WO2010003460A1

WO2010003460A1 - A roll for a fiber web machine and a method for manufacturing the roll

Info

Publication number: WO2010003460A1
Application number: PCT/EP2008/059011
Authority: WO
Inventors: Hugues Serain
Original assignee: Metso Paper, Inc.
Priority date: 2008-07-10
Filing date: 2008-07-10
Publication date: 2010-01-14

Abstract

The invention relates to a rollfor a fiber web machine, comprising a roll body (10), a cover (11), andan elastomer (15) positioned only partially between thecover (11) and theroll body (10).The roll is manufacturedby applying an uncured orcured elastomer (15) on only a part of a roll body (10), applying an uncured cove r(11) on at least a part of theroll body (10), wherein theuncured cover (11) covers at least a part of theelastomer (15) and covers at least a part of theroll body (10) that is not covered by theelastomer (15), and curing the uncured cover (11) and, if applicable, the elastomer (15).

Description

A roll for a fiber web machine and a method for manufacturing the roll

Field of the Invention The present invention relates to a roll for a fiber web machine, and more particularly to a roll used in paper production. The present invention also relates to a method for manufacturing a roll for a fiber web machine.

Background of the Invention

In the paper and board industry rolls are widely used.

The surface of a roll body is not always a suitable material for the desired application, so that covers for roll bodies have been developed. Typically, roll bodies (10) used in paper making are covered with a cover (11) to provide optimal surface properties for transport or treatment of the paper web (12) as shown in Fig. 1. Also, combinations of covers with further materials (hereinafter denoted as covering) specifically matched to the desired application are in use. This results in a great variety of coverings with distinct features satisfying the specific performance demands .

Examples for the demands made on coverings are improved release properties of the transported material, improved resistance of the roll towards corrosives or other aggressive substances, and specific drying or heating properties. Therefore, by the use of roll coverings, the properties of such a roll can be adjusted without replacing the potentially highly expensive roll body. Currently, rolls having covers of plastics, elastomers, like rubbers, and composite materials are in use, for example in calenders, size process, press rolls, etc. Composite covers made of epoxy resin and fiber web are disclosed in the United States Patent Application Publication US 2002189749 Al.

Multilayer covers including a rubber base layer, a rubber top stock layer and a polyurethane coating are known from the European Patent Application EP 1783270 Al. These covers provide soft covers having a surface of polyurethane.

Summary of the Invention The object of the present invention is to provide an improved roll for a fiber web machine and in particular an improved covering for a roll body and an improved manufacturing method.

The object of the invention is achieved by a roll for a fiber web machine according to claim 1, and a manufacturing method according to claim 28. Particular embodiments of the invention are set forth in the subclaims.

As a result of the inventors studies it was found, that when covers are trimmed to size before use (13), as shown in Fig. 2, very often de-bonding (14) of their edges (axial ends) occurs. Before trimming, the cover (11) usually extends 200 to 400 mm over the finish edges of the cover (the axial ends when the cover is ready for use) . When the trimming to size is effected, at this position the internal stresses are released, and de-bonding (14) shows up. De- bonding is often caused by a mismatch in thermal expansion properties of the roll body and the cover material, resulting in residual stress. This residual stress can also be caused by shrinkage due to the cross-linking of the polymer.

The de-bonding problem can arise for many different types of roll covers, especially for roll that are heavily loaded against another roll. According to a first aspect of the invention, there is provided a roll for a fiber web machine, comprising a roll body, a cover, and an elastomer positioned only partially between said cover and said roll body, i.e. where the elastomer does not form a continuous layer between the roll body and the cover. Due to this technical solution, the de- bonding of the cover can at least be significantly reduced.

The covering according to the invention can be further improved by the following embodiments. In an embodiment of the first aspect of the invention thermoset elastomers, preferably chlorosulfonate-based (CSM) , based on chlorinated polyethylene (CPE) or acrylonitrile-based, such as acrylonitrile rubber (NBR) or hydrogenated NBR (HNBR) or differently modified NBR (XNBR) are especially preferable in the invention, as they can bear high temperatures without deteriorating. This is especially important for a preferred production method according to the present invention.

The elastomer may also be a thermoplastic elastomer, preferably based on thermoplastic polyurethane, styrene butadiene styrene and/or polyolefin. In the production process, a thermoplastic elastomer is advantageous as it can be easily applied to the roll body.

