EP1075564B1

EP1075564B1 - Extended-nip press roll and a press section of a paper machine applying it

Info

Publication number: EP1075564B1
Application number: EP99906273A
Authority: EP
Inventors: Jorma Laapotti
Original assignee: Metso Paper Oy
Current assignee: Valmet Technologies Oy
Priority date: 1998-03-04
Filing date: 1999-02-25
Publication date: 2003-05-02
Anticipated expiration: 2019-02-25
Also published as: EP1075564A1; DE69907440D1; FI980491A; ATE239130T1; WO1999045195A1; FI980491A0; DE69907440T2; FI111860B

Abstract

The invention relates to an extended-nip press roll (10) for a paper machine, comprising a stationary central axle (15), a loading shoe (11), and hydraulic loading elements (12) situated between the stationary axle (15) and the loading shoe (11), by means of which elements an active frontal face (18) of the loading shoe (11) is pressed against an inner face fo a flexible hose mantle (16) of the extended-nip press roll (10) in order to produce a compression pressure in an extended-nip zone (EN; EN1;EN2) formed by said extended-nip press roll with its backup roll (20). The loading shoe (11) and its loading and oil-drain arrangements are substantially symmetrical in relation to the axial centre plane (K-K) of the extended-nip press roll (10) so that the direction of rotation of the hose mantle (16) may be either direction and as required by the position of the extended-nip press roll (10). In addition, press section geometries applying these extended-nip press rolls (10) are presented.

Description

The invention relates to an extended-nip press roll for a paper machine, comprising a stationary central axle, a loading shoe, and hydraulic loading elements situated between said stationary axle and said loading shoe, by means of which elements an active frontal face of the loading shoe is pressed against an inner face of a flexible hose mantle of the extended-nip press roll in order to produce a compression pressure in an extended-nip zone formed by said extended-nip press roll with its backup roll, the loading shoe and the loading arrangements of the loading shoe being substantially symmetrical in relation to the axial centre plane (K-K) of the extended nip press roll.

Moreover, the invention relates to a press section of a paper machine comprising at least two extended nips.

Extended-nip rolls, or hose rolls, of prior art are designed and constructed so that they have a given direction of rotation, and the prior-art rolls do not operate when rotating in an opposite direction, because the structure of the press shoe and the circulation and drain systems of oil do not allow a change in the direction of rotation. However, press sections applying extended-nip zones and extended-nip press rolls today employ two or even more extended-nip rolls, which are, in addition, arranged such that, in said extended-nip rolls, the direction of rotation of their hose mantle changes because an extended-nip roll is both in the upper and in the lower position in the same press section. This leads to the fact that extended-nip rolls must be especially designed so as to take the direction of rotation into consideration, which increases manufacturing and spare part costs. Moreover, said multi-nip extended-nip presses must have an extended-nip replacement roll of its own for both directions of rotation. This increases capital, storage and spare part costs considerably, since the typical price of an extended-nip hose roll is of the order of 5 to 15 million FIM.

With regard to prior-art structures of extended-nip rolls, i.e. hose rolls, reference is made to US-4 705 602 A and by way of examples to the following FI patent applications of the applicant: FI 830995, FI 892517, FI 892518, FI 925943 and FI 943041.

The principal object of the present invention is to eliminate the above-noted drawbacks and to provide a new extended-nip press roll and press section arrangements that apply them in a paper machine.

With a view to achieving the objectives stated above and those that will come out later, the extended-nip press roll in accordance with the invention is mainly defined by the characterizing features of claim 1.

The press section in accordance with the invention is in turn characterized in that in extended nips of the press section there are extended-nip press rolls in accordance with the invention in positions having directions of rotation which are different from one another, and which extended-nip press rolls form extended-nip zones with their backup rolls, through which zones a paper web is passed.

The structure of the extended-nip press roll in accordance with the invention is such that its direction of rotation can be changed without changing the internal structure of the roll. This is useful for the reason that, for instance, in a press section comprising two extended nips, the extended-nip rolls may be totally identical, although their positions and directions of rotation are opposite. In that case, a preassembled spare extended-nip roll is suitable for positions requiring opposite directions of rotation. Advantages are also achieved in design and manufacture of extended-nip rolls, since the direction of rotation of the roll may be either direction so that only one kind of extended-nip rolls and their spare rolls are needed.

