Method and device for dewatering of a paper web by pressing

Abstract: Method and device in the manufacture of paper or board for dewatering of the paper web (W) that is being manufactured. The paper web (W) is transferred from the forming wire (10) onto the wire (80) in the drying section while constantly on support of a fabric that receives water, a transfer febric, or of any other, corresponding transfer surface (105') as a closed draw, at a particularly high speed, which is, as a rule, higher than about 25...30 m/s. Dewatering of the paper web (W) is carried out by means of two subsequent extended press nips (NP1, NP2), whose length (z) in the machine direction is larger than z > about 100 mm. After the first extended press nip (NP1), through which the web is passed between two fabrics (20, 30) the web is transferred by means of a suction roll (40) to a single upper fabric (40) passing through the second extended nip (NP2), which has a smooth faced counter roll (105) in a lower position.

Description: The invention concerns a method for dewatering of a paper or board web according to the preamble of claim 1, being based on "Zum Einsatz von Schuhpressen" bei Schuchpressen bei Schreib-und Druckpapieren", Wochenblatt für Papierfabrikation, N. 5, 1988, page 177, Fig 15. Further, the invention concerns a paper making machine according to the preamble of claim 7, being based on the above mentioned prior art document. One of the most important quality requirements of all paper and board qualities is uniformity of the structure both microscopically and macroscopically. The structure of paper, in particular of printing paper, must also be symmetric. The good printing properties required from printing paper mean good smoothness, evenness and certain absorption properties at both faces. The properties of paper, in particular the symmetry of density, are affected considerably by the operation of the press section in a paper machine, which has also a decisive significance for the evenness of the transverse profiles and longitudinal profiles of the paper. Increased running speeds of paper machines provide new problems, which are mostly related to the running quality of the machine. At present, running speeds of up to about 1400 m/min. are employed. At these speeds, so-called closed press sections, which comprise a compact combination of press rolls fitted around a smooth-faced centre roll, usually operate satisfactorily. As examples of such press sections should be mentioned the applicant's "Sym-Press II" and "Sym-Press O" press sections (" " = trade marks). One item that requires development is the centre roll in the compact press sections and the material of said roll, which has commonly been rock, which, however, being a natural material, has certain drawbacks. Dewatering by means of pressing is energy-economically preferable to dewatering by evaporation. This is why attempts should be made to remove a maximum proportion of water out of a paper web by pressing in order that the proportion of water that must be removed by evaporation could be made as low as possible. The increased running speeds of paper machines, however, provide new, so far unsolved problems expressly in the dewatering taking place by pressing, because the press impulse cannot be increased sufficiently by the means known in prior art, above all because, at high speeds, the nip times remain unduly short and, on the other hand, the peak pressure of compression cannot be increased beyond a certain limit without destruction of the structure of the web. When running speeds of paper machines are increased, the problems of running quality of paper machines are also manifested with increased emphasis, because a watery web of low strength cannot withstand an excessively high and sudden impulse of compression pressure or the dynamic forces produced by high speeds, but web breaks and other disturbance in operation are produced with resulting standstills. With a modern printing paper machine, the cost of a break standstill is at present about 40,000 FIM per hour. Further drawbacks of the prior-art press sections include the requirement of suction energy of the suction rolls commonly employed in them as well as the noise problems arising from the suction rolls. Also, the suction rolls with their perforated mantles, interior suction boxes, and other suction systems are components that are expensive and require repeated servicing. Further problems which are manifested with more emphasis at high speeds of paper machines and for which, at least not for all of them, satisfactory solutions have not yet been found, include the quality problems related to the requirements of evenness of the longitudinal and transverse property profiles of the paper web. The