TECHNICAL FIELD The invention relates to a paper or board machine forming section according to the preamble of claim 1.

BACKGROUND ART WO publication 2009/068728 discloses a hybrid forming section comprising a lower wire loop which constitutes a first single wire section following a breast roll. The beginning of the first single wire section comprises a first dewatering zone which consists of at least one stationary, first forming shoe and a pulsating strip cover following it. The first forming shoe comprises a straight cover provided with through holes and under pressure affecting through the holes of the cover. The holes are constituted of openings or slots substantially in the longitudinal direction of the machine, whereby non-pulsating dewatering is applied on the stock travelling on top of the lower wire. The forming section further comprises a first multilayer head box for supplying a slice jet at the beginning of the first forming shoe. A first upper wire loop forms a first twin wire section with the lower wire loop after the first forming shoe. Figures 5 and 6 disclose formers with two separate partial forming units. The first twin wire section of the hybrid former is followed by a second upper wire unit in which the second upper wire forms a second single wire section. A second single layer head box supplies a slice jet at the beginning of the second single wire section. The first partial web formed in the hybrid former and the second partial web formed on the second upper wire loop are combined in a joining point formed by an inner roll of the second upper wire loop and the lower wire loop. The joining point is followed by a short twin wire section on which the joining of the two partial webs is secured. The combined web is then conducted with the lower wire loop to the pick up point. The upper part of the lower wire loop is essentially straight. FI patent 121147 discloses a pre-press, a forming section and an apparatus for producing a multi layer web. The forming section in Figure 6 comprises a first wire loop for forming a first partial web and a second wire loop for forming a second partial web. The first wire loop has a first essentially horizontal forming section followed by a second downwardly directed section. The second wire loop has also a first essentially horizontal forming section followed by a second downwardly directed section. The first and the second wire are joined on the downwardly directed section in a pre-press nip. The travel direction of the wires is turned into a horizontal travel direction after the pre-press nip with a turning roll situated within the second wire loop. The combined web is then conducted with the first wire to a pick up point.

Problem of the prior art multiply forming sections is that the height of the former is very high and that causes very complicated forming section structures and leads to very expensive solutions.

SUMMARY OF THE INVENTION The object of the invention is to achieve a compact paper or board machine forming section.

The forming section according to the invention is characterized by the features in the characterizing portion of claim 1.

The forming section according to the invention comprises:

- a first wire loop passing over a first breast roll and forming a first single wire forming section in a first direction after the first breast roll,

- a first head box for supplying a slice jet on the first wire loop at the beginning of the first single wire forming section to form a first web, - a first turning roll within the first wire loop for directing the first wire loop into a downwards inclined slope after the first single wire forming section,

- a second wire loop passing over a second breast roll and forming a second single wire forming section in a second direction after the second breast roll, said second direction being opposite to the first direction,

- a second head box for supplying a slice jet on the second wire loop at the beginning of the second single wire forming section to form a second web,

- a second turning roll within the second wire loop for directing the second wire loop into a downwards inclined slope after the second single wire forming section, - a joining roll within the second wire loop after the second turning roll forming a joining point to the first web and to the second web between the first wire loop and the second wire loop, said joining point being below the horizontal level of the first single wire forming section,

- the first single wire forming section and the second single wire forming section being essentially on the same horizontal level, and further

- a pick-up unit within a pick-up fabric loop forming a pick-up point between the first wire loop and the pick-up fabric loop.

The former according to the invention is characterized in that the first wire loop and the second wire loop are joined together in the joining point for combining the first web and the second web to be a combined web such that the first wire loop and the second wire loop are wrapped around the joining roll by a wrap angle a, and

that after the joining roll the first wire loop is separated from the second wire loop for transferring the combined web to the pick-up point such that the first wire loop travels in a horizontal or upward inclined direction between the joining point and the pick-up point.

The forming section according to the invention preferably comprises at least one additional wire loop for forming at least one twin wire section with the first wire loop or with the second wire loop. The forming section according to the invention is compact and it is easy to be converted to various web grades. The former can be used in a first embodiment for producing a three layer board web with the smooth surface facing upwards or in a second embodiment for producing a three layer board web with the smooth surface facing downwards. The first embodiment is achieved when the additional wire loop is positioned in connection with the first wire loop and the second embodiment is achieved when the additional wire loop is positioned in connection with the second wire loop. The first framework comprises vertical support beams with first support points at the upper end and the second framework comprises vertical support beams with second support points at the upper end, said first and second support points being adapted to receive third support points at the lower ends of vertical support beams of the third framework.

