WO2003004389A1

WO2003004389A1 - Method and apparatus for pressing a paper web against a reel

Info

Publication number: WO2003004389A1
Application number: PCT/FI2002/000608
Authority: WO
Inventors: Petri Paloviita; Teppo Kojo; Tatu PITKÄNEN; Petteri Lannes; Topi Tynkkynen; Raimo Virta; Petri Enwald; Aaron Mannio
Original assignee: Metso Paper, Inc.
Priority date: 2001-07-04
Filing date: 2002-07-04
Publication date: 2003-01-16
Also published as: FI20011456A0

Abstract

In the method for pressing a paper web against a reel, a paper web is guided onto the periphery of a rotating paper reel (R) formed thereof and pressed against the periphery of the reel (R) in a nip (N, N'). The paper web is pressed against the periphery of the reel (R) in the nip (N, N') by means of a pneumatic press device (1). The invention also relates to an apparatus for pressing a paper web (W) against a reel, which contains a device that forms a nip (N, N') and that is arranged to press the paper web (W) against the periphery of a rotating paper reel (R). The device is a pneumatic press device (1).

Description

Method and apparatus for pressing a paper web against a reel

The invention relates to a method for pressing a paper web against a reel, in which method a paper web is guided onto the periphery of a rotating paper reel formed thereof, and pressed against the periphery of the reel in the nip. The invention also relates to an apparatus for pressing the paper web against the reel.

In the final end of a paper machine or finishing machine for paper a reel-up is used that reels the full-width paper web coming from the machine at the production speed around a reeling core, thus forming a machine reel that functions as one kind of a storage for the paper web before further processing. The reeling core is a reel spool which is arranged rotatable and which is supported at its ends in a supporting structure, and it is advantageously rotated with a drive of its own. The reel-up also contains a reeling cylinder that is journalled rotatable and that is rotated with a drive of its own. The function of the reeling cylinder is to guide the incoming web into a reel and ensure a sufficient pressure contact to the reel that is being formed. For this purpose the machine reel is pressed mechanically against the reeling cylinder by means of force devices coupled to the ends of the reeling core to form a reeling nip. As a result of the loading of the machine reel conducted by means of force devices, a predetermined linear load is effective in the reeling nip, which is one factor affecting the quality of the reel formed of the paper web. By means of sufficient linear pressure the aim is also to prevent access of air with the web to the reel.

As an example of such a reel-up type it is possible to mention for example the Finnish patent 91383 and the corresponding European patent 483092.

In a continuous reel-up in which the production of machine reels is constant, the reel change takes place without reducing the running speed of the web. Thus, the reel that is becoming full in the change situation is transferred off the nip contact with the reeling cylinder, and the nip preventing the access of air is produced with a separate press roll that is transferred in contact with the reel before the transfer of the reel. This arrangement is also presented in the aforementioned Finnish and European patents.

A method for finishing the surface of a machine reel with the purpose of controlling the air problem is also disclosed in the Finnish patent 95683 and in the corresponding European patent 714373. In this context, a press device is also disclosed that is brought in contact with the surface of the machine reel before the reel is conveyed off the nip contact with the reeling cylinder in a change situation.

Gravity and the loading taking place at the ends of the reeling core, i.e. reel spool, cause an uneven nip load in the reeling nip formed between the paper reel and the reeling cylinder. This is detected as large loads in the ends of the machine reel, whereas closer to the middle the load is smaller. The access of air to the machine reel becomes easier and on the other hand, the escape of air in the lateral direction from between the surface layers is prevented as a result of too large a linear load effective in the ends of the reel. Attempts have been made to reduce the air problems by using grooves in the reeling cylinder or a fragmentary roll as a press roll. However, these cause markings on certain paper grades. If the surface of the web is soft or otherwise sensitive, the surface pattern of the cylinder or roll may be copied on the web, and the web must be rejected.

It is an aim of the invention to eliminate the loading and air control problems resulting from prior art, and to present a method and apparatus in which the aforementioned marking problems do not occur. To attain this purpose, the method according to the invention is primarily characterized in that the paper web is guided onto the periphery of a reel and simultaneously pressed against the periphery of the reel with a pneumatic press device.