evenness of the web that is produced also affects the running quality of the whole paper machine, and it is also an important quality factor of finished paper, which is emphasized in respect of copying and printing papers when the requirements on the speeds of copying and printing machines and on the uniformity of the printing result are increased. The property profiles of the paper that is produced in the machine direction are also affected significantly by oscillations of the press section, the transverse variations of properties by the transverse profiles of the nip pressures in the press nips, and with increasing running speeds of the machine these profile problems tend to be increased remarkably. Recently, running speeds even as high as about 40 m/s = 2400 m/min have been contemplated as running speeds of paper machines. The realization of such high speeds, in particular in wide machines, creates ever more serious problems to be solved, of which problems some of the most important ones are the running quality of the machine and adequate dewatering capacity at high speeds. In respect of the prior art most closely related to the invention, reference is made to the US Patents Nos. 4,483,745 (Beloit Corp.), 4,526,655 (Valmet Oy), 4,561,939 (Beloit Corp.) as well as to the published patent applications WO-85/00841 (J. M. Voith GmbH), DE-OS-3742848 (Sulzer-Escher Wyss GmbH), and to the FI Patent Applications 842114 (Valmet Oy), 842115 (Valmet Oy), and 850665 (Valmet Oy). Thus, the object of the present invention is to provide novel solutions for the problems discussed above so that the above drawbacks in prior art and the drawbacks that will come out later are substantially avoided. An object of the invention is to provide a method for dewatering of a paper web by pressing at high speeds, in particular at speeds of about 25...40 m/s, so that the adjustability of the press section is versatile, the properties of quality of the web produced can be kept high, and the web is not subjected to excessive dynamic forces that produce breaks. Further, by means of the invention, one of the aims is that the overall construction of the press section, in particular its frame construction, should be such that the replacement of press rolls and press fabrics can be accomplished quickly so as to minimize the standstill times. In view of achieving the objectives stated above and those that will come out later, the method of the invention is characterized by the features of the characterizing part of claim 1. On the other hand, the paper making machine of the invention is characterized by the features of the characterizing part of claim 7. In the present invention, it has been successfully possible to combine certain component solutions in a novel and inventive way, some of which solutions are in themselves known in paper machine technology, so that the problems discussed above, which are of different natures, have been brought under control and been solved by means of a novel overall concept. The most important objective achieved by means of the invention is a satisfactory running quality of the paper machine even at speeds as high as about 30...40 m/s. This has been achieved because of a "linear" draw of the web and of a nip arrangement that provides sufficiently long nip times. The method and the press section in accordance with the invention are intended for use above all with thin paper qualities, whose grammage is lower than 120 g/m 2 and with which a closed draw of the web is indispensable at the high web speeds meant in the invention. The invention also achieves a sufficiently cautious and gentle start of the dewatering, which is important because at high speeds the water contents in the web after the former also tend to be higher. According to the invention, the extended-nip presses are accomplished by means of hose rolls or band rolls and provided with a number of different possibilities of setting or active regulation, whereby it is possible to control the profiles of properties of the web both in the machine direction and in the transverse direction. In the most advantageous embodiment of the invention, a new extended-nip press, which has been developed by the applicant and is marketed by the applicant under the trade mark "Sym-Belt Press" and which is based on the use of a so-called hose roll, is utilized in a novel way. When fitted in its environment in accordance with the invention, said "Sym-Belt Press" provides several advantages of synergism, of which should be mentioned that said press produces practically no oscillations at all, for which reason it is well suitable also for very high speeds, said press permits keeping of the nip loads at a sufficiently low level in particular in the initial part of the