FI84637B - FOERFARANDE OCH ANORDNING VID FORMNING AV PAPPERS- ELLER KARTONGBANA. - Google Patents

Description

84637

Method and apparatus for forming a paper or paperboard web Förfarande och anordning vid formning av pappers-eller kartongbana 5

The present invention relates to a method for forming a paper or paperboard web from a fibrous material, which method is applied in a wire section of a paper machine or the like formed at least initially at the initial end by a substantially horizontal a first 15 single-wire dewatering zones in which the fibrous layer formed after the initial dewatering through the lower wire is passed over a lower wire support system as a direct extension of the single-wire zone, in which gravity dewatering through the lower wire fiber layer so that the dewatering of the fibrous layer continues in the region of the second dewatering zone, after which the upper wire loop is detached from the formed fibrous web, which. . is directed forward to monitor the flow of the lower wire loop for the next 25 processing steps of the web.

The invention further relates to a web-forming apparatus for carrying out the method of the invention, comprising a substantially horizontal downstream wire loop and an interoperable upper wire unit having an upper wire loop, and a headbox provided with between the common runs of the lower wire and the upper wire and in which the two-wire forming zone has within the lower wire loop and the upper wire loop various organs and organ groups affecting dewatering.

2 84637 1 In the oldest methods of forming a paper or board web, webing takes place horizontally in the so-called with a fourdrinier section, where water is removed from the fiber suspension along the entire length of the wire section in only one direction downwards. In this case, the upper and lower surfaces of the produced paper differ from each other in such properties that the upper surface of the paper is smoother than the lower surface, which has a more or less clearly visible pattern caused by the forming wire, i.e. the so-called viiramarkkeeraus. The top and bottom surfaces of the paper also differ in fiber composition in that the top surface of the web contains significantly more fine and short fibers and fillers than the bottom surface from which this paper fines have been significantly washed away during the unidirectional dewatering process and as a result. for use in printing, it is important that both surfaces of the paper are as similar as possible. The difference in paper surfaces is called 15 one-sidedness.

Types of paper machines are already known which can reduce the one-sidedness of the paper. Two main groups can be distinguished from these, namely the actual double wire formers and the so-called hybrid formers. In the actual twin wire formers, the web formation from start to finish takes place between the two wires. In hybrid formers, the web is initially formed on one wire, after which this partially formed web is passed between the two wires for final solidification of the mutual position of the fibers.

25 The advantage of hybrid formers is e.g. the fact that they can be obtained with relatively simple modifications from the existing fourdrinier wire sections by placing the upper wire loop on the middle or the rest of the upper run of the lower wire in cooperation with it. In addition to improving the quality of the paper to be produced, the removal of water from the wire section can be made more efficient and thereby increase the speed of the paper machine. One hybrid former is disclosed in the applicant's FI application 820742, which is intended mainly for the production of newsprint and similar printing paper types with a working speed of the order of 900 m / min and above.

35 Known hybrid formers are generally not suitable for the production of thick grades of paper and board because at the beginning of the two-wire section following the first single-wire dewatering zone, the passage of the wires and the partially web-formed fibrous layer between them is immediately the so-called. over the surface of the forming shoe. The curvature causes an internal cut in the web, which is larger the thicker the web. In this case, the fibrous layer is subjected to a considerably high dewatering pressure between the wires, which is directly proportional to the tension of the outer wire and inversely proportional to the radius of curvature of the guide surface in question.

10

Due to space issues and other structural factors, in known hybrid formers, e.g., disclosed in FI patent 75375 (cf. U.S. Pat. No. 4,614,566), the radius of curvature of the wire reversal member is so small that it is relatively sudden to the forming effect of the forming web. at this stage is far too large in the case of thick paper and board produced in that former. Excessive compression then causes damage to the fibrous layers and impairs the properties of the finished product, especially its strength, but also, for example, pressure. In the worst case, excessive compression will result in a web of so-called "curating" and causing production interruptions.

With regard to the state of the art related to the present invention, reference is further made to U.S. Patent 4,769,111 to A. Ahlström Corporation and Applicant's FI Patent Application Nos. 885609 and Valmet-Ahlström Inc. FI Patent Applications Nos. 885606 and 885607 filed with this application.

The main object of the present invention is to provide a multi-species hybrid former which can cover a wide basis weight and speed range, so that papers and paperboards can be produced with the same former in a wide basis weight range as high as 30 g / m to 500 g / m and a speed range of 100 m / min - 1200 m / min.

