PAPERMAKING MACHINE

Abstract

A papermaking machine including a Yankee including a body provided with a metal mantle with circular cross-section and two end heads on which are formed or mounted two respective coaxial pins arranged along a rotation axis of the Yankee, the body being configured to rotate with a predetermined angular speed around said rotation axis. Inside the body is arranged a fixed electromagnetic induction heating system including one or more inductors interacting electromagnetically with the mantle to produce induced electric currents in the same mantle, the inductors being arranged near the radially innermost surface of the mantle. In the machine is arranged a structured web configured for transporting a sheet of fibrous material up to the contact of the latter with the mantle of the Yankee.

Claims

1-12. (canceled)

13. A papermaking machine, comprising: a Yankee having a body comprising a metal mantle with circular cross-section and two end heads on which are formed or mounted two respective coaxial pins arranged along a rotation axis of the Yankee, said body being configured to rotate with a predetermined angular speed around said rotation axis, wherein inside said body is arranged a fixed electromagnetic induction heating system comprising one or more inductors interacting electromagnetically with the mantle to produce induced electric currents in the same mantle, said one or more inductors being arranged near the radially innermost surface of the mantle, and in which is arranged a structured web configured for transporting a sheet of fibrous material up to the contact of the latter with the mantle of the Yankee.

14. The papermaking machine according to claim 13, wherein the Yankee has an external diameter between 2.00 m and 7.500 m, and the mantle has an axial length between 3.00 m and 7.400 m.

15. The papermaking machine according to claim 13, wherein the electromagnetic induction heating system extends axially, parallel to the rotation axis of the Yankee, and along the inner surface of the mantle, but is shorter than the inner surface of the mantle, leaving a free space in front of each of the end heads.

16. The papermaking machine according to claim 13, wherein the radially outermost side of the electromagnetic induction system is at a radial distance from the internal surface of the mantle is between 20 cm and 1 mm.

17. The papermaking machine according to claim 13, wherein said electromagnetic induction system comprises a single inductor in the form of a solenoid developed around the rotation axis of the Yankee, the solenoid being formed by coil turns concentric to said rotation axis.

18. The papermaking machine according to claim 13, wherein said electromagnetic induction system comprises a single toroidal inductor developed parallel to the rotation axis the Yankee.

19. The papermaking machine according to claim 13, wherein said electromagnetic induction system includes a plurality of inductors, each of which comprises a solenoid developed around the axis of the Yankee and formed by coils concentric to said axis.

20. The papermaking machine according to claim 13, wherein said electromagnetic induction system comprises a plurality of inductors axially placed side by side.

21. The papermaking machine according to claim 13, wherein said electromagnetic induction system comprises a plurality of inductors, each of which consists of a solenoid formed by coils wound around respective radial axes.

22. The papermaking machine according to claim 13, wherein said electromagnetic induction system comprises a plurality of inductors arranged circumferentially around the axis of the Yankee.

23. The papermaking machine according to claim 17, wherein the inductor or the inductors are at a radial distance from the inner surface of the mantle and the inductors are formed by coils comprising conductors with a predefined diameter spaced apart by a pitch of predefined value, wherein the value of the said radial distance is less than or equal to the difference between said pitch and said diameter.

24. The papermaking machine according to claim 17, wherein the inductor or the inductors have a side radially closer to the mantle and a side radially more distant from the mantle, wherein said side radially closest to the mantle is at a radial distance from the inner surface of the mantle, the inductors are formed by coils comprising conductors of predefined diameter spaced from each other by a pitch of predefined value, wherein the value of said radial distance is less than or equal to the difference between said pitch and said diameter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In the drawings attached by way of example, not to be considered in a limiting sense:

[0023] FIG. 1 shows a papermaking machine provided with a Yankee in accordance with the present invention in a possible operating configuration;

[0024] FIG. 2 shows a papermaking machine equipped with a Yankee in accordance with the present invention in a further possible operating configuration;

[0025] FIG. 3 represents a schematic vertical sectional view illustrating some parts of a Yankee dryer according to the present invention;

[0026] FIG. 4 represents a detail relating to a possible operating configuration of a Yankee dryer in accordance with the present invention;

[0027] FIG. 5A represents a schematic longitudinal section view of a Yankee in accordance with the present invention;

[0028] FIG. 5B represents an enlargement of FIG. 5A and highlights the magnetic field lines which intercept the Yankee mantle;

[0029] FIG. 6 shows a view of a possible embodiment of an inductor for a Yankee in accordance with the present invention;

