WO2008129131A1

WO2008129131A1 - A system for replacing a fabric/belt in a web forming machine, a lifting device used for replacing a fabric/belt in a web forming machine, and a method for replacing a fabric/belt in a web forming machine

Info

Publication number: WO2008129131A1
Application number: PCT/FI2008/050207
Authority: WO
Inventors: Jukka T. Koskinen; Aaron Mannio; Samppa J. Salminen; Jyrki Savela; Veli-Matti Vainio
Original assignee: Metso Paper, Inc.
Priority date: 2007-04-20
Filing date: 2008-04-18
Publication date: 2008-10-30
Also published as: FI20075281A0; DE112008001016T5; FI20075281A; FI119599B

Abstract

The invention relates to a system for replacing a fabric/belt in a web forming machine, including a fabric/belt (24) that forms a closed loop, vertical beams (20) for supporting rolls and equipment of the fabric/belt loop (24), and an openable intermediate structure (26) between the vertical beams (20). The intermediate structure (26) includes a lifting device (10) which further includes a pressure chamber (30) partially defined by edge surfaces (32). In the system, the fabric/belt (24) is adapted to be taken through the intermediate structure (26) while the pressure chamber (30) is pressurized with a medium (34). In addition, the pressure chamber (30) includes, between the edge surfaces (32), a sliding surface (31) provided with one or more flow openings (33) and having on outer surface (35), and the flow openings (33) are adapted to open to the outer surface (35) for creating a sliding layer (37) with the medium (34) discharging from the flow openings (33). The invention also relates to a corresponding system and method.

Description

A SYSTEM FOR REPLACING A FABRIC/BELT XN A WEB FORMING MACHINE, A LIFTING DEVICE USED FOR REPLACING A FABRIC/BELT IN A WEB FORMING MACHINE, AND A METHOD FOR REPLACING A FABRIC/BELT IN A WEB FORMING MACHINE

The invention relates to a system for replacing a fabric/belt in a web forming machine, including a fabric/belt that forms a closed loop, vertical beams for supporting rolls and equipment of the fabric/belt loop, and an openable intermediate structure between the verti cal beams, with the intermediate structure including a lifting device which further includes a pressure chamber partially defined by edge surfaces, and with the fabric/belt being adapted in the system so as to be taken through the intermediate structure while the pressure chamber is pressurized with a medium. The invention also relates to a corresponding lifting device and a method.

Methods are known from 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 is provided with cantilever beams for supporting the frame part after the removal of the spacer blocks . Cantilevering is a robust solution involving 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 includes a special fabric introduction device on the front side between the vertical frame beams. In this introduction device, the pulling apparatus is a roll assembly surrounded by a belt. The 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. Consequently, 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 may damage the fabric to be replaced.

Cantilevering can also be replaced, for example, with a solution proposed in publication WO 2006/106178. In this case the gap between the frames is created by means of a pressure chamber which is confined to a band touching them. On the other surface of the band, in turn, the fabric is taken through the gap thus created. In the embodiments proposed in the publication, sealing of the sealing elements against the band is not very simple. Also, the required parts are custom-built. Furthermore, in the embodiments proposed, the sealing forms a border on the band surface. When the fabric is pulled through this border, a border lubrication condition can appear in the sealing, which hinders the introduction of the fabric when the chambers are pressurized. For this reason, it is necessary to first create a gap between the chambers for the fabric using a jack. After jacking, the chambers can be pressurized. This procedure slows down the fabric replacement. Consequently, there is a need for creating a novel system in which the fabric to be replaced can be pulled to between the pressurized chambers . The solution of publication WO2006/106178 also requires a band between the fabric and the chamber to be replaced.

