PRESS SECTION AND SHOE PRESS THEREFOR

Abstract: A press section in a machine for manufacturing a web (1) of fibrous material, comprising a shoe press with extended press nip, said shoe press having a counter roll (2) with a cylindrical press body (6); a press shoe (3) with a concave surface for cooperation with the press body (6); an impermeable belt (4) running through the press nip in sliding contact with the press shoe (3); a clothing (5) running in a loop around guide rolls and through the press nip in contact with the web, and being capable of receiving and carrying liquid along with it; a movable heat transfer means (9) for continuous transfer of heat to the web in the extended press nip; and a heat source (10) for heating the heat transfer means (9). According to the invention the counter roll comprises a sleeve that forms said heat transfer means (9) and encloses the press body. The invention also relates to a shoe press, a press section with a roll press, and treatment sections with roll and shoe calenders with sleeves of the type described.

Description: Press section and shoe press therefor The present invention relates to a press section in a machine for manufacturing a continuous web of fibrous material, comprising one or more presses, at least one of which is a shoe press with extended press nip comprising - a rotatable counter roll including a cylindrical press body, - a press shoe having a concave surface for pressure-generating cooperation with said press body, - an impermeable belt running through the press nip in sliding contact with the concave surface of the press shoe, - a clothing running in a loop around a plurality of guide rolls and through the press nip in contact with the web, and being capable of receiving and carrying liquid along with it, - a movable heat transfer means for continuous transfer of heat to the web in the extended press nip, and - at least one heat source for continuous heating of the heat transfer means. The invention also relates to a press section in a machine for manufacturing a continuous web of fibrous material, comprising one or more presses, at least one of which is a roll press comprising - a first rotatable press roll, - a second rotatable press roll defining a press nip with the first press roll, at least the first press roll including a cylindrical press body, - a clothing running in a loop around a plurality of guide rolls and through the press nip in contact with the web, and being capable of receiving and carrying liquid along with it, - a movable heat transfer means for continuous transfer of heat to the web in the press nip, and - at least one heat source for continuous heating of the heat transfer means . The invention also relates to a shoe press with extended press nip for a press section in a machine for manufacturing a continuous web of fibrous material, comprising - a rotatable counter roll including a cylindrical press body, - a press shoe having a concave surface for pressure-generating cooperation with said press body, - an impermeable belt running through the press nip in sliding contact with the concave surface of the press shoe, - a clothing running in a loop around a plurality of guide rolls and through the press nip in contact with the web, and being capable of receiving and carrying liquid along with it, - a movable heat transfer means for continuous transfer of heat to the web in the extended press nip, and - at least one heat source for continuous heating of the heat transfer means. The invention also relates to a treatment section in a machine for shape and/or surface changing mechanical treatment of a continuous web of fibrous material, comprising at least one roll calender comprising - a first rotatable roll, - a second rotatable roll defining a nip with the first roll, at least the first roll including a cylindrical body, - a movable heat transfer means for continuous transfer of heat to the web in said nip, and - at least one heat source for continuous heating of the heat transfer means. The invention also relates to a treatment section in a machine for shape and/or surface changing mechanical treatment of a continuous web of fibrous material, comprising at least one shoe calender with extended nip comprising - a rotatable counter roll including a cylindrical body, - a shoe having a concave surface for nip-forming cooperation with said cylindrical body, - an impermeable belt running through the extended nip in sliding contact with the concave surface of the shoe, - a movable heat transfer means for continuous transfer of heat to the web in the extended nip, and - at least one heat source for continuous heating of the heat transfer means. Pressing a wet paper web in a press section at elevated temperature has been shown to result in a number of beneficial effects. The technology, known, as impulse technology, impulse drying or impulse pressing, was first described in SE-7803672-0 , corresponding to US-4 , 324 , 613. The top pressure utilized in the process described therein lies within the range of 3-8 MPa and the surface temperatures between 150°C and 350°C for a cylinder in a press nip of conventional type. The dwell time in such a press nip, however, is only a few milliseconds, which is too short a time to be able to take full advantage of the favourable effects of pressing at high temperature. It has therefore been proposed subsequently to utilize impulse drying in a heated shoe press in which the nip is extended so that the dwell time for the heat treatment is greatly extended. In impulse drying high temperature and high pressure are combined for a brief period of time in order to give extremely high heat flows to the web. The envelope surface of a steel or cast iron roll has maximum heat flow in the range of 2-8 M /m 2 , which results in extremely high dewatering speeds. The mechanism forming the basis of these high dewatering speeds, with consequent high dry solids content has not yet been fully discerned. One theory presented is that, through its expansion, the steam which is developed in the vicinity of the hot surface of the heat-transfer element nearest the fibrous web helps to displace water remaining in the fibrous web, into the felt that is in contact with the fibrous web. Another theory is the reduced viscosity of the water caused by the high temperature, in combination with water at high temperature (>100°C) being quickly vaporized when the web leaves the nip and the pressure thus drops to atmospheric pressure so that high dry solids contents are obtained. According to said SE-7803672-0 a burner supplies heat to one roll in a press with two rotating rolls. The heat is supplied to the envelope surface of the roll immediately before the press nip. The patent specification states that the roll may have a surface layer with low thermal conductivity, thereby enabling it to maintain a high temperature . US-4, 738, 752 describes an extended, heated press nip where the fibrous web encounters a hot surface formed by a