ARRANGEMENT, METHOD AND DEVICE FOR CONTROLLING AIR FLOWS IN A DRYER SECTION OF A WEB FORMING MACHINE

The invention relates to an arrangement in a dryer section of a web forming machine for controlling air flows during tail threading, where a tail is arranged to be taken from a dryer cylinder to a turning roll in several positions of the dryer section over an interval supported to a fabric, and where the dryer cylinder and the fabric form an opening gap. In addition, the invention also relates to a corresponding method and device.

In tail threading of a paper machine, a tail that is notably narrower than the actual production width is transported through the machine. The tail width can be 100 - 500 mm, for example, while the web production width can be, for example, 8 - 12 meters . The tail is taken through the machine at the production speed.

Mainly due to high machine speeds, the behavior of the tail may be quite unstable. In the dryer section, for example, a rotating dryer cylinder and a fabric arranged to travel via it, convey air with them generating thus negative pressure in the opening gap between the dryer cylinder and the fabric. Runnability components located in the pocket space between the dryer cylinders and turning rolls make this vacuum effect even more efficient. Air leaks to the pocket space through the fabric. A depressurized turning roll also aspirates air from the pocket.

When viewing the machine in the lateral direction, the above mentioned effects do not cause problems at the machine center, since compensation air cannot access the center from the edges. Instead, an intense cross flow is created at the machine edges, where the tail is usually transported, due to air flowing in from the machine sides. The cross flow is the more intense, the

higher the machine speed is. As the consequence to this phenomenon, the front side edge of the tail may rise to an upright position, i.e. detach from the fabric surface. One of the consequences is at least stretching of the tail edge or even a wrinkle, both of which may cause a break in a later stage.

The object of this invention is to provide an arrangement for the dryer section of a web forming machine for controlling air flows during tail threading, which, for example, improves the reliability of tail threading. The characteristic features of the arrangement according to the invention are set forth in claim 1, those of the method in claim 12, and those of the device in claim 16.

In the arrangement according to the invention, the tail is arranged to be taken from a dryer cylinder to a turning roll in several positions of the dryer section over an interval supported to a fabric. The dryer cylinder and the fabric form together an opening gap. The gap is arranged to be covered at least partially on the outside of the tail for restricting air flows in the cross-machine direction in connection with the opening gap. Thus, for example, strong and harmful cross flows aspirated to inside the machine from its sides can no more disturb the tail travel and/or its spreading to the full width. With the invention, the tail is kept attached to the fabric surface in a desired manner over its entire width and over its entire portion that is supported to the fabric.

According to one embodiment, the opening gap can be covered in the cross-machine direction at least partially on the outside of the front side tail edge. Thus the cover can be easily fastened to the frame constructions of the machine, for example.

According to one embodiment, the opening gap can be covered in the cross-machine direction immediately at its opening point. The vacuum effect is the most intense immediately after opening of the gap and in the condition following that, since even several vacuum-inducing factors can influence these points.

In connection with tail threading, the cover element can be arranged in one or more optional positions in the cross-machine direction. The cover can be located in connection with the tail edge, in connection with the fabric edge, in connection with the dryer cylinder shell edge, or in connection with the dryer cylinder head. Various arrangement methods provide a great degree of freedom for arranging bracketing for the cover and sealing for the edges of the opening gap.

The cover can be plate-like or it can also have elongated extension even in the cross-machine direction. Thus it is arrangeable even between the fabric and the dryer cylinder, i.e. inside the opening gap. The cross-directional extension of the cover in comparison to a plate-like cover element reduces, for example, the risk of damage of fabrics, which can appear with a plate-like cover element, for example.

In addition, the position of the cover element can be modifiable. In this case, after successful tail threading, for example, the cover element can be moved away from the tail threading position, such as from inside the machine. With the capability of moving, any web material attached to the device detaches and, in addition, the device does not collect any web material at breaks occurring possibly during the production.

Other additional benefits achievable with the invention become evident from the description, and the characteristic features are set forth in the appended claims .