The objective of the invention is to provide a novel system for replacing a fabric in a web forming machine, which system can be modified for various operating situations better than before. The characteristic features of the method according to the present invention are that the pressure chamber includes, between the edge surfaces thereof, a sliding surface equipped with one or more flow openings and having an outer surface, with the flow openings being adapted to open to the outer surface for creating a sliding layer with a medium that discharges from the flow openings. Another object of the inventi- on is to provide a novel lifting device for replacing a fabric in a web forming machine, the design of said lifting device being simpler than before. The characteristic features of this lifting device according to the invention are that the pressure chamber includes, between its edge surfaces, a sliding surface having an outer surface, and the sliding surface is provided with flow openings, and a sliding layer is adapted to be created on the outer surface of the sliding surface using a medium that is adapted to discharge from the flow openings in the sliding surface. Still another object of the invention is to provide a novel method for replacing a fabric that forms a closed loop in a web forming machine, in which method the fabric can be pulled to between the pressurized chambers. The features of the method according to the present invention are that a sliding surface, provided with one or more flow openings, is used in the pressure chamber between the edge surfaces, said sliding surface having an outer surface, and the flow openings are adapted to open to the outer surface, and a sliding layer is formed by means of a medium discharging from the flow openings .

A web forming machine has several fabrics forming a closed loop which must be replaced when required. For the replacement, the method according to the invention for replacing a fabric in a web forming machine can be used. In this application, a 'web forming machine' or a 'fiber web forming machine' refers to machines that are used in the production of paper and board, having replaceable fabrics. These include, for example, paper, board, tissue and pulp machines as well as belt calenders . Closed loops are, for example, forming section fabrics (or wires) and press section felts. A web forming machine includes a fabric that forms a closed loop, which can be, for example, a calender belt. Calender belts can also be made of metal. The fabric is supported indirectly as a fabric cycle with rolls that are supported to vertical frame beams . An openable intermediate structure is included between the vertical beams . The intermediate structure is used to create a gap between the front side vertical frame beams for replacing a fabric in a web forming machine. The intermediate structure includes a lifting device provided with a pressure chamber. The pressure chamber is partially defined by edge surfaces. The pressure chamber is pressurized with a medium, and the fabric is taken through the lifting device included in the intermediate structure. In addition, the pressure chamber includes, between the edge surfaces, a sliding surface having an outer surface. The sliding surface is provided with flow openings, and a sliding layer is created on the outer surface of the sliding surface using a medium that discharges from the flow openings in the sliding surface. Thus the pressure of the medium is used to maintain the gap created between the supporting beams . This gap can additionally be created by means of the pressure of the medium. For the invention, it is essential that the gap is maintained with the medium pressure during the fabric replacement. Then the fabric can be led through the gap from between the beams . After being created, the gap is maintained with a 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. Furthermore, grabbing devices can have cords attached thereto and winches for facilitating pulling.

In one embodiment the pressure chamber is used to maintain the gap, and the fabric is pulled to the gap confined by the pressurized pressure chamber. This embodiment is very advantageous since it does not require separate actuators for creating the gap when placing the fabric in the gap. Compared to prior art technique, this embodiment is enabled by a novel edge surface design. In other words, the lifting device according to the invention enables pulling the fabric to the gap which is maintained with the lifting device without separate actuators. When the gap is maintained without separate actuators, replacing the fabric becomes simpler than before.

Figure 1 shows a press section construction of a web forming machine, viewed from the back side, including lifting devices according to the invention, Figure 2 shows back and front side beams, viewed in the machine direction of a web forming machine, with lifting devices according to the invention between said front side beams,

Figure 3 shows an embodiment of a lifting device according to the invention, Figure 4a is a machine-directional view of a lifting device according to the invention with a fabric in the gap,

Figure 4b is a cross-directional sectional view of a lifting device shown in Figure 4 with a fabric in the gap,

Figure 5 shows an intermediate structure with the lifting device in the unpressurized state, Figure 6 shows the intermediate structure in a disassembled state, Figure 7a shows an embodiment of a lifting device in which only one of the pressure chambers is circled by a band,

Figure 7b shows an embodiment of a lifting device in which neither of the pressure chambers is circled by a band, Figure 7c shows an embodiment of a lifting device in which one side is provided with sealing elements and the other side with a pressure chamber including a sliding surface, and Figure 7d shows an embodiment of a lifting device according to the invention equipped with larger rolls than in Figure 7a.