[0030] FIG. 7 shows a view of a possible embodiment of an inductor for a Yankee in accordance with the present invention;

[0031] FIG. 8 shows a view of a possible embodiment of an inductor for a Yankee in accordance with the present invention;

[0032] FIG. 9 shows a view of a further possible embodiment of an inductor for a Yankee in accordance with the present invention;

[0033] FIG. 10 shows a view of a further possible embodiment of an inductor for a Yankee in accordance with the present invention;

[0034] FIG. 11 shows a view of a further possible embodiment of an inductor for a Yankee in accordance with the present invention;

[0035] FIG. 12 shows a view of a further possible embodiment of an inductor for a Yankee in accordance with the present invention;

[0036] FIG. 13 shows a view of a possible embodiment of an inductor group for a Yankee dryer according to the present invention;

[0037] FIG. 14 shows a view of a possible embodiment of an inductor group for a Yankee dryer according to the present invention;

[0038] FIG. 15 shows a view of a possible embodiment of an inductor group for a Yankee dryer according to the present invention;

[0039] FIG. 16 shows a view of a further possible embodiment of a group of inductors for a Yankee dryer according to the present invention;

[0040] FIG. 17 shows a view of a further possible embodiment of a group of inductors for a Yankee dryer according to the present invention;

[0041] FIG. 18 shows a view of a further possible embodiment of a group of inductors for a Yankee dryer according to the present invention;

[0042] FIG. 19 shows a view of a further possible embodiment of a group of inductors for a Yankee dryer according to the present invention; and

[0043] FIG. 20 shows a view of a further possible embodiment of a group of inductors for a Yankee dryer according to the present invention.

DETAILED DESCRIPTION

[0044] Reduced to its essential structure and with reference to the figures of the attached drawings, a Yankee (1) for a machine according to the present invention is a body comprising a metal mantle (2) with a circular cross section and two end heads (3) on which two respective coaxial pins (4) are formed or mounted, arranged along an axis of rotation (x-x) of the Yankee. A transmission (5) acts on the pins (4) by which the rotation speed of the Yankee around the axis (x-x) is controlled. The outer surface of the mantle (2) forms a heat exchange surface with a sheet of paper produced upstream of the Yankee to reduce its water content, i.e. increase its dryness. The sheet of paper can be produced, with methods per se known to those skilled in the art, in a machine for the production of structured paper which, for example, comprises a forming zone (A) in which the sheet is formed starting from a fibrous suspension of predefined composition, a pre-drying zone (B) of the sheet downstream of the formation zone (A), along which the water content of the sheet is progressively but partially reduced, and a drying zone (C) downstream of the pre-drying area (B), where the Yankee (1) is installed. In the area (A) for forming the sheet there is arranged and acting a pick-up belt (NA) which transports the sheet towards the pre-drying area (B). In the pre-drying station (B) a structured conveyor web (NB) is arranged and acting which, at the entrance to the pre-drying station (B) receives the sheet from the pick-up belt (NA).

[0045] The structured paper is produced by adhering the sheet to the Yankee (1) when the sheet has a relatively high degree of dryness (typically greater than 30% and preferably greater than 60%). The sheet has a three-dimensional structure due to the conformation of the structured belt (NB) which transports it from the previous stations (A, B) of formation and partial reduction of the water content, up to the contact with the Yankee. The sheet is made to adhere to the surface of the Yankee by effect of a slight pressure exerted by a transfer roller or by effect of a slight winding around the cylindrical surface of the Yankee by means of the web itself. In this case, the pressure exerted by the roller or by the web is preferably the minimum required to guarantee the transfer of the sheet onto the surface of the Yankee, thus avoiding damage to the structure of the same paper. The transition of the paper from the structured web to the Yankee can also be carried out using a higher level of pressure or using pressure rollers of different types (for example suction presses) in order to obtain also a partial removal of the water contained in the sheet and to facilitate the adhesion of the sheet to the mantle of the Yankee, at the cost of greater compression exerted on the sheet with consequent partial flattening of the three-dimensional structure. In FIG. 1 and FIG. 2, in the entry section of the drying area (C) there is a transfer roller (6) which pushes the sheet of paper onto the Yankee (1) with a predetermined pressure.

[0046] The structured web (NB) can consist, for example, of a fabric suitable for structuring paper (for example a TAD type fabric). In this case the structured paper, i.e. characterized by a three-dimensional structure along its thickness, which takes up the shape of the fabric itself. Normally, in these cases, the paper is brought into contact with the cylindrical surface of the Yankee and made to adhere to it only in correspondence with the upper protuberances (knuckles), which represent, compared to the surface, a limited percentage (typically between 10% to 60%, preferably between 20% and 40%).

