EP2398961A1

EP2398961A1 - Arrangement for dampening vibration in a fiber web machine

Info

Publication number: EP2398961A1
Application number: EP10743442A
Authority: EP
Inventors: Tommi Korolainen; Seppo Kupiainen; Arto Puranen
Original assignee: Metso Paper Oy
Current assignee: Valmet Technologies Oy
Priority date: 2009-02-20
Filing date: 2010-02-11
Publication date: 2011-12-28
Also published as: FI121276B; FI20095165A0; FI20095165A7; EP2398961A4; WO2010094834A1

Abstract

The invention relates to an arrangement for dampening vibration in a fiber web machine, the arrangement including two rolls (10, 11) adapted in a nip contact. The shafts (12, 13) of the rolls (10, 11) are supported with support means (14, 15). The arrangement includes force elements (16) adapted to influence the shaft (12) at a distance from the support means (14) for dampening vibrations of the rolls (10, 11). The force elements (16) are arranged between the shafts (12,13) of the opposite rolls (10, 11) or between the shaft (12) of the first roll (10) and the support means (15) of the second roll (11).

Description

ARRANGEMENT FOR DAMPENING VIBRATION IN A FIBER WEB MACHINE

The invention relates to an arrangement for dampening vibration in a fiber web machine, including two rolls adapted in a nip contact with the shafts thereof being supported with support means, and with the arrangement including force elements adapted to influence a shaft at a distance from the support means for dampening roll vibration.

In fiber web machines, pairs of rolls adapted in a nip contact are used for processing the fiber web. Such roll pairs exist at the press, size press and reel, for example. Vibration often occur in the roll pairs causing crushing in the fiber web, clothing and/or roll cover. Crushing restricts the operating speed of a fiber web machine as well as reduces the service life of clothing and a roll cover. The quality of the end product also decreases. Crushing of the end product is concerned when variation of gloss or opacity or other inhomogenei- ty is visually detectable in the end product.

A roll pair composed of a deflection-compensated roll and a coated counter roll set in a nip contact is sensitive to vibrations. Vibrations are caused, for example, by roll inaccuracies, deforming of the roll cover during use, and thickness variations in the fiber web or clothing traveling via the nip. Prolonged vibration further intensifies deformation, particularly that of the cover and the clothing, causing self-excited vibration. As regards crushing, the worst form of vibration is such in which the rolls vibrate in opposite phases in the nip direction. Then the deformation of the fiber web, roll cover and the clothing is the strongest. At the same time, the mechanical stress subjected to the roll pair increases and noise problems also appear. The vibration in the nip direction is referred to as nip vibration. EP patent No. 1333122 discloses an arrangement for dampening vibrations of a roll pair. It is proposed that dampening is provided by subjecting the static shaft of one of the rolls to a force that is in the opposite phase relative to the movement of this shaft by means of a force element. The force is applied to a distance from the support means of the roll. The effects of the proposed arrangement are, however, insufficient for most roll pairs. That is, the dampening effect is low. In addition, extra stresses are caused to the roll pair and its environment by the force. The adjustment and use of the arrangement are also difficult.

The object of the invention is to provide a novel arrangement in a fiber web machine for dampening vibration, the arrangement being simpler in design than previously but more versatile and efficient than before for its operation. The characteristic features of this invention are that force elements are arranged between the shafts of the opposite rolls or between the shaft of the first roll and the support means of the second roll. In other words, roll pairs are connected together as a functional entity, the vibrations of which can be efficiently dampened without causing extra stresses to surrounding constructions. The assembly of the arrangement can be formed of various components according to the specific dampening requirement. Further- more, various functions can be included in the arrangement to be able to prevent problems in advance or at least mitigate their effects.

The invention is described below in detail by making reference to the enclosed drawings which illustrate some of the embodiments of the invention, in which

Figure Ia shows a first embodiment of an arrangement according to the invention, Figure Ib is a principle diagram showing deformations and forces caused by the vibrations of an arrangement according to the invention without dampening,

Figure Ic shows forces opposite to those of Figure Ib without dampening,

Figure 2a shows a second embodiment of an arrangement according to the invention,

Figure 2b shows a third embodiment of an arrangement according to the invention.

Figure Ia shows an arrangement according to the invention seen in the machine direction. The arrangement is meant for dampening vibrations in a fiber web machine. Fiber web machines include paper and board machines, for example. In the applica- tion examples, two rolls 10 and 11, adapted in a nip contact relative to each other, are examined. A fiber web that is led through the thus forming nip deforms due to the effect of the nip load (not shown) . In addition, at the press, for example, one or even two fabrics travel through the nip. In a soft calender, for example, only one fiber web travels through the nip. In a soft calender, the top roll 11 is a thermoroll, for example, and the bottom roll 10 is a deflection-compensated roll. The shafts 12 and 13 of both rolls 10 and 11 are supported with support means 14 and 15. The construction of the support means is described in more detail later. In addition, the arrangement includes force elements 16 that are adapted to influence the shaft 12 at a distance from the support means 14 for dampening vibrations of the rolls 10 and 11.

