EP1739228A1 - Machine for manufacturing a fibrous web - Google Patents

Abstract

The machine has a press section, where a fibrous material sheet (1) is guided in the section with press rollers (5, 14) by a central roller (8) forming press nips (9, 12). The sheet is passed together with a transfer tape (10) by the nips formed between the central and press rollers. Line forces, which are produced by the press roller (5) and the press nip (9) that forms the central roller, amount to maximum 30 kilo Newton / meter.

Description

The invention relates to a machine for producing a paper or another fibrous web having a press section, in which the fibrous web can be guided via a central roll forming two press nips with first and a second press roll.

From the DE 100 22 087 A1 is a press section for a paper machine known. The press section has two pressing points, which are each formed by a press roller cooperating with a shoe press roll. A first upper felt, the paper web coming from a forming wire, an underfelt and a press jacket of a first shoe press roll pass through the first press point. The underfelt continues with the paper web to the second press site. Together with a second top felt and a press jacket of a second press site, the paper web then passes through the second press site. The paper web follows the underfelt further up to a take-off roll, through which it is transferred to a first dryer wire which transfers the paper web to the dryer section. Guide rollers and suction rollers are provided for deflecting the upper felt and the lower felt. In press sections known from the prior art, support by a transfer belt is necessary due to the low strength of the paper web.

From the WO 00/55423 For example, a press section for a paper machine is known, in which a central roll (FIG. 1) is used, which cooperates in two press nips with a press roll and a shoe press roll. In each of the two press nips the fibrous web is guided on both sides: in the first press nip by a felt and a transfer belt, in the second press nip by the transfer belt and another band.

As high-speed paper machines, the following configurations are currently implemented for the production of high-quality SC-A paper (SC = super calendered): what are known as roll-blade shapers, i. H. Screen former with a forming roller and drainage strips, without flexible strips in conjunction with a downstream conventional press section built with three press nips. The press nips can also be formed by shoe press rolls. Subsequently, a free-standing press unit is preferably arranged for a fourth press nip. Outside the paper machine, the fibrous web is smoothed by at least two calenders with a plurality of nips (multinip calenders). The calenders follow the speed of calendering paper machine production.

To set the required inlet moisture and the most uniform possible moisture distribution over the entire width of the web, the fibrous web is usually dried in the dryer section to a residual moisture content of 2 to 3% and moistened before the reeling station still within the paper machine with the help of a Wasserauftragsaggregates, such as a Düsenfeuchters. The residence time of the wound with the paper web of the after winding in the paper machine to the calendering of the paper web in the calenders is between 0.5 and 2 hours. Thanks to the drying out and the long dwell time, a very good moisture distribution in all directions within the paper web can be assumed.

The integration of the multinip calender in the paper machine (on-line process) generally results in a significant speed increase of the calendering process. Due to the shorter residence time in the nip and due to other web running conditions, the online process has cost advantages compared to the classic offline process described above; At the same time, however, it leads to quality disadvantages, which manifest themselves in particular in the printability in the gravure printing process in the form of print unrest and a higher number of missing dots (missing dots).

Such on-line processes are carried out in the following manner: A roll-blade former with or without flexible twin-mesh bars is used in conjunction with two freestanding shoe presses or a freestanding roller press and a subsequent shoe press in conjunction with a multi-pin calender.

Alternatively, a roll-blade former with or without flexible strips in the twin-wire area and a conventional three-nip press with or without Schuhnip used in conjunction with a multi-pin calender.

Or a roll-blade former without flexible strips in the twin-wire area and a conventional three-nip press with or without Schuhnip and a freestanding fourth press in conjunction with a multi-pin calender used.

Compared to an offline process, productivity in an on-line process can be significantly higher due to the loss of rewinding losses caused by winding, unwinding and rewinding the web after calendering.