The invention, which is not limited to the embodiments set forth below, is described in more detail by making reference to the enclosed drawings, in which

Figure 1 shows an arrangement according to the invention seen from the side of a paper machine, Figures 2a and 2b are top views of simplifications for some embodiments , Figures 3a and 3b show another embodiment of the cover element in a simplified design, Figure 4 is a top view illustrating basic examples of the arrangement,

Figure 5 is a side view illustrating an embodiment of the cover element bracketing,

Figure 6 shows a third embodiment of the arrangement, Figure 7 shows a fourth embodiment of the arrangement in connection with the first dryer group, and

Figures 8a - 8c show basic examples of the various extensions of the cover element in the cross-machine direction and of its contacts to the machine structures.

Figure 1 provides a side view of an arrangement according to the invention for controlling air flows during tail threading in a multicylinder dryer of a web forming machine; in this case of a paper machine. In the context of the invention, the web forming machine can as well be understood as a board machine, a tissue machine, or a pulp machine. The figure illustrates a dryer cylinder 10 and two depressurized turning rolls 11, 12 for the dryer section of the paper machine. The dryer section can be a multicylinder dryer known as such in which the order of rotating elements 10 - 12 can also be opposite to that shown in Figure 1. Here the dryer cylinders are located in the top

plane and the turning rolls in the bottom plane, and there are several successive items of both in their planes. The turning roll 11, 12 can also be without vacuum and its vacuum induction method is not limited in any way by the basic idea of the invention. Figure 1 shows additionally, as accessory equipment, the doctor 25 of the dryer cylinder 10 and a runnability component 19, indicated with broken line, which can be, for example, a component known with the applicant's product name Hi-Run.

A tail 13 that is remarkably narrow in comparison to the actual production width can be transported in the dryer section supported in a corresponding manner as is done for a full-width paper web. The tail 13 travels in the area above the dryer cylinder 10 between a fabric 14 and the heated shell 26 of the dryer 10 (Figures 2a, 2b, 3a) . In the area below the depressurized turning roll 11, 12, the tail 13 travels aspirated to the surface of the fabric 14. The fabric 14 is then between the tail 13 and the shell of the depressurized turning roll 11, 12.

In several positions of a dryer section of a web forming machine, the tail 13 is transported, in connection with tail threading, from a dryer cylinder 10 to a turning roll 12 over an interval 16 (Figure 5) supported to a fabric 14. The fabric

14 detaching from the dryer cylinder 10 towards the turning roll 12 forms an opening gap 15 with the cylinder 10. The length of the interval 16 supported to the fabric 14 can be, for example, 300 - 1800 mm.

In the arrangement according to the invention, the opening gap

15 is arranged to be covered at least partially at least on the outside of the tail 13 for restricting air flows in the cross- machine direction in connection with the opening gap 15. In other words, the object of covering is the interval 16 at the

opening gap 15 or at least part of it, over which distance the tail 13 is supported only to the fabric 14.

Figures 2a, 2b and 3a illustrate some embodiments of the 5 invention. Covering according to the invention can be limited, in the lateral direction of the machine, to take place immediately in connection with the edge 13 ' of the tail 13 or, on the other hand, only at a distance from the edge 13 ' of the tail 13. The cover element can of course extend partially to

10 the area of the tail, too, in the cross-machine direction, but it is still detached from the tail so as to avoid its damaging. In any case, thanks to the cover element, such air flows cannot flow inside the machine from the sides of the dryer section which could disturb the travel of the tail 13 or its attachment

15 to the fabric 14 within the area of the opening gap 15. Air flows entering the gap 15, i.e. inside the machine, from a spacious machine hall and/or hood space can be quite intensive relative to the air flows appearing in connection with, for example, a closing gap, which flow in the opposite direction in

20 comparison to the opening gap 15, i.e. from inside to outside of the machine. Without a cover element 18 according to the invention, the air flow is unrestrictedly directed straight to the edge 13' of the tail 13 in the opening gap 15, because the cross air flow from the machine side arrives in the opening gap

25 15 directly to the same side of the fabric 14 on which the tail 13 is located.

The gap 15 can be covered / closed / overlaid, no matter which expression is used, at least partially in the cross-machine

30 direction, optionally in the connection of both edges of the tail 13, but at least in the connection of the front side 17 tail edge 13 ' . The purpose of covering is to cut off or at least essentially restrict an intense cross flow generated by air flowing inside from the machine sides. Since the tail 13 is

35 taken through the machine near the front side edge 17 of the machine, the air flows entering the machine via this area

affect this tail edge 13 '. In addition, bracketing for the element 18 used for covering can be more easily arranged on the front side 17. If the cover 18 is of a type that is moveable with an actuator 22 (Figure 4) , then it may also be easier to arrange the drive power lines for the actuator 22 on the front side 17.

