PLANT FOR THE PRODUCTION OF A FIBROUS WEB

Description

[0001] The invention relates to a plant for producing a fibrous web, in particular a long-fiber paper or wet-laid nonwoven web, comprising a binder screen section having a binder screen for applying an aqueous binder to the fibrous web and a drying section having a drying screen for drying and consolidating the fibrous web, wherein the binder screen section and the drying section are arranged at a distance from one another so that the fibrous web is guided from the binder screen to the drying screen in a free draw.

[0002] Such a system is already known from the document WO 2009 / 144195 A1 from the applicant.

[0003] In the plant described therein, a fiber suspension unit, for example a glass fiber slurry, is produced by adding a glass fiber having a fiber length in the range of 6 to 40 mm, preferably 8 to 30 mm, in particular 10 to 25 mm, to typical white water in a pulper to disperse the glass fiber in the white water to form the glass fiber slurry with a fiber concentration of approximately 0.2 to 1.0 percent by weight, and the slurry is added to a white water stream. This glass fiber slurry is then applied to an inclined screen running at least partially at an angle to the horizontal in a web former with at least one at least single-layer, preferably multi-layer headbox, and dewatered. The dewatering of the glass fiber slurry forms a glass fiber wet nonwoven.The resulting glass fiber wet-lay is then transferred to a binder screen of a binder screen section, which runs at least partially horizontally or approximately horizontally. In this binder screen section, at least one aqueous binder, such as an aqueous urea-formaldehyde (UF) resin-based binder, is applied to the wet glass fiber wet-lay using at least one binder feeder. The excess binder is then vacuumed off. The aqueous binder solution is preferably applied to the wet glass fiber wet-lay using a curtain coater or a swap and squeeze applicator, although other application methods such as spraying are also suitable. The wet and still unbonded glass fiber wet-lay is then transferred to a drying section comprising a drying screen for drying and curing (polymerization) of the binder, which bonds the glass fibers together in the glass fiber nonwoven.The drying section can, for example, comprise a heated continuous oven or a drum or belt dryer, whereby the glass fiber mat is typically exposed to a temperature of 100 to 250 °C, but for no longer than 1 to 2 minutes. Finally, the glass fiber mat, which has a basis weight range of 40 to 200 g / m2 and a binder content of 10 to 30%, is wound onto winding cores in a winder to form winding rolls, which can then be fed to subsequent processing or finishing stations.

[0004] The publication WO 2009 / 144195 A1 already points out the following problem, which occurs when transferring the still wet and unbonded glass fiber mat from the binder screen to the dryer screen, if, for example, a transfer roller is used instead of an open draw roller: The roller surface quickly becomes contaminated with glass fibers as soon as it comes into contact with the very wet and sticky glass fiber mat due to the binder application. This contamination causes significant production downtime and, consequently, poor runnability, as the system must be completely shut down and the glass fiber-contaminated roller must be cleaned. Although designs for "online" roller cleaning are occasionally used, the cleaning results achieved with them are more than unsatisfactory, both in terms of cleaning quality and cleaning times.The costs for such constructions, including the necessary maintenance of spare parts for a reserve roller, are usually not negligible.

[0005] WO 2009 / 144195 A1 proposes dispensing with the roller or similar device and transferring the fibrous web from the binder fabric to the dryer fabric in a free-flowing process. The web is supported in this area by an air flow from a blower device for contactless suspension of the fibrous web. The blower device extends across the entire width of the nonwoven web, blowing air onto it from above.

[0006] Although this concept has proven successful, in practice, the problem of wrinkles forming in the fibrous web during the transfer from the binder fabric to the dryer fabric under free draw occasionally arises, sometimes leading to web breaks. This problem occurs more frequently the higher the speed at which the web is fed through the system and / or the lower the basis weight of the web.

[0007] The invention is based on the objective of avoiding or at least reducing the aforementioned problems. In particular, the transfer of the wet and still unbonded fibrous web from the binder wire section to the dryer section in an open draw is to be made more reliable, so that it does not negatively impact the runnability of the system and functions without wrinkling and / or web breaks even at high machine speeds and / or low specific web weights.

