A YANKEE DRYING CYLINDER AND A TISSUE PAPER MAKING MACHINE

Abstract

The invention relates to steel Yankee cylinders for tissue-making machines and tissue-making machines using such steel Yankee cylinders wherein the outer surface (9) of the cylindrical shell of the steel Yankee cylinder is formed by a steel of the grade P690 as defined in European Standard EN 10028-6:2017 or a similar steel.

Claims

1. A steel Yankee drying cylinder (2) comprising: a cylindrical shell (3) having two axial ends (4, 5), and an end wall (6, 7) being joined to each axial end (4, 5) by means of a circumferential weld bead (8), the cylindrical shell (3) further having an outer surface (9) and an inner surface (10), wherein the outer surface (9) of the cylindrical shell (3) is formed by steel of the grade P690 as defined in European Standard EN 10028-6:2017 or a similar steel which has the following composition by weight: C equal to or greater than 0.12% and equal to or less than 0.20% Si equal to or greater than 0.10% and equal to or less than 0.80% Mn equal to or greater than 1.00% and equal to or less than 1.70% Cr equal to or greater than 0.10% and equal to or less than 1.50% Mo equal to or greater than 0.30% and equal to or less than 0.70% V equal to or greater than 0.005% and equal to or less than 0.12% Nb equal to or greater than 0.005% and equal to or less than 0.060% B equal to or greater than 0.0006% and equal to or less than 0.005% P equal to or less than 0.025% S equal to or less than 0.010% N equal to or less than 0.015% Cu equal to or less than 0.30% Ni equal to or less than 2.50% Ti equal to or less than 0.05% Zr equal to or less than 0.15% Al equal to or less than 0.01% Remainder iron and impurities.

2. The steel Yankee drying cylinder according to claim 1, wherein the cylindrical shell (3) is made of a P690 grade steel or a similar steel which has the following composition by weight: C equal to or greater than 0.12% and equal to or less than 0.20% Si equal to or greater than 0.10% and equal to or less than 0.80% Mn equal to or greater than 1.00% and equal to or less than 1.70% Cr equal to or greater than 0.10% and equal to or less than 1.50% Mo equal to or greater than 0.30% and equal to or less than 0.70% V equal to or greater than 0.005% and equal to or less than 0.12% Nb equal to or greater than 0.005% and equal to or less than 0.060% B equal to or greater than 0.0006% and equal to or less than 0.005% P equal to or less than 0.025% S equal to or less than 0.010% N equal to or less than 0.015% Cu equal to or less than 0.30% Ni equal to or less than 2.50% Ti equal to or less than 0.05% Zr equal to or less than 0.15% Al equal to or less than 0.01% Remainder iron and impurities.

3. The steel Yankee drying cylinder according to claim 1, wherein the sum of the percentages by weight of Nb Ti, V, Zr in the P690 grade steel or a similar steel is equal to or greater than 0.015%.

4. The steel Yankee drying cylinder according to claim 1, wherein the sum of the percentages by weight of V, Ti, Nb, and Al in the P690 grade steel or a similar steel is equal to or greater than 0.02%

5. A tissue paper making machine (1) comprising a steel Yankee drying cylinder (2) according to claim 1 and a creping doctor (12) with a creping blade (13) which is arranged to act against the outer surface (9) of the Yankee drying cylinder (2).

6. The tissue paper making machine (1) according to claim 5, wherein the machine (1) further comprises a device (14) for applying liquid coating onto the outer surface (9) of the Yankee drying cylinder (2).

7. The tissue paper making machine (1) according to claim 5, wherein the machine further comprises a Yankee drying hood (16) that is arranged to be capable of blowing hot air against the outer surface (9) of the cylindrical shell (3) over a part of the circumference of the cylindrical shell (3).

8. The tissue paper making machine (1) according to claim 5, wherein the upper yield strength (ReH) measured by ISO 6892-1:2019 of the P690 grade steel or similar steel is equal to or greater than 690 MPa and the corresponding tensile strength measured by ISO 6892-1:2019 preferably is equal to or greater than 770 MPa and equal to or less than 940 MPa.

9. A cylindrical shell (3) for a Yankee cylinder that comprises an outer surface (9) made of P690 grade steel as defined in European Standard EN 10028-6:2017 or a similar steel with the following composition by weight: C equal to or greater than 0.12% and equal to or less than 0.20% Si equal to or greater than 0.10% and equal to or less than 0.80% Mn equal to or greater than 1.00% and equal to or less than 1.70% Cr equal to or greater than 0.10% and equal to or less than 1.50% Mo equal to or greater than 0.30% and equal to or less than 0.70% V equal to or greater than 0.005% and equal to or less than 0.12% Nb equal to or greater than 0.005% and equal to or less than 0.060% B equal to or greater than 0.0006% and equal to or less than 0.005% P equal to or less than 0.025% S equal to or less than 0.010% N equal to or less than 0.015% Cu equal to or less than 0.30% Ni equal to or less than 2.50% Ti equal to or less than 0.05% Zr equal to or less than 0.15% Al equal to or less than 0.01% Remainder iron and impurities.