A conventional press section, which is designed as a three-nip press without an additional free-standing fourth press generally shows a very strong structural two-sidedness of the paper due to asymmetric dewatering conditions in the press, as in the second and third press nip the dewatering takes place only to the top. When operating a shoe tip in the third position, the dry content may indeed be increased significantly, which generally leads to a higher speed and consequently also to a higher productivity. However, the heavier dewatering to the top further increases paper two-sidedness. Therefore, for high quality papers a free-standing fourth press with drainage reversal to the bottom is absolutely necessary. The disadvantage of this concept, however, is that the paper web must be conveyed over two areas in the open draw. It runs freely between the central roll after the third press and from the fourth press. This has a negative impact on the runnability of the paper web. The paper web overstretches. It can tears and transverse contractions occur, which significantly reduce the maximum speed potential.

It is the object of the invention to provide a machine in which the press section, in particular for high quality SC papers, in terms of runnability, d. H. runtime and material efficiency, and product quality, paper surface roughness and missing dots are improved.

According to the invention this object is achieved in a machine of the type mentioned in that the fibrous web can be passed together with a transfer belt through the press nips formed between the central roller and the press rollers.

Advantageous developments of the invention are contained in the subclaims, the description and the drawings.

Preferably, the line force generated in the first press nip formed by the first press roll and the central roll is at most 50kN / m, preferably at most 30kN / m. As a result, the fibrous web 1 is transferred to the transfer belt 10 in the region of the press nip 9 gently.

For further mechanical dewatering after the wire section, the paper web, supported and guided by press felts or impermeable or permeable transfer belts, passes through several press nips formed by pairs of rolls. Due to the intensive contact of the paper web with the felt surface in the press nip, it is necessary for high-quality papers, each paper side the final contact with a smooth roller or a smooth transfer belt to enable. This smoothing takes place in a conventional press section with or without Schuhnip on the central roll and for the upper side in a subsequent press in which the paper web passes through a fourth press nip.

In the two last press nips a macro-smoothing of the surface of the paper web takes place at a high press pulse, which leads to an improved calenderability in the following multinip calender. It can be seen that due to wet-smoothness in the press section, for a given PPS roughness after calendering, the required calendering line forces may be lower by up to 100 kN / m. This results in a significantly improved quality of the final product, since negative effects of the calendering, such. As black satin or volume decrease, be significantly reduced.

In order to be able to achieve even higher production speeds according to this concept, maximum dry contents must be achieved after passing through the press section, and the required web courses must be minimized in order to avoid overstretching and thus cracks in the dryer section. The operation of a shoe tip in the third press nip can increase the dry content compared to conventional roll nips by up to four percent. However, this positive effect is at the expense of the surface quality and thus the printability, in particular the felt-contacting surface of the paper web. Likewise, the first press nip may be formed as a Schuhnip to further increase the dry content.

To produce high-quality uncoated magazine papers (SC papers), the use of a fourth press nip is essential, with the paper web being led through the press nip together with an underfelt for smoothing. This nip can also be used as a Schuhnip with extended residence time to enhance the smoothness effect.

Instead of the felt used according to the prior art in the third press nip an impermeable, smooth transfer belt is now used, thereby avoiding that the paper web continued in the free train of the central roll must become. Rather, the paper web is removed shortly before reaching the fourth press nip, which is arranged in a free-standing press, with the aid of a vacuumed transfer roller and transferred to another suction roll with the underfelt or a permeable, absorbable transfer belt.

The transfer suction roll advantageously has a rubberized mantle surface. It may also have a drilling pattern in its roll shell.

For safe removal of the paper web, the roller can be variably adjusted in its immersion depth with respect to the paper web and the transfer belt. For this purpose, an adjusting device is provided, by means of which the roller is movable.

In order to increase the positive smoothness effect of the press section, novel press felts can be used in all positions. An extremely fine surface of the press felts is due to the use of a certain amount of molten fiber material. By this measure, the negative appearing felt marks are drastically reduced.

The advantages of the invention are that highest production speeds due to the achievement of maximum dry contents after passing through the wire section and the press section and as a result of minimizing the free draws in the press section by the use of the transfer belt are possible. Due to the wet smoothness effect in the press section on both sides of the paper web also a gentle calendering is possible. By means of the press section constructed according to the invention, best printability properties, especially for gravure printing, are achieved on account of improved topography properties of the base paper.

