METHOD AND DEVICE FOR PRODUCING OR TREATING A WEB OF FIBROUS MATERIAL

Abstract

A process for the production or treatment of a fibrous web, in particular a paper or cardboard web, includes the following steps: a. drying of the fibrous web in a dryer section; b. subsequent cooling of at least one first side of the fibrous web by way of convection cooling, whereby the fibrous web has a temperature of 65 C. or less on at least the first side after cooling, in particular 50 C. and less; c. apply steam to at least the first side of the fibrous web, in particular the temperature on the first side after steam application is at least 70 C., optionally more than 80 C. or 90 C.; and d. treatment of the fibrous web in at least one calendering nip.

Claims

1. A method for producing or treating a web of fibrous material, the method comprising the steps of: drying the web of fibrous material in a drying section; subsequently cooling at least a first side of the web of fibrous material by way of convection cooling, the web of fibrous material after cooling having a temperature of 65 C. or less on at least the first side; applying steam onto the at least one first side of the web of fibrous material, the temperature after applying steam being at least 70 C.; and treating the web of fibrous material in a single calendering nip (3), the calendering nip including a heated roll and a counter element, and a distance between an end of applying steam and the calendering nip being not greater than 1 m, the web of fibrous material running at a speed of between 600 m/min and 1600 m/min.

2. The method according to claim 1, wherein the web of fibrous material is smoothed by way of a wet press prior to the drying section, wherein the web of fibrous material is a paper web or a cardboard web.

3. The method according to claim 1, wherein a surface temperature of the first side of the web of fibrous material on entering the calendering nip (3) is at least 60 C.

4. The method according to claim 1, wherein the heated roll has a surface temperature of 220 C. or more and comes into contact with the first side of the web of fibrous material.

5. The method according to claim 1, wherein the heated roll is heated by way of a heating fluid, wherein the heating fluid is supplied to the heated roll at a temperature of at least 240 C.

6. The method according to claim 1, wherein the calendering nip is operated at a maximum linear load of 150 N/mm.

7. The method according to claim 1, wherein no moistening of the web of fibrous material occurs between leaving the dryer section and the step of subsequently cooling.

8. The method according to claim 1, wherein the web of fibrous material is a cardboard web including at least two layers and having a basis weight between 100 g/m.sup.2 and 600 g/m.sup.2.

9. The method according to claim 1, wherein the web of fibrous material after cooling having a temperature of 50 C. or less on at least the first side, and wherein the temperature on the first side of the web of fibrous material after applying steam is at least 80 C. or 90 C.

10. A device for producing or treating of a web of fibrous material, the device comprising: a drying section configured for drying the web of fibrous material; a calender having a single calendering nip configured for treating the web of fibrous material, the calendaring nip including a heated roll and a counter element, the device being configured for treating the web of fibrous material at a speed of between 600 m/min and 1600 m/min; a steam blow box positionedwhen viewed in a direction of travel of the web of fibrous materialupstream from the calender, the steam blow box being configured for applying steam to a first side of the web of fibrous material; and a convection cooling device positioned between the drying section and the steam blow box, the convection cooling device being configured for cooling at least the first side of the web of fibrous material by way of convection to a temperature of 65 C. or less.

11. The device according to claim 10, wherein the calendaring nip is configured for smoothing the web of fibrous material.

12. The device according to claim 10, wherein the convection cooling device is configured for passive cooling through a free section of the web of fibrous material, wherein a length of the free section is at least 5 m.

13. The device according to claim 10, wherein the convection cooling device includes or consists of a convection cooler configured for active cooling, wherein the convection cooler is configured for blowing air onto at least the first side.

14. The device according to claim 13, wherein the convection cooler is configured for blowing air onto both the first side of the web of fibrous material and a second side of the web of fibrous material.

15. The device according to claim 13, wherein the convection cooler is structured and arranged for conditioning the air.

16. The device according to claim 15, wherein the convection cooler conditions the air by at least one of tempering, humidifying, and dehumidifying the air.

17. The device according to claim 10, wherein the calendering nip includes a heated roll and a counter element, wherein the heated roll is configured for being heated to a surface temperature of 220 C. or more and for coming into contact with the first side of the web of fibrous material.

18. The device according to claim 10, wherein the calender includes a thickness calibration device configured for a calibrating a thickness.

19. The device according to claim 18, wherein the thickness calibration device is implemented by way of at least one of a thermal calibration and a deflection control roll.

20. The device according to claim 10, further comprising an additional steam blow box configured for applying steam onto a second side of the web of fibrous material, and wherein a distance between (a) at least one of the steam blow box and the additional steam blow box and (b) the calendering nip is a maximum of 1000 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0077] The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: FIG. 1 shows a device according to one aspect of the current invention;

[0078] FIG. 2 shows a device according to an additional aspect of the current invention; and

[0079] FIG. 3 shows a convection cooler for use in a device according to an additional aspect of the invention.

[0080] Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

[0081] FIG. 1 shows a device according to one aspect of the present invention which is suitable for carrying out a method according to the present invention. A drying section 10 is provided in which a fibrous web 1, such as a paper or cardboard web 1, is dried. Web 1 exits drying section 10 with a low residual moisture of usually less than 12%, for example 7% or 8%, and a high temperature, for example between 75 C. and 90 C.