Figure 1 shows the press section 12 of a web forming machine 12. The press section 12 is equipped with a system according to the invention for replacing a fabric in a web forming machine. A press nip 14 is formed between a top roll 16 and a bottom roll 18. Figure 1 illustrates the web forming machine seen from the back side, from the center of the machine in the cross direction, in which case the front side beams 21, consisting of vertical beams 20 and horizontal beams 22, are partly hidden behind the rolls . The weight of the rolls and equipment is supported particularly by the vertical beams, which can also be inclined. The beams providing support in the direction of the force of gravity are referred to as vertical beams, without restricting, however, the shape or position of the beam. The fabric 24 in the press section 12 is supported as a closed loop with the help of 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 openable intermediate structure 26 is arranged between the front side beams 20. Located in connection with the intermediate structure, there is a lifting device 10 including a pressure chamber 30 partially defined by edge surfaces. In the system, a fabric/belt is adapted to be taken through the intermediate structure while the pressure chambers are pressurized with a medium. In addition, Figure 3 shows that the edge surfaces 32 of the pressure chamber 30 include a sliding surface 31 that is provided with one or more flow openings 31 and has an outer surface. The flow openings are adapted to open to the outer surface for forming a sliding layer 37 with a medium discharging from the flow openings. In the situation shown in Figure 1, the lifting devices 10 are deactivated and the fabric 24 is in place in the press section 12. In turn, when the fabric is moved to or from the web forming machine, the fabric is taken through the gap created by a lifting device. The term '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. The fabric can also include a sealing system and protective surfaces, which can cover the entire fabric width. When using the lifting device 10, which is a medium lifting device, pressurized medium 34 is led to the pressure chamber 30. Leading the medium 34 to the pressure chamber 30 takes place along a 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 indirectly pressurized. The pressure supply equipment can be separate for using the lifting device, or the pressure can be taken from the mill supply net. Figure 1 shows several possible locations for the lifting device 10, but also an application of only one lifting device per a fabric cycle is also possible.

Figure 2 provides a machine-directional 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. 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 lifting devices 10 are deactivated, i.e. unpressurized. In this condition the load is supported by the bracket constructions arranged in intermediate structures 26.

Figure 3 shows one embodiment of a lifting device 10 according to the invention used for replacing a fabric in a web forming machine. The lifting device includes a pressure chamber 30 provided with edge surfaces 32. The fabric 24 is adapted to be taken through the lifting device 10 while the pressure chambers 30 are pressurized with a medium. In addition, the pressure chamber includes, between the edge surfaces thereof, a sliding surface 31 having an outer surface, and the sliding surface 31 is provided with flow openings . On the outer surface of the sliding surface 31, a sliding layer 37 is adapted to be created with a medium which is adapted to discharge from the flow openings on the sliding surface 31. The gap required for leading the fabric is maintained in the lifting device by means of the medium pressure.

When using the lifting device 10 shown in Figure 3 in a system according to the invention when taking the fabric 24 through the intermediate structure, or more precisely, the lifting device 10, the sliding surface 31 is adapted against a band 39 included in the lifting device. Preferably, the surface of the band set against the sliding surface has low friction. Thus even a low pressure is sufficient for creating both the required gap and the sliding layer. The surface of the band can be, for example, teflonized, for reducing friction. The other surface of the band, in turn, preferably has higher friction, which facilitates pulling the fabric through the lifting device by the rotation of the band. The surface of the band on the fabric side can be rough also in connection with a non-driven application in order that the band and the fabric travel together through the construction.

The lifting device shown in Figure 3 includes guides 41 for supporting the band 39. Here the guides 41 are rolls 43. When the guides 41 are rolls 43, it is very practical to use a band that creates a loop. The rolls can be driven or non-driven. With driven rolls, the fabric can be taken to the gap without external actuators for creating the gap. In other words, driven rolls enable running the fabric directly to between pressurized pressure chambers. On the other hand, when the rolls are non- driven, a very simple embodiment can be achieved for the entire construction.

Figure 4a shows a lifting device 10 according to the invention seen from the front side with a fabric 24 in the gap 45, i.e. between the pressure chambers 30. A band 39, supported by rolls or guides, is shown. In the situation illustrated, the pressure chambers 30 are pressurized. The lifting device 10 can be linked to form a connection with the front side 42 vertical beams 20 (Figure 2), in which case it maintains a gap between the front side vertical beams .