The first wire loop is preferably supported at least on a first framework comprising horizontal and vertical support beams with first support points and the second wire loop is preferably supported at least on a second framework comprising horizontal and vertical support beams with second support points, said horizontal support beams of the first framework being on the same horizontal level with the horizontal support beams of the second framework. An additional wire loop can be supported on an additional framework comprising horizontal and vertical support beams with additional support points for connecting said additional framework to the first framework and/or to the second framework.

When the former is followed by a SymPress B press section there is a need to have the smooth surface facing downwards in the web produced by the former.

The smooth surface facing downwards of the web produced in the former will settle against the smooth centre roll in the SymPress B press section.

When the former is followed by an OptiPress press section there might be a need to have the smooth surface facing upwards in the web produced by the former. The smooth surface facing upwards of the web produced in the former will settle against the smooth upper fabric in the OptiPress press section.

The forming section according to the invention can also comprise at least one additional wire loop for forming at least one twin wire section with the first wire loop and at least one additional wire loop for forming at least one twin wire section with the second wire loop.

The former can also be used in a third embodiment for producing a four layer board web. This third embodiment is achieved by positioning a first third wire loop in connection with the first wire loop and by positioning a second third wire loop in connection with the second wire loop.

The total height of the former according to the invention is less than 7 m in all embodiments. The height of a corresponding prior art former is more than 10 m. The fact that the joining point for joining the first partial web and the second partial web is clearly below the level of the first single wire forming section makes it possible to position the second single wire forming section on the same horizontal level as the first single wire section. The total height of the former will be the same in all four embodiments. The drive motors and other equipment on the drive side will in a lower former be on a lower level, which means that the requirements for the frameworks are less rigid.

BRIEF DESCRIPTION OF THE DRAWINGS

Some specific embodiments of the invention are described in the following in detail with reference to the accompanying figures, in which:

Figure 1 shows a first embodiment of a forming section according to the invention. Figure 2 shows a second embodiment of a forming section according to the invention.

Figure 3 shows a third embodiment of a forming section according to the invention.

Figure 4 shows a fourth embodiment of a forming section according to the invention. DETAILED DESCRIPTION OF SOME SPECIFIC EMBODIMENTS

Figure 1 shows a first embodiment of a forming section according to the invention. The former comprises a first wire loop 11 passing over a first breast roll 12 and forming a first single wire forming section SI in a first direction Dl after the first breast roll 12. A first head box 100 supplies a first slice jet at the beginning of the first single wire forming section SI . The former comprises further a second wire loop 21 passing over a second breast roll 22 and forming a second single wire forming section S2 in a second direction D2 after the second breast roll 22. The second direction D2 is opposite to the first direction Dl . A second head box 110 supplies a second slice jet at the beginning of the second single wire forming section S2. The first single wire forming section SI and the second single wire forming section S2 are essentially horizontal.

The former comprises further an additional wire loop or in other words a third wire loop 31 forming a first twin wire section Tl with the first wire loop 11. The first twin wire section Tl follows immediately after the first single wire section SI . The third wire loop 31 is situated above the first wire loop 11.

The first wire loop 11 comprises further a first turning roll 13 being situated within the first wire loop 11 for turning the running direction of the first wire 11 to a downwardly directed inclined run. The second wire loop 21 comprises a second turning roll 23 being situated within the second wire loop 21 for turning the direction of the second wire loop 21 into a downwards inclined run. The second wire loop 21 comprises further a first joining roll 24 being situated within the second wire loop 21 and forming a joining point Jl with the first wire loop 11.

The first partial web Wl formed in the first hybrid forming section SI, Tl is joined with the second partial web W2 formed in the second single forming section S2 in said joining point Jl . After the joining point Jl the combined web W is wrapped along the first joining roll 24 between the first wire loop 11 and the second wire loop 21 by a wrap angle a, which is between 15° - 90°. This ensures good bond strength of the combined web W and makes possible to create low forming section structure. After the first joining roll 24 wrap angle a follows an upwardly directed inclined run during which the second wire 21 is separated from the first wire 11 and directed to the return rotation. The combined web W is attached to the first wire 11 at the point where the second wire 21 is separated from the first wire 11 with suitable suction means. The final combined web W travels thereafter further on the horizontal run or on the upwards inclined run of the first wire 11 to a pick-up point PP. This ensures that whole forming section height remains low and forming section frames can be easily transformable to various paper grades. The final combined web W is transferred in the pick-up point PP from the first wire 11 with a pick-up unit 210 being situated within a pick-up fabric loop 200. The pick-up unit 210 forms a pick-up point PP with the first wire 11. The pick-up unit is preferably a suction box or a suction roll. The first wire 11 is directed to the return rotation after the pick-up point PP. The lowest point of the joining roll 24 is on the same level or on a lower level than the lowest point of the pick-up unit 210. The first head box 100 is advantageously a two layer head box and the second head box 110 is advantageously a one layer head box in this first embodiment of the invention. The lower surface of the second partial web W2 formed in the second single wire section S2 will form the smooth top surface of the final combined web W. Said lower surface of the second partial web W2 will be situated against the second wire 21 in the second single wire section S2. The smooth top surface of the final combined three layer web W will be the surface of the board that is to be printed.

