EP0468005B1 - Arrangement for guiding a web from the press part to the dryer part of a papermaking machine - Google Patents

Abstract

PCT No. PCT/EP91/00049 Sec. 371 Date Oct. 2, 1991 Sec. 102(e) Date Oct. 2, 1991 PCT Filed Jan. 15, 1991 PCT Pub. No. WO91/12370 PCT Pub. Date Aug. 22, 1991.Arrangement for the transfer of a paper web from the press section 10 to the dryer section 20 of a paper machine, where a water-absorbent felt belt 11 of the last press 13, 14 has at the same time the function of a transfer felt 11; i.e., the transfer felt 11 transports the paper web 9 from the press section 10 to the dryer section 20. There, the transfer felt serves to force the paper web onto at least the first drying cylinder 21. This drying cylinder and additional drying cylinders 22 lie therefore outside the continuous loop of the transfer felt 11.

Description

The invention relates to an arrangement for transferring a fibrous web, preferably paper web (hereinafter referred to as "web"), from the press section to the dryer section of a paper machine, in particular with the features specified in the preamble of claim 1. According to this, it is an arrangement in which an endless belt running through the last press nip of the press section, which is designed as a water-absorbent felt belt, has a double function: the felt belt takes at least part of the im-press nip from the web in the usual way squeezed out water to remove it. In addition, this felt belt guides the web from the press section into the dryer section, running together with the web at least over the first dryer cylinder of the dryer section. This felt tape is therefore called "transfer felt" below.

Such an arrangement is known from EP 0346659. It has the following features in detail: The last press of the press section has only a single felt belt, namely a bottom felt, which at the same time has the function of the transfer felt. The web to be dewatered thus comes into direct contact with the top roller of the last press. This top roller therefore has a smooth and generally hard outer surface, for example formed from granite or artificial stone. It is generally known that in such an arrangement the web adheres to the top roller a little behind the press nip and with a certain tension from the top roller must be deducted. The web runs at least a short distance, ie without support from the transfer felt. In addition, it is inevitable that the web, which is still relatively damp there and therefore has only a low strength, suffers a certain longitudinal expansion. This longitudinal stretching is undesirable because it has a negative effect on the quality properties of the finished web; for example, this results in an undesirable cross-contraction of the web. To make matters worse, the aforementioned longitudinal expansion takes place unevenly over the web width; because the edges of the web are usually stretched more than the central area of the web. This creates uneven quality properties of the finished web, measured over the web width.

Another feature of the proposal mentioned is that the first drying cylinder of the dryer section is arranged within the loop of the transfer felt. The web therefore does not come into direct contact with this first drying cylinder. This results - particularly at high working speeds - in the danger that the paper web will lift off from the transfer felt due to the centrifugal force on the first drying cylinder.

An arrangement is known from US Pat. No. 4,648,942 in which the last press has the following features: the web runs there between two felt belts through the press nip and from there to a separating device arranged in the bottom felt; there the upper felt detaches from the web, which continues with the lower felt, until it is transferred to the drying section by means of the first dryer fabric of the dryer section and by means of a suction suction roll. In the last press, the lower roll is designed as an extended-nip press roll; ie this roller has a flexible, rotating (tubular or band-shaped) and liquid-tight pressing element, which by means of a Press shoe is pressed onto the top roller. A disadvantage of this arrangement is that the web comes into contact with the relatively hard and coarse dryer fabric very early, ie while it is still relatively moist and soft. As a result, there is a risk that the dryer fabric leaves permanent impressions in the paper web. Such embossings may be accepted for coarse paper types, which are intended for packaging purposes, for example, but not, for example, for printing and writing papers. In addition, the adherence of the paper web to the relatively coarse surface is not always guaranteed, especially at high speeds.

• 1. Eine Längsdehnung der Bahn soll mit Sicherheit vermieden werden; d.h. die Bahn darf sich an keiner Stelle frei (d.h. ohne Stützung durch ein mitlaufendes Band) fortbewegen. Dies gilt für die Pressenpartie, für den Bereich zwischen der Pressen- und der Trockenpartie und zumindest für den Anfangsbereich der Trockenpartie. Somit darf die Bahn in der Pressenpartie nicht in direkten Kontakt mit einer glatten und harten Walzen-Mantelfläche kommen, von der sie unter Aufwendung einer gewissen Zugspannung abgezogen werden müßte.
• 2. Die Bahn soll erst möglichst spät mit einem Trockensieb in Kontakt kommen, um der Gefahr bleibender Einprägungen vorzubeugen.
• 3. Die Anordnung soll insbesondere für die Herstellung feiner Papiersorten (z.B. von Druck- und/oder Schreibpapieren), darunter auch relativ dünner Papiere bei extrem hohen Geschwindigkeiten (Größenordnung 2000 m/min oder darüber) geeignet sein.

