Method Of Moistening Paper Web And Paper Web Moistening Device

Abstract

A paper web moistening device comprises several moistening nozzles (2) in the cross direction of a paper web for blowing water mist comprising air and water onto the paper web (3) surface. At least one means for removing water 5 mist and/or air from the vicinity of the paper web (3) surface is arranged be-tween the moistening nozzles. This means is arranged closer to the paper web (3) surface than the moistening nozzles (2).

Description

BACKGROUND OF THE INVENTION

The invention relates to a method of moistening a paper web comprising moistening the paper web by a moistening device by spraying water mist onto the paper web surface and by removing excess water mist from the moistening device.

The invention further relates to a paper web moistening device comprising a body, moistening nozzles and at least one means for removing water, water mist or air from the moistening device.

The paper web is moistened to control the paper web moisture profile, for instance. Moistening can also be used for managing the curling of the paper web in the paper machine. Furthermore, in online calendering, for example, the controlling of certain quality measures requires high-grade moistening with water.

The moistening device is provided with several moistening nozzles in the cross direction of the paper web for blowing water mist containing air and water onto the paper web surface. One moistening apparatus of this kind is disclosed in DE 952 765.

Moistening devices exist where the above-mentioned moistening nozzles are arranged in several successive rows. The nozzles in successive rows may overlap with one another. A problem associated with moistening devices is how to achieve a sufficiently even moistening result. A moving paper web carries air and air is also blown by the moistening nozzle. The air currents generated make the controlling of the moistening nozzle response difficult, i.e. the fact which point of the paper web is in reality moistened by moistening nozzle. In the moistening device, the current may cause the nozzles at different points in the lateral direction to moisten the same point of the paper web, which results in too moist and too dry points in the paper web. Furthermore, the controlling of the moistening nozzle response is so difficult that the adjustment of the moistening nozzles becomes very complicated.

BRIEF DESCRIPTION OF THE INVENTION

The object of the present invention is to provide a new and improved method of moistening a paper web and a paper web moistening device.

The method according to the invention is characterized in that the removal of water mist and/or air occurs closer to the paper web surface than the spraying of water mist.

The paper web moistening device according to the invention is further characterized in that the moistening device comprises a means that extends closer to the paper web surface than the moistening nozzles for removing water mist and/or air from the vicinity of the paper web surface.

The basic idea of the invention is that several moistening nozzles are arranged in the body of the paper web moistening device. At least one means for removing water mist and/or air from the vicinity of the paper web surface is arranged between the moistening nozzles so that the means extends closer to the paper web than the moistening nozzle. By means of the invention, the desired moisture profile can be achieved with a very high accuracy. Furthermore, the detrimental effect of air currents on moisture nozzle responses can be prevented, which facilitates the controlling of the moistening device. The idea of an embodiment is that the means for removing water mist and/or air from the vicinity of the paper web surface is a discharge nozzle. The idea of another embodiment is that before the moistening nozzles, the moistening device comprises a slit nozzle having substantially the same width as the paper web for blowing air against the machine direction of the paper web to decrease the laminar air current travelling along with the paper web. The purpose of this is also to improve the moisture profile produced by the moistening device. The idea of a third embodiment is that the nip side of the moistening device is provided with a slit nozzle having substantially the same width as the paper web for blowing air in the direction opposite to the machine direction of the paper web to prevent water mist from spreading into the environment from the moistening device.

This description discloses the use of air and water in moistening but other gases and liquids may also be employed. Thus, in this description, the term “air” refers to any gas or gas mixture usable in moistening the paper web and the term “water” refers to any liquid or liquid mixture suitable for moistening the paper web.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be described in greater detail in the accompanying drawing, where

FIG. 1 is a schematic and cross-sectional side view of a paper web moistening device, and

FIG. 2 is a schematic top view of the moistening device according to FIG. 1.

For the sake of clarity, the figures illustrate the invention in a simplified manner. Like reference numbers refer to like parts in the figures.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a paper web moistening device where the body 1 is provided with moistening nozzles 2. The body 1 is a beam arranged in the cross direction of the paper web 3. The moistening device is arranged below the paper web 3. The paper web 3 moves in the direction of arrow A. The paper web 3 may be a paper or cardboard web already manufactured in a paper machine or a fibrous web in a paper machine or cardboard machine, still containing moisture that is to be removed in the paper machine. The moistening device is typically arranged below the paper web 3, but if desired, it may also be mounted above the paper web 3 or both above and below the paper web. The particular purpose of the moistening device is to increase the moisture content of the paper web 3.

Water mist is blown or sprayed by moistening nozzles 2 towards the paper web 3 surface, the water mist being typically a mixture of air and water. The cone-shaped water mist spray achieved by means of the moistening nozzle 2 is illustrated by arrows B in the accompanying drawing.

