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Title:
A ROLL FOR A FIBER WEB MACHINE
Document Type and Number:
WIPO Patent Application WO/2011/135156
Kind Code:
A1
Abstract:
The invention relates to a roll cover for a roll of a fiber web machine comprising at least one thermoplastic polymer in the form of a tape.

Inventors:
PAASONEN JAN (FI)
Application Number:
PCT/FI2010/050353
Publication Date:
November 03, 2011
Filing Date:
April 30, 2010
Export Citation:
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Assignee:
METSO PAPER INC (FI)
PAASONEN JAN (FI)
International Classes:
F16C13/00; D21F3/08; D21G1/02
Foreign References:
FI111025B2003-05-15
US6315704B12001-11-13
Attorney, Agent or Firm:
TURUN PATENTTITOIMISTO OY (Turku, FI)
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Claims:
CLAIMS

1 . A roll cover for a roll of a fiber web machine, characterised in that it comprises at least one thermoplastic polymer in the form of a tape.

2. A roll cover according to claim 2, characterised in that the width of the tape is 50-150 mm and its thickness is 0.1 -15 mm.

3. A roll cover according to any of the previous claims, characterised in that it further comprises fibers, fillers, additives and/or processing aid agents.

4. A method for manufacturing a roll cover for a roll of a fiber web machine, comprising - winding a tape comprising at least one thermoplastic polymer around a roll shell body, thus forming partially superposed layers of tape, while applying localised heating on at least a portion of the part of the tape entering into contact with the tape of the previous and/or following layer.

5. A method according to claim 4, characterised in that the source of localised heating is selected from the group consisting of hot air, laser, ultrasound and a combination thereof.

6. A method according to claim 4 or 5, characterised in that said thermoplastic polymer is selected from the group consisting of thermoplastic polyurethanes, polyesters, polycarbonates, polyphenylene sulphides, polyether sulphones, polyether ether ketones, polyether imides and mixtures thereof.

7. A roll cover for a roll of a fiber web machine, obtainable by the method of any of the claims 4-6.

8. A roll of a fiber web machine comprising a roll cover according to any of the claims 1 -3 or 4-7. 9. A manufacturing or treatment apparatus for a cellulosic fiber web comprising a roll according to claim 8.

Description:
A ROLL FOR A FIBER WEB MACHINE

FIELD OF THE INVENTION

The present invention relates to a roll cover for a roll of a fiber web machine as well as to a method for manufacturing a roll of a fiber web machine and a roll of a fiber web machine.

BACKGROUND OF THE INVENTION

Paper, board, finishing and tissue machines use several different types of rolls, such as press rolls, suction rolls and calender rolls. It is known that these rolls, which are typically made of metal, can be covered by polymers.

The role of the cover is important for the process, as the paper web or the like is typically led to a calender unsupported, i.e. without the support of a fabric, to a nip formed between a calender roll, covered by a polymer, and a hard-faced counter roll. In such nip, the paper web is thus in direct contact with the roll surfaces. As stated, nipped calender rolls and other rolls have several effects on the paper web, i.e. on the gloss and smoothness of the finished paper, and also on the paper bulk. The size of the calender rolls is typically 4-12 m in length and 400-1500 mm in diameter. The magnitude of linear loads in these rolls can be as high as 300- 600 N/mm. The covering process involves typically the application of tapes consisting of fibers and an epoxy resin. A typical manufacturing method of such cover is disclosed in Fl 94 782 B. It would be however interesting to use thermoplastic polymers in roll covers, as they can have better properties, especially in view of the resistance to wear, impact strength and heat generation. The working temperatures of thermoplastic polymers are however significantly higher than the working temperatures of the thermoset polymers used at the moment, for example as high as 300 °C or even 400 °C. The use of such high working temperatures in the manufacture of roll covers leads to very high residual stresses in the finished cover, making their use unsuitable.