In the pneumatic press device, the mechanical guidance of the web on the reel and subsequent pressing of the web against the reel in the reeling nip is replaced with air pressure acting against the reel. The air pressure can affect the web directly or via a supporting member, such as a belt or the like, travelling along with the web. By varying the air pressure in the cross-machine direction, i.e. in the lateral direction of the machine, it is possible to profile the pressure effect as well as the pressure in the nip, i.e. to obtain a desired distribution of the pressure in the cross direction. The air pressure can be affected by adjusting the blowing efficiency of the corresponding air blowing nozzle. Especially the loading effect in the cross-machine direction can be arranged such that the pressure is higher in the middle than at the edges. By means of this distribution the access of air in the middle of the reel is prevented and the air is allowed to flow freely from the reel to the edges. Similarly, it is possible to implement the guidance of the web entering the reel in the cross direction either in such a manner that the web is centered into the correct point in the direction of the central axis of the reel, or the location of the same is varied (oscillation is conducted) in the axial direction.

The pneumatic press device is preferably implemented with a wide blowing front that is directed in a pressure-transmitting connection with the paper web. The distance between the nozzles that produce the blowing and the web, as well as the blowing efficiency of the nozzle can be utilized to adjust the loading in the cross direction and to obtain the desired loading distribution. Similarly, it is possible to adjust the general level of the loading pressure in the nip.

It is a considerable advantage of a pneumatic press device that the effect of the press device guiding the web onto a reel and pressing it against the reel in the nip is not restricted to any physical shape determined definitively already at the designing and manufacturing stage, for example to the dimensions of a roll or a cylinder, but by means of the intensity, distance and direction of the air currents it is possible to change the effect of the press device. The nip can be implemented without a contact to the peripheral surface of the reel. Furthermore, it is possible to implement the nip with as small a number of mechanically wearing parts as possible. The press device is out of contact with the web and the reel (no mechanical contact) and its effect to the web/reel takes place by means of the pressure of a gaseous medium. The pneumatic press device can replace the reeling cylinder forming the actual reeling nip, or it can replace the press roll or the like, by means of which an additional nip is formed when the machine reel is detached from the actual reeling cylinder. By means of the mechanical press device according to the invention it is also possible to replace both devices in the same reel-up.

In all alternatives the control of the nip can be conducted for example by means of closed loop force control, e.g. by means of force measurement sensors. The nip force is not affected by friction or deflections either, which cause problems in mechanical press devices.

Structurally, it is possible to implement the press device as a pipe or a box containing a nozzle or nozzles that continues/continue as a carrier surface located opposite to the web (a so-called float nozzle). Thus, an overpressurized air cushion is produced between the carrier surface and the web as a result of the blow coming from the nozzle/nozzles, said air cushion producing the desired nip pressure.

In the following, the invention will be described in more detail with reference to the appended drawings, in which

Fig. 1 shows a side-view of the apparatus according to the invention,

Fig. 2 shows a front-view of the apparatus according to the invention,

Fig. 3 shows a side-view of an alternative embodiment of the apparatus according to the invention,

Fig. 4 shows a side-view of yet another embodiment of the apparatus according to the invention, and

Fig. 5 shows the structure of a press device of an apparatus according to the invention. Fig. 1 shows a continuous reel-up of a paper web. The paper web is passed as a continuous web from a paper machine or finishing machine for paper, and it is guided around a rotating reel spool 2 to form a machine reel R. The reel spool 2 is arranged to rotate in the supporting structures of the reel-up for example in such a manner that the bearing housings in the ends of the reel spool are supported on supporting surfaces K, such as reeling rails (illustrated by means of broken lines) located in the reel-up. The reel spool 2 is connected to a drive of its own to rotate the reel spool and the reel R.