10. The cylindrical shell (3) for a Yankee cylinder according to claim 9, wherein said cylindrical shell consists of P690 grade steel or a similar steel with the following composition by weight: C equal to or greater than 0.12% and equal to or less than 0.20% Si equal to or greater than 0.10% and equal to or less than 0.80% Mn equal to or greater than 1.00% and equal to or less than 1.70% Cr equal to or greater than 0.10% and equal to or less than 1.50% Mo equal to or greater than 0.30% and equal to or less than 0.70% V equal to or greater than 0.005% and equal to or less than 0.12% Nb equal to or greater than 0.005% and equal to or less than 0.060% B equal to or greater than 0.0006% and equal to or less than 0.005% P equal to or less than 0.025% S equal to or less than 0.010% N equal to or less than 0.015% Cu equal to or less than 0.30% Ni equal to or less than 2.50% Ti equal to or less than 0.05% Zr equal to or less than 0.15% Al equal to or less than 0.01% Remainder iron and impurities.

11. The cylindrical shell for a steel Yankee according to claim 9, wherein the sum of the percentages by weight of Nb, Ti, V, Zr in the P690 grade steel or a similar steel is equal to or greater than 0.015%.

12. The cylindrical shell for a steel Yankee according to claim 9, wherein the sum of the percentages by weight of V, Ti, Nb, and Al in the P690 grade steel or a similar steel is equal to or greater than 0.02%.

13. The cylindrical shell according to claim 9, wherein the shell has a maximum thickness which is equal to or less than 50 mm thick and the upper yield strength (ReH) measured by ISO 6892-1:2019 of the P690 grade steel or a similar steel is equal to or greater than 690 MPa and the corresponding tensile strength measured by ISO 6892-1:2019 is equal to or greater than 770 MPa and equal to or less than 940 MPa.

14. The cylindrical shell according to claim 9, wherein the shell is greater than 50 mm thick and equal to or less than 100 mm thick and the yield strength measured by ISO 6892-1:2019 of the P690 grade steel or a similar steel is equal to or greater than 670 MPa and the corresponding tensile strength measured by ISO 6892-1:2019 is equal to or greater than 770 MPa and equal to or less than 940 MPa.

15. The cylindrical shell according to claim 9, wherein the shell is greater than 100 mm thick and the yield strength measured by ISO 6892-1:2019 of the P690 grade steel or a similar steel is equal to or greater than 630 MPa and the corresponding tensile strength measured by ISO 6892-1:2019 is equal to or greater than 720 MPa to 900 MPa.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0016] FIG. 1 is a schematic cross-sectional representation of a Yankee.

[0017] FIG. 2 is an enlargement of a part of FIG. 1

[0018] FIG. 3 is a schematic side view of the inventive tissue making machine during operation.

[0019] FIG. 4 is a schematic representation of the creping doctor acting against the Yankee drying cylinder.

[0020] FIG. 5 is a schematic side view showing how the tissue making machine may have a Yankee drying hood.

DETAILED DESCRIPTION OF THE INVENTION

[0021] With reference to FIG. 1, the Yankee drying cylinder 2 of the present invention is a steel Yankee drying cylinder that comprises a cylindrical shell 3 having two axial ends 4, 5. It should be understood that the cylindrical shell 3 is a circular cylindrical shell. An end wall 6, 7 is joined to each axial end 4, 5 by means of at least one circumferential weld bead 8. A single weld bead may be applied from inside the shell or, more preferably, from outside the shell. If two weld beads are used then a first weld bead may be applied from outside the shell and a second weld bead applied from inside the shell or, as an alternative, a first weld bead may be applied from inside the shell and a second weld bead applied from outside the shell. The shell can be joined to the end walls in, for example, the way disclosed in EP 2920360 B1 or in EP 2126203 B1. The end walls may optionally be provided with thermal insulation, for example as disclosed in EP 2475819 B1 or in WO 2016/026662 A1. As can be seen in FIG. 2, the cylindrical shell 3 has an outer surface 9 and an inner surface 10. With further reference to FIG. 2, preferably circumferential grooves 11 are formed in the inner surface 10 of the cylindrical shell 3. In the groves 11, condensate water will be accumulated during operation and the Yankee drying cylinder 2 is preferably provided with means for evacuating condensate water from the grooves 11, for example as disclosed in U.S. Pat. No. 5,090,135 or in EP 2614182 B1.

