any reference number appearing in multiple drawings refers to the same object or feature throughout the drawings, unless otherwise indicated.

[0031] DETAILED DESCRIPTION

[0032] When referring to a “paper machine” or a “tissue paper machine” herein, this is to be understood as a machine suitable for producing paper from a pulp.

[0033] It is to be noted that all dimensions given herein are to be understood as being within manufacturing tolerances or at least not differing more than 10 %. Also, when it is stated that a feature is substantially constant or substantially uniform, this is also to be understood as being constant or uniform within manufacturing tolerances or at least not differing more than 10 %.A paper machine 100 according to the invention will now be described briefly with reference to Fig. 1 , followed by a more detailed description of a transfer nip TN of the paper machine 100 with reference to Fig. 2 onwards and of controlling an actuator 60 to change linear load in the transfer nip TN during operation. Since the present invention concerns the transfer nip TN in a drying section 102, other sections and components of the paper machine 100 will be described only in passing.

[0034] The term “nip profile” as used herein is to be understood as a pressure curve in a machine direction in the transfer nip TN in the paper machine 100.

[0035] Fig. 1 discloses schematically a paper machine 100 comprising a forming section 101, the drying section 102 and a reel section 103. In the forming section 101, stock is injected into a forming nip to form a paper web W as is already well known in the art, and the paper web W is transported on a fabric in a machine direction MD to the drying section 102 where moisture is removed to create a finished paper P. The paper P is then transferred to the reel section 103 where the paper P is reeled onto a roll before being removed from the paper machine 100 as a finished tissue paper product. The machine direction MD is defined as a direction from the forming section 101 to the reel section 103, i.e. a main direction of travel of the paper web W.

[0036] As long as the paper web W is newly formed and wet, it must be transported on a fabric that serves to support and protect the paper web W. After forming, the paper web W may in some embodiments travel also through a press section 104 before reaching the drying section 102. The drying section 102 comprises at least one drying roll in the form of a Yankee dryer 20 (see Fig. 2 onwards), but there may also be at least one other drying roll such as a through-air diyer, TAD. The design and operation of the Yankee dryer 20, as well as a TAD or any other kind of dryer is already well known in the art and will not be described further herein. Furthermore, moisture may be removed through at least one dewatering nip in the drying section 102.

[0037] While transported in the drying section 102, the paper web W is supported by a structured fabric 10 (see Fig. 2 onwards) but there may also be at least one other fabric on which the paper web W is transported between the forming section 101 and the drying section 102, such as e.g. a felt. When the paper web W is transferred from one fabric to another, this may take place in a transfer nip where pressure is applied to cause the paper web W to release one fabric and instead adhere to the next.

[0038] In the drying section 102, the paper web W is transferred to the Yankee dryer 20 from the structured fabric 10 in the transfer nip TN as shown in Fig. 2. The web W is typically doctored from the Yankee dryer 20 by a doctor blade and is passed in the form of the finished paper P to a reel-up.

[0039] In contrast to transfer nips known from the prior art, the transfer nip TN of the present invention is formed by the Yankee dryer 20 and a press assembly 30 that is in the form of an extended nip press 30. The extended nip press 30 thus acts as a counter member for the Yankee dryer 20 to form the nip.

[0040] In the extended nip press 30, an extended press nip is formed by extending a press body 31 towards the Yankee dryer 20 to form the transfer nip TN. In the prior art, extended nips are known mainly as dewatering nips, but the present inventors have realized that there are numerous advantages to using an extended nip press to transfer the paper web W without dewatering it. In particular, using the extended nip press 30 enables changing the pressure and thereby the linear load in the nip during operation, thereby giving operators of the paper machine 100 the possibility of designing the nip depending on paper grade, coating on the Yankee dryer, moisture content at the transfer nip, and other factors. It also enables a shorter nip so that transfer to the Yankee dryer is rendered swift and accurate.

[0041] When the term “extended nip press” is used herein, this is to be understood as an arrangement where the press body 31 is extended into the nip. In contrast, a prior art transfer nip instead often comprises a transfer roll.