Roll covers of thermoplastic material are disclosed for example in documents EP 1047831 and EP 861694. In EP 1047831 a roll cover is disclosed comprising successive layers of fiber reinforcement and thermoplastic polymer. EP 861694 discloses a roll cover made of speciality thermoplastics material by hypersonic plasma spraying. These covers have however not been commercialized due to the high cost of the polymer material and/or technical problems either in the manufacturing or in performance of the cover or both. There thus exists a need to provide a method for manufacturing roll covers comprising thermoplastic polymers as their main component or as a matrix material in a fiber composite. A roll cover made with such method and having at least one thermoplastic polymer as its main component or matrix would thus also be interesting for its superior properties. OBJECTS AND SUMMARY OF THE INVENTION

An object of the present invention is to minimise or even totally eliminate the problems existing in the prior art. An object of the present invention is therefore to create a cover of a roll that has better wear resistance, better impact strength and lower heat generation than the prior art covers. An object of the invention is also to provide a manufacturing method for making such covers, and for making covers comprising thermoplastic polymers either as their main component or as matrix material.

Another object of the invention is to provide a cover and a method for manufacturing a cover of a roll in a single step or in only a few steps instead of several steps as in the prior art.

The invention relates to a roll cover for a roll of a fiber web machine comprising at least one thermoplastic polymer in the form of a tape.

The invention also relates to a method for manufacturing a roll cover for a roll of a fiber web machine, comprising - winding a tape comprising at least one thermoplastic polymer around a roll shell body, thus forming partially superposed layers of tape, while applying localised heating on at least a portion of the part of the tape entering into contact with the tape of the previous and/or following layer. The invention also relates to a roll of a fiber web machine comprising a roll cover according to the present invention.

BRIEF DESCRIPTION OF THE DRAWING

Figure 1 schematically presents a portion of a roll cover according to a first embodiment of the invention. Figure 2 presents a manufacturing method for a roll cover according to the present invention.

Figure 3 schematically presents a portion of a roll cover according to a second embodiment of the invention.

Figure 4 schematically presents a portion of a roll cover according to a third embodiment of the invention.

Figure 5 schematically presents a portion of a roll cover according to a fourth embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to a roll cover for a roll of a fiber web machine comprising at least one thermoplastic polymer in the form of a tape.

A typical method for manufacturing a roll cover for a roll of a fiber web machine comprises

- winding a tape comprising at least one thermoplastic polymer around a roll shell body, thus forming partially superposed layers of tape, while applying localised heating on at least a portion of the part of the tape entering into contact with the tape of the previous and/or following layer.

In the method according to the present invention, the tape material is thus heated locally and in a focused manner for a short period of time, long enough to melt the surface of the material but short enough for preventing any degradation of the material or creation of important residual stresses to the finished cover. It is preferable to locally heat both the "old" layer as well as the "new" layer, i.e. the previous layer and the layer being applied. This localised heating and melting of the polymer material results in a good adhesion between the two consecutive layers, as the polymer molecules of the consecutive layers are entangled with each other.

Now it has thus been surprisingly found that it is possible to manufacture a roll cover that has the above-mentioned beneficial properties, as there is now provided a method for manufacturing such covers, without having the previous problems of high residual stresses due to the high working temperatures needed. It is thus now possible to provide roll covers comprising thermoplastic polymers in a significant amount. Thermoplastic polymers have been used in roll covers also earlier, but only in very low amounts and in the form of particles embedded into a matrix material. Here the thermoplastic polymer forms the essential part of the cover, while it naturally can comprise also fillers, fibers, additives, processing aid agents and other such agents.

The source of localised heating is preferably selected from the group consisting of hot air, hot gas, laser, ultrasound and a mixture thereof. These can also be characterised as polymer welding. In the method according to the present invention, the tape is preferably applied to the roll shell body by means of a tape guiding member that guides the tape into the right position and in such an angle that an optimal lead length with desired cover thickness is achieved.

A further advantage of the present invention is thus that it allows the manufacture of a roll cover in one step, and that no later curing steps are needed. The manufacturing time is thus reduced. The cover can also be manufactured close to its final thickness in one step, this further reducing the manufacturing time.

The thermoplastic polymer applied to form a cover according to the present invention is typically in the form of a tape. This tape has a length and a width, the width being the distance from a first edge to a second edge, and being considerably smaller than the length of the tape. The tape also has a thickness that is considerably smaller than the width of the tape. The tape used in the present invention can have a width of 50-150 mm and a thickness of 0.1 -15 mm.