The lubricating-oil drain system in the extended-nip press roll in accordance with the invention is such that lubricating oil drains from the roll with both directions of rotation when the press shoe is in an upper or in a lower position or even in an intermediate position. The structure of the press shoe is such that power consumption is minimized, in particular in a chamber area in a hydrostatic middle area of the front and rear ends of hydrodynamic shoes. The press shoe is shaped so that breaking of a glide belt mantle caused by a paper clod is minimized in the area of the hydrostatic chamber. When the direction of rotation of the extended-nip roll changes, the lubrication situation of the press shoe is ensured by a tilting system of the press shoe, by means of which the compression pressure at the front edge of the shoe can be regulated so as to be lower than the pressure at the rear edge.

The invention also encompasses press sections which apply extended-nip press rolls that are identical with one another in accordance with the invention and which comprise at least two extended-nip rolls in accordance with the invention, which extended-nip rolls are in positions having directions of rotation different from each other, and which extended-nip press rolls form extended-nip zones with their backup rolls. The backup roll may be, for example, a smooth-faced centre roll of the applicant's Sym-Press II™ press section or, alternatively, the press section comprises at least two separate successive extended-nip press zones, between which the web preferably has a closed draw which is provided by utilizing press fabrics and suction transfer rolls and/or special transfer fabrics in a manner known in itself.

In the following, the invention will be described in detail with reference to some embodiment examples of the invention shown in the figures of the accompanying drawing, the invention being by no means narrowly confined to the details of said embodiment examples.

Figure 1 shows an extended-nip press roll in accordance with the invention in its lower position forming an extended-nip zone with a backup roll situated in an upper position.

Figure 1A shows, in a manner corresponding to that of Fig. 1, an extended-nip press roll of the invention and an embodiment of its press shoe where a hydrostatic chamber is provided by means of arcs of a circle.

Figure 1B shows a section IB―IB in Fig. 1A of the press shoe of Fig. 1A, i.e. a section in a cross-machine direction.

Figure 2 shows an extended-nip press roll identical with that of Fig. 1 in a upper position such that the direction of rotation of the extended-nip roll is opposite to the direction of rotation of the extended-nip roll shown in Fig. 1.

Figure 3 is an axonometric view of the press shoe of the extended-nip press roll illustrated in Figs. 1 and 2.

Figure 4 is an axial vertical sectional view of the extended-nip press along the line IV―IV indicated in Fig. 1.

Figure 5 shows a Sym-Press II™ press section of the applicant where two extended-nip press rolls in accordance with the invention are employed in positions where their directions of rotation are opposite to each other.

Figure 6 shows a press section of a paper machine which is provided with two successive extended-nip rolls in accordance with the invention, which press section uses a totally closed draw from a forming wire to a drying wire, and in which press section the extended-nip press rolls are in positions where their directions of rotation are opposite to each other.

The extended-nip press shown in Figs. 1, 1A, 2 and 4 comprises an extended-nip press roll 10 (hereafter a hose roll 10) in accordance with the invention and a backup roll which is a press roll 20 provided with a smooth cylinder mantle 21. Alternatively. the backup roll 20 may be a variable-crown roll, which may also have a hollow face, if a paper web W runs through an extended nip zone EN between two felts. As shown in Figs. 1, 1A and 2, a glide belt mantle 16 loaded by a press shoe 11 in its area A-A, a press felt 22 and the paper web W being pressed run through the extended-nip zone EN. In Figs. 1 and 2, the paper web W is situated at one side thereof against an outer face of a loop of the water-receiving press felt 22 and at the other side thereof against the smooth face 21 of the backup roll 20.

In accordance with this invention, the hose roll 10 is symmetrical in structure with respect to its axial centre plane K―K. Partly owing to this, the hose roll 10 having the same structure can be used in a lower position shown in Figs. 1, 1A and 4 and in an upper position shown in Fig. 2. In the lower position shown in Figs. 1, 1A and 4, the direction of rotation of the hose mantle 16 is opposite to the direction of rotation of the hose mantle 16 situated in the upper position shown in Fig. 2. In Figs. 1, 1A and 4, the direction of rotation of the hose mantle 16 is clockwise and, in a corresponding way, in Fig. 2 counterclockwise. Thus, in press sections of a paper machine comprising two or more nips, hose rolls 10 of the same structure can be used in different extended nips, because the direction of rotation of the hose mantle 16 can be changed, i.e. the direction of rotation of the hose mantle 16 can be either direction without the functional properties of the hose roll 10 being substantially altered.