The interval 16 supported to the fabric 14 (Figure 5) can be closed at the opening gap 15, and more particularly, starting immediately from the root of the gap 15, where the fabric 14 and the tail 13, designed to travel along its surface, detach from the dryer cylinder 10. It is exactly in this position that the effect of harmful air flows, detaching the tail 13 from the fabric 14, is the greatest. This harmful effect is further increased by a possible runnability component 19 located in the space between the dryer cylinders 10 and rolls 12 and a depressurized turning roll 12, which, for its part, aspirates air through the fabric 14.

Covering according to the invention can be realized using a construction 18, which may be composed of at least one component. The dimensions of the cover 18, as seen from the side of the machine, may correspond to at least to the dimensions and shape of the opening gap 15. Figure 1 shows two possible, sizes and shapes for the cover element 18, 18', the larger one with broken lines and the smaller one with solid lines. In both cases the cover element 18, 18' fills the cross- sectional shape of the gap 15 uniformly from each side; however, such that for example the dryer cylinder 10, fabric 14 and other moving surfaces cannot get damaged. The cover construction 18, 18' can be curved at the edge on the dryer cylinder 10 side. At the edge on the side of the depressurized turning roll 12, the covering construction 18, 18' can be rather rectilinear starting from the root of the gap 15, following the travel route of the fabric 14. In case the cover 18' extends so far in the direction of the gap 15 that it also

achieves the fabric section supported to the depressurized turning roll 12, the cover 18' may be curved following the curvature of the depressurized turning roll 12. At the edge opposite to the opening gap 15, the cover component 18, 18' can be relatively straight.

According to a first embodiment, the cover construction 18.1 can be a triangular plate, planar in the lateral direction of the machine. Such constructions are shown in the embodiments of Figures 2a, 2b and 6. Instead of a plate construction, the cover construction 18.2 can also have elongated extension in the cross-machine direction. In this case, in addition to covering the gap 15 in the cross direction, the cover construction 18.2 can be used for filling the gap space 15 defined by the fabric 14 and the dryer cylinder 10. An example of such beam-like cover construction 18.2 is shown in Figures 3a, 3b and 6. One angle 18* has been cut off from the triangular cover beam 18.2 shown in Figure 3b. When the beam 18.2 is in place, the angle 18* is positioned more internally within the machine in the cross-machine direction. With a removed angle 18*, the cover component 18.2 having also elongated extension in the cross direction can be removed from inside the machine after tail threading, and it is allowed even a small position change in connection with the removal without damaging the fabric 14, for example. A beam-like cover component 18.2 is also easy as regards its cleanability and avoids the spinous tip, oriented towards the gap 15, of the plate-like cover component 18.1.

As can be seen from Figures 2a, 2b and 3a, the cover construction 18.1, 18.2 can be arranged in many different positions in the cross-machine direction in connection with tail threading. The cover element 18.1, 18.2 can be arrangeable between the fabric 14 and the dryer cylinder 10 or even outside the machine, in which case it is not even within the gap 15. In Figure 2a, the cover 18.1 is defined in connection with the

front side 17 edge 14' of the fabric 14. In Figure 2b, it is outside the front side 17 edge 13' of the tail 13. However, in Figures 2a and 2b the cover 18.1 is arranged such that it does not disturb or harm the travel of the tail 13 or the fabric 14. In this case, its distance from a moving edge or surface can be 0 - 100 mm, such as 0 - 70 mm, and more particularly 10 - 30 mm or even below 20 mm. The cover 18.1 can also be in connection with the edge 26' of the cylinder 10 shell 26 (not shown) or immediately in connection with the head 10' of the cylinder 10, such as is shown in Figure 4.