[0008] This object is achieved by the features of the independent claims. The dependent claims relate to advantageous developments of the invention. In particular, the object is achieved according to the invention in a system of the type mentioned above by arranging at least one air extraction device at the edge of the system in the region of the gap between the binder wire section and the dryer section.

[0009] The inventors have recognized that the primary cause of wrinkling in the fibrous web is the air currents generated by the binder fabric and the counter-rotating dryer fabric in the transfer area between the binder fabric and the dryer section, particularly at high operating speeds and / or low basis weights of the web. These air currents generate turbulence, particularly in the edge area of ​​the system. This stretches the fibrous web, leading to wrinkling or even web tearing in the system. This is described in more detail below. Figure 2 illustrated schematically.

[0010] An initial approach to positively influencing airflow was to use baffles. In areas where airflow influences the web path, baffles are used to guide the flow.

[0011] These direct the airflow so that the track path is not affected. However, this solution approach had the disadvantage that the airflow can be variable. Depending on the season, the temperature in the hall, or whether the gates or doors in the hall are open or closed, the thermals and thus the airflow in the area in question change. This means that the position of the deflectors must be constantly adjusted to ensure trouble-free operation.

[0012] This problem could only be solved through the inventive use of at least one air extraction device. This at least one air extraction device enables a stable flow to be generated in the transfer area between the binder wire and dryer sections, which is not influenced by the aforementioned disruptive factors.

[0013] Surprisingly, it has been found that it is entirely sufficient to position at least one air extraction device only at the edge. This was not anticipated beforehand. If it had proven necessary to provide an air extraction device extending essentially across the entire width of the system below the fibrous web in the threading area to ensure stable air flow in the threading area, this would inevitably have led to very high maintenance and cleaning costs for the air extraction device, since in the threading area, sticky fibers repeatedly fall from the still wet and unglued fibrous web due to the binder. This approach, using at least one air extraction device, would therefore also have been impractical.

[0014] Preferably, the at least one air extraction device is arranged, viewed vertically, substantially below the fibrous web conveyed in free tension, but does not extend from the edge of the system to below the fibrous web conveyed in free tension. "Substantially below, viewed vertically," means that the at least one air extraction device is arranged predominantly, preferably entirely, below the fibrous web in the vertical direction, i.e., in the direction of gravity, when the web is conveyed from the binder wire section to the dryer section during normal operation of the system. At the same time, however, the at least one edge-side air extraction device should not extend, viewed horizontally, from the edge to below the fibrous web conveyed in free tension, in order to avoid the aforementioned problem of high cleaning and maintenance costs.

[0015] The term "air extraction device" preferably refers to a suction box. Such a suction box typically has an opening through which the air is extracted. The air extraction device can be connected to a negative pressure source, such as a vacuum pump, via piping or the like.

[0016] The invention has proven particularly efficient when an air extraction device is arranged on both the drive side and the driver side of the system. In this case, it is advantageous if the drive-side and driver-side air extraction devices are designed such that the negative pressure they generate can be adjusted independently of each other. In other words, the same negative pressure does not always have to be present at both air extraction devices, nor does it require the same amount of air to be extracted per unit of time. The adjustment can be made via a closed-loop or open-loop control system. However, it is normally sufficient to adjust the negative pressure only once.

[0017] In order to generally avoid or at least reduce the contamination and maintenance problems described above, it is advantageous if the installation space below the fibrous web guided in free tension is kept clear, at least in the area between a last roller of the binder wire section, over which the binder wire is guided when it releases the fibrous web, and a first roller of the dryer section, over which the dryer wire is guided when it receives the fibrous web. Air can then be extracted particularly efficiently from this cleared installation space by the at least one, preferably two, air extraction device(s).

[0018] With regard to an efficient design of the binder section, it is proposed that the binder screen runs horizontally or approximately horizontally at least in sections and / or that the binder screen section has at least one binder headbox.

[0019] In addition, it is advantageous if the plant further comprises a forming section for dewatering an aqueous suspension, which is arranged upstream of the binder wire section in the process direction of the fibrous web through the plant, wherein the forming section preferably comprises an inclined wire former which has an inclined wire running at least in sections at an angle to the horizontal and at least one at least single-layer, preferably multi-layer, headbox.

