JPH0373678B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for stabilizing the running of a paper web in the drying section of a paper machine, in which the paper web is supported by a drying wire or equivalent fabric. transferred from one line of drying cylinders to another;
Thus, in one line of drying cylinders the web lies between the drying wire and the cylinder surface, and in the other line of drying cylinders the web lies between the outer surface of the drying wire. The method also includes spraying means which cause the web to travel between the lines of the drying cylinder in a common run of the web and the drying wire. It is stabilized.

The invention furthermore relates to an apparatus for applying the method according to the invention, the apparatus comprising a support structure and associated with this structure a common run of drying wire and web between the lines of each drying cylinder. A nozzle box is provided against which the air is directed.

Web breakage within the drying section of a high speed paper machine is an essential factor limiting the increase in paper machine speed. The object of the invention is to provide a device which makes it possible to significantly reduce web breakage due to web flapping and the drawbacks caused by such breakage.

The invention provides that one or several rolls or cylinders of a group of drying cylinders are provided inside the wire loop, while the other one or more rolls or cylinders are outside this loop. It is intended for use in conjunction with so-called single felt transfers, which constitute single felt transfers. In the following, designated wire is used instead of fabric, but it is meant to refer to any suitable fabric, such as felt or any type of mesh fabric, such as plastic.

Single felt transfer itself is within the prior art. For example, US Pat. No. 796,601 defines a felt run diagram for a single felt transfer.

To the applicant's knowledge, single felt transfers were not introduced into commercial use until approximately 70 years after their invention.
The application of single felt transfers has been primarily in high speed paper machines.

It is well known that a thin layer of air accompanies all moving surfaces. There is no slippage between the air and the moving surface, and the air particles that come into contact with the moving surface move at the same speed as the moving surface.

The chute defined by the fabric (felt or wire) and the cylinder surface (cylinder or roll) is called the entry nip when the fabric enters the chute, and the entrance nip when the fabric exits the chute. It is called the exit nip.

In both the inlet nip and the outlet nip, if the entire nip interface between the boundary layers is not air permeable, air flow will occur in a direction opposite to that of the boundary layer. At that point, the flow is blocked by the boundary layer, so positive pressure prevails in the direction across the fabric in the inlet nip, and in the outlet nip, the suction effect of the flow in the boundary layer suppresses the fabric. Negative pressure has an advantage in the transverse direction.

When an air permeable fabric, i.e., a wire, is used in a manner known in the art, the pressure difference across the wire, generated by flowing in the boundary layer, causes the flow of air through the wire. It gives birth to

As is well known, the first and second
drying groups are usually provided with a so-called single fabric transfer system, in which in the upper cylinder the paper web is located between the fabric and the cylinder, and in the lower cylinder the paper web is located between the fabric and the cylinder. This is achieved by being located above.

Several problems have traditionally been encountered in single fabric transfers, which are due to pressure differences on different sides of the fabric caused by flow in the boundary layer. It is something. Air tends to flow through the wire from the high pressure side to the low pressure side, thus breaking the supporting contact between the fabric and the paper web. The problem areas are the exit nip and the entrance nip. In both places,
The pressure difference across the wire tends to cause the paper web to detach from the wire. When this detachment occurs, the paper web begins to behave erratically due to the air flow created within the pocket. The detached web is often forced onto the lower cylinder by the effect of centrifugal force. The result is severe wrinkling within the entrance nip and, in the worst case, web breakage.

Various seal structures have been developed to eliminate the above problems. Their purpose is to prevent boundary layer flow following the moving surface from entering the nip. For example, German patent application publication no.
No. 2712184 describes a seal structure for this purpose.

The flapping of the paper web that occurs in the area of single wire transport is due to the boundary layer flow and pecking forces mentioned above. As mentioned above, Fabrik/
In the chute or nip defined by the web and cylinder surface, positive or negative pressure is generated by the effects of boundary layer flow. These pressures tend to separate the web from the fabric. Furthermore, due to the effect of the picking force, the paper web has a tendency to follow along a denser and smoother surface, i.e. the cylinder, which also tends to cause the web to detach from the fabric. It is.

In the upper nip, the flapping of the web occurs mostly on both sides, whereas in the lower nip the web is observed to flapping over its entire width. This is due to the fact that air flows from both sides of the paper machine into the upper nip, where negative pressure predominates. If the web is only slightly separated from the fabric, the edges of the web will begin to flap due to the transverse air flow. On the other hand, there is a positive pressure in the lower nip and air flows out of the nip to both sides of the paper machine and through the fabric where the web is forced to rise away from the fabric.