[0022] With further reference to FIG. 3, the inventive Yankee drying cylinder 2 is used in a tissue paper making machine 1. When the Yankee drying cylinder is used in the machine 1, a creping doctor 12 is used. The creping doctor 12 has a creping blade 13 that is arranged to act against the outer surface 9 of the shell 3 of the Yankee drying cylinder 2. In FIG. 3, the Yankee drying cylinder is represented as rotating about its axis of rotation A in the direction of arrow R, i.e. clockwise in FIG. 3. As can be understood from FIG. 3, the shell has a circular cylindrical shape. The Yankee drying cylinder is so arranged in the tissue paper making machine that it is rotatable about the axis of rotation A.

[0023] As can be seen in FIG. 3, a fibrous web W (shown schematically and incompletely with dashed and solid lines) is formed in a forming section 17 between a forming fabric 18 and a fabric 24 which may be a water-absorbing felt. The fibrous web W is formed from stock injected from a head box 19. The newly formed fibrous web W is carried on the felt 24 to a nip N between a press roll 21 and the Yankee drying cylinder 2. The press roll 21 that is used in the nip against the Yankee may conceivably be, for example, a shoe roll with a design as disclosed in U.S. Pat. Nos. 7,527,708; 9,885,153 or EP 2085513 B1 but other rolls than a shoe roll may also be considered. The wet fibrous web W may be subjected to a degree of dewatering in the nip N which then serves as a dewatering press nip. The nip N could also be essentially just a transfer nip in which no substantial dewatering occurs. The nip N may optionally be preceded by a suction turning roll 20. The fibrous web W is transferred onto the heated outer surface 9 of the cylindrical shell 3 of the Yankee drying cylinder 2 and the fibrous web W is then dried by heat that comes from hot steam that is supplied into the Yankee drying cylinder 3. The dried fibrous web W is then creped off from the Yankee drying cylinder by the doctor 12 and sent to a reel-up 25.

[0024] During operation, the tissue paper making machine may be running at a speed which is in the range of 1200 m/min-2000 m/min. However, higher speeds may also be considered and machine speeds in the range of 2000 m/min-2300 m/min may also be used or possibly even speeds up to 2400 m/min. In all embodiments of the invention, the Yankee may have a diameter in the range of, for example, 2 mto greater than 7 m. Some diameters are more common than others, for example 3.5 m; 3.66 m; 4.88 m or 5.5 m. The width of the Yankee 2 may be, for example, in the range of 0.6 m for pilot machines to greater than 7 m. For example, the width could be 3 m or 5 m. However, the Yankee could also have other dimensions than the ones given above.

[0025] With reference to FIG. 4, the doctor 12 preferably includes a blade holder 23 that holds the creping lade 13. During operation, the creping blade 13 will act against the outer surface 9 of the shell 3 to crepe a dried fibrous web from the outer surface 9.

[0026] With reference to FIG. 5, the tissue paper making machine may be provided with a Yankee drying hood 16 that is arranged to be capable of blowing hot air against the outer surface 10 of the cylindrical shell 3 over a part of the circumference of the cylindrical shell 3. The Yankee drying hood may be, for example, such a Yankee drying hood as is disclosed in EP 2963176 B1 but other Yankee drying hoods may also be considered and the inventive machine may also operate without a Yankee drying hood. A further doctor 12 is indicated in FIG. 5. This further doctor is optional and may be a cleaning doctor for scraping off fiber residue from the Yankee drying cylinder.

[0027] The tissue paper making machine preferably also comprises a device 14 for applying liquid coating onto the outer surface 9 of the Yankee drying cylinder 2. The liquid coating typically comprises polyvinyl alcohol and other chemical agents. Coating that is applied may comprise, for example, 50-65% by weight polyvinyl alcohol (PVOH), an adhesive that constitutes 15-30% by weight of the coating, a modifier/release agent that constitutes 5-30% by weight of the coating and preferably also phosphate. Phosphate used for such coating may be, for example, mono-ammonium phosphate, Di-ammonium phosphate, trisodium phosphate or tetra phosphate. Instead of the above-mentioned phosphates (or in combination with one or several of them), phosphoric acid may be used in the coating. A supply system for supplying liquid coating is symbolically indicated by the reference numeral 26.