One starting point for the present invention has been the applicant's 35 "Sym-Former R" (TM) former (cited above in Pat. 75375), which has proven to work best in practice at relatively low basis weights and high speeds. It is therefore an object of the present invention to further develop the applicant's "Sym-Former R" former so that its scope can be extended to thick paper grades and paperboards so that even lower speeds are possible.

5 When the above-mentioned "Sym-Former" type formers have been used to achieve relatively high basis weights, it has been found that the quality of the paper suffers in particular from its formation and smoothness. The object of the present invention is to avoid this disadvantage as well and to guarantee good quality factors for the paper and board to be produced over a wide range of speed and basis weight, above all the formation and symmetry of the paper.

It is also an object of the present invention to provide such a former, some embodiments of which are particularly well suited for the rebuilding of old flat wire parts.

15

It is a further object of the present invention to provide a method and a former in which microturbulence to improve formation and smoothness can be applied to a web in a suitable dewatering step.

The object of the present invention is to provide a multi-species former in which, at least at the beginning of the web formation, excessive dewatering pressures due to web tightening can be avoided, which are used only in the final stage of web formation when the web has reached a sufficient degree of felting.

25

A further non-essential object of the invention is to provide a multi-purpose method and a web forming section in which the two-wire dewatering zone does not fall below the level of the lower wire, which has the advantage both in terms of web formation and in that the frame structures of the previous flat wire section can be used.

It is a non-essential additional object of the present invention to provide a method and a multispecific web in which, if necessary, a secondary headbox can be used to feed a second or 35 grades of pulp onto an emerging fibrous layer.

In order to achieve the above and later objects, the method according to the invention is mainly characterized in that the web-forming method is selected according to the basis weight of the quality to be produced, so that a support system and a suction and foil apparatus opposite it within the upper wire loop, in which initial dewatering is initially carried out mainly through the upper wire, and in another alternative web-forming method for producing thinner web grades, said suction and foil equipment is followed by a two-wire dewatering cycle that takes place in the upper wire loop si in a zone of curvature directed upwardly in a relatively short sector guided by the forming roll or the like, after which the double-wire forming zone is guided to curve downwards under a relatively large radius of curvature guided by the forming shoe 20 or the like, and that the web is guided to follow the second

The device according to the invention, in turn, is mainly characterized in that the two-wire second dewatering zone is substantially and relatively long initially planar and as a direct immediate extension to the single-wire beginning, after which the two-wire zone is guided and then a forming shoe is arranged inside the lower wire loop, the guide surface with a relatively large radius of curvature preferably provided with a strip cover guiding the two-wire zone to curve downwards, and that a suction and foil apparatus is arranged inside the upper wire loop. - from the lower position to the upper position with the former adjusted for thinner, usually 2 ralnal in the range of 30 to 120 g / m for the manufacture of grades.

6 84637 1 The former of the invention is used at high speeds and in small 2 basis weight ranges (generally less than 120 g / m 2) as a Sym-Former type hybrid former with the suction and foil unit of the upper wire unit raised to the upper position. In this case, you usually operate in the speed range 800-1200 m / min.

5

When it becomes necessary to produce thicker grades of paper or paperboard on the same paper machine, e.g. in the basis weight range of 100-500 g / m and even more so, using slower speeds, the former according to the invention is adjusted! to operate so that the suction and foil unit 10 of the upper wire unit is pivoted onto a self-adjusting planar support beam inside the lower wire unit, whereby dewatering can be blocked. After most of the water has been removed, the final dewatering is performed using a "Sym-Formern-type two-wire suitably curved two-wire section arranged so that the relatively thick partially felted web is not subjected to too sharp and long changes of direction and shear forces.

In the invention, it is necessary to direct the dewatering through the upper wire loop after the single-wire initial dewatering zone, and in this case it is possible to utilize, for example, This dewatering device further comprises at least one multi-foil water collecting trough connected to the suction source.

30 In addition to this dewatering device inside the upper wire loop, there are a series of wire support beams inside the lower wire loop, which are intended to reduce or substantially prevent dewatering through the lower wire and to apply upward the formation of the existing web is improved. These wire support beams 7 84637 1 are loaded against each lower wire loop, e.g. by means of compressed air hoses. The compression on the web is thus self-adjusting.

