WO2007144459A1

WO2007144459A1 - A method, lifting device and arrangement for replacing a fabric in a web forming machine and a corresponding web forming machine

Info

Publication number: WO2007144459A1
Application number: PCT/FI2007/050299
Authority: WO
Inventors: Simo Horsma-Aho; Aaron Mannio
Original assignee: Metso Paper Oy
Current assignee: Valmet Technologies Oy
Priority date: 2006-06-13
Filing date: 2007-05-25
Publication date: 2007-12-21
Anticipated expiration: 2008-12-13
Also published as: AT506024A2; FI20065403A0; CN101466893A; AT506024A3; CN101466893B; AT506024B1; DE112007001348T5; FI118479B

Abstract

The invention relates to a method for replacing a fabric in a web forming machine. In the method, the front side (42) of the web forming machine comprises beams (21) between which beams (21) a gap is created for replacing a fabric forming a closed loop (24). After creating the gap, the gap is maintained with a medium lifting device (10), in which medium lifting device (10) pressurizable chambers (30) defined by sealing elements (32) are arranged on both sides of the fabric (24). The sealing elements (32) are sealed against the fabric (24) when pressurizing the chambers (30). The invention also relates to a corresponding lifting device, arrangement, and web forming machine.

Description

A METHOD, LIFTING DEVICE AND ARRANGEMENT FOR REPLACING A FABRIC IN A WEB FORMING MACHINE AND A CORRESPONDING WEB FORMING MACHINE

The invention relates to a method for replacing a fabric in a web forming machine, in which method the front side of the web forming machine comprises beams between which a gap is created for replacing a fabric that forms a closed loop. The invention also relates to a corresponding lifting device, arrangement, and web forming machine.

Methods are known prior art in which a paper machine frame is equipped with removable spacer blocks . These spacer blocks are removed from their positions for replacing a fabric that forms a closed loop. Generally, the back side of the frame part comprises cantilever beams for supporting the frame part after the removal of the spacer blocks. Cantilevering is a robust solution which includes solid constructions for directing stresses as desired to the foundations of the paper machine hall. It is known that abandoning the cantilevering system is desired since its implementation causes remarkable costs. Cost savings are achieved since the foundations of the paper machine hall become lighter and less space is required for constructing .

Cantilevering can be replaced, for example, with a solution according to patent FI 103421, in which the web forming machine comprises a special fabric introduction device on the front side between the vertical frame beams . In the introduction device, the pulling apparatus is a roll assembly surrounded by a belt. This introduction device enables abandoning the cantilevering system, but it is complicated for the design and includes multiple wearing parts . The parts are additionally custom-built so that their manufacturers are few in number. In addition, the fabric is subjected to mechanical compression as the frame weight comes across it. Then the fabric may damage due to the mechanical compression force. When using a roll assembly construction, dirt can attach to the belt surrounding the roll assembly, which damages the fabric to be replaced.

The object of the invention is to provide a novel method for replacing a fabric in a web forming machine, which method is suitable for different kinds of fabrics. The characteristic features of this method according to the invention become evident from the appended claim 1. Another object of the invention is to provide a novel arrangement for replacing a fabric in a web forming machine, which arrangement is simpler in design than heretofore. The characteristic features of this arrangement according to the invention become evident from the appended claim 7. Still another object of the invention is to provide a novel lifting device for replacing a fabric that forms a closed loop in a web forming machine, which lifting device can be used to replace a fabric without causing extra stress to the fabric. The characteristic features of this lifting device according to the invention become evident from the appended claim 5. The invention also relates to a novel web forming machine, simpler than before, in which various kinds of fabrics can be replaced without causing extra stress to the fabric. The characteristic features of this web forming machine according to the invention become evident from the appended claim 11. In the solution according to the invention, a medium is surprisingly used for maintaining gaps between the frame beams . Then a fabric can be replaced through these gaps maintained with the medium without the fabric damaging.