A polyurethane composition, preferably a polyurethane composition originating from a pre-polymer with isocyanate terminations, polyol, and optional reaction accelerators or processing aids can also be used as said elastomer. A combination of the mentioned elastomer materials may also be employed. In order to obtain a desired hardness and other properties, the elastomer may comprise reinforcing fillers, such as carbon black and/or silica, preferably in an amount of 5 to 100 parts by weight per 100 parts of a base elastomer. In case silica is used, the addition of such products as silane improves the bonding and dispersion of the fillers (usually fibers) in the elastomer. The elastomer should have a hardness ranging from 25 to 100 Shore A, preferably from 50 to 98 Shore A, and more preferably about 95 Shore A or 20 P&J (Pushey Jones) . A hard elastomer is less deformable by the pressures that arise when the covering is in use, e.g. in a calender. Thus, the stresses originating from deformation of the elastomer are minimized. Although the elastomer is not limited to a certain distribution pattern on the roll body, it is preferably provided in strips around said roll body. Strips can be easily applied to the roll body in the production process, and as the strips of the elastomer provide an effective barrier (in an axial direction) , they can prevent moisture from reaching regions beyond the strip. These strips preferably have an axial size of 10 to 300 mm, usually 75 mm in the production process and are trimmed to about half of their size in the final covering of a preferred embodiment.

It is preferable that the elastomer is positioned at the axial ends of the cover i.e. at the places where the highest stresses in the cover occur. In combination, elastomer strips positioned at the axial ends of the cover provide superior prevention of de-bonding and degrading of the cover. Usually, the elastomer will not extend to the areas of the roll which are in contact with e.g. the paper web .

The elastomer may extend beyond the axial ends of the cover. This ensures that the very axial ends of the cover are bonded to the elastomer and, thus, to the roll body. In this case, the cover is highly protected from de-bonding and moisture under the cover. It is also preferable that the elastomer is adhered to the roll body and/or the cover by one or more adhesives. These adhesives are preferably selected from the group consisting of phenolic resins, melamine-based resins, formol-based resins, urea-based resins, polyepoxide resins, reinforced polyester resins, polypropylene resins, polycarbonate resins, polyurethane resins, cyanacrylic resins, and chloroprene styrene butadiene resins. The adhesives improve the bonding of the elastomer to the roll body, the cover and/or further layers.

Also a tack promoter can be provided between the roll body and said elastomer, further improving the bonding especially during production.

A primer adhesive provided directly on the roll body is especially preferable, as it can further improve the bonding of the elastomer to the roll body. The primer is designed for good bonding to the roll body and to the elastomer. If an adhesive is used in combination with a primer, the primer is designed for superior bonding to the roll body, while the overlaying adhesive is designed for superior bonding to the elastomer. The primer and the overlaying adhesive usually show very good bonding to each other, thus resulting in an improved bonding of elastomer and roll body. A highly preferable option is that the curing (cross- linking) system of the elastomer is compatible with the curing system of the cover. Especially when curing the two materials together (at the same time) , superior adhesion is achieved, as cross-linking between the elastomer and the cover is possible. In this context, a cross-linking system of the elastomer is preferably based on a metallic oxide and/or peroxide system. Also, it is preferable that the respective curing systems work at similar temperatures. When using thermoplastic elastomers, the curing temperature of the cover material should at least be 20 ⁰C less than a melting temperature of the elastomer, so that the elastomer does not deteriorate or lose its shape during the curing of the cover in a preferred production process.

For further improving the bonding of the roll body to overlaying materials, it is desirable that the roll body has a surface roughness Ra of at least 2 μm, preferably of from 10 to 15 μm, and a surface roughness Rz of at least 10 μm.

In an especially preferred embodiment of the present invention, the cover is a plastic cover, preferably a composite cover comprising a polymer matrix and reinforcing fibers, said polymer matrix preferably comprising an epoxy resin. Plastic covers, especially composite covers are preferred as they provide easily adjustable surface properties, ranging from improved release properties of the paper to longer durability as well as better chemical and mechanical resistance. Furthermore, the effect of edge lifting is most severe for composite covers, so that the application of the present invention is highly beneficial for this kind of covers.

The cross-linking system of such a cover can be anhydride based or preferably amine-based, such as multifunctional cycloaliphatic, aromatic and/or aliphatic amines. The curing temperature of the cover preferably ranges from 90 to 220 ⁰C, more preferably from 120 to 160 ⁰C. Low and medium curing temperatures are preferred as the elastomer should not be deteriorated during the curing process of the cover.