The transfer belt preferably has a smooth surface and is in particular water-impermeable. The transfer belt can also be at least light permeable to air. The ventilation caused thereby improves the web picking behavior.

Furthermore, the use of a cleaning device for the transfer belt is advantageous.

According to a particular embodiment of the invention, the fourth press nip is formed on a separate press. In this case, the upper roller of the fourth press is formed in particular with a smooth surface. The fibrous web coming from the compact press forming the first three press nips has a roughness two-sidedness, since the upper side is rougher than its lower side. By using a smooth top roller in the fourth press this two-sidedness can be compensated.

The decrease of the fibrous web from the smooth roll in the fourth press can be effected by a suction element, in particular a suction roll. The suction roll preferably has a porous cover, more preferably a soft, felt-like cover. By these measures, a good Bahnabnahme is possible.

A good web removal from the suction element results according to a further embodiment of the invention by a further suction roll. This is preferably wrapped by the dryer fabric of a subsequent dryer section, so that the fibrous web is transferred directly through the dryer fabric in the dryer section.

The transfer element for transferring the fibrous web from the transfer belt to the fourth press nip preferably has a soft, in particular air-permeable, reference. For example, the cover may be made of plastic or a felt. Hereby a good transfer can be achieved.

Also preferred and advantageous is when the transfer element is driven. This ensures a safe transfer of the fibrous web become.

As a transfer element can be provided in addition to a transfer suction and a particular air-permeable belt loop. For example, a felt belt with a fine pile can be used. In the area of the web, the web loop in the web-guiding area can be in particular vacuumed, i. On the side facing away from the fibrous web are subjected to negative pressure, for example by foils, suction boxes or other known suction devices. Hereby, good guidance and / or transfer of the fibrous web can be ensured.

The belt loop can also wrap around several guide rollers. In this case, preferably at least one roller of the belt loop is driven. This results in a larger belt loop for the transmission of the fibrous web with corresponding advantages.

The upper roller of the fourth press nip is wrapped in a further embodiment of the invention with a smoothing belt. As a result, the smoothing surface can be easily changed by changing the band. For example, this may be necessary to optimize the web delivery performance of smooth surfaces. The smoothing strip in particular has a smooth surface. In addition, the smoothing tape may be dense or permeable to air.

The smoothing belt can basically be designed like the transfer belt. In particular, all three bands, smoothing belt, transfer belt and belt of the belt loop, can be made equal. This results in a uniform treatment of the fibrous web.

According to a further embodiment of the invention, the arrangement is such that the transfer of the fibrous web through the transfer element takes place directly in the region of the free felt train of the fourth press. In this case, in the transfer area in the felt loop, a suction element for better Bahnabgabe or railway recording be provided. Space can be saved thanks to the direct rail transfer. In addition, the production is simplified.

The transfer element can also have at least two vacuum zones, specifically a pickup zone and a holding zone. The vacuum in the pickup zone is preferably higher than that in the holding zone. This allows a particularly good and yet gentle web transfer can be achieved.

Fig. 1

eine erste Variante einer erfindungsgemäßen Vorrichtung,

Fig. 2

eine Variante zur Fig. 1,

Fig. 3

eine weitere Variante zur Fig. 1, und

Fig. 4

noch eine Variante zur Fig. 1.

Embodiments are illustrated in the drawings and will be described below. They show, in each case in a schematic representation,

Fig. 1

a first variant of a device according to the invention,

Fig. 2

a variant of FIG. 1,

Fig. 3

a further variant of FIG. 1, and

Fig. 4

another variant of FIG. 1.

A fibrous web 1, coming from a wire section, passed through a press section. In this she is guided, supported by a lower felt 2 and a top felt 3, through a first press nip 4, which is formed by a press suction roll 5 with a shoe press roll 6 with shoe press zone 7. After the press nip 4, the underfelt 2 is again separated from the fibrous web 1, so that this, resting on the top felt 3, is passed between the press suction roll 5 and a central roll 8 through a second press nip 9.

