CN111886380B

CN111886380B - Yankee dryer for drying a wet fibrous web

Info

Publication number: CN111886380B
Application number: CN201980021071.0A
Authority: CN
Inventors: O·荣松
Original assignee: Valmet AB
Current assignee: Valmet AB
Priority date: 2018-04-27
Filing date: 2019-04-18
Publication date: 2021-06-11
Anticipated expiration: 2039-04-18
Also published as: EP3749803A1; SE1850509A1; CN111886380A; WO2019209164A1; EP3749803A4; SE542227C2

Abstract

The invention relates to a yankee dryer cylinder (1) for drying a wet fibrous web (W), having a shell (6) made of steel and having a cylindrical shape with a central axis (a), the shell (6) being symmetrical around the central axis. The housing (6) extends in an axial direction and has two axial ends (7, 8) and an intermediate portion (9) located between the axial ends (7, 8). An end cap (10, 11) for each axial end (7, 8) of the housing (6) is fixed to the housing (6) such that the housing (6) and the end caps (10, 11) form a hollow interior volume (V). Each end cap (10, 11) has an outer periphery (12) at which the end cap (10, 11) is secured to the housing (6), each end cap (10, 11) having a central annular opening (23) defining an inner periphery (13) at which the end cap (10, 11) is secured to the attachment ring (14). Each end cap (10, 11) comprises an inner wall (15) and an outer wall (16), each of the outer and inner walls (15, 16) having an outer periphery (17, 19) adjacent the housing (6) and a central opening (21, 22) defining an inner periphery (18, 20) adjacent the attachment ring (14) for each of the outer and inner walls (16, 15). In at least one region between the outer periphery (12) of the end caps (10, 11) and the inner periphery (13) of the end caps (10, 11), the inner and outer walls (15, 16) are spaced apart from each other in the axial direction of the housing (6). The end caps (10, 11) are welded to the housing (6) and the attachment ring (14), the inner and outer walls (15, 16) are bent or inclined inwardly in the axial direction of the housing (6) such that in a radial direction away from the outer periphery (12) of the end caps (10, 11) and towards the central axis (a) of the housing (6), the distance in the axial direction of the housing (6) from the outer and inner walls (15, 16) to the middle portion (9) of the housing (6) decreases such that the distance in the axial direction from each of the inner and outer walls (15, 16) to the middle portion (9) of the housing (6) is smaller at the inner peripheries (18, 20) of the inner and outer walls (15, 16) than at the outer peripheries (17, 19) of the inner and outer walls (15, 16).

Description

Yankee dryer for drying a wet fibrous web

Technical Field

The present invention relates to a yankee dryer for drying a wet fibrous web.

Background

Yankee dryers are used for drying wet fibrous webs and they are used in particular for manufacturing tissue paper grades, i.e. such paper grades as are used for e.g. bathroom, kitchen towel or facial tissue purposes. These paper grades may have, for example, 15g/m²-40g/m²Basis weight in the range of (a). When making tissue paper, the wet fiber web is dried on a yankee dryer filled with a heat medium (usually hot steam). Heat from the steam is transferred to the outer surface of the yankee dryer such that water in the wet fiber web in contact with the outer surface of the yankee dryer is evaporated. For many years, such yankee dryers have been made of cast iron. However, it has also been suggested that yankee dryers may be made of steel, examples of such yankee dryers being disclosed for instance in US patent No.8,438,752. The yankee dryer is provided with end walls or covers so that the inside of the yankee dryer will be a closed volume capable of containing hot steam. US patent No.9,428,861 discloses a yankee dryer in which the end walls comprise an inner cover and an outer cover, and an insulating layer is used, which may be in the form of a coating. The object of the present invention is to provide an improved steel yankee dryer cylinder, which has high strength and effective insulation. These and other objects are achieved by the present invention as will be explained below.

Disclosure of Invention

The present invention relates to a yankee dryer for drying a wet fibrous web. The yankee dryer cylinder of the invention has a shell, which is made of steel and has a cylindrical shape with a central axis. The housing is symmetrical about its central axis, extends in an axial direction and has two axial ends and an intermediate portion between the axial ends. There is an end cap for each axial end of the housing, the end caps being made of a steel material and secured to the housing such that the housing and the end caps form a hollow interior volume. The outer periphery of each end cap is secured to the housing and the inner periphery is secured to the attachment ring. Each end cap includes an inner wall and an outer wall, each of the outer wall and the inner wall having an outer periphery adjacent the housing and a central opening defining an inner periphery adjacent the attachment ring. The central openings of the inner and outer walls are coaxial with each other and together form an opening in the end cap in which the attachment ring fits. In at least one region between the outer periphery of the end cap and the inner periphery of the end cap, the inner wall and the outer wall are spaced apart from each other in the axial direction of the housing. Each end cap is welded to the housing and to the attachment ring. The inner wall and the outer wall are curved or inclined inwardly in the axial direction of the housing such that the distance in the axial direction of the housing from both the outer wall and the inner wall to the intermediate portion of the housing decreases in a radial direction away from the outer periphery of the end cap and toward the central axis of the housing. The distance is reduced such that the distance in the axial direction from each of the inner and outer walls of the housing to the intermediate portion is smaller at the inner peripheries of the inner and outer walls than at the outer peripheries of the inner and outer walls.

In an embodiment of the invention, the design of the end cap may be such that for at least a part of the radial distance from the connection of the end cap with the housing towards the centre axis of the housing, the inner wall is inclined or curved more inwardly than the outer wall, such that in the radial direction towards the centre axis of the housing the distance between the inner wall and the outer wall (i.e. the distance in the axial direction of the housing) increases.