As a general observation, flapping of a web generally begins at its edges, but such flapping at the edges of the web spreads over the entire width of the web until the web is exposed to the drying wire. This results in complete detachment and damage, or at least wrinkles in the web.

In the applicant's Finnish patent application no. 803891, a method and an installation are suggested with which the drawbacks due to flow in the boundary layer can be reduced.
However, the device suggested in the same application does not allow for the inability to prevent edge flapping occurring in the upper nip, especially when using a single wire transport system to modernize older paper machines. It has been recognized that this is the case when converting to a paper machine equipped with means. In older paper machines, the free stretch between each cylinder is extremely long, and they are extremely sensitive to flapping.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and apparatus for preventing flapping of the edges of the web, particularly in the upper nip, in paper machines equipped with a single wire transfer system. be. A further object is to provide a method and apparatus for facilitating the passage of the ends of a paper web through a drying station.

In order to achieve the above and the following purposes,
The method according to this invention has the following main characteristics:
Air jets are blown in the area of approximately both edges of the web on the sides of the drying wire in a direction opposite to the direction of travel of the drying wire and the web, and these air jets are connected to the drying cylinder. In the wedge-shaped space between the web and at least the bottom line of said wedge-shaped space is oriented towards the drying wire.

On the other hand, the device according to the invention has, as its main feature, a nozzle box inserted into the support of the support structure and arranged close to the areas of the ends of the web, in which the nozzles Inside the boxes, several nozzle holes are provided on the supporting side of these boxes facing the drying wire, and the orientation of the nozzle openings in these nozzle holes is such that the direction of drying is opposite to the running direction of the wire. The curved shape of the support surface which is directed towards the wire, ie defined by the nozzle bore, is configured such that the direction of the jet is opposite to the running direction of the drying wire.

By means of the device according to the invention, the jet can be placed in the optimum position by rotating its support beam or its corresponding support member about an axis parallel to the axis of rotation of the drying cylinder. flapping of the side areas of the web as well as the resulting defects can both be minimized.

The invention will now be described in detail with reference to the accompanying drawings, but the invention is not limited to the details of these drawings.

In the single wire transfer system according to FIG.
The paper web W lies below the wire 12 in the upper cylinder 10 of the drying station and above the wire 12 in the lower cylinder. The flow in the boundary layer creates a negative pressure in the upper nip K- and a positive pressure in the lower nip K+. The harmful effects of the positive pressure generated in the lower nip K+ are successfully eliminated by the method and device described in the above-mentioned Finnish Patent Application No. 803,891. However, the flapping of the edge W' of the paper web W in the upper nip K- illustrated in FIGS. 2A and 2B can be controlled by the method and apparatus described in the above-mentioned application. This is particularly true in the case of older paper machines that have been modernized and are equipped with single wire transport systems.

In the embodiment shown in FIGS. 3 and 4, the device 20 according to the invention is arranged close to the run of the transfer wire 12 and the web between the drying cylinders 10 and 11 on the side of the transfer wire 12. A tubular beam 22 is provided, which beam 22 is connected to the cylinder 1.
It is parallel to the rotation axes of 0 and 11. This beam 2
2 is supported at its ends by supports (not shown) and is rotatable about axis A--A for purposes to be explained below. Pipes 21a and 21b are connected to both ends of the beam 22, and air for blowing is introduced into the device 20 from within these pipes. The supply of blowing air is illustrated by the arrow Fin. In the area of the ends of the beam 22 inside the ends 10' of the cylinder 10, nozzle boxes 23a and 23b are attached to this beam 22. These nozzle boxes 23a and 23b have a closed outer part 24 and an inner part 25 provided with a closed end and several nozzle holes 26 parallel to each other.
It is defined by. The inner surface with the nozzle holes 26 forms the bearing surface 25 of the device according to the invention. The nozzle boxes 23a and 23b are web W
is located in the side area W′ of.

According to the method according to the invention, the transfer wire 1
An air jet _F1 is blown out from the nozzle hole 26 in a direction opposite to the running direction of the web W and the web W. Air jet discharged from nozzle 26
The blowout effect of F ₁ compensates for the negative pressure that prevails in this region opposite the web W in the chute K-, and also compensates for the harmful effects of this negative pressure. This injection effect is indicated by arrow _F2 . This allows the web W and each edge W' thereof to remain stable in contact with the transfer wire 12 and form the fold W _p shown in FIG. 2A.
is not formed.

The spraying method shown in Figures 3 and 4 is
Even if the conditions are such that flapping is likely to occur, such as in the case of old paper machines where the free stretching section between the drying cylinders 10 and 11 is long, the flapping of the edge W' of the web W can be prevented. It is possible to remove it.