Optionally, the second press nip 9 can be operated such that the line force generated is a maximum of 50 kN / m, preferably a maximum of 30 kN / m. This very low line force, also called "kissing contact", becomes a gentle one Treatment of the fibrous web in the second press nip 9 ensures the press section, wherein the "kissing contact" is essentially there to transfer the fibrous web 1 from the Squeeze roll 5 to the central roll 8. It should be noted that the "Kissing Contact" operation can of course also be applied to all embodiments described in the following figures.

In order to ensure a good smoothing on the central roller 8 side facing, a transfer belt 10 is passed together with the fibrous web 1 through the press nip 9. Subsequently, the top felt 3 is led away from the press suction roll 5.

The fibrous web 1 is then passed together with the transfer belt 10 and another top felt 11 through a press nip 12 which is formed by the central roll 8 and a shoe press roll 14 equipped with a shoe press zone 13.

Then, the fibrous web 1 is sucked off by a transfer suction roll 15 from the transfer belt 10 and transferred by means of another transfer suction roll 16 onto a lower felt 17. Thereafter, the fibrous web 1 is passed together with the lower felt 17 through the belonging to a free-standing press unit press rollers 18, 19, which together form a fourth press nip 20.

The upper roller 19 of the fourth press nip 20 has a smooth surface. From this roller 19, the fibrous web 1 is removed by means of a suction roller 21 with a porous, preferably soft cover. From the roller 21, in turn, the fibrous web is removed by a suction roller 22. The suction roll 22 is thereby looped by a drying wire 23 of the subsequent drying section, of which two drying cylinders 24 and 25 and a duo stabilizer 26 are shown. Instead of the Duostabilisators also a HiDryer can be used.

The embodiment of FIG. 2 is largely consistent with that of FIG. In contrast to the variant of FIG. 1, however, only the third press nip 12 is formed as a shoe press nip. In addition, the transfer suction roll 15 is replaced by a belt loop 27, which is formed in particular by an air-permeable felt with fine pile. The belt loop 27 is guided over a suction roll 28 and a driven roll 29. In the region of the fibrous web 1 between the suction roll 28 and the drive roller 29 suction elements 30 may be arranged. These are, for example, foils, suction boxes or other suction devices known in paper technology.

The variant of FIG. 3 is largely consistent with the variant of FIG. 2. In contrast to the variant of FIG. 2, in the variant of FIG. 3, however, the upper roller 19 of the fourth press nip 20 is looped around with a smoothing belt 31. This smoothing belt 31 in particular has a smooth surface and may be dense or permeable to air. In particular, the smoothing belt 31 may be formed like the transfer belt 10. Likewise, the band of the belt loop 27 may be formed in the same way.

It should also be noted that the rolls 6 forming the first press nip 4 illustrated in FIGS. 2 and 3 may of course also comprise a shoe press unit 7.

The variant of FIG. 4 in turn largely coincides with the variant of FIG. The difference is that the fibrous web 1 is transferred by the transfer suction roll 15 directly in the region of the free felt train of the felt 17 of the fourth press 18, 19 to this. In the transfer area can be provided in the felt loop 17, a suction element 32 for better web recording or delivery. In the illustrated embodiment, the transfer suction roll 15 has a pickup zone 33 and a holding zone 34, wherein the vacuum in the pickup zone 33 is greater than in the holding zone 34. Basically can also be provided more vacuum zones.

In all variants shown, the transfer belt 10 is also provided with a cleaning device. This consists of a spray tube 35, a dirt removal roller 36 and a collecting and collecting device 37th

Claims (35)