[0020] The plant may also further comprise a fiber suspension unit for producing the aqueous suspension for the forming section.

[0021] At the end, the system may also comprise a winder for continuously winding the fibrous web onto winding cores to form winding rolls, wherein the winder is located downstream of the drying section in the process direction of the fibrous web through the system.

[0022] It is not mandatory, but possible, for at least one, preferably adjustable, blowing device to be provided between the binder wire section and the dryer section for contactless, suspended guidance of the fibrous web using air or another flowable medium, which has several independently controllable blowing zones transverse to the running direction of the fibrous web. The mode of operation of such a blowing device, which blows from above onto the fibrous web in the transfer area to promote contactless, suspended guidance of the fibrous web, is described in detail in the aforementioned document WO 2009 / 144195 A1, to whose content, and with regard to further advantageous embodiments of the blowing device, explicit reference is hereby made.

[0023] A further aspect of the present invention relates to the use of a previously described plant according to the invention for producing a fibrous web, in particular a long-fiber paper or wet-laid nonwoven web, wherein, during normal operation of the plant, air is extracted from the area between the binder wire section and the dryer section by means of the at least one edge-side air extraction device.

[0024] The present invention has proven particularly effective when the fibrous web is a wet-laid glass fiber mat. The transfer of the not yet dry and therefore sticky glass fiber mat from the binder wire to the dryer section is particularly susceptible to the contamination problem described above.

[0025] Furthermore, the advantages of the present invention are particularly effective when the fibrous web is produced at a speed of at least 170 m / min and / or when the fibrous web has a basis weight of less than 30 g / m 2<, since in this case the risk of wrinkling of the fibrous web in the transfer area between the binder wire and the dryer section is particularly high.

[0026] Further features and advantages of the invention will become apparent from the following description of a preferred embodiment with reference to the drawing.

[0027] It shows Fig. 1 shows a schematic layout of a plant for producing a fibrous web according to the prior art; Fig. 2 shows a schematic side view of the transfer area between the binder wire and dryer sections according to the prior art; Fig. 3 shows a schematic side view of the transfer area between the binder wire and dryer sections according to the present invention; and Fig. 4 shows a schematic three-dimensional view of the transfer area between the binder wire and dryer sections according to the present invention.

[0028] The Figure 1 shows a schematic layout of a plant 1 for producing a fibrous web 2, in particular a long-fiber paper or wet-laid nonwoven web.

[0029] This plant 1 for producing the fibrous web 2 comprises a fibrous material suspension unit 3, a forming section 4, which has an inclined screen 5 running at least in sections at an angle α to the horizontal H and at least one at least single-layer, preferably multi-layer headbox 6, a binder screen section 7, which has a binder screen 8 running at least in sections horizontally or approximately horizontally and at least one binder headbox 9, a drying section 10 having a dryer screen 11 and a winder 12 for continuously winding the fibrous web 2 onto winding cores 13 to form winding rolls 14.

[0030] In the fiber suspension unit 3, all components required to produce an aqueous suspension, such as water, chopped fibers, binders, and the like, are placed in a first container ("pulper") 15 equipped with a stirrer 16 and then in a second container ("pulper") 17, also equipped with a stirrer 18; the aqueous suspension is transported by pumps 19, 20. The aqueous suspension can, for example, be a glass fiber slurry comprising glass fibers with a fiber length in the range of 6 to 40 mm, preferably 8 to 30 mm, in particular 10 to 25 mm, and so-called white water, and having a fiber concentration of approximately 0.2 to 1.0 percent by weight.

[0031] The fiber suspension unit 3 is followed by the next process step, namely the dewatering of the aqueous suspension and the formation of the fiber web 2 with the aid of the inclined screen 5 arranged in the forming section 4. For this purpose, the aqueous suspension is applied to the inclined screen 5 by means of an at least single-layer, preferably multi-layer, headbox 6. The water filtered from the aqueous suspension below the inclined screen 5 is recirculated according to arrow 21 and, for example, added to the aqueous suspension leaving the second container ("pulper") 17 of the fiber suspension unit 3.