[0028] During operation, the creping doctor 12 may act against the outer surface 9 of the cylindrical shell 3 with a linear load which may, in some cases, be as high as 10 kN/m. This means that the cylindrical shell 3 is subjected to wear. For Yankee drying cylinders made of steel, this can be a very serious problem and it has been the standard procedure to give them a protective layer, a so called metallization layer of a hard material that is resistant to coating. However, cracks may occur in such hard layers that can quickly lead to delamination of the entire layer such that operation of the machine must be interrupted. Moreover, the doctor blade can be damaged by cracks and delamination. When a crack catches the doctor blade, the doctor blade can be deformed, and this may be a source of streaks in the paper. Therefore, elimination of the metallization layer is actually desirable from a process point of view.

[0029] The inventor of the present invention has now found that it is possible to entirely avoid the use of a hard metallization layer by using a steel of the steel grade P690 or a similar steel with a composition and properties as described in the following for making the cylindrical shell 3 such that the outer surface of the shell 3 is formed by a steel of the grade P690 or a similar steel. In a first embodiment of the invention the cylindrical shell is formed of a P690 grade steel or a similar steel. In a second embodiment of the invention the cylindrical shell is formed of inner cylindrical shell made of steel and is covered with a continuous outer layer of a P690 grade steel or a similar steel. This continuous outer layer of P690 grade steel or similar can be formed of annular or spiral strips of P690 grade steel or a similar steel which are welded, for example by their edges and/or by through holes bored through the strips. to the underlying steel shell. Alternatively the continuous outer layer of P690 grade steel or a similar steel can be formed of a plurality of plates of a P690 grade steel or a similar steel, the plates being welded to the inner cylindrical shell by their edges and/or through holes bored through the plates.

[0030] The hardness of the P690 grade steel or similar steel outer surface preferably is equal to or greater than 770 MPa and equal to or less than 940 MPa.

[0031] In each embodiment, the surface against which the doctor blade 13 acts will this be formed by steel of the steel grade P690 or a similar steel. This is possible without laser hardening as suggested in AT 519996 A2. The steel grade P690 has been found to be so resistant to wear that it does not need any metallization layer and similar steels will have the same wear resistance. Moreover, it has such properties with regard to welding, strength and heat transfer that are required for a Yankee drying cylinder.

[0032] Steel of a grade of P690 steels or a similar steel for use in the present invention has the following composition in weight percent: [0033] C equal to or greater than 0.12% and equal to or less than 0.20% [0034] Si equal to or greater than 0.10% and equal to or less than 0.80% [0035] Mn equal to or greater than 1.00% and equal to or less than 1.70% [0036] Cr equal to or greater than 0.10% and equal to or less than 1.50% [0037] Mo equal to or greater than 0.30% and equal to or less than 0.70% [0038] V equal to or greater than 0.005% and equal to or less than 0.12% [0039] Nb equal to or greater than 0.005% and equal to or less than 0.060% [0040] B equal to or greater than 0.0006% and equal to or less than 0.005% [0041] P equal to or less than 0.025% [0042] S equal to or less than 0.010% [0043] N equal to or less than 0.015% [0044] Cu equal to or less than 0.30% [0045] Ni equal to or less than 2.50% [0046] Ti equal to or less than 0.05% [0047] Zr equal to or less than 0.15% [0048] Al equal to or less 0.01%

[0049] Remainder iron and impurities.

[0050] Preferably, in a steel of grade P690 or a similar steel the percentage by weigh of Nb, Ti, V, Zr is equal to or greater than 0.015%.

[0051] Optionally, if there is aluminium present then the sum of V, Ti, Nb, and Al is equal to or greater than 0.02%

[0052] Preferably for products made of a P690 grade steel or a similar steel which have a maximum thickness which is equal to or less than 50 mm thick the upper yield strength (ReH) measured by ISO 6892-1:2019 of the P690 is equal to or greater than 690 MPa and the corresponding tensile strength measured by ISO 6892-1:2019 preferably is equal to or greater than 770 MPa and equal to or less than 940 MPa.

[0053] Preferably for products made of a P690 grade steel which are greater than 50 mm thick and equal to or less than 100 mm thick the yield strength measured by ISO 6892-1:2019 of the P690 is equal to or greater than 670 MPa and the corresponding tensile strength measured by ISO 6892-1:2019 preferably is equal to or greater than 770 MPa and equal to or less than 940 MPa.

[0054] Preferably for products made of a P690 grade steel which are greater than 100 mm thick the yield strength measured by ISO 6892-1:2019 of the P690 is equal to or greater than 630 MPa and the corresponding tensile strength measured by ISO 6892-1:2019 preferably is equal to or greater than 770 MPa and equal to or less than 940 MPa.

[0055] Thanks to the invention, the risk that the machine must be shut down because of damage to the drying surface of the Yankee is significantly reduced.