The cover preferably has a hardness ranging from 80 to 96 Shore D. Also, a glass transition temperature (Tg) from 80⁰C to 250⁰C is preferred. This provides optimal properties for paper making, especially when used in a calender .

In a preferred embodiment, the cover is made of bisphenol A or bisphenol F having a chemical functionality of 2 or more. Optionally tri-functional or tetra-functional resins may be additionally used. The bisphenol provides low viscosity at 15 to 80⁰C, while the multi-functional resins increase the Tg of the cover. Optional fillers, such as silica, silicon carbide, alumina and/or calcium carbonate increase the dimensional stability and/or adjust the heat expansion properties of the cover. Among others, compositions including Nanosilica (company Nanoresin) can also be used as the silica filler. The cover is not necessarily made of a single material or composite material layer. Especially a cover having a multilayer structure can be advantageous. Usually, composite covers, i.e. covers having at least one composite layer, comprise reinforcing layers and external layers. A combination of multiple layers allows optimization of the cover properties to the respective application. It is preferable that the cover comprises at least one reinforcing layer to provide a high stability. The reinforcing layers are typically close to the roll body. Also, it is possible that a composite cover comprises an external layer of a different polymer. An external layer of e.g. thermoset polyurethane can be beneficial for use on a drilled suction press roll, a blind hole pressing roll or a grooved pressing roll. Composite covers topped by a polyurethane cover, which can be seen as a further layer of a composite-based cover, provide high stability in combination with a smooth surface.

The composite cover comprises fiber reinforcement in the polymer matrix. Reinforcing fibers are preferably provided as continuous fibers wound on the roll body or as a woven or non-woven fiber mat. Such fibers are usually contained in reinforcing layers. Therefore, it is especially preferable that reinforcing fibers have a high specific modulus and high dimensional stability. The fibers may be glass fibers (glass E fibers) , carbon fibers, such as stretched and pyrolized carbon fibers, aramid fibers, para- aramid fibers, polyethylene fibers, polypropylene fibers, basalt fibers and/or silicium fibers. The fibers can also serve to adjust the properties of the cover, e.g. surface properties or chemical resistance. Furthermore, fibers that are capable of absorbing a high, or, in contrast a very low amount of moisture, or fibers having hydrophilic surface properties can be used to adjust the properties (mainly the surface properties) of the cover. Typical fibers used for reinforcing the cover are thermally stable high modulus filaments and/or multifilaments that can be parallel

(roving) or intermeshed (fabrics, leno weaved fabrics, warp knitting or malimo) . Therefore, it is preferable that the fibers are included in the resin as filaments, multifilaments and/or textile combinations of these. Especially the textile combinations are easily applied to the roll body, resulting in effective production.

The fibers may also be included in the resin as fillers, such as organic or mineral very small fibers having a length of 1 to 10 μm, called whiskers or chopped fibers having a length of 10 to 2000 μm. Those fibers usually serve to adjust the surface properties of the cover, as also described for the above reinforcing fibers.

According to a second aspect of the invention, there is provided a method for manufacturing a covering for a roll body, comprising the steps of applying an uncured or cured elastomer on only part of a roll body, applying an uncured cover on at least part of said roll body, wherein said uncured cover covers at least part of said elastomer, and curing the uncured cover and, if applicable, the elastomer. The method according to the second aspect of the present invention can be further improved by the following embodiments .

Thermoset elastomers, preferably chlorosulfonate-based (CSM) , based on chlorinated polyethylene (CPE) or acrylonitrile-based, such as acrylonitrile rubber (NBR) or hydrogenated NBR (HNBR) or differently modified NBR (XNBR) are especially preferable as the elastomer of the invention, as they can bear the high temperatures required for the curing of the cover.

The elastomer may also be a thermoplastic elastomer, preferably based on thermoplastic polyurethane, styrene butadiene styrene and/or polyolefin.

A polyurethane composition, preferably a polyurethane composition originating from a pre-polymer with isocyanate terminations, polyol, and optionally reaction accelerators or processing aids can also be used as said elastomer.

The elastomers may also comprise reinforcing fillers, such as carbon black and/or silica, preferably in an amount of 5 to 100 parts by weight per 100 parts of a base elastomer. The fillers can provide a desired hardness of the elastomer .

In the method, the elastomer is preferably provided in strips around the roll body, as strips can be easily produced and applied using usual techniques.