rotatable press roll or a metal belt passing in a loop around a plurality of guide rolls. The press roll or belt is heated by a heat source. The press roll may have a first coaxial layer and a second coaxial layer extending around the first layer and having a coefficient of thermal conductivity that is greater than that of the first layer. The first layer may consist of ceramic, whereas the second, outer layer consists of metal and has a thickness of 0.0127-1.27 cm. The layers are in intimate contact with each other and, together, form a unitary body. When a roll of the described known types is heated from the outside, the outer layer will be hotter than the layer or layers disposed inside the outer layer which is rigidly joined to the next inner layer. The outer layer will therefore expand more than the inner layer, thereby causing stresses to arise between the two layers. If the roll is homogenous, the same differences will arise in expansion and stresses between the outer and inner parts where the transition between the parts is without specific bounds. To reduce the risk of damage in the roll as a result of such stress differences, the initial heating of the roll must take place slowly. Another problem is that it is difficult to maintain the geometric shape of the roll across the machine direction, due to difficulties in maintaining the same temperature along the envelope surface of the roll and at the end walls. Considerable stresses also arise between these construction elements since they cannot expand freely independently of each other, and the envelope surface becomes arc-shaped outwardly or inwardly across the machine direction. Since the inner layer or part of the roll will also absorb some of the thermal energy supplied, the heating costs will be high. One drawback with the use of a metal belt as heat-transfer means is that it must be arranged in a loop with at least two rolls, thus constituting a space-consuming configuration. To allow the surface of the belt to be cleaned with a doctor, a counter roll must be arranged inside the loop of the belt in front of the doctor. Another drawback is that the belt cannot usually be coated with layers to achieve certain release properties and certain thermal conductivity properties. A number of the problems discussed above exists also in roll presses and calenders which would supply heat to the web. The object of the present invention is to at least essentially reduce the problems discussed above and to provide an improved heat transfer means. Said press sections, treatment sections and shoe press according to the invention are characterized in that the said counter roll, first press roll and first roll, respectively, comprise a sleeve that forms said heat transfer means and encloses the cylindrical body. In drying a web the improved heat transfer means enables that the beneficial effects of impulse drying can be utilized more efficiently than has previously been possible. The invention will be described in more detail with reference to the drawings. Figure 1 is a view in perspective of a shoe press, the counter roll of which having a rigid sleeve the diameter of which being shown greatly exaggerated. Figure 2 is a section through the shoe press in accordance with Figure 1. Figure 3 is a section through a part of the counter roll and its sleeve in accordance with Figure 1. Figure 4 shows a counter roll with a rigid sleeve in accordance with a second embodiment . Figure 5 shows a counter roll with a rigid sleeve in accordance with a third embodiment and a cambered press body . Figure 6 shows a part of -a counter roll with a rigid sleeve in accordance with a fourth embodiment. Figures 7 and 7a show a counter roll with a rigid sleeve in accordance with a fifth embodiment. Figures 8 and 8a show a counter roll with a rigid sleeve in accordance with a sixth embodiment. Figure 9 shows a shoe press similar to the one in Figure 1 but with a rigid sleeve in accordance with a seventh embodiment for geared operation by means of cooperating toothed elements on both sleeve and press body. Figure 9a is a detail enlargement of the part ringed in in Figure 9. Figure 10 shows a shoe press similar to the one in Figure 9 but with a flexible sleeve in accordance with a further embodiment for geared operation by means of cooperating toothed elements. Figure 10a is a detail enlargement of the part ringed in in Figure 10. Figure 11 is an end view of a roll press according to the invention. Figure 12 is an end view of a roll calender according to the invention. Figure 13 is an end view of a shoe calender according to the invention. Figures 1 and 2 show schematically parts of a shoe press with extended press nip, included in the press section of a machine for manufacturing a continuous web 1 of cellulosic fibrous material, for instance. The invention is particularly applicable, but is not exclusive to paper or board machines for manufacturing paper and board, respectively. The paper machine may be designed for manufacturing soft paper or printing paper, e.g. newspaper, or any other grade of paper. The shoe press comprises a rotatably journalled counter roll 2, a press shoe 3, an impermeable, flexible belt 4 and a clothing 5, which is in direct contact with the web 1 and is capable of receiving liquid in liquid form and gaseous form from the web, and carrying it out of the press nip. The counter roll 2 comprises a stable cylindrical press body 6 having shaft journals 30 for rotary journalling of the counter roll in bearing housings (not shown) . The press body 6 rotates about an axis of rotation 11 and has an envelop surface with circular cross section. The press shoe 3 has a concave surface 7 for pressure-generating cooperation with the corresponding convex press body 6 in order to obtain the extended press nip. The belt 4 runs through the press nip in sliding contact with the concave surface 7 of the press shoe. In the embodiment shown the shoe press is provided with a shoe press roll comprising said press shoe 3 and belt 4 which is rigidly mounted at rotatable peripheral end portions 8. Alternatively, the flexible belt may run in a loop around a plurality of rolls, in which loop the press shoe is thus mounted. The clothing 5 of the shoe press runs in a loop around a plurality of guide rolls (not shown) and through the extended press nip. The web 1 is carried to the press nip by the clothing 5 and is separated from the clothing 5 after the press nip. Alternatively the web runs in an open draw before the press nip. The clothing 5 usually consists of a press felt, but a permeable belt with through openings and possible recesses disposed or extending therebetween may be used, or an impermeable belt with recesses of suitable depth, shape and extension. Said recesses are situated on the side facing towards the web 1. Said openings and recesses are arranged to receive liquid from the web and carry the liquid out of the press nip. The openings and recesses also give the web a structured