In other embodiments, the yankee dryer cylinder may be designed such that the distance between the inner wall and the outer wall in the axial direction of the shell remains constant in the radial direction from the shell towards the central axis of the shell.

In an advantageous embodiment of the invention, each of the outer wall and the inner wall is welded to the housing and to the attachment ring, and both the inner wall and the outer wall are bent or inclined inwardly in the axial direction of the housing, the outer wall and the inner wall may be spaced from each other such that the distance between the inner wall and the outer wall increases in a radial direction away from the outer circumference of the end cap and towards the central axis of the housing.

In an embodiment of the invention, at least one of the outer wall and the inner wall comprises at least two sections that have been welded together, wherein a weld (weld) extends in a radial direction from an outer circumference of the end cap to an inner circumference of the end cap.

In an advantageous embodiment of the invention, both the inner wall and the outer wall comprise at least two sections that have been welded together.

In embodiments where both the inner and outer walls comprise two or more sections that have been welded together, the sections of the outer wall are preferably (but not necessarily) rotated relative to the sections of the inner wall such that the weld joining the sections of the inner wall has an angular position that is different from the angular position of the weld joining the sections of the outer wall.

Preferably, both the outer wall and the inner wall comprise at least four sections that have been welded together. Embodiments of the invention are envisaged in which one or both of the outer and inner walls comprise more than four sections that have been welded together. For example, the inner and/or outer wall comprises six sections that have been welded together or eight sections that have been welded together.

Preferably, the at least one steel reinforcing element is welded to both the outer wall and the inner wall and connects the outer wall with the inner wall.

According to an embodiment of the invention, the outer wall is welded to the housing and to the attachment ring, wherein the inner wall is divided into a radially outermost portion adjacent to the inner wall of the housing and a radially innermost portion adjacent to the attachment ring. In this embodiment, the reinforcement ring is placed between the inner wall and the outer wall and is welded to the outer wall, to the radially outermost portion of the inner wall and to the radially innermost portion of the inner wall, and the inner wall is welded to the outer wall at its outer and inner peripheries.

In an embodiment of the invention, at least one of the end caps, and preferably each end cap, comprises a peripheral ring extending around the periphery of at least one of the end walls, the peripheral ring having the same diameter as the housing. In such embodiments, at least one of the inner wall and the outer wall is welded to the peripheral ring, and the peripheral ring is welded to the housing.

In some embodiments using a peripheral ring, the outer wall is welded directly to the peripheral ring and to the attachment ring, while the inner wall is divided into a radially outermost portion adjacent the housing and a radially innermost portion adjacent the attachment ring. The radially innermost portion may then be welded to the attachment ring and the radially outermost portion may be welded to the peripheral ring or to the outer wall.

In all embodiments, at least one stiffening element may be placed between and welded to both the inner and outer walls such that at least one slit is formed in the outer wall and the outer wall is welded to the at least one stiffening element through the at least one slit (34). The at least one stiffening element welded to the outer wall by the at least one slit may be annular.

Drawings

Fig. 1 is a side view giving a schematic representation of an inventive yankee dryer cylinder for use in a paper machine.

Fig. 2 is a schematic cross-sectional view taken along the axis of the yankee dryer cylinder according to the present invention.

Fig. 3 is a front view of the sidewall without the attachment ring.

Fig. 4 is a front view similar to fig. 3, but also showing an attachment ring.

Fig. 5 is a front view of two elements as part of a side wall.

Fig. 6 is a side view showing the same elements as in fig. 5.

Fig. 7 is a view similar to fig. 4, but schematically indicating how the side walls may be formed from sections.

Fig. 8 is a sectional view taken along the axis of the yankee dryer cylinder according to the first embodiment of the invention.

Fig. 9 is a cross-sectional view corresponding to fig. 8, but showing a portion of the end cap 10 in greater detail.

Fig. 10 is a cross-sectional view similar to fig. 9, but showing a second embodiment of the invention.

Fig. 11 is a sectional view along the axis of the yankee dryer cylinder according to the third embodiment of the invention.

FIG. 12 is a cross-sectional view similar to FIG. 11 but showing a fourth embodiment of the invention.

FIG. 13 is a schematic elevational view of an end wall illustrating one form that a second embodiment of the present invention may take.

Fig. 14 is an elevation view of a section forming a portion of an inner or outer wall.

Fig. 15 is a side view of the segment shown in fig. 14.

FIG. 16 is an elevation view of two sections ready to be welded together to form an inner or outer wall.

FIG. 17 is an elevation view showing four sections ready to be welded together to form an inner or outer wall.

FIG. 18 is a cross-sectional side view similar to FIG. 11 but showing a fifth embodiment of the invention.

Figure 19 is a schematic representation of a front view of the end cap 10 of the embodiment shown in figure 18.

Fig. 20 is a cross-sectional side view similar to fig. 11 and 18, but showing a sixth embodiment of the invention.

Fig. 21 is a side view of the element of fig. 20.

