WO2008071238A1

WO2008071238A1 - Paper machine roll and a method for manufacturing the same

Info

Publication number: WO2008071238A1
Application number: PCT/EP2006/069785
Authority: WO
Inventors: Robertus Stapels; Tomi Norrby
Original assignee: Metso Paper, Inc.
Priority date: 2006-12-15
Filing date: 2006-12-15
Publication date: 2008-06-19
Also published as: DE112006004163T5

Abstract

A paper machine roll comprises a core member (1) and an elastic cover (2,102,202,302), wherein the surface of said elastic cover has varying wear resistance properties along the roll length. The roll is manufactured by a formation of a basic roll cover (2a) on a roll core member (1) by overlapping a plurality of layers (20-23) having different properties and grinding and/or machining the basic roll cover (2a) for achieving a cover surface which comprises along the length of the roll at least one zone constituted by the cross-section of one of the layers (20-23).

Description

yPAPER MACHINE ROLL AND A METHOD FOR MANUFACTURING THE

SAME"

The present invention relates to a paper machine roll and a method for manufacturing the same. The invention relates in particular to a roll for an elastic covered roll in a calendar, particularly in a multinip calendar or soft calendar, or a press roll in the press section of a paper machine.

Paper machine rolls, in particular coated soft rolls are widely used in paper machines and in paper finishing devices, for example such like calenders.

Multinip calenders, soft calenders and similar paper finishing equipment usually consist of a plurality of rolls forming a number of nips through which the paper runs while undergoing a certain finishing treatment by pressure, possibly also by heat and pressure. The nips are formed each by a combination of a soft and a hard roll. Soft rolls are usually formed as coated, in particular polymer-coated rolls which, however, do not have an uniform rigidity in the longitudinal direction of the roll. Since in such kind of rolls, the end areas of the metal core member are more rigid than the middle area thereof, a higher nip load is present in the lateral areas than in the middle area of the soft roll. Thus, in the case of a calender, the quality in the lateral areas of the paper web can suffer as a result of this higher load.

In order to solve the above mentioned problem, efforts have been made for controlling the nip load over the roll length. In addition or alternatively to such a nip load control aiming at a uniform load profile, there are known technical solutions, for example such disclosed in the documents GB-795 523, US-5, 662, 574, US-5,412,870 and US- 6,039,840 providing certain deformation characteristics, both for the core member of the soft roll and for its cover or cover system. Different deformation characteristics of the polymer coating material have been used and also different thicknesses and/or layer constructions, all these technical measures aiming at providing an equalized loading in the longitudinal direction of the roll.

It is an object of the present invention to provide an improved paper machine roll, in particular a soft roll for a calender, which has improved functional characteristics for providing a better calendering result .

The object of the invention is also to provide a method for manufacturing of the above-mentioned paper machine roll.

The above object is achieved by the combination of the features set forth in each of the independent claims. Preferable embodiments of the paper machine roll according to the invention and the method for manufacturing the same are set forth in the subclaims.

The present invention is a result of the understanding that in a paper machine and paper finishing equipment completely uniform operating conditions can never be achieved. Such a attempt to achieve uniform operating conditions and/or to design a roll cover by using fillers, fibres and additives targeting the wear behaviour of the complete cover is a question of a compromise between performance and costs.

One of the results of a non-uniform load or uneven paper properties (for example drier end area) in the longitudinal direction of the roll, i.e. in the cross- machine direction, is the non-uniform wear of the roll cover. What mostly occurs is more wear at the cover edges than at the cover centre of the roll. With progressing cover wear the load profile changes with resulting effect on paper properties. The resulting uneven length wear profile is therefore one of the main reasons to remove a covered roll from a paper machine.

A typical position in a paper machine where the wear of roll covers determines the paper machine shutdowns for roll changes is the calender, specifically the multi-nip calender where high load and hard paper promotes the wear of the soft roll covers. However, there are also other positions in a paper machine, for instance the press section where composite covers are used and where the same problems might occur.

The present invention is also based on the understanding that completely uniform operating conditions, in particular a uniform load over the roll length can hardly be achieved under usual manufacturing conditions. Uniform operating conditions are a compromise between performance and costs, wherein an appropriate covering design, for example through fillers, fibres and additives can significantly contribute for increasing the time needed to wear down to an undesired ground profile of the roll cover. Thus, the aim of the invention is in particular to provide a paper machine roll and a method for manufacturing the same which contribute for achieving more uniform operating conditions.