appearance which increases the bulk of the web. Instead of a permeable belt or impermeable belt, an open wire or closed wire which has a sealing layer facing away from the web, may be used. Moreover, the shoe press comprises a movable means 9 for continuous transfer of heat to the web 1 when the latter passes through the extended press nip, and a heat source 10 which is arranged at a predetermined point before the press nip, e.g. about 30°-330°, preferably 30°-120° before the press nip for continuous heating of said heat transfer means 9 at start-up to a desired operating temperature and during operation to maintain this operating temperature. The heat source may be fixed or movable, e.g. oscillating. According to the present invention the counter roll 2 comprises a sleeve forming said heat transfer means 9 and at least enclosing the whole of the axial part of the cylindrical press body 6 active in the press nip, the sleeve being permitted to expand freely in relation to the press body 6 during said heating before the press nip, without unfavourable stresses arising in the sleeve. The sleeve 9 has an inner side 17 and an outer side 18, the inner side 17 being arranged to be brought into contact with the press body 6 within the zone of the press nip. The sleeve 9 consequently lacks any mechanical or adhering connection or other such permanent, fixing connection which would prevent such free expansion of the sleeve 9 axially and radially in relation to the cylindrical press body 6 outside the press nip where heating occurs, and which would instead give rise to unfavourable stresses in the sleeve. Flat, circular rings 12 are fitted at the end surfaces of the cylindrical press body 6. These rings 12 have a somewhat larger outer diameter than that of the cylindrical press body 6, in order to provide axial end stops 13 for the sleeve 9, as can be seen in Figure 3. Even during operation the sleeve 9, which is axially expanding due to heating, is free from contact with one or both of these end stops 13 in order to avoid axial stresses in the sleeve so that the straightness of the sleeve can be ensured. The sleeve 9 is thus completely free from permanent, locking connections in all directions so that it is permitted to expand free from stress both axially and radially in relation to the cylindrical press body 6 during heating. During operation the press body 6 is arranged to press the sleeve 9 firmly at a contact point 14 within the press nip upon pressure-generating cooperation of the press shoe 3 with the press body 6 to form a sufficient friction force at said contact point 14 between opposing surfaces of the press body 6 and the sleeve 9 so that the sleeve 9 is forced round by the press body 6 at the same speed as the latter at said contact point . The sleeve 9 may be homogenous, i.e. made of the same piece of material all the way through without layers, or may consist of two or more coherent layers of different materials, at least one of which acts as at least carrier for the other layer (s) . The sleeve 9 may be in the form of a rigid, form-stable sleeve or a flexible sleeve, which is thus not form-stable . In Figures 1-3 the sleeve 9 is illustrated schematically as a cylindrical, rigid, form-stable sleeve with an outer side 18 having constant, circular cross section and constituting the envelope surface of the rigid sleeve, and with an inner side 17 having constant, circular cross section and being coaxial with the envelope surface 18. The diameter of the rigid sleeve 9, however, is shown as greatly exaggerated in relation to that of the press body 6. The sleeve 9 shown in Figures 1-3 thus has constant wall thickness, measured between the inner side 17 and the outer side 18 in all arbitrary cross sections between the parallel end planes of the sleeve. The wall thickness of the sleeve 9 is selected depending on each specific use, with varying desires of properties of the sleeve. The wall thickness of the sleeve is sufficiently large to ensure that the sleeve is rigid and form-stable, i.e. is at least self-supporting so that, when resting on a flat support, it retains its radius all around and does not collapse to a non-circular form. It should preferably be so rigid and form-stable that it is not noticeably deformed by normal stresses during assembly and operation. The rigid sleeve 9 has sufficient wall thickness for it not to be subjected to too great stresses in the press nip that may arise as a result of differences in radius between the various construction elements . During operation the rigid sleeve 9 rotates about its own axis of rotation, i.e. its central axis 15, which is situated eccentrically in relation to the axis of rotation or central axis 11 of the press body 6, the eccentric displacement, i.e. the distance between these axes 11, 15, corresponding to half the difference between the outer diameter of the press body 6 and the inner diameter of the sleeve 9, i.e. the radial difference. It will be appreciated that in a starting position, when the press shoe 3 and the counter roll 2 are displaced vertically from each other a distance corresponding to said difference in diameter, the sleeve is suspended on the press body 6 and its central axis 15 is thus situated below the central axis 11 of the press body 6. The concave surface 7 of the press shoe 3 has a radius adapted to the radius of the rigid, cylindrical sleeve 9. The sleeve is so rigid and stable that it acquires a pressing function through influence from the press body, i.e. the pressure from the press body at the contact point so shortened is transplanted forwards and backwards, seen in direction of rotation, through the sleeve to the press nip so that the length of the press nip will be approximately the same length as the width of the shoe. A slight deformation will arise in the passing section when the rigid sleeve 9 passes the press shoe 3, as a result of differences between the inner radius of the sleeve and the outer radius of the press body. However, this slight deformation will disappear as soon as the pressure ceases after the press nip, and no damaging stresses occur in the rigid sleeve since it is sufficiently thick to withstand this loading. The rigid sleeve thus still fulfils the property of being "form-stable" as this is defined in this patent application. Alternatively, the wall of the rigid sleeve can be made so thin that the wall is shaped to the press body, provided the material in the wall can withstand this deformation without it becoming a permanent deformation. Thanks to the free space 16 inside the sleeve 9, only slight amounts of heat will be consumed by the press body. During operation this space 16 containing air is in the shape of a crescent. Transfer of heat from the sleeve 9 to the press body 6 only occurs within the contact point 14 in the press nip. However, the amounts of heat consumed here are in any case small since the contact surface here constitutes a very small proportion of the circumference and the fact that