Figure 4b, in turn, provides a cross-directional sectional view of a lifting device 10 according to the invention. The cross section is provided so that the pressure chamber is also visi- ble in the cross sectional view. A fabric 24 is between the pressure chambers 30 and the pressure chambers 30 are pressurized. More precisely, the fabric 24 is between bands 39 placed on the outer surfaces 35 of sliding surfaces 31. The bands are between sliding layers 37 located on the sliding surfaces 31 that have been created by a medium 34. It is true, however, that in the real life the bands typically partly also touch the sliding surfaces themselves. On the whole, the thickness of the sliding layer in Figure 4b is exaggerated for illustrating the principle. With high flow and pressure, the thickness of the sliding layer increases, but it is not necessary to make this distance as great as is shown in Figure 4b. Providing an insufficiently thick sliding layer requires an insufficiently high pressure and great flow.

The lifting device 10 shown in Figure 4b includes two pressure chambers 30 with the sliding surfaces 31 thereof adapted against each other. In this embodiment, the fabric 24 is adapted to be taken through the pressure chambers 30 while the pressure chambers 30 are pressurized with a medium.

The illustration in Figure 4b reveals that the edge surfaces 32 rise up during pressurization since the sliding surface 31 is pressed outwards, i.e. away from the background surface 47, due to the pressure. A pressurized medium within the pressure chambers 30 maintains a gap when flowing out of the chamber through flow openings 33 on the sliding surface 31. Because the edge surfaces 32 move away from the background surface during pressurization of the chamber 30, it is possible to implement a construction in which the chamber takes very little space once the pressure is released. Thus, such a lifting device takes very little space during the operation of a web forming machine.

Figure 5 shows a lifting device 10 according to the invention in a condition during the operation of a web forming machine. In this condition, the pressure chambers 30 are unpressurized and the bracket constructions are connected to each other. The frame is supported during the operation of the web forming machine with a protective structure 48, placed in connection with the lifting device 10, and with the actual bracket const- ructions. The main purpose of the protective construction is to prevent the operator from putting his/her fingers inside the lifting device when the pressure chambers are pressurized. By means of dimensioning, the edges of the protective structure are adapted to connect when the pressure is released. Thus the protective structure functions partly as a bracket construction. The actual bracket constructions are set around the lifting device. The bracket constructions can also be located on several sides in connection with the lifting device. The lifting device can be implemented in many ways according to the inven- tion and the same applies to the bracket construction. It is essential that the lifting device has a sliding surface provided with flow openings. On the sliding surface of the chamber, a sliding layer is adapted to be created with a medium which is adapted to discharge from the flow openings on the sliding surface. When the pressure is released from the chamber, the chambers do not support the frames any more making the bracket constructions to join.

The intermediate structure and the lifting device shown in Figure 5 are adapted as an integral construction which is removably fastened to between the vertical beams as one entity. In this case, replacing the lifting device for maintenance is simpler than before.

The sides a and b of the lifting device shown in Figure 5 measure about 900. In turn the height c of the lifting device is 400 mm. The diameter of the pressure chamber is about 700 mm.

The medium used in the lifting device is gasous in which case the fabrics to be replaced do not aspirate it becoming wet at the same time. Preferably, the medium is normal compressed air, in which case it can be freely released to the hall space. Air can be taken form the mill network or it can be pressurized with a separate compressor. Preferably, pressurization is performed with an inexpensive compressor, since the required pressure level can be, for example, 3 bar and the required flow can be 10 m3/min per each lifting device.

Figure 6 shows a lifting device according to the invention in a disassembled state. This allows a more detailed view of the main components of the lifting device. Particularly the design of the pressure chamber 30 is clearly visible from the figure.

The pressure chamber 30 is composed of an edge surface 32 and a sliding surface 31. The edge surface 32 surrounds the sliding surfaces 31 on each side. The shape and the design of the edge surfaces and the sliding surface can be very versatile. It is essential that a medium can discharge to the sliding surface from the flow openings on the sliding surface. The number of flow openings from which the medium is discharged, can be one or more. The exemplifying embodiment of Figure 6 has one flow opening 33. The sliding surface can be mainly at one or more levels. In the case of Figure 6, the sliding surface 31 is divided into three parts, which in Figure 6 are an edge part 50, a center part 52 and a hole part 54. The edge part 50 is lower than the center part 52. Similarly, the hole part 54 is lower than the center part 52. A medium is adapted to discharge to the outer surface 35 of the sliding surface 31 from the flow opening 33 in the hole part 54. The higher center part of the sliding surface can also include flow openings. The pressure chamber 30 is further adapted to be located within a band cycle created by the band 39 that is supported with rolls 43. When the pressure chamber 30 is located within a band cycle created by the band 39, the sliding surface 31 is in contact with the inner surface of the band cycle created by the band 39.