The body 1 of the moistening device is provided with water discharge outlets 4, through which excess water mist or condensed water can exit from the space between the moistening device and the paper web 3. The water discharge outlets 4 are connected to discharge pipes, which are not shown in the figures. The discharge of water mist and water can be intensified by low pressure. The water discharge outlets 4 are located farther from the paper web 3 surface than the moistening nozzles 2.

The moistening nozzles 2 are arranged in rows in the cross direction of the paper web 3. The moistening nozzles 2 in successive rows overlap, i.e. they are at different points in the lateral direction, as appears from FIG. 2.

A discharge nozzle 5 having substantially the same width as the paper web 3 is arranged between the second and the third row of moistening nozzles. The discharge nozzle 5 is used for air suction as illustrated by arrow C. The discharge nozzle 5 is connected to a discharge pipe, which is not shown in the figures. The generation of suction does not require a very great low pressure or low pressure is not necessarily needed at all, provided that air can be removed through the discharge nozzle 5, i.e. that the current is high enough for keeping the discharge nozzle 5 open. At the same time, the discharge nozzle 5 removes excess water mist.

The distance hi of the moistening nozzles 2 from the paper web 3 surface is typically 50 to 150 mm. The discharge nozzle is arranged closer to the paper web 3 surface than the moistening nozzles 2, in which case the distance h2 of the discharge nozzle 5 from the paper web 3 is smaller than the distance h1 of the moistening nozzles 2 from the paper web 3. In that case, air currents caused by the movement of the paper web 3 and by the first and second rows of moistening nozzles can be absorbed by the discharge nozzle 5 without the air currents interfering with the operation of the moistening nozzles in the third and fourth rows of moistening nozzles. In that case, the responses of the moistening nozzles in successive rows do not turn or overlap but each moistening nozzle moistens only its own point in the paper web 3, which provides a very even moistening result. Furthermore, the desired moistening profile can be achieved very accurately and relatively easily.

The distance h2 of the discharge nozzle 5 from the paper web 3 is typically 10 to 15 mm. Preferably, this distance h2 is at most 50 mm. In any case, the distance h2 of the discharge nozzle 5 is smaller than the distance h1 of the moistening nozzles 2 from the paper web 3. Preferably, the distance h2 of the discharge nozzle 5 from the paper web 3 is at least 20 mm smaller than the distance h1 of the moistening nozzles 2 from the paper web 3. Particularly preferably, the distance h2 of the discharge nozzle 5 from the paper web 3 is at least 50 mm smaller than the distance h1 of the moistening nozzle 2 from the paper web 3.

The dimension of the moistening device in the machine direction A of the paper web 3 may be 1 m, for example, when the moistening device comprises four successive nozzle rows as in the appended figures. The dimension of the moistening device in the machine direction A of the paper web may vary between 0.5 and 1.5 m, for example, and the number of successive moistening nozzle rows may vary from two to ten, for instance. The moistening device naturally has the same width as the paper web 3 and the number of moistening nozzles depends on the paper web width 3, the shape of moistening nozzle responses and on the desired moistening efficiency.

The front edge of the moistening device comprises a first slit nozzle 6 having the same width as the paper web 3. The first slit nozzle 6 blows air against the machine direction A of the paper web 3 in accordance with arrow D. The purpose of this blow is to remove the laminar air current carried along with the paper web 3 that interferes with the evenness of the moistening nozzle 2 sprays. The slit nozzle 6 has a planar surface that guides the air current D. The planar surface may be slightly curved so that the air current D curves in the direction of the curved surface.

The nip side of the moistening device comprises a second slit nozzle 7. Also, the second slit nozzle 7 has substantially the same width as the paper web 3. The second slit nozzle 7 also blows air against the machine direction of the paper web 3 in accordance with arrow E. The structure and operation of the slit nozzle 7 correspond to those of the first slit nozzle 6. The air current E blown by the second slit nozzle 7 is used to prevent the water mist from spreading into the environment from the moistening device.

For the sake of clarity, the appended figures do not show pipes, connectors or other arrangements for bringing air and water into the moistening device and for carrying air and water away from the moistening device.

The machine line for fibrous web may comprise several successive moistening devices in the machine direction. At least one moistening device is provided with the structure according to the solution described here. The described solution can also be arranged in two successive moistening devices or, if desired, in more than two moistening devices and even in all moistening devices. The described moistening device is preferably utilized in moistening mechanical uncoated papers, such as SC paper. One preferred solution is to arrange the described moistening device in connection with a multi-roll calender or a multi-roll calender having two stacks of rolls.