Detailed Description

With reference to fig. 1, a yankee dryer 1 is used in a paper machine, and the yankee dryer 1 may be a yankee dryer 1 according to the invention, fig. 1 being understood to represent possible configurations in which the yankee dryer of the invention may be used. Of course, it should be understood that the yankee dryer 1 of the present invention can also be used in other configurations, and that fig. 1 represents only an example of a possible installation. In fig. 1, a wet fibrous web W is carried by a fabric 3, which may be, for example, a water-absorbent felt. The web W is carried by the fabric 3 in the direction of arrow S to the nip formed between the press roll 4 and the yankee dryer 1. The press roll 4 is preferably an extended nip/shoe roll, such as the one disclosed in US patent No.7527708, but other rolls, such as suction rolls or skew-compensating rolls, may also be used. In the nip between the press roll 4 and the yankee dryer 1, the wet fibrous web W is transferred to the smooth outer surface of the yankee dryer being rotated in the direction of arrow R around the central axis a of the yankee dryer 1. The yankee dryer 1 has journals 29 placed in bearings (not shown). The yankee dryer 1 is heated from the inside by a hot fluid, which is usually hot steam at a certain overpressure. As the wet fiber web travels over the surface of the yankee dryer, the web W is dewatered by evaporation as the heat in the steam is transferred to the wet fiber web through the shell of the yankee dryer, as is known in the art. The dried fibrous web is then creped from the outer surface of the yankee dryer by means of a doctor blade 2. Thereafter, the web will travel for further processing, such as reeling up on a reel-up. The yankee dryer may optionally be provided with a yankee hood 5, such as for example the yankee hood disclosed in EP 2963176.

The yankee dryer design of the present invention will now be explained in more detail.

With reference to fig. 1 and 2, the yankee dryer cylinder according to the invention has a shell 6, having a cylindrical shape. The shell 6 is made of steel and is symmetrical about its central axis a, which is the axis about which the yankee dryer rotates when it runs in the paper machine. The housing extends in an axial direction (i.e. in the direction of the central axis a) and it has two axial ends 7, 8 and an intermediate portion 9 between the axial ends 7, 8. It will be appreciated that the intermediate portion 9 is not a separate element, but an integral part of the housing 6. For the purposes of this patent application, the concept of bringing out the intermediate portion is only for the purpose of defining the direction with respect to the axial ends 7, 8, and it may simply be considered as the portion of the housing 6 that is equidistant from the axial ends, i.e. the portion of the housing 6 that is located in the middle between the axial ends 7, 8 of the housing 6. The expression "intermediate portion" can be understood to mean an imaginary line of any small width of the housing 6 or even just the middle between the axial ends 7, 8. The yankee dryer has an

end cap

10, 11 for each axial end 7, 8 of the shell 6, which end cap is made of a steel material and is fixed to the shell 6, such that the shell 6 and the end caps 10, 11 form a hollow interior volume V.

Referring to fig. 3, each

end cap

10, 11 has an outer periphery 12 which is circular and matches the cylindrical shape of the housing 6. It should be understood that although fig. 3 only shows the end cap 10, the statements regarding the end cap 10 also apply to the end cap 11. Each

end cap

10, 11 is fixed to the housing 6 and each

end cap

10, 11 has a central annular opening 23 which defines the inner periphery 13 of the

end cap

10, 11. Referring to fig. 4, it can be seen that the attachment ring 14 is placed in the annular opening 23. The attachment ring is used for attachment of the journal 29 (see fig. 1), i.e. for receiving the journal 29.

With further reference to fig. 5 and 6, each

end cap

10, 11 includes an inner wall 15 and an outer wall 16. Each of the outer wall 16 and the inner wall 15 has an

outer periphery

17, 19 adjacent the housing 6 and a

central opening

21, 22 defining an

inner periphery

18, 20 adjacent the attachment ring 14 for each of the outer wall 16 and the inner wall 15 (the attachment ring 14 is not shown in fig. 5 and 6).

The

central openings

21, 22 of the inner and

outer walls

15, 16 are coaxial with each other and together form a central annular opening 23 in the end caps 10, 11, the attachment ring 14 fitting in said central annular opening 23.

An embodiment of the present invention will now be described in more detail with reference to fig. 8. It should be understood that the statements below with respect to the end cap 10 shown in fig. 8 also apply to the end cap 11. In fig. 8, it can be seen that in the region between the outer periphery 12 of the end cap 10 and the inner periphery 13 of the end cap 10, the inner wall 15 and the outer wall 16 of the end cap 10 are spaced apart from each other in the axial direction of the housing 6. The end cap 10 is welded to the housing 6 and to the attachment ring 14. The inner wall 15 and the outer wall 16 are curved or inclined/deflected inwardly in the axial direction of the housing 6. Since the inner and outer walls are deflected inwardly, the distance in the axial direction from both the outer wall 16 and the inner wall 15 to the intermediate portion 9 of the housing 6 decreases in the radial direction from the outer periphery 12 of the end cap 10 toward the central axis a of the housing 6.

Referring to fig. 2, it can be seen that at the periphery of the end cap 10 there is a first distance D1 from the end cap 10 to the intermediate portion 9, whereas at the intersection of the end cap 10 with the attachment ring 14 (and where the end cap is fastened to the attachment ring 14) there is a distance D2 in the axial direction from the end cap 10 to the intermediate portion 9 of the housing 6. As can be seen in fig. 2, D1 is greater than D2(D1 > D2).