The invention is based on the object of specifying an arrangement for transferring a web from the press section to the dryer section of a paper machine which meets all of the following requirements:

• 1. A longitudinal stretching of the web should be avoided with certainty; ie the web must not move freely at any point (ie without the support of a moving belt). This applies to the press section, for the area between the press section and the dryer section and at least for the initial area of the dryer section. Thus, the web in the press section must not come into direct contact with a smooth and hard roll surface, from which it would have to be pulled off using a certain tensile stress.
• 2. The web should only come into contact with a dryer fabric as late as possible to prevent the risk of permanent impressions.
• 3. The arrangement is intended in particular for the production of fine types of paper (for example printing and / or writing papers), including relatively thin papers at extremely high speeds (of the order of 2000 m / min or above).

This object is achieved by the characterizing features of claim 1.

The essence of the invention consists in the combination of the previously only individually known features, namely guiding the web through the last press of the press section between two belts (of which the "first belt" as before also functions as the transfer felt running from the press section to the dryer section has) and separating the web from the "second belt" by means of a separating device which works in such a way that a free web tension is avoided. This achieves two effects at the same time: firstly, any longitudinal stretching of the paper web within the press section and when transferring it to the dryer section is avoided; on the other hand, the transfer felt is heated as it runs over at least the first drying cylinder of the dryer section, so that it returns to the last press at a higher temperature than before. This increases the drainage capacity of the last press; because the heated felt now has a lower flow resistance for the water to be absorbed from the paper web.

These advantages mentioned, namely the elimination of the longitudinal stretching of the paper web and the increase in the dewatering capacity of the last press, now work together in such a way that an above-average increase in the working speed is possible in the manufacture of the above-mentioned fine paper types (including in particular thin paper types), namely on Values around 2000 m / min or above. Furthermore, since the transfer felt works primarily as a wet felt and must therefore have a relatively fine structure, the paper web adheres better to the felt in the transfer lines, especially at the planned high working speeds.

In claim 2 an important further idea of the invention is given. Thereafter, in addition to the functions already mentioned, namely water absorption in the last press nip and transfer of the web into the dryer section, the transfer felt performs a third function by pressing the web at least onto the first dryer cylinder of the dryer section. I.e. the arrangement is such that the web always comes into direct contact with that drying cylinder or drying cylinders over or over which the transfer felt runs. This ensures that the drying of the web starts quickly from the start. In addition, it is avoided that an additional felt or wire belt is required on the drying cylinder (s) mentioned in order to keep the web in contact with the transfer felt.

In addition, there is the further advantage that the paper web in the initial area of the dryer section (ie at least on the first drying cylinder) is pressed by the transfer felt onto the drying cylinder or cylinders. Since the transfer felt, as already mentioned, has a fine structure, the risk in the initial area of the dryer section is avoided that permanent impressions are caused in the paper web, as can be caused by a much coarser dryer fabric. In other words, the invention makes it much easier than before to produce fine papers with the desired high quality properties.

The separating device mentioned in claim 1 and required behind the last press nip can be carried out in quite different ways: a suction box or a suction roller can be provided in a known manner. Or a first suction guide roller of the dryer section is used as a separating device. The arrangement of such a suction guide roller in front of the first drying cylinder is often desirable in order to obtain the largest possible wrap angle on the first drying cylinder.

To further increase the drainage capacity of the last press, this will preferably be designed as a long-gap press; i.e. has one of the two rollers - instead of a normal one, e.g. metallic roller shell - a flexible circumferential (tubular or band-shaped) pressing element which can be pressed onto the other roller by means of a support device (preferably a press shoe).

