WO2007128869A1

WO2007128869A1 - Method and arrangement in web control at a junction point of the sub-totalities of a web-forming machine

Info

Publication number: WO2007128869A1
Application number: PCT/FI2007/050217
Authority: WO
Inventors: Tuomo Juvakka; Jari Savela
Original assignee: Metso Paper, Inc.
Priority date: 2006-05-08
Filing date: 2007-04-24
Publication date: 2007-11-15
Also published as: FI20065301A0; CN101438003B; DE112007001097T5; FI118481B; AT506026A2; AT506026A3; AT506026B1; CN101438003A; DE112007001097B4

Abstract

The invention relates to a method in web control at a junction point of the sub- totalities of a web- forming machine. In the method, depending on the control requirement, either the web (18) is detached from a feeding fabric (14) and is transferred to a receiving fabric (15), so that a transfer connection is formed between the fabrics (14, 15) in question. Alterna¬ tively, the web (18) is broken by removing a transfer connection between the fabrics (14, 15). Irrespective of the control require¬ ment, the web (18) is, in addition, broken by guiding the web (18) towards a barrier (22), which is arranged after the detachment point of the web (18), in the direction of travel of the receiving fabric (15), at a distance from the receiving fabric (15). The invention also relates to an arrangement in web control at a junction point of the sub- totalities of a web-forming machine.

Description

METHOD AND ARRANGEMENT IN WEB CONTROL AT A JUNCTION POINT OF THE SUB-TOTALITIES OF A WEB-FORMING MACHINE

The present invention relates to a method in web control at a junction point of the sub-totalities of a web-forming machine, in which method, depending on the control requirements, either the web is detached from a feeding fabric belonging to the sub-totality preceding the junction point and is trans- ferred to the receiving fabric belonging to the sub-totality following the junction point, so that a transfer connection is formed between the fabrics in question, or the web is broken by removing a transfer connection between the fabrics .

The invention also relates to an arrangement in web control at a junction point of the sub-totalities of a web-forming machine .

US patent number 5281308 discloses an arrangement according to the preamble. In it, a web-threading tail is first cut from the web travelling on top of the forming fabric acting as the feeding fabric. When web threading is started, the threading tail is transferred, using the vacuum effect of a vacuum pick-up roll, from the forming fabric to the press fabric acting as the receiving fabric. Once web threading has succeeded, the threading tail is spread to form a full-width web, which at the same time transfers to the press fabric. Thus, during production the full-width web transfers from the forming fabric to the press fabric, assisted by a vacuum. However, web threading of this kind is slow and the cutting of the edge tail requires its own means. Cutting can easily fail, in which case the entire web threading must be started from the beginning.

Nowadays so-called closed threading is used in the press section, and consequently the press section lacks web-threading means . Thus the manner of threading referred to above cannot be applied. Therefore nowadays the web is transferred in a full-width form from the forming fabric to the press fabric. In practice, when starting the transfer, the pick-up roll and thus the press fabric is moved towards the forming fabric, when the web is captured onto the press fabric. However, in the transfer, the web detaches untidily from the forming fabric and becomes folded many times. Before starting the transfer, the part of the web being run down from the forming wire to the pulper is often pulled along. Thus the web enters the press nip in the press section as an untidy and even thick lump of pulp. Even though the press nip is usually unloaded, or so-called open during web threading, the lumps of pulp cause point impacts in the press nip. Particularly the belt jacket of a long-nip roll is sensitive to such impacts. In practice, when a pulp lump enters even the open press nip, it causes point pressure impacts in the belt jacket. In such an event, the lubricating oil film between the loading shoe and the belt jacket disappears, in which case the belt jacket is damaged, or at least wears locally more rapidly than in other areas. The same problem also appears in a web cut, in which the pick-up roll must be raised off the forming wire in the middle of production, and the web run down to the pulper. A web cut must often be made suddenly, in which case, despite quick opening, the press nip will be loaded. Then even small local pressure impacts will lead to the aforementioned problems. In web cutting the web also tears untidily and parts of the web travel from the pulper to the press-nip and even farther into the web-forming machine.