[0047] The structured web (NB) can also be made from a layer of absorbent or draining material with a relief reported on the paper side, preferably made of polymeric elastic material such as polyurethane, having a distributed structure, preferably to form a lattice, whose function is to create compression surfaces of the sheet against the Yankee surface distinct from other areas in which the sheet undergoes very little, if any, compression. This solution makes it possible to create on the same sheet a weave of compressed fibers which give high resistance to the product, while at the same time maintaining areas with a high absorption capacity in correspondence with the areas which have undergone limited compression. In jargon, in this case, the paper is defined as textured or marked paper.

[0048] In FIG. 1 and FIG. 2 the arrow MD shows the direction of the sheet along the machine. Downstream of the Yankee (1) a section (D) can be arranged for collecting the sheet in the form of reels (R1, R2).

[0049] A hood (7) can be arranged on the Yankee (1).

[0050] In FIG. 1 the pre-drying area (B) comprises a compression unit (Z2) with a pressure roller and an underlying counter-roller to exert a pressure of a predetermined value on the sheet supported by the structured web (NB). Downstream of the compression unit (Z2), with respect to the direction followed by the sheet directed towards the Yankee (1), there is a TAD section (TD). In the variant of FIG. 2, the compression unit (Z2) comprises two pressure rollers and an underlying counter-roller to exert a pre-set pressure on the sheet supported by the structured web (NB). Also in this case, downstream of the compression unit (Z2), with respect to the direction followed by the sheet directed towards the Yankee (1), there is a TAD section (TD). In a further variant embodiment, not shown in the drawings, the pre-drying zone (B) can optionally comprise only a TAD section upstream of the Yankee (1).

[0051] In the drying section (C) the sheet is in contact with the outer surface of the mantle of the Yankee (1) from the entry point (P1) to the exit point (P2) for a section with an angular extension (a) greater than 180. In the scheme of FIG. 2, the sheet is indicated by the reference S. At said exit point (P2) a creping scraper (8) can be arranged for detaching the sheet from the Yankee (1) and, downstream of the creping scraper (8) with respect to the direction of rotation (1C) of the Yankee, there is a cleaner scraper (80). The sheet, in alternative configurations, could be detached from the Yankee even without the use of a scraper, but through the use of support belts which collect the sheet at the end of its passage from the Yankee surface.

[0052] For example, the Yankee (1) has an external diameter comprised between 2.00 m and 7.500 m, and an axial length comprised between 3.00 m and 7.400 m.

[0053] Inside the Yankee (1) there is a fixed electromagnetic induction heating system made up of one or more inductors (H; HN) positioned and configured to produce alternating electromagnetic fields with pre-established frequency and amplitude according to the thermal power to be generated. In case of installation of a plurality of inductors (HN) distributed in the axial direction and fed independently or in groups, it is possible to carry out a partial control of the thermal power generated, in the axial direction, in the mantle. In this way it is possible to compensate for any unevenness in the transversal humidity profile of the dried paper, by acting on the solenoids acting on the areas corresponding to the bands where the paper has greater humidity, by increasing the electric power supply. The electromagnetic fields produced by the inductors, which vary over time, induce the generation of electric currents in the metallic material of the Yankee mantle and, due to the Joule effect, the mantle itself is subject to heating. The heat thus generated is used to dry the sheet (F). The induction heating system makes it possible to generate a uniform thermal imprint on the surface of the mantle (2) of the Yankee, i.e. a uniform heat distribution along the generatrix lines of the cylindrical surface which defines the mantle.

[0054] The electromagnetic induction heating system extends axially, i.e. parallel to the axis (x-x) of the Yankee, along the inner surface of the mantle (2) but is preferably shorter than the latter, leaving a free space (10) in front of each of the end heads (3). In this way, the electromagnetic interaction with the mantle (2) extends solely or almost exclusively to a central area (20) of the latter intended for contact with the sheet (F). This reduces the energy transmission to the lateral parts of the mantle (2) which do not come into contact with the sheet (F).

[0055] Preferably, the radially outer side of the electromagnetic induction system is at a radial distance from the inner surface of the mantle (2) comprised between 20 cm and 1 mm, more preferably said radial distance is comprised between 5 cm and 2 mm and, even more preferably, between 2 cm and 5 mm.