The transfer felt can take over either the function of the bottom felt or the function of the top felt in the last press. Both variants are described in detail below. The "second endless belt" required according to claim 1 can either - like the transfer felt - be designed as a water-absorbent felt belt; or it is designed as an elastic press belt with a relatively low water absorption capacity. In addition, it is possible that the second band directly forms the flexible (tubular or band-shaped) pressing element of an extended-gap press. In this case, only a single water-absorbent felt belt (namely the transfer felt) is provided in the last press.

Appropriately, measures will be taken which serve to further increase the drainage capacity of the last press, namely by reducing the rewetting of the web behind the press nip as far as possible. For this purpose, it can be provided to guide the transfer felt a little behind the press nip without the web over an auxiliary guide roller and from there back to the separating device. In this case, the web runs behind the press nip initially only with the second belt and then changes on the separating device, which is designed as a take-off suction roll, onto the transfer felt.

If the last press is designed as an extended-gap press with a press shoe, the press shoe according to DE-OS 38 15 278 can be used design in such a way that it also takes over the function of the separating device, the rewetting of the web also being reduced.

Various embodiments of the invention are described below with reference to the drawings.

Fig. 1 shows schematically the last press and the first dryer group of a paper machine.

FIGS. 2 and 4 to 6 show modifications of the arrangement according to FIG. 1.

FIG. 3 shows a cross section through the press shoe of an extended-nip press roll (enlarged detail from FIG. 2).

1 shows a section of a paper-making machine with part of the press section 10 and with the beginning part of a drying section 20. In FIG. 1, a double-felt press with an upper long-nip press roll 14 and with a counter-roll 13 below is first seen the long nip press roll 14 are shown schematically, a flexible circumferential tubular press jacket 14a and a press shoe 14b with which the press jacket can be pressed against the counter roll. The usual stationary support body in which the press shoe 14b can slide in the radial direction and all other details are omitted. The extended press nip formed by the press jacket 14a and the counter roll 13 is designated by 19. A bottom felt 11, an upper felt 12 and the paper web 9 to be dewatered (and then dried) run through it. This is removed from a preceding felt belt 8 by means of a take-off suction roller 16 located in the upper felt 12.

The two felt belts 11 and 12 are usually designed as usual as water-absorbent wet felts. Alternatively, a flexible press belt can be provided instead of the upper felt 12, the water absorption capacity of which is less than that of the lower felt 11. The lower felt 11 also serves as a transfer felt; i.e. it transfers the paper web 9 from the press section 10 into the drying section 20. It is essential that the transfer felt 11 also serves to press the paper web 9 onto at least the first drying cylinder 21, preferably onto a group of, for example, four drying cylinders 21 and 22. Therefore, all of these drying cylinders 21, 22 lie outside the endless loop of the transfer felt 11.

Behind the press nip 19, both felt belts 11 and 12 (together with the paper web in between) can run together to a separating device 17. This is in Fig. 1 in the loop of the transfer felt 11 and is designed as a suction roll with a removal suction zone 17a, so that from here the paper web 9 runs together with the transfer felt 11. An alternative is shown in FIG. 1 with dash-dotted lines: the transfer felt 11 is diverted behind the press nip 19 without the web 9 via an auxiliary guide roller 42 and then runs back to the separating device 17. In the area of this diversion, the transfer felt 11 is conditioned, for example by the fact that the separating device 17 designed as a suction roll has a conditioning suction zone 17b. Alternatively or in addition to this, the auxiliary guide roller 42 can be designed as a suction roller or as a blowing roller; or a pipe suction device is provided (Fig. 4, number 43).

In front of the first drying cylinder 21, the transfer felt 11 runs together with the paper web 9 over a guide roller 23. In addition, a guide roller 24, 25 is provided behind each of the drying cylinders 21, 22. These guide rollers are all located within the loop of the transfer felt 11, so that the paper web 9 is in the area of the guide rollers on the outside of the transfer felt and is therefore subject to a certain centrifugal force. In order to counteract the centrifugal force, the guide rollers 23, 24, 25 are designed in a known manner as suction rollers. From the last suction guide roll 25, the transfer felt 11 runs over an adjustable guide roll 26 and over further guide roll 27 back to the guide roll 15 of the press section 10. Between the guide rolls 25 and 26, the paper web 9 is fed with the help of a further felt belt or dryer fabric 28 and with the help of a take-off suction roll 29 removed from the transfer felt 11 and fed to a subsequent drying station, not shown.