A web forming machine has several fabrics forming a closed loop which must be replaced when required. In this application, a

'web forming machine¹ is used to refer to machines, used in the production of paper and board, including replaceable fabrics . These include, for example, paper, board, tissue and pulp machines as well as belt calenders. Closed loops are, for example, forming section wires and press section felts. For replacing fabrics, gaps are created between the vertical frame beams on the front side of the web forming machine. A fabric forming a closed loop can be replaced via these gaps . Surprisingly, after creating the gap, the gap is maintained by means of a medium lifting device, in which the lifting effect is based on the pressure conveyed by the medium, in a way that differs from the known technique. In the known technique, the lifting effect is based on the mechanical contact subjected to a fabric by the device. Surprisingly, pressurizable chambers are arranged on both sides of a fabric, wherein the sealing elements delimiting these are sealed against the fabric when the chambers are pressurized. Thus the pressure of the medium is used to maintain the gap created between the supporting beams. A fabric can be led between the beams through the gap, which after creating is maintained with the medium lifting device. A fabric can be led to or from the web forming machine. Leading a fabric through the created gap is performed at its simplest by pulling the fabric from the fabric edge. Grabbing devices can be added to the fabric edge for facilitating pulling. The method according to the invention, simpler than before, for replacing a fabric enables using new frame designs. As the construction is simpler than before, its manufacture is notably less expensive. At the same time, the use of several custom-built components is avoided, which additionally allows to put the component manufacturers under competition more efficiently. In practice, replacing a fabric through the gap is performed via the medium, in which case the replacement is almost frictionless . In other words, for transferring the fabric, less force is needed than before. Also, the pressure applied to the fabric is uniform in the entire area defined by the sealing elements, which allows avoiding harmful pressure peaks. With the medium lifting device, exerting harmful force on the fabric is thus avoided. In addition, the device according to the invention, avoids using a belt known in prior art. The belt used in the solution according to prior art can become soiled whereby it may create a remarkable risk of damage to the fabric to be replaced.

In one embodiment of the method, an actuator is used for creating the gap. The actuator can be, for example, an overhead crane, a jack, or a medium lifting device. The use of the actuator is stopped once the fabric is brought between the sealing elements provided in the medium lifting device. The term 'fabric' is used here to refer to the fabric in a very wide sense. For example, pieces of fabric attached to the fabric are considered as fabric. Such pieces of fabric can be used since handling them is in some cases easier than that of a fabric. Pieces of fabric can also prevent fabric damage during the replacement. As a whole, the actuator is used to create and maintain the gap until the fabric is present between the sealing elements of the medium lifting device. While the fabric is present between the sealing elements, the chambers arranged on both sides of the fabric can be pressurized. When pressurizing the chambers, the sealing elements seal against the fabric whereby the medium lifting device maintains the gap created enabling the fabric to be taken through the gap. Advantageously, pressurizing the chambers is performed before removing the lifting effect of the actuator so that a mechanical stress otherwise momentarily subjected to the fabric is avoided. Likewise, the described arrangement can be implemented in reversed order when removing a fabric from the gap. By setting the actuators to maintain the gap before releasing the pressure from the medium lifting device, a mechanical stress otherwise momentarily subjected to the trailing edge of the fabric is avoided.

The invention is described below in detail by making reference to the enclosed drawings, which illustrate some of the embodiments of the invention, in which Figure 1 is a sectional view in the machine direction of a press section construction of a web forming machine comprising medium lifting devices according to the invention, Figure 2 shows the back and front side beams of a web forming machine, sectioned in the cross-machine direction, with medium lifting devices according to the invention between the front side beams,

Figure 3 shows a second embodiment of a medium lifting device according to the invention,

Figure 4 is a cross-sectional view in the machine direction of a medium lifting device according to Figure 3 with a fabric between the sealing elements,

Figure 5 shows a third embodiment of a medium lifting device according to the invention,

Figure 6 is a cross-sectional view in the machine direction of a medium lifting device according to Figure 5 with a fabric between the sealing elements,

Figure 7 is a cross-sectional view in the machine direction of a fourth embodiment comprising sealing elements that press into the surfaces of the medium lifting device, and removable support blocks , Figure 8 is a top view of a fifth embodiment of a medium lifting device according to the invention, Figure 9a shows an embodiment of sealing devices, in the unpressurized state, for implementing a medium lifting device according to the invention, Figure 9b shows the sealing devices of Figure 9a in the pressurized state, Figure 9c shows sealing devices of Figure 9b in the pressurized state in connection with a fabric, and Figure 9d shows a fabric between pressurized sealing elements according to Figure 9c.