In Figure 6, the sides of the lifting device frame are provided with profiles for fastening elements . These profiles enable connecting the lifting device easily in place. In addition, the intermediate structure 26 and the lifting device 10 are adapted as an integral construction which is removably fastenable to between the vertical beams as one entity. Then the lifting device can be removed from its place as a whole. The lifting device thus creates a single entity as such which is replaced with a new one as required.

The lifting device according to the invention shown in Figure 6 can be implemented simple for its total construction. Then it is possible to replace individual components as well, such as the pressure chamber. The pressure chamber is an air cushion type chamber in which case the medium, i.e. air, discharging from it creates the sliding layer in connection with the pressure chamber .

Figures 7a - 7c show various embodiments of the lifting device 10 according to the invention. Each of them has benefits of its own, and they suit to very different applications. The embodiment shown in connection with Figures 3 - 6 has two chambers, and a band is present in connection with the sliding surfaces of both chambers. This is not the case in Figures 7a - 7c.

Figure 7a shows an embodiment which has two pressure chambers 30 facing each other, provided with a sliding surface 31 with a flow opening 33. Of these, in connection with the sliding surface 31 of the lower pressure chamber 30, there is a band 39 supported with guides 41, more precisely with rolls 43. This band can be rotatable by means of a drive or it can be non-dri- ven. Providing a drive helps, for example, in taking the fabric to between the sliding surfaces without separate actuators required for creating a gap.

Figure 7b shows an embodiment in which, when the fabric 24 is taken through the intermediate structure, the sliding surface 31 of the lifting device 10 is adapted against the fabric 24. The lifting device has two pressure chambers 30 facing each other, provided with a sliding surface 31 with a flow opening 33. When using pressure chambers 30 with flow openings 33 facing each other, without a band, a very simple embodiment is achieved. When the lifting device 10 is in the pressurized state, the fabric 24 is against the sliding surface 31. More precisely, the fabric 24 is supported by the sliding layer 37, created by a medium, on top of the sliding surface 31. Then the gap 45 is maintained by the lifting effect of the medium. In other words, the fabric 24 is not tightly attached to the outer surface of the sliding surface 31 but the sliding layer 37 created by the medium is between these. 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 can be maintained between the vertical beams through which the fabric can be pulled. The chamber construction of the lifting device is not sealed but the medium leaks controllably. In addition, the medium can be conveyed along with the fabric. With suitable dimensioning and medium pressure the lifting device operates as designed regardless of leaks . In the press section, where the fabric to be replaced is a felt, pressure is prefereably led through two pressure chambers. In other words, the medium is led from opposing pressure chambers to both, in which case a channel is included in con- nection with both chambers for leading the medium. Thus both chambers are pressurized directly. This 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. Then the pressurized medium lifts and separates the surfaces without generating forces that damage the fabric.

Figure 7c shows an embodiment having a pressure chamber 30 provided with a sliding surface 31 with a flow opening 33 set above the fabric 24, and a pressure chamber 30' defined by sealing elements 55 below the fabric 24. This embodiment can be well used in connection with a fabric that is permeable to a medium. Then the medium creates a pressure in both pressure chambers by which pressure the frame is supported. This allows pulling the fabric through the gap 45. The lifting device according to the invention can thus be provided with only one chamber with a sliding surface.

Figure 7d shows an embodiment which has two pressure chambers 30 facing each other, provided with a sliding surface 31 with a flow opening 33. Of these, in connection with the sliding surface 31 of the lower pressure chamber 30, there is a band 39 supported with rolls 43. The first one of the rolls is located on the machine side of the pressure chamber while the other roll is located on the front side of the web forming machine, seen from the pressure chamber. Such an arrangement is advantageous in connection with driven rolls in order to provide a large contact area between the fabric and the band.

