Yankee drying cylinders and tissue paper making machines

Abstract

The present invention relates to a steel Yankee cylinder for a tissue making machine and to a tissue making machine using such a steel Yankee cylinder, the outer surface (9) of the cylindrical shell of which is made of grade P690 steel or a similar steel as defined in European Standard EN10028-6:2017.

Description

[Technical Field]

[0001] The present invention relates to a steel Yankee dryer cylinder and to a machine for producing tissue paper comprising such a Yankee dryer cylinder. [Background technology]

[0002] Machines for producing tissue paper typically include a Yankee drying cylinder, the interior of which is heated by high-temperature steam during operation. Hereinafter, the term "Yankee" will be used to refer to the Yankee drying cylinder. The wet fibrous web transferred to the Yankee is dried on the outer surface, or "drying surface," of the Yankee, and then creped from the drying surface (outer surface) of the Yankee by a creping doctor. In the 20th century, Yankees were often made of cast iron, but in recent years, Yankees have been made of welded steel. Steel Yankees are considered advantageous because they are lighter than cast iron Yankees with the same required strength. An example of a steel Yankee is disclosed in EP 2126203 B1. As mentioned above, the creping doctor is used to crepe the already dried fibrous web from the surface of the Yankee. In practice, this means that the surface of the Yankee can be subjected to pressure from the doctor blade. Cast iron typically has an HB hardness (i.e., Brinell hardness) of 220 to 260, so cast Yankees have a relatively hard surface. This means that the surface is not easily worn away by contact with a doctor blade pressed against it. However, experience has shown that even cast iron Yankees are subject to significant wear. For this reason, metallizing the Yankee surface has long been practiced to achieve a harder surface. In the context of this patent application, the terms "to metallize" and "metallization" refer to a process in which the Yankee's exterior (dry) surface is coated with a hard layer that may be based on an element or alloy, or a mixture of a metal powder with at least one carbide or nitride and optionally other elements, or a metal matrix containing at least one carbide or nitride and optionally other elements. The coating is typically applied to the Yankee surface by spraying. An example of this technique is disclosed in U.S. Pat. No. 4,064,608.Other examples are disclosed in U.S. Patent Nos. 5,123,152; 6,171,657; and 10,240,291. It should be noted that many different compositions for the hard layer have been proposed. For example, as suggested in the aforementioned U.S. Patent No. 6,171,657, the hard layer may be an iron alloy containing about 20 to about 47 weight percent chromium, about 2.5 to about 6.5 weight percent boron, about 1.7 to about 2.7 weight percent silicon, and less than about 8 weight percent molybdenum. It should be noted that in the context of Yankee, the term "coating" can also be used to refer to a liquid coating, which is fundamentally different from a hard coating applied as part of the manufacturing process. A liquid coating is one that is continuously sprayed onto the surface of the Yankee during operation. When discussing the application of a hard layer to improve hardness and abrasion resistance, the term commonly used by those skilled in the art is "metallization," and this term and the term "metallize" will be used in this patent application and any patent that may be granted based thereon to refer to the application of a hardness and abrasion-resistant layer permanently bonded to the Yankee steel dryer surface, regardless of the exact composition of this layer (unless used in reference to other documents cited herein that use the term differently). Such a layer will hereinafter be referred to as a "metallization layer." The term "cover / coating," as used hereafter in this patent application, will refer to the application of a temporary liquid coating during operation of the tissue paper making machine (unless used in reference to other documents cited herein that use the term differently).

[0003] The steel used to make steel Yankees has a significantly lower hardness than cast iron. Typical values ​​for the hardness of such steels are around 140HB, or in some cases in the range of 120-170HB.

