Shell for a nip roll The present invention relates to a composite shell for a nip roll in a paper/board or finishing or converting machine, comprising a plurality of fiber layers extending lengthwise and/or circumferentially of the shell. The invention relates also to a method for manufacturing a composite shell for a nip roll in a paper/board or finishing or converting machine, comprising a polymeric matrix material and a plurality of fiber layers extending lengthwise and/or circumferentially of the shell. The invention relates further to a method for manufacturing a composite shell (1) for a nip roll in a paper/board or finishing or converting machine, comprising reinforcing fibers and a matrix material of ceramics.

The term composite refers to a structure which comprises reinforcing fibers, e. g. carbon, boric or glass fibers or mixtures thereof, and a matrix material which can be polymeric, ceramic or metallic. The ceramic material comprises various oxides and carbides, such as e. g. Al-, B-, Cr-, Ti-, Si-, Sn-, W-, Zn-, Zr-oxides and- carbides and mixtures thereof, as well as various nitrides, such as e. g. BN and Si3N4.

A composite shell for a nip roll, comprising a plurality of divergent fiber layers, is prior known in the field, e. g. from the patent publication FI 100264. Regarding the prior art composite shells for nip rolls, the strength thereof has been attempted to be enhanced by different orientations of fibers constituting the fiber layers in the axial direction of the roll or in divergent directions along the circumference. One problem in conventional composite shells in connection with nip rolls is the exposure thereof to local bending stresses, resulting in problems in terms of strength. Such a local bending stress may lead e. g. to the peeling of fiber layers which constitute the composite shell. Thus, an object of the present invention is to provide such a nip roll shell which has an increased strength in the depthwise direction in addition to an axial and circumferential strength. In order to achieve this object, a nip roll composite shell of the invention is characterized in that the shell is provided with means, extending at least partially in its depthwise direction

and existing within the shell material and providing a depthwise reinforcement for the shell.

A method of the invention for manufacturing a composite shell for a nip roll, comprising a polymeric matrix material and a plurality of fiber layers extending essentially lengthwise and/or circumferentially of the shell, is characterized in that the fibers used in the method for building the fiber layers are dipped in a resin admixed with short fibers, which in a finished shell provide the shell with an increased depthwise strength. A method according to another aspect of the invention for manufacturing a composite shell for a nip roll in a paper/board or finishing machine, comprising reinforcing fibers and a substantially integral matrix material of ceramics, is in turn characterized in that the method involves first the manufacturing of a three-dimensional fiber structure affording an added depthwise strength and the matrix material is introduced by thermal processes, such as a thermal injection, as a plasma vapour into the fiber structure for producing an integral matrix.

The invention will now be described in more detail with reference to the accompanying drawings, in which: fig. 1 shows a nip roll in a schematic sectional view, and figs. 2-5 show a few exemplary embodiments for a nip roll shell of the invention in cross-sectionally taken schematic partial views.

Fig. 1 depicts one embodiment for a nip roll 10, wherein a stationary central axle 12 is provided with loading shoes 11 loading a shell 1 in the nip direction. The shell is made of a composite material.

Fig. 2 shows in a cross-sectionally taken enlarged partial view a composite shell 1 constructed in a normal fashion from continuous-strand reinforcing fibers 3, e. g. carbon fibers, and a polymeric matrix material, in the manufacture of which the resin used for bonding the reinforcing fibers 3 is admixed with short fibers 2, at

least some of which extend, as far as a finished shell is concerned, depthwise of the shell providing an added depthwise strength for the shell wall. In the manufacture of a composite shell as shown in fig. 2, the fibers 3 used for fabricating the fiber layers are dipped in a resin, e. g. epoxy resin, which is admixed with short fibers, e. g. carbon fibers, whereby, after the resin is set, said short fibers provide an increased depthwise strength for the finished shell.

Fig. 3 shows a cross-sectionally taken enlarged partial view of a nip roll composite shell 1, including lengthwise fibers 5, transverse fibers 3, and rectangularly waving fibers 4, bonding the discussed lengthwise and transverse fibers and building a three-dimensional fiber structure and extending at least principal in the depthwise direction of the wall of the shell 1 (an arrow S).

Figs. 4-5 show a cross-sectionally taken enlarged partial view of a nip roll composite shell 1, including lengthwise fibers 5 and fibers 4, constituting together with the discussed lengthwise fibers a three-dimensional fiber structure and extending in a wavelike or serrated pattern and being placed at least partially in the depthwise direction of the shell 1. The wavelike or serrated fibers 4 provide a finished shell with a strength depthwise of the shell after the setting of a resin or a ceramic material used for bonding the fibers. When using a ceramic matrix, the reinforced fiber structure is first formed e. g. on top of a mould and the matrix is introduced by thermal processes, such as a thermal injection, as a plasma vapour into the fiber structure for producing an integral matrix and resulting in a so-called ceramic composite.

In this application, the term"at least partially depthwise of the shell"refers to the direction which extends through the wall of a shell in the radial direction of a roll, the arrow S in figs. 3-5, or diagonally relative thereto.

The various embodiments for a composite structure described above in reference to figs. 2-5 are also conceivable to be implemented as various combinations thereof, wherein the depthwise dimension of a shell comprises layers of various composite structures. One such combination can be for example a base layer

wound from continuous-strand reinforcing fibers, having its inner and/or outer surface provided with a three-dimensional fiber structure. In addition to the fiber structure, it is also possible to employ various matrix materials in various depthwise locations of a shell, whereby, for example, the layer constituting the inner surface can be provided with a polymeric matrix material and the layer constituting the outer surface with a ceramic material.