If necessary, a secondary headbox or boxes can also be used in the invention, with which a shower of either the same or different pulp quality is fed onto the forming web before the two-wire forming zone, which can control the overall web formation process and, if necessary, provide different layer structures, e.g.

10

The wire support beam used according to the invention, i.e. a wire table placed inside the lower wire loop as a direct and immediate extension of the single wire dewatering zone, provides web formation and smoothness microturbulence and in addition a self-adjusting gut area in the delicate stage of web formation, the pressures caused by the tension of the wires are applied, but the gap area between the wires is adjusted and shaped quite freely into the shape determined by the outgoing water.

20

In the following, the invention will be described in detail with reference to some application examples of the invention shown in the figures of the accompanying drawing, to the details of which the invention is in no way narrowly limited.

25

Figure 1 shows a first embodiment of the invention adjusted to a "Sym-Former" mode of operation, in which paper having a relatively low basis weight is produced at a high speed with a former.

Fig. 2 shows the same former as Fig. 1 adjusted to a mode of production which can produce high basis weight paper or board grades even at low speeds.

Figure 3 shows a modification of the invention adjusted to a high square-35 weight grade manufacturing mode.

Fig. 4 shows a third alternative embodiment of the invention using two foil and / or suction boxes in an upper wire unit.

Figure 5 shows an embodiment of the invention using 5 secondary headboxes and producing relatively thick cardboard grades.

Figure 6 shows in detail a vertical cross-section of a foil and suction box assembly according to the invention and of a wire support and sealing device inside the lower wire loop.

The web forming device schematically shown in Figs. and suction boxes 27 located between the forming shoe 26 and roll 35 (Fig. 3) and the drum roll 28 for running the down wire 20.

20

The web forming apparatus shown in Figs. 1-5 further includes an upper wire loop 10 which, under the guidance of the guide rollers 11, 11a and 11b, covers the lower wire loop in the region of the two-wire dewatering zone. Inside the upper wire loop 10, there is further a dewatering apparatus 40, which is shown in more detail in Figure 6. The apparatus 40 first comprises an autoslice-type dewatering cabinet, most preferably connected to a suction chamber. In addition, the dewatering device 40 comprises two or three water collecting trays, the bottom part of which opposite the upper wire 10 consists of foil strips.

30

The following describes the differences between the different formers shown in Figures 1-5.

Figures 1 and 2 show the same former in two different modes of operation, Figure 1 shows a "Sym-Former" mode of operation in which relatively 2 thin, generally about 30-120 g / m, grades of paper are produced at high speed. Figure 2 9 84637 1 shows the same boiler in an operating mode in which thicker grades 2 are produced, about 120-500 g / m, generally at a lower speed.

According to Figures 1 and 2, the two-wire forming zone has, after the forming roll 16 with the hollow surface 16 ', one forming shoe 26 with a strip cover 26' with a relatively large radius of curvature R, generally R = 5 ... 9 m. After the shoe 26 a number of flat boxes 27 follow. In Fig. 1, the two-wire zone is formed starting from the starting line of sector a of the roll 16 and ending at line B. In Fig. 2, the two-wire zone is formed from the line Aq at the guide roll 11a starting at the above-mentioned line B.

In Fig. 3, the forming shoe 26 of Figs. 1 and 2 has been replaced by a shorter forming shoe 26A and then by a subsequent forming roll 25, 15 which is preferably smooth and closed. The radius of the forming roll 25 is substantially smaller than the radius of curvature R of the strip cover 26A 'of the shoe 26A,

A

which is generally in the range Rf = 0.8 to 1.5 m. Otherwise, the structure is as shown in Figures 1 and 2 above.

The structure shown in Fig. 4 is similar to that shown in Figs. 1 and 2 except that a suction and foil apparatus 40A similar in structure and function to the previous watering apparatus 40 is arranged above the forming shoe 26, except that the foil contour delimiting the underside of the latter apparatus 40A -25 a curvature corresponding to the shape of the shoe cover 26 'of the shoe 26. After the forming shoe 26, a leveling box 27a follows inside the lower wool loop 20 and then a second forming roll 16a inside the upper wool loop 10, which is preferably smooth and closed.

The structure shown in Fig. 5 is similar to that shown in Figs. 1 and 2, except that Fig. 5 uses a secondary headbox 60 through which a pulp jet is fed through the lip cone 61 before the two-wire forming zone onto the single-layer flat surface portion 20a. The mass qualities of the primary jet J and the secondary jet 35 may be the same or different. In the latter case, e.g., layered board grades are produced.