N According to the invention, the force elements 16 are arranged between the shafts 12 and 13 of the opposite rolls 10 and 11 or between the shaft 12 of the first roll 10 and the support means 15 of the second roll 11. Regardless of the embodiment, the force element thus joins the rolls as a functional entity, the vibration of which can be dampened better than before. In addition, the use and adjustment of the force element are easier and more accurate than previously. The force element can also be locate'd more freely than before and its construction can be selected from several alternatives. The force element is connected to the shaft or the support means with any suitable method. Advantageously, clearance-free links and rigid support arms are used.

At the simplest, the force elements are arranged as passive damping elements. That is, the damping elements resist the movement of the shaft/shafts dampening in this way their vibration and reducing thus the amplitude of vibration. The nip vibration dampens at the same time. Most commonly the two rolls are adapted vertically on top of each other. That is, the shafts are located in a vertical line. In this case the so called nip vibration causes deflection of the shafts in such a way that as the center parts of the shafts 12 and 13 separate from each other, the ends of the shafts 12 and 13 approach each other. The principle of this is illustrated in Figure Ib. An opposite movement is seen in Figure Ic showing that as the center parts of the shafts 12 and 13 approach each other, the ends of the shafts 12 and 13 separate from each other. Figures Ib and Ic show the principles of the support points relative to which the shafts 10 and 11 bend. An advantageous location for the damping element is particularly at the shaft ends whereby the portion of the free end of both shafts creates a lever arm relative to the turning point of the support means. Particularly in an embodiment in which the damping element is adapted in contact with both shafts, efficient dampening is achieved since the shaft ends move a maximum distance to the opposite directions. Thus the damping element is subjected to the movements of both shafts which can be simultaneously dampened. In the embodiment of Figure Ia, both rolls 10 and 11 are provided with static shafts 12 and 13 around which a roll shell 17 and 18 is mounted with bearings. In a passive damping element, the force resisting the shaft movement is, for example, friction or shearing force of an elastic material. In both cases the kinetic energy converts mainly to heat. Regardless of passivity, the resistance of the damping element can be adjustable. The damping element according to the invention works well particularly toward nip vibration because the shaft ends then move in the opposite phases as well. Then the relative movement is the greatest at the damping element. In practice, the greater this relative movement is, the better the damping element functions. Examples of damping elements include a hydraulic shock absorber, a mag- neto-rheological hydraulic or elastomeric damper, a friction damper, a viscoelastic damper or a squeeze film damper.

Instead of passive damping elements, semi-active damping elements can be used for changing periodically the natural frequency of a roll system composed of rolls. In practice, the above listed damping elements can be used semi-actively as well. In semi-active use, the damping element is used to change the natural frequency of the arrangement whereby the self-excited vibration dampens or its generation is completely prevented. In other words, the rigidity of a semi-active damping element is varied whereby the natural frequency of the whole arrangement changes, which stops the development of self-excited vibration. In practice, the use of the same oper^¬ ating parameters causes crushing, the elimination of which has been attempted by changing the operating speed or the nip load, for example. However, changes in the operating parameters affect significantly the production itself, which further brings new problems. A semi-active damping element according to the invention allows changing the natural frequency without changing the operating parameters. In practice, the damping element changes the rigidity of the arrangement, which then influences the natural frequency. The changing interval of the natural frequency is determined specifically for each case and the change is performed according to a programmed schedule or when required. For example, when nip vibrations appear, the natural frequency of the arrangement is first changed to avoid problems . In case nip vibration continues in spite of the change, other measures are taken for dampening the vibration. One repair alternative is to recondition or renew the roll cover.

A third method according to the invention to dampen vibrations is to use active damping elements. In practice this means actuators that actively resist the movement of the shafts for dampening their vibrations. The resisting force is applied to the shafts in phases that are opposite relative to the shaft movements. An active damping element thus provides force variation at the frequency of harmful nip vibration but in the opposite phase. Then the force variation resists harmful vibration and reduces it. An active damping element may also have passive and/or semi-active functions in which case suitable dampening can be provided for each condition. Especially an active damping element requires continuous control, which is based on the actual vibrations of the arrangement. Figure Ia shows the principle of a control system 19 having sensor assemblies 20 in the roll 11, the shaft 13, and the bearing assembly 22. The force element 16 is then controlled based on vibrations detected by the sensor assembly. A corresponding sensor assem- bly is provided in the other roll as well (not shown) . The location and the number of sensors can vary. The control system can be independent or it is a part of the machine control system. A corresponding control system can be used with passive and semi-active damping elements as well. In practice, an active damping element is any actuator, the movement of which is advantageously linear.