According to an embodiment of the second aspect, the uncured elastomer is extruded on said roll body as a strip, thus simplifying the production. It is also possible that the elastomer is formed by cutting a calendered stock sheet.

In case an uncured elastomer is used, it is preferable that it comprises methacrylate, preferably in an amount of 5 to 50 parts by weight per 100 parts of a base elastomer. The methacrylate can be used to adjust the hardness of the elastomer. Especially, when an acrylonitrile-based rubber is used as said elastomer, its hardness is preferably adjusted using methacrylate, and the curing process of the elastomer is preferably based on peroxide.

In a further embodiment of the invention, it is preferred that the elastomer is of thermoset polyurethane which is applied to the roll by a rotational casting process. This enables an easy and uniform application of the elastomer. The elastomer can be applied by means of a pressing wheel to equally distribute the elastomer. It may also be desirable that the elastomer is kept in position by a mechanical system, such as an adhesive tape or string. This is especially relevant if the elastomer is not capable of binding firmly to the roll body at any stage of the production process.

Sand blasting said roll body as a first step to yield a surface roughness as defined above is a good option. Furthermore, applying a primer on said roll body before applying said elastomer can improve bonding. Applying an adhesive on said roll body before applying said elastomer is also beneficial for bonding. If a primer and an adhesive are used, applying the adhesive on the primer before applying the elastomer is a reasonable procedure. Finally, applying an adhesive on said elastomer before applying said uncured cover may improve the bonding of the cover to the elastomer .

The mechanical fixing may be removed after the adhesive or primer provides a sufficient fixing of the elastomer, as it is no longer required in this case.

To simplify the application of the adhesive materials, said primer and/or said adhesive may be diluted in a solvent or solvent mixture prior to application, the dilution having a solid content preferably ranging from 10 to 80 % by weight.

As a matter of course, a solvent mixture is also possible. The dilution can be applied using a paintbrush, a roller or a spray gun, depending on the viscosity. In order to prevent undesirable effects, the solvent should be evaporated usually for 10 to 120 minutes before a further layer is applied.

The covering is usually laid down wider in axial size than it is required in final use to ensure a homogeneous surface of the cover/covering at the positions where it is intended to be in contact with the handled material, e.g. the paper web. In this case it is preferable to imply a further step of trimming the covering to size after curing, or possibly after gelation. The surface of the covering needs to show a homogeneous structure because unevenness, e.g. a pattern in the covering, could create defects on the paper. For this reason, the fiber substrate of an external layer of a composite cover is preferably not made of fabric, knitted textile or roving. Non-woven fabrics such as spun-bond non- woven and also wet-bond non-woven fabrics are usually used for the external layers.

Although the roll body is usually made of metal, plastic roll bodies, especially composite roll bodies, can be used, as well.

After the cover has been cured, it can further be treated mechanically and/or chemically to obtain the final surface properties. A mechanical treatment can be a lathe and/or grinding method. The final thickness of a cover is usually 5 to 30 mm.

The cover can be produced by wetting a fiber strip with an uncured resin, resulting in a resin impregnated substrate layer, and wrapping said wetted fiber strip around the roll body. Alternatively, the fiber strip may first be wrapped around said roll body and then wetted or not wetted at all. Such a strip usually has a width ranging from 1 to 1000 mm, preferably from 50 to 250 mm. Here, it is desirable to wrap the strip around the roll body as a helix, wherein the lead of the helix is smaller or equal to the width of the resin impregnated substrate strip.

Especially when producing covers for large rolls the heat transfer tends to become very slow, which is due to the high mass of the roll. Therefore, the uncured resin should be jellified prior to the curing process of the cover, preferably at temperatures ranging from room temperature to 85 ⁰C. This process usually requires 10 to 20 hours. By this the resin stays in position as long as the curing has not been finished.

As described above, it is preferred that the resin of the cover is cured at relatively low temperatures ranging from 90 to 220 ⁰C, preferably 120 to 160 ⁰C. Furthermore, it is very important that the temperature gradients (ramps) are chosen to be very small, i.e. slow heating and cooling, so that the stresses originating from temperature gradients in the cover remain small. In this context, it is preferable if the uncured elastomer is cured at the time of the curing phase of said uncured cover. Especially in case the curing systems are compatible, superior bonding of the elastomer and the cover is achieved. Therefore, it is also preferable that the elastomer is not (fully) cured (cross-linked) during the gelation phase of the cover.