the heat is transported from one surface to another. The temperature in the hot surface of the sleeve at the beginning of the press nip may generally be within the range of 150°C-400°C. Since the rigid, cylindrical sleeve 9 remains round during operation, a constant distance between the sleeve 9 and the heater 10 is maintained at constant operating temperature . Figure 4 shows another embodiment of a rigid sleeve 9, the inner side 17 of which is provided with a plurality of endless grooves 19 which are axially uniformly distributed and extend round the circumference to form corresponding cams 31, the cylindrical surfaces of which form the inner side 17 of the sleeve that determines the wall thickness of the sleeve. With such grooves, the contact surface with the press body 6 is decreased by about 50% in the shown embodiment, and the amount of heat transferred to the press body is thus also reduced. Such a sleeve provided with grooves is therefore advantageous from the energy aspect and also from the heating aspect during start-up, since the heating takes place more quickly without the press body 6 being negatively affected. The sleeve 9 is retained against the press body by means of rings 12 forming stops, as described in the embodiment according to Figure 3. Figure 5 shows a further embodiment of a rigid sleeve 9 having a cylindrical envelope surface 18 and a cambered inner side 17, the press body 6 having a correspondingly cambered outer side so that the space 16 remains constant, seen in one and the same longitudinal section. Axial guidance of the sleeve is thus achieved in relation to the press body without the need for any mechanical stop. The thickness of the sleeve thus varies over its entire length and is narrowest in the middle. The variations in thickness lie within the thickness values and intervals specified in this patent application. Figure 6 shows an additional embodiment of a rigid sleeve 9, one end of which is provided with or designed with a radially inwardly directed flange 20. A circular ring 12 is then mounted at one end surface of the press body 6, the ring 12 having a peripheral recess 21 for receipt of the sleeve flange 20 and to form an axial, outer stop 22 to retain the sleeve 9 on the press body 6 while still allowing it to expand freely in relation to the press body 6 towards its other end which is entirely free. A small gap exists between the flange 20 and stop 22 or between the flange 20 and press body 6 to allow a movement of the sleeve 9 circumferentially in relation to the press body 6. Figures 7 and 7a show a further embodiment of a rigid sleeve the inner side of which being provided with a recess 23 running around the inner side, in which a flat ring 24 is received to function as axial stop for the sleeve. The ring 24 is rigidly mounted on the press body 6. Figures 8 and 8a show an additional embodiment of a rigid sleeve 9, both ends of which carry a flat ring 25 rigidly mounted on the sleeve 9. The ring 25 is suitably inserted into recesses 26 in the ends of the sleeve 9 and has an inner diameter less than the inner diameter of the sleeve so that a stop 27 is obtained to retain the sleeve 9 on the press body 6, the sleeve 9 being somewhat longer than the press body 6 so that a small space 28 is obtained between each stop ring 25 and the opposing end surface of the press body 6. Figures 9 and 9a show a further embodiment of the press body 6 and rigid sleeve 9 of the counter roll. The press body 6 is provided at its ends with a toothed ring 32 having external teeth, the sleeve 9 being provided on its inner side 17 with a toothed ring 33 having internal teeth in order to obtain a toothed engagement within the area of the press nip. The teeth do not engage with each other after the press nip. The sleeve 9 is thus caused to rotate by means of gear transmission, whereas the sleeves described previously here are driven by means of friction engagement between the surfaces meeting in the press nip. Alternatively, the toothed rings of the sleeve are mounted on the end surfaces of the sleeve, in which case the toothed ring of the press body are also mounted on its end surfaces (not shown) . According to another alternative (not shown) , the sleeve is provided at one end with a toothed ring which is in engagement with tooth elements of an external drive member, in which case a similar drive arrangement is provided at the other end of the sleeve. Like the ring 25 of the sleeve depicted in Figure 8, the toothed ring 33 has the same, or substantially the same coefficient of linear expansion as the sleeve in order to avoid undesired stresses in the sleeve upon heating. Figures 10 and 10a show an embodiment of a sleeve 9 which is flexible. The end portions of the flexible sleeve 9 are provided with axial slots 34 to form a circumferential engagement portion 35, with which toothed rings 36 arranged on the press body 6 are brought into engagement within the area of the press nip. The wall thickness of the rigid sleeve 9 is generally within the interval 5-100 mm, preferably 15-40 mm. The difference between the internal diameter of the rigid sleeve 9 and the external diameter of the press body 6 is generally within the interval 0.01-100 mm, preferably 0.5-10 mm, measured at room temperature. During operation, when the rigid sleeve is hot, this difference in diameter is naturally considerably greater. The smaller the wall thickness of the sleeve 9, the quicker a high surface temperature will be obtained without high stresses arising, since the mass to be heated in radial direction is correspondingly less. By making the wall of the rigid sleeve 9 sufficiently thick, the surface of the sleeve in contact with the web can be treated as a conventional press roll surface to be cleaned by a doctor, for example. When the rigid sleeve 9 consists of several layers, one of the layers is a carrier layer, mainly functioning as a stabilizing carrier, with sufficient wall thickness for the carrier layer to be provided with a surface layer, for instance, having the desired property or properties. The carrier layer may be provided on its outer side with a surface layer of a suitable material to obtain desired release property and/or a desired thermal conductivity of the surface of the cylindrical sleeve 9. A particular thermal conductivity may be desirable in order to control the supply of heat to the web and thus prevent delamination of the web. Delamination is the phenomenon when the web bursts as it leaves the press nip due to the vapour pressure in the web being greater than the forces holding the web together can withstand. The cylindrical press body 6 may on its outer side be provided with a surface layer of one or more suitable materials in order to increase its resistance to wear and/or resistance to corrosion, and/or to provide insulation so that the amount of heat transferred from the sleeve 9 to the cylindrical press body 6 is further reduced within the press nip. Alternatively or additionally the