Figs. 5 and 6 described in more detail further on show some particularly advantageous press sections, which both apply two hose rolls 10 which are identical in structure with each other in accordance with the invention.

In the following, the structure of the hose roll 10 illustrated in Figs. 1, 1A, 1B, 2, 3 and 4 is described in more detail.

Fig. 3 is an axonometric view of the structure of the press shoe 11. As stated, it is essential that the press shoe 11 is symmetrical with respect to its longitudinal centre plane K―K so that the direction of rotation of the hose mantle 16 may be changed in the hose roll 10 without problems. The press shoe 11 has an active frontal face 18 that is pressed against an inner face of the flexible hose mantle 16. Hydrostatic chambers 19₁―19_N open onto the frontal face 18. When loading cylinders 12 of the press shoe 11 are supplied with pressures of different magnitude in a cross direction of the machine, the distribution of compression pressure can be regulated in the cross direction of the machine. Typically, N ≈ 150―1500 kN/m. Regulation of the compression pressure in the cross direction of the machine is generally about ± 5―15% max. of the basic loading.

As shown in Fig. 4, two loading cylinder series 12 are supplied, in the direction of the arrow O_in through a tube bundle 25, with different pressures P₁―P_N, by whose means the pressure distribution in the nip can be regulated, in a manner known in itself, both in the cross direction and in the machine direction in the extended-nip zone EN. So-called lubricating oil is introduced into the hydrostatic chambers 19₁―19_N through the tube bundle 25 and through capillary nozzles 17 (Fig. 1B), the rate of flow of which oil can be regulated, in which connection the rate of flow and the compression loading of the press shoe together determine the oil pressure P produced in the static chambers 19₁―19_N. The oil pressure P in the chambers 19₁―19_N produces a compression pressure in the area of the static chambers.

As shown in Fig. 4, the upper press roll 20 is journalled on

bearing supports

23a, 23b at its

axle journals

22a and 22b. The roll 20 is rotated by a drive means 24. The mantle 16 of the hose roll 10 is arranged to be rotatable about a central axle 15. The central axle 15 is carried by

supports

27a and 27b, which are supported on a frame part 50. Lubricating and loading oils are passed to the hose roll 10 from its driving side through the tube bundle 25 and the oils are returned through the operating side by means of a hose 26 to circulation O_out.

There are partition portions 19a at the ends of and between the chambers 19₁―19_N of the press shoe 11. The frontal face 18 of the press shoes 11 is symmetrical in relation to the plane K―K, comprising, starting from the outer edges, rounded edge parts having a radius of curvature R₃, which edge parts continue as front and

rear edge parts

11a and 11b having a substantially larger radius of curvature R₄. The

parts

11a and 11b having the radius of curvature R₄ position the press shoe 11 pivotally between the inner plane faces of support parts 14. The support parts 14 are attached to the central axle 15, which is stationary. The extended-nip zone EN is loaded by the frontal face 18 of the press shoe 11 as positioned by the inner faces of the support parts 14 and supported by the loading cylinders 12. The extended-nip zone EN is formed between lines A―A comprising, on both sides of its symmetry centre plane K-K from the edge inwards, plane portions A―B of the frontal face 18, portions B-C having a radius of curvature R₂, and plane portions C―D. The radius of curvature R₂ of the curved portion B―C = R₁ + P + Δ, where R₁ is the radius of the backup roll 20, PT is the thickness of the fabric 22 + that of a hose mantle, such as the belt 16, and Δ is an additional length Δ ≈ 0―5 mm. The radius of curvature R₄ is preferably R₄ ≈ 0.5 x L where L (Fig. 3) is the total length of the shoe 11, i.e. the distance between the

parts

11a and 11b in the machine direction. There are oil-drain troughs 13 and oil-drain tubes 60 inside the hose mantle 16 on both sides of the supports 14 of the press shoe 11. The press shoe 11 scrapes lubricating oil into the oil-drain trough 13 and the oil flows through its centre tube out O_out of the hose roll 10 aided by an internal positive pressure through the above-mentioned hose 26. When the press shoe 11 is in a lower position as shown in Fig. 2, lubricating oil drains from an "oil puddle" by means of an air pressure that raises it through the centre tube (not shown) of the hose roll 10 out of the hose roll 10.