[0004] Because the steel grades used for Yankee drying cylinders typically have a much lower hardness (around 140HB) than cast iron (220-260HB), it has become necessary to metallize the steel Yankees. Various metallization layers for steel Yankees have been proposed. In a 2007 paper, Jorg Baubock (with the umlaut omitted from the second o for Jorg and the umlaut omitted from the fifth o for Baubock) discussed a "metallic coating" with a surface hardness said to be twice that of cast iron ("Application of a Steel Yankee in Tissue Machines," TAPPI Yankee Dryer Safety Committee, Jacksonville 10 / 23 / 07). However, details about the exact composition were not provided. In a 2008 paper by Luca Mignani ("Advances with Steel Yankee Dryers," TISSUE WORLD, Asia 2008), Mignani suggested that steel Yankee dryers could be provided with a "metal coating" (i.e., a metallized layer). The "metal coating" could be, for example, an alloy with a high Cr and Ni content and could have a hardness of 60 HRC. While hardness measured according to HRC does not directly correspond to Brinell hardness, a value of 60 HRC can be said to correspond to approximately 600 HB. In the same paper, Mignani also suggested that INFINIKOTE® could be used. INFINIKOTE® is a trademark owned by Valmet Corporation and refers to Yankee dryer metallization using a thermally sprayed metal coating. Mignani's paper suggests a hardness value of "50-60 HRC," or approximately 500-600 HB, in this case.

[0005] As an alternative to metallization, laser hardening of the steel Yankee shell has been proposed. Such a solution is disclosed in AT519996A2. According to this document, it is possible to achieve hardness values ​​of up to 400HB.

[0006] However, both currently known metallization and laser hardening techniques add additional steps to the Yankee manufacturing process, making it more complex.

[0007] With respect to metallized steel Yankees, the present inventors also point out that streaks may occur in paper dried on such dryers.

[0008] The inventors have also found that the Yankee metallization can crack and / or delaminate, necessitating a halt to production and machine shutdown, which can be very disruptive and costly.

[0009] It is therefore an object of the present invention to provide a steel yankee that is adequately protected against surface wear and that is easy to manufacture, and to provide a machine having such a steel yankee.It is a further object of the present invention to provide a steel yankee that prevents or reduces streaking in paper dried on the machine. Summary of the Invention

[0010] The present invention relates to a steel Yankee drying cylinder comprising a cylindrical shell having two axial ends, an end wall joined to each axial end by a circumferential weld bead, and the cylindrical shell further having an outer surface and an inner surface, the inner surface having a circumferential groove formed therein.

[0011] According to an embodiment of the invention, the cylindrical shell is made entirely from a steel of the P690 family of steels or a similar steel as defined in European Standard EN 10028-6:2017. The outer surface of the shell is therefore made from such a steel, i.e. a P690 steel grade steel or a similar steel having the composition defined in claim 1. In another embodiment of the invention, the cylindrical shell is made from a different grade of steel, and an outer layer made from a P690 grade steel or a similar steel is applied to the outer cylindrical surface of the cylindrical shell.

[0012] The present invention also relates to a tissue paper making machine comprising the steel Yankee drying cylinder of the present invention and a creping doctor having a creping blade, the creping doctor being positioned in contact with the outer surface of the Yankee drying cylinder.

[0013] In an embodiment of the present invention, the tissue paper making machine further comprises an apparatus for applying a liquid coating to the outer surface of the Yankee dryer cylinder.

[0014] The paper making machine further includes a Yankee drying hood selectively positioned to blow hot air against the outer surface of the cylindrical shell around a portion of the circumference of the cylindrical shell.

[0015] In an embodiment of the present invention, a cleaning doctor blade may be positioned behind the creping doctor blade in the direction of Yankee rotation and before the coating device so as to contact the outer surface of the shell.

[0016] According to a first embodiment, the machine may additionally comprise at least one through-air drying cylinder. In this embodiment, the imprinting fabric may be an air-permeable fabric arranged to transport the fibrous web over at least a portion of the circumference of the through-air drying cylinder and to convey the fibrous web from the at least one through-air drying cylinder to a transfer nip formed between the press roll and the Yankee. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic cross-sectional view of a Yankee. [Figure 2] FIG. 2 is an enlarged view of a portion of FIG. [Figure 3] FIG. 3 is a schematic side view of the tissue making machine of the present invention in operation. [Figure 4] FIG. 4 is a schematic diagram of a creping doctor contacting a Yankee drying cylinder. [Figure 5] FIG. 5 is a schematic side view showing how a tissue making machine may have a Yankee drying hood. DETAILED DESCRIPTION OF THE INVENTION

