Today mechanical vibrations of rolls, occurring at a frequency below 200 Hz, have become an increasing problem in paper or board machines. This is primarily due to continuous speed increases of paper machines. Particularly the problems caused by the vibration in the tangential direction of the roll pe- riphery, i. e. so called peripheral vibration, have increased along with rising machine speeds. Hence, peripheral vibration is today as serious a problem in respect of the runnability of a paper or board machine as the other type of mechanical vibra- tion of rolls, i. e. longitudinal, beam-like vibration of rolls.

Vibrations significantly hinder the production of paper and board restricting thus increasing of machine speeds. Vibration problems increase exponentially with a rising speed. Vibration has become a more serious problem than before particularly in the roll nips. At the moment, it is vibrating rolls that are a bottleneck in many paper and board machines. It is simply necessary to run paper and board machines so slowly that vibra- tions cannot grow to harmful levels.

Today the roll shell of the paper and board machines is manu- factured by casting or by bending from a steel sheet. The shell is rounded by machining and, if required, it is provided with machined grooves and coated. The rolls, however, lack a special damping against vibrations, but instead damping is simply based on the inherent characteristics of steel or casting.

The composition on the roll surface is not involved in damping of vibrations, but damping of vibrations takes place elsewhere.

If it is desired to minimize the vibration, particularly in the nip, the surface material of the roll does not actually have any significance.

In fact, particularly rubbery and similar elastic materials rather tend to generate vibration on the outer surface of the roll.

The object of the present invention is to provide a damping arrangement, which can be used to create efficient damping particularly for the two above-mentioned mechanical roll vibra- tion types, i. e. beam-like vibration of a roll and peripheral vibration of a roll. The invention is characterized in that the damping arrangement additionally includes at least one essen- tially rigid internal shell and a damping structure arranged between the shell and the internal shell, of which the internal shell is arranged at a distance from the shell inner surface in the radial direction of the roll and which is essentially concentric with the shell, and the outermost surface of the damping structure is arranged immobile in relation to the shell inner surface and the innermost surface of the damping struc- ture is arranged immobile in relation to the outer surface of the inner shell, whereby the forces produced during the roll vibration by the movement differences between the shell and the inner shell will convert, in the damping structure, to shearing forces, which will essentially be extinguished in the damping structure.

Preferable embodiments of the invention are described in the dependent claims.

The damping arrangement according to the invention thus com- prises two essentially rigid shells and a vibration-damping structure arranged between them. As a result, the movement

differences created due to bending of the two rigid shells are converted to shearing forces, which will then be extinguished in the damping structure. The damping structure can be composed of a vibration-damping material, whose rigidity characteristics are essentially lower than those of the roll shell and the inner shell. When rapidly reverting stresses are led to this type of flexible material, having a high internal friction, stresses are efficiently extinguished. On the other hand, it is possible to use an intermediate structure, which converts as great a portion of stresses as possible to shearing forces.

According to the damping arrangement, it is possible to prefer- ably first form a damping element, which comprises an essen- tially rigid inner shell and a vibration-damping damping layer to be arranged on the outer surface of the inner shell, and to further install this damping element as a whole inside the roll to be damped. An important aspect in the solution according to the invention is both a maximum possible rigidity of the roll shell and the inner shell and also a rigidity difference be- tween the roll shell and the inner shell so that the rigidity of the shell is higher than the rigidity of the inner shell.

This provides maximum shearing forces between the shells in relation to the movements of the shells. Thus the invention is also characterized in that the inner surface of the damping element, i. e. in this case the inner shell, is also rigid and continuous. The inner shell should thus be stiff so that the deformations will take place specifically in the vibra- tion-damping material. The task of the damping material, not of the shells, is to yield and extinguish the shearing stresses.

Another important aspect of the invention is a maximum thick- ness of the damping layer. That is, a maximum possible distance in the roll radial direction between the shell and the inner shell is aimed at. Namely, it has been discovered that the thickness of the damping layer correlates directly with the capability of the damping element to damp vibrations. This is

due to the fact, among others, that the greater the mutual distance between the shells in the roll radial direction, the greater are the movement differences between them during the roll vibration. When the movement differences are great, me- chanical stresses will also increase between the shells con- nected through the damping layer. The stresses again will produce shearing stresses in the damping layer. In the damping layer these rapidly reverting shearing forces are extinguished and thus the vibration movements of the roll are damped.