Figure 1 depicts a press section 12 of a web forming machine, which can be, for example, a paper or board machine, sectioned in the machine direction of the web forming machine. A press nip 14 is formed between the top roll 16 and the bottom roll 18. The section of Figure 1 has been made at about the center of the machine and the view is from the back side, in which 5 case the front side beams 21, consisting of beams 20 and horizontal beams 22, are partly hidden behind the rolls. The force of gravity is supported particularly by the vertical beams, which can also be inclined. For beams supporting in the direction of the force of gravity, a term 'vertical beam' is

10 used, which does not define the shape or position of the beam. The fabric 24 in the press section 12 is supported as an endless loop with rolls 16, 18, 19. The rolls 16, 18, 19, in turn, are further supported by beams 21, or more precisely by a frame consisting of vertical 20 and horizontal beams 22. An

15 openable intermediate structure 26 is arranged between the front side beams 21. Surprisingly, a medium lifting device 10 is set in connection with the intermediate structure. In the condition shown in Figure 1 the medium lifting devices 10 are deactivated and the fabric 24 is in place in the press section

20 12. The medium lifting device 10 includes a pressurizable chamber 30 and sealing elements 32. In the pressurized state, with the fabric between the sealing elements, a chamber is present between both sides of the fabric, and the sealing elements defining the chamber seal against the fabric. The term

25 'fabric' also refers to the pieces of fabric, attached in connection with the fabric, which can be used for leading the fabric to between the sealing elements. When using the medium lifting device 10, a pressurized medium 34 is led to the chamber 30. The medium 34 is led to the chamber 30 along a

30 channel 36. For pressurizing the medium 34, pressure supply equipment 28 is needed. By pressurizing the medium with the pressure supply equipment, the chamber is consequentially pressurized. The pressure supply equipment can be dedicated equipment for the use of the medium lifting device, or the

35 pressure can be taken from the mill supply net. Figure 1 shows several possible locations for the medium lifting device 10; however, an application of one medium lifting device per a fabric loop is possible.

Figure 2 provides a cross view of back side 38 vertical beams 40 and front side 42 vertical beams 20 of a press section or a forming section of a web forming machine. Medium lifting devices 10 according to the above described arrangement are set between the front side 42 vertical beams 20 of the press or forming section of the web forming machine. In Figure 2 the medium lifting devices 10 are deactivated, i.e. unpressurized. In this condition the load is supported by the support blocks 44 located in connection with the medium lifting devices 10 and the surfaces 46 of the medium lifting devices 10.

Figure 3 shows a second embodiment of a lifting device or a medium lifting device 10 according to the invention. The medium lifting device is used for replacing a fabric that forms a closed loop in a web forming machine. The medium lifting device comprises opposite surfaces 46 between which the fabric is adapted to be taken. The gap required for transferring the fabric is maintained between the surfaces by means of the medium pressure. At least one pressurizable chamber 30, which in case of Figure 3 is open, is included in connection with each of the surfaces 46. The state of being open means that the chambers are not against each other or against the fabric. The chambers 30 are defined at the edges' by sealing elements 32. According to the invention, the sealing elements are adapted to seal against the fabric when the chamber is pressurized. In the proposed application in a web forming machine, grabbing points 58 are also included in connection with the medium lifting device. An actuator 56 is used to open a gap between the surfaces, within which the fabric is set. The actuator 56 is advantageously a jack 48, and the extensions 50 serve as grabbing points 58. The jack is used to increase the interval between the extensions whereupon a gap, within which the fabric is set, is created also between the sealing elements. Using a jack is simple and a jack is a reliable solution. In addition, the extensions 50 required by the jack are easy to manufacture.

