The present invention relates to a method for replacing a used dryer fabric in a plant for drying of a web-formed material, preferably a paper web, wherein the web-formed material is heated by heated cylinders, against which the web-formed material is pressed with the aid of a dryer fabric, which cylinders are arranged inside a housing which completely or essentially completely surrounds the drying plant.

The present invention also relates to a device for carrying out the method.

Web-formed materials, such as paper or pulp, are usually dried either in a contactless manner by blowing hot air against the web-formed material or by contact with heated surfaces, primarily cylinders. In cylinder drying of a web-formed material, for example paper, the web-formed material is heated by heated cylinders against which the web-formed material is pressed by the web tension and/or with the aid of a fabric. The term fabric is in the following used to describe any type of felt or wire in any material suitable to be used in the drying of a web-formed material such as paper. The dryer fabrics are subjected to considerable stresses and have to be replaced relatively often. This is a laborious, time-consuming and space-demanding procedure. Since, for example, paper dryers are very large, usually not only a lower dryer fabric and an upper dryer fabric are used but the drying plant may be divided into 6-8 dryer sections with separate fabrics. The shutdown periods for replacement are then often very long and the loss of production is considerable.

All drying of paper or pulp entails discharging large quantities of steam from the material. To create a tolerable working environment and to save energy as far as possible, the drying plants are therefore enclosed in housings, below named hoods, which are almost completely closed and where supply air and exhaust air are controlled such that any leakage through the openings of the hood, inter alia when feeding the paper web, or the like, in and out, passes from the outside and inwards.

When replacing dryer fabrics, this hood is, of course, an obstacle and inversely the hood has to be adapted such that new fabrics may be passed in and the worn fabrics be taken out. Since the dryer fabrics are heavy, lifting devices must, in practice, be provided inside the hood. To make possible this and to make room for personnel to work inside the hood, the hood must be made considerably higher than what is justified by the drying plant itself.

In US 5,823,462 an improved method for exchange of e.g. a dryer fabric is recently revealed. It is said to be directed to use an exchange device for a transport belt utilized in, e.g. a dryer section of a machine for the production of a web of material. The exchange device includes a spooler that removes a used transport belt and that inserts a new transport belt. The spooler is supported by a mobile carrier device that moves the spooler, guided via a roller device, to a predetermined location inside the dryer section for exchanging the transport belt. This particular arrangement obviates the need for a separate installation to serve the exchange device within the machine using the transport belt. Thus, a machine prepared for an exchange device according to this invention may be constructed to use up less space and be more cost efficient than the prior art devices.

The method includes moving a carrier device to a predetermined location for the transport belt exchange, moving the carrier device into the web production machine, perpendicularly to the running direction of the web, and moving the spooler into the machine by the roller device, also perpendicularly to the running direction of the web and then rolling up the used transport belt, and inserting the new transport belt. Because the carrier device may be brought to a predetermined site where the transport belt exchange is to occur, permanent foundations specifically dedicated to carry an exchange device within the web production machine are no longer necessary.

This method may save some space and cost but still has some of the major disadvantages of the earlier known methods, e.g. space required in the premises and that personnel are forced to work inside the dryer hood.

It is a main object of the present invention to provide a simple and reliable method for replacing a fabric in a plant for drying of a web-formed material.

It is a second object of the present invention to provide a simple method for replacing a fabric in a plant for drying of a web-formed material with a considerably reduced length of the shutdown period during the fabric replacement.

It is a third object of the present invention to provide a simple method for replacing a fabric in a plant for drying of a web-formed material with considerably reduced disturbance to other activities in the premises during the fabric replacement.

It is a fourth object of the present invention to provide a simple and reliable method for replacing a fabric in a plant for drying of a web-formed material, which permits a saving of space by reducing the height of the hood which surrounds the drying plant.

It is a fifth object of the present invention to provide a simple and reliable method for replacing a fabric in a plant for drying of a web-formed material without forcing personnel to work inside the hood.

In addition, it is an object of the invention to suggest a device suitable for use with the embodiment of the method.

