METHOD FOR CONNECTING TUBES OF A TUBE BUNDLE HEAT EXCHANGER TO A TUBESHEET OF THE TUBE BUNDLE HEAT EXCHANGER

Abstract

The present invention relates to a method for connecting tubes (125) of a tube bundle heat exchanger to a tube plate (130) of the tube bundle heat exchanger, wherein the tubes (125) are cohesively connected to the tube plate (130) by laser welding, during the course of which a laser beam (211) is generated and is focused on a location to be welded in a connecting region (250) between tube (125) and tube plate (130), wherein the laser beam (211) is moved so as to perform a first movement over the connecting region (250) and a second movement which is superposed on the first movement and which differs from the first movement, and wherein, by means of the second movement, melt bath dynamics are influenced in targeted fashion and/or a vapour capillary that forms is modified in targeted fashion.

Claims

1. A method for connecting tubes (121, 125) of a tube bundle heat exchanger (100) to a tubesheet (130) of the tube bundle heat exchanger (100), wherein the tubes (121, 125) are connected to the tubesheet (130) in a material-bonding manner by means of laser welding, in the course of which a laser beam (211) is generated and focused on a location to be welded in a connecting region (250) between the tube (125) and the tubesheet (130), wherein the laser beam (211) is moved in such a way that it produces a first movement over the connecting region (250) and a second movement superposed on the first movement, which is different from the first movement, and wherein melt bath dynamics are influenced by the second movement in a targeted manner and/or a vapor capillary that forms is modified in a targeted manner.

2. The method as claimed in claim 1, wherein the vapor capillary that is formed is modified into an elongate or oval form.

3. The method as claimed in claim 1, wherein a main direction of extent (251) of a weld seam (260) is predetermined by the first movement and/or wherein a width (302) of the weld seam (260) is predetermined by the second movement.

4. The method as claimed in claim 1, wherein the first movement and/or the second movement are produced by movement of individual optical elements (223, 226) in a beam path of the laser beam (211).

5. The method as claimed in claim 4, wherein at least one mirror (223, 226) in the beam path of the laser beam (211) is rotated.

6. The method as claimed in claim 1, wherein the first movement and/or the second movement are produced by a device for laser welding (200) or part of a device for laser welding (200) being moved.

7. The method as claimed in claim 6, wherein a laser head (220) of the device for laser welding (200) is moved.

8. The method as claimed in claim 1, wherein the first movement is a circular movement, the radius (301) of which corresponds substantially or completely to the radius of a tube (125).

9. The method as claimed in claim 1, wherein the second movement is a circular and/or elliptical and/or translational movement alternating in its direction.

10. The method as claimed in claim 9, wherein the second movement is performed with a transversal deflection of 0.15-0.25 mm, in particular 0.23 mm, and/or with a longitudinal deflection of 0.15-0.25 mm, in particular 0.23 mm.

11. The method as claimed in claim 9, wherein the second movement is performed with a frequency of 3000-4500 Hz, in particular 3500 Hz.

12. The method as claimed in claim 1, wherein the tubes (121) and/or the tubesheet (130) are respectively produced from steel or a nonferrous metal and/or are respectively produced from aluminum or an aluminum alloy.

13. The method as claimed in claim 1, wherein the tubes (121) and the tubesheet (130) of a straight-tube heat exchanger, of a U-tube heat exchanger or of a helically coiled tube bundle heat exchanger (100) are connected to one another.

14. The method as claimed in claim 1, wherein the laser beam (211) is generated by a CO.sub.2 laser, CO laser, solid-state laser, Nd:YAG laser (210), Nd-glass laser, erbium-YAG laser, disk laser, fiber laser and/or diode laser.

15. A device (200) for laser welding, which is designed for connecting tubes (121, 125) of a tube bundle heat exchanger (100) to a tubesheet (130) of the tube bundle heat exchanger (100), wherein the device (200) has a laser (210) for generating a laser beam (211), a first control unit (230) for activating a first traversing mechanism (231) for producing a first movement of the laser beam (211) and a second control unit (240) for activating a second traversing mechanism for producing a second movement of the laser beam (211), the first and second control units (230, 240) being designed to carry out a method as claimed in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] FIG. 1 schematically shows a preferred configuration of a tube bundle heat exchanger which has been produced by means of a preferred embodiment of a method according to the invention.

[0046] FIG. 2 schematically shows a preferred configuration of a device according to invention which is designed to carry out a preferred embodiment of a method according to the invention.

[0047] FIG. 3 schematically shows part of a preferred configuration of a device according to the invention which is designed to carry out a preferred embodiment of a method according to the invention.

[0048] FIG. 4 schematically shows part of a tube bundle heat exchanger which is worked in the course of a preferred embodiment of a method according to the invention.