sleeve 9 may be provided on its inner side with such a surface layer. Materials suitable to provide a surface layer with the desired release property and desired thermal conductivity that may be mentioned are aluminium oxide, chromium oxide and zirconium oxide based ceramics. Suitable materials to increase the wear resistance are tungsten and chromium carbides and chromium steel. Suitable materials to increase the corrosion resistance are nickel, chromium, and cobalt based alloys. Suitable insulating materials are zirconium oxide based ceramics. Suitable materials for a homogenous sleeve (i.e. one without layers) and for the carrier layer of a sleeve consisting of at least two layers include nodular iron, cast steel and weldable high-strength structural steel. A sleeve that is flexible has a wall thickness generally within the interval 0.4-5.0 mm, preferably 0.8-2.3 mm. The difference between the internal circumference of the flexible sleeve and the external circumference of the press body is generally within the interval 0-100π mm, preferably O.lπ-lOπ mm, measured at room temperature. During operation, when the flexible sleeve 9 is hot, this difference in circumference is naturally considerably greater. Since the sleeve 9 is flexible, a cleaning doctor can be arranged at a suitable location so that the sleeve is bent in towards the press body which will therefore function as a counter- support . Like the rigid sleeve, the flexible sleeve may consist of two or more layers . Any suitable heat source 10 may be used, although an induction heater is currently preferred. Examples of other heat sources are electric heaters, infrared heaters, laser heaters and gas burners. To obtain a symmetrical web the press may suitably comprise a second shoe press provided with a sleeve of the type described or another structure but inverted, so that the sleeve is disposed in under-position in order to transfer heat to the other side of the fibrous web. The press body of the shoe press may be a roll called solid roll, modified in accordance with the invention, but it is also possible to use a curvature-compensated roll. Since the contact area between the hot sleeve and the shell body of the curvature-compensated roll is small, little heat is transferred to the roll. Sufficient heat can be conducted away with the oil in the roll to maintain a reasonable temperature and thus sufficient viscosity in the oil to achieve satisfactory functioning of the roll. The temperature of the web may be increased before the press nip by arranging one or more steam boxes in the felt loop and/or close to the free side of the web. Figure 11 shows schematically parts of a roll press included in the press section of a machine for manufacturing a continuous web 101 of cellulosic fibrous material, for instance. The roll press comprises a first or upper rotatably journalled press roll 102, a second or lower rotatably journalled press roll 103 and a clothing 105, which is in direct contact with the web 101 and is capable of receiving liquid in liquid form and gaseous form from the web, and carrying it out of the press nip that is defined by the two press rolls. The upper press roll 102 comprises a stable cylindrical press body 106 having shaft journals (not shown) for rotary journalling of the press roll 102 in bearing housings. As for the rest, the press body 106 is arranged and designed in the same way as described above in connection with the shoe press. Likewise the clothing 105 is arranged and designed in the same way as described above. The roll press has a movable sleeve-formed heat transfer means 109 and a heat source 110 which are arranged and designed in the same way as described above in connection with the shoe press. Figure 12 shows schematically parts of a roll calender included in the treatment section of a machine in which a continuous web 201, e.g. a paper or board web, is subjected to a form and/or surface changing mechanical treatment in one or more nips . The web may be coated or uncoated. In the last-mentioned case the machine may be included as a part of a paper machine, for instance, upstream of the reel-up. The roll calender comprises a first or upper rotatably journalled roll 202 and a second or lower rotatably journalled roll 203, said rolls defining a roll nip with each other. The upper roll 202 comprises a stable cylindrical body 206 having shaft journals (not shown) for rotary journalling of the upper roll 202 in bearing housings. As for the rest, the cylindrical body 206 is arranged and designed in the same way as described above in connection with the shoe press. The roll calender has a movable sleeve- formed heat transfer means 209 and a heat source 210 which are arranged and designed in the same way as described above in connection with the shoe press. Figure 13 shows schematically parts of a shoe calender with extended nip included in the treatment section of a machine in which a continuous web 301, e.g. a paper or board web, is subjected to a form and/or surface changing mechanical treatment in one or more nips . The web may be coated or uncoated. In the last-mentioned case the machine may be included as a part of a paper machine, for instance, upstream of the reel-up. The shoe calender comprises a rotatably journalled counter roll 302, a shoe 303 and an impermeable, flexible belt 304. The counter roll 302 comprises a stable cylindrical body 306 having shaft journals (not shown) for rotary journalling of the counter roll 302 in bearing housings. As for the rest, the cylindrical body 306 is arranged and designed in the same way as described above in connection with the shoe press. The shoe 303 has a concave surface 307 for cooperation with the corresponding convex body 306 of the counter roll 302 in order to obtain the extended nip. The flexible belt 304 runs through the nip in sliding contact with the concave surface 307 of the shoe. In the embodiment shown the shoe calender is provided with a roll including said shoe 303 and belt 304 which is rigidly mounted at rotatable peripheral end portions (not shown) . Alternatively, the flexible belt may run in a loop around a plurality of rolls, in which loop the shoe is thus mounted. Further, the shoe calender has a movable sleeve-formed heat transfer means 309 and a heat source 310 which are arranged and designed in the same way as described above in connection with the shoe press. The web-contacting elements 203, 209 and 304, 309 and their surfaces of the roll calender and shoe calender are constructed and designed in accordance with the basic conceptions described above in connection with the shoe press and simultaneously taking into consideration each specific type of calendering that is to be carried out under supply of heat for each specific continuous web running through the nip, said considerations being well known for the expert in the technique of calendering, e.g. those being basis of shoe calenders of the type OptiDwell™ which is sold by Valmet Corporation, Finland.