10 84637 1 The web forming apparatus shown in Figs. 2-5 operates to produce thick grades 2 2 (120 g / m to 500 g / m) as follows. The headbox 19 feeds the pulp jet J to the horizontal initial portion 20a of the lower wire loop 20, i.e. to the first dewatering zone, in the area of which the dewatering only takes place downwards through the lower wire 20, carefully intensified by suitable dewatering means 23, e.g. foil boxes. The fibrous layer formed on the surface of the lower wire loop 20 continues to pass to the second dewatering zone formed when the upper wire loop 10 is guided near the lower wire loop 20 at a small angle d (Fig. 6), preferably 2-5 °. ).

In Figures 2-5, the second two-wire dewatering zone is divided into several sections. The dewatering apparatus 40 15 located inside the upper wire loop 10 and the wire support apparatus 30 inside the lower wire loop 20 cooperating therewith form the first section of the second dewatering zone. The first dewatering zone 20a and the relatively long first section relative to the second dewatering zone are in the same horizontal plane up to the forming roll 16 which turns the wires 10,20 20 upwards at a small angle equal to the size of the sector a where the common passage of the wires 10 and 20 bypasses the forming roll. 16. Sector a forms the second section of the two-wire dewatering zone. The compression pressure between the wires 10,20 (p = T / R) further removes water from the resulting web W, which is thrown into the water collecting trough 13 by the centrifugal force 25.

The upper wire 10 is detached by means of a guide roll 11b from a web W on the surface of the lower wire 20, which continues to travel to the roll 14. The suction boxes 27 are intended to ensure that the web W does not follow the wire 10 which returns to the roll 11a. A pick-up roll 14 with a suction zone 14a with a release felt 15 is placed near the driver roll 28, by means of which the web W is transferred from the wire part to the press part (not shown).

The former shown in Figure 1 is adjusted to a mode of production which produces thinner grades of paper, generally with a basis weight of about 30-120 g / m 2. In this case, the dewatering apparatus 30 acts as a direct and immediate extension of the single-wire initial portion 20a, and the micro-turbulence provided by the dewatering apparatus 11 84637 and its support beam grooves 35 (Fig. 6) completes the dewatering through the lower wire 20 and affects web formation.

The initial portion 20a of the substantially horizontal single-wire dewatering zone belonging to the lower wire unit of Figure 1 is followed by a two-wire section between lines A2-B, after which the web W follows the lower wire 20. The lower wire section is, for example, a previous, pre-modernized Four-drinier flat wire section 100 , to which a special upper wire unit 70 according to the invention is connected in connection with the modernization.

The single-wire initial section 20a has, for example, dewatering equipment for the former Fourdrinier flat wire section, such as foil strips 23 and / or suction boxes, and suction boxes 27 at the end of the double-wire section.

15

The upper wire unit 70 includes a body portion with horizontal and vertical beams 71,72 to which the various portions are attached. From the beginning of the two-wire section 10, the passage of the upper wire loop 10 is guided by an open forming roll 16 provided with a hollow surface 16 ', followed by a forming shoe 26 with an insole lid 26' having a radius R of curvature-20. The two-wire dewatering zone ends in the area of the last suction box 27.

According to Fig. 1, the upper wire unit 70 includes a vertically pivotable body portion 75 secured to a horizontal beam 71 by transfer screws 17a and 17b or the like. The first guide roll 11a of the upper wire 10 is mounted on the body portion 75. In Fig. 1, the body portion 75 and the dewatering apparatus 40 'and the first guide roll 11a' resting thereon are shown in an upturned position, from which it can be returned to the position shown in Fig. 2 when the paper type to be manufactured cooperates.

At the initial portion 20a of the single-wire dewatering zone, dewatering takes place by water-firing members 23 between the lip gap of the headbox 19 and the apparatus 30, such as a chest and foil strips. With the single-wire initial portion 20a, the dewatering takes place downwards through the lower wire 10 to the extent that a sufficient proportion remains for the upward dewatering. After the line Aj, the common run of the wires 10 and 20 curves upwards i2 84637 ^ in a short sector a of magnitude a = 10 ° ... 35 °, preferably, _o Oco a “15 ... 25.

By grooving 35 (Fig. 6) in the beam of the wire support apparatus 30, a microturbulence is obtained which finishes and improves the formation of the web W before the start of the two-wire zone.