The present invention relates to a method for replacing a used dryer fabric in a plant for drying of a web-formed material, preferably a paper web, wherein the web-formed material is heated by heated cylinders, against which the web-formed material is pressed with the aid of a fabric, which cylinders are arranged inside a hood which completely or essentially completely surrounds the drying plant.

A new fabric is placed, in reeled-up state, in an unreeling device. A used fabric, present in the drying plant, is cut, with an essentially transverse section, thus opening a loop. One of the ends of the used fabric, created by the cutting, is attached to an end of the new fabric. The other end of the used fabric is attached to a reeling device. The new fabric is pulled into the drying plant and the used fabric is reeled up with the reeling device. The new fabric is detached from the used fabric and from the unreeling device, when the new fabric has been pulled, completely or almost completely, into the drying plant, and the two ends of the new fabric are joined together, thus forming a closed dryer fabric loop.

In the method according to the invention, the new fabric is placed, in reeled-up state, on the roof of the hood, in an unreeling device movable along the roof of the hood and an opening is made in the roof of the hood over essentially the whole width of the hood, or at least exceeds the width which corresponds to the fabric. One of the ends of the used fabric, created by the cutting, is attached to one end of the new fabric, by passing one of said ends through the opening in the roof. The other end of the used fabric is attached to a connecting element on a reeling device on the roof of the hood, which reeling device is movable along the roof, by passing one of said ends of the used fabric or the connecting element through the opening in the roof. The drive system of the drying plant is run at a crawl, thus pulling the new fabric into the drying plant and the used fabric is reeled up with the reeling device on the roof of the hood.

The present invention also relates to a device for carrying out the above method in a drying plant, with a hood which completely or essentially completely surrounds the drying plant.

The device comprises at least one hatch or the like in the roof of the hood covering an opening over essentially the whole width of the hood, or at least over the width corresponding to the fabric and a carriage, the width of which corresponds essentially to the whole width of the hood, or at least exceeds the width which corresponds to the fabric. Means on the roof of the hood, intended for cooperation with wheels or the like of the carriage, permit movement of the carriage along the hood, that is, in a direction parallel to or anti-parallel to the principal direction of movement of the web-formed material. The carriage includes an unreeling device adapted to carry a reeled-up new fabric and to brake the unreeling, as well as a reeling device provided with a drive device to reel up a used fabric.

The present invention thus relates to a method and a device for replacing a used dryer fabric in a plant for drying a web-formed material, preferably when drying a paper web in a cylinder dryer plant. The drying of the web-formed material takes place at least substantially inside a hood, which completely or essentially completely surrounds the drying plant. In this context, as mentioned before, fabric means any form of cloth, felt or the like which supports the web-formed material and with the aid of which the web-formed material is pressed against, for example, heated cylinders.

In known methods for replacing a dryer fabric, the new fabric is brought into the hood in reeled-up state, often through doors in the vertical hood walls and the actual replacement operation takes place using personnel and lifting devices inside the hood. This is a time-consuming and trying operation which also to a great extent blocks space at the side of the hood.

According to the present invention, it is therefore suggested that a new fabric should instead be placed, in reeled-up state, on the roof of the hood and that the new fabric should be fed into the drying plant through a sufficiently wide opening in the roof of the hood while at the same time feeding out the old fabric through the same opening and reeling up said fabric. To carry out this, the old, used fabric in question is cut off, such that the loop previously formed by the fabric is opened. This "cutting" may, of course, advantageously take place in a prepared position on the fabric. One of the created ends of the used fabric is attached to an end of the new fabric and the other end of the used fabric is attached to a reeling device on the roof of the hood. The unreeling device, for the new fabric, and the reeling device, for the used fabric, are suitably arranged on a carriage which is movable along the roof of the hood. The roof is advantageously provided with means, such as rails or the like, to facilitate the movement for the carriage.

In or adjacent to the opening in the roof of the hood, the new fabric suitably makes contact with one or more supporting rolls cooperating with the unreeling device and the used fabric makes contact with one or more supporting rolls cooperating with the reeling device to secure free passage through the opening. Instead of using supporting rolls, it is also possible to use, for example, guide vanes and/or supporting plates.