Claims: C L A I M S 1. A press section in a machine for manufacturing a continuous web (1) of fibrous material, comprising one or more presses, at least one of which is a shoe press with extended press nip comprising - a rotatable counter roll (2) including a cylindrical press body (6) , - a press shoe (3) having a concave surface for pressure-generating cooperation with said press body (6) , - an impermeable belt (4) running through the press nip in sliding contact with the concave surface of the press shoe (3) , - a clothing (5) running in a loop around a plurality of guide rolls and through the press nip in contact with the web (1) , and being capable of receiving and carrying liquid along with it, - a movable heat transfer means (9) for continuous transfer of heat to the web (1) in the extended press nip, and - at least one heat source (10) for continuous heating of the heat transfer means (9) , characterized in that the counter roll (2) comprises a sleeve that forms said heat transfer means (9) and encloses the press body (6) . 2. A press section as claimed in claim 1, characterized in that the web (1) is arranged to run through the press nip in direct contact with the sleeve and said clothing (5) . 3. A press section as claimed in claim 1 or 2 , characterized in that the sleeve (9) is arranged to enclose the press body (6) in a loose relation therebetween so that the sleeve (9) is permitted to expand freely in all directions in relation to the press body (6) during said heating before the press nip. 4. A press section as claimed in any one of claims 1-3, characterized in that the sleeve (9) is a rigid, form-stable sleeve having an envelope surface (18) with circular cross section, which rigid sleeve has predetermined, constant or axially varying wall thickness . 5. A press section as claimed in claim 3, characterized in that the wall thickness of the rigid sleeve (9) is within the interval 5-100 mm, preferably 15-40 mm. 6. A press section as claimed in claim 4 or 5 , characterized in that the internal diameter of the rigid sleeve (9) is 0.01-100 mm, preferably 0.5-10 mm, larger than the external diameter of the press body (6) , measured at room temperature . 7. A press section as claimed in any one of claims 1-3, characterized in that the sleeve (9) is a flexible sleeve with predetermined, constant wall thickness. 8. A press section as claimed in claim 7, characterized in that the wall thickness of the flexible sleeve (9) is within the interval 0.4-5.0 mm, preferably 0.8-2.3 mm. 9. A press section as claimed in claim 7 or 8, characterized in that the circumference of the internal surface of the flexible sleeve (9) is 0-100π mm, preferably O.lπ-lOπ mm, larger than the circumference of the external surface of the press body (6) . 10. A press section as claimed in any one of claims 1-9, characterized in that the sleeve (9) is homogenous. 11. A press section as claimed in any one of claims 1-9, characterized in that the sleeve (9) consists of two or more layers, one of which is a form-stable carrier layer. 12. A press section as claimed in claim 11, characterized in that on its outer side the sleeve (9) has a surface layer of a material giving the desired releasing ability and/or desired thermal conductivity. 13. A press section as claimed in claim 11 or 12, characterized in that the outer side of the press body (6) and/or the inner side (17) of the sleeve have/has a surface layer of a material that provides increased resistance to wear and/or increased resistance to corrosion. 14. A press section as claimed in any one of claims 11-13, characterized in that the outer side of the press body (6) and/or the inner side (17) of the sleeve (9) have/has a surface layer of a material forming heat insulation. 15. A press section as claimed in any one of the preceding claims, characterized in that the sleeve (9) on its inner side is provided with a plurality of axially uniformly distributed, circumferential grooves (19) arranged to reduce the heat transfer from the inside of the sleeve to the press body (6) through reduced contact surface . 16. A press section as claimed in any one of the preceding claims, characterized in that the press body (6) is cambered and in that the inner side (17) of the sleeve (9) is cambered in accordance with the press body (6) . 17. A press section as claimed in any one of the preceding claims, characterized in that the press body (6) is arranged to press the sleeve (9) firmly at a contact point (14) within the press nip upon pressure-generating cooperation of the press shoe (3) with the press body (6) to produce a sufficient friction force at said contact point (14) between opposing surfaces of the press body (6) and the sleeve (9) so that the sleeve (9) is forced round by the press body (6) and at the same speed as the latter at said contact point . 18. A press section as claimed in any one of the preceding claims, characterized in that the sleeve (9) and the press body (6) are provided with cooperating tooth elements (32, 33) arranged to be brought into engagement with each other only within the area of the press nip in order to drive the sleeve (9) at the same speed as the press body (6) within said engagement area. 19. A press section as claimed in any one of the preceding claims, characterized in that the counter roll (2) comprises stop elements (13; 22; 27) arranged at at least one end of the counter roll (2) to retain the sleeve (9) on the press body (6) in axial direction while at the same time allowing free axial expansion of the sleeve (9) upon heating. 20. A press section as claimed in any one of claims 7-16, characterized in that the flexible sleeve (9) is provided with axial slots (34) around its end portions, and in that the press body (6) is provided at its ends with tooth elements (36) arranged to be brought into engagement with the slots (34) of the sleeve (9) only within the area of the press nip in order to drive the sleeve (9) at the same speed as the press body (6) within said engagement area. 21. A press section as claimed in any one of the preceding claims, characterized in that it comprises a second sleeved shoe press designed in accordance with any one of claims 1-20 but inverted, with the sleeve in a position on the other side of the web (1) for treating the other side of the web with heat during pressing in a corresponding manner. 22. A press section in a machine for manufacturing a continuous web (101) of fibrous material, comprising one or more presses, at least one of which is a roll press comprising - a first rotatable press roll (102) , - a second rotatable press roll (103) defining a press nip with the first press roll (102) , at least the first press roll (102) including a cylindrical press body (106) , - a clothing (105) running in a loop around a plurality of guide rolls and through the press nip in contact with the web (101) , and being capable of receiving and carrying liquid along with it, - a movable heat transfer means (109) for continuous transfer of heat to the web (101) in the press nip, and - at least one heat source (110) for continuous heating of the heat transfer means (109) , characterized in that the first press roll (102) comprises a sleeve that forms said heat transfer means (109) and encloses the press body (106) . 