Arrangement in connection with a fiber web production line

Abstract

 The present invention relates to an arrangement in connection with a fiber web production line, in particular in connection with a finishing device of a fiber web production line, which arrangement comprises at least one roll (11) and a belt (10) which belt is arranged to pass on the surface of the at least one roll. In the arrangement, the belt (10) has a thickness profile that compensates at least partly the tension variation due to deflection of the at least one roll (11).

Description

[0001] The invention relates to an arrangement in connection with a fiber web production line according to the preamble of claim 1.

[0002] As known from the prior art, fiber web such as paper and board webs are manufactured in machines which together constitute a paper/board-manufacturing line which can be hundreds of meters long. Modern fiber web machines can produce more than 450 000 tons of paper a year. The speed of the machine can exceed 2000 m/min and the width of the fiber web can be more than 11 meters.

[0003] In manufacturing lines known from the prior art fiber web making takes place as continuous process. A fiber web completing in a machine is wound with a reel-up around a reeling shaft i.e. reel spool into a machine roll (a parent roll) the diameter of which can be more than 3,5 m and the weight more than 100 tons. The purpose of reeling is to modify the web manufactured as planar into a more easily processable form. In the reel-up the continuous process of the machine breaks for the first time and shifts into periodic operation. The machine roll web produced in paper/board-making is full-width and even more than 100 km long so it must be slit into partial webs with suitable width and the partial webs are wound to partial rolls (customer rolls) with suitable length for the customers of the paper/board mill. The slitting and winding take place as known from prior art in an appropriate separate machine i.e. in a slitter-winder.

[0004] As known from the prior art in fiber web production lines typically comprise an assembly formed by a number of apparatuses arranged consecutively in the production line. A typical production and treatment line comprises a head box, a wire section and a press section as well as a subsequent drying section and a reel-up. The production and treatment line can further comprise finishing devices, for example a calender and/ or a coater. The production and treatment line also comprises typically at least one slitter-winder for forming customer rolls as well as a roll packaging apparatus.

[0005] In publication EP 1470289 is disclosed a calender device for calendering a coated or uncoated fibrous web, said device comprising an endless belt adapted to extend around at least one guiding element, one counter-element begin disposed outside the belt loop to provide a contact area with the belt, such that the belt and the counter-element establish there between a web processing zone for passing a web to be calendered there through, wherein inside the belt loop is mounted one press element for squeezing the belt against the counter-element, and wherein the processing zone length is defined by means of the disposition/adjustment of the belt's guiding element and/or by means of the design of the counter-element, the contact pressure adapted to be applied to a web within the processing zone is adapted to be adjustable within the range of about 0.01 MPa to about 70 MPa at a temperature of -70 to 400 degrees Celsius and the calender device is allowing a dwell or residence time in the processing zone of 0.01 to 10 s, wherein the belt comprises a metal belt, has a thickness of about 0.1 to 3 mm and a tensile stress within the range of about 10 MPa to about 500 MPa, and wherein the belt has its heating provided by means of a liquid-gas, natural-gas or electrically operated infrared radiator or an induction heating device, and/or the belt has its heating implemented by providing the belt loop with said at least one heatable roll, by way of which the belt is heated as a contact heat transfer, whereby the roll can be heated by any prior art heating method.

[0006] In publication EP 2278067 is disclosed a calender that has a web treating device that includes two contact surfaces for forming a treatment gap and where one of the surfaces is formed by a band with elastic surface and revolving around guide rolls and where the other surface is an outer wall of a heatable roll and further a counter element is provided for the heatable roll.

[0007] In publication EP 2270280 is disclosed a calender where the nip has been formed between a heatable roll and a counter element, which calender further comprises a band with elastic surface and rotating around guide rolls and the band presses a fiber web against the heatable roll.

[0008] In publication EP 2317008 is disclosed a method and a device for opening a belt calender nip and belt calender comprising a belt and guide rolls and a counter roll.

[0009] In metal belt calenders known from prior art one problem is that deflection of rolls creates tension differences to the belt. Typically the tension of the belt is greater in the edge areas of the belt than in the middle area of the belt. These tension differences influence directly among other things to the cross-direction contact pressure distribution between the roll and the belt and thus to the quality of the finished product. Thus rolls with greater diameters are needed in order to achieve sufficiently low tension difference distribution. Similar problem occurs also in other applications in connection with fiber web machines, in which a roll and a belt combination is used, for example in presses, in formers and in drying devices and also in connection with sizing or coating devices and in connection with reels and winders.

[0010] An object of the present invention is to provide for an improved arrangement to eliminate or at least minimize the above problems and disadvantages.

[0011] In view of achieving the objects stated above and those that will come out later the arrangement in accordance with the invention in mainly characterized by what is presented in the characterizing part of claim 1.

[0012] According to the invention the arrangement in connection with a fiber web production line, in particular in connection with a finishing device of a fiber web production line the arrangement comprises at least one roll and a belt, which belt is arranged to pass on surface of the at least one roll and in the arrangement belt has thickness profile that compensates at least partly the tension variation due to deflection of the at least one roll.

[0013] According to an advantageous embodiment of the invention in the arrangement metal belt has thickness profile that compensates at least partly the tension variation due to deflection of rolls. According to an advantageous feature of the invention the thickness profile variation evens out / compensates the cross direction tension distribution but the tensile stress distribution in cross-direction does not change significantly.

[0014] According to an advantageous feature of the invention the edge areas of the belt are thinner than the middle area of the belt such that the thickness profile of the belt corresponds to the deflection profile of the rolls.