The short sector a is followed by a very short straight run of the wires 10 and 20, after which, in the area of the shoe 26, dewatering takes place upwards through the upper wire 10 due to the compression and centrifugal forces between the wires 10 and 20. The trailing edge of the forming shoe 26 is followed by a straight common run of the wires 10 and 20.

In the mode of operation according to Figure 1, the former according to the invention functions as a hybrid-type double wire former to produce thinner grades as described above, the details of the structure and operation of which refer to the applicant's above-mentioned FI patent 75375.

Fig. 6 shows the water-20 removal apparatus 40 belonging to the wire part according to Figs. 1-5 with its main structural details and the lower wire support member system cooperating therewith.

The dewatering apparatus 40 is formed by an integrated combination of generally two to four (three in the figures) suction and water collection chambers 46, 47, 48, with 25 different chambers separated by partitions 47b and 48b. Each chamber 46,47,48 has an air vent (not shown) and an outlet passage 49 connected to the suction source. A water collection passage 46a belonging to the first suction chamber 46 is formed between the body beam 46b of the dewatering apparatus 40 and the baffle 46c. At the lower end of the channel 46a there is a transverse foil scraper 51 and an adjustable mandrel 53 for forming a gap E extending over the width of the former, through which water compressed from the fibrous layer between the wires 10 and 20 flows into the first chamber 46.

The foil scraper 51 of the apparatus 40 of Figure 6 is followed in the same plane by a plurality of similar foils 51 'and 51 ". The foils 51' collect, at but below the first suction chamber 46, water diverging from the fiber i3 84637 ^ through the channel 47a. between the partition wall 47b and the baffle plate 47c. Accordingly, the water collected by the subsequent foils 51 "is directed to the third suction chamber 48 through a passage 48a formed between the rear wall 48d of the dewatering device and the baffle plate 5c.

The channel 46a of Figure 6 and the associated foil scraper 51 and control strip 52 form a suction-assisted dewatering member. When thick and thick board species are produced at low speeds with a former, the operation of the autoslice-10 system is best assisted by suction, with a vacuum of 6-8 kPa being most suitable. At this stage, the amount of upward dewatering and, in part, the amount of vacuum generated can be influenced by adjusting the height of the gap E between the strip 52 and the foils 51.

The dewatering effect of the suction-assisted dewatering member of Fig. 6 and the associated first suction chamber 46 is local and is limited to the tip of the first foil scraper 51. The dewatering area of the second suction chamber 47 is wider and is determined by the number of foils 51 'shown in Fig. 6 as one example in the case of seven.

The effect of the foils 51 'is based on co-operation with the wire support apparatus 30 inside the lower wire loop 20. It is essential for the support apparatus 30 and its operation that it can provide a gradually increasing compression of the lower wire 20 against the forming web W in the desired manner in the area of the dewatering apparatus 40. The operation of the third suction chamber 48 is analogous to that of the second suction chamber 47.

The vacuum 30 in the second and third chambers 47, 48 of Figure 6 is preferably considerably higher than in the first, namely about 10-20 kPa in chamber 47 and about 15-30 kPa in chamber 48, depending on the web material to be produced.

In Fig. 4, the water collection system 40A is shown to comprise two successive air chambers 35, below which e.g. two strips can contact the wire 10. Said strips limit the suction channels of the apparatus 40A on the outlet side of their mouth in the direction of the wire 10.

i4 84637 1 With respect to Figure 4, it is a further feature of the invention that in some embodiments of the invention, especially those best suited for rebuilding flat wire portions, the forming zone does not extend to the lower T-T side of the single wire portion 20a. According to Fig. 4, after the forming roll 16a, the two-wire zone having the suction boxes 27 inside the lower wire 20 is returned to the level T-T determined by the single-wire initial portion 20a, which is preferably horizontal.

JO In the apparatus of Fig. 6, the dewatering process takes place by producing thick grades with the former of Figs. 2-5 as follows. In the first dewatering zone 20a of the former, the fibrous layer partially formed on the surface of the lower wire loop 20 enters the space between the wires 10 and 20, the friction angle d of which is determined by the position of the roller 11a adjustable by the device 18 guiding the wire 10. The surface of the fibrous web meets the strip 52 of the upper wire 10 before. At this point, the portion of the wire support apparatus 30 supporting the lower wire loop 20 also begins, as a result of which the dewatering of the fiber layer begins to take place mainly upwards.