In view of the functioning of the method according to the invention, it is essential that the spraying reaches the contact line B between the web W and the upper cylinder 10.

Air jet discharged from nozzle opening 26
The best direction for F ₁ depends on many local factors, such as the operating speed of the paper machine. Therefore, the support surface 25 of the blowout member and the wire 12 adjacent thereto
The angle .alpha. is configured to be variable even during driving, and in this way it is possible to find the optimal direction of the jet _F1 for each driving speed and driving condition.

The most important advantage of the invention is that the method and apparatus according to the invention provides a method and apparatus for blowing the paper web W, since the blowing air jet F ₁ discharged from the nozzle 26 does not directly encounter the paper web W itself at any point. The goal is not to dry out the edges too much.

The method according to the invention is furthermore intended to facilitate the guiding of the ends of the web, if desired, since with this method the marginal strip remains in contact with the wire 12. This is because it is maintained. This method can also be used for guiding only the ends, at which point the necessary blowing air can be taken from the compressed air network via a pressure reducing valve. Web W
The spray switch is turned off after the beam has passed at full width. The use of compressed air as the blowing air simplifies the equipment.

As mentioned above, the angle α can be adjusted even during running, and therefore it is possible to search for the optimum angle α from the standpoint of minimizing flapping and breakage of the web. Generally, the most advantageous angle α lies in the range 5° to 15°.

As can be seen in FIG. 4, the front edge of the carrier surface 25 has a certain small play Δ with respect to the opposite transfer wire 12, which is independent of the rotation angle α. The magnitude of this play Δ is preferably within the range of 10 to 25 mm. Width L of nozzle opening is 300 to 600mm
It is preferable that it is within the range of . In one nozzle box, the number of nozzle holes is, for example, 2 to 10.
, preferably about 3 to 6.

As can be seen in FIG. 4, the carrying surface 25 of the spraying means extends over approximately half the length of the common run of the drying wire 12 and the web W. In implementation, the supporting surfaces 25 of the nozzle boxes 23a, 23b
The length of is generally between 30 and 60% of the free running section of the drying wire 12 and the web.
The nozzle holes 26 are oriented such that the direction of jet F ₁ is opposite with respect to the direction of travel of the drying wire. Alignment of each jet can also be achieved by using a foil nozzle, in which the jets are rotated by a curved portion of the carrier surface defined by the nozzle opening. Directed in the opposite direction to the direction of travel. The geometry and characteristics of the foil nozzle are described in the applicant's Finnish patent application no. 781375. In the same application, the nozzle is
It is stated that a drying or supporting gas stream under negative pressure is thereby directed onto the web or the like. This nozzle includes a nozzle box with one nozzle hole on one of its sides, which is connected on the one hand by a flow front plate;
On the other hand, it is defined by a wall which continues as a curved flow-guiding surface and also as a part forming a support surface. This nozzle hole is arranged in the direction of the gas flow before the plane of the inlet edge of the curved guide surface. The ratio of the nozzle hole to the radius of curvature of the guide surface is selected such that when a gas flow velocity develops, the gas flow leaves the curved guide approximately before the trailing edge of the guide surface.

The device according to the invention is provided in connection with the above-mentioned wedge-shaped space K- in the line of the upper cylinders of the drying station in all upper cylinders 10 at least in the initial part of the drying station where the web forces are still low. It is being If necessary, the device 20 according to the invention can be arranged in relation to every wedge-shaped space K- with negative pressure on the side of said wedge-shaped space K- in which a web with negative pressure is arranged. It's fine.

The device according to the invention is very advantageously used in conjunction with the device described in the Applicant's Finnish Patent Application No. 803,891.

Various details of the invention as set forth in the claims herein may be changed without departing from the spirit of the invention as defined therein.

[Brief explanation of drawings]

FIG. 1 shows a part of a drying group of a paper machine, which is known per se and is equipped with a single wire transfer system, in which positive and negative pressures are generated in the nip to detach the web from the wire. Indicates that there is a trend. Figures 2A and 2B illustrate the separation of the web from the wire due to the effects of negative pressure and peck forces generated within the upper nip. FIG. 3 shows a device according to the invention. FIG. 4 is an enlarged sectional view taken along the - line in FIG. 3. 10, 11...Drying cylinder; 12...Drying wire; 22...Tubular beam (support structure); 23
a, 23b... Nozzle box; 24... Outer part; 25
...Inner part; 26...Nozzle slot; W...
Paper web; W'...Edge of paper web; _F1 ...Air jet; K+...Lower nip; K-...Upper nip.