Essential is also that the damping characteristics are directed in the damping layer in such a manner that maximum damping is achieved in the longitudinal direction of the roll as well as in the tangential direction of the roll periphery. More pre- cisely, the rigidity of the damping material is highest both in the roll longitudinal direction and in the tangential direction of the roll periphery.

In practice, rubber has turned out to be the best possible damping material in the damping layer. However, other materials can also be applied in the solution according to the invention.

For example polyurethane, which is light and has high internal friction, is well applicable as the material of the damping layer. Various elastomers can also be used.

Other advantages are also achieved with the solution according to the invention. Firstly, it is applicable to both present and new rolls. That is to say, the damping element can be formed preferably complete even before bringing it inside the roll to be damped. The damping layer is first attached on the outer surface of the inner shell, the outer surface of the damping layer is subjected to a treatment for fastening to the inner surface of the outer shell, and finally the thus formed damping element is guided to inside the roll, where the attachment of the outer surface of the damping layer to the inner surface of the shell takes place.

In this way the damping elements can be adapted as complete directly to the inner surface of the shell. The damping ar- rangement according to the invention can be easily adapted for rolls of various sizes. This kind of module structure has advantages particularly in the case of old rolls. On the other hand, the arrangement can be adapted in all nip rolls and process rolls.

Due to the construction it is also possible to avoid additional cross seams improving thus the durability and strength of the construction. In addition, it is possible to adapt, inside a single roll, several adjacent damping elements, each of which extends over a part of a distance only in the longitudinal direction of the roll.

The invention is described below in detail by making reference to the enclosed drawings, which illustrate some of the embodi- ments of the invention, in which Figure 1 is a cross sectional view of the roll equipped with a damping arrangement according to the invention, Figure 2 is a sectional view of the roll of Figure 1 along the cutting line A-A, Figure 3 is a cross sectional view of another embodiment of the roll equipped with a damping arrangement accord- ing to the invention, Figure 4a is a sectional view of the roll of Figure 3 along the cutting line B-B, Figure 4b is a partial enlargement of Figure 4a, Figure 5a shows a modification of the damping structure of Figure 4a, Figure 5b is a partial cross sectional view of the structure of Figure 5a, Figure 6 illustrates the manufacturing method of the inner shell of the roll according to the invention.

Figure 1 is a cross sectional view of roll 1, in which vibra- tion damping is arranged using the damping structure 4 formed by the inner shell 3 and the damping layer 4'. The damping structure can be a damping element 13, adapted to the dimen- sions of the roll 1 to be damped, which can be guided to inside the roll 1 as a whole. The outer surface of the damping layer 4'is forced against the inner wall 10 of the shell 2 applying sufficient force, for example, by means of the turnbuckle screws 6 indicated in Figure 1, for fastening. This is better illustrated in the sectional view of the roll 1 shown in Figure 2. The surfaces of the damping layer 4'and the inner shell 3 are attached to each other in an immobile manner. The surfaces can be attached for example by gluing or by vulcanizing. After stretching the inner shell 3 it is locked in form for example by a longitudinal weld 7.

Both the shell 2 and the inner shell 3 should yield as little as possible. During the roll 1 vibration the shell 2 and the inner shell 3 tend to bend according to the vibrations, but in a different way due to their different structures. As a result, the shearing forces generated by the stresses caused by the movement differences are conducted to the damping structure 4, where they are eliminated and vibration is thus damped. Damping of vibrations of the roll 1 is the best, when the distance between the shell 2 and the inner shell 3 in the radial direc- tion of the roll and thus their mutual movement differences are as great as possible.

As regards damping, essential is thus the thickness of the damping layer, and maximization of it is aimed at. This is exactly for achieving a great movement difference between the shell 2 and the inner shell 3. The ratio of the thickness of the damping layer 4'relative to the thickness of the shell 2 is preferably 6-60%, more preferably 30-50%. In the embodi- ment of Figure 1 the optimized thickness of the damping layer 4'is 50 mm.

Another important aspect in the damping arrangement is a high rigidity of the shell and the inner shell as well as a rigidity difference between the shell and the inner shell. This provides maximum shearing forces between the shells when the roll tends to vibrate. The ratio of thickness of the inner shell 3 and the shell 2 is of class 1-10%, preferably 3-6%. In one embodi- ment of the invention according to Figure 1 the thickness of the shell 2 is arranged at 120 mm and the thickness of the inner shell 3 is 5 mm.