Machine for producing a paper or other fibrous web (1) with a press section, in which the fibrous web (1) has a central roller (8th, 8th and 8th) which forms two press nips (9, 12) with a first (5) and a second press roller (14) ) is feasible,
characterized,
in that the fibrous web (1) together with a transfer belt (10) can be guided through the press nips (9, 12) formed between the central roll (8) and the press rolls (5, 14). Machine according to claim 1,
characterized,
in that the line force generated in the first press nip (9) formed by the first press roll (5) and the central roll (8) is at most 50 kN / m, preferably at most 30 kN / m. Machine according to claim 1 or 2,
characterized,
in that the fibrous web (1) can be conveyed by a transfer element (15), in particular a transfer suction roll (15), from the transfer belt (10) onto a further felt, in particular an under felt (17), and through a fourth press nip (20). Machine according to claim 3,
characterized,
that the transfer-suction roll (15), a rubberized jacket surface and / or has a drilling pattern in the mantle surface. Machine according to claim 3 or 4,
characterized,
in that the transfer suction roll (15) is adjustable in its immersion depth with respect to the transfer belt (10) and the fibrous web (1). Machine according to one of claims 1 to 5,
characterized,
in that the second press roll (14) is designed as a shoe press roll and comprises a shoe press zone (13). Machine according to one of the preceding claims,
characterized,
that the first press roller (6) is constructed as a shoe press roll and a shoe press zone (7). Machine according to one of the preceding claims,
characterized,
that the transfer belt (10) has a smooth surface. Machine according to one of the preceding claims,
characterized,
that the transfer belt (10) is impermeable to water. Machine according to one of the preceding claims,
characterized,
that the transfer belt (10) is at least slightly permeable to air. Machine according to one of the preceding claims,
characterized,
in that a cleaning device (35, 36, 37) for the transfer belt (10) is provided. Machine according to one of the preceding claims,
characterized,
in that the fourth press nip (20) is formed on a separate press (18, 19). Machine according to one of the preceding claims,
characterized,
in that the surface of the upper roller (19) of the fourth press nip (20) is smooth. Machine according to one of the preceding claims,
characterized,
that the decrease of the fibrous web from the upper roll (19) of the fourth press nip (20) by a suction element, in particular a suction roll (21). Machine according to claim 14,
characterized,
that the suction roll (21) has a porous cover. Machine according to one of claims 14 or 15,
characterized,
that the suction roll (21) has a soft, felt-like cover. Machine according to one of claims 14 to 16,
characterized,
in that the removal from the suction element (21) is effected by a suction roll (22). Machine according to claim 17,
characterized,
that the suction roll (22) from the drying wire (23), a subsequent drying section (24, 25, 26) is wrapped. Machine according to one of the preceding claims,
characterized,
that the transfer element (15) is provided with a soft, air-permeable cover. Machine according to one of the preceding claims,
characterized,
that the transfer element (15) is driven. Machine according to one of the preceding claims,
characterized,
that a particular air-permeable belt loop (27) is provided as a transfer element. Machine according to one of the preceding claims,
characterized,
that the belt loop (27) is designed as a felt, in particular with a fine pile. Machine according to claim 21 or 22,
characterized,
that the belt loop (27) is subjected to suction in the web-guiding area. Machine according to one of claims 21 to 23,
characterized,
that the belt loop (27) wraps around a plurality of guide rollers. Machine according to one of the preceding claims,
characterized,
that the upper roller (19) of the fourth press nip (20) is looped around with a smoothing belt (31). Machine according to claim 25,
characterized,
that the smoothing belt (31) has a smooth surface. Machine according to one of claims 25 or 26,
characterized,
that the smoothing belt (31) is impermeable to air. Machine according to one of claims 25 or 26,
characterized,
that the smoothing belt (31) is permeable to air. Machine according to one of claims 25 to 28,
characterized,
that the transfer belt (10) and the smoothing strip (31) are of identical design. Machine according to one of claims 25 to 28,
characterized,
that all three bands, transfer belt (10), smoothing belt (31) and belt loop (27) are formed the same. Machine according to one of the preceding claims,
characterized,
that the transfer of the fibrous web (1) through the transfer member (15) directly in the region of the free Filzzuges of the felt (17) of the fourth press (18, 19) to said felt (17). Machine according to claim 31,
characterized,
in that a suction element (32) is arranged in the transfer region. Machine according to one of the preceding claims,
characterized,
in that the transfer element (15) has two or more suction zones (33, 34). Machine according to claim 33,
characterized,
in that the transfer element (15) has a pickup zone (33) and a holding zone (34). Machine according to claim 34,
characterized,
that the vacuum of the pickup zone (33) is greater than the vacuum of the holding zone (34).

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