With further reference to fig. 8, it can be seen that at the outer periphery of the end cap 10, there is a first distance d1 in the axial direction between the inner wall 15 and the intermediate portion 9, while at the point where the inner wall 15 meets the attachment ring 14, there is a second distance in the axial direction from the inner wall 15 to the intermediate portion 9, the first distance d1 being greater than the second distance d2(d1 > d 2). It can thus be seen that the distance in the axial direction from the inner wall 15 to the intermediate portion 9 of the housing 6 decreases in the radial direction from the outer periphery of the inner wall 15 towards the central axis a. The same is true for the outer wall 16. It can therefore be said that the distance in the axial direction from each of the inner and

outer walls

15, 16 to the intermediate portion 9 of the housing 6 is smaller at the

inner peripheries

18, 20 of the inner and

outer walls

15, 16 than at the

outer peripheries

17, 19 of the inner and

outer walls

15, 16. In fig. 8, a stiffening element 26 is shown placed between the inner wall 15 and the outer wall 16. The reinforcing element 26 may take many different shapes. One or several such stiffening elements 26 may be used. The reinforcing element 25 is preferably made of steel and is preferably welded to both the inner wall 15 and the outer wall 16. It is contemplated that such reinforcing elements 26 may be made of another metallic material than steel. For example, cast iron or bronze may be considered. If the material of the reinforcing element 26 is not suitable for welding, the reinforcing element 26 may be fixed to the inner and

outer walls

15, 16 by other means, such as screws or rivets. Non-metallic reinforcing elements 26, for example made of ceramic material, are also conceivable. However, it is believed to be preferred to use a reinforcing element 26 made of steel and welded to the inner and

outer walls

15, 16.

As can already be seen in fig. 8, the inner wall 15 is inclined towards the middle portion 9 of the housing 6 by a greater angle than the outer wall 16. Thus, the distance between the inner wall 15 and the outer wall 16 increases in a radial direction from the outer circumference of the end cap 10 toward the central axis a and the attachment ring 14.

Referring now to fig. 9, fig. 9 is an enlarged view of some of the elements shown in fig. 8. In the region where the inner and

outer walls

15, 16 are connected with the attachment ring 14, there is a first distance S1 between the inner and

outer walls

15, 16. Away from the central axis a, in the radial direction R, there is a second distance S2 between the inner wall 15 and the outer wall 16, and the second distance S2 is less than the first distance S1. In the region where the inner and outer walls are connected with the housing 6, there is a third distance S3 between the inner and

outer walls

15, 16, and the distance S3 is less than the distance S2(S1S2S 3). In the embodiment of fig. 8 and 9, the distance S between the inner wall 15 and the outer wall 16 decreases linearly in the radial direction R from the attachment ring 14 to the housing 6, but embodiments are also conceivable in which the distance decreases in a non-linear manner (and increases in the opposite direction). In fig. 9, the distances S1, S2, S3 may be selected such that: s1 is in the range of 200mm-300mm, S2 is in the range of 100mm-200mm, and S3 is in the range of 10mm-90 mm. In one embodiment contemplated by the inventors, the distance S1 proximate the attachment ring 14 may be about 250mm, the distance S2 halfway from the attachment ring 14 may be about 150mm, and the distance S3 proximate the housing 6 may be about 50 mm. The thickness of each of the inner and

outer walls

15, 16 in fig. 9 may be in the range 20mm-45 mm. For example, the thickness of each of the inner and

outer walls

15, 16 may be 25mm or 40 mm.

The inner surface of the shell 6 is preferably provided with grooves 31 in which hot steam can condense and transfer heat to the outer surface of the shell 6 for evaporating water from the wet fibre web W.

In a preferred embodiment, one or several reinforcing elements 26 may be welded to at least one of the inner wall 15 or the outer wall 16 or to both. Such reinforcing elements may increase the strength of the end caps so that the end caps may better resist the internal pressure in the yankee dryer when filling the yankee dryer with pressurized steam. The at least one reinforcing element 26 may have a ring-like shape, or it may be in the shape of multiple pieces distributed around the circumference of the end cap 10.

It is understood that embodiments are conceivable in which the distance S between the inner wall 15 and the outer wall 16 does not vary linearly in the radial direction R. It should also be understood that embodiments are envisaged (which differ from the embodiments of fig. 8 and 9): the distance S between the inner wall 15 and the outer wall 16 (the distance in the axial direction of the housing) increases only for a part of the way between the outer periphery/periphery of the end cap 10 and the attachment ring 14.

However, in a preferred embodiment of the invention, the end cap 10 is designed such that the inner wall 15 is inclined or curved more inwardly than the outer wall 16 for at least a part of the radial distance from the connection of the end caps 10, 11 with the housing 6 towards the central axis a of the housing 6, such that the distance S between the inner wall 15 and the outer wall 16 increases in a radial direction towards the central axis a of the housing 6.

Preferably, each of the outer wall 16 and the inner wall 15 is welded to the housing 6 and to the attachment ring 14 by a weld 30. In all embodiments, both the inner and

outer walls

15, 16 are curved or inclined inwardly in the axial direction of the housing 6. Preferably, the outer wall 16 and the inner wall 15 are spaced apart from each other such that in a radial direction away from the outer circumference of the end cap and towards the central axis of the housing, the distance S between the inner wall 15 and the outer wall 16 increases such that the distance is greater at the location where the inner and

outer walls

15, 16 are welded to the attachment ring 14 than at the location where the inner and

outer walls

15, 16 are welded to the housing 6.

