Roll of a fiber web machine and method of manufacturing a fiber web machine roll

[001] The invention relates to a fiber web machine roll according to the preamble of patent claim 1 , comprising a body, and the outer surface of the body, the outer surface comprising an functional area providing an functional surface extending relative to the longitudinal axis of the roll from the center area of the roll towards the edges, the outer surface further comprising end surfaces at the edges of the shell.

[002] The invention also relates to a method according to the preamble of patent claim 14 for manufacturing a roll of a fiber web machine where coating material is disposed onto the outer surface of the body to produce a coating over the outer surface from the first end of the coating to the other.

[003] Rolls coated by methods known in the prior art are employed in fiber web machines and fiber web treating apparatus in very different positions. For example calender rolls, such as machine calender rolls with hard surfaces and also soft rolls or corresponding devices of multi-roll calenders may be mentioned as examples of the use. Soft coatings of the rolls are usually made of organic polymers or mixtures those, which often contain also inorganic materials. The soft coatings of rolls often have a composite structure containing layers of different materials.

[004] Multi-roll calenders are composed of a number of rolls disposed one on top of another, the surfaces of the rolls being alternatingly soft and hard. The hard rolls used in typical multi-roll calenders are of metal, usually steel and/or cast iron, and the soft rolls have been filled with paper or fabric, and recently polymer-coater rolls have increasingly been used as soft rolls in multi-nip calenders.

[005] Finnish patent 105939 may be referred to as an example of the prior art, the publication disclosing a roll, the body of which has been relieved in axial direction at the end portions so that the diameter of the body reduces at a certain axial distance towards the ends of the roll. The loading is balanced by providing a thicker coating on the relieved end portions of the body, in other words the thickness of the coating increases at the corresponding axial distance towards the ends of the roll so that the total thickness of the coating increases at the distance mentioned or, in case of a composite roll, the thickness of one coating layer increases at the distance mentioned. Prior art also discloses a calender, the nip of which is formed of two rolls with hard surface, a so-called hard-nip calender. Hard-nip calenders are used to smooth out profile variations of a fiber web such as paper either in aftertreatment or as a so-called on-line process as intermediate calendering for example prior to a surface sizing or coating station. A common feature of hard-nip calenders is that they have a hard nip formed by two rolls.

[006] The material of these rolls is in general cast iron or they may be also of steel. The rolls of hard-nip calenders have also been coated with for example thermal spray coatings. A general problem with hard coatings is the risk of cracks under heavy loading. In most cases the cracking comes up in the end regions of the roll where the nip loading is heavy, among other things due to deflection, and even possible very small misalignments greatly influence the emergence of the problem. The risk of the emergence of cracks increases particularly when hard-coated rolls rotate against each other under load. Then the load may locally exceed the strength of the coating material, and the coating cracks. In the worst case the shear and press tensions in the interface of the coating and the roll shell grow so high that the coating peels off locally. Edge cracking or peeling off of the coating causes in practice stopping of the process which results in production losses and replacing the whole coating which is technically a very challenging task.

[007] In this context, a hard coating means a coating with hardness of 700 - 2000 HV ₀ , ₃ (Vickers hardness testing using the load of a 300 g mass).

[008] The object of the invention is to provide a roll of a fiber web machine according to the preamble of patent claim 1 , comprising a body, and the outer surface of the body, the outer surface comprising an functional area forming an functional surface extending relative to the longitudinal axis of the roll from the center area towards the edges, and the outer surface further comprising at the edges of the shell end surfaces, the risk of cracking of the surface being minimized at the functional area.

[009] This object is achieved mainly by providing at the transition area between the end surfaces and the functional surface a discontinuity zone which minimizes the influence of the tensions of the materials of the end surfaces and the functional surface across the transition area.

[0010] The object of the invention is to provide a method according to the preamble of patent claim 14, according to which a roll of a fiber web machine may be manufactured where the cracking risk of the surface on the functional area is minimized.

[0011] This object is achieved mainly by providing a discontinuity zone in the coating at a distance from the end of the coating.

[0012] According to a preferred embodiment of the invention a coating has been supplied on the outer surface of the roll body and the discontinuity zone is provided in this coating.

[0013] The diameter of the roll is preferably essentially equal in the functional area between the discontinuity zones and at the end surfaces outside the discontinuity zones. Then, while two rolls are in nip contact, the end surfaces

work as areas accepting load whereby the loading of the functional surfaces does not rise excessively high.

[0014] The rest of the additional characteristic features of the invention are disclosed in the appended patent claims.