press section and makes it possible to keep the nip times at a reasonable level even at very high speeds (30...40 m/s). Further, said "Sym-Belt Press" provides entirely novel possibilities to control and to regulate the distribution of the nip pressures in the extended-nip zone both in the machine direction and in the transverse direction. Further advantages include low power consumption, elimination of difficulties of oil treatment, reduced wear of the mantle of the hose roll, and reasonable dry solids content of the web even at high speeds (30...40 m/s). In respect of the details of the constructions of said hose rolls, reference is made to the US Patent No. 4,584,059 as well as to the applicant's FI Patent No. 66,932 and FI Patent Applications Nos. 892517 and 892518. One possibility to accomplish the extended-nip zone employed in the invention is the press solution described in the applicant's FI Pat. Appl. No. 891380, in which the press band loop is relatively short and has a run guided by a press shoe and a leading roll or an equivalent guide member, and in which solution the ends of the band have been sealed in a novel way. Thus, there is no risk of oil splashes, and the distributions of the nip pressures both in the machine direction and in the transverse direction are adjustable. In the following, the invention will be described in detail with reference to a number of different embodiments of the invention illustrated in the figures in the accompanying drawing, the invention being not strictly confined to the details of said embodiments. Figure 1 shows a version of the invention provided with two subsequent "Sym-Belt Presses" (" " = applicant's trade mark), of which extended nips one press fabric is employed in the latter nip. Figure 2 is an axonometric, partly sectional view of a hose roll of a "Sym-Belt Press" applicable in the invention. Figure 3 is an axonometric view of a press shoe that can be loaded and profiled in a versatile way and that is fitted inside the hose roll and employed in a press as shown in Fig. 10. Figure 4 shows an alternative construction that accomplishes an extended nip and that is provided with a closed glide belt loop. To begin with, the features of construction of the press geometries as shown in Fig. 1 will be described. As is shown in Fig. 1, with a closed draw of the web in a paper or board machine, the press section comprises a first upper fabric 20 that receives water, onto which fabric the web W is transferred on the suction zone 21a of the pick-up roll 21 at the pick-up point P from the forming wire 10, whose return run starts from the wire drive roll 12. According to Fig. 1, the press has two subsequent press nips, which remove water from the web W efficiently and between which the web W has a fully closed draw so that it is constantly supported by a fabric. In Fig. 1, both nips NP 1 and NP 2 are so-called extended nips, whose press zone is substantially longer than that in a normal sharp roll nip. The more detailed embodiments of the extended nips will be returned to later, mainly in connection with the descriptions related to Figs. 2, 3 and 4. In Fig. 1, the first upper fabric is guided by alignment, tensioning and guide rolls 22 and conditioned by conditioning devices 23. The first extended nip NP 1 includes a lower fabric 30 that receives water, being guided by alignment, tensioning and guide rolls 32 and conditioned by conditioning devices 33. The first extended nip NP, and so also the second extended nip NP 2 are accomplished in a "Sym-Belt Press" of the applicant, and the details of the construction of said press will be discussed later. In respect of its main features, the construction of the press is such that the extended nip NP 1 is composed of a flexible hose mantle and of a backup roll. Inside the hose mantle, there is a hydrostatically and/or hydrodynamically lubricated glide shoe 210, the hydraulic loading means fitted in connection with said shoe pressing the shoe 210 against the hollow-faced backup roll 35,55. The backup roll 35,55 is a hollow-faced press roll, for example the applicant's adjustable-crown "Sym-Z Roll" (" " = trade mark). According to Fig. 1, the press section includes a second upper fabric 40, onto which the web is transferred as a closed draw by means of the suction zone 41a of the suction roll 41. After the first nip NP 1 , it is ensured that the web W follows the first lower fabric 30 by means of a suction box 36 or a corresponding foil arrangement. The second upper fabric 40 is guided by alignment, tensioning and guide rolls 42 and conditioned by conditioning devices 43. According to Fig. 1, the second extended nip NP 2 is also formed in connection with a hose roll 45, which is similar to the hose roll at the extended nip