Figure 4 is a cross-sectional view in the machine direction of the medium lifting device 10 of Figure 3 with a fabric 24 between the surfaces 46 and with the chambers 30 pressurized. Upon pressurizing, the sealing elements 32 lift up from their grooves 52 whereby the surfaces 46 serving as backgrounds for the chambers 30 function as pressure surfaces during use. The sealing elements 32 lift up from the grooves when the seal elements 33 serving as their backgrounds change shape due to the chamber pressure. When the seal elements 33 are brought in connection with the chamber 30 pressure, they change from a flat shape (Figure 7) to round thus pushing the sealing elements 32 out of the grooves 52. When the sealing elements 32 rise from the grooves 52, the actual chambers 30 are created. The pressurized medium in the chambers 30 maintains the gap between the surfaces 46 of the medium lifting device 10. The medium lifting device 10 can be linked in connection with the front side 42 vertical beams 20 (Figure 2) , in which case it maintains a gap between the front side vertical beams . The sealing elements 32 coming out of their grooves 52 as a consequence of pressurization enables to implement a construction in which the surfaces become completely joined when releasing the pressure. Thus the entire area of the surfaces supports the load during the use of the web forming machine. When the medium lifting device 10 is in the pressurized state, the fabric 24 is sealed against the sealing elements 32. When the fabric 24 is taken between the surfaces 46, the sealing elements 32 are sealed against the fabric 24, whereupon the lifting effect of the medium maintains the gap. In other words, the sealing elements 32 are sealed against the fabric 24 when the chamber 30 is pressurized. Sealing of the fabric 24 against the sealing elements 32 does not mean a perfect tightness but a sufficient tightness . The significance of the fabric as a part of sealing is essential, so the fabric is a functional part of the whole. It is essential that the force of the medium pressure can keep the paper machine ' s front side vertical beams separated from each other. Then a gap is maintained between the vertical beams through which the fabric can be pulled. Tightness should be interpreted in terms whether the desired goal is achieved with it. In practice, leaking occurs on the boundary surfaces between the sealing elements and the fabric, which also lubricates the intervals between the fabric and the sealing elements. In addition, some of the medium can also be conveyed away from between the chambers along the fabric, in which case leaking also occurs. With a suitable dimensioning and medium pressure the medium lifting device operates as designed regardless of leaks.

In the embodiment shown in Figure 4, extensions 50 for a jack are arranged on the side of the medium lifting device. The jack can be used to move the surfaces 46 and the sealing elements 32 apart from each other. Thus a gap, within which the fabric can be set, is created between the sealing elements and the surfaces. In Figure 4 the fabric 24 is already between the sealing elements 32. The term 'fabric' is used here to refer also to a piece of fabric attached to the fabric, since the fabric can have pieces of fabric attached thereto which are used to start pulling the fabric to between the sealing elements and thus also to between the surfaces . A thin or wedge-like piece of fabric can be used to pull the fabric to between the chambers that are ready pressurized without forming a gap between the beams with an actuator.

Figure 5 shows a third embodiment of the medium lifting device 10 according to the invention. In this embodiment the most obvious difference compared to the embodiment of Figure 3 is that the sealing elements 32 remain outside the surface 46 also for the duration of the machine operation. In this embodiment the sealing elements 32 need not go into the surface 46 as the sides are provided with removable support blocks 44. The stress during operation is thus directed via the support blocks between the frame beams. The version with support blocks is an advantageous embodiment, since manufacturing fixed sealing elements is more economical and they are more reliable than moving sealing elements. In addition, the alignment profiles 54 can be set inwardly, in which case the fabric is easier to replace. The alignment profiles can also be curved surfaces, for example, in addition to what is shown in the figure. Furthermore, the vertical travel distance can be very short whereby directing extra stresses to the beams forming the frame is avoided. For illustrative purposes, the support blocks are drawn higher than they need be in Figure 5, so the distance between the sealing elements is remarkably great. As mentioned above, the interval is advantageously short, in which case it is possible to avoid directing extra stresses to the frame. The medium lifting device 10 includes extensions 50, the interval of which can be increased with a jack. When increasing the interval between the extensions with a jack, the support blocks can be moved away from their places and the fabric can be taken to between the sealing elements.

Figure 6 provides a cross-sectional view in the machine direction of the medium lifting device of Figure 5 with a fabric 24 between the surfaces 46. The sealing elements 32 seal against the fabric 24 and the medium pressure keeps the surfaces 46 separated from each other. The term 'surface¹ also refers to other surfaces than planes although in the case of the figures the surfaces are planes. The surfaces can as well be inwardly curved, for example. 'Surfaces' refer widely to the area on which the pressure is exerted in the medium lifting device generating a lifting force. Advantageously the old fabric is removed intact from the machine. When the extensions 50 are on both sides of the medium lifting device, the fabric can be placed and removed without cutting it. When the old fabric is cut, extensions are needed in the frame of the medium lifting device only in the machine's front side frame, on the side of the roll assembly, so that the new fabric can be put in place without using extra pieces of fabric attached to the fabric .