In the solution according to the invention, the aim is to preferably optimize the damping characteristics of the damping layer 4'as regards both the peripheral vibration and the beam-like vibration. This is considered also when forming possible holes or openings in the damping layer. In this case, a net-like structure is aimed at for the damping layer. The holes, as for their shape and size, are arranged so that the rigidity of the damping layer is the highest precisely in the longitudinal direction of the roll and in the tangential direc- tion of the roll periphery. With this it is possible to maxi- mize the capability of the damping layer to damp vibrations in these directions.

In Figure 1, the rubber mat forming the damping layer 4'is provided with holes 5, which extend through the entire damping layer 4'in this embodiment. The actual purpose of the holes 5 is to reduce the mass of the damping layer. It is remarkable that the mass of the damping material has no significance as regards the damping efficiency itself.

If only one continuous damping element is located in the roll, it should extend essentially over the entire roll length as shown in Figure 1. This provides efficient damping of vibra- tions. In addition, it should be noted that the inner shell 3 is open at the ends and detached from the head components of the roll 1. It is, however, also possible to use two or more

separate damping elements inside one roll, extending over the roll longitudinal direction only for a part of the distance. In this case damping is directed particularly to the peripheral vibration. If several elements are used that extend only for a part of the distance in the longitudinal direction of the roll and that are essentially detached from one another, each ele- ment damps vibration within its specific frequency range. Thus each element can be arranged, if desired, to damp within ex- actly a specific frequency range. Damping will of course, in this case, too, be directed to the beam-like vibration of the roll, but damping is not, however, as efficient. If it desired to achieve efficient damping of the beam-like vibration when using several damping elements inside one roll, the elements must be arranged continuously attached to each other.

In particular, if the material used for the damping layer is polyurethane according to one embodiment of the invention, the damping element can be ready cast to the shell even at the mounting site. It should also be noted that in the arrangement according to the invention the installation of the damping layer and the inner shell inside the roll can be naturally carried out even in completely different stages.

According to another further embodiment of the invention it is also possible to arrange so that instead of a balancing circle that is commonly used in roll balancing, balancing is carried out by arranging the balancing elements to the sides of the damping element/s.

On the other hand, in so called tube rolls balancing is today carried out by means of a polyurethane composition. A polyure- thane composition is cast on the inner surface of the roll shell a quarter of the roll at a time using a net grid. Accord- ing to another further embodiment of the invention, balancing nets and the polyurethane composition could be replaced with

for example two damping elements and locate separate balancing elements in connection with the damping elements.

Figure 3 shows a cross sectional view of roll 1 having two damping elements 13 according to the invention. Both damping elements 13 have the above-mentioned inner shell 3 and the damping structure 4. Here, however, the damping structure 4 is composed of an intermediate structure 8, which is connected to the inner surface 10 of the shell 10 and/or to the outer sur- face 11 of the inner shell 3 by means of damping components 9 made of vibration-damping material. The intermediate structure is used to convert the stresses to shearing forces, which are efficiently damped in the damping components. In the left damping element 13 ring-like damping components 9 and an inter- mediate structure 8 are used. Functionally similar parts are referred to using identical reference numbers. Ring-like compo- nents are easy to manufacture and install. In addition, they provide a good stiffening effect on the roll, but damping is reduced primarily due to the reduced amount of damping material and shearing forces. Damping material can be added by using a longitudinal intermediate structure 8, which is shown on the right in Figure 3. Here the damping elements 13 are arranged at a point, which is essentially at a distance of a quarter of the shell 2 length, from the shell 2 ends. This positioning provides excellent damping against beam-like vibrations with relatively small damping elements. According to the invention, the length of the inner shell 3 is in this case 500-2000, more preferably 1000-1500 mm. A similar damping element can also be used in non-rotating structures, such as doctor beams.

Figure 4a is a sectional view of Figure 3. According to the invention, the intermediate structure 8 is composed of one or more profile components 12. In addition, the profile component 12 comprises at least one part deviating from the radial direc- tion of the roll 1. This construction changes as much as over 90% of stresses caused by the movement differences to shearing

forces. Thus the damping material acts optimally providing good damping. At the same time, thin damping components can be used, which reduces the total mass of the damping arrangement. Ac- cording to the invention, the thickness of the damping compo- nent is 5-30%, more preferably 10-20%, of the distance between the shell and the inner shell.