NP 1 . The lower press member at the nip NP 2 is a smooth-faced 105' press roll 105, in connection with whose lower sector a doctor 107 operates, which doctors the web W o going to broke handling and the leader band to the broke handling arrangement placed below (not shown). The smooth face 105' of the press roll 105 makes sure that, after the extended nip NP 2 , the web W follows the face 105' of the lower roll 105, from which it is detached by means of a transfer nip N 5 and is transferred on support of the drying wire 80, which is guided by the guide roll 81, to the drying section, of which the first heated drying cylinders 82 and leading cylinders 83 are shown in the figures. Single-wire draw is employed at least in the first cylinder group in the drying section. From Fig. 1, it can be concluded directly that the run of the web W to be pressed through the press section is highly linear without major curves. Owing to the linear path of the web, the dynamic forces applied to the web remain sufficiently low in view of minimizing the risk of breaks. In preferred embodiments, the magnitude of the angle a of change in the direction of the web W is in the range of a ≈ 10...30° and, as a rule, a < 15°. An exception from this may be formed by the pick-up roll 21 and its suction zone, at which locally even a high negative pressure may be employed, as well as, in Fig. 1, by the smooth-faced 105' lower press roll 105 and its turning sector b. Out of the reasons stated above, a press geometry as shown in Fig. 1 is not preferable when the maximum speed range (30...40 m/s) of the applications of the invention is employed. In the press construction described above, the closed draw is accomplished so that it has been possible to minimize the dynamic forces applied to the web W and the risks of break. Thus, the running quality is satisfactory even at high speeds (30...40 m/s). Moreover, when extended nips NP 1 and NP 2 accomplished by means of hose rolls 200;300 have been employed in a press section in accordance with the invention, it has been possible to ensure a sufficient dewatering capacity and dry solids content even at high speeds without applying compression stages of excessively high peak pressures to the web W. It is a further important property of the extended-nip presses employed in the invention that in them practically no oscillations arise. It is a further important feature of the invention that the length z of the extended-nip zones NP 1 and NP 2 (z is, as a rule, in the range of z = 100...300 mm) in the machine direction is sufficiently large so that sufficiently long nip times are produced at said high speeds (25...40 m/s) as well as a sufficient compression impulse even though the peak pressure of the compression is kept reasonable and such that even a web with a very high water content (for example, k o ≈ 10 %) can be pressed without deterioration of the structure of the web. Said length z of the extended-nip zones NP 1 and NP 2 in the machine direction is in the invention, as a rule, always z > 100...300 mm, preferably z = 200 mm. In such a case, in the extended nips NP 1 and NP 2 , it is possible to use maximal compression pressures, which are of the order of p = 3...9 MPa, preferably in the range of p = 5...8 MPa. As comes out above from Fig. 1, the passage of the paper web W through the entire press section is highly "linear" and substantially horizontal. In the following, with reference to Figs. 2, 3 and 4, the hose rolls 200 and 300 employed in the embodiments of the extended nips NP used in the press section in accordance with the invention will be described. According to Fig. 2, the hose roll 200 comprises an elastic mantle 201, which is made, e.g., of fabric-reinforced polyurethane, so that the hose mantle 201 is made of rubber-like stretching material, whose maximum elongation is, e.g., about 20...40 %. The thickness of the hose mantle 201 is, e.g., about 2...5 mm. To the hose mantle 201, annular ends 202a and 202b are fixed permanently, the inner parts of said ends being fixed and sealed against revolving axle journals 207a and 207b, which are mounted on the frame parts 110 of the machine by means of fixed bearing supports. The hose roll 200 includes a stationary inner frame 205, around which the hose mantle 201 with its ends 202a,202b revolves on the bearings 206a and 206b. As is shown in Fig. 3, cylinder block sets 203, two sets side by side, are fitted in the inner frame 205. In the bores placed in the sets of cylinder blocks 203, hydraulic support members 206,207 of the glide shoe 210 operate, which members are, thus, placed in two rows, e.g., with a spacing of about 25 cm in the transverse direction one after the other. The two rows of the hydraulic support members 206,207 support