A second embodiment of the present invention will now be explained with reference to fig. 10. The embodiment of fig. 10 is substantially similar to the embodiment of fig. 9. However, unlike the embodiment of fig. 9, the distance S1 between the inner wall 15 and the outer wall 16 remains constant all the way from the housing 6 to the attachment ring 14. In fig. 10, the angle α is shown. This is the angle between the inner wall 15 and a plane perpendicular to the central axis a of the housing 6. In the embodiment of fig. 10, the angle a is the same for the inner wall 15 and the outer wall 16. In the embodiment of fig. 9, the respective angles are different for the inner wall 15 and the outer wall 16, and in the embodiment of fig. 9, the angle α of the inner wall 15 is greater than the angle of the outer wall 16. The angle alpha may be different as the case may be, but in many practical embodiments the angle alpha may be in the range of 5-40 or 10-30, but other angles are also contemplated. For example, small angles of 1-4, or in some cases, angles greater than 40, may be tested.

In many practical embodiments, the distance S1 in FIG. 10 may be in the range of 50 mm-300. In one embodiment contemplated by the inventors, the distance S1 in fig. 10 may be 100 mm. However, other values for distance S1 in fig. 10 are also contemplated. The thickness of each of the inner and

outer walls

15, 16 in fig. 10 may be in the range 20mm-45 mm. For example, the thickness of each of the inner and

outer walls

15, 16 may be 25mm or 40 mm.

A third embodiment of the present invention will now be explained with reference to fig. 11 and 13. In the embodiment of fig. 11, the inner wall 15 is divided into a radially outermost portion 27 adjacent the housing 6 and a radially innermost portion 28 adjacent the attachment ring 14. The outer wall 16 is welded to the housing 6 and to the attachment ring 14, for example by means of a weld 30 shown in fig. 11. An annular (ring-shaped) reinforcing element 26a is placed between the inner wall 15 and the outer wall 16, as can be seen in fig. 11 and 13. The annular reinforcing element 26a is welded to the outer wall 16, for example by means of a weld 30 as shown in fig. 11. The annular reinforcing element 26a is also welded to the radially outermost portion 27 of the inner wall 15 and to the radially innermost portion 28 of the inner wall 15, for example by means of a weld 30 as shown in fig. 11. The inner wall 15 is welded at its outer and

inner peripheries

17, 18 to the outer wall 16.

Referring to fig. 7 and 13, at least one of the outer wall 16 and the inner wall 15 comprises at least two sections 24, 25 that have been welded together by a weld seam extending in a radial direction from the outer periphery 12 of the end caps 10, 11 to the inner periphery 13 of the end caps 10, 11. In fig. 13, the

sections

25a, 25b, 25c and 25d constitute the outer wall 16.

A fourth embodiment will now be explained with reference to fig. 12. The embodiment of fig. 12 is generally similar to the embodiment of fig. 11, but differs from the embodiment of fig. 11 in that the radially innermost portion 28 of the inner wall 15 is welded to the attachment ring 14, while the radially outermost portion 27 of the inner wall 15 is welded to the housing 6.

Another aspect of the present invention will now be explained with reference to fig. 7 and with reference to fig. 13. In a preferred embodiment of the invention, both the inner and

outer walls

15, 16 may be made of sections that have been welded together. Each of the inner and

outer walls

15, 16 preferably comprises at least two sections 24, 25 that have been welded together. Preferably, at least four sections are used for both the inner wall 15 and the outer wall 16. For larger yankee dryers, eight sections may be used for the inner wall 15 and eight sections may be used for the outer wall 16. Preferably, the sections of each

wall

15, 16 are of the same size and have the same shape (except for differences due to, for example, manholes).

Referring to FIG. 7, the outer wall 16 of the end cap 10 includes four

sections

25a, 25b, 25c and 25d welded together along weld lines indicated by X in FIG. 7. The inner wall 15 also comprises four

sections

24a, 24b, 24c and 24d welded together along weld lines indicated by Y in figure 7. The section 25 of the outer wall 16 is rotated relative to the section 24 of the inner wall 15 (i.e., clockwise/counterclockwise rotation as shown in fig. 7) so that the weld Y connecting the sections 24 of the inner wall 15 has an angular position (angular position in the circumferential direction of the casing 6) different from the angular position of the weld X connecting the sections 25 of the outer wall 16. A four-segment configuration of the outer wall 16 can also be seen in fig. 13. With reference to fig. 7, it will be appreciated that the

sections

24a, 24b, 24c and 24d are not directly visible in fig. 7, as they are hidden behind the

sections

25a, 25b, 25c and 25d forming the outer wall 16. However, the reference numerals 24a-24d and the weld line Y indicate the positions of the segments 24a-24 d.

In the embodiment of fig. 11, there are generally more sections for the inner wall 15 than for the outer wall 16, since the inner wall 15 is also divided into a radially outermost part and a radially innermost part.

It will be appreciated that in both the embodiment of fig. 8 and the embodiment of fig. 11, the inner wall 15 and the outer wall 16 may be made of multiple sections, as indicated in fig. 7 and 13.

Reference will now be made to fig. 14, 15 and 16. In fig. 14, the section 24b is shown in elevation view, and the section 24b is intended as part of the inner wall 15. The segment 24b has undergone bending, which is symbolically represented by the bending line 32. Section 24b appears as a truncated cone when viewed from the side, as shown in fig. 15. The section 24b represents half of the complete inner wall 15. Referring to fig. 16, two

such sections

24a and 24b may be combined with each other by welding to form the complete inner wall 15. Of course, the inner wall 15 may be formed by more than two