With the drive system of the drying plant moving at a crawl, the new fabric is thereafter pulled into the drying plant while at the same time reeling up the used fabric with the reeling device on the roof of the hood. When the old fabric has been pulled, completely or essentially completely, out of the hood, and the new fabric has been pulled, completely or essentially completely, into the drying plant, the new fabric is detached from the used fabric and from the unreeling device and the two ends of the new fabric are joined together so as to form a closed dryer fabric loop, whereupon the opening is closed.

If more than one dryer fabric is to be replaced, the method is repeated at two or more openings. The carriage may then be moved between the openings along the hood, resting with wheels, or the like, on rails or similar means to facilitate the movement, and its position is fixed at each opening with locking elements adapted thereto.

The invention will now be described in greater detail with reference to the accompanying drawings, wherein

• Figures 1 to 8 schematically show an embodiment of the invention step by step.

Figure 1 shows a simplified vertical section of a drying plant 1 for paper comprising a dryer section 2, in a hood 1a with a roof 1b consisting of a ceiling 3 and an outer panel 4. On the roof there is a carriage 5 which is capable of being moved along the roof 1b by means of wheels 14 resting on means (not shown).

The dryer section 2 comprises a dryer fabric 6a, a plurality of drying cylinders 7, a plurality of guide rolls 8, between the drying cylinders 7, and fabric rolls 9 over which the dryer fabric 6a is closed in a loop.

The roof 1b is openable by means of a hatch 4a in the outer panel 4 and a detachable section 3a in the ceiling. The hatch 4a consists of one or more removable panel elements. The entire outer panel may, for practical reasons, be built up of such removable elements.

The carriage 5 comprises an unreeling device 10 for a new fabric 6b and a reeling device 11 for the used fabric 6a.

Figure 2 shows a corresponding vertical section with the panel hatch 4a and the ceiling section 3a removed, thus forming an opening 43.

Figure 3 shows a corresponding vertical section with the carriage 5 placed across the opening 43. The carriage 5 is provided with upper supporting rolls 13 for the unreeling and reeling, respectively, of the fabrics and corresponding lower supporting rolls 12 are arranged near the used fabric 6a. These lower supporting rolls 12 may be part of the dryer section 2 or be connected to the carriage 5 by means of suitable elements (not shown).

Figure 4 shows the new fabric 6b, partly unreeled from the unreeling device 10, and a corresponding connecting element 6c, partly unreeled from the reeling device 11, so that the respective ends are close to the fabric 6a present in the dryer section 2.

Figure 5 shows how the fabric 6a, present in the dryer section 2, has been cut with an essentially transverse section so that the loop has been opened and that the respective ends have been connected to the new fabric 6b, which is partly unreeled from the unreeling device 10 and the connecting element 6c, which is partly unreeled from the reeling device 11.

Figure 6 shows a position where the new fabric 6b has been partly pulled into the dryer section 2, unreeled from the unreeling device 10 and a corresponding piece of the old fabric 6a has been pulled out of the dryer section 2 and reeled up onto the reeling device 11.

Figure 7 shows a position when the new fabric 6b has been completely pulled into the dryer section 2, unreeled from the unreeling device 10 and the whole of the old fabric 6a has been pulled out of the dryer section 2 and reeled up onto the reeling device 11.

Figure 8 shows the corresponding position when the new fabric 6b has been completely pulled into the drying section 2, and the new fabric 6b has been detached from the unreeling device 10 as well as from the old fabric 6a, and the released ends, of the new fabric 6b, have been joined together so that the new fabric 6b forms a closed loop around drying cylinders 7, guide rolls 8 and fabric rolls 9.

According to the proposed method, the carriage 5 is thereafter moved from its position across the opening 43 and the opening 43 is closed by placing the ceiling section 3a and the hatch 4a in the outer panel 4 in position. If any further fabric is to be replaced, the method is repeated with the carriage 5 in a new position across another opening.

The invention is not, of course, limited to the embodiment described above, but may be varied in a plurality of ways within the scope of the following claims.