a support plate 209, to which a glide shoe 210, e.g., of aluminium is attached, in whose area an extended nip zone NP is formed against a backup roll. The glide shoe 210 is provided with a smooth glide face 211, which operates as a press member against the smooth inner face of the hose mantle 201. The glide shoe 210 has a series of hydrostatic chambers 212 placed one after the other, which chambers contribute to the formation of a hydrostatic loading pressure and to oil lubrication of the glide face 211. Each of the subsequent cylinder blocks 203 communicates with a pipe connector 214, to which pipes 213 of loading medium pass so that a separately adjustable pressure can be passed into each individual block in the series of cylinder blocks 203. In this way, the pressure profile in an extended-nip zone NP can be regulated and controlled precisely and in a versatile way both in the machine direction and in the transverse direction. The pressure ratio p 2 /p 1 of the two different rows of support members 206,207 is, as a rule, chosen invariably as p 2 /p 1 = 1.5...2, whereas the pressure passed into each block is freely adjustable within certain limits. An example of the distribution of the nip pressure in an extended-nip zone NP is such a distribution in the machine direction in which the nip pressure (the pressure applied to the web W) at the front edge of the shoe 210 rises, owing to the hydrodynamically generated pressure, to about 40 bars, whereupon the pressure remains at this value as invariable, and in the trailing area of the shoe there is still an increase in the pressure, while the peak pressure is about 70 bars, from which value the pressure goes abruptly to zero at the trailing edge of the shoe 210. As was stated, said distribution of pressure can be varied so as to obtain an optimal pressing result. In any case, the compression pressure at the hose roll 200 and the distribution of said pressure in the machine direction can be arranged such that the start of the dewatering, while the dry solids content of the web W is still relatively low, can be carried out so gently that the fibre structure of the web W is not deteriorated. In Fig. 2, a regulation system related to the invention is sketched, by whose means the pressure profiles of the extended nip NP in the transverse direction and in the machine direction can be controlled. The regulation system is illustrated by the block 250, from which a series of regulation signals c 1 is given which regulate the hydraulic pressures fed through the pipes 213. To the regulation system 250, a feedback signal is received from separate wirings 214, which is illustrated by the series of signals c 2 . Further, the system 250 communicates with a measurement arrangement 260, by whose means the different profiles of the paper web W produced, such as moisture or thickness profiles, are measured, and this provides a series of feedback signals c, for the regulation system 250, which produces the series of regulation signals c 1 . The hose roll 200 is oil-tight, and the interior of the hose 201 can be arranged as slightly pressurized. From the glide faces 211 of the glide shoes 210, a slight leakage of oil takes place, which oil is collected from inside the hose mantle 201 and passed through the pipe 215 back to the oil circulation. The hose roll 200 shown in Figs. 2 and 3 is preferably mounted on fixed bearing supports, in which case the extended nip NP must be opened by means of a movement of the backup roll. This is necessary, because a play of, e.g., about 40 mm for movement of the glide shoes 210 of the hose roll is not sufficient for opening the nip NP sufficiently, e.g., for replacement of the fabrics. Fig. 4 shows a second embodiment of a hose roll 300. Therein a band 301 loop, is used that is longer than the circular hose mantle 201. Said band 301 is guided from inside and the extended nip NP is loaded by a hydrostatically and hydrodynamically loaded glide shoe 310, which is fitted inside the band 301 loop and which has a hydrostatically loadable series of pressure fluid chambers 312 in the area of the extended nip NP. Inside the band loop 301, a beam 305 is fitted, which is provided with a series of hydraulic loading members 306 and 307, by whose means the glide shoe 310 can be loaded in a controlled way. The band loop 301 is guided by a leading roll 311, in whose connection a spreader roll 312 is operative. Both ends of the band loop 301 are closed by means of end pieces so as to prevent oil leakages and splashes, of which end pieces one piece 312a is shown in Fig. 4. The more detailed embodiment of the band roll shown in Fig. 4 comes out, e.g., from the applicant's FI Pat. Appl. No. 891380 (corresp. US Pat. Appl. 486,754). The backup roll used in an