[0015] Several advantages are obtained with the invention. Compared with the present solutions, one of the most significant advantages provided by the structure according to the invention is a remarkable prolongation of the lifetime of the functional coating and a reduction in unexpected damages. Further, by using a roll according to the invention, particularly with old fiber web machines, no modern quick-opening apparatus for the nip or web break monitoring automatics are required and thus the apparatus remains simple and the investment costs lower.

[0016] The end coating carries the load caused by incorrect alignment. The material of the end coating is stiffer and thus it is not particularly susceptible to cracks. On the other hand, cracking of the end coating does not cause problems as the discontinuity zone between the end coating and the functional coating stops the crack from advancing to the functional coating area.

[0017] The invention and its operation are described in the following with reference to the accompanying schematic drawing of which

Figure 1 illustrates prior art coated rolls in nip contact,

Figure 2 illustrates rolls according to a preferred embodiment of the invention in nip contact,

Figures 3a...3e illustrate various embodiments according to the invention of detail III of figure 2.

[0018] Figure 1 illustrates an approach according to the invention, applied in a roll of a fiber web machine, in nip contact with another, corresponding roll 10.

For clarity of illustration, the figure illustrates only the other ends of the rolls. Roll 10 comprises a body 15 which constitutes the shell of the roll structure, end blocks 20 at both ends of the roll and shaft journals 25 connected to the end blocks. The end blocks have been secured to the roll body which in this case is a cylindrical member and thus the roll is a so-called tube roll. The outer surface 30 of the roll 10 has been provided with a coating 35 arranged in connection with the body 15. Figure 1 illustrates the rolls so that one side of the longitudinal axis illustrates the roll surface and the other side the cross section.

[0019] Figure 1 illustrates the problem situation strongly exaggerated. For example due to the deflection of the rolls the end surfaces 45 at the end regions 40 of the roll coatings of the rolls in nip contact are subjected to very high nip forces and the risk of cracking of the coating is very high. A crack of this kind 50 can proceed unchecked to the functional surface 55, which participates in the treating of the fiber web causing deterioration of the fiber web quality. When this happens the coating is damaged for good and must be replaced.

[0020] Figure 2 illustrates a fiber web machine roll 10 according to a preferred embodiment of the invention in nip contact with another corresponding roll 10, however so that for the clarity of illustration only the other ends of the rolls have been illustrated and it is self-evident that the roll comprises a corresponding end also at its other end. Figure 2 further illustrates the rolls so that one side of the longitudinal axis 65 illustrates the surface of the roll and the other side the cross section.

[0021] The roll 10 according to this embodiment comprises a body 15 constituting the shell of the roll, end blocks 20 at both ends of the roll and shaft journals 25 connected to the end blocks. The end blocks have been secured for example by bolts (not illustrated) to the body 15, which here is a cylindrical member and thus the roll is a so-called tube roll. Naturally the invention may

be applied also in other types of rolls. The outer surface 30 of the roll comprises a functional surface 55 extending in relation to the longitudinal axis of the roll from the center area towards the edges, arranged in connection with the body 15 and comprising also a functional area 60 of the functional surface 55. Further, the outer surface 30 of the body comprises end surfaces 45 at the edges of the shell, outside the functional area, the surfaces extending outside the functional area towards the end blocks and forming the end areas 40 of the outer surface 30.

[0022] In the embodiment of figure 2, the functional surface and the end surfaces comprise a coating. The thickness of the coating is typically 50 - 500 μm. The outer surface 30 formed by the coating 35 in the embodiment of figure 2 extends over the functional surface 55 and the functional area 60, forming also the end surfaces 45 at the edges of the coatings, on the end areas 40. There is a discontinuity zone 75 arranged in the transition area 70 in the coating 35 between the end surfaces 45 and the functional surface 55. In this embodiment the discontinuity zone has been produced by continuing the coating 35 of the functional area 60, or extending it, over the transition area to the end areas 40 thus forming end surfaces 45, and after that thinning down the coating 35 locally for example by grinding thus forming a recess 80 in the coating 35. The form profile of the thinned-down zone can naturally vary. In this way the discontinuity zone in the roll surface minimizes the influence of the tensions of the materials of the end surfaces 45 and the functional surface 55 across the transition area. This has the effect that the possibility of proceeding of a crack potentially arising in the coating 35 forming the end surface to the coating 35 of the functional area 60 is minimized, even eliminated.

[0023] Different types of coatings are preferably used in the functional area 60 and the end area 40. A particularly suitable coating in the end area is for example a weld coating. The transition between the coatings is arranged in the transition area 70.

[0024] The invention is particularly suitable for use in a roll of a hard nip calendar, in other words the roll is coated with a hard coating. In the actual functional area 60 the functional coating is preferably for example a cermet coating, such as WC-Co-Cr or some other ceramic material coating. In practice the fiber web is located and/or runs in the functional area 60.