An advantageous shaping and dimensioning example of the press shoe 11 and in particular of its frontal face 18 shown in Figs. 1 and 3 is described in the following.

There is a hydrodynamic area extending from the point A to the point B of the press shoe 11 in Fig. 1, which area is preferably parallel to a tangent to the radius R₂ of the portion B―C and has a length of about 0―25 mm. A short length A-B is advantageous in respect of a rapid pressure drop at the trailing edge and in respect of minimizing the rewetting of the web W that is being pressed, but the length A―B must, however, be sufficiently long in order to form a good lubricating oil layer. If the length A―B is alternatively zero, the radius R₃ shall be relatively large, for instance, about 50―100 mm, in order to form a sufficient hydrodynamic wedge. From the line B to the line C of the frontal face 18 of the press shoe 11, the radius of curvature of the shoe is R₂. The length B―C is about 10-50 mm. In the curved areas B-C, hydrodynamic wedges are formed when "tilting" with the loading cylinder series 12 by forces F₁,F₂. The nip pressure in the extended-nip zone EN is produced by means of two series of loading cylinders 12 and by means of a pressure P of the pressure oil introduced into the hydrostatic chambers 19₁―19_N. There are two series (rows) of loading cylinders 12 adjacent to each other in the machine direction. The separate cylinders may also be replaced with two chambers extending in the cross direction of the machine and with piston parts having the shape of the chambers and movably sealed against said chambers, and a loading pressure is passed "under" the piston parts sealed to the walls of the chamber. By changing the magnitude of the loading forces F₁ and F₂ of the loading cylinders 12 and the relation between them, said "tilt", i.e. the pressure distribution of the frontal face 18 of the loading shoe 11 in the machine direction can be changed.

The area extending from the line C in the frontal face 18 of the press shoe 11 to the centre line D in Fig. 1 is preferably a straight area having an angle a of inclination (a ≈ 1―5°) or a wedge area having slightly concave or convex sides. The chambers confined by the lines C and D may also be formed of a radius R₆ that is smaller than the radius R₂ and of corner roundings of the chambers 19₁―19_N (Fig. 1A). The machine-direction length of the hydrostatic chambers 19₁―19_N is, for example, about 20―120 mm. The hydrostatic chambers 19₁―19_N are supplied with pressure oil O through the capillaries 17.

The extended-nip roll 10 shown in Figs. 1A and 1B is otherwise similar to that shown in Figs. 1, 2 and 3 except that, in Figs. 1A and 1B, the hydrostatic chambers 19₁―19₄―19_N of the press shoe are defined by circular arc parts R5, R6, R8 and R9 which define the above-mentioned partition portions 19a. The alternative shaping of the hydrostatic chambers 19₁―19₄ shown in Fig. 1B is advantageous in particular in respect of the durability of the glide belt mantle 16.

An advantageous dimensioning example of the press shoe shown in Fig. 1B is presented in the following:

R5 = 40―200 mm, preferably 60―120 mm

R6 = 5―15 mm, preferably 7―10 mm

R7 = 10―50 mm, preferably 15―30 mm

R8 = 5―20 mm, preferably 7―15 mm

R9 = 5―20 mm, preferably 7―15 mm

H1 = 1―10 mm, preferably 3―6 mm

H2 = 0―2 mm, preferably 0.1―0.5 mm (H2 may also be = H1)

L1 = 7―40 mm, preferably 10―25 mm

L2 = 50―300 mm, preferably 70―200 mm

17 = a capillary nozzle through which pressure oil is introduced into the hydrostatic chambers 19₁―19_N

d = 0.5―4 mm (diameter of the capillary nozzle), preferably 1―3 mm.

The above dimensioning is also suitable for use in the embodiment of Figs. 1, 2 and 3.