A pre-cured elastomer can be most easily provided by cutting a pre-cured or thermoplastic elastomer to size. In case of a pre-cured elastomer, a possible adhesive on said elastomer should have sufficiently cross-linked when the gelation phase is finished. In a specifically preferred embodiment, the elastomer is made of liquid thermoset polyurethane that is cast by a rotational casting method. This provides an easy measure to apply the elastomer and leads to a homogeneous distribution of the elastomer.

Especially, but not solely if a pre-cured elastomer is used, it may be the case that the adhesive resin or the roll body is not tacky enough for keeping the elastomer in position; in this case, part of the elastomer can be applied onto the roll body or the adhesive as a solution with an appropriate solvent, so that the surface becomes tackier for the rest of the elastomer.

In the following the invention will be further explained by means of examples with reference being made to the enclosed drawings and different steps of the manufacturing method of the roll.

Brief Description of the Drawings

Figure 1 shows a conventionally covered roll. Figure 2 a-c shows a conventionally covered roll at different production stages.

Figure 3 shows a preferred embodiment of the invention with strips of elastomer.

Figure 4 shows the preferred embodiment of Fig. 3 after trimming to size.

Figure 5 illustrates the gelation process of a preferred embodiment of the invention.

Cleaning of the roll body As shown in Fig. 1, a common roll body (10) has two shafts (9) at its axial extremities. These shafts (9) are designed and machined to shape to fit the bearings (19) that will allow the rotation of the roll as shown in Fig. 5. A roll body (10) can be a solid roll, a hollow roll and even a roll that has several layers. Also, roll bodies (10) having a non-rotating roll core and a rotating roll mantle can be used. Roll bodies (10) usually are from 500 mm to 15,000 mm long (axial size), and have a diameter of 100 mm to 2,000 mm. Their weight is commonly in a range of from 1 kilogram to 75 tons. The roll bodies (10) are in most cases metallic, e.g. of cast iron with various variations of the alloy, or welded steel. But also other metals and alloys, and even composite materials can be used. Also, a combination having a roll core and roll mantle of differing materials is conceivable. In order to remove an old cover or fouling, a mechanical treatment can be used. Hence, an old cover can be removed by turning on a lathe or in a cryogenic way. Residual contaminations are removed by a chemical process, such as chemical reduction or cleaning with soap. Surface treatment

In a further step the surface of the roll body (10) is treated by sand blasting or grit blasting to achieve a desired surface roughness and removal of surface oxidation.

Preparation of the Elastomer (15) The elastomer (15) may be a pre-cured elastomer or an uncured elastomer, with the latter being preferred.

Pre-cured elastomer

As a pre-cured elastomer any composition that is not deteriorated by the curing process of the cover can be used. Chlorosulfonate (CSM) , chloroprene (CR) , chlorinated polyethylene (CPE) , acrylonitrile (NBR, HNBR, XNBR) rubber elastomers are good candidates. Also thermoplastic elastomers (TPE) like styrene butadiene styrene (SBS) and preferably thermoplastic polyurethane can be used.

A pre-cured elastomer is trimmed to size (usually in form of strips) in preparation of the production process of the covering.

Uncured elastomer

Any composition that is not deteriorated by the curing process of the cover can be used as an uncured elastomer. Therefore, the uncured counterparts of the above described cured materials are good candidates.

Chlorosulfonate-based uncured elastomers, such as Hypalon (company DuPont) are especially preferred. An exemplified mixture for chlorosulfonate-based uncured elastomers is: Base elastomer e.g. Hypalon 100 parts by wt . Reinforcing filler e.g. Silica or carbon black 5 to 100 parts

Silane 0.5 to 2 parts Naphtenic plasticizer 2 to 20 parts

Anti Oxygen 0.5 to 3 parts

Magnesium Oxide 3 to 10 parts

Peroxide 1 to 10 parts

Zinc Oxide 3 to 10 parts Zinc trimethacrylate 5 to 50 parts

In case NBR rubbers are used as the elastomer, a curing (cross-linking) process based on peroxide is preferred.

Primer adhesives and further adhesives

An uncured elastomer is usually capable of adhering to the roll body (10) without further adhesives. In the case of pre-cured elastomers, this is not always the case. However, in both cases the use of an (uncured) primer adhesive and/or further (uncured) adhesives on the roll body will provide improved adhesion.