[0042] The press arrangement 30 of Fig. 2 comprises a support 34 in which the press shoe 31 is arranged and further comprises at least one actuator 32 for extending the press shoe 31 into the nip. If the press shoe 31 comprises a flexible material, it suitably comprises at least one internal pressure chamber 32 (shown in dashed lines inside the press shoe 31) with the actuator 60 (see Fig. 4 onwards) that supplies a pressurized fluid to cause the press shoe 31 to stretch and extend into the nip. If the press shoe 31 comprises a non-flexible material such as metal, the actuator 60 is suitably configured to extend the press shoe 31 as a whole into the nip by operating an external pressure chamber, e.g. in the form of a hose, or alternatively the actuator 60 is a hydraulic or mechanic actuator that acts on the press shoe 31 directly.

[0043] Fig. 2 also shows a flexible jacket 70 with an interior side 71 against which the press shoe 31 of the extended nip press 30 presses and an outside 72 that contacts the structured fabric 10 on which the paper web W is held. The extended nip press 30 also suitably comprises a supply of lubricating fluid (e.g. oil) that is supplied to a first side 37 of the press shoe 31 to decrease friction between the press shoe 31 and the interior side 71 of the flexible jacket The flexible jacket 70 typically comprises polyurethane and is shaped as a tube that extends in a cross-machine direction, said cross-machine direction being a direction that is perpendicular to the machine direction MD. Thus, the flexible jacket 70 has an axial direction that coincides with the cross-machine direction and at its axial ends the flexible jacket 70 is normally connected to end walls that are rotatably arranged so that the flexible jacket 70 is able to rotate. Suitably, a source of pressurized air may be connected so that an enclosed space formed by the flexible jacket 70 and the end walls may be filled with pressurized air. The flexible jacket 70 and the extended nip press 30 may together be seen as an extended nip roll 80. The press shoe 31 is elongated and extends along the interior surface 71 of the flexible jacket 70 in a direction transversal to a direction of rotation of the flexible jacket 70 in order to be able to press against an entire width of the paper web W in the transfer nip TN. For this purpose, the press shoe 31 may have a length that is equal to or larger than an intended width of the paper web W, but in some embodiments the press shoe 31 may instead have a length that is shorter than the intended width of the paper web W.

[0044] The extended nip press 30 of Fig. 2 is shown in an active state, i.e. when the transfer nip TN is formed by the press shoe 31 extending towards the Yankee dryer 20 so that the structured fabric 10 carrying the paper web W is pressed against the Yankee dryer 20 and the paper web W is transferred from one to the other.

[0045] Fig. 3 shows the same components as Fig. 2 except for the flexible jacket 70, the structured fabric 10 and the paper web W that have been removed to show the extended nip press 30 more clearly. Thus, Fig. 3 shows a rest position of the extended nip press 30 where the transfer nip TN is not active.

[0046] In Fig. 3, a surface 21 of the Yankee dryer 20 is shown, and on the first side 37 of the press shoe 31 a working surface 36 is disclosed. This working surface 36 is a part of the first side 37 that is active in the transfer nip TN, i.e. that is extended into the transfer nip TN and transfers a force to the paper web W when the transfer nip TN is active. The press shoe 31 in some embodiments also comprises an entry surface 38 and / or exit surface 35 that are not active in the transfer nip TN.

[0047] Various embodiments of the invention will now be described with reference to Fig. 4 onwards. To avoid repetition, these embodiments will be described mainly in those features that are particular to each embodiment or that differ from each other. Therefore, it is to be understood that all features not specifically stated as differing from one embodiment to another are to be seen as similar or identical. Also, features from one embodiment may freely be incorporated into another embodiment where technically feasible.

[0048] Fig. 4a-4b disclose a first embodiment in which the press shoe 31 comprises a polymer and has at least one internal pressure chamber 50’, 50”. The press shoe 31 may be made from only one material or may be formed from a plurality of materials of which at least one is a polymer. The actuator 60 is configured to operate the press shoe 31 by supplying pressurized fluid, e.g. hydraulic oil, into the internal pressure chambers 50’, 50” from at least one source 51 of pressurized fluid. In Fig. 4a-4b, the extended nip press 30 is shown with two separate sources 51 of pressurized fluid but it is to be noted that a single source 51 could alternatively be used. The internal pressure chambers 50’, 50” can be pressurized at the same pressure level or at different pressure levels, as desired.