The beam elements 31 of the apparatus 30 of Fig. 6 are supported by longitudinal support beams 33 via air-pressurized rubber hoses 32, which in turn are supported by transverse housing beams 34. The pressure in the hoses 32 can be adjusted so that the load against the down wire 20 and fiber gradually increases. The hoses 32 use a rather low pressure, e.g. 10-50 cm 1 ^ 0, whereby the web W in the formation stage is subjected to very careful compression and the dewatering pressure is self-adjusting. The surface of the elements of the apparatus 30 is provided with grooves 35 extending transversely over the entire width of the wire 20, which allow a slight removal of water 30 also through the lower wire 20 and which provide microturbulence which improves the formation of the web W.

In Fig. 6, the dewatering process continues in the area between the top line of the web W and the tip strip 52, where a water layer forms on the inner surface 35 of the top wire 10, which accumulates in the wedge-shaped space between the wire 10 and the tip strip 52 and the subsequent tip strip 52 and the foil strip. 46a to the first chamber 46 of the dewatering device, either by its kinetic energy and / or by the vacuum in the chamber. The strip 52 can be adjusted in the height direction by means of adjusting devices 53, whereby the amount of water and possibly also the air entering the duct 46a can be adjusted. These 5 adjustments, both in terms of the angle of intersection d between the wires 10 and 20 and the gap leading to the channel 46a and the pressure exerted by the support system, depend, of course, on the type of paper or board to be produced.

The suction-assisted system 10 based on the use of the control strip 52 shown in Fig. 6 can in some cases be replaced by a structure in which the control strip 52 is replaced by a roll whose rotational speed and height position, i.e. the distance from the wire 10, are arranged to be adjustable.

In the following, the claims are defined, within the scope of the inventive idea defined by them, the various details of the invention may vary and differ from those set forth above by way of example only.

20 25 30 35

Claims (12)