23. A press section as claimed in claim 22, characterized in that the web (101) is arranged to run through the press nip in direct contact with the sleeve (109) and said clothing (105) . 24. A press section as claimed in claim 22 or 23, characterized in that the sleeve (109) is arranged to enclose the press body (106) in a loose relation therebetween so that the sleeve (109) is permitted to expand freely in all directions in relation to the press body (106) during said heating before the press nip. 25. A press section as claimed in any one of claims 22-24, characterized in that the sleeve (109) is a rigid, form-stable sleeve having an envelope surface with circular cross section, which rigid sleeve has predetermined, constant or axially varying wall thickness . 26. A press section as claimed in claim 25, characterized in that the wall thickness of the rigid sleeve (109) is within the interval 5-100 mm, preferably 15-40 mm. 27. A press section as claimed in claim 25 or 26, characterized in that the internal diameter of the rigid sleeve (109) is 0.01-100 mm, preferably 0.5-10 mm, larger than the external diameter of the press body (106) , measured at room temperature . 28. A press section as claimed in any one of claims 22-24, characterized in that the sleeve (109) is a flexible sleeve with predetermined, constant wall thickness . 29. A press section as claimed in claim 28, characterized in that the wall thickness of the flexible sleeve (109) is within the interval 0.4-5.0 mm, preferably 0.8-2.3 mm. 30. A press section as claimed in claim 28 or 29, characterized in that the circumference of the internal surface of the flexible sleeve (109) is 0-100π mm, preferably O.lπ-lOπ mm, larger than the circumference of the external surface of the press body (106) . 31. A press section as claimed in any one of claims 22-30, characterized in that the sleeve (109) is homogenous . 32. A press section as claimed in any one of claims 22-30, characterized in that the sleeve (109) consists of two or more layers, one of which is a form- stable carrier layer. 33. A press section as claimed in claim 32, characterized in that on its outer side the sleeve (109) has a surface layer of a material giving the desired releasing ability and/or desired thermal conductivity. 34. A press section as claimed in claim 32 or 33, characterized in that the outer side of the press body (106) and/or the inner side of the sleeve have/has a surface layer of a material that provides increased resistance to wear and/or increased resistance to corrosion. 35. A press section as claimed in any one of claims 32-34, characterized in that the outer side of the press body (106) and/or the inner side of the sleeve (109) have/has a surface layer of a material forming heat insulation. 36. A press section as claimed in any one of claims 22-35, characterized in that the sleeve (109) on its inner side is provided with a plurality of axially uniformly distributed, circumferential grooves arranged to reduce the heat transfer from the inside of the sleeve to the press body (106) through reduced contact surface. 37. A press section as claimed in any one of claims 22-36, characterized in that the press body (106) is cambered and in that the inner side of the sleeve (109) is cambered in accordance with the press body (106) . 38. A press section as claimed in any one of claims 22-37, characterized in that the press body (106) is arranged to press the sleeve (109) firmly at a contact point within the press nip upon pressure-generating cooperation of the second press roll (103) with the press body (106) to produce a sufficient friction force at said contact point between opposing surfaces of the press body (106) and the sleeve (109) so that the sleeve (109) is forced round by the press body (106) and at the same speed as the latter at said contact point. 39. A press section as claimed in any one of claims 22-38, characterized in that the sleeve (109) and the press body (106) are provided with cooperating tooth elements arranged to be brought into engagement with each other only within the area of the press nip in order to drive the sleeve (109) at the same speed as the press body (106) within said engagement area. 40. A press section as claimed in any one of claims 22-39, characterized in that the first press roll (102) comprises stop elements arranged at at least one end of the first press roll (102) to retain the sleeve (109) on the press body (106) in axial direction while at the same time allowing free axial expansion of the sleeve (109) upon heating. 41. A press section as claimed in any one of claims 28-37, characterized in that the flexible sleeve (109) is provided with axial slots around its end portions, and in that the press body (106) is provided at its ends with tooth elements arranged to be brought into engagement with the slots of the sleeve (109) only within the area of the press nip in order to drive the sleeve (109) at the same speed as the press body (106) within said engagement area . 42. A press section as claimed in any one of claims 23-41, characterized in that it comprises a second sleeved roll press designed in accordance with any one of claims 23-41 but inverted, with the sleeve in a position on the other side of the web (101) for treating the other side of the web with heat during pressing in a corresponding manner. 43. A shoe press with extended press nip for a press section in a machine for manufacturing a continuous web of fibrous material, comprising - a rotatable counter roll (2) including a cylindrical press body (6) , - a press shoe (3) having a concave surface for pressure-generating cooperation with said press body (6) , - an impermeable belt (4) running through the press nip in sliding contact with the concave surface of the press shoe (3) , - a clothing (5) running in a loop around a plurality of guide rolls and through the press nip in contact with the web (1) , and being capable of receiving and carrying liquid along with it, - a movable heat transfer means (9) for continuous transfer of heat to the web (1) in the extended press nip, and - at least one heat source (10) for continuous heating of the heat transfer means (9) , characterized in that the counter roll (2) comprises a sleeve that forms said heat transfer means (9) and encloses the press body (6) . 44. A shoe press as claimed in claim 43, characterized in that the web (1) is arranged to run through the press nip in direct contact with the sleeve and said clothing (5) . 45. A shoe press as claimed in claim 43 or 44, characterized in that the sleeve (9) is arranged to enclose the press body (6) in a loose relation therebetween so that the sleeve (9) is permitted to expand freely in all directions in relation to the press body (6) during said heating before the press nip. 46. A shoe press as claimed in any one of claims 43-45, characterized in that the sleeve (9) is a rigid, form-stable sleeve having an envelope surface (18) with circular cross section, which rigid sleeve has predetermined, constant or axially varying wall thickness . 