EMBODIMENT(S) OF THE INVENTION

[0049] In FIG. 1, a preferred configuration of a tube bundle heat exchanger 100 is schematically shown in the form of a helically coiled tube bundle heat exchanger which has been produced by means of a preferred embodiment of a method according to the invention.

[0050] In FIG. 1a, the tube bundle heat exchanger 100 is shown in a sectional view. The tube bundle heat exchanger 100 has a shell 110, which has a fluid inlet 111 and a fluid outlet 112 in order to pass a first fluid through the shell 110.

[0051] Arranged within the shell 110 is a bundle of tubes 120 comprising a multiplicity of tubes 121. A second fluid may be passed through the tubes 121. The tubes 121 are coiled helically around a core tube 140. The individual tubes 121 are connected in a material-bonding manner to tubesheets 130 of the heat exchanger 100.

[0052] The tubesheets 130 have along their circumference bore regions 131 with bores 132, each of the tubes 121 of the bundle of tubes 120 being connected in a material-bonding manner to the respective tubesheet 130 at one of these bores 132.

[0053] The heat exchanger 100, the tubes 121 and the tubesheets 130 are for example produced from an aluminum alloy, e.g. from an aluminum-magnesium-manganese alloy.

[0054] In FIG. 1b, part of the helically coiled tube bundle heat exchanger 100 (the bundle of tubes 120, the tubesheets 130 and the core tube 140) from FIG. 1a is shown in a perspective view. As can be seen in FIG. 1b, the tubesheets 130 are fastened to the core tube 140 for example by way of supporting arms 133.

[0055] In order to connect each of the tubes 121 in a material-bonding manner to the respective tubesheet 130 at one of the bores 132, these material-bonding tube-tubesheet connections are produced in the course of a preferred embodiment of the method according to the invention by laser welding with beam oscillation.

[0056] In FIG. 2, a preferred configuration of a device 200 according to the invention for laser welding which is designed to carry out such a preferred embodiment of the method according to the invention is schematically shown. In FIG. 2, it is shown by way of example how with this laser welding unit 200 one of the tubes, denoted in FIG. 2 by 125, can be connected in a material-bonding manner to one of the tubesheets 130 of the helically coiled tube bundle heat exchanger 100 according to FIG. 1 in the course of its production process.

[0057] The laser welding unit 200 has a laser 210, for example an Nd:YAG laser, and a laser head 220. The laser 210 generates a laser beam 211, which is coupled into the laser head 220. Appropriate optical elements are arranged in the laser head 220 in order to focus the laser beam 211 on a location to be welded in a connecting region 250 between the tube 125 and the tubesheet 130.

[0058] The focused laser beam 211 impinges on the location to be welded in the connecting region 250, whereby the tube 125 and the tubesheet 130 are at least partially melted, so that a melt bath 253 is created. When the laser beam is moved over the connecting region, the melted material converges behind the laser beam and solidifies to form the weld seam 260.

[0059] The laser welding unit 200 also comprises a first control unit 230 and a first traversing mechanism 231 in order to produce a first movement of the laser beam 211. For this purpose, the traversing mechanism 231 is appropriately activated by the first control unit 230.

[0060] By means of the traversing mechanism 231, in particular the entire laser welding unit 200 can be moved, in particular both the laser 210 and the laser head 220 together. In the course of this, the laser welding unit 200 may for example be rotated both about a z axis and about an x axis.

[0061] The tubesheet 130 in this case extends for example in a plane defined by the x axis and a y axis, the z axis being oriented perpendicularly in relation to this plane.

[0062] According to this first movement or main movement, the laser beam 211 is moved over the connecting region along a first direction 251. This first direction 251 corresponds in particular to a main direction of extent of the connecting region or a main direction of extent of the weld seam 260 produced. This first direction 251 also extends in particular parallel to a circumference 252 of the tube 125.

[0063] A second control unit 240 and a second traversing mechanism are also provided, in order to produce a second movement of the laser beam 211. The second traversing mechanism is explained in detail further below with reference to FIG. 3. It should be pointed out that the first control unit 230 and the second control unit 240 may be provided combined in a common control unit. The same applies to the two traversing mechanisms.

[0064] Individual optical elements in the laser head 220 can be moved by means of the second traversing mechanism, whereby a second movement is superposed on the first movement of the laser beam 211. This second movement is explained in detail further below with reference to FIG. 4.

[0065] In FIG. 3, the laser head 220 from FIG. 2 is shown schematically in a sectional view. The laser beam 211 generated by the laser 210 is coupled into the laser head by a lens 221 and in this example first impinges therein on a deflecting mirror 222. The laser beam 211 then impinges on a first rotatable mirror 223 and after that on a second rotatable mirror 226. Subsequently, the laser beam 211 impinges on a focusing lens 229, after which it leaves the laser head.