The point in which the web W enters the peripheral surface of the reel R and is laid on top of it, i.e. on top of the web layers wound at an earlier stage around the reel, is the reeling nip N. The web W is guided to the reeling nip and pressed against the reel R in the reeling nip N by means of a pneumatic press device 1 that produces the blowings of air directed against the plane of the web. The blowing of air conducted over the entire width of the web produces an air cushion on that side of the web that forms the outer surface in a finished machine reel R, the pressure of said air cushion determining the loading pressure in the reeling nip N as well. In practice, the blowings can be produced by means of a nozzle slot extending over the entire width of the web or nozzle openings or slots positioned at fixed intervals in the lateral direction of the web. The nozzle or nozzles may open on the surface of a pipe or box extending in the cross-machine direction. In the drawing, the direction of the blow of air is illustrated with an arrow 1a. The blowings can also be directed as blowings that are separate in the travel direction of the web W, for example radially from a blow box or pipe by directing the nozzles in a corresponding manner. The nozzle/nozzles are off the surface of the reel, and blowings of air are directed freely towards the surface of the reel, causing a nip pressure of predetermined magnitude when hitting the peripheral surface of the reel.

As can be seen in Fig. 1 , the pneumatic press device 1 can be rotated around an axis substantially parallel to the axis of rotation of the reel, to change the area of influence of the air cushion in the travel direction of the web W (arrow A). Similarly, the distance of the press device from the nip N can be changed by arranging for example the bearings of the axis of rotation of the press device so that the can be moved along a linear guide (arrow B). It is obvious that the press device can also be moved in other ways in relation to the travel of the web W. The box or pipe that forms the press device and is equipped with nozzles can be arranged to rotate around its longitudinal axis by means of bearings, which bearings can, in turn, be arranged to move along the guides to change the distance of the press device 1. The pipe, box, or nozzle structure can be provided with deflection compensation.

Advantageously, the nozzle structure provides a slightly longer nip in the machine direction. It is also possible to control the pressure distribution in such a nip in the travel direction of the web. Similarly, it is possible to adjust the length of the nip in the machine direction. A long nip can be produced for example by means of a float nozzle which will be described in more detail hereinbelow.

At least one blow can be directed as a wide front against the incoming direction of the web (the direction of the blowing has a motion component opposite to the travel direction of the web), wherein it, in addition to the overpressurized air cushion, causes tightening of the surface layer of the reel and enhances the removal of air from the reel.

Especially the distance of the press device 1 from the axis of rotation of the reel R, i.e. the central axis of the reel spool 2 can be arranged variable in synchronization with the growth of the reel R, i.e. the distance is increased at the same speed as the radius of the reel R grows, wherein the location with respect to the reeling nip N remains unaltered. It is, however, possible that the pneumatic press device 1 remains constantly in the same position (excluding small changes of position intended for pressure adjustment) and the reel spool 2 is transferred further away from the press device 1 simultaneously with the growth of the radius of the reel R. The transfer can take place by means of transfer devices connected to the ends of the reel spool, such as carriages that can be transferred by means of actuators by principles known as such. Fig. 2 shows the pneumatic press device 1 in a front view i.e. approximately in the travel direction of the web W. As can be seen in the drawing, the blowing of air coming from the press device 1 is effective over the entire width of the web W. The arrows located at different points in the cross-machine direction illustrate the force of the blowing of air occurring at the corresponding location. As can be seen in the drawing, it is possible to arrange a stronger blow, and correspondingly a higher nip pressure in the middle of the reeling nip N while the blow and the respective nip pressure is weaker at the edges. The air exiting from the edges of the reel is as a result of this illustrated with arrows C. The press device 1 is advantageously of such a type that the intensity of the blowings in the cross-machine direction can be adjusted to profile the pressure of the air cushion and consequently the nip pressure in the transverse direction of the web.

Furthermore, by means of the direction of the blowings of air it is possible to affect the exit of air. When the nozzles are arranged to blow diagonally sidewards (from the middle towards the outer edges of the web), a profiling effect is also attained. The blowing thus pushes the air out of the ends of the reel.

It has also been detected that the pneumatic press device has the capability of guiding the web in the cross direction, if the position of the device is changed in the plane of the web. If the press device is turned in an inclined position substantially in the plane of the web, it is possible to make the web entering the reel to move in the cross direction. Thus, it is possible to center the web to the correct location, or by changing the position of the press device continuously between two positions it is possible to implement oscillation in the cross direction of the web i.e. moving of the web back and forth in the cross direction of the web. The same effect can be attained by profiling the air cushion effective against the web in such a manner that the web moves sidewards.