Figure 4 is a top view of the basic embodiments illustrated in Figures 2a and 2b. The cover 18 arranged outside the machine is also visible here. In addition, the figure shows some bracketing possibilities for the cover element 18. The cover plate 18 according to the invention is fast to install. The cover plate 18 can be bracketed to the machine constructions 20 in such a way that the plate 18 can be easily moved aside for maintenance/replacement. The element 18 can be fastened by the brackets 21 to a suitable machine frame construction 20, a shaft of a runnability component, or a doctor beam. As can be seen from Figure 4, the cover element 18 can also be equipped with transfer elements 22 for placing it to its tail threading position or for removing it from its tail threading position. The transfer device 22 possibly fastened to the machine frame 20, such as a linear guide, can be actuated, for example, by a medium, such as pneumatic medium, and its operation can be controlled with the machine's tail threading automation. A turning movement of the cover element is also possible for removing it from its tail threading position. A turning movement is more challenging for the implementation, and the tip of the cover element 18 can be designed with roundings to protect the fabric 14. The cover construction 18 that is transferrable from inside the machine is also easy to clean.

The cover element can also be used to guide the tail threading air blow at a doctor to the correct destination facilitating also in this way the tail threading procedure.

5 Figure 5 shows still another basic embodiment of the bracket assembly as seen from the side. The dryer cylinder 10 is mounted to the machine frame 20 with a bearing assembly 23. The cover plate 18 is also supported in the frame 20 with a bracket arm 21.

10

Figure 6 shows an embodiment in which the cover construction 18.1, 18.2 is integrated to a tail threading device 27 of the gap 15, and the air flow 31 led inside is discharged from the opposite end of the pipe (arrows) . Figure 6 is a diagrammatic

15 view showing also the edges 10 ', 14 ' and 13 ' of the dryer cylinder 10, fabric 14 and tail 13. With the tail threading blow device 27, the tail 13 is detached from the surface of the cylinder 10 and forced to travel along the surface of the fabric 14 further to the turning roll 12. The advantage of this

20 embodiment is that it does not require separate bracketing but the cover construction 18.2 can form a certain type of collar 28 in the bracket assembly 29 of the blow device 27.

The embodiment of Figure 6 can be implemented both with a

25 plate-like cover element solution (darkened component 18.1) and with a cover construction 18.2 with cross-directional extension as shown with the line marking. The cover construction 18.2 with cross-directional extension settles firmly within the area of the collar 28. The end 30 of the blow pipe may be designed

30 as downwardly slanting to avoid sticking of rags of web / tail strip to it and to allow them to drop down more easily under gravity. In addition, the embodiment can be implemented as yielding. This ensures that even a large accumulation of paper or a fabric failure cannot damage the device 24, but the device

35 24 goes down giving way if a possible block of paper hits it.

The material of the cover component 18 according to the invention can be, for example, metal, composite, plastic, or plexi, in which case it can be even transparent. The cover plate surfaces located near moving surfaces can be lined with teflon, for example, forming thus a sliding surface. Then the fabric 14 can wear the cover element 18 to obtain its shape and the element 18 can be even attached to the surface of the moving fabric 14, nevertheless, without damaging it.

Figure 7 shows still another embodiment of an arrangement according to the invention while viewing the machine's dryer section 32 from side. The cover element 18 according to the invention may be placed in the dryer section 32 in connection with each opening gap or at least at some of these, such as in the initial part of the dryer section 32. Thus, starting from the initial part of the dryer section 32, 1/3 of the opening gaps of the dryer section, for example, can be equipped with a cover element 18.3, 18.4 according to the invention.

Figure 7 shows a portion of the initial part of the dryer section 32 and more particularly, its first dryer group 32.1 in its entirety. The plate-like component 18.3, 18.4 blocking the cross-directional flows oriented towards the interior of the machine in the opening gap 15.1, 15 is now installed outside the heads 10', 12' of the dryer cylinders 10 and rolls 12. In this case the air flow block 18.3, 18.4 does not follow precisely the form of the gap 15.1, 15 as seen from the side of the machine, but it can extend over the gap 15, for example, for arranging suitable sealing. Being a light construction, the gap cover 18.3, 18.4 according to the invention is suitable for closing even larger areas, such as the first opening gap 15.1, which has a wider geometry in comparison to the later gaps 15. In the first opening gap 15.1 the web travels almost vertically downward, whereas in the opening gaps 15 that follow it, the web travels in a slightly inclined direction and thus the opening gap is smaller in these positions, as seen from the

side. In the first gap 15.1 the gap cover 18.3 can extend even up to the level of the lowest station of the turning roll 12 or even below that .