The tape can be flat, but it can also have different shapes as is described below. The thermoplastic polymer material is preferably in the form of a profiled tape obtained directly from an extruder or the like. The shape of the tape can for example be such that when wound around a roll shell body, the consecutive layers lock each other into place.

In this context, by calender roll is meant a roll having a polymeric cover or layer covering its main surface that is in contact with the web during the calendering. It is clear that the cover according to the invention is suitable for other rolls employed in the machines for making and/or treating paper or board webs, or tissues. Such machines are paper and board machines as such, including their drying sections and on-line calenders, as well as off-line calenders for cellulosic webs, such as supercalenders. Moreover, when paper web is mentioned in this text, it is clear that also webs of board, tissue and other webs comprising mainly cellulosic fibers are covered by this expression, which is only used for simplicity of wording.

It is also to be noted that a typical roll for a fiber web machine such as paper, board, finishing or tissue machine comprises a cylindrical roll shell body. The roll shell body is typically made of metal, such as cast iron. The thickness of a finished roll cover is about 5-20 mm, preferably 8-15 mm, while the tape can have a thickness of about 0.5-5 mm and a width of 100-200 mm, preferably about 150 mm. By the term thermoplastic polymer it is to be understood any polymer and elastomer that can be re-melted and re-shaped, as opposed to thermoset polymers that cannot be re-melted once they have been made.

According to an embodiment of the invention, the thermoplastic polymer is selected from the group consisting of thermoplastic polyurethanes, polyesters, polycarbonates, polyether sulphones, polyether ether ketones, polyether imides and mixtures thereof. Especially suitable polymers are polyether sulphones, polyether ether ketones and polyether imides.

The cover of the present invention may also contain fibers such that the tape is for example in the form of a fiber tape where the thermoplastic polymer forms the matrix. The fibers may also be for example in the form of woven mat, nonwoven felt, continuous fibers or short fibers embedded in the matrix.

The cover of the present invention may contain fillers that are admixed with the matrix material. With the fillers, properties of the cover can be improved or its cost can be cut. Typically, fillers are used to improve wear resistance and to adjust matrix stiffness and hardness. Fillers applicable in the invention are inorganic fillers, such as metal, ceramic and mineral fillers, for example aluminium oxide, silicon oxide, carbides, nitrides, glass, carbon, silicates and mica in many different particle forms like powder, balls, pearls, fibers etc. The cover of the invention may also contain other additives and processing aid agents such as polymerization initiators, activators and accelerators, hardeners, plasticizers, thermal stabilators, antioxidants, antiozonants, pigments etc. for promoting the process and improving physical properties of the cover. These agents are typically mixed with the thermoplastic polymer. The tape used in the present invention can be such that at least one characteristic of the tape varies in a predetermined manner along the width of the tape. The tape can thus comprise a first edge zone extending from the first edge towards the second edge to a distance that is 5 - 50 % of the width of the tape, a second edge zone extending from the second edge towards the first edge to a distance that is 5 - 50 % of the width of the tape, and optionally a core zone between the first edge zone and the second edge zone, each of these zones having different characteristics.

The tape may therefore comprise, in its width direction, at least two zones having different characteristics. The transition from one zone to another can occur either continuously or it can occur sharply. Preferably the tape comprises two zones that are each about 36 - 65 %, for example 50 % of the whole width of the tape.

One edge of the tape can thus be for example softer than the other edge of the tape, and thus the whole cover can be made as single pass. Indeed, the cover can be manufactured by a single pass-method, i.e. it is a single coiled cover. In this embodiment, the tape may be either in direct contact with the roll shell body, or there may be a layer of primer between the roll shell body and the cover made of tape. The primer layer may be used for example to enhance the adhesion of the cover to the roll shell body, depending on the cover materials used.