sections

24a, 24 b. As shown in fig. 17, the inner wall 15 may include 4

sections

24a, 24b, 24c and 24d, which may be welded or conceivably connected by other methods. It should be understood that the inner wall 15 may include six sections, eight sections, ten sections, or twelve sections. The inner wall 15 may also comprise more than twelve sections. Embodiments are envisaged in which the inner wall 15 may comprise an odd number of sections, for example three sections, five sections, seven sections or a number of sections greater than seven. However, the number of segments is preferably even. For smaller yankee dryers a relatively small number of sections may be suitable, whereas for larger yankee dryers (i.e. yankee dryers with a relatively large diameter) it may be suitable to use a larger number of sections for the inner wall 15. What has been stated above with reference to fig. 14-17 in relation to the inner wall also applies to the outer wall 16, which may in the same way comprise a plurality of segments that have been welded together. Preferably, the same number of sections is used for the outer wall 16 and the inner wall 15. For example, if the inner wall 15 has four sections, it is preferred that the outer wall 16 also has four sections. However, embodiments are conceivable in which the inner wall 15 and the outer wall 16 do not have the same number of sections. Embodiments are also contemplated in which both the outer wall 16 and the inner wall 15 have been formed from a single piece (e.g., sheet metal piece). The material in the sections is preferably steel.

A fifth embodiment will now be explained with reference to fig. 18. The embodiment of fig. 18 is similar in many respects to the embodiment of fig. 11. However, in the embodiment of fig. 18, at least one of the end caps 10, 11 (preferably both end caps 10, 11) includes a peripheral ring 33 that extends around the periphery of at least one of the

end walls

10, 11. The peripheral ring 33 has the same diameter as the housing and at least one of the inner wall 15 and the outer wall 16 is welded to the peripheral ring and the peripheral ring 33 is welded to the housing 6 by means of the weld 30. As shown in fig. 18, the outer wall 16 is welded to the peripheral ring 33, while the inner wall 15 is welded at its periphery to the outer wall 16, rather than being welded directly to the peripheral ring 33. However, it will be appreciated that both the inner wall 15 and the outer wall 16 may be welded to the peripheral ring 33 at their radially outer peripheries.

In the embodiment of fig. 18, the outer wall 16 is welded directly to the peripheral ring 33 and to the attachment ring 14, while the inner wall 15 is divided into a radially outermost portion 27 adjacent to the housing 6 and a radially innermost portion 28 adjacent to the attachment ring 14, and the radially innermost portion is welded to the attachment ring 14 and the radially outermost portion is welded to the outer wall 16. However, the radially outermost portion 27 may alternatively be welded directly to the peripheral ring 33.

With further reference to fig. 18, at least one stiffening element 26a is placed between the inner wall 15 and the outer wall 16 and welded to the inner wall 15 and the outer wall 16. The at least one reinforcing element 26a is preferably annular (i.e. ring-shaped) and symmetrical about the central axis a of the housing 6.

In the embodiment of fig. 18, at least one slit 34 is formed in the outer wall 16, and the outer wall 16 is welded to the at least one reinforcing element 26a through the at least one slit 34. Preferably, more than one slit 34 is used, for example, two slits 34 are used, see also fig. 19. It will be appreciated that welding the outer wall 16 to the

stiffening elements

26, 26a may also be used in the embodiments of fig. 8, 12 and 11. One or

several stiffening elements

26, 26a (annular or not) may also be used in the embodiment of fig. 10, and

such stiffening elements

26, 26a may optionally be welded to the outer wall 16 by one or several slits 34. With further reference to fig. 19, it can be seen how the

sections

25a, 25b, 25c and 25d, which together form the outer wall 16, are provided with slits 34 (i.e. through openings in the sections), by means of which the

sections

25a, 25b, 25c and 25d can be welded to an annular reinforcing element 26a placed between the outer wall 16 and the inner wall 15. In fig. 19, the outer wall 16 is shown with four

sections

25a, 25b, 25c and 25d, but it is understood that more or less than four sections may be used. For example, the outer wall 16 may have four sections or eight sections.

Referring to fig. 20 and 21, a sixth embodiment of the present invention will now be explained. The embodiment of fig. 20 is substantially similar to the embodiment of fig. 18, but the stiffening ring 26a shown in fig. 18 has been replaced by a plurality of stiffening sheets 35 extending in the radial direction of the yankee dryer 1 from the attachment ring 14 towards the shell 6. Such a reinforcing sheet 35 is shown separately in fig. 21. The reinforcement sheet 35 is a reinforcement element that performs substantially the same function, preferably made of steel, and is shaped to fit into the space between the inner wall 15 and the outer wall 16, and to be in contact with both the inner wall 15 and the outer wall 16. More than one such reinforcing sheet 35 is used, and preferably at least three such reinforcing sheets 35 are provided in the embodiment of fig. 20. Even more preferably, at least four such reinforcing tabs 35 are used. Preferably, the reinforcing tabs 35 are distributed around the circumference of the end caps 10, 11 with the same angle between all the reinforcing tabs. In one embodiment contemplated by the inventors, eighteen such reinforcing tabs 35 are used, which are spaced apart from each other by 20 ° in the circumferential direction of the end caps 10, 11. Each reinforcing tab 35 may be welded to the inner wall 15 and the outer wall 16 through the slit 34 in substantially the same manner as explained with reference to fig. 18 and 19. It is clear that the slits 34 in the embodiment of fig. 19 may have a different shape than the slits 34 shown in fig. 19. In order to allow a reliable welding, the reinforcing sheet 35 should preferably have a thickness of at least 20mm and preferably at least 25 mm. For example, each reinforcing sheet 35 may have a thickness in the range of 25mm-40 mm. In one embodiment contemplated by the inventors, eighteen sheets each having a thickness of 30mm were used.