The adjustment of the press device can be optimized to comply with the requirements of different paper grades, wherein for example when the grade is changed or in accordance with the air permeability of the paper grade it is possible to change the shape of the pressure effect of the air cushion both in the cross direction and in the machine direction (travel direction of the web). This provides a considerable advantage when compared to a reeling cylinder or press roll with a fixed physical form, because the transverse profile, the deflection caused by gravity, or the surface area of the nip in reeling cylinders and press rolls with a fixed physical form cannot be changed anymore after the designing work.

The press device can also be effective only on a part of the width of the web, advantageously in the area located symmetrically on both sides of the longitudinal central line of the web.

Fig. 1 shows a press device by means of which a reeling nip N is produced substantially during the entire reeling process of the machine reel R, i.e. the press device 1 replaces the reeling cylinder used in reel- ups. Fig. 3 shows an alternative in which a conventional reeling cylinder that is journalled rotatable is used as a device forming the actual reeling nip, but the pneumatic press device 1 is in this case a device forming an additional nip N' that guides the continuously incoming web W onto the periphery of the machine reel R and presses it in the nip N' against the periphery in a situation in which the machine reel R has been conveyed off the reeling cylinder for the purpose of a reel change. The pneumatic press device 1 can be arranged movable for example in the machine direction, wherein it can be moved while being in the additional nip forming contact with the reel at the same time when the reel R is transferred. The additional nip can be formed by means of the press device 1 before the machine reel R is detached from the actual nip contact N. Principles for controlling the nip pressure of the additional nip in the transverse direction of the web and adjusting the pressure can be similar to the principles described above with reference to the actual reeling nip N, and the structure of the press device 1 and the possibilities to move the device can be similar in relation to the web W and the additional nip N'

The scope of the invention also includes the idea according to which both the press device forming the actual reeling nip and the press device forming the additional nip in the change situation are pneumatic press devices, which are both implemented by means of an air blowing front directed from one or several nozzles in a suitable manner.

Fig. 4 shows an embodiment in which the flow of air of the air press device is not guided directly against the surface of the reel, but the linear load of the air press device is transmitted to the surface of the reel through a special transmitting material, which may be a suitable flexible elongated supporting element moving in the travel direction of the paper web.

Fig. 4 shows a slack or slightly tensioned film/belt loop 3 as well as the above-described air press device 1 inside the loop. The film or belt is pressed against the surface of the reel by means of the air press device 1 , i.e. between the air cushion and the reeling nip N there is a thin supporting element or "transmitting material" transmitting the pressure onto the surface of the reel. The essential aspect is that the tension of the film/belt is not adjusted to adjust the nip, and the film/belt does not pull the reel, but the pressure in the nip is produced as a result of the air press device 1 that directs a blow of air against the rear side of the film or belt. Advantageously, the tension of the belt can be very low, and it can be implemented in the manner shown in the drawing, wherein a drive roll 4 tightens the lower side of the loop, but not the upper side that travels via the nip. Thus, the nip is located in the slack section of the loop after the drive roll 4 in the travel direction of the supporting element. The belt may contain a toothing or the like at the edges so that it remains in its position even when it is slack. The web can be introduced to the nip N along the belt/film for example in the section following the drive roll 4, or the web may enter the surface of the reel already before the nip (broken line).

The film or belt is advantageously impermeable, wherein the current of air is not blown directly against the reel R, but the linear load is transmitted through the film or belt 3 against the surface of the reel. The belt can also measure the nip load, and to implement this, it contains pressure sensitive material that operates as a pressure sensor that gives a signal proportional to the pressure. Such a sensor can be a known film sensor that reacts to pressure. Also in the alternative of Fig. 4, the angle and/or distance of the air press device 1 can be changed to change the shape of the nip or the nip force. The angle of rotation around the cross-machine axis is marked with a symbol α. The device can also be of the type profiling in the cross direction according to the principle of Fig. 2.

By means of the transmitting material according to Fig. 4, direct contact of air with the surface of the reel is prevented, which is useful especially when paper grades that are liable to break and/or that are air permeable are reeled. The transmitting material also balances the load in a suitable manner, but it does not, however, prevent the pressure profiling in the cross direction.

The embodiment of Fig. 4 can be used as a press device that forms the actual reeling nip N. It is, however, possible that it is only used for forming the additional nip N'.