[0049] Fig. 4a shows the first embodiment in the rest position where the transfer nip TN is not active. In this state, the internal pressure chambers 50’, 50” are not pressurized and the press shoe 31 is in its neutral state.

[0050] Fig. 4b shows the first embodiment in an active position where the transfer nip TN is formed by the actuator 60 operating the internal pressure chambers 50’, 50” to expand the press shoe 31 and thereby extend the first side 37 with the working surface 36 towards the Yankee dryer 20 to form the nip.

[0051] Fig. 5a-5b show a second embodiment where the press shoe 31 comprises a metal and where the actuator 60 is in the form of a displacement device 33 such as a mechanical or hydraulic actuator that is configured to operate the press shoe 31 by moving it towards the Yankee dryer 20 to extend it into the transfer nip TN.

[0052] Fig. 5a shows the rest position and Fig. 5b shows the active position where the transfer nip TN is formed between the press shoe 31 and the Yankee dryer 20. In Fig. 5b, the actuator 60 is shown as using an arm 33’ for moving the press shoe 31 , but it is to be noted that the displacement of the press shoe 31 can be achieved also in other ways, such as by the displacement device 33 expanding or a plurality of arms or supports contacting the press shoe 31 to move it into the nip. The press shoe 31 may be made from only one metal or metal alloy (such as e.g. steel), but alternatively the press shoe 31 may be made from any combination of materials where at least one is a metal. In some embodiments, the press shoe 31 may also comprise a coating or a top section made from a softer material such as a polymer.

[0053] Fig. 6a-6b disclose a third embodiment where the press shoe 31 comprises a metal and where the actuator 60 is configured to operate the press shoe 31 by supplying pressurized fluid to an external pressure chamber 40 (such as e.g. a hose). Also shown is a source 41 of pressurized fluid, and it is to be noted that this source 41 may be similar or identical to the sources 51 used in the first embodiment.

[0054] As for the previous embodiments, Fig. 6a shows the rest position and Fig. 6b shows the active position where the external pressure chamber 40 is expanded to move the press shoe 31 into the transfer nip TN.

[0055] For all the embodiments described herein, the pressure of the press shoe 31 into the transfer nip TN and thereby the resulting linear load in the nip is controlled by operating the actuator 60 as desired. This means that the linear load in the transfer nip TN can be controlled depending on properties of the tissue paper machine 100 (such as machine speed, heat expansion of the Yankee dryer 20 during use) or properties of the paper web W (such as paper grade, moisture content). The nip profile and the linear load of the transfer nip TN are changed during operation, e.g. by an operator increasing or decreasing the pressure at which the press shoe 31 is extended into the transfer nip TN. It is a particular advantage of the present invention that the nip profile and the linear load in the transfer nip TN can be changed, since this results in a significant improvement in the transfer of the paper web W to the Yankee dryer 20. By improving the transfer as such, the amount of coating used on the Yankee dryer 20 can also be decreased. It is particularly advantageous that the nip profile and thereby the linear load in the transfer nip TN can be changed during operation, since this enables switching from one tissue paper product to another without having to interrupt operation of the tissue paper machine 100.

[0056] Fig. 8 discloses a control unit 90 that is operatively connected to the actuator 60 and configured to control the actuator 60 to change the pressure with which the actuator 60 causes the press shoe 31 to extend into the nip, thereby also changing the linear load in the nip. The control unit 90 is also operatively connected to at least one input device 91, 92, 93 through which the control unit 90 is able to receive input regarding the tissue paper machine 100 or regarding the paper web and / or finished tissue paper. Even though the control unit 90 is shown connected to three input devices 91, 92, 93 in Fig. 8 it is to be understood that any number of input devices 91, 92, 93 can be used. It is also to be noted that the control unit 90 and input devices 91, 92, 93 can be used with any embodiment of the extended nip press of the tissue paper machine 100 shown herein.