Advantageous application methods and locations of force elements were described above. In addition to external installa- tion, internal installation can be used. Then the force element is located between the roll shell and the support means. Exter- nal and internal installations can also be used simultaneously. In this case it is possible to use different damping elements in such a way, for example, that passive damping elements are installed externally and active damping elements are installed 5 internally. In addition, the force elements are advantageously arranged in the vicinity of both roll ends, which allows achieving maximum and above all uniformly distributed dampening.

Figure 2b shows an arrangement in which the shafts 12 and 13 of

10 both rolls 10 and 11 are static and the shafts 12 and 13 are provided with roll shells 17 and 18 mounted with bearings. In addition, the support means of the rolls 10 and 11 are bearing assemblies 21 and 22 that are arranged rigidly in contact with each other. Then the bearing assemblies 21 and 22 allow bending

15 of the shafts 12 and 13. A rigid mutual connection of the bearing assemblies contributes to the dampening according to the invention and reduces vibrations of the arrangement. In other words, the arrangement is an integral whole which is independent of the rigidity of surrounding constructions. In

20 this way, transmission of external vibrations to the roll pair and vice versa is avoided. In addition, the shaft movements are accurately conveyed to the force elements. On the other hand, a pivoting mechanism 23 permitting the movements of the shafts 12 and 13 can also be arranged between the support means 14 and

25 15 of the rolls 10 and 11 (Figure Ia) .

In Figure 2a, the bottom roll 10 is a deflection-compensated roll provided with a static shaft 12 and a roll shell 17 mounted with bearings on the shaft. The shaft 13 of the top roll 11

30 is supported rotatably. In this case, according to the invention, an auxiliary bearing assembly 24 is arranged for the shaft 13 that is adapted to rotate, for connecting a force element 16. In other words, the auxiliary bearing assembly 24 allows the rotation of the shaft 13 while simultaneously con-

35 veying the dampening force of the force element. Here the force elements are additionally supported to the support means 14 of the opposite roll 10. In this case, too, the arrangement is kept as one single entity.

The embodiments of Figures Ia and 2a are dimensioned specifi- 5 cally for the dampening according to the invention. That is, the shafts are unnecessarily long. An arrangement according to the invention can also be provided in existing roll pairs. In the embodiment of Figure 2b, the arrangement includes two overhanging shafts 25 adapted as an extension for both shafts 10 12 and 13. In the embodiment according to Figure 2a, the overhanging shaft would be an extension for one shaft only. A one-sided force element installation may be necessary to use in such conditions, for example, where the roll drive equipment is located immediately as an extension to the shafts.

Claims

1. Arrangement for dampening vibration in a fiber web machine, the arrangement including two rolls (10, 11) adapted in a nip contact, with the shafts (12, 13) thereof being supported with support means (14, 15), and the arrangement including force elements (16) adapted to influence the shaft (12) at a distance from the support means (14) for dampening vibration of the rolls (10, 11), characterized in that the force elements (16) are arranged between the shafts (12, 13) of the opposite rolls (10, 11) or between the shaft (12) of the first roll (10) and the support means (15) of the second roll (11) .

2. Arrangement according to claim 1, characterized in that the force elements (16) are arranged as passive damping elements .

3. Arrangement according to claim 1, characterized in that the force elements (16) are arranged as semi-active damp- ing elements for changing periodically the natural frequency of a roll system composed of the rolls (10, 11) .

4. Arrangement according to claim 1, characterized in that the force elements (16) are arranged as active damping elements.

5. Arrangement according to any of claims 1 - 4, charac^¬ terized in that the support means of the rolls (10, 11) are bearing assemblies (21, 22) that are arranged rigidly in con- tact with each other.

6. Arrangement according to any of claims 1 - 4, characterized in that a pivoting mechanism (23) is arranged between the support means (14, 15) of the rolls (10, 11) .

7. Arrangement according to any of claims 1 - 6, characterized in that the force elements (16) are arranged in the vicinity of both ends of the rolls (10, 11) .

5 8. Arrangement according to any of claims 1 - 7, characterized in that the arrangement includes one or more overhanging shafts (25) adapted as an extension of either one or both of the rolls (12, 13) .

10 9. Arrangement according to any of claims 1 - 8, characterized in that the shafts (12, 13) of both rolls (10, 11) are static and roll shells (17, 18) are mounted with bearings on the shafts (12, 13) .

15 10. Arrangement according to any of claims 1 - 8, charac^¬ terized in that the shaft (12, 13) of at least one roll (10, 11) is supported rotatably.

11. Arrangement according to claim 10, characterized in

20 that an auxiliary bearing assembly (24) is arranged for the shaft (12, 13) that is adapted to rotate, for fastening a force element (16) .