When starting a paper machine after a stoppage or a web break, the paper has to be passed through the machine again. Thus, from the edge of the paper web, a narrow edge strip is separated, which is first run through the machine. When the edge strip is made to travel through the machine or part of the machine, it can be spread to a full-width web.

There are various guide systems available to make the edge strip follow the path of paper web travel formed by cylinders and rolls. Generally, in that case, rope systems, so-called threading ropes, are used, which travel outside the web egde, the tail being guided in between the ropes.

On-line threading of the edge strip with fast-running paper machines is a problem, especially if the line involves processing devices which require complicated transfers. It is difficult to guide a fast moving tail along the correct path. Similarly, the fact that the tail tends to break when it hits obstacles during its travel, poses a problem.

In addition to the conventional rope transfer, attempts have been made to solve the problem with different belt support devices, air blows, suction devices, etc. These devices do help to achieve successful threading in relatively straightforward and simple transfers, but e.g. for an on-line calender they do not provide an adequate solution.

Thus, the tail plays an important role in the beginning of the production run of the paper machine, and its transfer must proceed without disturbance. The tail itself should be strong enough to sustain the mechanical stresses of web feeding and not to break for example when hitting obstacles. Especially in the edge zone of the paper web, the strength of the web is a problem also in other respects, and thus, to strengthen the tail, Finnish patent 72550 suggests feeding of auxiliary pulp on the edge area of the paper web for strengthening the edge strip and also for reducing the tendency of the paper web to break in the

production run. This requires changes in the feeding of the pulp in the headbox, or a particular device for feeding the auxiliary pulp.

The purpose of the invention is to present a method for strengthening either the edge strip or the full-width paper web, without a need for special auxiliary pulp, wherein threading becomes more reliable. To attain this purpose, the method according to the invention is primarily characterized in what will be presented in the characterizing part of the appended claim 1. The thickness of the paper web, i.e. the thickness of either the full-width paper web in the production run or the tail can be increased simply by folding it double along its longitudinal direction at least on part of its width.

The device according to the invention is, in turn, characterized in what will be presented in the characterizing part of the appended claim 10. A folding device, equipped with a guide surface turning the edge of the web, can be placed in a suitable location in the machine, in the case of threading after a device of separating the tail before threading guiding means.

As for the other preferred embodiments of the invention, reference is made to the appended dependent claims and the description hereinbelow.

In the following, the invention will be described in more detail with reference to the appended figures, in which Fig. 1 shows a cross-section of a tail produced with the method according to the invention, Fig. 2 shows a cross-section of a tail according to a second alternative, Fig. 3 shows a device according to the invention schematically, and Fig. 4 shows an implementation of the device viewed in a direction perpendicular to the plane of a web.

In this context, the following terms will be used for the different parts: Paper web: all continuous, web-like materials travelling in machine direction, either a full-width web, or any web narrower than that, such as a tail.

Tail: a narrow part separated from a wider paper web for threading.

Full-width web: a paper web travelling through the machine in the production run of paper.

In the method according to the invention, threading is performed with a rope method known as such, but the tensile strength of the tail T is increased for the duration of threading by folding it double at a line L extending in the longitudinal direction of the tail. it is possible to perform folding in at least two different ways. Fig. 1 shows a method of folding the tail T double at one longitudinal line L. Thus, the thickness of the tail increases at least on some part of the width of the folded tail.

Consequently, the edges do not have to meet, but the main objective is to increase the thickness of the tail at least in the zone where the tail touches threading ropes or is otherwise subjected to mechanical stress.

Fig. 2 shows a second method, in which the tail T is folded by turning the edge zones of the tail to the middle towards each other at two parallel folding lines L. Thus, the edges of the tail material can also overlap in the middle of the tail.

The edge of the tail is usually more or less rough and contains cracks, wherein it tends to tear easily. Thus, the folding strengthens the edge of the tail by making it intact and double. Thereby the method substantially improves the tensile strength and tear resistance of the tail.

Other advantages of the method include: - Applicability also in existing machines to enhance threading for example in coating sections, calenders and finishing devices in general.

- The method does not utilize glues, adhesive tapes and other materials that increase risks/purification needs.

- The tendency of the tail to stick to solid obstacles is reduced, because the tail is narrower, and the edge is straight and smooth, resulting in a smaller friction.

- The method increases the stiffness of the tail, wherein it stays better on the rolls and does not wander off.

- The speed of the threading ropes can be somewhat increased from the nominal rate to remove slacks/bags, because the tail holds better.

Fig. 3 shows a device according to the invention. In the figure, a folding device 2 is located in the direction of the travel of the paper web after a diagonal cutter 1, which separates, in a way known as such, from the edge area of the web a tail T, having the width of ca. 15 to 50 cm, which is guided forward with auxiliary means known as such, in a gap between threading ropes 3a, 3b, the rest of the web being guided to the pulper. The figure shows the location of the device in the end of the drying section before the calender, but basically, the device can be placed in any location of the machine where above-described problems occur.