[0057] The control unit 90 comprises processing circuitry that is configured to receive input (in the form of input signals from input devices 91, 92, 93 comprising sensors or detector or comprising user interface for receiving manual input), determine a desired change of linear load in the transfer nip and / or a desired pressure in the nip to achieve a desired change of linear load based on at least one criterion (that may be predetermined or that may be updated based on input received in the user interface), and to control the actuator 60 to apply this change (by sending a control signal to the actuator 60 that causes the actuator 60 to change the pressure with which it presses the press shoe 31 into the extended nip). Changing the linear load in the nip is advantageous for three main reasons, namely, to decrease wear of components of the tissue paper machine, to improve runnability and to achieve desired properties of the finished tissue paper.

[0058] The input devices 91, 92, 93 may be sensors or detectors that measure or detect a parameter of the tissue paper machine 100 or of the web in any part of the tissue paper machine 100 or the finished tissue paper. Alternatively, at least one input device 91, 92, 93 may be a user interface configured to receive manual input from an operator.

[0059] In some embodiments, one input device 91 is configured to measure or detect at least one wear parameter of the tissue paper machine 100. The wear parameter may be a parameter of an actual state of a component of the tissue paper machine 100 such as a wear of the structured fabric 10 determined by measuring surface roughness, elasticity or water absorption. Alternatively, the wear parameter may be a parameter of an expected state of the component based on operational parameters of the tissue paper machine 100 such as duration of high pressure of the press shoe 31 against the structured fabric 10 of current lifetime of production of tissue paper with various properties. In response to the measured, detected or received wear parameter, the control unit 90 is able to control the actuator 60 to e.g. decrease the pressure in the transfer nip to extend the lifetime of the structured fabric 10. Other components of the tissue paper machine 100 that are present in the transfer nip may also be monitored in this way and pressure in the transfer nip may be adapted to better suit such components and prolong their lifetime while at the same time producing tissue paper having the desired properties for each paper grade.

[0060] In some embodiments, one input device 92 is configured to measure or detect at least one runnability parameter of the tissue paper machine 100 such as adhesion of the web to the Yankee dryer 20 (e.g. determined by a sensor arranged in connection with the Yankee dryer 20 or in connection with the finished paper where insufficient adhesion can be detected by observing surface properties or edge properties of the produced tissue paper). Other runnability parameters include web breakage indicators such as portions of the web moving in unexpected ways (e.g. twitching or folding) or the web being absent from the tissue paper machine 100. This is suitably determined by an optical sensor that detects properties of the web before or after the transfer nip. In the event of complete or partial breakage, the web generally adheres better to the Yankee dryer 20 with a higher linear load in the transfer nip, but in some cases a lower linear load can alternatively improve adhesion to the Yankee dryer 20 to decrease the risk of breakage. Other runnability properties such as an amount of coating applied to the Yankee dryer 20 may also be measured or detected by the input device 92.

[0061] In some embodiments, one input device 93 is configured to measure or detect at least one property of the finished tissue paper. When a tissue paper having a high bulk is desired, a lower linear load in the transfer nip is preferably applied to increase the bulk. Conversely, when a tissue paper having increased hardness is desired, a higher linear load is preferably applied. The property of the finished tissue paper may be determined by measuring or detecting properties of a roll of finished paper, but alternatively the property may be determined by measuring the web during drying on the Yankee dryer 20 or in the reel section 103 of the tissue paper machine 100.

[0062] Preferably, sensor data is repeatedly received by the control unit 90 to evaluate the effect of a previous change of operation of the actuator 60 so that a future operational change can be determined based also on results of the previous change.

[0063] Furthermore, in some embodiments the various kinds of input devices and the input they provide as described above may also be combined, so that the control unit 90 is configured to receive any number of parameters and to determine a change of operation of the actuator 60 in response to at least these parameters.

[0064] When the tissue paper machine 100 is operating, the control unit 100 is configured to receive input from the input devices 91, 92, 93 at given times or continuously and to determine the change in linear load and / or pressure into the nip that is suitable to improve runnability, adjust properties of the finished tissue paper or decrease wear of the tissue paper machine 100. The control unit 90 then operates the actuator 60 to apply this change.