In Fig. 1, the drying cylinders 21 and 22 form an essentially vertical row of cylinders. Instead, the drying cylinders could also be arranged in an essentially horizontal row.

In FIG. 2, in contrast to FIG. 1, the long nip press roll 14 is arranged below the counter roll 13. Another difference from FIG. 1 is that a special separating device (as in FIG. 1, item 17) is not provided for separating the upper felt 12 from the paper web 9 and from the transfer felt 11. Two other variants are shown. According to the first variant shown in full lines, both felt belts 11 and 12 run together with the paper web in between up to the first suction guide roller 23a. If necessary, this can have a pre-suction zone 23b, which lies in front of the point where the two felts run onto the suction guide roller. The top felt then runs over a guide roller 18a and the further guide rollers 18 back to the take-off suction roller 16.

According to a second variant, shown with dash-and-dot lines, the two felt belts 11 and 12 separate shortly behind the outlet from the extended press nip 19. This is aimed at to rewet the press nip 19 behind the press nip Reduce paper web from the top felt 12 as much as possible. In order to achieve this, the following is provided on the press shoe 14b according to FIG. 3 (as known per se from DE-OS 38 08 293): The press shoe 14a is divided into an upper part 34 and a lower part 35 acting as a piston. The latter is shown in FIG a pressure chamber 32 arranged; This is a recess of the fixed support body 31. Sealing strips and associated sealing strip supports 38 and 39 are used to guide the press shoe and to seal the pressure chamber 32. The middle part of the sliding surface 33 of the press shoe upper part 34 forms the concave-shaped contact surface with the width b. In the running direction behind the contact surface, the press shoe upper 34 has a convexly curved guide surface 36. The radius of curvature K thereof can be approximately equal to the radius R of the orbit of the press cover 14a. From the outlet end A of the press nip, the two felt belts 11 and 12 (in between the paper web 9) and the press jacket 14a initially run over the guide surface 36. Only at point B, that is to say shortly before the outlet-side end of the press shoe upper part 34, does it rise the upper felt 12 from the paper web 9 and runs from here to the guide roller 18a '(Fig. 2). Air can enter the upper felt 12 between the positions A and B, so that the paper web 9 safely detaches from the upper felt 12 at the point B and moves with the lower felt (transfer felt 11) (in the direction of the suction guide roller 23a, FIG. 2). The width of the guide surface 36 (in the direction of web travel) is designated by d.

Fig. 4 differs from Fig. 1 in that there is no top felt in the press. In this case, the tubular press jacket 14a of the extended-nip press roll 14 assumes the function of the second belt (provided according to claim 1). The non-rotating (radially displaceable) press shoe 14b can be replaced by a rotatable roller body 46, as indicated by dash-dotted lines. The transfer felt 11 is diverted behind the press nip 19 without the web 9, namely past a pipe suction device 43 and via an auxiliary guide roller 42 and finally back to the one designed as a suction roller Separating device 17. This is arranged such that the inflatable press jacket 14a forms a small looping zone on the suction roll 17. This ensures a secure transfer of the web 9 from the press jacket 14a to the transfer felt 11. In front of the press nip 19, a take-off suction roll 15 'is provided in the loop of the transfer felt 11, which ensures that the web 9 changes from the preceding felt belt 8 to the transfer felt 11.

1 to 4, the bottom felt 11 of the last press 13, 14 has the function of the transfer felt. 5, on the other hand, the arrangement is such that the top felt 11 'has the function of the transfer felt, the top roller being designed as an extended-nip press roller 14. The bottom felt is designated 12 '. The press shoe 14b can in turn be designed according to FIG. 3, so that the two felt belts 11 'and 12' separate at the outlet end of the press shoe. The upper felt 11 'in turn guides the paper web 9 first over a first suction guide roller 23 and then alternately over drying cylinders 21, 22 and further suction guide rollers 24 and 25. Schematically, scrapers 40 are indicated, which rest on the free part of the cylinder surfaces. Such scrapers are also present in the construction according to FIGS. 1, 2 and 4, but are omitted in the drawing. In FIG. 5, hot air blow boxes 41 are also indicated, which blow hot air onto the paper web at the suction guide rollers 24 and which can additionally extract exhaust air.