The first wire loop 11 is supported on a first framework Fl, the second wire loop 21 is supported on a second framework F2 and the third wire loop 31 is supported on a third framework F3. The first Fl, second F2 and third F3 framework all comprises horizontal and vertical support beams. Two of the vertical support beams Via, Vlb at the tending side of the former in the first framework Fl comprise first support points Pla, Plb that have been adapted to receive corresponding third support points P3a, P3b of the vertical support beams V3a, V3b at the tending side of the third framework Fl . There are naturally corresponding vertical support beams on the drive side of the former i.e. four vertical support beams all together. The support points Pla, Plb and P3a, P3b can be formed of flanges positioned at the ends of the support beams. The flanges could be fastened with bolts. There are further two vertical support beams V2a, V2b at the tending side of the former in the second framework F2, which are also adapted to receive the third framework F3. The latter portion of the first wire loop 11 after the joining point Jl is supported on the lower portion of the second framework F2. Figure 2 shows a second embodiment of a forming section according to the invention. This second embodiment corresponds to the first embodiment shown in Figure 1 except for the position of the additional wire loop 31. The additional wire loop or in other words the third wire loop 31 forms a first twin wire section Tl with the second wire loop 21 in this embodiment. The additional third wire loop 31 in this second embodiment is a mirror image of the third wire loop 31 in the first embodiment. The first turning roll 13 in the first wire loop 11 is advantageously supported on a first swinging arm 13a. The first swinging arm 13a of the first turning roll 13 in the first wire loop 11 is arranged in the first embodiment in Figure 1 in an upper position when acting in the first twin wire section Tl and in this second embodiment in a lower position. A first guide roll 15 in the first wire 11 loop can be moved as shown by the arrow in the Figures in order to adapt the length of the first wire loop 11 depending on the position of the first turning roll 13 in the first wire loop 11.

The second turning roll 23 in the second wire loop 21 is also supported on a second swinging arm 23 a. The second swinging arm 23 a of the second turning roll 23 in the second wire loop 21 is arranged in the first embodiment in Figure 1 in a lower position and in this second embodiment in an upper position when acting in the first twin wire section Tl . A second guide roll 25 in the second wire 21 loop can be moved as shown by the arrow in the Figures in order to adapt the length of the second wire loop 21 depending on the position of the second turning roll 23 in the second wire loop 21. The first partial web Wl formed in the first single forming section SI is joined with the second partial web W2 formed in the second hybrid forming section S2, Tl in a joining point Jl . After the joining point Jl the combined web W is wrapped along the first joining roll 24 between the first wire loop 11 and the second wire loop 21 by a wrap angle a, which is between 15° - 90°. After the first joining roll 24 wrap angle a follows an upwardly directed inclined run during which the second wire 21 is separated from the first wire 11 and directed to the return rotation. The combined web W is attached to the first wire 11 at the point where the second wire 21 is separated from the first wire 11 with suitable suction means. The final combined web W travels thereafter further on the horizontal run or on the upwards inclined run of the first wire 11 to a pick-up point PP. The lowest point of the joining roll 24 is on the same level or on a lower level than the lowest point of the pick-up unit 210.

The first head box 100 is advantageously a one layer head box and the second head box 110 is advantageously a two layer head box in this second embodiment of the invention. The lower surface of the first partial web Wl formed in the first single wire section S 1 will form the smooth bottom surface of the final combined web W. Said lower surface of the first partial web Wl will be situated against the first wire 11 in the first single wire section S 1. The smooth bottom surface of the final combined three layer web W will be the surface of the board that is to be printed.