[0025] The end surfaces 45 and the functional surfaces 55 of the coating 35 have cross sections of equals diameter whereby the end surfaces work during the nip contact of the rolls as supporting areas and consequently the load of the functional surfaces cannot rise excessively high. In other words the diameter of the roll 10 is in the area of the end surfaces 45 essentially equal to that in the area of the functional surfaces.

[0026] . Figure 3f illustrates the detail III of Figure 2 modified according to a preferred embodiment of the invention. In this embodiment the coatings 35' of the end surfaces 45 have been manufactured of a material different from the material of the coating 35 of the functional surface 55. The end surfaces 45 have then preferably been produced of a material manufactured by means of weld coating or laser coating, the material being stiffer than the material of the functional surface, and having at least partly a metallurgic bond with the material of the body 15 of the roll itself. The coating material of the end surfaces 45 may also be cermet material, having a larger share of metal than ceramic material.

[0027] In the embodiment illustrated in figure 3f the discontinuity zone 75 has been carried out according to the embodiment of figure 2 so that the coating 35 of the functional surface 55 and the coatings 35' of the end surfaces are manufactured on the body separately and the discontinuity zone 75 is produced for example by grinding the coatings 35' and 35 for example locally by forming a recess 80 in the coatings, or by providing already in the coating stage a suitable recess between the coatings. In this way the discontinuity zone in the surface of the roll minimizes the influence of tensions of the materials of the

end coatings 45 and functional surface 55 across the transition area. The discontinuity zone 75 may be ground also much narrower than illustrated in Figure 3f.

[0028] Figure 3e illustrates the detail III of figure 2 modified according to another preferred embodiment of the invention. Also here the coatings 35' of the end surfaces 45 are of different material than those of the coatings 35 of the functional surface 55 but the coating 35 of the functional surface 55 , i.e. the hard coating is supplied on top of the coating 35' of the end surfaces. In this embodiment the bonding strength of the coating 35 of the functional surface 55 to the base material, in this case to the coating 35' of the end surfaces 45 in the area of the end coatings must not be so strong that a crack can proceed from the end coating to the functional surface 55, in other words to the functional area 60.

[0029] In the embodiment of figure 3a the discontinuity zone 75 has been carried out so that the coatings 35' of the end surfaces 45 are of different material than the material of the coating 35 of the functional surface 55. After the coating, the coatings 35', 35 have been thinned out with a very narrow blade locally thus forming a slot-like recess 80 in the coating 35. In this way the discontinuity zone in the surface of the roll minimizes the influence of the tensions of the materials of the end surfaces 45 and the functional surface 55 across the transition area.

[0030] In the embodiment of figure 3b the discontinuity zone 75 has been carried out so that, prior to coating, a narrow protecting piece 80' has been provided in the roll body 15 around the shell surface in the transition area 70. Subsequent to the coating process, the protecting piece 80' is removed whereby a discontinuity zone 75 has been created in the transition area.

[0031] In the embodiment of figure 3c the discontinuity zone 75 has been provided so that the coating 35 of the functional surface 55 continues or is

arranged to extend to the transition area and the end area is formed by a radial projection 15' of the roll body 15 extending around the entire shell. The coating is essentially at the same level with the surface of the end area. In this way the discontinuity zone in the roll surface between the projection 15' and the coating 35 of the functional surface minimizes the influence of the tensions of the materials of the end surfaces 45 and the functional surface 55 across the transition area.

[0032] In the embodiment of figure 3d the discontinuity zone 75 has been carried out so that the coating 35 of the functional surface 60 continues or has been arranged to extend over the transition area to end areas 40 thus forming end surfaces 45 but there is a radial projection 15" in the roll body extending around the entire shell, the height of the projection from the surface of the body preferably being equal to the thickness of the coating 35 to be applied. In this way there is no coating at the projection 15" in the roll in operating condition.

This forms a discontinuity zone in the surface of the roll and minimizes the influence of the tensions of materials of the end surfaces 45 and the functional surface 55 across the transition area. It is clear that the cross section of the projection may differ from the rectangle illustrated in figure 3d, it may be for example a chamfered projection.

[0033] It must be understood that only a few preferred embodiments of the invention have been described above. Thus it is evident that the invention is not limited to the embodiments presented but it may be modified in many ways within the scope of protection defined by the appended patent claims. The invention may be applied in rolls in different positions in a fiber web machine where hard-surfaced rolls are needed, such as presses. Different features described in connection with the various embodiment of the invention may be utilized within the principle of the invention in the other embodiments presented and/or different entities may be combined from the features presented if desirable and the technical prospects are there.