Primers and adhesives used for uncured elastomers are: Phenolic resins, melamine-based resins, urea-based resins, formol-based resins, polyexpoxide resins, reinforced polyester resins, polypropylene resins, polycarbonate resins, polyurethane resins, or mixtures of these. For pre- cured elastomers polyurethane resins, polyepoxide resins, cyanacrylic-based resins and/or chloroprene styrene butadiene-based resins are preferred. Commercially available resins for use as adhesives are Chemlok or Chemsil (company Lord) .

In case a primer adhesive is used, a single layer is applied on the roll body. This layer can be located where the elastomer is to be positioned and, additionally, where the cover will be located. When using a primer, a second layer of a further adhesive is applied on the primer layer. Further layers of adhesives are possible, although no significant improvement will be achieved. For ease of application, the primer and the adhesives are diluted in a solvent or solvent mixture. The dilution has a solid content of 10 to 80 %. A subsequent layer (of adhesive or elastomer) is not applied before the solvent of the previous layer is evaporated, which usually takes 10 to 120 minutes. A further layer of rubber solution made of the uncured elastomer itself is applied if the primer or adhesive is not tacky enough.

Adhesion of the elastomer (15)

As shown in Fig. 3, the elastomer (15) is positioned in a manner centered around the location where the covering is intended to have its axial ends in use (16) .

Uncured elastomers For non-liquid uncured elastomers a sheet is laminated from a rubber calender or is extruded in a rubber extrusion process; if the thickness of the laminated sheet is smaller than the desired thickness, multiple sheets have to be superimposed. The sheet is then cut to size and the resulting strip is positioned and pressed to the roll body with a manual pressing wheel. A strip can also be extruded directly on the roll body and can then be pressed on. In case the roll body or the adhesive is not tacky enough, tack is provided by heating the roll body or the elastomer, or by refreshing the surface of the elastomer or the adhesive with an appropriate solvent.

In case of a liquid uncured elastomer, a rotational casting process as shown in Fig. 5 is used. A urethane composition consisting of a pre-polymer with isocyanate terminations is mixed with a polyol composition, containing accelerators and/or process aids. This mixture is adjusted so that it jellifies on the roll body (10) before the roll body (10) has made a quarter rotation. As a result, the elastomer (15) will remain in position. The shape of the elastomer

(15) can be regulated by the material flow, the axial speed of casting and the rotational speed of the roll body (10) .

Pre-cured elastomers

A pre-cured elastomer can be cut to size and positioned on the roll body. In most cases it is necessary to apply a primer and/or adhesive in order to provide sufficient adhesion to the roll body. If an adhesive is used, the elastomer is kept in position by an adhesive tape, a string or any other mechanical fixing method until the adhesive provides sufficient adhesion.

Thermoplastic elastomers are heated to obtain a tacky surface and are then applied to the roll body. Alternatively, the roll body can be heated. In these cases, an adhesive is not necessary. Post-processing

In case of a pre-cured elastomer a further layer of adhesive is applied to provide adhesion between the elastomer (15) and the cover (10) . Composition of the cover (11)

A composite cover is selected as a cover (11), which will be described in the following.

Resin for the composite

Epoxy resins are used, which have a composition of: - Bisphenol A or Bisphenol F, with a chemical functionality of 2 or more

- tri- or tetra-functional resins or Novalac (to increase Tg)

- fillers, such as silica, silicon carbide, alumina, calcium carbonate (to reduce heat expansion or to increase dimensional stability)

- silane, if silica is used as filler (for improved dispersion of the silica)

- processing aids The cross linking system is anhydride-based or preferably amine-based.

Reinforcing fiber layers

Reinforcing fiber layers are close to the roll body, and the fibers have a high specific modulus and a high dimensional stability. Glass fibers (glass E fibers) , stretched and pyrolized carbon fibers, aramid and para- aramid fibers, high modulus polyethylene fibers (commercially available as Dyneema) , high modulus polypropylene fibers, basalt fibers, and silicium fibers are used. The fibers are included in the resin as fillers, such as organic or mineral very small fibers having a length of 1 to 10 μm, called whiskers or chopped fibers having a length of 10 to 2000 μm, or most frequently as filaments, multifilaments and textile combinations of those, or as parallel fibers that are not bonded together (called roving) . However, for reinforcing layers bonded fibers are preferred. Bonding is performed by a weaving process (fabrics) , a knitting process, such as wrap knitting or jersey knitting, a non-woven process, such as spun- bond/wet-bond needle punching or malimo, gluing or melting.