[0018] Referring to FIG. 1 , the Yankee drying cylinder 2 of the present invention is a steel Yankee drying cylinder comprising a cylindrical shell 3 having two axial ends 4, 5. It should be understood that the cylindrical shell 3 is a circular cylindrical shell. End walls 6, 7 are joined to each axial end 4, 5 by at least one circumferential weld bead 8. A single weld bead can be applied from the inside of the shell, or more preferably, from the outside of the shell. When two weld beads are used, a first weld bead can be applied from the outside of the shell and a second weld bead can be applied from the inside of the shell. Alternatively, a first weld bead can be applied from the inside of the shell and a second weld bead can be applied from the outside of the shell. The shell can be joined to the end walls in a manner such as that disclosed in EP 2920360 B1 or EP 2126203 B1. Optionally, the end walls may be thermally insulated, as disclosed, for example, in EP 2475819 B1 or 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. Still referring to FIG. 2, preferably, a circumferential groove 11 is formed in the inner surface 10 of the cylindrical shell. Condensed water may accumulate in the groove 11 during operation. The Yankee drying cylinder 2 is then preferably provided with means for draining condensed water from the groove 11, as disclosed, for example, in U.S. Pat. No. 5,090,135 or EP 2614182 B1.

[0019] With further reference to Figure 3, the Yankee dryer cylinder 2 of the present invention is used in a tissue paper making machine 1. When a Yankee dryer cylinder is used in the machine 1, a creping doctor 12 is used. The creping doctor 12 has a creping blade 13 positioned to contact the outer surface 9 of the shell 3 of the Yankee dryer cylinder 2. In Figure 3, the Yankee dryer cylinder is shown rotating about its axis of rotation A in the direction of arrow R, i.e., "clockwise" in Figure 3. As can be seen from Figure 3, the shell has a circular cylindrical shape. The Yankee dryer cylinder is positioned in the tissue paper making machine so that it is rotatable about the axis of rotation A.

[0020] As can be seen in FIG. 3 , a fibrous web W (shown diagrammatically and incompletely in dashed and solid lines) is formed in the forming section 17 between a forming fabric 18 and a fabric 24, which may be an absorbent felt. The fibrous web W is formed from stock injected from a headbox 19. The newly formed fibrous web W is transported on the felt 24 to a nip N between a press roll 21 and a Yankee drying cylinder 2. The press roll 21 used for the Yankee in the nip is envisioned as a shoe roll having a design such as that disclosed in U.S. Pat. No. 7,527,708; U.S. Pat. No. 9,885,153; or EP 2085513 B1, for example, although rolls other than a shoe roll are also contemplated. The wet fibrous web W can be dewatered to some extent in the nip N, which then functions as a dewatering press nip. The nip N may also be essentially a simple transfer nip, without substantial dewatering. Optionally, a suction rotating roll 20 may be provided prior to the nip N. The fibrous web W is transferred to the heated outer surface 9 of the cylindrical shell of the Yankee drying cylinder 2. The fibrous web W is then dried by heat from high-temperature steam supplied into the Yankee drying cylinder 3. The dried fibrous web W is creeped from the Yankee drying cylinder by the doctor roller 12 and sent to the winding section 25.

[0021] In operation, the tissue paper making machine may operate at a speed ranging from 1200 m / min to 2000 m / min. However, higher speeds are also contemplated. And, machine speeds ranging from 2000 m / min to 2300 m / min, and even possibly even 2400 m / min, may be utilized. In all embodiments of the present invention, the Yankee may have a diameter ranging from, for example, 2 m to over 7 m. Some diameters are more common than others, e.g., 3.5 m; 3.66 m; 4.88 m; or 5.5 m. The width of Yankee 2 may range from 0.6 m to over 7 m, e.g., for a pilot machine. For example, the width may be 3 m or 5 m. However, the Yankee may have dimensions other than those mentioned above.

[0022] 4, the doctor blade 12 preferably includes a blade holder 23 that holds the creping blade 13. During operation, the creping blade 13 may contact the outer surface 9 of the shell 3 and crepe the dry fibrous web from the outer surface 9.