The folding device 2 contains a suitably shaped guide surface 2a which rubs against the edge of the tail T and turns (by ploughing) it gradually to a curved shape to such an extent that it folds when it touches the next solid surface which is in contact with the tail. The guide surface 2a is located and shaped in such a way that it touches the travel path of the tail in the edge zone of the tail T and constantly deviates the same more and more off the original direction and towards the other edge of the tail. The guide surface thus contains, in the direction of travel, successive points of contact to the tail, which are directed more and more towards the middle to turn the edge of the tail to a wider angle with respect to the initial direction, as viewed in cross-section. The guide surface 2a can be formed of short successive sections, or it can be continuous, wherein it is preferably made of a plate material. The plate can be perforated for pressurized air supply or treated in other ways to reduce friction between the paper and the plate.

The guide surface 2a is followed as soon as possible by a surface against which the egde of the tail finally folds. The tail can fold into the

final shape according to Fig. 1 or 2 against the surface of a cylinder located after the guide surface 2a and being one of the standard parts of the machine, such as a drying cylinder 4 presented in Fig. 3. The edge of the tail can be turned either onto the side of the cylinder surface (the alternative shown in Fig. 3), or to the opposite side with respect to the cylinder. A continuous support means 5, such as a wire or a textile fabric presses the tail left in between into its shape, if the effect of the cylinder is not sufficient. For the folding, it is also possible to arrange a special nip between two surfaces, which can be a nip formed by two rolls arranged for this purpose in particular, or a nip between an existing cylinder and an auxiliary roll. Possible auxiliary rolls and nips can be integrated in the same structure with the guide surface/s 2a and they can function as extensions to these surfaces.

Similarly, all means present in the folding can be arranged with the help of actuators known as such, to be moved to a folding position in contact with the tail, and off the contact to a passive position. In Fig. 3, the structure supporting the guide surface is on the opposite side of the tail T with respect to the next cylinder 4, but it can also be located on the same side with the cylinder 4 When one fold is formed according to Fig. 1, the edge of the strip is turned preferably on the side of the middle area of the web, i.e. the edge cut by the diagonal cutter is turned towards the outer edge of the web. Thereby the edge remains closer to the side of the machine and the edge subjected to the draw is intact.

When producing two folds according to Fig. 2, it is possible to use a device in which the guide surfaces 2a are on opposite sides of the tail T, or two successive devices can be used, wherein one edge is folded first and after that the opposite edge.

The device can also be integrated in the diagonal cutter 1, wherein it is provided with a corresponding guide surface for turning the edge of the tail T, as well as possibly a nip for performing the final folding. The guide surface can be turned away from the travel path of the paper web during diagonal cutting. If the guide surface 2a is located on that side of the tail which is located in the middle area of the paper web, and it is arranged to turn the edge cut by the diagonal cutter towards the outer

edge of the tail, it can be kept in function also during diagonal cutting when spreading the tail, wherein a double thickness remains constantly on an area with a certain width at the edge on the side of the diagonal cutter when diagonal cutting proceeds, and a strong edge is achieved in that area. Fig. 4 shows schematically the arrangement in question, viewed from the direction of arrow IV in figure 3, and it also shows a nip N which performs the final folding.

The device is to be placed in a location where there is tension in the web, e.g. as in Fig. 3, before the first drying cylinder 4, so that folding according to the description above, performed with the ploughing method, would be successful, i.e. there is draw in the tail/spreaded web. After the last drying cylinder 4, the tail is guided through a calender by means of threading ropes 3a, 3b.

The invention also covers the idea, whereby the tail can also be folded three-fold, wherein the edge skirts of Fig. 2 would overlap each other on a wide area in the middle of the folded tail. Similarly, the folding could have a Z-shaped cross-section. A sufficient increase in the strength without an excessive increase in the bending stiffness of the tail is best achieved with a folding which produces double thickness.

Furthermore, the invention is not restricted solely to the threading of a paper web, but it can also be used in the production run to strengthen the edge of the web in some parts of the machine. Thus, in this context a paper web transfer refers to the transfer of a full-width paper web or part of the paper web, i.e. the tail, separated with a diagonal cutter.

During the production run, one or both edges of the web can be folded, wherein folding is naturally performed by using the guide surface 2a of the folding device 2 at the edge of the web to turn a part of a particular width, e.g. only approximately 5 to 10 cm, towards the middle. In the folding, it is possible to use similar parts of the paper machine following the folding device 2, as on the tail T. The thicker edge zones thus formed can later be separated from the web. The folding device/s 2 can operate only during the production run, and the threading can be performed in another way.

Folding can be used both during threading and during the production run. In this case it is advantageous to use the same folding devices.

For example, the alternative described above in connection with diagonal cutting, is well applicable. The guide surface 2a which folds the tail T is, in this case, integrated in the diagonal cutter, and after diagonal cutting the same guide surface 2a remains in operation on the edge of the full-width web. On the opposite edge, i.e. on the edge on the side of the tail, there is another folding device 2 whose guide surface 2a similarly turns the edge towards the middle. This folding device can be be moved to its operational position at the desired moment, i.e. it can start to operate already during diagonal cutting. It can also operate already during threading, in the folding of the tail T, wherein the result is a tail according to Fig. 2, folded from both edges to the middle.

In this context, paper machine refers to all machines which produce paper-based material in the form of a continuous web from a fibrous raw material, irrespective of the grammage, in other words also to board machines, as well as to paper web finishing machines too.