Figure 7 shows a fourth embodiment of the medium lifting device according to the invention. In this embodiment the sealing elements 32 go inside the grooves 52 provided on the surfaces 46 being protected therein. The sealing elements lift up from the grooves once the seal elements 33 functioning as their backgrounds are pressurized and thus round (Figure 4) . In Figure 7 the seal elements 33 are, however, unpressurized and thus flat. The sides are additionally provided with support blocks 44. In this case the support blocks 44 are so designed that when in place, the surfaces 46 join. Thus the stress during operation is directed to the whole surface area. In this application with support blocks, alignment profiles do not interfere with taking the fabric in place, so that the sealing elements need to protrude from the surface only slightly. In addition, it is possible to avoid stresses subjected to the frame beams .

The medium lifting device must have two surfaces between which the pressure affects. The pressure can be led to between the surfaces through either one or two surfaces . In the forming section, where the replaceable fabric is a wire, the pressure is advantageously led through one surface 46 only (Figure 6) . In other words, the medium 34 is led to only one of the opposite chambers 30, in which case a channel 36 is included only in connection with one of the chambers 30 (Figure 6) . Such a simple structure is possible because the wire is permeable to the medium and the pressure can affect between the surfaces of the medium lifting device. Although only one of the chambers is directly pressurized, both chambers are consequentially pressurized as the medium goes through the wire. In the press section, in contrast, where the replaceable fabric is a felt, the pressure is advantageously led through two surfaces 46

(Figure 7) . In other words, the medium 34 is led to both of the opposite chambers 30, in which case a channel 36 is included in connection with both chambers 30 (Figure 7) . In other words, both chambers are directly pressurized. Such a structure is required because all felts used are not permeable to the medium sufficiently as regards a one-sided pressure supply. In other words, a two-sided pressure supply enables the same pressure on both sides of even an impermeable fabric. Thus the pressurized medium lifts and separates the surfaces without generating forces that damage the fabric .

Generating a uniform pressure is aimed at within the area defined by the sealing elements. The pressure can be equalized, for example, by leading the pressure via several channels. However, multiple channels in connection with one chamber can complicate the design. For equalizing the pressure, even the design of the sealing elements can be utilized. Seen from above, a sealing element 32 can have a circular design or it can be at least rounded at the corners (Figure 8) . Using a design without sharp angles, a more uniform pressure can be achieved within the area defined by the sealing elements . In addition, the bottom of the chamber can be so designed that the pressure is more uniformly distributed.

Below is a description showing how a fabric forming a closed loop is replaced with a new one utilizing a medium lifting device according to the invention without cutting the old fabric. First, a gap is created between the sealing elements using an actuator external to the frame as seen from the machine. The support blocks are removed at the same time. After this the fabric is drawn in to between the sealing elements . Once the fabric is present in the entire area between the sealing elements, the medium lifting device is pressurized and the actuator is depressurized. As the medium lifting device is pressurized, the sealing elements seal against the fabric. After the sealing elements have sealed against the fabric, the medium lifting device maintains the gap between the sealing elements, through which the fabric is pulled. Thereafter, the fabric is drawn out of the machine between the sealing elements and thus between the surfaces . Even with the fabric removed, the pressurization of the chambers is maintained and the surfaces are kept separated until the pressure is released from the chambers . Then the sealing elements seal against each other maintaining the pressure. After removing the old fabric, a new fabric is set in place to replace the old one. Placing the new fabric is started by creating a gap between the sealing elements provided in the medium lifting device using the actuator located on the machine side. The fabric to be placed in the machine is placed in the gap so formed. When the fabric is within the gap, the medium lifting device is pressurized again and the actuator located on the machine's roll assembly side is removed. Once the actuator is removed, the fabric is drawn in place. Finally the support blocks are set back in place and the pressure is released. After this the web forming machine is ready for use.

