SE538065C2 - Yankee cylinder made of steel - Google Patents

Abstract

ABSTRACT The inVention relates to a steel-n1ade Yankee cylinder 1 that coniprises a cylindricalshell 2 With two axial ends 3, 4. An end Wall 5, 6 is connected to each axial end 3, 4 bymeans of at least one circuniferential Weld bead 7. The end Walls 5, 6 have supportjournals 9, 10 by means of Which the Yankee cylinder 1 n1ay be supported in bearings.The inVentiVe Yankee cylinder 1 has a sn1ooth inner surface 11 Without grooves and theWall thickness T of the cylindrical shell 2 is constant oVer the axial extension of thecylindrical shell 2 all the Way to the at least one circuniferential Weld bead 7 thatconnects the cylindrical shell 2 to each end Wall 5, 6.

Description

The present invention relates to a steel-made Yankee cylinder having a cylindrical shelland end walls welded to the axial ends of the cylindrical shell.

BACKGROUND OF THE INVENTION In a paper making machine for making tissue paper, a newly formed f1brous web whichis still wet is dried on a Yankee drying cylinder. The Yankee drying cylinder is typicallyfilled with hot steam which may have a temperature of up to 180°C or even more. Thehot steam heats the Yankee drying cylinder such that the extemal surface of the Yankeecylinder reaches a temperature suitable for effective evaporation of water in a wetfibrous web such as a tissue paper web. The steam is norrnally pressurized to such anextent that the Yankee cylinder is subj ected to substantial mechanical stress due to the intemal pressure. The overpressure inside the Yankee cylinder during operation may beabout 1 MPa (10 bar).

The weight of the Yankee cylinder as well as centrifugal forces may also contribute tothe mechanical stress. The Yankee cylinder must be made to withstand such mechanicalstress. Yankee drying cylinders have usually been made of cast iron but it is known thata Yankee cylinder can also be made of welded steel. EP 2126203 discloses a Yankeecylinder for drying paper which is made of steel and has a cylindrical shell j oined to twoends through a respective circumferential weld bead made between opposing surfaces ofeach end and the cylindrical shell. The cylindrical shell is made such that, close to eachof its end edges, it has a portion of cylindrical wall of a thickness gradually increasingfrom a zone of minimum thickness to a zone of maximum thickness in correspondence of which the circumferential weld bead is formed.

In addition to being strong enough to withstand mechanical stress, a Yankee dryingcylinder should preferably also be easy to manufacture. Therefore, it is an object of thepresent invention to provide a design of a Yankee drying cylinder that has suff1cientstrength and that allows the Yankee drying cylinder to be manufactured easily and at alow cost.

DISCLOSURE OF THE INVENTION The inventive steel-made Yankee cylinder comprises a cylindrical Shell having tWoaxial ends. An end Wall is connected to each axial end by means of at least onecircumferential Weld bead and the end Walls have support j oumals by means of Whichthe Yankee cylinder may be supported in bearings. According to the invention, theYankee cylinder has a smooth inner surface Without grooves and the Wall thickness ofthe cylindrical shell is constant over the axial extension of the cylindrical shell all theWay to the circumferential Weld bead that connects the cylindrical shell to each end Wall.

The Wall thickness of the cylindrical shell may be in the range of 20 mm - 50 mm andpreferably in the range of 20 mm - 40 mm.

In advantageous embodiments of the invention, the cylindrical shell may be connectedto each end Wall by means of a circumferential Weld bead on the outside of the Yankeecylinder and by means of a corresponding back Weld bead on the inside of the Yankee cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shoWs a longitudinal section of a Yankee drying cylinder.

Figure 2 shoWs a cross section of a part of the Yankee drying cylinder of Figure 1.

DETAILED DESCRIPTION OF THE INVENTION With reference to Figure 1, the inventive Yankee cylinder 1 is a steel-made Yankeecylinder that comprises a cylindrical shell 2 Which is made of steel and Which has tWoaxial ends 3, 4.- An end Wall 5, 6 is connected to each axial end 3, 4 by means of at leastone circumferential Weld bead 7. As can be seen in Figure 1, the end Walls 5, 6 furtherhave support joumals 9, 10 by means of Which the Yankee cylinder 1 may be supported in bearings (not shoWn).

Inside the Yankee drying cylinder, there may be an intemal tie 12 Which is provided With ho les 13 for the passage of ducts of a condensate removal system (not shown). The tie 12 may be connected to the end walls 5, 6 by fastening means 14 such as bolts, screws or other fastening elements.