[0032] In the following process step, at least one aqueous binder, such as an aqueous urea-formaldehyde (UF) resin-based binder, is applied by means of a binder head 9 to the still-wet fibrous web 2 resting on the binder wire 8 of the binder wire section 7. In this binder wire section 7, the excess binder is then also vacuumed off in a known manner. The aqueous binder can also be applied to the still-wet fibrous web 2 using a curtain coater or an exchange and squeeze applicator, in a manner not shown; however, other application methods, such as spraying, are also suitable.

[0033] The next process step dries and consolidates the still-wet fibrous web 2 by curing (polymerizing) the binder, which bonds the glass fibers together in the glass fiber mat. For this purpose, it is passed through the drying section 10, which has the dryer screen 11 and comprises two heated continuous ovens 22 (shown) or a drum or belt dryer (not shown). The fibrous web 2 is typically exposed to a temperature of 100°C to 250°C, but for no longer than 1 to 2 minutes.

[0034] In a final process step, the fibrous web, which has a basis weight range of 40 to 200 g / m 2 and a binder content of 10 to 30%, is wound in the winder 12 onto winding cores 14 to form winding rolls 13 in order to then be fed to subsequent processing or finishing stations.

[0035] Furthermore, an adjustable blowing device (not shown) for contactless floating guidance of the fibrous web 2 by means of air or another flowable medium can be provided between the binder wire section 7 and the dryer section 10, which has a plurality of independently controllable / regulatable blowing zones transversely to the running direction of the fibrous web 2.

[0036] Fig. 2shows a schematic side view of the transfer area 24 between the binder wire section 7 and the dryer section 10, as well as the problem of the formation of wrinkles F in the prior art. The fibrous web 2 is transported on the binder wire 8 to a last roller 25 of the binder wire section 7, then guided in a free draw to a first roller 26 of the subsequent dryer section 10, where it is picked up by the dryer wire 11 and transported further. The arrows with the filled tips illustrate the air flows that are dragged along by the binder wire 8 of the fibrous web 2 and the dryer wire 11 on their surfaces. These air flows cause turbulence in the space between the two rollers 25 and 26, which has a negative effect on the fibrous web 2 guided in the free draw. In particular, shortly before the fibrous web 2 is fed onto the dryer fabric 11, it tends to form folds F.These wrinkles are critical for the further processing of the fibrous web 2 and can even lead to the tearing of the fibrous web 2.

[0037] Fig. 3 shows essentially the same schematic side view of the transfer area 24 as Fig. 2 , but with the solution according to the invention, which prevents the formation of wrinkles in the fibrous web 2. An essential component of this solution is an air extraction device 27, which is arranged in the transfer area 24 vertically below, but at the edge of, the fibrous web 2 guided in free tension. In other words, the air extraction device 27 is not located directly below the fibrous web 2, but is arranged in the cross-machine direction (direction orthogonal to the image plane of the Fig. 2 ) is arranged offset laterally to the latter. The air extraction device 27 has an opening area 28 (cf. Fig. 4), which is directed towards the free space between the two rollers 25 and 26 in order to extract air from this space and then discharge it in a targeted manner (see downward arrow of air extraction device 27). In this way, turbulence in the transfer area 24 between the two rollers 25 and 26 can be largely avoided, so that the fibrous web 2 is not in danger of forming wrinkles F. At the same time, the air extraction device 27 is largely protected from contamination by its edge-side arrangement relative to the as yet unbonded fibrous web 2.

[0038] Preferably, the system 2 according to the invention comprises on both its driver and drive sides such an air extraction device 24 as shown in Fig. 4 shown schematically. In the three-dimensional representation of the Fig. 4For the sake of clarity, only the first roller 26 of the dryer section 10, a portion of the dryer fabric 11, which moves in the direction of the arrow, and the two edge-side air extraction devices 27 are shown. The above-mentioned opening area 28 can be seen on one of these two air extraction devices 27. The two air extraction devices 27 are designed here as suction boxes. List of reference symbols

[0039] 1 Plant 2 Fibre web 3 Fibre suspension unit 4 Forming section 5 Inclined wire 6 Headbox 7 Binder wire section 8 Binder wire 9 Binder headbox 10 Dryer section 11 Dryer wire 12 Winder 13 Winding core 14 Winding roll 15 First container ("pulper") 16 Agitator 17 Second container ("pulper") 18 Agitator 19, 20 Pumps 21 Recirculation circuit 22 Continuous furnace 24 Transfer area 25 Last roller of the binder wire section 26 First roller of the dryer section 27 Air extraction device 28 Opening area αAngle FFold HHorizontal