According to the present invention, wear as such is not a reason to remove a covered roll from the paper machine. If the cover wear is uniform over the cover length, then the proper operation of the covered roll can continue even if its cover wear causes a decrease in cover thickness. Thus, in cases where the cover is normally worn into a crown shape, the cover grinding interval can be increased by use of a covering that has more wear resistance at the cover ends. However a crown shape is just one of the possible non-uniform shapes, and it can be any other shape varying in the cross-machine direction as well.

According to a first aspect of the present invention there is provided a paper machine roll comprising a core member and an elastic cover, wherein the surface of the elastic cover has varying wear resistance properties along the roll length.

In an embodiment of this paper machine roll the wear resistance of the edge zones of the cover surface close to the roll ends is higher than the wear resistance of the middle zone of said cover surface.

The cover of the paper machine roll according to the first aspect of the present invention can be formed by at least one single layer having wear properties varying along the roll length, and/or by a plurality of layers having different wear properties and extending over different cover portions along the roll length. The layer or the layers of the cover of the paper machine roll according to the present invention preferably has/have a substantially constant thickness and substantially constant wear properties along the roll length.

According to a particularly preferred embodiment at least a portion of the roll surface is formed by a cross-section of at least one of the cover layers. In the practice at least the edge zones of the cover surface close to the roll ends will be constituted by zones formed by cross-sections of said layers. In the normal case these zones have a wear resistance increasing toward the roll ends. However the wear resistance distribution can be designed also in a different way, where this is appropriate because of particular paper processing conditions and/or specifics of the paper machine.

Depending on the machining and/or grinding angle cutting the multilayer structure of the roll cover, the cover surface zone being closest to the roll ends will be formed either by the outermost or innermost layer of the multilayer structure.

According to another aspect of the present invention there is provided a method for manufacturing a paper machine roll, said method comprising a formation of a basic roll cover on a roll core member by overlapping a plurality of layers having different properties; and grinding and/or machining the basic roll cover for achieving a cover surface which comprises along the length of the roll at least one zone constituted by the cross-section of one of said layers .

It is to be noted that such a method is not only applicable for the manufacturing of paper machine rolls where the wear resistance of the cover increases toward the roll ends, but also for the manufacturing of paper machine rolls where any kind of other cover properties should be altered along the roll length. According to an embodiment of the method according to the invention the layers are formed on a longitudinally convex roll structure, which can preferably represent an integral part of the roll core member.

More preferably, the longitudinally convex roll structure could be a part of the cover and can be formed as a staircase multilayer structure consisting of a plurality of overlapping layers coated one over the other on the roll core member.

In the following, the invention is further explained by means of Examples with reference to the enclosed Figures.

In the Figures:

Fig. 1 shows a paper machine roll according to a first embodiment of the present invention;

Figs. 2, 3 and 4 show an Example of a method for manufacturing a paper machine roll according to the invention;

Fig. 5 shows a partial cross-sectional view of a paper machine roll according to a second embodiment of the present invention;

Fig. 6 represents a partial cross-sectional view of a paper machine roll according to a third embodiment of the present invention;

Fig. 7 is a cross-sectional view of a paper machine roll according to a fourth embodiment of the present invention.

A first embodiment of a paper machine roll according to the invention shown in Fig. 1 comprises a core member 1 consisting of a metal cylinder. On the core member 1 there is provided a roll cover 2 having a multilayer structure. The multilayer structure consists of layers 4 - 10 and layers 11 - 16 extending substantially in parallel to the axis Ia of the core member 1, i.e. also in parallel to the surface of the core member. While the layers 11 - 16 constitute a kind of a staircase inner multilayer structure, the outer layers 4 - 10 have different wear properties and extend over different cover portions along the roll length. Each of these layers has a substantially constant thickness and substantially constant wear properties along the roll length. However, the layers 4 - 10 have in this order, i.e. toward the roll ends 3 an increasing wear resistance.