Alternatively, the partition portions 19a of the hydrostatic chambers 19₁―19₄ shown in Figs. 1B and 3 may also be removed altogether, in which connection the hydrostatic chamber is continuous over the entire cross direction of the shoe, i.e. then H2 = H1. However, the ends of the press shoe 11 are provided with walls shown in Fig. 3 defining the hydrostatic chamber. This embodiment uses, however, capillary nozzles 17 which distribute the pressure lubricating oil fairly evenly in the width direction of the machine especially as the length H1 is small, i.e. H1 ≈ 1―3 mm, although the leakage from the hydrostatic chambers 19₁―19_N at the various points of the press shoe 11 would even vary to some extent because of differences in compression pressure.

The right shaping of the hydrostatic chambers 19₁―19_N and their partition walls 19a or their possible removal is advantageous specifically in respect of the durability of the belt 16. Sharp bending of the belt 16 caused by "paper clods" is reduced and pressure peaks are lowered. Also, instances of poorer local lubrication caused by the partition walls 19a of the press shoe 11 and streaks of higher temperature caused by them in the belt 16 may be reduced or totally eliminated.

In Fig. 4, the upper roll 20 is a backup roll of the extended-nip press roll 10, which backup roll may be, for example, a rigid, so-called tube roll or a variable-crown roll provided with a static axle and glide shoes. The backup roll 20 is provided with the drive 24, which comprises an electric motor and a gear which is situated on the driving side of the machine. The lower roll is a hose roll 10 provided with a hose mantle 16 in accordance with the invention, which roll is not provided with a drive. The upper roll 20 and the lower hose roll 10 are connected to each other at their

bearing housings

23a,27a and 23b,27b by means of connecting

means

27c and 27d which bear a high load and which can be opened in connection with replacement of fabrics. In the extended-nip roll 10, the pressure oil for the loading cylinders 12 of the press shoe 11 and the high-pressure lubricating oil for the static chambers 19₁―19_N of the press shoe 11 are preferably introduced O_in from the driving side of the machine. Depending on the width of the machine, grouping of the loading cylinders 12 and the internal measurements of the extended-nip roll 10, there are totally about 5―40 of these pressure oil tubes, measuring lines for pressure and temperature, and supply lines for an internal air pressure in the extended-nip roll. They are advantageously placed on the driving side of the machine, so that they need not be detached for the time of replacement of the belt mantle 16 or the press fabrics 22. The oil fed into the hose roll 10 is generally drained from the operating side by means of one or two fairly large hoses or tubes 26. For the time of replacement of the press felts 22 and the belt mantle 16, a flange joint 26a of said oil-drain hose or tube 26 is opened for removing the tubes out of the path of pushing the fabrics into the machine.

In the following, with reference to Figs. 5 and 6, two particularly advantageous press section geometries are described where the extended-nip roll, i.e. the hose roll 10 in accordance with the invention is applied. The features common to Figs. 5 and 6 are described first. The paper web W is separated from a forming wire 30 at a pick-up point PP and transferred by the action of a suction zone 30a of a pick-up roll on a lower face of a first press felt and a pick-up felt 31 into a first nip N₁, which is a roll nip N₁ in Fig. 5 and an extended nip EN₁ in Fig. 6. In Fig. 5, the first roll nip N₁ is formed between an upper press suction roll 29 and a hollow-faced lower press roll 28. The web W and the upper felt 31 travel over a suction zone 29a of the suction roll 29 through a second roll nip N₂. The second nip N₂ is formed between the press suction roll 29 and a smooth-faced 21 centre roll 20. In Fig. 5, the first roll nip N₁ is double-felted also comprising a lower felt 32. The second nip N₂ is single-felted and only the upper felt 31 travels through it. The web W adheres to the face of the smooth-faced 21 centre roll 20, and the web W is passed to a first extended nip EN₁ of the press section, through which a water-receiving upper felt 33 travels.

In Fig. 5, there is a second separate extended nip EN₂, which is provided with a lower felt 34. The web W is separated as a short free draw WP from the face 21 of the centre roll 20 and passed, while guided by a guide roll, by means of a suction zone 37a of a transfer suction roll 37 onto a water-receiving lower felt 34, which runs through the second extended nip EN₂. In the extended nip EN₂ there is a press roll 20 provided with a smooth face 21, from which roll the web W is passed as a short free draw WP, while guided by a guide roll, onto a drying wire 40 and further over drying cylinders 42 and reversing suction cylinders 43 in a multi-cylinder dryer.