The method of use described in the previous chapter is only one alternative and variations can be made in it as required. For example, if the sealing elements are hard and there is a risk of fabric damage when pulling out the fabric from between the pressurized sealing elements, a gap can be maintained with the actuators before the edge is pulled out from between the sealing elements . Thus no harmful forces are exerted on the fabric. A piece of fabric can also have been attached to the fabric which piece of fabric comes out last from between the sealing elements. Then a possible harmful force is not exerted on the fabric but on this piece of fabric, and the fabric can be set in place intact without using an actuator in this stage.

A fabric removed from a web forming machine can additionally be cut. Then the cut fabric can be drawn out of the machine without creating a gap in the vertical beams. In this case, a medium lifting device is used in the fabric replacement only for putting the fabric in place.

In Figures 4 and 6 the support blocks 44 have been drawn on two sides only, but they can also encircle the medium lifting device on all sides. Such embodiment of a medium lifting device 10 in which the support blocks 44 are on all sides is shown in Figure 8 as seen from above. The number of support blocks 44 is four in this embodiment and the jacks 48 functioning as actuators are integrated to part of the support blocks 44. When the support blocks 44 are placed on all sides of the medium lifting device, the sealing elements 32 are protected from all sides during operation. Access of impurities to the sealing elements is thus prevented avoiding in this way the harmful effect of impurities in connection with the installation of fabrics. In addition, the load during operation is divided to four support blocks. When the jacks are integrated to the support blocks, creating a gap is very easy as separate jacks are not needed, but the jacks are ready present in connection with the medium lifting device. Embodiments have been set forth in connection with the figures in which one medium lifting device has one chamber on both sides of the fabric. There could also be more than one chamber, but an embodiment with one chamber is the most advantageous due to its easy implementation.

A medium lifting device can also be used as actuator. In this case, a medium lifting device is used to create a gap between the surfaces so that the desired support block can be replaced with a higher support block, for example. The support blocks can also be so dimensioned that the support block becomes suitably higher by turning it. Other support blocks are removed. Thereafter, the pressure is released so that the higher support block supports the load and the surfaces are kept separated. After this, the fabric is placed between the sealing elements and the medium lifting device is pressurized again. The support block is removed and the fabric is pulled in place. When the medium lifting device is pressurized without having a fabric between the sealing elements, the sealing elements seal against each other.

In the embodiments set forth above, one medium lifting device has one chamber on both sides of the fabric. In practice, one medium lifting device can also have more than one chamber on both sides of the fabric. In such an application, the gap can be created with the second chambers and the fabric can be placed between the sealing elements of the second chambers. Here, too, a gap is first created using an actuator and then a fabric is placed within the gap created between the sealing elements with the actuator. After this pressure is applied to the chambers between the sealing elements of which the fabric is located. In this embodiment the actuator is a medium lifting device.

Figure 9a shows one embodiment of sealing elements 32, in the unpressurized state, for implementing a medium lifting device 10 according to the invention. Above the surface 46, a chamber is adapted to be formed when the medium lifting device is in the unpressurized state. The medium lifting device 10 comprises a pressure groove 60, to which a medium is conveyed for creating a chamber in connection with the surface 46.

Figure 9b shows the sealing elements 32 of Figure 9a in the pressurized state. In this state, a medium has been led to the pressure groove 60. The medium led to the pressure groove 60 has made the sealing part 62 of the sealing element 32 rise up. Thus a chamber 30 has been created in connection with the surface 46. The fabric defining the chamber is not shown.

Figure 9c shows the pressurized sealing element 32 of Figure 9b in connection with a fabric 24. A medium led to the pressure groove 60 is conveyed to the chamber 30 beside the sealing part, whereupon a fabric-supporting pressure is present in the chamber 30 located between the surface 46 and the fabric 24.

Figure 9d shows a fabric 24 between the pressurized sealing elements 32 according to Figure 9c. Then chambers 30 are formed between the surfaces 46 and the fabric. A pressure is present between the chambers keeping the surfaces 46 separated from each other. The fabric 24 is moved in the direction of the arrow 64. The sealing elements are so designed that the fabric can be pulled to between the sealing elements even in the pressurized state. Then the old removable fabric can be cut, for example, in which case the design of the sealing elements can be optimized for moving the fabric to one direction.

