Method of making a steel Yankee cylinder

The invention relates to a method of making a steel Yankee cylinder 1 by welding a cylindrical shell 2 to two end walls 3, 4 such that the cylindrical shell 2 and the end walls 3,4 together form the Yankee cylinder 1. The welding operation is carried out exclusively from the outside of the Yankee cylinder 1 and in the welding operation is carried out as a butt welding operation in which a backing material 7 is used on the inside of the Yankee cylinder 1 such that, between each end wall 3, 4 and the cylindrical shell 1, a single weld bead 8 is formed which extends all the way between the opposing surfaces 5, 6 and completely fuses the opposing surfaces 5, 6 of each end wall 3, 4 and the cylindrical shell 2 respectively.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage Application, filed under 35 U.S.C. § 371, of International Application No. PCT/SE2014/051278, filed Oct. 29, 2014, which claims priority to Swedish Application No. 1351368-4, filed Nov. 19, 2013, the contents of both of which as are hereby incorporated by reference in their entirety.

BACKGROUND

Related Field

The invention relates to a method of making a steel Yankee cylinder by welding a cylindrical shell to two end walls.

Description of Related Art

In the production of paper, drying cylinders are used on which wet fibrous webs are dried by heat that causes the water in the fibrous web to evaporate. Paper machines for making tissue paper (e.g. kitchen, towel or toilet paper) normally have only one drying cylinder which is referred to as a “Yankee” cylinder and which usually has a larger diameter than drying cylinders used in such machines that are intended for other paper grades (e.g. newsprint, printing paper or paperboard). The Yankee cylinder is usually made in cast iron but it has also been suggested that the Yankee cylinder be manufactured by other methods. U.S. Pat. No. 4,320,582 discloses how an outer shell may be formed of steel plates butt-welded to form a cylindrical weldment and rings of forged steel butt-welded to the weldment at its ends. The rings have flanges to which heads are bolted. WO 2008/105005 discloses a steel-made Yankee cylinder which has a cylindrical shell and two ends that have been welded to the cylinder by a circumferential weld that includes a weld bead on the outside of the Yankee cylinder and a weld bead on the inside of the Yankee cylinder.

Since a drying cylinder such as a Yankee cylinder is to be filled with hot steam, it must meet the requirements of a pressure vessel. In practice that means that high demands are made on the quality of the weld. To achieve this, welding is performed both from the inside of the Yankee cylinder and from the outside. However, welding from the inside is problematic since the temperature may reach very high levels and the welder must work under very pressing conditions. Gas must be evacuated during the welding operation and fresh air must be supplied. Even with good ventilation, the working conditions for the welder will be very demanding and possibly hazardous.

Therefore, it is an object of the present invention to provide a method of making a Steel Yankee cylinder which is less demanding for the operator that performs the welding and which either eliminates or reduces the requirement for ventilation during the welding operation.

BRIEF SUMMARY

According to the invention, a steel Yankee cylinder is made by welding a cylindrical shell to two end walls such that the cylindrical shell and the end walls together form the Yankee cylinder. Each end wall is welded to the cylindrical shell by a circumferential weld between opposing surfaces of each end wall and the cylindrical shell respectively. According to the invention, the welding operation is carried out exclusively from the outside of the Yankee cylinder. Moreover, the welding operation is carried out as a butt welding operation in which a backing material is used on the inside of the Yankee cylinder such that, between each end wall and the cylindrical shell, a single weld bead is formed. The single weld bead that is formed extends all the way between the opposing surfaces and completely fuses the opposing surfaces of each end wall and the cylindrical shell respectively.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

With reference toFIG. 1, a steel Yankee1comprises a cylindrical shell2to which two end walls3,4have been welded such that the cylindrical shell2is connected to each end wall by a weld bead8.

FIG. 2is a cross-sectional schematic representation of a part of the cylindrical shell2and an end wall4before the end wall4and the cylindrical shell2have been welded to each other. As can be seen inFIG. 2, a surface6on the cylindrical shell2is placed opposing a surface5on an end wall4. When the opposing surfaces5,6of the cylindrical shell2and the end walls3,4are joined by a weld bead8, the cylindrical shell2and the end walls3,4will form together a Yankee cylinder. As can also be seen inFIG. 2, a lip protrudes from the end wall4such that the lip can extend below the inner surface9of the cylindrical shell2. The lip can form a backing material7which can be used during the welding operation as will be explained in the following. It should be understood that the lip that forms a backing material7is ring-shaped such that can follow the inner periphery of the cylindrical shell2.

With reference toFIG. 3, the inventive method comprises welding the cylindrical shell2to the two end walls3,4such that the cylindrical shell2and the end walls3,4together form the Yankee cylinder1. WhileFIG. 3only shows the end wall4on one side, it should be understood that welding of the other end wall3to the cylindrical shell2takes place in the same way. Each end wall3,4is welded to the cylindrical shell2by a circumferential weld between the opposing surfaces5,6of each end wall3,4and the cylindrical shell2respectively. According to the invention, the welding operation is carried out exclusively from the outside of the Yankee cylinder1and the welding operation is carried out as a butt welding operation in which a backing material7is used on the inside of the Yankee cylinder1. The welding acts on the entire area between the opposing surfaces5,6of each end wall3,4and the cylindrical shell2and filler material and molten material penetrates through the whole area such that the weld bead8that is formed extends all the way between the opposing surfaces5,6. Instead of an outer weld bead and an inner weld bead, there is a single weld bead8that completely fuses the opposing surfaces5,6of each end wall3,4and the cylindrical shell2respectively. The backing material7keeps filler material and molten material from the cylindrical shell2and the end walls3,4in place and prevents such material from leaving the area where the weld bead8is formed.

In the embodiment shown inFIG. 3, the backing material7is formed by a lip that protrudes from an end wall3,4and extends into the area on the inside of the cylindrical shell2. However, with reference toFIG. 4, the backing material7may instead be formed by a lip that protrudes from each axial end of the cylindrical shell2and extends into an area radially inside of the opposing end wall3,4.

When the welding operation has been completed, the backing material7can be removed by grinding. Preferably, the single weld bead8which has been formed between each end wall3,4and the cylindrical shell2is subjected to grinding on both the outside and the inside of the Yankee cylinder1. After grinding, a cross section of the welded joint may look like inFIG. 5.FIG. 5also shows how the cylindrical shell2may have circumferential grooves10separated by circumferential flanges11for heat transfer. During operation of the Yankee cylinder1, the circumferential flanges11serve to improve heat transfer to the outer surface of the Yankee cylinder1and condensate will be received in the grooves10. As can be seen inFIG. 5, the thickness of the wall of the cylindrical shell2may increase in a direction towards the area of the weld bead8.

It should be understood that the backing material7need not necessarily be integral with the cylindrical shell2or the end walls3,4. Instead, the backing material7could be a separate element.

The butt welding may be carried out a s a single V butt welding operation as indicated inFIG. 2,FIG. 3andFIG. 4but it could also be carried out as a single U butt welding operation. It should be understood that, in this context, the terms “single V and “single U” refer to the shape of the opposing surfaces5,6. InFIGS. 2, 3 and 4, the opposing surfaces5,6form a “V”.

The welding method used can be arc welding, for example manual metal arc welding (MMA), shielded metal arc welding (SMAW) or gas metal arc welding (GMAW).

Thanks to the invention, a steel Yankee drying cylinder can be manufactured in a way that reduces the need for ventilation during the welding. Since only a single weld bead is made, production of the Yankee drying cylinder also becomes faster and easier.