[0065] Fig. 7 discloses an experiment where a prior art transfer nip formed between a Yankee dryer and a transfer roll is compared to the transfer nip TN of the present invention with the extended nip press 30. The horizontal axis shows the length of the nip (in mm), with the vertical axis showing the nip pressure (in MPa).

[0066] The experiments shows that the present invention achieves a shorter nip length than the prior art transfer roll and that a pressure peak is formed with a significantly larger pressure than is achieved by the transfer roll. Thus, the curve with linear load of 25 kN / m of the extended nip press 30 according to the invention has a pressure peak that exceeds any pressure achieved by the prior art transfer roll with linear load of 40 kN / m. Similarly, for the curve with linear load of 60 kN / m according to the invention the pressure peak is significantly higher than any pressure achieved with the transfer roll of the prior art with linear load of 90 kN / m. This pressure peak ensures that the transfer from the structured fabric to the Yankee dryer 20 is closer to the ideal transfer in a single line across the nip when using the present invention than is possible through the prior art.

[0067] It is to be noted that features from the various embodiments described herein may freely be combined, unless it is explicitly stated that such a combination would be unsuitable.

Claims

CLAIMS1. Tissue paper machine (100) comprising- a forming section (101) for forming a paper web,- a drying section (102) for drying the paper web,- a structured fabric (10) for transporting the paper web, wherein the drying section (102) comprises a Yankee dryer (20) and a non-dewatering transfer nip formed (TN) between the Yankee dryer (20) and a press assembly (30) for transferring the paper web (W) from the structured fabric (10) to the Yankee dryer (20), wherein the transfer nip (TN) is an extended press nip, the press assembly (30) comprising a press shoe (31) and an actuator (60) configured to operate the press shoe (31) for extending a working surface (36) on a first side (37) of the press shoe (31) towards the Yankee dryer (20) to form the transfer nip (TN), wherein the actuator (60) is configured to generate a desired linear load in the transfer nip (TN) by operating the press shoe (31) to extend into the transfer nip (TN) with a desired pressure, and wherein the actuator (60) is configured to change the linear load in the transfer nip (TN) during operation of the tissue paper machine (100) by increasing or decreasing the pressure with which the press shoe (31) is extended into the transfer nip (TN) .

2. Tissue paper machine according to claim 1, wherein the press shoe (31) comprises a metal and wherein the actuator (60) is configured to operate the press shoe (31) by displacing the press shoe (31) towards the Yankee dryer (20) such that the working surface (36) is pressed into the transfer nip (TN) .

3. Tissue paper machine according to claim 1, wherein the press shoe(31) comprises a polymer and also comprises at least one internalpressure chamber (50’, 50”, and wherein the actuator (60) is configured to operate the press shoe (31) by supplying a pressurized fluid into said at least one internal pressure chamber (50’, 50”) so that the press shoe (31) is expanded to extend the working surface (36) towards the Yankee dryer (20) to form the transfer nip (TN).

4. Tissue paper machine according to any previous claim, further comprising a control unit (90) and at least one input device (91, 92, 93), wherein the control unit (90) is configured to receive input from the at least one input device (91, 92, 93), to determine a desired change of pressure and / or linear load in the transfer nip (TN) and to operate the actuator (60) to apply this change.

5. Tissue paper machine according to claim 4, wherein the at least one input device (91, 92, 93) comprises a sensor or detector for determining at least one wear parameter of the tissue paper machine.

6. Tissue paper machine according to claim 4 or 5, wherein the at least one input device (91, 92, 93) comprises a sensor or detector for determining at least one runnability parameter of the tissue paper machine.

7. Tissue paper machine according to any of claims 4-6, wherein the at least one input device (91, 92, 93) comprises a sensor or detector for determining at least one property of finished tissue paper produced by the tissue paper machine (100).

8. Tissue paper machine according to any of claims 4-7, wherein the at least one input device (91, 92, 93) comprises a user interface for receiving a manual input with at least one wear parameter, runnability parameter or property of finished tissue paper.

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