With the arrangement acc. Fig. 5 can possibly incurred waste (when tearing off the paper web) on the press side facing the cylinder row 21, 22 down unhindered. In contrast, in Fig. 1, 2 and 4 possibly incurred committee on the other side of the cylinder row 21, 22 must be carried down. The adjustable Guide roller 26 as shown in FIG. 1 are brought into the position shown with dash-dotted lines, so that the reject between the suction guide rollers 25 and 29 can fall down.

Fig. 6 differs from Fig. 5 only in that - similar to Fig. 2 - the lower roll is designed as an extended-nip press roll 14. Behind the press nip, the transfer felt (top felt 11 ') without the web 9 is guided via two auxiliary guide rollers 44 and 45 to a separating device 17' designed as a take-off suction roller. The felt conditioning devices already mentioned above are not shown in FIG. 6.

Claims (12)

1. Arrangement for transferring a web, preferably paper web from the press end section (10) to the drying section (20) of a paper-making machine, wherein a first endless belt (11), which is constructed as a felt belt able to absorb water (referred to hereafter as the "transfer felt") together with the web (9) travels not solely through the last pressing gap (19) of the press end section, but also over at least the first drying cylinder (21) of the drying section, characterised by the following features:

   a) a second endless belt (12 or 12' or 14a) travels - as known per se - in addition to the first belt (11) through the last pressing gap (19) of the press end section (10), so that at this point the web (9) is located between the two belts (11, 12);

   b) behind the said last pressing gap (19), the transfer felt (11), together with the web (9) and the second belt (12) travels over a separating device (17 or 36) known per se, on which the second belt (12) separates from the web (9).
2. Arrangement according to Claim 1, characterised in that the drying cylinder or cylinders (21, 22), over which the transfer felt (11) travels together with the web (9), lies/lie outside the endless loop of the transfer felt (11).
3. Arrangement according to Claim 2, characterised in that immediately before the first drying cylinder (21), the transfer felt (11) together with the web (9) travels over a guide roller (preferably suction guide roller 23), which is located within the loop of the endless transfer felt (11).
4. Arrangement according to Claim 3, characterised in that the guide roller (preferably suction guide roller 23) is located between the separating device (17 or 36) and the first drying cylinder (21).
5. Arrangement according to Claim 3, characterised in that the suction guide roller (23a) simultaneously forms the separating device.
6. Arrangement according to one of Claims 1 to 5, characterised in that the transfer felt (11) travels over the lower pressing roller (13 or 14) of the last press.
7. Arrangement according to one of Claims 1 to 5, characterised in that the transfer felt (11) travels over the upper pressing roller (14) of the last press.
8. Arrangement according to one of Claims 1 to 7, characterised in that the second belt (12 or 12') is constructed as a felt belt able to absorb water.
9. Arrangement according to one of Claims 1 to 7, characterised in that the second belt (12 or 12') is constructed as an elastic pressing belt, whereof the capacity to absorb water is less than that of the transfer felt.
10. Arrangement according to one of Claims 1 to 7, characterised in that the second belt (14a) is a flexible, tubular and liquid-tight pressing casing, which can be pressed by means of a support device (press shoe 14b or roll body 46) against a counter-roller.
11. Arrangement according to one of the preceding Claims, characterised by the following features:

    a) behind the first pressing gap (19), the transfer felt (11) travels without the web (9) over at least one auxiliary guide roller (42) and from the latter back to the separating device (17), which is constructed as a removal suction roller lying within the endless loop of the transfer felt (11) and comes into contact with the second belt (12 or 14a), in order to separate the web (9) from the latter;

    b) a felt-conditioning device (17b; 43) is provided on the path of the transfer felt (11) free from the web (9).
12. Arrangement according to one of Claims 1 to 10, characterised by the following features:

    a) the last pressing gap (19) of the press end section (10) is formed by a long gap pressing roller (14) with a flexible, peripheral (tubular or belt-shaped) pressing member (14a), which can be pressed by means of a press shoe (14b) against a counter-roller (13);

    b) in the direction of travel of the web behind the pressing gap (19), the press shoe (14b) has a guide surface (40) of substantially convex curvature, over which the flexible pressing member (14a) travels in contact with the transfer felt (11);

    c) the second belt (12) constructed as a felt belt is guided behind the pressing gap (19) so that it travels first of all together with the web (9) and with the transfer felt (11) over part of the guide surface (40) having a convex curvature and then separates from the web (9) (in the region of the guide surface at the outlet side, at the point B).

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