[0066] The rotatable mirrors 223 and 226 may be formed in each case for example as hollow mirrors. The first mirror 223 may be rotated about a first axis 225 by a first adjusting mechanism 224. The second mirror 226 may be rotated about a second axis 228 by a second adjusting mechanism 227. The axes 225 and 228 are in particular perpendicular to one another. The adjusting mechanisms 224 and 227 together form the aforementioned second traversing mechanism for producing the second movement of the laser beam 211.

[0067] For this purpose, the second control unit 240 activates the adjusting mechanisms 224 and 227 in order to rotate the rotatable mirrors 223 and 226 correspondingly to superpose the second movement of the laser beam 211 on the first movement.

[0068] In FIG. 4, examples of the first movement and the second movement of the laser beam, which can carried out in the course of a preferred embodiment of a method according to the invention, are schematically shown. In FIGS. 4a to 4e, the tube 125 and part of the tubesheet 130 are respectively shown schematically in a plan view.

[0069] In FIG. 4a, an example of the first movement of the laser beam 211 is schematically shown. The first movement in this case runs along the circumference 252 of the tube 125 in the connecting region 250. The first movement is consequently a circular movement around the center point of the tube 125; the first direction of movement 251 runs parallel to the circumference 252 of the tube 125. A radius 301 of this circular movement corresponds in this case for example to the outer radius of the tube 125.

[0070] In FIG. 4b, an example of the second movement of the laser beam 211 is schematically shown. The second movement is in this example likewise a circular movement. The diameter 302 of this circular movement corresponds in this example to a width of the connecting region 250. In particular, the diameter 301 of this circular movement likewise corresponds to the width of the weld seam 260.

[0071] The second movement may for example also be elliptical, as shown in FIG. 4c. In this example, for example twice the length of the semi-minor axis 303 of the corresponding ellipse corresponds to the width of the connecting region 250 and further in particular to the width of the weld seam 260.

[0072] In FIG. 4d, an example of the movement of the laser beam 211 as a superposition of the first movement according to FIG. 4a and the second movement according to FIG. 4b is schematically shown. The laser beam 211 is consequently moved over the connecting region 250 as a superposition of a circular movement with a radius 301 and a circular movement with a diameter 302. The center point of the second movement in the form of the circular movement according to FIG. 4b lies in this case for example on the circumference 252 of the tube 125.

[0073] For positive influencing of the melt bath dynamics and targeted modification of the vapor capillary that is formed during the laser welding, in particular in the case of deep welding with comparatively high laser beam intensities (cf. the relevant statements further above in the description), the second movement is performed with a transversal deflection of between 0.15 and 0.25 mm and a longitudinal deflection of 0.15 to 0.25 mm. If the longitudinal deflection and the transversal deflection are the same, there is a circular second movement, otherwise an elliptical second movement is obtained. A circular second movement with a transversal deflection and a longitudinal deflection of 0.23 mm has proven to be particularly advantageous. The frequency of this second movement lies here in the range of 3000-4500 Hz; in particular, a frequency of 3500 Hz is particularly advantageous. In this way, the risk of porosity in the welded connection can be greatly reduced by the second movement.

[0074] In FIG. 4e, an example of a produced tube-tubesheet connection is shown. The movement of the laser beam 211 according to FIG. 4d has the effect that the tube 125 and the tubesheet 130 are melted in particular over the entire width of the connecting region. Once the melt has solidified, the weld seam 260 has consequently been produced, the width of the weld seam 260 corresponding to the width of the connecting region 250.

LIST OF REFERENCE NUMERALS

[0075] 100 Tube bundle heat exchanger, helically coiled tube bundle heat exchanger

[0076] 110 Shell

[0077] 111 Fluid inlet

[0078] 112 Fluid outlet

[0079] 120 Bundle of tubes

[0080] 121 Tubes

[0081] 125 Tube

[0082] 130 Tubesheets

[0083] 131 Bore region

[0084] 132 Bores

[0085] 133 Supporting arms

[0086] 140 Core tube

[0087] 200 Laser welding unit, device for laser welding

[0088] 210 Laser, Nd:YAG laser

[0089] 211 Laser beam

[0090] 220 Laser head

[0091] 221 Lens

[0092] 222 Deflecting mirror

[0093] 223 First rotatable mirror, hollow mirror

[0094] 224 First adjusting mechanism

[0095] 225 First axis

[0096] 226 Second rotatable mirror, hollow mirror

[0097] 227 Second adjusting mechanism

[0098] 228 Second axis

[0099] 229 Focusing lens

[0100] 230 First control unit

[0101] 231 First traversing mechanism

[0102] 240 Second control unit

[0103] 250 Connecting region

[0104] 251 First direction; main direction of extent of the weld seam

[0105] 252 Circumference of the tube 125

[0106] 253 Melt bath

[0107] 260 Weld seam

[0108] 301 Radius of the circular first movement

[0109] 302 Diameter of the circular second movement

[0110] 303 Semi-minor axis of the elliptical second movement