[0056] In the diagrams of FIG. 5A, FIG. 6, FIG. 7 and FIG. 8 there is a single inductor (H) in the form of a solenoid developed around the (x-x) axis of the Yankee. The solenoid is formed by coil turns concentric with said axis (x-x).

[0057] With reference to FIG. 5A, the inductor (H) extends axially inside the Yankee (1) for a length (LH) shorter than the length (L2) of the mantle (2).

[0058] The terminals (HT) of the inductor (H) can be passed through one of the pins (4).

[0059] In the diagrams of FIGS. 9-12 there is a single toroidal inductor (H) developed parallel to the axis (x-x) of the Yankee. The toroidal inductor is formed by coils parallel to the inner surface of the mantle (2). Also in this case, preferably the radially outer side of the inductor (H) is at a radial distance from the inner surface of the shell (2) between 20 cm and 1 mm, more preferably said radial distance is between 5 cm and 2 mm and, even more preferably, between 2 cm and 5 mm. Also in this case, the terminals (HT) of the inductor (H) can be passed through one of the pins (4).

[0060] In the diagrams of FIGS. 13-15 there are a plurality of inductors (HN) each of which consists of a solenoid developed around the axis of the Yankee and formed by coil turns concentric to said axis. In this example, the inductors (HN) are arranged axially side by side. Also in this case, the terminals (HT) of the inductors (HN) can be passed through one of the pins (4).

[0061] In the diagrams of FIGS. 16-20 more inductors (HN) are provided, each of which is formed by a solenoid consisting of coil turns wound around respective radial axes (RHN). The inductors

[0062] (HN) in this case are arranged circumferentially around the axis of the Yankee. Also in this case, the terminals (HT) of the inductors (HN) can be passed through one of the pins (4). In the drawings, the reference HP indicates cores of ferromagnetic material which can optionally be used to make the inductors (HN).

[0063] By using a plurality of inductors (HN) arranged as in the diagrams of FIGS. 13-15 it is also possible to control the thermal power transmitted to the mantle (2) in a differentiated manner along the axial direction of the Yankee to produce axially variable thermal profiles. By using a plurality of inductors (HN) arranged as in the diagrams of FIGS. 16-20 it is also possible to control the thermal power transmitted to the mantle (2) in a circumferentially differentiated way to vary the heat transmission in the circumferential direction.

[0064] Preferably, the inductor consists of one or more solenoids geometrically configured such that the electromagnetic field produced is intercepted exclusively or almost exclusively by the cylindrical mantle (2) of the Yankee, minimizing the projection of the electromagnetic field lines towards the end heads (3), with which the sheet does not come into contact.

[0065] In practice, the Yankee mantle constitutes an armature in Near Field geometric conditions. In this way, in addition to directing the electromagnetic energy towards the mantle with greater spatial precision, reducing the start-up transients, the projections of the electromagnetic fields towards the end heads are reduced, which also contributes to increasing safety for operators on the site where the Yankee is installed.

[0066] The substantial absence of electromagnetic fields outside the volumetric areas affected by the presence of the mantle therefore makes it possible to limit the amount of energy transmitted by the electromagnetic fields to the end heads, reducing the amount of energy dispersed in the environment and not effectively directed towards the sheet being dried.

[0067] The use of the Near Field for the induction of the mantle allows, in other words, to intercept the greatest possible number of electromagnetic field lines by the mantle, reducing the leakage of electromagnetic fields from the volume delimited circumferentially by the mantle and simplifying the realization of the end heads.

[0068] From the construction point of view, preferably in accordance with the present invention, the following condition is satisfied:

[0069] SP-d, where S is the radial distance of the inductor from the internal surface of the Yankee mantle, d is the diameter of the conductors forming the coil turns (HS) and P is the pitch between the coil turns of the inductor (or individual inductors).

[0070] It is noted that, in general, all other conditions being equal, turns more spaced apart from each other will imply a lower spatial density of the local field, therefore a lower temperature generated on the mantle, compared to turns wound with a smaller winding pitch, i.e. closer turns.

[0071] More preferably, in accordance with the present invention, S and the difference P-d are of the same order of magnitude and have substantially the same value, i.e. the following condition is satisfied: SP-d, where S, d and P have the meaning indicated above.

[0072] Accordingly, according to the present invention, a geometric configuration of the inductor system (understood as a single solenoid or as a plurality of solenoids) is achieved in which the distance between the spiral windings of the inductor system and the internal surfaces of the armature consisting of the Yankee mantle is approximately equal or less than the pitch between the coils (HS) reduced by said diameter (d).