[0082] For further processing of web 1, a calender 2 is provided in FIG. 1. In this example, calender 2 is shown as roll calender 2, equipped with a heating roll 4 and a counter roll 5, which together form calendering nip 3. Heating roll 4 can have a surface temperature of 220 C. or more and is in contact with first side 1a of fibrous web 1. Counter roll 5 can be designed as a bending compensation roll. However, any other type of calender can also be provided, such as shoe or ribbon calenders that have an extended calendering nip 3. Usually, a measuring device such as a scanner can also be provided following calender 2. After calender 2, especially after the scanner, web 1 can then be wound rewound. Alternatively, provision can also be made for further process steps to follow after calender 2. For example, one or more coating units may be provided.

[0083] In order to achieve the desired volume-protective smoothing, way 6 is provided for convection cooling of web 1 following the drying section. In the design shown in FIG. 1, web 1 is guided via guide rolls 8 to a convection cooler 6, in which it can be actively cooled. For this purpose, air is blown at least onto first side 1a of web 1, especially onto both sides of web 1. Even if only one side of web 1 is to be smoothed, it can be advantageous to design convection cooler 6 in such a way that air is blown onto both sides of web 1. On the one hand, this leads to more efficient cooling of web 1. On the other hand, a more stable web travel can be achieved if air is blown simultaneously or at very short time intervals onto both sides of web 1.

[0084] This air can be taken directly from the environment, for example, from a cooler region of the production line such as the machine basement; or it can be conditioned prior to applying it onto fibrous web 1. In particular, cooling of the air, for example by way of a suitable heat exchanger, is advantageous, as this can significantly improve the cooling effect of convection cooler 6, so that a much lower web temperature can be achieved following convection cooler 6.

[0085] Following convection cooling, web 1 is supplied with steam on at least first side 1a. For this purpose, a steam blow box 7 is provided in the device shown. The steam is supposed to condense at web 1 and moisten as well and heat the region near the surface. In order to allow the steam to condense as well as possible, it is advantageous if the web temperature subsequent to the convection cooling ways or before entering steam blow box is 50 C. or less. With active convection coolers 6, the temperature can also be lowered significantly, for example to 45 C. or 40 C.

[0086] If both sides of fibrous web 1 are to be treated, in particular smoothed, a second steam blow box may also be provided, which is arranged in such a way that it compresses the second side of the fibrous web with steam.

[0087] After leaving the steam blow box 7, web 1at least on first side 1ahas the temperature and moisture gradients that are desired to achieve volume-protective smoothing. Since fibrous web 1 tends to equalize such gradients again over time, it is advantageous to guide web 1 as quickly as possible after steam blow box 7 into calendering nip 3. It is therefore optional to place steam blow box 7 very close to calendering nip 3, so that the distance between steam blow box 7 and calendering nip 3 is a maximum of 1000 mm, in particular a maximum of 500 mm.

[0088] The design shown in FIG. 2 differs from that in FIG. 1 only in the design of the ways for convection cooling. Instead of active cooling by way of a convection cooler 6, convection cooling is realized in FIG. 2 as passive cooling by way of a free section of fibrous web 1. To improve cooling of web 1, it is advantageous if the free section is at least 5 m, optionally at least 7 m long. In order to achieve the longest possible free distance, in the design according to FIG. 2, web 1 between drying section 10 and steam blowing box 7 is diverted several timesfor example twice, three times, four times or moreby guide rolls 8, so that even with a limited structural length of the device, a sufficient free distance can be provided for the cooling of lane 1.

[0089] FIG. 3 shows a schematic section of a convection cooler 6 for active cooling of fibrous web 1, as it can be used, for example, in a design according to FIG. 1. Two rows of nozzles 61 are provided, each of which blow an air flow 62 onto fibrous web 1. Nozzles 61 of the upper row therein supply first side 1a of web 1 with an air flow 62; nozzles 61 of the lower row supply the second side. Nozzles 61 extend over the entire width of web 1 (CD-Cross Direction) and are arranged one behind the other in the direction of travel machine direction (MDMachine Direction). FIG. 3 shows two or three nozzles 61 per row as an example. In practical applications, however, it can also be significantly more, for example 10, 12, 15 or more nozzles per row, in order to achieve the desired cooling of lane 1. It is advantageous to provide a distance between nozzles 61 of each row in the MD direction. The distance, which can correspond in particular to the MD expansion of a nozzle 61, allows a trouble-free discharge of air flow 62 after impinging on web 1.

[0090] Regardless, such a convection cooler 6 is very compact. Already with an MD extension between 1 m and 2 m, for example 1.5 m, excellent cooling of the web can be achieved. However, larger MD extensions of up to 4 m, 5 m or 6 m are also possible.

[0091] An active convection cooler 6 with two rows of nozzles, as shown here, has the advantage that web 1 is cooled from both sides, allowing for faster cooling. In addition, the web travel of web 1 will also be stabilized. By applying an air flow 62 onto first side 1a, the web turns downwards. Air flows 62 from lower nozzles 61 act against this, and guide web 1 back upwards. As a result of alternately depressing and lifting, web 1 travels in a slight wave motion, but essentially stable and straight through convection cooler 6.

[0092] The air for air flows 62 can simply be ambient air, which is usually 30 or more in the vicinity of a paper machine and can also be quite humid. Alternatively, the air can also be conditioned, for example cooled to 25 or 20 C. and, if necessary, dehumidified.

COMPONENT IDENTIFICATION LISTING

[0093] 1 Fibrous web [0094] 1a first side [0095] 2 Calender [0096] 3 Calendering nip [0097] 4 Heating roll [0098] 5 Counter Roll [0099] 6 Convection coolers [0100] 7 Steam blow box [0101] 8 Guide roll [0102] 10 Dryer section [0103] 61 Nozzle [0104] 62 Airflow

[0105] While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.