extended nip NP as shown in Fig. 4 is an adjustable-crown roll 160, e.g. an adjustable-crown roll marketed by the applicant under the trade mark "Sym-Z Roll", which forms an extended nip NP by means of its sector C with the band roll 300. A corresponding roll can be used together with the hose roll 200. The roll 160 has a cylinder mantle 161, against whose smooth inner face 162 a series of glide shoes 165 operates, which is provided with hydraulic lubrication and loading chambers 166. The series of shoes 165 is loaded by means of a series of hydraulic actuators 164. If the backup roll 160 is employed together with the fabric 60 as a member that receives water, the outer face of the mantle 160 is provided with a hollow face. On the other hand, if the principal purpose of the roll 160 is to heat the web 60, e.g., by means of induction heating devices 170, a smooth mantle face is employed on the roll. According to Fig. 4, in connection with the mantle 161 of the roll 160, a heating device is provided, e.g. an inductive heating device 170, by whose means the temperature profile of the roll mantle, and thereby the profile and the dewatering capacity of the extended nip, can be affected. The roll 160 can also be used so that it has a smooth outer face and that by its means the web W is pressed directly, in which case there is no fabric 60 in between, and in this way the web W can be heated directly, thereby affecting the viscosity of the water present in the web and the elastic properties of the web W, thus promoting the dewatering and the transverse profile of the dry solids content. The dry solids content k out of the web as it departs from the press section in accordance with the invention is, as a rule, in the range k out = 35...65, preferably in the range k out = 40...55.

Claims: Method for dewatering a paper or board web by pressing in a paper machine, in which the web (W) is passed from a former section to a press section and subsequently into a drying section, the paper web having been drained in the former section, wherein the dewatering is effected by passing the paper web on water receiving fabrics through the press section having two subsequent dewatering extended press nips (NP1, NP2) formed by a hose roll or a band roll and a counter roll, and wherein the web has a closed draw constantly supported by a water receiving fabric from the pick-up point (P) of the forming wire (10) to the second extended press nip (NP2), the method comprising the following steps: a) transferring the web from the pick-up point (P) on the forming wire (10) onto the lower face of a first upper water receiving fabric (20); b) passing the web between the first upper fabric (20) and a fast lower water receiving fabric (30) through the first extended press nip (NP1); c) causing the web to follow the first lower fabric (30) after the first extended press nip (NP1); d) transferring the web from the first lower fabric (30) to a second upper water receiving fabric (40); e) passing the web together with the second upper fabric (40) through the second extended press nip (NP2); e1) the second extended press nip (NP2) being formed between the hose or band roll in a top position and a smooth-faced cylindrical counter roll (105) in a lower position: e2) the web being in direct contact with the smooth-faced cylindrical counter roll (105) during the passage through the second extended nip (NP2); and f) passing the web along part of the circumference of the cylindrical counter roll (105) after the second extended nip press (NP2), characterised in that A) the paper web is transferred from the smooth-faced cylindrical counter roll (105) of the second extended press nip (NP2) to the drying wire (80) by means of a transfer nip formed between the counter roll and a guide roll (81) around which the drying wire is arranged to pass ; B) the length of each of the two subsequent extended nips (NP1, NP2) is more than about 1 00 mm; C) the web is passed through the press section at a speed higher than about 25 m/s; D) the transfer of the web from the first lower fabric (30) to the second upper fabric (40) is effected by means of a suction roll (41) located between the first and second extended press nips; E) the distribution of compression pressure in at least one of the extended press nips is regulated and/or selected both in the transverse direction of the web and in the machine direction of the web for setting or controlling the different profiles of the properties of the web. Method as claimed in claim 1, characterized in that said suction roll (41) is wrapped by said second upper fabric (40). Method as claimed in any of the claims 1-2, characterized in that the maximum compression pressure (P) used in the extended-nip zones (NP1, NP2) is adjusted