YANKEE DRIER FOR PAPER PRODUCTION

Abstract

A Yankee drier for paper production including a body having a metal mantle with circular cross-section and two side 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 the rotation axis. Inside the 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, the one or more inductors being arranged near the radially innermost surface of the mantle.

Claims

1-12. (canceled)

13. A Yankee drier for paper production comprising: a body comprising a metal mantle with circular cross-section and two side heads on which are formed or mounted two respective coaxial pins arranged along a rotation axis of the Yankee, said body 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.

14. The Yankee drier according to claim 13, further comprising an external diameter of the drier 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 Yankee drier according to claim 13, wherein the electromagnetic induction heating system extends axially, parallel to the rotation axis of the Yankee, along the inner surface of the mantle, but the electromagnetic induction heating system is shorter than the mantle, leaving a free space in front of each of the heads.

16. The Yankee drier 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 between 20 cm and 1 mm.

17. The Yankee drier according to claim 13, wherein the electromagnetic induction system comprises an inductor in the form of a solenoid developed around the rotational axis of the Yankee, the solenoid being formed by coils concentric to said rotational axis.

18. The Yankee according to claim 13, wherein the electromagnetic induction system comprises a single toroidal inductor formed by coils developed parallel to the axis of the Yankee.

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

20. The Yankee drier according to claim 13, wherein the electromagnetic induction system comprises a plurality of inductors axially placed side by side.

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

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

23. The Yankee drier according to claim 17, wherein the inductor is at a radial distance from the inner surface of the mantle, the inductor is 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 Yankee drier according to claim 17, wherein the inductor has a side radially closer to the mantle and a side radially more distant from the mantle, in which 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 made up of conductors of predefined diameter spaced from each other by a pitch of predefined value, and 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

[0025] In the drawings attached by way of example, not to be considered in a limiting sense:

[0026] FIG. 1 shows a papermaking machine provided with a Yankee drier in accordance with the present invention;

[0027] FIG. 2 represents a schematic vertical sectional view showing some parts of a Yankee dryer according to the present invention;

[0028] FIG. 3 represents a possible operating configuration of a Yankee dryer in accordance with the present invention;

[0029] FIG. 4 represents another possible operating configuration of a Yankee dryer in accordance with the present invention;

[0030] FIG. 5A represents a schematic longitudinal section view of a Yankee in accordance with the present invention;

[0031] FIG. 5B represents an enlargement of FIG. 5A and highlights the magnetic field lines intercepting the Yankee mantle;

[0032] FIG. 6 shows a view of a possible embodiment of an inductor for a Yankee drier in accordance with the present invention;

[0033] FIG. 7 shows a view of a possible embodiment of an inductor for a Yankee drier in accordance with the present invention;

[0034] FIG. 8 shows a view of a possible embodiment of an inductor for a Yankee drier in accordance with the present invention;

[0035] FIG. 9 shows a view of a further possible embodiment of an inductor for a Yankee drier in accordance with the present invention;

[0036] FIG. 10 shows a view of a further possible embodiment of an inductor for a Yankee drier in accordance with the present invention;

[0037] FIG. 11 shows a view of a further possible embodiment of an inductor for a Yankee drier in accordance with the present invention;

[0038] FIG. 12 shows a view of a further possible embodiment of an inductor for a Yankee drier in accordance with the present invention;

[0039] FIG. 13 shows a view of a possible embodiment of an inductor group for a Yankee dryer according to the present invention;

[0040] FIG. 14 shows a view of a possible embodiment of an inductor group for a Yankee dryer according to the present invention;

[0041] FIG. 15 shows a view of a possible embodiment of an inductor group for a Yankee dryer according to the present invention;

[0042] FIG. 16 shows a view of a further possible embodiment of a group of inductors for a Yankee drier according to the present invention;

[0043] FIG. 17 shows a view of a further possible embodiment of a group of inductors for a Yankee drier according to the present invention;

[0044] FIG. 18 shows a view of a further possible embodiment of a group of inductors for a Yankee drier according to the present invention;

[0045] FIG. 19 shows a view of a further possible embodiment of a group of inductors for a Yankee drier according to the present invention; and

[0046] FIG. 20 shows a view of a further possible embodiment of a group of inductors for a Yankee drier according to the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0047] Reduced to its essential structure and with reference to the figures of the attached drawings, a Yankee drier (1) 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 tissue paper or MG paper which, for example, comprises a forming zone (A) in which the sheet is formed starting from a fibrous suspension of predefined composition, a draining zone (B) of the sheet downstream of the formation zone (A), along which the water content of the sheet is progressively reduced, and a drying zone (C) downstream of the draining zone (B), where the Yankee (1) is installed.

[0048] In FIG. 1 the arrow MD shows the direction of the sheet along the machine.

[0049] Downstream of the Yankee (1) a section (D) can be arranged for collecting the sheet in the form of reels (R1, R2).

[0050] In the entry section of the drying area (C) there is a presser (6) which compresses the sheet of paper on the Yankee (1) with a pre-set pressure. For example, the presser (6) can consist of a shoe press, a blind-holes roller or a suction roller.