The invention is intended to create a new type of method in web control at a junction point of the sub-totalities of a web-forming machine, which method can be implemented in different web-control situations, without damaging the sub-totali- ties. In addition, the invention is intended to achieve a new type of arrangement in web control at a junction point of the sub-totalities of a web-forming machine, the construction of which arrangement is simple and durable, and which can be placed in connection with different kinds of junction point. The characteristic features of the method according to the present invention are stated in the accompanying Claim 1. Correspondingly, the characteristic features of the arrangement according to the invention are stated in the accompanying Claims 7. According to the invention, the web is cut in a controlled manner at various transfer stages, so that the problems according to the prior art can be avoided. Cutting can be achieved simply and economically without pre-settings . Thus cutting will operate as planned, even in surprising situations. The arrangement according the invention is simple and can be placed in existing web-forming machines without extensive alterations. It is also important to prevent excess parts of the web from entering the sub-totalities. For example, damage to the long-nip rolls forming the press nip is avoided. This will increase the operating life of belt jackets in particular and avoid sudden breakages of the belt jacket. At the same time, web threading and web breaks can be made less carefully than before, if this is necessary for some reason. At the same time, web threading and web breaking are accelerated while the junction point remains cleaner. Thus there is less need for cleaning than before, allowing web threading to be started sooner after a web break, which improves the efficiency of the web-forming machine.

In the following, the invention is examined in detail with reference to the accompanying drawings depicting some embodi- ments of the invention, in which

Figure 1 shows one location of the arrangement according to the invention at the junction point between the forming section and the press section, Figure 2 shows another location of the arrangement according to the invention at the junction point between the forming section and the press section,

Figures 3a-d show the various consecutive stages of a first embodiment of the method according to the invention,

Figure 3e shows an enlargement of the stage of Figure 3d,

Figures 4a-d show the various consecutive stages of a second embodiment of the method according to the inven- tion,

Figure 4e shows an enlargement of the stage of Figure 4d,

Figure 5 shows a third location of the arrangement according to the invention at the junction point between the forming section and the press section, Figure 6 shows a location of the arrangement according to the invention in the press section, and

Figure 7 shows a third embodiment of the barrier according to the invention.

Figures 1, 2, 5, and 6 show four press sections 10 that are, as such, known, as well as part of the web-forming section 11 preceding them. Figure 5 shows, in addition the horizontal impingement-drying unit 13 after the press section 10, which starts the drying section 12. Correspondingly, Figure 6 shows the impingement dryer 34 and the vertical impingement-drying unit 13, which starts the drying section 12, following the press section 10. All four press sections are sub-totalities of four large web-forming machines, which can be paper or board machines. Usually, the web-forming section includes at least one forming fabric, which supports the web being manufactured and carries it forward. Correspondingly, the press section includes at least one press fabric, which also supports the web and carries it forward. The web-forming machine is intentionally divided into sub-totalities, which are a drying section and finishing section, in addition to the forming and press sections. Between the consecutive sub-totalities, the web can be run down to a pulper or other broke processing. Thus in a web break, for example, web threading can be started from the sub-totality preceding the problem location. For example, if the web breaks in the press section, the web can be run down at the end of the forming section and production started again with web threading to the press section.

The matter thus concerns web control , the need for which varies. A web-forming machine also includes means for creating and removing the necessary transfer connection, for example, in order to control the web between the forming fabric and the press fabric, according to the control requirement at the junction point at any time. In other words, depending on the control requirement, the transfer connection is formed at the web taken from the forming fabric to the press fabric. On the other hand, the transfer connection can be removed, in which case the web is run down to the pulper. The various control requirements are described later in greater detail. In practice, the means 19 are usually connected to the pick-up roll 20 arranged to support the press fabric, the position of which can be adjusted relative to the forming fabric 16 (Figures 1 and 2) . Stated more generally, the web is detached from the feeding fabric belonging to the sub-totality preceding the junction point, and transferred to the receiving fabric belonging to the sub-totality following the junction point, so that a transfer connection is forming between the fabrics in question. On the other hand, the web is cut by removing the transfer connection between the fabrics . The operation in question can thus be implemented at the junction points of the various sub-totalities, mainly depending on the construction of the web-forming machine.