[0023] Referring to Figure 5, the tissue paper making machine may be provided with a Yankee drying hood 16 arranged to blow hot air against the outer surface 10 of the cylindrical shell 3 over a portion of the circumference of the cylindrical shell 3. The Yankee drying hood may be, for example, a Yankee drying hood as disclosed in EP2963176B1, although other Yankee drying hoods are also contemplated. The machine of the present invention may also operate without a Yankee drying hood. A further doctor blade 12' is shown in Figure 5. This further doctor blade is optional and may be a cleaning doctor blade for scraping fibrous residue from the Yankee drying cylinder.

[0024] The tissue paper making machine also preferably includes an apparatus 14 for applying a liquid coating to the outer surface 9 of the Yankee dryer cylinder 2. The liquid coating typically consists of polyvinyl alcohol and other chemical agents. The applied coating may include, for example, 50-65% by weight of polyvinyl alcohol (PVOH), an adhesive constituting 15-30% by weight of the coating, a modifier / release agent constituting 5-30% by weight of the coating, and preferably further a phosphate. The phosphate used in such a coating may be, for example, monoammonium phosphate, diammonium phosphate, trisodium phosphate, or tetraammonium phosphate. Phosphoric acid may be used in the coating instead of (or in combination with) one or more of the above-mentioned phosphates. A supply system for supplying the liquid coating is symbolically indicated by reference numeral 26.

[0025] During operation, the creping doctor 12 may contact the outer surface 9 of the cylindrical shell 3 with a line load as high as 10 kN / m, which means that the cylindrical shell 3 is subject to wear. For steel Yankee drying cylinders, this can be a very serious problem. It has been standard practice to provide a protective layer, a so-called "metallized layer," made of a hard material that can withstand coatings. However, cracks can develop in such hard layers, and the entire layer can quickly peel off. This forces the machine to shut down. Furthermore, the doctor blade can be damaged by the cracks and peeling. If the doctor blade gets caught in a crack, it can deform. This can cause streaks in the paper. Therefore, from a process point of view, it is actually preferable to have no metallized layer.

[0026] The inventors of the present invention have discovered that by using steel grade P690 steel or a similar steel having the composition and properties described below to manufacture the cylindrical shell 3 and forming the outer surface of the shell 3 from grade 690 steel or a similar steel, the use of a hard metallized layer can be avoided entirely. In a first embodiment of the present invention, the cylindrical shell is formed from P690 grade steel or a similar steel. In a second embodiment of the present invention, the cylindrical shell is formed from an inner cylindrical steel shell and is covered by a continuous outer layer of P690 grade steel or a similar steel. This continuous outer layer of P690 grade steel or a similar steel may be formed from an annular or spiral strip of P690 grade steel or a similar steel welded to the underlying steel shell, for example, by its edges and / or by perforations drilled in the strip. Alternatively, the continuous outer layer of P690 grade steel or similar steel may be formed from a plurality of plates of P690 grade steel or similar steel welded to the inner cylindrical shell by their edges and / or by through holes drilled in the plates.

[0027] The hardness of the outer surface of the P690 grade steel or similar steel is preferably greater than or equal to 770 MPa and less than or equal to 940 MPa.

[0028] Therefore, in each embodiment, the surface that the doctor blade 13 contacts is formed from steel grade P690 or a similar steel. This is possible without laser hardening as suggested in AT519996A2. Steel grade P690 has been found to be so wear-resistant that a metallized layer is not required, and similar steels may have the same wear resistance. Additionally, it has the properties required for Yankee drying cylinders with respect to welding, strength, and heat conduction.

[0029] The P690 grade steel or similar steel used in the present invention has the following composition in weight percent: C not less than 0.12% and not more than 0.20%; 0.10% or more and 0.80% or less Si; Mn not less than 1.00% and not more than 1.70%; 0.10% to 1.50% Cr; not less than 0.30% and not more than 0.70% Mo; V not less than 0.005% and not more than 0.12%; 0.005% or more and 0.060% or less Nb; 0.0006% or more and 0.005% or less B; not more than 0.025% P; S less than 0.010%; ≤0.015% N; not more than 0.30% Cu; Not more than 2.50% Ni; not more than 0.05% Ti; not more than 0.15% Zr; not more than 0.01% Al; The remainder is iron and impurities.