The reinforcing fibers thus manufactured to a strip are then wetted and wrapped tightly around the roll body (and the elastomer) . It is also possible to apply layers of un- wetted fiber strips in combination with layers of wetted strips .

Surface fiber layers

Fiber layers for modifying the surface properties are applied on the surface of the cover, i.e. as external layers. These layers comprise fiber compositions that are moisture absorbing, such as (natural or synthetic) cellulose-based fibers, fibers absorbing few moisture like polyester, or fibers that provide chemical resistance.

The external layers should have a plain surface, so that non-woven fabrics such as spun-bond non-woven and wet-bond non-woven fabrics are used instead of fiber strips having a pattern (e.g. a weaving pattern) . Just as in the case of the reinforcing layers, the fiber strip is wetted before being wrapped around the roll body. Wrapping of the cover

Wrapping is performed by using a wrapping machine. The mat has a width of 1 mm to 1,000 mm, usually from 50 to 250 mm. The fiber mat is wrapped around the roll body as a helix in multiple layers (reinforcing layers, external layers) . The helix has a lead smaller or equal to the width of the mat, so that no gaps are produced. The uncured cover is manufactured to be wider (100-300 mm in each axial direction) and thicker (2-5 mm) than desired for the final cover. In case the roll is not wide enough for this procedure, cardboard or wooden extensions are attached to the roll before wrapping.

Gelation of the cover resin For large roll bodies (10) having a reasonable weight heating of the roll body (10) and/or the uncured cover (11) may take a very long time. As shown in Fig. 5, in these cases the composite resin is jellified so that it does not lose its form during the curing process. The gelation is performed at temperatures of below 85 ⁰C for about 10 to 20 hours. Heating is performed using infrared radiation (18) produced by an infrared heating device (17) . The uncured elastomer is sufficiently hardened at the gelation stage so that it stays in position at these temperatures. Curing (cross-linking)

The curing of the composite cover is performed at temperatures of about 90 to 220 ⁰C, preferably about 120 to 160 ⁰C. For a small roll body (10) the curing takes about 24 hours, while for a large roll body (10) up to 360 hours are required. The temperature gradients of the ramps are chosen to be very small, so that a uniform temperature distribution is achieved.

The cross-linking system of the uncured elastomer is compatible with the cross-linking system of the cover. Hence, the additives are selected in a way that the cross- linking of the elastomer proceeds just as slowly as the cross-linking of the cover resin, so that a strong adhesion can be achieved. For a cured elastomer that has been fixed by using an adhesive, the adhesive is chosen to sufficiently cross-link during the gelation phase, so that the elastomer can absorb the stresses that occur during the curing phase. In the case of thermoplastic elastomers, the curing temperature is chosen to be not higher than 20 ⁰C below the melting temperature of the elastomer.

After the cover (11) is completely cured, the temperature can be reduced to room temperature, again with very small temperature gradients.

Mechanical shaping

The cooled-down covering is processed by lathe or grinding to bring the cover thickness to its desired size and to obtain the desired shape. Furthermore, surface oxidation that occurred during the curing process is removed by this treatment .

Trimming of the covering

Finally, the covering is cut or trimmed to its final axial size. Here, it is especially preferable that the elastomer (15) is positioned to be centered around the trimming position, so that it is trimmed together with the cover (15) . In this way, it is capable of absorbing the stresses that occur at this time. The resulting roll is shown in Fig. 4.

Claims

1. A roll for a fiber web machine, comprising a roll body (10) , a cover (11) , and an elastomer (15) positioned only partially between said cover (11) and said roll body (10) .

2. The roll according to claim 1, wherein said elastomer (15) is at least one of the following: a thermoset elastomer, preferably chlorosulfonate- based (CSM) , based on chlorinated polyethylene (CPE) or acrylonitrile-based, such as acrylonitrile rubber (NBR) or hydrogenated NBR (HNBR) or differently modified NBR (XNBR) ; a thermoplastic elastomer, preferably based on thermoplastic polyurethane, styrene butadiene styrene and/or polyolefin; a polyurethane composition, preferably a polyurethane composition originating from a pre-polymer with isocyanate terminations, polyol, and optional reaction accelerators or processing aids.

3. The roll according to claim 1 or 2, wherein said elastomer (15) is provided in strips around said roll body (10) .

4. The roll according to one of claims 1 to 3, wherein said elastomer (15) is positioned at the axial ends of said cover (11) .