Figures 3a - e show a first control requirement, which in this case is the starting of web threading, which is also referred to as picking. In this case, an embodiment is examined, in which the web is transferred from the web-forming section to the press section. In other words, the web 18 is detached from the forming fabric 16 and transferred to the press fabric 17, when a transfer connection is formed between the forming fabric 16 and the press fabric 17. In Figure 3a, the web 18 travels supported by the forming fabric 16 and is run down into the pulper. When the web threading is started, the pick-up roll 20 is moved towards the web 18 on the forming fabric 16, which is shown in Figure 3b. Due to the adhesion of the press fabric 17 and the vacuum effect created by the pick-up roll 20, the web 18 moves to follow the press fabric 17. At the same time, the web 18 detaches from the forming fabric 16. In the prior art, this stage is very poorly defined and the web tears unevenly. According to the invention, however, the web is, in addition, cut by guiding it towards a barrier, which is arranged in the direction of travel of the press fabric after the web detaching point, at a distance from the press fabric. Stated more generally, the barrier is arranged in the direction of travel of the receiving fabric, after the point of detachment of the web, at a distance from the receiving fabric. In Figures 1, 2, 5, and 6, the location of the barrier 22 is shown schematically by a rectangle. When it strikes the barrier, the web breaks in a controlled manner and a clean edge is formed in it. In some applications, the cut end of the web can be folded double, the effect of which on the press nip and its loading being, how- ever, non-existent. In other words, by means of a controlled break the drawbacks of the prior art are avoided. In Figure 3d, the web 18 has already broken and progresses on the under surface of the press fabric 17. The broken part of the web drops into the pulper without travelling to the press nip. Figure 3e shows an enlargement of the situation according to Figure 3d. The solid thin line shows the position of the web 18 at the moment of impact. Otherwise, the web 18 is shown by a broken line.

Figures 4a - e show a second control requirement, which in this case is a web break. In this case too, an embodiment is exam- ined, in which the web is transferred from the web-forming section to the press section. In other words, the web is broken by removing the transfer connection between the forming fabric and the press fabric. In Figure 4a, the web 18 travels during production from the forming fabric 16 to the press fabric 17. When required, for example in a web break in the press section, the pick-up roll 20 is raised off the forming fabric 16, which is shown in Figure 4b. In addition, the vacuum effect of the pick-up roll 20 is usually removed, in which case the web 18 starts to follow the forming fabric 16. A moment later, the web 18, which may be slightly creased, strikes the barrier 22 according to the invention and breaks in a controlled manner. The end of the web then becomes even, which avoids the drawbacks of the prior art. In Figure 4d, both parts follow their own fabrics without detrimental pulp lumps. Figure 4e shows the situation according to Figure 4d, in which the web 18 strikes the barrier 22 and breaks in a controlled manner.

According to the invention, the web can be cut irrespective of the control requirement, which avoids, for example, point impacts in the press nip. At the same time, dirtying and thus the need for cleaning are reduced. The barrier according to the invention is arranged, in the direction of travel of the receiving fabric, after the web detachment point, at a distance from the receiving fabric. The barrier is preferably arranged in the direction of gravity beneath the receiving fabric. This achieves the advantageous operation described above, in which the broken parts of the web drop into the pulper by gravity.