[0030] Preferably, in steel of grade P690 or similar steel, the weight percentages of Nb, Ti, V, Zr are greater than or equal to 0.015%.

[0031] Optionally, when aluminum is present, the sum of V, Ti, Nb and Al is not less than 0.02%.

[0032] Preferably, for products made from P690 grade steel or similar steel having a maximum thickness of 50 mm or less, the upper yield strength (ReH) of P690 as measured in accordance with ISO 6892-1:2019 is greater than or equal to 690 MPa, and the corresponding tensile strength as measured in accordance with ISO 6892-1:2019 is preferably greater than or equal to 770 MPa and less than or equal to 940 MPa.

[0033] Preferably, for products made of P690 grade steel having a thickness greater than 50 mm and a thickness not greater than 100 mm, the yield strength of P690 as measured according to ISO 6892-1:2019 is not less than 670 MPa, and the corresponding tensile strength as measured according to ISO 6892-1:2019 is preferably not less than 770 MPa and not greater than 940 MPa.

[0034] Preferably, for products made of P690 grade steel having a thickness of more than 100 mm, the yield strength of P690 as measured according to ISO 6892-1:2019 is greater than or equal to 630 MPa and the corresponding tensile strength as measured according to ISO 6892-1:2019 is preferably greater than or equal to 770 MPa and less than or equal to 940 MPa.

[0035] The present invention significantly reduces the risk of having to shut down the machine due to damage to the drying surface of the Yankee.

Claims

1. A steel Yankee drying cylinder (2) comprising a cylindrical shell (3) having two axial ends (4, 5), end walls (6, 7) joined to each axial end (4, 5) by a circumferential weld bead (8), said cylindrical shell (3) further having an outer surface (9) and an inner surface (10), the outer surface (9) of the cylindrical shell (3) is made of steel of grade P690 as defined in European Standard EN 10028-6:2017 or a similar steel; Said steel of grade P690 or similar steels has the following composition by weight: C of 0.12% or more and 0.20% or less; 0.10% or more and 0.80% or less Si; 1.00% or more and 1.70% or less of Mn; 0.10% or more and 1.50% or less of Cr; Mo, not less than 0.30% and not more than 0.70%; 0.005% or more and 0.12% or less of V; 0.005% or more and 0.060% or less of Nb; 0.0006% or more and 0.005% or less B; ≤0.025% P; not more than 0.010% S; not more than 0.015% N; not more than 0.30% Cu; 2. Not more than 50% Ni; not more than 0.05% Ti; not more than 0.15% Zr; not more than 0.01% Al; Remainder iron and impurities; A steel Yankee drying cylinder.

2. The cylindrical shell (3) is made of P690 grade steel or similar steel, Said steel of grade P690 or similar steels has the following composition by weight: C of 0.12% or more and 0.20% or less; 0.10% or more and 0.80% or less Si; 1.00% or more and 1.70% or less of Mn; 0.10% or more and 1.50% or less of Cr; Mo, not less than 0.30% and not more than 0.70%; 0.005% or more and 0.12% or less of V; 0.005% or more and 0.060% or less of Nb; 0.0006% or more and 0.005% or less B; ≤0.025% P; not more than 0.010% S; not more than 0.015% N; not more than 0.30% Cu; 2. Not more than 50% Ni; not more than 0.05% Ti; not more than 0.15% Zr; not more than 0.01% Al; Remainder iron and impurities; 2. The steel Yankee drying cylinder of claim 1.

3. the sum of the weight percentages of Nb, Ti, V, and Zr in the P690 grade steel or similar steel is equal to or greater than 0.015%; 3. A steel Yankee drying cylinder according to claim 1 or 2.

4. the sum of the weight percentages of V, Ti, Nb, and Al in the P690 grade steel or similar steel is equal to or greater than 0.02%; 3. A steel Yankee drying cylinder according to claim 1 or 2.

5. 5. A tissue paper manufacturing machine (1) comprising: a steel Yankee drying cylinder (2) according to any one of claims 1 to 4; and a creping doctor (12) having a creping blade (13), the creping doctor (12) being arranged to contact the outer surface (9) of the Yankee drying cylinder (2).