47. A shoe press as claimed in claim 46, characterized in that the wall thickness of the rigid sleeve (9) is within the interval 5-100 mm, preferably 15-40 mm. 48. A shoe press as claimed in claim 46 or 47, characterized in that the internal diameter of the rigid sleeve (9) is 0.01-100 mm, preferably 0.5-10 mm, larger than the external diameter of the press body (6) , measured at room temperature . 49. A shoe press as claimed in any one of claims 43-45, characterized in that the sleeve (9) is a flexible sleeve with predetermined, constant wall thickness. 50. A shoe press as claimed in claim 49, characterized in that the wall thickness of the flexible sleeve (9) is within the interval 0.4-5.0 mm, preferably 0.8-2.3 mm. 51. A shoe press as claimed in claim 49 or 50, characterized in that the circumference of the internal surface of the flexible sleeve (9) is 0-100π mm, preferably O.lπ-lOπ mm, larger than the circumference of the external surface of the press body (6) . 52. A shoe press as claimed in any one of claims 43-51, characterized in that the sleeve (9) is homogenous. 53. A shoe press as claimed in any one of claims 43-51, characterized in that the sleeve (9) consists of two or more layers, one of which is a form-stable carrier layer. 54. A shoe press as claimed in claim 53, characterized in that on its outer side the sleeve (9) has a surface layer of a material giving the desired releasing ability and/or desired thermal conductivity. 55. A shoe press claimed in claim 53 or 54, characterized in that the outer side of the press body (6) and/or the inner side (17) of the sleeve have/has a surface layer of a material that provides increased resistance to wear and/or increased resistance to corrosion. 56. A shoe press as claimed in any one of claims 53-55, characterized in that the outer side of the press body (6) and/or the inner side (17) of the sleeve (9) have/has a surface layer of a material forming heat insulation. 57. A shoe press as claimed in any one of claims 43-56, characterized in that the sleeve (9) on its inner side is provided with a plurality of axially uniformly distributed, circumferential grooves (19) arranged to reduce the heat transfer from the inside of the sleeve to the press body (6) through reduced contact area. 58. A shoe press as claimed in any one of claims 43-57, characterized in that the press body (6) is cambered and in that the inner side (17) of the sleeve (9) is cambered in accordance with the press body (6) . 59. A shoe press as claimed in any one of claims 43-58, characterized in that the press body (6) is arranged to press the sleeve (9) firmly at a contact point (14) within the press nip upon pressure-generating cooperation of the press shoe (3) with the press body (6) to form a sufficiently large friction force at said contact point (14) between opposing surfaces of the press body (6) and the sleeve (9) so that the sleeve (9) is forced round by the press body (6) and at the same speed as the latter at said contact point. 60. A shoe press as claimed in any one of claims 43-59, characterized in that the sleeve (9) and the press body (6) are provided with cooperating tooth elements (32, 33) arranged to be brought into engagement with each other only within the area of the press nip in order to drive the sleeve (9) at the same speed as the press body (6) within said engagement area. 61. A shoe press as claimed in any one of claims 43-60, characterized in that the counter roll (2) comprises stop elements (13; 22; 27) arranged at at least one end of the counter roll (2) to retain the sleeve (9) on the press body (6) in axial direction while at the same time allowing free axial expansion of the sleeve (9) upon heating. 62. A shoe press as claimed in any one of claims 49-58, characterized in that the flexible sleeve (9) is provided with axial slots (34) around its end portions, and in that the press body (6) is provided at its ends with tooth elements (36) arranged to be brought into engagement with the slots (34) of the sleeve (9) only within the area of the press nip in order to drive the sleeve (9) at the same speed as the press body (6) within said engagement area . 63. A counter roll (2) for a shoe press with extended press nip, comprising a rotatable cylindrical press body (6) , characterized in that it comprises a sleeve (9) as defined in any one of claims 43-69. 64. A treatment section in a machine for shape and/or surface changing mechanical treatment of a continuous web (201) of fibrous material, comprising at least one roll calender comprising - a first rotatable roll (202) , - a second rotatable roll (203) defining a nip with the first roll (202) , at least the first roll (202) including a cylindrical body (206) , - a movable heat transfer means (209) for continuous transfer of heat to the web (201) in said nip, and - at least one heat source (210) for continuous heating of the heat transfer means (209) , characterized in that the first roll (202) comprises a sleeve that forms said heat transfer means (209) and encloses said cylindrical body (206) . 65. A treatment section as claimed in claim 64, characterized in that the first roll (202) and its sleeve (209) and cylindrical body (206) are designed, arranged and equipped in accordance with any one of claims 24-41 of the press section. 66. A treatment section in a machine for shape and/or surface changing mechanical treatment of a continuous web (301) of fibrous material, comprising at least one shoe calender with extended nip comprising - a rotatable counter roll (302) including a cylindrical body (306) , - a shoe (303) having a concave surface for nip-forming cooperation with said cylindrical body (306) , - an impermeable belt (304) running through the extended nip in sliding contact with the concave surface of the shoe (303) , - a movable heat transfer means (309) for continuous transfer of heat to the web (301) in the extended nip, and - at least one heat source (310) for continuous heating of the heat transfer means (309) , characterized in that the counter roll (302) comprises a sleeve that forms said heat transfer means (309) and encloses the cylindrical body (306) . 67. A treatment section as claimed in claim 66, characterized in that the counter roll (302) and its sleeve (309) and cylindrical body (306) are designed, arranged and equipped in accordance with any one of claims 24-41 of the press section.

Inventors: BENGTSSON JAN MARTIN, BROX ERIK, HELGESSON LEIF ERIK, JANSSON KJELL SUNE EVALD, KILIAN ANNA MALIN KATARINA, NICANDER JAN WILHELM, SAEFMAN NILS-ERIK, TOERNQVIST KENTH ROGER, BENGTSSON, JAN, MARTIN, BROX, ERIK, HELGESSON, LEIF, ERIK, JANSSON, KJELL, SUNE, EVALD, KILIAN, ANNA, MALIN, KATARINA, NICANDER, JAN, WILHELM, SAEFMAN, NILS-ERIK, TOERNQVIST, KENTH, ROGER
Applicants: VALMET KARLSTAD AB, VALMET-KARLSTAD AB
Application year: 1999
Main classification: D21F3
IPC codes: D21F3