Claims

1. Installation (1) for producing a fibrous web (2), in particular a long-fibre paper web or a wet-laid non-woven web comprising a binder-wire section (7) having a binder wire (8) for applying an aqueous binder to the fibrous web (2), and a drying section (10) having a drying wire (11) for drying and consolidating the fibrous web (2), wherein the binder-wire section (7) and the drying section (11) are disposed at a mutual spacing in such a way that the fibrous web (1) is guided from the binder wire (8) to the drying wire (11) in a free draw, characterized in that at least one air extraction device (27) is disposed on the periphery of the installation (1), in the region of the spacing between the binder-wire section (7) and the drying section (11).

2. Installation (1) according to Claim 1, characterized in that the at least one air extraction device (27), when viewed in the vertical direction, is disposed substantially below the fibrous web (2) guided in the free draw, but does not extend from the periphery of the installation (1) to below the fibrous web (2) guided in the free draw.

3. Installation (1) according to Claim 1 or 2, characterized in that the at least one air extraction device (27) is a suction box.

4. Installation (1) according to one of the preceding claims, characterized in that one air extraction device (27) is in each case disposed on the drive side as well as on the operator side of the installation.

5. Installation (1) according to Claim 4, characterized in that the drive-proximal and the operator-proximal air extraction devices (27) are designed in such a manner that the vacuum emanating from them can be adjusted independently of one another.

6. Installation (1) according to one of the preceding claims, characterized in that the installation space below the fibrous web (2) guided in the free draw is kept vacant, at least in the region between a last roller (25) of the binder-wire section (7), over which the binder wire (8) is guided when the latter releases the fibrous web (2), and a first roller (26) of the drying section (10), over which the drying wire (11) is guided when the latter receives the fibrous web (2).

7. Installation (1) according to one of the preceding claims, characterized in that the binder wire (8) runs horizontally or approximately horizontally at least in portions and / or the binder wire section (7) has at least one binder headbox (9).

8. Installation (1) according to one of the preceding claims, characterized in that the installation (1) furthermore comprises a forming section (4) for dewatering an aqueous suspension, which is disposed upstream of the binder wire section (7) in the processing direction of the fibrous web (2) through the installation (1), wherein the forming section (4) preferably comprises an inclined wire former which has an inclined wire (5) extending at an angle (α) to the horizontal (H) at least in portions, and at least one at least single-layer, preferably multi-layer, headbox (6).

9. Installation (1) according to Claim 8, characterized in that the installation (1) furthermore comprises a fibrous material suspension unit (3) for producing the aqueous suspension for the forming section (4).

10. Installation (1) according to one of the preceding claims, characterized in that the installation (1) furthermore comprises a winder (12) for continuously winding up the fibrous web (2) onto winding cores (13) to form wound rolls (14), wherein the winder (12) is disposed downstream of the drying section (10) in the processing direction of the fibrous web (2) through the installation (1).

11. Installation (1) according to one of the preceding claims, characterized in that at least one, preferably actuatable, blowing device for the non-contact floating guidance of the fibrous web (2) by means of air or another free-flowing medium is provided between the binder wire section (7) and the drying section (11), having a plurality of blowing zones that can be controlled / feedback-controlled independently of one another transversely to the running direction of the fibrous web (2).

12. Use of an installation (1) according to any one of the preceding claims for the production of a fibrous web (2), in particular a long-fiber paper or wet-laid non-woven web, wherein in the intended operation of the installation (1) air is extracted from the region between the binder-wire section (7) and the drying section (11) by means of the at least one peripheral air extraction device (27).

13. Use according to Claim 12, characterized in that the fibrous web (2) is wet-laid glass fibre non-woven web.

14. Use according to Claim 12 or 13, characterized in that the fibrous web (2) is produced at a speed of at least 170 m / min.

15. Use according to one of Claims 12 to 14, characterized in that the fibrous web (2) has an area weight of less than 30 g / m2.