The first wire loop 11 is supported on the first framework Fl, the second wire loop 21 is supported on the second framework F2 and the third wire loop 31 is supported on the third framework F3. The first Fl, the second F2 and the third F3 framework all comprise horizontal and vertical support beams. Two of the vertical support beams V2a, V2b at the tending side of the former in the second framework F2 comprise second support points P2a, P2b adapted to receive corresponding third support points P3a, P3b of the vertical support beams V3a, V3b at the tending side of the third framework F3. There are naturally corresponding vertical support beams on the drive side of the former i.e. there are four vertical support beams all together. The support points P2a, P2b and P3a, P3b can be formed of flanges positioned at the ends of the support beams. The flanges could be fastened with bolts. The first Fl and the second F2 frameworks are thus as such ready to receive the third framework F3 without any changes in said frameworks. It is thus easy to modify the former according to the invention to be either a former according to figure 1 or a former according to figure 2. The only thing that needs to be done is to change the position of the third wire loop 31, to change the position of the first turning roll 13, to change the position of the second turning roll 23 and to swap the head boxes 100, 110. The latter portion of the first wire loop 11 after the joining point Jl is supported on the lower portion of the second framework F2. It is naturally also possible to use a first additional wire loop 31 in connection with the first wire loop 11 and a second additional wire loop 41 in connection with the second wire loop 21. Both head boxes 100, 110 would thus be preferably two layer head boxes. This third embodiment of a former according to the invention is shown in figure 3. In this third embodiment of the invention the former comprises a first wire loop 11 passing over a first breast roll 12 and forming a first single wire forming section SI in a first direction Dl after the first breast roll 12. A first head box 100 supplies a first slice jet at the beginning of the first single wire forming section S 1. The former comprises further a second wire loop 21 passing over a second breast roll 22 and forming a second single wire forming section S2 in a second direction D2 after the second breast roll 22. The second direction D2 is opposite to the first direction Dl . A second head box 110 supplies a second slice jet at the beginning of the second single wire forming section S2.

The former comprises further a first additional wire loop 31 forming a first twin wire section Tl with the first wire loop 11. The first twin wire section Tl follows immediately after the first single wire section S 1. The first additional wire loop 31 is situated above the first wire loop 11. The former further comprises a second additional wire loop 41 forming a second twin wire section T2 with the second wire loop 21. The second twin wire section T2 follows immediately after the second single wire section S2. The second additional wire loop 31 is situated above the second wire loop 21. The second additional wire loop 41 is a mirror image of the first additional wire loop 31.

The first turning roll 13 in the first wire loop 11 is advantageously supported on a first swinging arm 13a. The first swinging arm 13a of the first turning roll 13 in the first wire loop 11 is arranged in an upper position when acting with the first twin wire section T 1. The second turning roll 23 in the second wire loop 21 is also supported on a second swinging arm 23 a. The second swinging arm 23 a of the second turning roll 23 in the second wire loop 21 is also arranged in an upper position when acting with the second twin wire section T2.

The first partial web Wl formed in the first hybrid forming section SI, Tl is joined with the second partial web W2 formed in the second hybrid forming section S2, T2 in said joining point Jl . After the joining point Jl the combined web W is wrapped along the first joining roll 24 between the first wire loop 11 and the second wire loop 21 by a wrap angle a, which is between 15° - 90°. After the first joining roll 24 wrap angle a follows an upwardly directed inclined run during which the second wire 21 is separated from the first wire 11 and directed to the return rotation. The combined web W is attached to the first wire 11 at the point where the second wire 21 is separated from the first wire 11 with suitable suction means. The final combined web W travels thereafter further on the horizontal run or on the upwards inclined run of the first wire 11 to a pick-up point PP. The final combined web W is transferred in the pick-up point PP from the first wire 11 with a pick-up unit 210 being situated within a pick-up fabric loop 200. The pick-up unit 210 forms a pick-up point PP with the first wire 11. The first wire 11 is directed to the return rotation after the pick-up point PP. The final web produced by such a former would thus be a four layer board web. The lowest point of the joining roll 24 is on the same level or on a lower level than the lowest point of the pick-up unit 210. The first single wire section SI and the second single wire section S2 are essentially on the same horizontal level. This means that also the slice opening of the first head box 100 and the slice opening of the second head box 110 are on the same horizontal level. The service platforms in the first framework Fl and the service platforms in the second framework F2 are also on the same horizontal level. The pick-up point PP is in the embodiments shown in the figures approximately at the same horizontal level as the joining point Jl . The pick-up point PP could naturally also be on a higher horizontal level if needed. It might in some cases be more appropriate to lead the web from the former to the press section from a higher horizontal level.