The method and arrangement according to the invention can also be exploited at other locations in the web-forming machine. In Figure 5, a barrier according to the invention is located at the junction point 21 between the press section 10 and the drying section 12. Here, the feeding fabric 14 is the lower felt 23 arranged to travel through the press nip, from which felt the web is picked onto the impingement-drying unit's 13 transfer wire 24 acting as the receiving fabric 15. In this case too, picking is based on the vacuum effect of the pick-up roll 20. At the same time, a blast 25, which also functions with at least certain types of felt, can also be arranged on the inner side of the transfer wire 24, which is more permeable than the felt 23. Stated more generally, the blast is arranged in connection with the barrier, so that the web is better controlled for cutting by blowing through the fabric. In other words, the cutting of the web is ensured by the blast. In Figure 5, the blast 25 is depicted by a downwards-facing arrow. In the embodiment of Figure 5, paper lumps entering the impingement-drying unit could destroy the fabrics by causing a contact with the blowing means. Blockages in the exit nozzles for the blast air would also be possible. In the embodiment of Figure 6, paper entering the exit nozzles would be an even greater risk than in the former case, as the impingement- drying is directly against the web.

The method and arrangement according to the invention can also be arranged in connection with a calender belonging to the web-forming machine, especially in intermediate calendering. In the sub-totality in question, the web is picked from the drying fabric, as the feeding fabric, onto the transfer fabric of the calender as the receiving fabric. Using the prior art, problems can arise especially in a shoe or belt calender, in which the belt jacket of the shoe roller can be damaged in a manner corresponding to that in the press section. Correspondingly, pulp lumps can cause deformations, which are copied in the calendering nip of the web, requiring the repair of the blade band of the belt calender. In the calendering application too blowing can be used as an aid in cutting.

In practice, the barrier is placed surprisingly close to the fabric. During the transfer connection, the gap can be arranged in such a way that the barrier comes close to the receiving fabric. For example, the gap can be less that 50 mm. This will avoid long web parts and the barrier will operate practically without delay. The intention is also to place the barrier close to the transfer point of the web, in the direction of travel of the web. The closer the barrier is to the transfer point, the closer it can be placed to the receiving fabric. The barrier is placed at a distance of less than 2000 mm, preferably less than 800 mm, to the transfer point in the case of the receiving fabric, or some other near support point of the fabric, such as a roll.

At its simplest, the barrier is installed permanently, in which case the construction becomes very simple. However, production conditions may often vary, in which case the barrier can include support elements 26 for adjusting the position and/or alignment of the barrier 22. In Figures 3e and 4e, the various directions of movement are shown by arrows. Important adjustments are the adjustment of the position of the barrier relative to the opening throat formed by the fabrics, and adjustment from the fabric. Besides, or instead of the aforementioned adjustments, the support elements can be arranged in such a way that the barrier has an operating position and a rest position. In that case, when cutting is required, the barrier is turned or moved to the operating position, and when the need terminates the barrier is turned or moved to the rest position (not shown) . This improves work safety while also avoiding damage to the fabrics. At the same time, the barrier remains clean. On the other hand, the support elements can be arranged to yield. In that case, when the fabric possibly strikes the barrier, the barrier will yield in the direction of travel of the fabric, thus avoiding the immediate danger of the web breaking. On the other hand, the sharp barrier can be advantageously turned to an alignment at right angles to the fabric. In that case, damage to the fabric will be avoided, but sufficient web cutting will be achieved, especially if blowing is used as an aid from the opposite side of the fabric. In practical tests, the barrier was arranged to form a blade 22 ' , which was turned against the direction of travel of the web 18. In other words, the web is broken according to the invention by cutting. In the embodiments shown, the blade that is the barrier remains stationary and the moving web is cut when it strikes the blade. The solution in question is simple and reliable in operation. In addition, the blade extends essentially over the entire width of the web. Thus the entire web is cut at one time. The blade can be formed of several blade pieces, or even of individual spikes. The blade is preferably toothed, in which case the points of the teeth make small starting holes in the web, from which the web will break easily.