When the fabric is taken through the intermediate structure, the sliding surface is adapted against the fabric. In other words, the sliding surfaces are immediately in connection with the fabric in which case the pressure of the medium keeps the fabric and the sliding surface or the fabric and the band surface separated from each other. The term 'sliding surface¹ is used to refer also to surfaces other than merely planes . The surfaces can as well be inwardly curved, for example. The surfaces can also include microshaping. Microshaping can improve fabric sliding between the sliding surfaces. 'Surfaces' refer widely to the area on which the pressure is exerted in the lifting device generating thereby a lifting force.

The lifting device has two surfaces between which the pressure affects . The pressure can be led to between the surfaces either through one or two surfaces. In the forming section, where the replaceable clothing is a fabric, the pressure can only be led through one surface, more precisely the pressure chamber 30

(Figure 7c) . In other words, the medium is led from opposing pressure chambers to only one, in which case a channel is included in connection with only one of the chambers for leading the medium. Such a simple structure is possible because the fabric (or wire) is permeable to the medium and the pressure can affect between the pressure chambers of the lifting device. Although only one of the chambers is directly pressuri- zed, both chambers are indirectly pressurized as the medium goes through the fabric (or wire) .

It is aimed to generate uniform pressure within the area of the sliding surface. The pressure can be equalized, for example, by leading the medium via several channels. However, multiple channels in connection with one chamber can complicate the design. For equalizing the pressure, the design of the pressure chamber can also be utilized. Seen from above, the pressure chamber can have a circular shape or it can be at least rounded from the corners. A more angular shape can be, for example, a parallelogram with the corners rounded in a large radius . Moreover, the pressure chamber can have an oval shape. The shape can thus be very freely modified according to the requirements of the application. Using a design without sharp corners, a more uniform pressure can be achieved within the area of the sliding surface.

It has been described above that the fabric can be pulled to a gap which is maintained with a lifting device. In such an embodiment, the fabric is pulled to the gap using a band that is rotated with driven rolls, for example. This embodiment is possible since the lifting device according to the invention enables gently sloping joining wall surfaces in the pressure chamber .

It is not always possible to pull the fabric to a gap which is maintained only with a lifting device according to the invention. In this case, a separate actuator can be used for creating the gap for putting the fabric in the gap. The actuator can be, for example, an overhead crane or a jack. The lifting device according to the invention can also include grabbing points in connection with it. In this case, an actuator, which is a jack, can be used to open a gap between the surfaces for putting the fabric thereto. Extensions can be used as the grabbing points. The jack is used to increase the interval between the exten- sions whereupon a gap is created between the sliding surfaces, too, to put the fabric thereto. Using a jack is simple and a jack is a reliable solution. In addition, the extensions required by the jack are easy to manufacture.

When a separate actuator is used for creating the gap, the use of the actuator is discontinued when the fabric has been taken to between the sliding surfaces of the lifting device. The term ' fabric ' is used here to refer to a fabric in a very wide sense. For example, pieces of fabric attached to a fabric are considered as a fabric. Such pieces of fabric can be used since in some cases it is easier to handle them than to handle a fabric. A fabric can also include a sealing system and protective surfaces . Sealing surfaces help control the flows and restrict the pressure to a desired range. Protective surfaces, in turn, prevent the fabric from damaging. Separate pieces of fabric can be used to prevent damaging of the actual fabric. As a whole, the actuator can be used to create and maintain the gap until a fabric is present between the pressure chambers of the lifting device. Once the fabric is present between the pressure chambers, the pressure chambers arranged on both sides of the fabric can be pressurized. When the pressure chambers are pressurized, the sliding surfaces move toward the fabric allowing the lifting device to maintain the gap created and enabling the fabric to be taken through the gap. Typically, in an embodiment in which a separate actuator is used for creating gaps, chambers are pressurized before removing the lifting effect of the actuator. In this way, a mechanical stress that would be otherwise temporarily subjected to the fabric, is avoided. Correspondingly, 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 lifting device, a mechanical stress otherwise temporarily subjected to the trailing edge of the fabric is avoided.

Preferably, the old fabric is removed intact from the machine. When the extensions are on both sides of the 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 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.