to the range 3-9 MPa, preferably 5-8 MPa, and that the distribution of pressure is fitted preferably such that in the initial part of the extended press nips the compression pressure is increased steeply, whereupon the compression pressure is kept substantially invariable, and in the rear end of the extended press nips the compression pressure is regulated such that it is higher than said area of invariable compression pressure. Method as claimed in any of the claims 1-3, characterized in that the dewatering pressing of the web (W) is started when the dry solids contend ko of the web (W) is = 10%, and water is removed out of the web so that after the press section its dry solids contend is kout = 35-65%, preferably kout = 40-55%. Method as claimed in any of the claims 1-4, characterized by applying a doctor device (107) to the smooth faced cylindrical counter roll (105). Method as claimed in any of the claims 1-5, characterized by conditioning the first fabrics (20,30) and the second fabric (40) with conditioning devices. Paper making machine in which a paper or board web (W) to be dewatered by pressing is passed from a former section to a press section and further into a drying section, which press section comprises two subsequent extended press nips (NP1, NP2) and water receiving press fabrics (20, 30, 40) passing through said extended press nips, wherein the water receiving fabrics are fitted in such a way that the paper web to be dewatered has a closed draw constantly supported by a water receiving press fabric from the pick-up point (P) on the forming wire (10) to the second extended press nip (NP2), the machine comprising: a) a first looped upper water receiving press fabric (20) arranged to pass through the first extended nip (NP1); b) a first lower water receiving press fabric (30) arranged to pass through the first extended press nip; c) said first extended nip press (NP1) being formed between a hose or band roll (25) and an opposite counter roll (35); d) a first suction pick-up roll (21) within the loop of the first upper press fabric (20) for transferring the web from the forming wire to the first upper press fabric (20); e) a second upper looped water receiving press fabric (40) arranged to pass through the second extended press nip (NP2); f) the second extended press nip (NP2) being formed between a smooth-faced cylindrical counter roll (105) in a lower position and a hose or band roll in a top position, the paper web being in direct contact with the smooth-faced counter roll (105) in the second extended press nip and following the face of the counter roll after the second extended press nip, characterised in that : A) the paper web (W) is transferred from the smooth-faced cylindrical counter roll (105) of the second extended to press nip (NP2) the drying wire (80) by means of a transfer nip (S) formed between the counter roll and a guide roll (81) around which the drying wire is arranged to pass; B) the length of the two extended press nips (NP1, NP2) is more than about 100 mm; C) a second suction pick-up roll (41) is provided between the first and the second extended press nips to transfer the web from the first lower press fabric (30) to the second upper press fabric (40); and D) a doctor (107) is arranged at the smooth-faced cylindrical counter roll of the second extended press nip (NP2). Paper making machine as claimed in claim 7, characterized in that said second suction pick-up roll (41) is placed within the loop of the second upper fabric (30). Paper making machine as claimed in any of the claims 7-8, characterized in that the first extended press nip (NP1) is formed between a cylindrical hollow faced press roll (35) in a lower position and the hose roll or band roll (201) in an upper position. Paper making machine as claimed in any of the claims 7-9, characterized in that the doctor (107) is arranged for passing the web to broke handling. Paper making machine as claimed in any of the claims 7-10, characterized in that at least one of the band or hose rolls (200,300) comprises a flexible band loop (301) with closed ends. Paper making machine as claimed in any of the claims 7-11, characterized in that at least one of the band or hose rolls (200,300) is a hose roll with closed ends. Paper making as claimd in any of the claims 7-12, characterized by conditioning devices (23;33;43) for conditioning the first fabrics (20,30) and second fabric (40).

Inventors: HIRSIMAEKI MARTTI, KARVINEN MIKKO, KIVIMAA JUHA, LAAPOTTI JORMA, PAJULA JUHANI, TASKINEN PEKKA, HIRSIMAEKI, MARTTI, KARVINEN, MIKKO, KIVIMAA, JUHA, LAAPOTTI, JORMA, PAJULA, JUHANI, TASKINEN, PEKKA, Hirsimäki, Martti
Applicants: METSO PAPER INC, METSO PAPER, INC.
Application year: 1991
Main classification: D21F3
IPC codes: D21F3