Figure 4b shows a partial enlargement of Figure 4a. Here damp- ing components of two different thicknesses are used. The outermost damping components are intended primarily for attach- ing the profile component 12 to the inner surface 10 of the shell 2. Instead, the innermost damping components are thick for providing sufficient damping. In addition, the profile component has an inclined section, due to which the stresses caused by the mutual movements of the shells are converted to shearing forces of the damping components. In this embodiment the inclined section forms an angle of 45° in relation to the roll radius. In addition, the thicknesses of the shell and the inner shell are 90 mm and 5 mm respectively. The innermost damping components are 10 mm thick. The damping components are preferably elongated sectors, which are attached to the profile component. On the other hand, the damping components can be for example quadrangular pieces, which are set at suitable inter- vals in the longitudinal direction of the profile component.

Damping components of other forms can also be used.

The inner shell can thus be formed of sheet metal material. In addition, according to the invention only one profile component is used, which is also made of sheet metal material. In this case for example laser cutting or welding can be used, achiev- ing then dimensional and profile accuracy of both the inner shell and the profile component. In the proposed embodiment the thickness of the profile component is 2 mm. Sheet and material thicknesses are dimensioned based on the requirement and the application. In the proposed embodiment longitudinal cells are formed in the roll, in which a medium can be conducted for

adjusting the roll temperature. On the other hand, the medium can for its part act as a damping material.

In the damping structure according to Figures 5a and 5b, com- pared to the solutions illustrated in Figures 4a and 4b there are additionally stiffening rings 16 and tensioning screws 15, each of which is installed in the rib 16'included in the stiffening rings 16. Here, too, an intermediate structure 8 binds the inner shell 3 to the shell 2. Damping components 9 are clenched, glued or screwed to the inner and outer surfaces of the corrugated sheet included in the intermediate structure 8. The damping component is made of elastomer or for example rubber and its layer thickness is approximately 10 mm. The corrugated sheet equipped with damping components is stretched against the outer shell by means of the above-mentioned stiff- ening rings, for example. After this, the corrugated sheet of the intermediate structure 8 is welded together in its longitu- dinal direction.

Next, a blank of the inner shell 3 is brought inside the inter- mediate structure 8, and the blank is stretched at place uti- lizing the stiffening rings 16 and tensioning screws 15 located at the ribs 16'of the stiffening rings 16. The inner shell 3 is also welded to create a continuous form. The tensioning screws 15 are used to tension and center the damping structure in place and the whole construction is kept in place by means of the pretensioning force of the tensioning screws. If de- sired, also glue can be used. This construction allows, for example, circulating water inside the roll. The distance be- tween the stiffening rings is approximately 35% (10%) of the inner shell diameter.

The construction described above provides much better damping than a mere damping layer (Figure 1) both calculatorily and based on practical tests. Generally good damping requires both a successful mechanism and a good damping medium. In this

example case the mechanism can transfer as much as 96% of the roll vibration to shearing forces of elastomer. Rubber, for example, has a good damping capability.

The manufacturing method of the inner shell 3 becomes evident from Figure 6, in which the ends of the blank bent to a cylin- der are equipped with a finger joint. The blank of the inner shell 3 has a cut 18 or a projection 19 at the ends of the periphery, alternating over the seam length. This provides a moderate tolerance for the dimensional accuracy of the blank, when the ends can move in relation to each other unlike in a straight abutment joint. Once the blank of the inner shell 3 is stretched in place, the projections 19 can be welded to the cuts 18 at the opposite end providing thus a seam that binds the ends.

The damping arrangement according to the invention is easy to implement and it can be used in connection with various rolls.

In addition, it is possible to produce a special damping ele- ment, which can be even retrofitted in existing rolls. Further- more, it is possible to utilize the sheet metal technique, which simplifies the manufacture of the damping arrangement according to the invention. Essential, however, is a formation of movement differences between the structures and the conver- sion of stresses caused by them into shearing forces, which are extinguished in the damping material. The roll according to the invention can be used among others as a nip roll, such as a coating roll, calender roll and a king roll of a cutter.

Nipless applications include for example spreading rolls and extraction rolls of a calender.