In all embodiments, the thickness of each of the inner wall 15 and the outer wall 16 may be in the range of 20mm-45mm, although other thickness values are contemplated.

For all embodiments of the invention, the following may be stated. Since the distance between the inner and

outer walls

15, 16 is greater near the central axis a than where the inner and outer walls join the housing, the strength of the end caps 10, 11 will be optimized where most needed (i.e., near the central axis a). At the same time, the inner wall 15 is connected to the shell 6 close to or at the axial end 7 of the shell 6, which means that the hot steam inside the yankee dryer 1 can heat the shell 6 substantially up to the axial end 7 of the shell 6.

Another advantage of the present invention resides in the use of the outer and

inner walls

15, 16, which allows the end caps 10, 11 to have a sandwich structure. The sandwich structure improves the structural strength of the end wall. At the same time, the air layer between the inner wall 15 and the outer wall 16 results in better insulation, thereby reducing heat losses.

Another advantage of the present invention is that the welded yankee cylinder can be more easily installed into existing machines without reducing the effective width of the yankee cylinder, since the inwardly projecting

end caps

10, 11 can accommodate existing bearings and journals.

If the

stiffening element

26, 26a is welded to the outer wall 16 by means of one or several slits 34, the weld can be inspected from the outside, which is preferred. In the embodiment of fig. 18, it can be noted that all welds 30 can be detected from the outside or from the inside by a worker located inside the yankee dryer 1.

It will be appreciated that although only the scheme using peripheral ring 33 is shown in fig. 18, the same scheme (i.e. peripheral ring 33 to which the end caps are fixed/welded) may also be used in the embodiments of fig. 8, 9, 10, 11 and 12. The use of the peripheral ring 33 provides the advantage that the end cap can be manufactured separately and then welded to the housing 6 as a single piece. However, it will be appreciated that such a manufacturing method is one in which the peripheral ring 33 is welded to the housing 6 before the other parts of the end cap are welded/connected to the peripheral ring 33.

In many practical embodiments of the invention, the yankee dryer may have a diameter in the range of 3.5 m-7 m. In many practical embodiments, the opening 23 in the end cap may have a diameter in the range of 1 m-2.5 m. For example, the yankee dryer may have a diameter of 5.5m (or about 5.5m), while the opening 23 in the end cover may have a diameter of 2m (or about 2 m).

Although the different embodiments of fig. 8, 9, 10, 11, 12, 18 and 20 have been described above with reference to one axial end 7, 8 of the housing 6, it will be appreciated that what applies to one axial end 7, 8 of the housing 6 also applies to the opposite axial end of the housing 6, so that each axial end 7, 8 of the housing 6 has an end cap of the same design. In principle, embodiments are conceivable in which end caps of different designs are combined with one another. For example, one axial end 7, 8 of the housing 6 may be provided with an end cap as shown in fig. 8, while an end cap at the other axial end of the housing 6 may have an end cap as shown in fig. 12. However, it is preferred that the end caps 10, 11 have the same design at both axial ends 7, 8 of the housing 6.

Although not shown in the drawings, it is preferable to provide a manhole on at least one of the end covers 10, 11 for purposes such as inspection, maintenance and repair. This applies to all embodiments.

As can be seen, for example, in fig. 10, the housing 6 may be designed to define a step at the outer periphery (periphery) 19 of the outer wall 16 that supports the outer wall 16, and a similar support step may also be provided for the inner wall 15 in the housing 6. In the same way, the attachment ring 14 may have corresponding steps to support the outer wall 16 and the inner wall 15 (see fig. 10).

In all embodiments of the invention, the yankee dryer cylinder 1 is preferably equipped with means for removing the condensation water from the grooves 31, such as for example those shown in EP 2614182B 1 or US patent No. 4476637.

Claims

1. Yankee dryer cylinder (1) for drying a wet fibrous web (W), the Yankee dryer cylinder (1) having a shell (6), the shell (6) being made of steel and having a cylindrical shape with a central axis (A), the shell (6) being symmetrical around the central axis, the shell (6) extending in an axial direction and having two axial ends (7, 8) and an intermediate portion (9) between the two axial ends (7, 8), an end cap (10, 11) made of a steel material for each axial end (7, 8) of the shell (6) and being fixed to the shell (6) such that the shell (6) and the end caps (10, 11) form a hollow interior volume (V) and wherein each end cap (10, 11) has an outer periphery (12), the end caps (10, 11) -fixed to the housing (6) at the outer periphery, -each end cap (10, 11) having a central annular opening (23) defining an inner periphery (13), at which inner periphery the end cap (10, 11) is fixed to an attachment ring (14), and wherein-each end cap (10, 11) comprises an inner wall (15) and an outer wall (16), each of the outer and inner walls (15, 16) having an outer periphery (17, 19) adjacent to the housing (6) and a central opening (21, 22) defining an inner periphery (18, 20) adjacent to the attachment ring (14) for each of the outer wall (16) and the inner wall (15), -the central openings (21, 22) of the inner and outer walls (15, 16) being coaxial to each other and together forming a central annular opening (23) in the end caps (10, 11), -the attachment ring (14) being fitted in the central annular opening (23), -the inner and outer walls (15, 16) are spaced apart from each other in the axial direction of the housing (6) in at least one area between the outer periphery (12) of the end cap (10, 11) and the inner periphery (13) of the end cap (10, 11), characterized in that the end cap (10, 11) is welded to the housing (6) and to the attachment ring (14), and the inner and outer walls (15, 16) are curved or inclined inwardly in the axial direction of the housing (6) such that in a radial direction away from the outer periphery (12) of the end cap (10, 11) and towards the centre axis (a) of the housing (6), the distance from both the outer and inner walls (15, 16) to the intermediate portion (9) of the housing (6) in the axial direction of the housing (6) decreases, such that from the inner and outer walls (15, 16) is smaller at the inner peripheries (18, 20) of the inner and outer walls (15, 16) than at the outer peripheries (17, 19) of the inner and outer walls (15, 16) in the axial direction to the intermediate portion (9) of the housing (6).