[0015] In this description and the following claims by the term edge areas are meant areas located in longitudinal direction of the belt beginning from the edge and extending to the middle of the belt in each edge correspondingly. According to an advantageous feature about 20% of the width of the belt from each edge is considered as edge area and thus about 60% of the width of the belt in the middle is considered to be middle area. Thickness ratio of edge areas and middle area of the belt, i.e. the ration of minimum and maximum thickness of the belt is 0,3 -0,9.

[0016] Advantageously thickness profile of the belt substantially follows cos(70) curve, which is a continuous curve. Also other configuration profiles are possible.

[0017] According to an advantageous feature the belt is arranged as an endless belt loop extending around at least one roll.

[0018] By the invention major advantages are achieved. For example rolls with smaller diameters than in prior art devices can be used and simultaneously desired tension distribution of the belt and contact pressure distribution between the roll and the belt is achieved.

[0019] In connection with the invention rolls with uniform diameter and/or rolls with changing diameter can be used. The rolls can also be with or without crown.

[0020] Further with the invention the belt can be made of metal or plastic material, for example of polymer material, or of support layer material with one or more coating layers. The support layer material can be metal or plastic material and the coating layers can be of elastic material. The properties of the belt are determined by the requirements of the intended use in connection with the production of fiber webs.

[0021] Rolls used in connection with the invention can be provided with coating and also rolls without coating can be used. Belt used in connection with the invention can be provided with coating on outer and/or inner side of the belt and also belts without coating can be used.

[0022] In the following the invention will be described in more detail with reference to the figures in the accompanying drawing, the invention being however not supposed to be in any way strictly confined to the details of said illustration.

Figures 1- 10 are schematic examples of calculation illustrations relating to a belt according to one example of the invention.

Figures 11 A - 11 D are schematic examples of some advantageous examples of belts according to the invention.

[0023] In the following description and figures same reference signs designate for similar components unless otherwise mentioned and it should be understood that the examples are susceptible of modification in order to adapt to different usages and conditions within the frames of the invention.

[0024] In the calculation examples of figures 1 - 10 roll diameter of 1 m was used and average belt thickness of 1 mm was used. In figure 1 calculation model is shown which model is a symmetric half model in axial direction. The belt is denoted by reference numeral 10 and rolls with reference numeral 11.

[0025] In figure 2 longitudinal tension stress of the belt is shown, when the belt thickness is even and width of the belt is 4 m. Roll are not shown for the sake of clarity. In figure 3 is shown contact pressure distribution between the belt and a roll in a case of figure 2. Figure 4 shows longitudinal tension stress, when belt thickness is even and width of the belt is 5, 4 m i.e. 1,35 multiple of the original width. In this case the tension stress variation increases due to increased roll deflection. In this case due to the uniform thickness of the belt also tension variation increases due to increased roll deflection. In figure 5 contact pressure distribution between the belt and a roll is shown in case of figure 4 and corresponding to the increased tension stress variation also the variation of contact pressure has increased. In figure 6 is shown longitudinal tension stress when the belt is provided with 55% thickness variation ("crown") in relation to the middle thickness and the width of the belt is 5.4 m 1.e. 1,35 multiple of the original. The tension stress variation is very similar to that of figure 4. In figure 7 is shown the contact pressure distribution between the belt and the roll in case of figure 6 and the contact pressure variation is very similar to that of figure 3. In figure 8 is shown relative average contact pressure distribution in CD-direction between the belt and the roll in different cases and numerical error is filtered. Figure 9 corresponds to figure 8 but in case of 5,4 m belt width and even thickness belt removed. Figure 10 corresponds to figures 8 and 9 but in the example with 55% thickness variation the rolls are with crown.

[0026] In figures 11A to 11D some advantageous examples crown forms of the belt 10 according to the inventions are shown. As can be seen from the figures many different forms of the crown of the belt are possible. It should also be understood that the crown form can also be on one side of the belt only. Above the invention has been described with reference to some preferred exemplifying embodiments of the same only, and the invention is, however, by no means to be strictly confined to the details of said embodiments and many modifications and variations are possible.

Claims

1. Arrangement in connection with a fiber web production line, in particular in connection with a finishing device of a fiber web production line, which arrangement comprises at least one roll (11) and a belt (10) which belt is arranged to pass on surface of the at least one roll, characterized in, that in the arrangement belt (10) has thickness profile that compensates at least partly the tension variation due to deflection of the at least one roll (11).

2. Arrangement according to claim 1, characterized in, that in the arrangement the belt is a metal belt.

3. Arrangement according to claim 1 or 2, characterized in, that in the arrangement the thickness profile variation of the belt (10) compensates the cross direction tension distribution but the tensile stress distribution in cross-direction is substantially unchanged.

4. Arrangement according to claim 1 or 2, characterized in, that in the arrangement edge areas of the belt (10) are thinner than the middle area of the belt (10) such that the thickness profile of the belt (10) corresponds to the deflection profile of the at least one roll (11).

5. Arrangement according to any one of claims 1 - 4, characterized in, that in the arrangement the thickness profile of the belt (10) substantially follows cos(70) curve

6. Arrangement according to any one of claims 1 - 4, characterized in, that in the arrangement the thickness ratio of minimum and maximum thickness of the belt (10) is 0,3 -0,9.

7. Arrangement according to claim 1, characterized in, that in the arrangement about 20% of the width of the belt from each edge is edge area.

8. Arrangement according to claim 1, characterized in, that the arrangement is provided in a calender of a fiber web machine.

9. Arrangement according to claim 1, characterized in, that the arrangement is provided in a press section of a fiber web machine.

10. Arrangement according to claim 1, characterized in, that the arrangement is provided in a sizer or a coater of a fiber web machine.

Drawing