As shown in Fig. 1 the layers 4 - 10 are arranged in a direction slightly inclined to the cylindrical surface of the core member 1 so as to wrap each side of the staircase structure toward the roll ends 3. Since the outer surface of the cover is also a cylindrical one this surface is formed by the inclined cross-sections of the layers 4 - 10. Due to this particular arrangement of the layers there is provided a paper machine roll comprising the core member 1 and a cover 2 the surface of which has varying wear resistance properties along the roll length. In the present embodiment the wear resistance of the edge zones of the cover surface close to the roll ends 3 is higher than the wear resistance of the middle zone of the cover surface. In the present embodiment the zone being closest to the roll ends 3 is formed by the outermost layer 10 of the cover 2.

Because at least the edge zones of the cover surface close to the roll ends 3 are constituted by zones formed by cross-sections of the layers 4 - 10, a more uniform wear of the roll can be provided along the roll length.

In the first embodiment shown in Fig. 1, the structure of the roll cover represents a kind of a roll cover system and is the result of a particular manufacturing method illustrated by Figures 2, 3 and 4.

According to an example of the method for manufacturing a paper machine roll according to the invention, a cylindrical metal core member 1 is initially provided with a basic roll cover 2a comprising a plurality of layers 11, 12, 13, 14, 15 and 16 arranged in the staircase form shown in Fig. 2. All these layers are constituted by one and the same material, so that they exhibit one and the same wear resistance and have the same mechanical properties.

As a next step, the staircase structure is covered by further layers 20, 21, 22 and 23 extending over the whole length of the staircase multilayer structure and completing the basic roll cover 2a. In this simplified example the layers 20 to 23 are constituted by one and the same material having a wear resistance higher than the wear resistance used for forming the staircase multilayer structure.

In the next step shown in Fig. 4, the basic roll cover including the multilayer structure of the layers 11-16 and 20-23 is machined and finally grinded so that finally the cover similar to that one shown in Fig. 1 is obtained.

Although some particular embodiments have been described above, the present invention can be carried out in many different ways, so that paper machine rolls of different composition length structure can be obtained still remaining within the scope of the present invention.

Referring to the second embodiment of the paper machine roll according to the invention shown in Fig. 5, there is provided a non-resilient core member 101 having a convex crown shape. On the core member 101 there is provided a cover 102 having a lower modulus of elasticity than the core member 101. The cover 102 is constituted by a plurality of layers 104-110 having substantially the same thickness and deformability, but different wear resistance increasing toward the outer surface and the ends of the roll. The method of manufacturing of this paper machine roll is similar to the method already explained with reference to the Figures 2 to 4 with the main difference that the structure constituted by the layers 11-16 is replaced by the crown shape of the core member 101.

As can be understood from the second embodiment shown in Fig. 5, the pressure produced in the middle portion of the roll during calendering will be greater than the pressure at the roll ends. However, because of the deformability of the cover 102 and its increasing thickness toward the roll ends, the working pressure would be progressively reduced towards the roll ends so that the working pressure of the roll in the corresponding roll nip will be equalized over the length of the roll. Further, even in case of occasional occurrence of higher load at the roll ends, the wear of the roll cover will be equalized over the roll length due to the working surface of the roll having a wear resistance being always higher at the ends of the roll than in the middle portion thereof.

Depending on the particular resiliency of the layer material used for forming the cover 102, the shape of this cover can be modified as shown in Fig. 6. According to the third embodiment shown in Fig. 6, the core member 201 has substantially the same shape as the core member 101 shown in Fig. 5. However, the cover 202 is constituted by one basic layer 204 formed by a polymer layer, for example polyethylene, natural or synthetic rubber, polyurethane, epoxy or any, preferably softer polymer material, the thickness of which is substantially constant over the middle area of the roll frame 201 and then gradually increases over a certain distance towards the roll ends. The outer surface of the basic layer 204 has a substantially cylindrical shape. On this outer surface, further layers 206, 208 and 210 are subsequently deposited one over the other almost in the same way as the deposition of the layers 20 to 23 shown in Fig. 3. After the deposition of the layers 206, 208 and 210, the outer surface of the roll is machined to the concave shape shown in Fig. 6. This machining causes a similar partial interrupting of the layers as already explained with regard to Fig. 4 so that a paper roll is obtained the outer surface of which has a progressively increasing wear resistance and deformability toward the roll ends.

When built in a calander, the relative stiffness of the ends of the roll core member is compensated for by the increased deformability of the polymer coating of the layer 204 in the lateral portions of the cover 202. By means of this structure, the loading of the roll can be equalized, because the lack of resilience is compensated for by means of the relief in the end areas of the roll. With other words, the elasticity of the roll cover in the end areas of the roll compensates for the additional load produced by an uneven deformation of the core member. In addition, due to the progressively changing wear resistance of the cover surface toward the roll ends, the wearing behaviour of the roll surface is equalized over the roll length even under occasional operating conditions where the nip load in the area of the roll ends is increased.