Fig. 5 shows a possible structure of the press device 1 , a so-called float-type nozzle. The press device is a pipe or box extending in the cross-machine direction that forms a substantially closed housing, to the inside of which pressurized air is conveyed. A slot-like nozzle 1b opens on the outer surface of the housing, one edge of said nozzle continuing as a carrier surface 1c lying opposite to the web. The carrier surface is thus formed of one wall portion of the housing. The overpressurized air cushion, that produces a fixed nip pressure in the nip N, is formed between the web W and the carrier surface 1c. Fig. 5 also shows two towards each other directed slot-like nozzles 1b, between which a shared carrier surface 1c of the nozzles is formed. It is also possible to provide the press device with only one slot-like nozzle 1 b that is directed either in the travel direction of the web or against the travel direction of the web. In the latter case a blowing against the incoming direction of the web is simultaneously created to tighten the surface layer of the reel and to enhance the removal of air. The structure according to Fig. 5 or the above-described structural alternatives are suitable for all alternatives according to Figs. 1 to 4. The minimum distance (marked with the letter d) of the carrier surface 1c from the reel can be advantageously varied, and it can be for example under 10 mm. By means of the two-slot air press device (nozzle beam) according to Fig. 5, an overpressure of approximately 2 to 3 kPa is generated by the 5 mm distance d of the beam from the nip. The distance can vary, depending on the desired pressure level. The overpressure can be small, only between 1 kPa to 10 kPa, i.e. the air press device is not used for producing large surface pressures in the nip, unlike in a mechanical nip. It has been found that this pressure level is sufficient for example when very slippery paper with a silicone surface is reeled. Since the necessary pressure level is low, the air supply to the inside of the air press device can be provided for example with a blower instead of using a pressurized air network.

In all above-described embodiments, it is possible to implement the control of the nip with a closed loop force control. One or more force measurement sensors (e.g. a pressure sensor) is/are placed in connection with the nozzle/nozzles, and a variable affecting the pressure of the gaseous medium, for example the blowing efficiency of the press device, is adjusted to maintain the desired nip force. It is also possible to affect the pressure by changing the distance of the press device from the nip, i.e. by means of position adjustment. When there are several force measurement sensors at different locations in the cross direction of the web, it is possible to adjust the blowing efficiency in the cross direction of the web to maintain the desired nip force profile.

In principle, the nip force could be adjusted by directly adjusting the force or pressure of the actuator that loads the press device (through the intermediate air cushion) against the outer surface of the reel in the nip, depending on the way in which the loading actuator is controlled. However, since the pressure level (overpressure of the air cushion typically under 10 kPa) is small when compared to the mechanical friction of the transfer mechanism of the press device, it is most advantageous to conduct the nip force adjustment in practice by measuring the pressure of the air cushion positioned against the nip and by using position adjustment. Thus, the variable which affects the pressure and which is influenced on the basis of the measurement result is especially the distance of the press device from the nip.

The shape and/or location of the surface of the reel can be constantly measured to position the press device in a correct position with respect to the nip, especially when the location of the nip changes as a result of the growth of the diameter of the reel.

Similarly, the pneumatic press device 1 preferably contains the possibility to adjust the length of the nip in the machine direction (travel direction of the nip). Thus, the length of the nip can be optimized for example according to the grade to attain the correct nip effect.

Although the reeling of machine reels in a continuous reel-up in such a manner that at least one pneumatic press device is used for forming the reeling nip or the additional nip is described above, it is also possible to apply the invention in other winding or reeling processes of the paper web, for example in a slitter winder in the winding of customer rolls. All the arrangements according to Figs 1 to 5 can thus be applied also to the winding of customer rolls, and the web W shown in the drawings can be considered as a part web obtained from a full- width web after the slitting operation. Thus, the air press device 1 can be shared by several adjacent customer rolls, or each customer roll may have an air press device of its own.

Claims

Claims:

1. Method for pressing a paper web against a reel, in which method a paper web is guided onto the periphery of a rotating paper reel (R) formed thereof, and pressed against the periphery of the reel (R) in a nip (N,N'), characterized in that the paper web is pressed against the periphery of the reel (R) in the nip (N, N') by means of a pneumatic press device (1).