A Yankee drying cylinder substantially of this kind is known from EP 2126203. In theknown Yankee drying cylinder, the inside of the cylindrical shell is provided withgrooves. Such intemal grooves are intended to improve heat transfer such that heatenergy is more effectively transferred to the wet paper web which is to be dried on theYankee drying cylinder. When such a cylinder is welded to end walls, care must betaken to ensure that the grooves do not cause such Variations in the distribution ofmechanical stress that could lead to dangerous peaks of mechanical stress. It is alsoimportant that the area of the weld bead is not subjected to any pressure peak. In EP2126203, it is suggested that the wall thickness of the cylindrical shell should increasein a direction from the grooves to the weld bead. However, such a profile is complicatedto manufacture and any mistakes in the shaping of the inner surface of the cylindricalshell could lead to a less than optimal distribution of mechanical stress. When thecylindrical shell has grooves, this may also lead to Variations in heat transfer.

The inventors of the present invention have found that a welded Yankee cylinder maybe designed in a different way. As best seen in Figure 2, the Yankee cylinder 1 has asmooth inner surface 11 without grooves (i.e. the cylindrical shell 2 is made withoutintemal grooves) and the wall thickness T of the cylindrical shell 2 is constant over theaxial extension of the cylindrical shell 2 all the way to the at least one circumferentialweld bead 7 that connects the cylindrical shell 2 to each end wall 5, 6. Since there are nogrooves on the inside of the cylindrical shell, not only will the Yankee drying cylinderbe easier to manufacture but the absence of circumferential grooves will also mean thatthe distribution of mechanical stress near the axial ends 3,4 of the cylindrical shell 2will become more uniform and easier to predict. As a consequence, the risk of unwantedpeaks in the mechanical stress in the area of the at least one weld bead 7 will bereduced.

The cylindrical shell 2 may optionally be connected to each end wall by means of only asingle circumferential weld bead which can be applied from the outside or the inside.However, in preferred embodiments of the invention, the cylindrical shell 2 is connectedto each end wall 5, 6 by means of a circumferential weld bead 7 on the outside of theYankee cylinder land also by means of a corresponding back weld bead 8 on the insideof the Yankee cylinder 1.

The heat transfer properties of the Yankee drying cylinder Will be somewhat inferior tothose of a Yankee drying cylinder With internal grooves. However, in many practical cases, the advantages mentioned above Will outweigh such considerations.

The Wall thickness T of the cylindrical shell 2 may be in the range of 20 mm - 50 mmand preferably in the range of 20 mm - 40 mm but embodiments are conceivable inWhich the Wall thickness T may be less than 20 mm or more than 40 mm.

As previously explained, the inventive Yankee drying cylinder may optionally havemeans for evacuating condensate from the inside of the Yankee drying cylinder. Such means for removing/evacuating condensate may take any suitable form.

Thanks to the design of the cylindrical shell With constant Wall thickness, the Yankeecylinder can be easily manufactured and mechanical Will be more evenly distributed.There Will be less variation in heat transfer compared to a Yankee cylinder With intemal grooves.

In the majority of practical embodiments, the Width of the inventive Yankee dryingcylinder may be in the range of 1.5 m - 7 m or in the range of 2 m - 5 m. The diameterof the Yankee drying cylinder may be in the range of 3 m - 6 m in many realistic embodiments but other numerical values may also be considered.

If it should be necessary to increase the heat transfer to the paper Web, spoiler bars mayoptionally be added to the Yankee drying cylinder, for example spoiler bars as disclosedin US patent No. 4195417. Such spoiler bars can be added whenever desired and later removed.

The end Walls 5, 6 may optionally be therrnally insulated, for example as disclosed inWO 2011/030363.

The thickness of the end Walls 5, 6 may realistically be in the range of 80 mm - 100 mm but thickness values outside this range are also possible.

Claims (2)

1. A steel-made Yankee cylinder (1) comprising a cylindrical Shell (2) havingtwo axial ends (3, 4), an end Wall (5, 6) being connected to each axial end (3,4) by means of at least one circumferential Weld bead (7, 8) and the endWalls (5, 6) having support joumals (9, 10) by means of Which the Yankeecylinder (1) may be supported in bearings, characterísed in that, the Yankeecylinder (1) has a smooth inner surface (11) Without grooves and in that theWall thickness (T) of the cylindrical shell (2) is constant over the axialextension of the cylindrical shell (2) all the Way to the at least onecircumferential Weld bead (7, 8) that connects the cylindrical shell (2) toeach end Wall (5, 6). A steel-made cylinder according to claim 1, Wherein the Wall thickness (T)of the cylindrical shell (2) is in the range of 20 mm - 50 mm, preferably inthe range of 20 mm - 40 mm. . A steel-made Yankee cylinder (1) according to any of claim 1 or claim 2, Wherein the cylindrical shell (2) is connected to each end Wall (5, 6) bymeans of a circumferential Weld bead (7) on the outside of the Yankeecylinder (1) and by means of a corresponding back Weld bead (8) on theinside of the Yankee cylinder (1).