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

7. The tissue paper manufacturing machine further comprises a Yankee drying hood (16) arranged to blow hot air onto the outer surface (9) of the cylindrical shell (3) over a portion of the outer periphery of the cylindrical shell (3). A tissue paper manufacturing machine (1) according to claim 5 or 6.

8. The upper yield strength (ReH) of said steel of grade P690 or similar steels, measured according to ISO 6892-1:2019, is at least 690 MPa, and the corresponding tensile strength, measured according to ISO 6892-1:2019, is preferably at least 770 MPa but not more than 940 MPa. A tissue paper manufacturing machine (1) according to any one of claims 5 to 7.

9. A cylindrical shell (3) for a Yankee cylinder, said cylindrical shell having an outer surface (9) made of P690 grade steel as defined in European Standard EN 10028-6:2017 or a similar steel; Said steel of grade P690 or similar steels has the following composition by weight: C of 0.12% or more and 0.20% or less; 0.10% or more and 0.80% or less Si; 1.00% or more and 1.70% or less of Mn; 0.10% or more and 1.50% or less of Cr; Mo, not less than 0.30% and not more than 0.70%; 0.005% or more and 0.12% or less of V; 0.005% or more and 0.060% or less of Nb; 0.0006% or more and 0.005% or less B; ≤0.025% P; not more than 0.010% S; not more than 0.015% N; not more than 0.30% Cu; 2. Not more than 50% Ni; not more than 0.05% Ti; not more than 0.15% Zr; not more than 0.01% Al; Remainder iron and impurities; A cylindrical shell (3) for a Yankee cylinder.

10. the cylindrical shell is made of P690 grade steel or similar steel; Said steel of grade P690 or similar steels has the following composition by weight: C of 0.12% or more and 0.20% or less; 0.10% or more and 0.80% or less Si; 1.00% or more and 1.70% or less of Mn; 0.10% or more and 1.50% or less of Cr; Mo, not less than 0.30% and not more than 0.70%; 0.005% or more and 0.12% or less of V; 0.005% or more and 0.060% or less of Nb; 0.0006% or more and 0.005% or less B; ≤0.025% P; not more than 0.010% S; not more than 0.015% N; not more than 0.30% Cu; 2. Not more than 50% Ni; not more than 0.05% Ti; not more than 0.15% Zr; not more than 0.01% Al; Remainder iron and impurities; Cylindrical shell (3) for a Yankee cylinder according to claim 9.

11. The sum of the weight percentages of Nb, Ti, V, and Zr in said steel or similar steel of grade P690 is not less than 0.015%.

11. A cylindrical shell for a Yankee cylinder according to claim 9 or 10.

12. the sum of the weight percentages of V, Ti, Nb, and Al in the P690 grade steel or similar steel is equal to or greater than 0.02%; 11. A cylindrical shell for a Yankee cylinder according to claim 9 or 10.

13. the cylindrical shell has a maximum thickness that is less than or equal to 50 mm thick; The upper yield strength (ReH) of said steel of grade P690 or similar steels, measured according to ISO 6892-1:2019, is at least 690 MPa, and the corresponding tensile strength, measured according to ISO 6892-1:2019, is preferably at least 770 MPa but not more than 940 MPa. Cylindrical shell according to any one of claims 9 to 12.

14. The cylindrical shell has a thickness of more than 50 mm and a thickness of not more than 100 mm; The yield strength of said steel of grade P690 or a similar steel, measured according to ISO 6892-1:2019, is at least 670 MPa, and the corresponding tensile strength, measured according to ISO 6892-1:2019, is preferably at least 770 MPa and at most 940 MPa. Cylindrical shell according to any one of claims 9 to 12.

15. The cylindrical shell has a thickness of more than 100 mm; The yield strength of said steel of grade P690 or similar steels, measured according to ISO 6892-1:2019, is greater than or equal to 630 MPa, and the corresponding tensile strength, measured according to ISO 6892-1:2019, is preferably greater than or equal to 720 MPa and up to 900 MPa. Cylindrical shell according to any one of claims 9 to 12.

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