2. The method according to claim 1 , characterized in that the web (W) is guided onto the periphery of the reel (R) and pressed against the periphery of the reel by directing a blow of gaseous medium into a pressure-transmitting contact with the paper web in a wide front extending in the cross direction of the paper web.

3. The method according to claim 2, characterized in that the blowing is directed between the plane of the web (W) and a carrier surface.

4. The method according to claim 2 or 3, characterized in that the blowing is effected as a blowing front corresponding substantially to the entire width of the web.

5. The method according to claim 2 or 3, characterized in that the blowing is effected for a part of the width of the web.

6. The method according to any of the preceding claims, characterized in that the force effect of the pneumatic press device (1) is directed towards the web in a profiled manner in the cross direction of the web (W).

7. The method according to any of the preceding claims, characterized in that the pneumatic press device (1) is used for forming the reeling nip (N) when the web (W) is reeled to form a substantially full-sized machine reel (R).

8. The method according to any of the preceding claims, characterized in that the pneumatic press device (1) is used for forming an additional nip (N) separately from a press device forming the actual reeling nip (N).

9. The method according to any of the preceding claims, characterized in that the pneumatic press device (1) is also used for guiding the web (W) onto the periphery of the reel (R).

10. The method according to any of the preceding claims, characterized in that the pneumatic press device is used for guiding the paper web (W) in the cross direction.

11. The method according to any of the preceding claims, characterized in that the pressure of the gaseous medium acting on the web (W) in the nip is kept in a set value by measuring said pressure and on the basis of the measurement affecting at least one variable influencing the pressure, advantageously the position of the press device with respect to the nip (N).

12. An apparatus for pressing a paper web against a reel, which contains a device that forms a nip (N, N') and that is arranged to press a paper web (W) against the periphery of a rotating paper reel (R), characterized in that the device is a pneumatic press device (1).

13. The apparatus according to claim 12, characterized in that the pneumatic press device (1) comprises a nozzle or nozzles which is/are directed to the vicinity of the web (W) to effect the blowing (1a) of a gaseous medium in a pressure-transmitting contact with the web (W).

14. The apparatus according to claim 13, characterized in that the pneumatic press device (1) in which the nozzle/nozzles is/are located is a pipe or box extending in the cross-machine direction.

15. The apparatus according to claim 14, characterized in that the pipe or box comprises a nozzle/nozzles as an extension of which there is a carrier surface lying opposite to the web.

16. The device according to any of the preceding claims 12 to 15, characterized in the press device (1) is rotatable around an axis substantially parallel to the axis of rotation of the reel (R).

17. The apparatus according to any of the preceding claims 12 to 16, characterized in that the distance of the press device (1) from the nip (N, N') is variable.

18. The apparatus according to claim 17, characterized in that it comprises a force sensor, a controller to which the sensor is connected, as well as an actuator to which the controller is connected to keep the pressure in a desired set value by changing the distance of the press device from the nip by means of the actuator.

19. The device according to any of the preceding claims 12 to 18, characterized in the pneumatic press device (1) is placed in a position in which the web is reeled into a substantially full paper reel (R) by means of the reeling nip (N) produced by the press device (1).

20. The apparatus according to any of the preceding claims 12 to 19, characterized in that the pneumatic force device (1) is a device that is separate from the device producing the actual reeling nip (N) and that is placed after the actual reeling nip (N) in the travel direction of the web in a position in which it produces an additional nip (N').

21. The apparatus according to any of the preceding claims 12 to 20, characterized in that between the pneumatic force device (1) and the reel (R) a flexible transmitting material (3) is placed that moves in the travel direction of the web (W) and transmits the force of the press device (1) to the peripheral surface of the reel (R).

22. The apparatus according to claim 21 , characterized in that the contact point of the transmitting material (3) to the reel (R) is located in the slack section of the loop of the transmitting material following the drive roll (4).

23. The apparatus according to claim 21 or 22, characterized in that the transmitting material is a substantially air impermeable film or belt.

24. The apparatus according to any of the preceding claims 21 to 24, characterized in that the transmitting material comprises pressure sensitive material that is arranged to give a signal proportional to the pressure produced by the press device (1).