Below is a description showing how a fabric forming a closed loop is replaced with a new one by utilizing a lifting device according to the invention without cutting the old fabric. First, a gap is created between the pressure chambers using an actuator external to the frame as seen from the machine. This creates a gap between the support constructions and the pressure chambers. After this, the fabric is threaded to between the pressure chambers . Once the fabric is completely in the area between the pressure chambers, the lifting device is pressurized and the pressure is released from the actuator. As the pressure chambers are pressurized, a sliding layer is created on their sliding surface. The lifting device maintains the gap between the pressure chambers for pulling the fabric therethrough. Thereafter, the fabric is drawn out of the machine between the pressure chambers and thus between the sliding surfaces. Even with the fabric removed, the pressurization of the pressure chambers is maintained and the surfaces are kept separated until the pressure is released from the chambers . Thus a sliding layer is present between the sliding surfaces keeping the sliding surfaces separated. 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 pressure chambers in the lifting device using the actuator located on the machine side. The fabric to be placed in the machine is placed in the gap thus formed. When the fabric is within the gap, the lifting device is pressurized again and the pressure of the actuator located on the web forming machine ' s roll assembly side is released. After the actuator, such as a jack, has been removed, the fabric is pulled in place. Finally, the pressure of the pressure chambers is released and the support constructions become connected. After this the web forming machine is again ready for use. Support constructions can include separate support pieces enabling a wider gap in the machine frame .

The application method described in the previous chapter is only one alternative and variations can be made in it as re- quired. If fabric damaging is a risk when pulling the fabric out from between the pressurized pressure chambers, it is possible to use an actuator for maintaining the gap between the pressure chambers before pulling out the fabric edge. In this case no harmful forces are exerted on the fabric. Attached to the fabric, there may also be a piece of fabric, which comes out last from between the pressure chambers . Thus 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. Sealing and protective surfaces possibly located in connection with the fabric also prevent the fabric from being damaged. Protective surfaces can be, for example, metal surfaces covering the fabric for the part going through the lifting device. Metal protective surfaces function at the same time as sealing surfaces although protecting is their main function.

In the above description, an actuator is included in connection with the intermediate structure, and the fabric is taken to the gap which is maintained by the actuator. The actuator can be, in addition to what is described above, a lifting device accor- ding to the invention. In this case there are at least two lifting devices in the cross direction of the web forming machine. The first lifting device is used to create a gap between the pressure chambers present in the second lifting device. After this, the fabric is pulled to the gap thus for- med. Then the second lifting device is pressurized and the pressure is released from the first one, whereby it is possible to pull the fabric to the gap between the pressure chambers of the first lifting device. The pressure chamber can thus be used correspondingly as an actuator in the same way as any other actuator.

A fabric removed from a web forming machine can additionally be cut. Then the cut fabric can be removed using a crane or pulled to the basement out of the machine without creating a gap in the vertical beams. In this case, a lifting device is used during fabric replacement only for putting a new fabric in place.

There may be several lifting devices according to the invention in connection with one vertical beam also in the machine direc- tion. This construction stabilizes their operation. In addition, the support constructions can have orienting profiles in which case the profiles of the support constructions guide the support constructions to join as desired when the gap is closing.

A central advantage of the invention is that a similar construction can be used in connection with fabrics of several different types. Furthermore, the invention enables at the same time abandoning several custom-made components, which addi- tionally allows putting the component manufacturers under competition more efficiently. In practice, fabric replacement is performed through a medium, in which case the replacement is almost frictionless . In other words, less force is needed than before for transferring the fabric. Also, the pressure applied to the fabric is uniform in the entire area defined by the sealing elements, in which case harmful pressure peaks are avoided. With a lifting device, exerting harmful force on the fabric is thus avoided.

It is also possible to contemplate leading the medium directly to between planar, low-surface and possibly microshaped frame surfaces for reducing the friction. In this case the frame surfaces are sliding surfaces provided with flow openings.

With edge surfaces, various constructions are widely referred to, which define a sliding surface provided with a flow opening. Edge surfaces can be flexible, made of rubber, for example. Such rubber edge surfaces deform due to pressure. Edge surfaces can also be shape-permanent, made of metal, for exam- pie. Metal edge surfaces do not notably deform due to pressure. The shape of the edge surfaces and the sliding surface can vary. Like for the edge surface, the material of the sliding surface can also be shapable or non-shapable, such as steel or bronze. This depends on the application. For the invention, it is essential that the sliding surface defined by the edge surfaces has flow openings for the medium. A flowing medium reduces the contact between opposed sliding surfaces . It is notable that friction reduces even though a great gap is not formed.