[0051] The section (B) can eventually integrate systems for reducing the water content of the sheet based on multiple concepts (application of vacuum using suction boxes or suction rollers in order to facilitate water drainage, pressing areas, devices for supplying thermal energy, devices based on the removal of water from the sheet through the principle of capillarity, forced blowing of hot air through the sheet, etc. . . . ). All these systems, even in combination with each other, are known per se. A hood (7) can be arranged on the Yankee (1).

[0052] 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.

[0053] The sheet (F) is conveyed by a web (9) from the forming area (A) to the drying area (C) and is associated with the web (4) also in the compression nip defined by the presser (6) in cooperation with the Yankee (1).

[0054] In the diagram of FIG. 3 the presser (6) is a shoe press and the web (9) is a felt. The same diagram shows a suction roller (SR) onto which the web (9) is guided upstream of the presser (6).

[0055] In the diagram of FIG. 4, the presser (6) is associated with a further presser (60), arranged downstream with respect to the direction of rotation (1C) of the Yankee. In this configuration, the web (9) is associated with the sheet in both the nips defined by the presser (6) and by the further presser (60) in cooperation with the Yankee (1). For example, the additional presser (60) consists of a blind-holes press.

[0056] The linear pressure exerted by the presser (6) in correspondence of the Yankee is preferably between 60 and 200 kN/m, more preferably between 90 and 150 kN/m and, even more preferably, between 90 and 120 kN/m. In a configuration of the type shown in FIG. 4, the linear pressure exerted by the additional presser (60) at the Yankee is preferably between 90 and 120 kN/m.

[0057] 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.

[0058] 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 paper being dried, 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.

[0059] 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 exclusively or almost exclusively over a central zone (20) of the latter. Thus, the energy transfer to the lateral parts of the mantle that do not come into contact with the sheet (F) is reduced.

[0060] 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.

[0061] 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).

[0062] With reference to FIG. 5, the inductor (H) extends axially inside the Yankee (1) for a length (LH) shorter than the length (L2) of the mantle (2). The terminals (HT) of the inductor (H) can be passed through one of the pins (4).

[0063] 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 cladding (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).

[0064] 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).

[0065] 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 (HN) in this case are arranged circumferentially around the axis of the Yankee.

[0066] 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 realize the inductors (HN).

[0067] 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.

[0068] 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 so as to circumferentially vary the thermal transfer.

[0069] Preferably, the inductor consists of one or more solenoids geometrically configured such that the produced electromagnetic field 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.

[0070] In practice, the mantle of the Yankee constitutes an armature in Near Field geometric conditions.

[0071] 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.

[0072] 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 that is dispersed in the environment and is not effectively directed towards the sheet being dried.

[0073] 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.

[0074] From the point of view of construction, preferably in accordance with the present invention, the following condition is satisfied:

[0075] SPd, 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 the individual inductors). 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 coil turns.

[0076] More preferably, in accordance with the present invention, S and the difference Pd are of the same order of magnitude and have substantially the same value, i.e. the following condition is satisfied: SPd, where S, d and P have the meaning indicated above. Therefore, 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 coil turns 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).

[0077] In this way, the magnetic fields of the individual coils intercept the mantle material being influenced in a limited way by the magnetic fields of the adjacent coil turns. Therefore, it is possible to concentrate the magnetic field effect of the single coil turn 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 heads, reducing the amount of energy which should be dispersed in the external environment.

[0078] 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.

[0079] From the description provided above, it is evident that a Yankee drier for the production of paper according to the present invention is a body comprising a metal mantle (2) with circular cross-section and two side 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), wherein 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). 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: [0080] the Yankee drier 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. [0081] 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 heads (3). [0082] the radially outermost side of the electromagnetic induction system is at a radial distance(S) 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. [0083] 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). [0084] the electromagnetic induction system comprises a single toroidal inductor (H) formed by coils developed parallel to the axis (x-x) of the Yankee. [0085] 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 coils concentric to said axis. [0086] the electromagnetic induction system comprises a plurality of inductors (HN) axially placed side by side. [0087] the electromagnetic induction system comprises a plurality of inductors (HN), each of which consists of a solenoid formed by coils wound around respective radial axes (RHN). [0088] the electromagnetic induction system comprises a plurality of inductors (HN) arranged circumferentially around the axis of the Yankee. [0089] 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), characterized in that the value of the said radial distance(S) is less than or equal to the difference between said pitch (P) and said diameter (d). [0090] the inductor (H) or the inductors (HN) have a side (HM) radially closer to the mantle (2) and a side (HW) radially more distant from the mantle (2), in which said side (HM) radially closest to the mantle (2) is at a radial distance(S) from the inner surface of the mantle (2), the inductors are formed by coils (HS) made up of conductors of predefined diameter (d) spaced from each other by a pitch of predefined value (P), and the value of said radial distance(S) is less than or equal to the difference between said pitch (P) and said diameter (d).

[0091] 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.