Claims (1)

[Scope of Claims] 1. A method for stabilizing the running of a paper web in a drying section of a paper machine, in which the paper web W is dried while being supported by a drying wire 12 or an equivalent fabric. cylinder 1
0, 11 from one line to the other, so that in one line of drying cylinders the web W is between the drying wire and the surface of the cylinder; In the other line of drying cylinders, the web runs over the outer surface of the drying wire, and the method also includes spraying means, thereby providing the web between each line of drying cylinders. In a type in which the running of the web is stabilized in a common running part of the web and the drying wire 12, the drying wire 1
Approximately both edges of the web W on the side No. 2
In the area W', an air jet F ₁ is blown in a direction opposite to the running direction of the drying wire and the wire, and these air jets F ₁ are directed to the drying cylinder 10 and the drying wire 12 . characterized in that the drying wire 12 is oriented in a wedge-shaped space K- between the web W supported by the drying wire 12 at least up to the bottom line B of this space K-; The above method. 2. Air is blown out _F2 by the air jets _F1 blown out from several subsequent nozzle holes to eliminate the negative energy present in this area on the opposite side of the web W in the wedge-shaped space K-. 2. A method according to claim 1, characterized in that pressure is compensated to keep this web W and its edge W' in contact with the transfer wire 12. 3. The blowing area generated by the air jet F ₁ is approximately 30 to 30 times the length of the common free running section of the drying wire 12 and the web W between the lines of the drying cylinders 10, 11.
3. Method according to claim 1 or 2, characterized in that it extends up to 60%. 4 The air jets F ₁ are generated and directed towards the drying wire 12 by means of foil nozzles, the nozzle holes of which lie in the plane of the inlet edge of the curved guide surface in the direction of the gas flow. previously located and the ratio of the width of the nozzle hole to the radius of curvature of the guide surface such that when a velocity of gas flow occurs, the curved guide is located approximately before the rear edge of the guide surface. 4. A method according to any one of claims 1 to 3, characterized in that the gas flow is chosen to depart from a surface. 5 Said air jets F ₁ are blown out from several subsequent nozzle holes 26 and the angle α between the carrying surface 25 of these nozzles and the drying wire 12 with them is preferably the same as that during running. To,
The adjustment is made so as to minimize the flapping of the web W, and furthermore, this adjustment is performed by the drying wire 1.
The spraying means is rotated about an axis A-A located close to the plane of the drying cylinder 2, and the axis A-A is rotated by the rotation of each of the drying cylinders 10, 11. 5. The method according to claim 1, wherein the method is parallel to the axis. 6 Nozzle boxes 23a, 23b in which air is directed towards the common running section of the drying wire 12 and web W between the lines of the support structure 22 and the related drying cylinders 10, 11;
is provided with nozzle boxes 23a, 23b which are fitted into the support part of one support structure 22 and which are located close to both edge areas of the web W. the nozzle box 23a facing the drying wire 12;
Several nozzle holes 26 are provided in these nozzle boxes on the supporting surface side 25 of 23b,
These directions are oriented by the drying wire 12 opposite to the running direction of the wire, i.e. the curved shape of the support surface 25 bounded by the nozzle hole 26 A device for stabilizing the running of a paper web in a drying section of a paper machine, characterized in that the direction of the jet blown out from the drying wire 12 is opposite to the running direction of the drying wire 12. 7 The support structure 22 is the drying cylinder 1
The web W is parallel to the rotation axis of 0 and 11.
an elongated beam 22 extending over the full width of the drying cylinder 1 at each end thereof;
A nozzle box 23a, which is swingably supported around one axis A-A parallel to the rotational axes of Nos. 0 and 11, and is positioned close to both edges W' of the web. 23b project from said beam 22, and these nozzle boxes are provided with closed ends and a carrying surface 25 which is further provided with a nozzle opening 26 and which faces said transfer wire 12. 7. Device according to claim 6, characterized in that: 8. The front edge of the supporting surface 25, on which the following several nozzle holes 26 are provided, is provided with a small play Δ, which is almost independent of the swing angle α of this supporting surface. An apparatus according to claim 6 or 7, wherein: 9. A patent claim characterized in that both ends of the elongated beam 22 are connected to inlet pipes 21a for blown air, and these inlet pipes are connected to the insides of the nozzle boxes 23a and 23b. The device according to any one of items 6 to 8 of the range. 10 The supporting surface 25 is provided with several substantially equally spaced nozzle holes 26 parallel to each other, the longitudinal direction of these nozzle holes being parallel to the axis of rotation of the drying cylinder. An apparatus according to any one of claims 6 to 9, characterized in that: 11. In at least the first part of the drying section, the drying section is arranged at a position of all such wedge-shaped spaces K- in a negative pressure region where the paper web W runs on the side of the wedge-shaped space. The device according to any one of claims 6 to 10.