The drawing and the related description are only intended to illustrate the inventive concept. The details of the invention may vary within the scope of the claims. Thus, for example, the moistening nozzles need not be arranged in rows in the cross direction of the paper web but they may be arranged otherwise in the moistening device. On the other hand, the distance between the rows of the moistening nozzles arranged in rows may vary between successive rows. Tests have shown that in the solution according to the appended figures, the two first moistening nozzle rows interfere with each other relatively little, and the result can be improved considerably by removing the air current from between the second and the third moistening nozzle row by the discharge nozzle 5. If desired, discharge nozzles 5 may be arranged between each moistening nozzle row or, if moistening nozzles are not arranged in rows, discharge nozzles may be mounted between all moistening nozzles. The discharge nozzle 5 needs not necessarily have the same width as the paper web 3 but there may be several discharge nozzles 5 one after another in the lateral direction of the paper web 3. On the other hand, the discharge nozzle 5 may be a single pipe, in which case discharge nozzles can be arranged everywhere in the moistening device between the desired moistening nozzles 2. In that case, a row may be formed of the discharge nozzles 5 in the cross direction of the paper web 3, in which case there are discharge nozzles next to or at a distance from one another in a row, whose function corresponds to that of the discharge nozzle 5 provided with a slit, which has the same width as the paper web 3 and is illustrated in FIGS. 1 and 2.

Instead of the discharge nozzle 5, the means for removing water mist and/or air from the vicinity of the paper web 3 surface may be any structure arranged to extend closer to the paper web than the moistening nozzle 2 and to remove air and/or water mist from the vicinity of the paper web 3 surface. As such, this structure does not require a discharge pipe or suction, but the structure may be formed by a partition wall, beam, spoiler, air doctor or another similar structure. Also a tap or taps arranged next to one another or a plate or plates may function as the means for removing water mist and/or air. In a manner corresponding to the one described in connection with the discharge nozzle 5, this structure enables removal of the interfering effect of air currents caused by the moistening nozzles and the movement of the paper web on the function of the other moistening nozzles. This function may be based, for example, on the fact that the current in the direction of the paper web 3 surface can be cut at a desired point and/or a current can be formed at a desired point in the direction away from the paper web surface for guiding excess air and/or water mist. If means of this kind for removing water mist and/or air is not itself provided with discharge pipes or suction, the excess air and/or water mist or condensed water removed by them from the vicinity of the paper web can be first collected onto the surface of the moistening device, i.e. onto a “floor level” formed by it, and removed through water discharge outlets 4 arranged in the body 1 of the moistening device, for example.

Claims

1. A method of moistening a paper web comprising spraying water mist onto the paper web surface by a moistening device and removing excess water mist and/or air closer to the paper web surface than where the spraying of water mist occurs.

2. A method according to claim 1, wherein water mist and/or air are/is removed by a discharge nozzle.

3. A method according to claim 1, wherein air is blown before the moistening device in the direction opposite to the machine direction of the paper web.

4. A method according to claim 1, wherein air is blown from the nip side of the moistening device in the direction opposite to the machine direction of the paper web.

5. A paper web moistening device comprising a body, moistening nozzles and at least one means that extends closer to the paper web surface than the moistening nozzles for removing water mist and/or air from the vicinity of the paper web surface.

6. A paper web moistening device according to claim 5, wherein moistening nozzles are arranged in at least two different positions in the machine direction of the paper web and that the means for removing water mist and/or air from the vicinity of the paper web surface is arranged in a position between the moistening nozzles.

7. A paper web moistening device according to claim 6, wherein the moistening nozzles are arranged in at least two rows in the moistening device and that the means for removing water mist and/or air from the vicinity of the paper web surface is arranged between the rows.

8. A paper web moistening device according to claim 5 wherein the means for removing water mist and/or air from the vicinity of the paper web surface has the same width as the paper web.

9. A paper web moistening device according to claim 5, wherein distance of the means for removing water mist and/or air from the vicinity of the paper web surface from the paper web is at least 20 mm smaller than the distance of the moistening nozzles from the paper web.

10. A paper web moistening device according to claim 5, wherein the distance of the means for removing water mist and/or air from the vicinity of the paper web surface from the paper web is at least 50 mm smaller than the distance of the moistening nozzles from the paper web

11. A paper web moistening device according to claim 5, further comprising a slit nozzle arranged in the front section of the moistening device for blowing air against the machine direction of the paper web.

12. A paper web moistening device according to claim 5, further comprising a slit nozzle arranged in its nip side for blowing air against the machine direction of the paper web.

13. A paper web moistening device according to claim 5, further comprising at least one water discharge outlet.

14. A paper web moistening device according to claim 5, wherein the means for removing water mist and/or air from the vicinity of the paper web surface is a discharge nozzle.

15. A paper web moistening device according to claim 5, wherein the moistening device is arranged in connection with a multi-roll calender.

16. A paper web moistening device according to claim 5, wherein the moistening device is arranged in connection with a multi-roll calender having two stacks of rolls.