Figures 3e and 4e show schematically the barrier's 22 support elements 26, which according to the invention are arranged to form a guard wall 27, or at least to form part of a guard wall. In one embodiment, the frame of the cutting-blade holder extends straight or curved down towards the pulper (not shown) . The frame then acts as a guiding guard wall, when it will prevent undesirable pulp lumps from rising from underneath the cutting blade and its holder, for example, when lifted by the lower felt of the first press nip and then along with the felt of the press nip. In addition, wall 28 that extends downwards, and in which lubricating sprays 29 are arranged, can be added to the frame of the holder. The lubricating sprays guide the web to the pulper and keep the wall and even the guide wall clean.

Figure 7 shows a third embodiment of the barrier 22 according to the invention, by means of which the web 18 can be cut during both picking and breaking. At the same time, the cut end of the web becomes straight and parts of the web are prevented from entering the press nip. In this case, the blade 22' is attached to a foil blade 30. In practice, a glass or carbon-fibre reinforced doctor blade can be used as the blade. In the direction of travel of the web 18, the first point of the foil blade 30 is arranged to be closer to the receiving fabric 15. In other words, the blade 22' is attached in such a way that its point bevel is above the upper surface of the foil blade 30. This creates a so-called receiving point, which is sure to cut the web during both picking and breaking. The foil blade 30 is supported on a support structure 31, only part of which is shown in Figure 7. A T-shaped piece 32 is attached by screws to the support structure 31, a corresponding T-shaped groove being arranged in the foil blade 30. Other kinds of attachment can also be used. Both the blade 22' and the foil blade 30 extend over essentially the entire width of the web 18. In the support structure 31, there is preferably also a moving mechanism, by means of which the blade 22 ' can be run from the operating position to the rest position and back (not shown) . In the example embodiment shown, the receiving fabric 15 is the press felt.

In the operating position of the arrangement, the distance of the blade from the receiving fabric is 2 - 20 mm, preferably 3 - 10 mm. In one tested embodiment, in the cutting position the point of the point bevel of the blade was at a distance of about five millimetres from the press felt. In the rest position, the blade is farther from the fabric, so that washing, for example, is possible. This also avoids fabric damage and the dirtying of the arrangement .

The arrangement is also well suited for controlling the picking and cutting of a heavy board web, which has often been problem- atic. In particular, the use of a foil blade can further improve the cutting effect of the blade. A foil blade set at a suitable angle will create a vacuum effect, if the foil blade is fitted sufficiently close to the fabric. In Figure 7, the direction of travel of the fabric 15 is shown by an arrow. At the same time, the blade 22' effectively prevents air drawn along by the receiving fabric from entering the area 33 of the vacuum. After cutting, the web comes to the area of the blade 22' in a loop along with the receiving fabric, the tail of the web hanging down. When the looped front edge of the web passes the blade, the front edge of the web enters the vacuum area 33. The vacuum created by the foil blade pulls the web towards the foil blade, so that the blade is certain to cut the web in a single pass over the entire width of the web. In other words, in this case the vacuum effect ensures the cutting of the web, making blowing unnecessary. Of course, in connection with thick press felts the blasts would be ineffective when blowing through the felt. The foil blade forms an opening throat together with the receiving fabric. The distance of the foil blade from the fabric and the dimensioning of the opening throat are arranged in such a way that the vacuum created by the opening throat will not detach the web from the support of the fabric during production. The vacuum only assists in cutting, when the web is otherwise already free of the fabric. The principle of the foil blade can also be used in a doctor-blade application using a corresponding opening throat (not shown) .

The method and arrangement according to the invention are advantageous in applications, in which the web is transferred on the press fabric to the press nip belonging to the press section, one component forming part of which is a long-nip roll . The barrier is used to prevent the formation of pulp lumps during cutting, which in turn eliminates problems in the press nip. In practice, the straight cut end of the web raises the loading shoe at one time, thus avoiding point pressure impacts on the belt jacket. This lengthens the life of the belt jacket. Consequently, fewer replacement belt jackets will be required, which will bring beneficial cost savings. The reduction in extra unplanned belt-jackets changes is also important, as it will increase the production time on the web-forming machine. Corresponding advantages are achieved in the impingement-drying and belt-calender applications described above .