[0073] In this way, the magnetic fields of the individual turns intercept the mantle material being influenced in a limited way by the magnetic fields of the adjacent turns. Therefore, it is possible to concentrate the magnetic field effect of the single turns more effectively. Furthermore, given that once the induced magnetic field has been created in the metallic material of the mantle, the resulting magnetic field is reduced (Faraday cage effect), it is easier to prevent electromagnetic induction from extending to the end heads, reducing the amount of energy which would be dispersed in the external environment.

[0074] With reference to the example shown in FIGS. 9-12, the inductor (H) has a side (HM) radially closer to the mantle (2) and a side (HW) radially more distant from the mantle (2), and said side (HM) radially closest to the mantle (2) is at a given radial distance from the inner surface of the mantle (2) and also in this case the inductors are formed by turns (HS) made up of conductors of predefined diameter spaced apart of a pitch of predefined value (P). This case is characterized by the fact that the value of the radial distance of the side (HM) from the inner surface of the mantle (2) is less than or equal to the difference between said pitch (P) and said diameter (d). The same applies if instead of the single inductor (H) there are several inductors thus constructed and aligned along the axis of the Yankee.

[0075] From the description provided above, it is evident that a papermaking machine according to the present invention comprises a Yankee (1) consisting of a body comprising a metal mantle (2) with circular cross-section and two end heads (3) on which are formed or mounted two respective coaxial pins (4) arranged along a rotation axis (x-x) of the Yankee, said body being configured to rotate with a predetermined angular speed around said rotation axis (x-x), characterized in that inside said body is arranged a fixed electromagnetic induction heating system comprising one or more inductors (H; HN) interacting electromagnetically with the mantle (2) to produce induced electric currents in the same mantle, said one or more inductors (H; HN) being arranged near the radially innermost surface of the mantle (2), and in which is arranged a structured web (NB) configured for transporting a sheet (F) of fibrous material up to the contact of the latter with the mantle (2) of the Yankee (1).

[0076] From the description provided above, it is also evident that a machine according to the present invention may also have one or more of the following features possibly combined between them: [0077] the Yankee (1) has an external diameter comprised between 2.00 m and 7.500 m, and the mantle (2) has an axial length comprised between 3.00 m and 7.400 m. [0078] the electromagnetic induction heating system extends axially, i.e. parallel to the axis (x-x) of the Yankee, along the inner surface of the mantle (2) but is shorter than the latter, leaving a free space (10) in front of each of the end heads (3). [0079] the radially outermost side of the electromagnetic induction system is at a radial distance from the internal surface of the mantle (2) comprised between 20 cm and 1 mm, more preferably at a radial distance comprised between 5 cm and 2 mm and, even more preferably, comprised between 2 cm and 5 mm. [0080] the electromagnetic induction system comprises a single inductor (H) in the form of a solenoid developed around the axis (x-x) of the Yankee, the solenoid being formed by coils concentric to said axis (x-x). [0081] the electromagnetic induction system comprises a single toroidal inductor (H) developed parallel to the axis (x-x) of the Yankee. [0082] the electromagnetic induction system includes a plurality of inductors (HN) each of which consists of a solenoid developed around the axis of the Yankee and formed by coil turns concentric to said axis. [0083] the electromagnetic induction system comprises a plurality of inductors (HN) axially placed side by side. [0084] the electromagnetic induction system comprises a plurality of inductors (HN), each of which consists of a solenoid formed by coil turns parallel to the inner surface of the mantle (2). [0085] the electromagnetic induction system comprises a plurality of inductors (HN) arranged circumferentially around the axis of the Yankee. [0086] the inductor (H) or the inductors (HN) are at a radial distance(S) from the inner surface of the mantle (2), the inductors are formed by coils (HS) consisting of conductors with a predefined diameter (d) spaced apart by a pitch of predefined value (P), and the value of the said radial distance(S) is less than or equal to the difference between said pitch (P) and said diameter (d). [0087] the inductor (H) or the inductors (HN) are at a radial distance(S) from the inner surface of the mantle (2), the inductors are formed by coils (HS) consisting of conductors with a predefined diameter (d) spaced apart by a pitch of predefined value (P), and the value of the said radial distance(S) is about equal to the difference between said pitch (P) and said diameter (d). [0088] the pitch between the turn coils (HS) is adjustable.

[0089] In practice, the execution details can in any case vary in an equivalent way as regards the individual elements described and illustrated, without thereby departing from the scope of the solution adopted and therefore remaining within the limits of the protection granted by the present patent in accordance with the attached claims.