In the press section alternative shown in Fig. 5, the press shoe 11 of the hose roll 10 of the invention in the third nip EN₁ is in a lower position. The press section is provided with a separate fourth extended-nip press EN₂, in which the upper roll 20 is a smooth-faced 21 press roll and the lower roll is a hose roll 10 in accordance with the invention, the press felt loop 34 running around said hose roll. In the fourth press EN₂, the press shoe 11 of the extended-nip roll 10 in accordance with the invention is in an upper position.

As shown in Fig. 6, both extended nips EN₁ and EN₂ are provided with two

felts

31,32/33,34. The upper roll in the first extended nip EN₁ is a press roll 20 provided with a hollow face 21' and the lower roll is an extended-nip roll 10 in accordance with the invention. After the extended nip EN₁, the web W is separated from an upper felt 31 and transferred by the action of a suction zone 35a of a transfer suction roll 35 onto a lower felt 32 and on it further by means of a suction zone 36a of a transfer suction roll 36 onto a second upper felt 33, which carries the web W into the second extended nip EN₂. The upper roll in the second extended nip EN₂ is a hose roll 10 in accordance with the invention having a direction of rotation that is opposite to that of the hose roll 10 serving as the lower roll of the first extended nip EN₁. Thus, the press section alternative illustrated in Fig. 6 comprises two extended nips EN₁ and EN₂ having rolls in different positions. The hose roll 10 of the first extended nip EN₁ is in a lower position (the press shoe 11 in the upper position of the hose roll 10) and the hose roll 10 of the second press nip E_N2 is in an upper position (the press shoe 11 in the lower position of the hose roll 10).

The reason for placing the hose rolls 10 in the different positions in the extended nips EN₁ and EN₂ as shown in Fig. 6 lies in the felt geometries of the press section which take into account the most advantageous transfers of the web W by means of transfer suction rolls 35,36,37 from one press felt 31,32,34 onto another 32,33,34, 40, as well as the angles of the press felts such that, for example, the press felts do not press the belt mantle 16 of the extended-nip press EN₁,EN₂ against the leading and trailing edges of the press shoe 11, which would cause sharp bending and reduced durability of the belt mantle 16. The symmetry of paper may also be affected by placing the hose rolls 10 of the invention in different positions especially if smooth belt mantles 16 and hollow-faced 21' backup rolls 20 of the extended-nip press are used.

The claims are presented in the following and the various details of the invention may vary within the inventive idea defined by said claims and differ from the disclosure given above by way of example only.