As a medium, various substances, such as oil, water or air, can be used in the medium lifting device. Because leaking occurs in spite of sealing, it is advisable to use a non-soiling and harmless medium. Using air as a medium is advantageous, because it does not soil at all and is harmless for the employees. In addition, in connection with a felt, using air is advantageous since a felt aspirates water in it. Treating a felt becomes difficult when it aspirates water in it. Using water, in turn, is advantageous because water is relatively incompressible and thus functions as a good pressure medium. The use of water is also favored by the fact that water cleans the sealing elements when flowing, whereupon impurities damaging the fabrics are washed off from the sealing element surfaces. Also, water does not actually soil although it wets . Water can be released to the floor and led further to the drain, which makes it convenient to use. In addition, water is riskless and harmless as regards safety at work.

Above, in connection with the fabric, it has been referred to felts and wires. However, replacing a wide belt is also possible utilizing the invention. For example, the replacement of a polymer belt or a metal belt in the press section or in the calender can be performed using equipment according to the invention.

An arrangement according to the invention can also be used in connection with machine rebuilds, where a problem may arise from the insufficiency of old cantilever constructions . By combining the solution according to the invention to an old machine it is possible, for example, to increase roll masses using still the old frame. Without the solution according to the invention, increased roll masses would cause stresses that are higher than a cantilevering system dimensioned for old, lighter rolls can endure.

The invention is described above referring to only some of its advantageous embodiments to which the invention is in now way strictly limited. Many other applications are also possible within the scope of the inventive idea defined in the claims .

Claims

1. A method for replacing a fabric in a web forming machine, in which method the front side (42) of the web forming machine comprises beams (21) , between which beams (21) a gap is created for replacing a fabric (24) that forms a closed loop, characterized in that after creating the gap, the gap is maintained using a medium lifting device (10) , in which medium lifting device (10) arranged on both sides of the fabric (24) , there are pressurizable chambers (30) defined by sealing elements (32), which are sealed against the fabric (24) as the chambers (30) are pressurized.

2. A method according to claim 1, characterized in that for creating the gap an actuator (56) is used, the use of which is stopped when the fabric (24) is between the sealing elements (32) and the chambers (30) are pressurized.

3. A method according to claim 1 or 2 , characterized in that a medium lifting device (10) is used as the actuator (56) .

4. A method according to any of claims 1 - 3 , characterized in that the chambers (30) are pressurized with air.

5. A method according to any of claims 1 - 3 , characterized in that the chambers (30) are pressurized with water .

6. A lifting device for replacing a fabric in a web forming machine, which lifting device comprises opposite surfaces (46) between which a fabric (24) forming a closed loop is adapted to be taken, characterized in that the lifting device is a medium lifting device (10) , in which at least one pressurizable chamber (30) is arranged in connection with both surfaces (46) , the chamber being defined by sealing elements (32) adapted to seal against the fabric (24) when the chamber (30) is pressurized.

7. An arrangement for replacing a fabric in a web forming 5 machine said web forming machine comprising:

- a fabric (24) forming a closed loop,

- beams (21) for supporting the fabric (24) , and

- an openable intermediate structure (26) between the vertical beams (20) ,

10 characterized in that the arrangement comprises : a medium lifting device (10) having at least one pressurizable chamber (30) on both sides of the fabric (24) said chambers (30) being defined by sealing elements (32) adapted to seal against the fabric (24) when the chamber (30)

15 is pressurized,

- pressure supply equipment (28) for pressurizing the medium (34) and thus for pressurizing the chambers (30) , and

- a channel (36) for conveying pressurized medium (34) to the chambers (30) .

20

8. An arrangement according to claim 7 , characterized in that the arrangement includes an actuator (56) for forming a gap, which actuator (56) is a jack (48) for which, provided in connection with the medium lifting device (10) , there are

25 extensions (50) located in such a way that when increasing the interval between the extensions (50) using the jack (48) , a gap, within which the fabric (24) is adapted to be placed, is created between the sealing elements (32) of the medium lifting device (10) .

30

9. An arrangement according to claim 7 or 8 , characterized in that the channel (36) is adapted to open only to the chamber (30) arranged on one side of the fabric (24) .

35 10. An arrangement according to claim 7 or 8, characterized in that the channel (36) is adapted to open to the chambers (30) arranged on both sides of the fabric (24) .

11. A web forming machine, characterized in that it comprises an arrangement according to any of claims 7 - 10.