A method of forming a paper or paperboard web (W) from a fibrous material, the method being applied to a wire section of a paper machine or the like formed at least initially at the beginning by a substantially horizontal lower wire loop (20) and an upper wire loop (10) cooperating therewith (10); the incoming fiber suspension jet (J) is fed to the upper part (20a) upstream of the lower wire loop (20), which forms the first single-wire dewatering zone 10, where the fibrous layer (W) formed after the initial dewatering through the lower wire (20) is passed 20) over a support system (30) in the area of which gravity dewatering through the lower wire (20) is substantially prevented, after which the partially dried fibrous layer is led to a second dewatering zone in the area of which the upper wire loop (10) may be covered a partially dried fibrous layer so that dewatering of the fibrous layer continues in the region of the second dewatering zone, after which the upper wire loop (10) is detached from the formed fibrous web (W) directed forward to follow the lower wire loop (20) to the web 20 (W); is selected according to the basis weight of the quality to be produced, so that in the production of higher basis weight web grades after the single wire dewatering zone (20a) the web (W) is led to an initial period of 25 two wire dewatering zones determined by the above-mentioned support system (30) inside the lower wire loop (20) and above opposite suction and foil apparatus (40), in which initial dewatering is carried out mainly through the upper wire (10), and in another alternative web-forming method for producing thinner web grades, said suction and foil the apparatus (40) is disconnected from the connection of the underlying wire (20) (Fig. 1), and that the above-mentioned web-forming steps are followed by a two-wire dewatering cycle under the control of a forming roll (16) or the like arranged inside the upper wire loop (10). i7 84637 ^ in a relatively short sector (a) in a curved zone, after which the two-wire forming zone is guided to curve downwards under the guidance of a forming shoe (26) or the like with a relatively large radius of curvature (R) and that after the two-wire forming zone 5 the web (W) is guided to follow another, ). A method according to claim 1, characterized in that the zone following the single-wire initial dewatering zone (20a) upstream of the lower wire is planar 10 with a relatively long initial part and a direct immediate extension to the former lower wire initial run (20a), and that said initial part is wound on the web (W). 31) by means of a groove (35) or the like by means of microturbulence. Method according to Claim 1 or 2, characterized in that the suction and foil box assembly (40) inside the upper wire loop (10) is raised to the upper position (40 ') together with at least the front guide roll (11a) of the upper wire (10) when the forming part is adjusted. operate in the range of 2 lower basis weights, generally 30-120 g / m (Figure 1), so that the two-wire web-forming zone begins in the short sector (a) of the forming roll (16) with the hollow surface (16 ') inside the upper wire loop (10) and that thicker paper grades , generally in a weight range of about 120-500 g / m 2, said upper wire unit part (75) is turned to a lower position so that the wire support apparatus (30) inside the lower wire loop (20) and the upside down suction and foil assembly inside the upper wire loop 25 40) (Fig. 2) form the initial period of the two-wire dewatering zone, in which the dewatering is carried out mainly upstream. through said suction and foil equipment (40). Method according to Claims 1 to 3, characterized in that the forming wire (16) inside the upper wire loop curves the two-wire zone upwards in a short sector (a), the size of which sector is selected in the range α = 10 ° to 45 °, preferably in the range α 15 ° ... 25 °, after which the two-wire zone is curved 35 downwards by a radius of curvature by a stationary shoe member (26) having a radius of curvature (R) substantially larger than the radius of the above-mentioned forming roll (16). ie 84637 Method according to one of Claims 1 to 4, characterized in that after the zone (a) of the hollow-surface (16 *) forming roll (16) inside the upper wire loop, the two-wire zone is curved downwards by a relatively short forming shoe (26A) with a relatively large radius of curvature (RA). , followed by a steeper downwardly curved zone guided by a second forming roller (25) within the lower wire loop (20) and that the two-wire zone is then guided over one or more planar boxes (27) or the like inside the lower wire loop (20) (Figure 3). 10 Method according to one of Claims 1 to 5, characterized in that the method uses a water collecting device (40A) arranged against the forming shoe (26) 15 for dewatering through the upper wire (10) after the upwardly curving zone of the two-wire forming zone (16) (Fig. 4). ). Method according to one of Claims 1 to 6, characterized in that, when producing thicker web grades above the single-wire dewatering zone (20a) before the start of the double-wire forming zone, secondary pulp (J 1) is fed from the secondary headbox (60) (Fig. 5). A web forming apparatus for carrying out the method according to any one of claims 1 to 7, comprising a substantially horizontal lower wire loop (20) and an interoperable upper wire unit (70) having an upper wire loop (10) and a headbox (19) arranged to feed the fiber J) a single-wire initial portion (20a) of the upper run of the lower wire loop, followed by a two-wire forming zone bounded between the common runs of the lower wire (20) and the upper wire (10) and having a two-wire forming zone 10 organs and groups of organisms, characterized in that the two-wire second dewatering zone is planar in its substantial and relatively long initial part and as a direct immediate extension to the single-wire initial part (20a), after which the two-wire zone 35 is guided k convex upwardly guided by a short sector (a) of the forming roll (16) with a hollow surface (16 ') arranged inside the upper wire loop, and then a forming shoe (26) is arranged inside the lower wire loop (20), preferably with a strip cover (26') provided with a guide surface having a relatively large radius of curvature (R) guiding the two-wire zone to curve downwards, and that a suction and foil-5 apparatus (40) is arranged inside the upper end of the upper wire loop (10) for raising by thick actuators (17a, 17b) from the operating position used to the upper position (40 ') with the former adjusted to produce thinner web grades, generally in the range of 30 to 120 g / m 2 (Fig. 1). Device according to claim 8, characterized in that a wire table (30) is arranged for said straight initial section of the two-wire dewatering zone, comprising lower wire self-adjusting support beams (31) inside the lower wire loop (20), which are also adapted to act as dewatering barriers and that the wire At 15 tables (30), a suction and foil device (40) is arranged inside the upper wire loop. Device according to Claim 8 or 9, characterized in that the wire table inside the lower wire loop (20) has self-adjusting cross-beams (31) supported by load hoses (32) or the like, extending from two or three suction chambers of the opposite dewatering device and their upper wire ( 10) for the guiding foil fleet (51,51 ', 51 "). H. Device according to one of Claims 8 to 10, characterized in that the suction and foil device (40) inside the upper wire loop (10) has a box system with at least two, preferably three, successive loop chambers (46, 47, 48), which the foil strips (51, 51 ', 52') of the lower part are adapted to guide the two-wire dewatering zone 30 as a direct and immediate extension of the single-wire initial section (20a). Device according to one of Claims 8 to 11, characterized in that, before the suction and foil corrugation (40), there is a suction-assisted device, the upper inclined channel (46a) of which communicates with the first suction chamber (46). with a tip strip (52) adjustable relative to the upper wire (10). 20 84637