Claims

An extended-nip press roll (10) for a paper machine, comprising a stationary central axle (15), a loading shoe (11), and hydraulic loading elements (12) situated between said stationary axle (15) and said loading shoe (11), by means of which elements an active frontal face (18) of the loading shoe (11) is pressed against an inner face of a flexible hose mantle (16) of the extended-nip press roll (10) in order to produce a compression pressure in an extended-nip zone (EN;EN₁;EN₂) formed by said extended-nip press roll with its backup roll (20), the loading shoe (11), and the loading arrangements of the loading shoe being substantially symmetrical in relation to the axial centre plane (K-K) of the extended nip press roll characterized in that oil-drain arrangements of the loading shoe, which comprise on both sides of the loading shoe inside the hose mantle loop (16) oil-drain troughs (13) and oil-drain tubes (60) connected to these, are substantially symmetrical in relation to the axial centre plane (K―K) of the extended-nip press roll (10) so that the direction of rotation of the hose mantle (16) may be either direction and as required by the position of the extended-nip press roll (10).
An extended-nip press roll as claimed in claim 1, characterized in that the loading shoe (11) of the extended-nip press roll is symmetrical in relation to the centre plane (K―K) of a frontal face area (A-A) forming the extended-nip zone, which plane (K―K) passes through the centre axis of the backup roll (20) of the extended-nip zone or close to it.
An extended-nip press roll as claimed in claim 1 or 2, characterized in that the extended-nip press roll (10) comprises, on both sides of its axial centre plane (K―K) situated symmetrically at the outer edges, areas having a large radius of curvature (R₄) which are supported between support parts (14) attached into connection with the central axle (15) of the extended-nip press roll (10), that the side parts (11a,11b) having said radius of curvature (R₄) are followed by edge parts having a smaller radius of curvature (R₃), which edge parts continue as plane parts (A-B) forming a hydraulic wedge, which plane parts are followed by parts having a radius of curvature (R₂) slightly larger than the radius of curvature (R₁) of the backup roll (20), which parts continue as plane or curved parts to the centre line of the loading shoe (11), on both sides of which there are series of hydraulic loading chambers (19₁―19_N) which are situated symmetrically and into which loading oil (O) can be introduced through capillaries (17).
An extended-nip press roll as claimed in any one of claims 1 to 3, characterized in that in the frontal face (18) of the loading shoe (11) of the extended-nip roll (10) there is a series of hydrostatic loading pressure chambers (19₁―19_N), which chambers can be supplied with a pressure medium having an adjustable pressure (P), preferably a lubricating and loading oil.
A press section of a paper machine comprising at least two extended nips (EN₁, EN₂), characterized in that in the extended nips (EN₁,EN₂) of the press section, there are extended-nip press rolls (10) as claimed in any one of the claims 1 to 4 in positions having directions of rotations which are different from one another, and which extended-nip press rolls (10) form extended-nip zones (EN₁,EN₂) with their backup rolls (20), through which zones the paper web (W) is passed.
A press section of a paper machine as claimed in claim 5, characterized in that, in the press section, a first double-felted (31,32) nip is a roll nip (N₁), whose upper felt (31) is a pick-up felt which also travels through a second roll nip (N₂) of the press section, which nip is formed between a press suction roll (29) common to said press nips (N₁,N₂) and a smooth-faced (21) centre roll (20), that a first extended nip (EN₁) of the press section is also formed in connection with said smooth-faced (21) centre roll (20), in which nip an extended-nip press roll (10) as claimed in any one of the claims 1 to 4 is an upper roll and said centre roll (20) is a lower roll, and through with extended nip (EN₁) a water-receiving upper press felt (33) is passed, and that the press section further comprises a second separate extended nip (EN₂), whose lower roll is an extended-nip press roll (10) as claimed in any one of the claims 1 to 4, and whose upper roll is a press roll (20).
A press section of a paper machine as claimed in claim 6, characterized in that, after the first extended nip (EN₁), the web (W) is separated from the smooth face (21) of the centre roll (20) and transferred onto the upper face of a lower fabric (34) of the second extended-nip zone (EN₂), from which the web (W) is separated after the second extended-nip zone (EN₂) on the face of its upper smooth-faced (21) press roll (20) and transferred on it further and preferably as a short free draw (WP) further onto a drying wire (40) of a first drying cylinder group in a dryer section that follows after the press section.
A press section of a paper machine as claimed in claim 7, characterized in that the press section comprises two successive extended-nip zones (EN₁,EN₂) through which the web (W) is passed as a closed draw.
A press section of a paper machine as claimed in claim 8, characterized in that both extended-nip zones (EN₁,EN₂) are provided with two water-receiving transfer fabrics and press fabrics or with it and a transfer belt so that the web (W) has a closed draw in the transfer after said extended-nip zones (EN₁,EN₂) and the press section onto the drying wire (40).
A press section of a paper machine as claimed in claim 9, characterized in that the upper press fabric in the first extended nip (EN₁) of the press section is a pick-up fabric (31), by means of which the web (W) is separated at a pick-up point (PP) from a forming wire (30), that after the first extended-nip zone (EN₁) the web (W) follows, preferably by means of a suction roll transfer (35,35a), a lower press fabric (32) of the first extended-nip zone (EN₁), on which fabric the web (W) is passed onto the upper press fabric (33) of the second extended-nip zone (EN₂) by means of a suction roll transfer (36,36a), and that after the second extended-nip zone (EN₂) the web (W) is arranged to follow the lower fabric (34) or a transfer belt of the second extended-nip zone (EN₂), on which fabric or belt the web (W) is passed, by means of a transfer suction zone (41a) of a transfer suction roll (41), as a closed draw onto the drying wire (40) of the first drying cylinder group in the dryer section that follows after the press section.
A press section of a paper machine as claimed in claim 10, characterized in that the first extended-nip zone (EN₁) has an extended-nip press roll (10) as claimed in any one of the claims 1 to 5 as a lower press roll and a press roll (20) provided with a hollow face (21') as an upper press roll, and that the second extended-nip zone (EN₂) has an extended-nip press roll (10) as claimed in any one of the claims 1 to 5 as an upper press roll and a press roll (20) provided with a hollow face (21') as a lower press roll.