The frame lifting movement can be implemented with a different actuator, and the lifting device according to the invention is suitable, for example, for a metal belt calender with light frame constructions. In a calender, the back side can even carry/relieve the front side load during the belt introduction. The pressure of the medium can be distributed to both sliding surfaces through multiple flow openings. The flow openings, i.e. pressure connections, can be holes, possibly counterbores or cavities. Holes or other flow openings may be joined by cavities. Each flow opening forms a small pressure chamber that supports the fabric/belt.

Claims

1. A system for replacing a fabric/belt in a web forming machine, including - a fabric/belt (24) that forms a closed loop, vertical beams (20) for supporting rolls and equipment of the fabric/belt loop (24) , and an openable intermediate structure (26) between the vertical beams (20) , with the intermediate structure (26) including a lifting device (10) which further includes a pressure chamber (30) partially- defined by edge surfaces (32), and with the fabric/belt (24) being adapted in the system so as to be taken through the intermediate structure (26) while the pressure chamber (30) is pressurized with a medium (34), characterized in that the pressure chamber (30) includes, between the edge surfaces (32), a sliding surface (31) provided with one or more flow openings (33), which sliding surface has an outer surface (35), with the flow openings (33) being adap- ted to open to the outer surface (35) for creating a sliding layer (37) with a medium (34) discharging from the flow openings (33).

2. A system according to claim 1, characterized in that when the fabric/belt (24) is taken through the intermediate structure (26) , the sliding surface (31) is adapted against the fabric/belt (24) .

3. A system according to claim 1, characterized in that when the fabric/belt (24) is taken through the intermediate structure, the sliding surface (31) is adapted against a band (39) included in the lifting device (10) .

4. A system according to claim 3, characterized in that the surface of the band (39) contacting the sliding surface (31) has low friction.

5. A system according to claim 3 or 4, characterized in that the lifting device includes guides for supporting the band.

6. A system according to any of claims 1 - 5, characterized in that the medium (34) is gasous.

7. A system according to any of claims 1 - 6, characterized in that the intermediate structure (26) and the lifting device (10) are adapted as an integral construction that is removably fastened to between the vertical beams (20) .

8. A system according to any of claims 1 - 7, characterized in that the lifting device (10) includes two pressure chambers (30) with the sliding surfaces (31) thereof adapted against each other, and the fabric/belt (24) is adapted to be taken between the pressure chambers (30) while the pressure chambers (30) are pressurized with the medium (34) .

9. A lifting device used for replacing a fabric/belt in a web forming machine, including a pressure chamber (30) with edge surfaces (32) , and the fabric/belt (24) is adapted to be taken through the lifting device (10) while the pressure chamber (30) is filled with a pressurized medium (34) , characterized in that the pressure chamber (30) includes, between the edge surfaces (32), a sliding surface (31) having an outer surface (35) , and the sliding surface (31) is provided with flow openings (33), and a sliding layer (37) is adapted to be formed on the outer surface (35) of the sliding surface (31) with a medium (34) , which is adapted to discharge from the flow openings (33) in the sliding surface (31).

10. A method for replacing a fabric/belt in a web forming machine, and the web forming machine includes a fabric/belt

(24) that forms a closed loop and is supported as a fabric/belt cycle with rolls supported to vertical beams (20) , and between the vertical beams (20), an openable intermediate structure (26) is used which includes a lifting device (10) provided with a pressure chamber (30) , and the pressure chamber (30) is partially defined by edge surfaces (32), and the pressure chamber (30) is pressurized with a medium (34) , and the fab- ric/belt (24) is taken through the intermediate structure (26) while the pressure chamber (30) is pressurized, characterized in that a sliding surface (31) having an outer surface (35) and provided with one or more flow openings (33) is used in the pressure chamber (30), between the edge surfaces (32), and the flow openings (33) are adapted to open to the outer surface (35) , and a sliding layer (37) is created with the medium (34) discharging from the flow openings (33) .

11. A method according to claim 10 where a gap (45) is main- tained with the pressure chambers (30) , characterized in that the fabric/belt (24) is pulled to the gap (45) confined by the pressurized pressure chamber (30) .