Figure 4 shows a fourth embodiment of the former according to the invention. This embodiment comprises three additional wire loops 31, 41, 51. The first additional wire loop is in connection with the first wire loop 11 and a second additional wire loop 41 in connection with the second wire loop 21. Both head boxes 100, 110 would thus be two layer head boxes. The third additional wire loop 51 is again in connection with the first wire loop and comprises a one layer head box 120. The same as in figure 3 the first wire loop 11 is also passing over a first breast roll 12 and forming a first single wire forming section SI in a first direction Dl after the first breast roll 12. A first head box 100 supplies a first slice jet at the beginning of the first single wire forming section SI . The former comprises further a second wire loop 21 passing over a second breast roll 22 and forming a second single wire forming section S2 in a second direction D2 after the second breast roll 22. The second direction D2 is opposite to the first direction Dl . A second head box 110 supplies a second slice jet at the beginning of the second single wire forming section S2.

The former comprises a first additional wire loop 31 forming a first twin wire section Tl with the first wire loop 11. The first twin wire section Tl follows immediately after the first single wire section S 1. The first additional wire loop 31 is positioned above the first wire loop 11. The former further comprises a second additional wire loop 41 forming a second twin wire section T2 with the second wire loop 21. The second twin wire section T2 follows immediately after the second single wire section S2. The second additional wire loop 31 is situated above the second wire loop 21. The second additional wire loop 41 is a mirror image of the first additional wire loop 31. The former further comprises a third additional wire loop 51 in connection with the first wire loop 11 such that the third additional wire loop 51 is also passing over a first breast roll 32 and forming a third single wire forming section S3 in a first direction D2 after the third breast roll 32. A third head box 120 supplies a first slice jet at the beginning of the third single wire forming section S3.

The first partial web Wl formed in the first hybrid forming section SI, Tl is joined with the second partial web W2 formed in the second hybrid forming section S2, T2 in said joining point Jl . After the joining point Jl the combined web W is wrapped along the first joining roll 24 between the first wire loop 11 and the second wire loop 21 by a wrap angle a, which is between 15° - 90°. After the first joining roll 24 wrap angle a follows an upwardly directed inclined run during which the second wire 21 is separated from the first wire 11 and directed to the a joining point J2 in which the combined W formed in the previous forming sections is joined with a third partial web W3 formed in the third single forming section S3. After the joining roll 34 the fifth wire loop 51 is separated from the first wire 11 and the final combined web W travels thereafter further on the horizontal run or on the upwards inclined run of the first wire 11 to a pick-up point PP. The final combined web W is transferred in the pick-up point PP from the first wire 11 with a pick-up unit 210 being situated within a pick-up fabric loop 200. The pick-up unit 210 forms a pick-up point PP with the first wire 11. The first wire 11 is directed to the return rotation after the pick-up point PP. The final web produced by such a former would thus be a five layer board web. The lowest point of the joining roll 24 is on the same level or on a lower level than the lowest point of the pick-up unit 210.

In other words, the forming section the further can comprise at least one additional wire loop 31, 41, 51 for forming at least one twin wire section Tl, T2 with the first wire loop 11 or with the second wire loop 21. It is also possible that the forming section further comprises at least one additional wire loop 31, 41, 51 for forming at least one twin wire section Tl , T2 with the first wire loop (11) and at least one additional wire loop 31, 41, 51 for forming at least one twin wire section Tl, T2 with the second wire loop 21.

The examples of the embodiments of the present invention presented above are not intended to limit the scope of the invention only to these embodiments. Several modifications can be made to the invention within the scope of the claims.

CLAIMS

1. A paper or board machine forming section comprising:

- a first wire loop (11) passing over a first breast roll (12) and forming a first single wire forming section (SI) in a first direction (Dl) after the first breast roll

(12),

- a first head box (100) for supplying a slice jet on the first wire loop (11) at the beginning of the first single wire forming section (SI) to form a first web (Wl),

- a first turning roll (13) within the first wire loop (11) for directing the first wire loop (11) into a downwards inclined slope after the first single wire forming section (SI),

- a second wire loop (21) passing over a second breast roll (22) and forming a second single wire forming section (S2) in a second direction (D2) after the second breast roll (22), said second direction (D2) being opposite to the first direction (Dl),

- a second head box (110) for supplying a slice jet on the second wire loop (21) at the beginning of the second single wire forming section (S2) to form a second web (W2),

- a second turning roll (23) within the second wire loop (21) for directing the second wire loop (21) into a downwards inclined slope after the second single wire forming section (S2),

- a joining roll (24) within the second wire loop (21) after the second turning roll (23) forming a joining point (Jl) to the first web (Wl) and to the second web (W2) between the first wire loop (11) and the second wire loop (21), said joining point (Jl) being below the horizontal level of the first single wire forming section

(SI),

- the first single wire forming section (SI) and the second single wire forming section (S2) being essentially on the same horizontal level, and further

- a pick-up unit (210) within a pick-up fabric loop (200) forming a pick-up point (PP) between the first wire loop (11) and the pick-up fabric loop (200),