According to a fourth embodiment of the present invention shown in Fig. 7, a concave outer surface of the roll can be produced where appropriate by using substantially the same layer structure already illustrated by the second embodiment shown in Fig. 5 with the difference that the core member is formed by a cylindrical core member 301 and an outer cylindrical crown shaped layer 305 attached to the core member by a binding agent layer 305a, and with the further difference that the outer roll surface is machined such that it assumes a concave shape.

In addition to the embodiments described above, a plurality of further embodiments of a paper machine roll according to the invention are possible as a combination of the particular features of the afore-mentioned embodiments .

For example, the cover 202 according to the third embodiment shown in Fig. 6 can be completed only by the provision of the basic layer 204 without further layers 206 to 210, provided this cover is formed for example by the method disclosed in US-5, 412, 870. According to this method, the cover 204 can be formed by a deposition of an appropriate material mix on the core member 201, said mix having changing component concentration so as to provide a progressively increasing wear resistance toward the roll ends. If desirable, the hardness of the cover 204 can also be changed over the roll length in an appropriate way as described in the afore-mentioned reference. For example, for changing the hardness (deformability) of the cover 204 in case of polyurethane material, the proportion of the diamine component in the mix can be changed during the cover deposition over the roll length, whereas the wear resistance can be modified by varying the amount of fillers, fibres or similar additives in the mix deposited on the core member 201. However, the hardness (deformability) of the cover 204 does not necessarily need to be changed, since due to the increasing thickness of the cover 204 toward the roll ends, it provides an increased compressibility.

Claims

1. A paper machine roll comprising a core member (1) and an elastic cover (2; 102; 202; 302), wherein the surface of said elastic cover has varying wear resistance properties along the roll length.

2. A paper machine roll according to claim 1, wherein the wear resistance of the edge zones of said elastic cover surface close to the roll ends (3) is higher than the wear resistance of the middle zone of said cover surface.

3. A paper machine roll according to claim 1 or 2, wherein said elastic cover (2) comprises at least one layer having wear properties varying along the roll length.

4. A paper machine roll according to claim 1 or 2, wherein said elastic cover (2) comprises a plurality of layers (4 - 16; 104, 106, 108, 110; 204, 206, 208, 210; 304, 306, 308, 310) having different wear properties and extending over different cover portions along the roll length.

5. A paper machine roll according to claim 4, wherein at least one of said layers (4 - 10) has a substantially constant thickness and substantially constant wear properties along the roll length.

6. A paper machine roll according to claim 4 or 5, wherein at least a portion of the roll surface is formed by a cross-section of at least one of said layers (4 - 10) .

7. A paper machine roll according to claim 6, wherein at least the edge zones of the elastic cover surface close to the roll ends (3) are constituted by zones formed by cross-sections of said layers (4 - 10).

8. A paper machine roll according to claim 7, wherein the zones have a wear resistance increasing toward the roll ends (3) .

9. A paper machine roll according to claim 7 or 8, wherein the zone being closest to the roll ends is formed by the outermost layer (10) of said elastic cover (2) .

10. A method for manufacturing a paper machine roll, said method comprising a formation of a basic roll cover (2a) on a roll core member (1) by overlapping a plurality of layers (20-23) having different properties; and grinding and/or machining the basic roll cover (2a) for achieving a cover surface which comprises along the length of the roll at least one zone constituted by the cross-section of one of said layers (20-23) .

11. A method according to claim 10, wherein the wear resistance of said layers (20-23) increases toward the cover surface.

12. A method according to claim 11, wherein said layers (20-23) are formed on a longitudinally convex roll structure (5; 105; 205; 305) .

13. A method according to claim 12, wherein said longitudinally convex roll structure (105; 205) represents an integral part of said roll core member (1).

14. A method according to claim 12, wherein said longitudinally convex roll structure (5) is a part of said cover (2) formed by a staircase structure consisting of a plurality of overlapping layers (11- 16) deposited one over the other on said roll core member ( 1 ) .

15. A paper machine roll obtainable by a method according to one of claims 10 to 14.