Claims

1. Method in web control at a junction point of the sub-totalities of a web-forming machine, in which method, depending on the control requirements, either

- the web (18) is detached from a feeding fabric (14) belonging to the sub-totality (10 - 12) preceding the junction point (21) and is transferred to the receiving fabric (15) belonging to the sub-totality (10 - 12) following the junction point (21), so that a transfer connection is formed between the fabrics (14, 15) in question, or

- the web (18) is broken by removing a transfer connection between the fabrics (14, 15), characterized in that, irrespective of the control requirement, the web (18) is, in addition, broken by guiding the web (18) towards a barrier (22), which is arranged after the detachment point of the web (18), in the direction of travel of the re- ceiving fabric (15) , at a distance from the receiving fabric (15) .

2. Method according to Claim 1 , characterized in that the web (18) is broken by cutting.

3. Method according to Claim 1 or 2 , characterized in that the breaking of the web (18) is ensured by means of blowing (25) .

4. Method according to Claim 1 or 2 , characterized in that the breaking of the web (18) is ensured by means of a vacuum effect.

5. Method according to any of Claims 1 - 4, characterized in that the receiving fabric (15) is arranged to be the press fabric (17), by means of which the web (18) is transferred to a press nip, one component forming part of which nip is a long-nip roll, belonging to the sub-totality (10).

6. Method according to any of Claims 1 - 4, characterized in that the receiving fabric (15) is arranged to be the drying fabric (24), by means of which the web (18) is transferred to a impingement-drying unit (13) belonging to the sub-totality (12).

7. Arrangement in web control at a junction point of the sub-totalities of a web-forming machine, which web-forming machine includes - a sub-totality (10 - 12) preceding the junction point (21) and a feeding fabric (14) in it,

- a sub-totality (10 - 12) following the junction point (21) and a receiving fabric (15) in it, and

- means (19) for forming a transfer connection between the fabrics (14, 15), or for removing a transfer connection between the fabrics (14, 15), in order to control the web (18) at the junction point (21) according to the control requirement at the time, characterized in that a barrier (22) is arranged after the detachment point of the web (18) , in the direction of travel of the receiving fabric (15) , at a distance from the receiving fabric (15) , for breaking the web (18) , by guiding the web (18) towards the barrier (22), irrespective of the control requirement.

8. Arrangement according to Claim 7 , characterized in that the barrier (22) is arranged beneath the receiving fabric (15) in the direction of gravity.

9. Arrangement according to Claim 7 or 8, characterized in that the barrier (22) includes support elements (26), for adjusting the position and/or alignment of the barrier (22) .

10. Arrangement according to Claim 9, characterized in that the support elements (26) are arranged in such a way that the barrier (22) has an operating position and a rest position.

11. Arrangement according to Claim 9 or 10, characterized in that the support elements (26) are arranged to be yielding.

12. Arrangement according to any of Claims 9 - 11, character- ized in that the support elements (26) are arranged to form a guard wall (27) , or part of a guard wall (27) .

13. Arrangement according to any of Claims 9 - 12, characterized in that the support elements (26) include a wall (28) , in which lubricating sprays (29) are arranged, fitted close to the barrier (22 ).

14. Arrangement according to any of Claims 7 - 13, characterized in that the barrier (22) is arranged to form a blade (22¹), which is turned against the direction of travel of the web (18) .

15. Arrangement according to Claim 14, characterized in that the blade (22') extends over essentially the entire width of the web (18) .

16. Arrangement according to Claim 14 or 15, characterized in that the blade (22') is attached to a foil blade (30), the first point of which in the direction of travel of the web (18) is arranged to be closer to the receiving fabric (15) .

17. Arrangement according to Claim 16, characterized in that the blade (22 ') is arranged in such a way that the point belonging to the blade (22') is closer to the receiving fabric (15) than the foil blade (30)).

18. Arrangement according to any of Claims 14 - 17, characterized in that, in the operating position of the arrangement, the distance of the blade from the receiving fabric (15) is 2 - 20 mm, preferably 3 - 10 mm.