The roll cover of the invention is thus preferably made by single pass-method, by using a suitable winding tension on the tape, and possibly a pressure applied on the roll shell body in its axial direction. By single pass-method is meant a method of manufacturing in which the entire cover is obtained by a single step winding from one end of the roll to the other end of the roll but not returning back or repeating, i.e. the different layers are manufactured at the same time. During the winding, the consecutive cycles of the tape can be overlapped to an extent, which depends on the width of the tape and the desired thickness of the cover. The wound tape preferably forms an angle a with the surface of the roll shell body. The angle a can be selected to be in a range of ± 5-60 Q depending on the specific embodiment and structure of the tape. Steep angles over 60 Q would increase the risk of cover failure especially in nip roll applications where radial loads are exerted to the cover but to some extent also in other rolls since the cohesion and homogeneity between two tape windings may be impaired. A preferable range would be around 45 Q or less, more preferably 30 Q or less.

The present invention further relates to a cover of a roll of a fiber web machine obtainable by the method as described above. The invention yet further relates to a roll of a fiber web machine comprising a cover as described above as well as to a manufacturing or treatment apparatus for a cellulosic fiber web comprising a roll according to this invention.

The invention also relates to a use of a tape as described above in the manufacture of a cover of a roll of a fiber web machine.

The present invention also relates to a calender for a fiber web machine comprising a roll according to the present invention. Typical multinip calenders comprise a number of rolls, arranged on top of each other. All or some of the calender rolls may comprise a cover according to the present invention. Especially the first and/or the last roll of a multinip calender may have a cover according to the present invention. The invention also relates to a machine for manufacturing or treating a cellulosic web comprising at least one roll according to the present invention. Possible machines for manufacturing or treating a cellulosic web are, for example, paper machines, board machines, tissue machines, on-line calenders, off-line calenders, etc.

The present invention yet further relates to a fiber web machine comprising at least one roll cover or a roll according to this invention.

All the embodiments and characteristics disclosed in this specification apply to all the different aspects of the invention, i.e. the embodiments listed for the method apply mutatis mutandis to the cover, tape, roll, calender, machine and use.

In this context, the term "comprising" is to be construed as an open term, i.e. that other features may be included in addition to those listed. Moreover, the reference numbers are not to be construed as limiting the scope of protection of the claims.

DETAILED DESCRIPTION OF THE DRAWING Figure 1 schematically presents a portion of a roll cover according to a first embodiment of the invention, shown as a cross-section cut along the rotational axis of the roll. A roll cover 1 is provided on the surface of the roll shell body 2. The cover comprises a tape essentially made of a thermoplastic polymer. The tape (having a width W), is wound helically around the roll shell body 2. The tape is wound in such a way that its first edge zone 3 is in contact with the roll shell body 2, while its second edge zone 4 forms the outer surface of the roll cover. The winding angle in Figure 1 is only for sake of clarity depicted to be higher than is practical or preferable. With each rotation of the roll shell body 2 the tape is wound with a lead t depending on the tape's dimensions and in such a manner as to provide the final roll cover without a need for other covering layers.

Figure 2 schematically presents a manufacturing method for a cover according to the present invention. The tape 5 from the tape supply 6 is wound around the roll shell body 2 which is rotated by the motor 7. Tape guiding member 8 guides the tape 5 in a right position and in such a winding angle that an optimal lead length with desired cover thickness is achieved. The guiding member 8 travels forward along a beam 9 by the force of a second motor 10 (along the directions shown with reference number 1 1 ). The motors are driven by a power supply 12. Heating means for heating the tape is preferably positioned such that the heating is directed between the tapes, in order for the tapes to attach to each other. The heating means can thus be positioned on the beam 9, even on the guiding member 8 or they can be positioned on a beam on their own. For sake of clarity, th heating means are not shown in Figure 2.

Figure 3 schematically presents a portion of a roll cover according to a second embodiment of the invention. In this embodiment, the tape 13 has been mold to a curved form so that the tape, when wound around the roll shell body 2, mechanically locks itself to place. Figure 4 schematically presents a portion of a roll cover according to a third embodiment of the invention, where the tape 14 has another shape for the mechanical locking of the wound tape on itself. Figure 5 schematically presents a portion of a roll cover according to a fourth embodiment of the invention. In this embodiment, the roll cover comprises two layers 15 and 16 having different properties, such as different hardnesses.