5. The roll according to one of claims 1 to 4, wherein said elastomer (15) extends beyond the axial ends of said cover (11) .

6. The roll according to one of claims 1 to 5, wherein said elastomer (15) is adhered to said roll body (10) and/or said cover (11) by one or more adhesives, said adhesives being preferably selected from the group consisting of phenolic resins, melamine-based resins, formol-based resins, urea-based resins, polyepoxide resins, reinforced polyester resins, polypropylene resins, polycarbonate resins, polyurethane resins, cyanacrylic resins, chloroprene styrene butadiene resins .

7. The roll according to one of claims 1 to 6, wherein a tack promoter is provided between said roll body (10) and said elastomer (15) .

8. The roll according to one of claims 1 to 7, wherein a primer adhesive is provided directly on said roll body

(10) .

9. The roll according to one of claims 1 to 8, wherein the curing system of said elastomer (15) is compatible with the curing system of said cover (11), the curing system of said elastomer (15) preferably being based on a metallic oxide and/or peroxide system.

10. The roll according to one of claims 1 to 9, wherein said cover (11) is a plastic cover, preferably a composite cover comprising a polymer matrix and reinforcing fibers, said polymer matrix preferably comprising an epoxy resin.

11. The roll according to claim 10, wherein the cross- linking system of said cover (11) is anhydride-based or preferably amine-based, e.g. using multifunctional cycloaliphatic, aromatic and/or aliphatic amines.

12. The roll according to claim 10 or 11, wherein said cover (11) is constituted of at least

(a) bisphenol A or bisphenol F having a chemical functionality of 2 or more, (b) optionally tri-functional or tetra-functional resins, and

(c) optionally fillers, such as silica, silicon carbide, alumina and/or calcium carbonate.

13. The roll according to one of claims 10 to 12, wherein said cover (11) has a multilayer structure.

14. The roll according to one of claims 10 to 13, wherein said fibers are included in the resin as fillers, such as organic or mineral very small fibers having a length of 1 to 10 μm, called whiskers or chopped fibers having a length of 10 to 2000 μm.

15. The roll according to one of claims 10 to 14, wherein said fibers are included in the resin as filaments, multifilaments and/or textile combinations of these.

16. A method for manufacturing a roll for a fiber web machine, comprising the steps of applying an uncured or cured elastomer (15) on only a part of a roll body (10), applying an uncured cover (11) on at least a part of said roll body (10), wherein said uncured cover (11) covers at least a part of said elastomer (15) and covers at least a part of said roll body (10) that is not covered by said elastomer, and curing the uncured cover (11) and, if applicable, the elastomer .

17. The method according to claim 16, wherein said elastomer (15) is provided in strips around said roll body (10) .

18. The method according to claim 16 or 17, wherein said elastomer (15) is extruded on said roll body (10) as a strip .

19. The method according to claim 16 or 17, wherein said elastomer (15) is formed by cutting a calendered stock sheet .

20. The method according to one of claims 16 to 19, wherein said elastomer (15) is applied by means of a pressing wheel.

21. The method according to one of claims 16 to 20, wherein said elastomer (15) is kept in position by a mechanical system, such as an adhesive tape or string.

22. The method according to one of claims 16 to 21, further comprising at least one of the following steps

(a) sand blasting said roll body (10) as a first step to yield a surface roughness Ra of said roll body (10) of preferably 2 μm or more, more preferably 10-15 μm and a roughness Rz of preferably 10 μm or more,

(b) applying a primer on said roll body (10) before applying said elastomer (15),

(c) applying an adhesive on said roll body (10), before applying said elastomer (15),

(d) applying an adhesive on said primer before applying said elastomer (15),

(e) applying an adhesive on said elastomer (15) before applying said uncured cover (11) .

23. The method according to claim 21 or 22, wherein said mechanical fixing is removed after the adhesive or primer provides a sufficient fixing of said elastomer (15) .

24. The method according to claim 22 or 23, wherein prior to application, said primer and/or said adhesive is diluted in a solvent or solvent mixture, the dilution having a solid content preferably ranging from 10 to 80 % by weight.

25. The method according to claim 24, wherein said dilution is applied using a paintbrush, a roller or a spray gun, depending on the viscosity.

26. The method according to claim 24 or 25, wherein said solvent is evaporated usually for 10 to 120 minutes before a further layer is applied.

27. The method according to one of claims 16 to 26, further comprising the step of trimming the resulting covering to size.