5 The cover plate 18.3, 18.4 can be installed also on both sides of the machine. In this case flows can be restricted during tail threading for controlling the spreadable tail as well and additionally for restricting cross flows during the machine operation within the dryer section 32. Thus the invention is

10 suitable for application in the production run, too, for calming down the edges of a full-width web. The gap cover 18.3, 18.4 according to the embodiment can be transparent and non- fracturing. An example of its material is transparent plexi or plastic. Transparency facilitates monitoring the web and tail

15 14 travel and behavior.

According to an embodiment, the gap cover 18.3, 18.4 according to the invention can be installed very close or even attached to the heads 10', 12' of the dryer cylinders 10 and turning

20 rolls 12 or to the shell edge. Figures 8a - 8c show examples of embodiments related to this . In this case the cover component 18 can be equipped, if required, with one or more wear blocks 33, which are in contact with the rotating or stationary component 10, 12 of the plexi cover 18, 18.2, for example,

25 against the end of its rotating part, and/or with an advancing surface, such as the edge 14' of the dryer fabric 14, sealing in this way the plexi cover 18 against the machine constructions 10, 12, 14, 19.

30 Even more generally, the sealing elements 33, 34 may be arranged between the cover element 18, 18.3, 18.4 and the machine constructions 10, 12, 14, 19 for bringing the cover element 18, 18.3, 18.4 in tight contact against the machine constructions 10, 12, 14, 19, 25 and thus for blocking leakage

35 of air flows to the gap 15, 15.1 from the front side of the machine. The distance between the plexi component 18.3, 18.4

and the end 10' , 12' of the rotating component 10, 12 can be as short as below 20 mm. Then also the piping for the pocket runnability component 19 can be arranged to define the pocket space. Sealing 34 between the cover plate 18.3, 18.4 and the machine constructions 20 can also be realized slightly more inwardly relative to the doctor beam 25 and the pocket space runnability box 19 located in the cross direction, either mechanically or by using blow seals (inset of Figure 7) . Then the blow seal 34 can be placed rather in the component 25 extending in the cross-direction than in the plate 18.3, 18.4. The seal 34 can extend in the vertical direction even up to the dryer cylinder 10.

Besides showing the sealing between the cover plate 18.2 and the machine constructions 10', 12', Figures 8b and 8c also illustrate embodiments of an elongated design of the cover component 18.2. Now the gaps 15 are viewed diagonally from the top as a basic section (Figure 7) . In both embodiments the cover component 18.2 is against the heads 10', 12' of the cylinder 10 and the roll 12 extending for a distance within the gap 15 in the cross-machine direction. In the embodiment of Figure 8b the cover component 18.2 extends up to the edge 13' of the tail 13 and in the embodiment of Figure 8c, at least partially, even on top of the tail 13. In both embodiments the cover component 18.2 can be additionally sealed in the cross- machine direction, too, against the shell of the cylinder 10 and the roll 12 or at least very close to them. Sealing is illustrated in Figures 8b and 8c by the thicker outline of the cover component 18.2. The embodiment shows clearly that the cross-sectional shape of the cover component 18.2 can conform to the cross-section of the gap 15 in the cross-machine direction and thus fill the gap 15 over a desired distance.

In addition to an arrangement, the invention also relates to a device, the basic description of which becomes clearly evident from the above described embodiments, as well as to a method in

a dryer section of a web forming machine for controlling air flows during tail threading. In the method, a tail 13 is transported from a dryer cylinder 10 to a turning roll 12 in several positions of a dryer section over an interval 16 supported to a fabric 14. The dryer cylinder 10 and the fabric 14 form together an opening gap 15. According to the method of the invention, the gap 15 is covered at least partially for restricting air flows in the cross-machine direction in connection with an opening gap 15. Covering can be limited to take place immediately at the edge 13 ' of the tail 13 being thus outside the tail 13, or up to a distance from the edge 13' of the tail 13.

A flow block according to the invention may as well be applied in the press section of a web forming machine (not shown) . There the block can be a plate-like cover, for example. It may be located after the nips, for example, and/or after the suction rolls and/or transfer rolls. The protection can be, for example, a plexi plate protruding from the gap, since the conditions in the press section, compared to the dryer section, are more soiling due to the moisture level of the web.

It is to be understood that the above description and the figures related thereto are intended only for illustrating the present invention. The invention is thus not limited merely to the above described embodiments or those set forth in the claims, but many different variations and modifications of the invention, which are possible within the inventional idea specified in the appended claims, will be apparent for one skilled in the art.