2. Yankee dryer cylinder (1), according to claim 1, wherein for at least a part of the radial distance from the connection of the end covers (10, 11) and the shell (6) towards the central axis (A) of the shell (6), the inner wall (15) is inclined or curved more inwardly than the outer wall (16) such that the distance (S) between the inner wall (15) and the outer wall (16) increases in the radial direction towards the central axis (A) of the shell (6).

3. Yankee dryer cylinder (1), according to claim 1, wherein, in said radial direction from said shell (6) towards said central axis (A) of said shell (6), the distance (S) between said inner wall (15) and said outer wall (16) in the axial direction of said shell (6) remains constant.

4. Yankee dryer cylinder (1), according to claim 1, wherein each of said outer wall (16) and said inner wall (15) is welded to said shell (6) and to said attachment ring (14), and both are curved or inclined inwardly in the axial direction of said shell (6), and wherein said outer wall and said inner wall are spaced apart from each other such that in a radial direction away from the outer periphery of said end closure and towards the central axis of said shell, the distance (S) between said inner and outer walls (15, 16) increases such that it is larger where said inner and outer walls (15, 16) are welded to said attachment ring (14) than where said inner and outer walls (15, 16) are welded to said shell (6).

5. Yankee dryer cylinder (1), according to claim 1, wherein at least one of said outer wall (16) and said inner wall (15) comprises at least two sections (24, 25) that have been welded together by a weld seam extending in a radial direction from said outer circumference (12) of said end closure (10, 11) to said inner circumference (13) of said end closure (10, 11).

6. Yankee dryer cylinder (1), according to claim 2, wherein at least one of said outer wall (16) and said inner wall (15) comprises at least two sections (24, 25) that have been welded together by a weld seam extending in a radial direction from said outer circumference (12) of said end closure (10, 11) to said inner circumference (13) of said end closure (10, 11).

7. Yankee dryer cylinder (1), according to claim 3, wherein said inner and outer walls (15, 16) each comprise at least two sections (24, 25) that have been welded together.

8. Yankee dryer cylinder (1), according to claim 5, wherein the section (25) of the outer wall (16) is rotated with respect to the section (24) of the inner wall (15) so that the weld joining the section (24) of the inner wall (15) has an angular position different from the angular position of the weld joining the section (25) of the outer wall (16).

9. Yankee dryer cylinder (1), according to claim 6, wherein the section (25) of the outer wall (16) is rotated with respect to the section (24) of the inner wall (15) so that the weld joining the section (24) of the inner wall (15) has an angular position different from the angular position of the weld joining the section (25) of the outer wall (16).

10. Yankee dryer cylinder (1), according to claim 4, wherein said outer wall (16) and said inner wall (15) both comprise at least four sections (24, 25) that have been welded together.

11. Yankee dryer cylinder (1) according to any of the previous claims 1-10, wherein at least one steel reinforcing element (26, 26a, 30) is welded to the outer wall (16) and the inner wall (15) and connects the outer wall (16) with the inner wall (15).

12. Yankee dryer cylinder (1), according to claim 1, wherein said outer wall (16) is welded to said shell (6) and to said attachment ring (14), wherein said inner wall (15) is divided into a radially outermost portion (27) adjacent to said shell (6) and a radially innermost portion (28) adjacent to said attachment ring (14), and wherein an annular reinforcing element (26a) is placed between said inner wall (15) and said outer wall (16) and is welded to said outer wall (16), to said radially outermost portion (27) of said inner wall (15) and to said radially innermost portion (28) of said inner wall (15), and wherein said inner wall (15) is welded to said outer wall (16) at its outer and inner peripheries (17, 18).

13. Yankee dryer cylinder (1), according to claim 1, wherein at least one of said end caps (10, 11) comprises a peripheral ring (33) extending around the periphery of at least one end wall (10, 11), said peripheral ring having the same diameter as said shell (6), and wherein at least one of said inner and outer walls (15, 16) is welded to said peripheral ring and said peripheral ring (33) is welded to said shell (6).

14. Yankee dryer cylinder (1) according to claim 13, wherein the outer wall (16) is welded directly to the peripheral ring (33) and to the attachment ring (14), wherein the inner wall (15) is divided into a radially outermost portion (27) adjacent to the shell (6) and a radially innermost portion (28) adjacent to the attachment ring (14), and wherein the radially innermost portion is welded to the attachment ring (14) and the radially outermost portion is welded to the peripheral ring (33) or to the outer wall (16).

15. Yankee dryer cylinder, according to claim 1, wherein at least one stiffening element (26, 26a) is placed between the inner wall (15) and the outer wall (16) and is welded to both the inner wall (15) and the outer wall (16), and wherein at least one slit (34) is formed in the outer wall (16) and the outer wall (16) is welded to said at least one stiffening element (26, 26a) through said at least one slit (34).

16. Yankee dryer cylinder (1), according to claim 15, wherein said at least one reinforcing element (26a) is annular.