Process for the continuous production of thin-walled hollow profiles which are composed of nonferrous metals and have small diameters and are corrugated in sections

Abstract

A process for the continuous production of thin-walled, radially closed hollow profiles which are composed of nonferrous metals and have a small cross section comprises supply of a flat strip of the nonferrous metal to a forming apparatus (212) at a first supply speed, where the thickness of the strip corresponds to the wall thickness of the hollow profile. The forming apparatus (212) is configured for continuous forming of the flat strip supplied into a shape corresponding to the hollow profile. After forming, two opposite edges of the flat strip rest flush against one another in a contact region. A welding apparatus (216) continuously welds the edges which rest flush against one another by means of a laser which emits light having a wavelength of less than 600 nm. The laser heats a point in a welding region which has a diameter which is less than 20% of the cross-sectional dimension of the hollow profile. The welded hollow profile is taken off from the welding region, provided in a corrugator (225) with parallel or helical corrugation in sections and taken up in an uptake device (226).

Claims

1. A process for the continuous production of a radially closed hollow profile having a wall thickness of less than 0.15 mm and a diameter smaller than 4 mm and which is composed of a nonferrous metal and is corrugated in sections, comprising: supply of a flat strip of the nonferrous metal at a first supply speed to a forming apparatus, where the thickness of the strip corresponds to the wall thickness of the hollow profile to be produced, continuous forming of the flat strip supplied into a shape corresponding to the hollow profile, where two opposite edges of the flat strip rest flush against one another in a contact region extending in the longitudinal direction of the hollow profile after forming, continuous welding of the edges resting flush against one another in the contact region without prior treatment to reduce reflections, wherein the edges to be welded are conveyed at the first supply speed past a welding region which is fixed in relation to an apparatus implementing the process, wherein an area in the welding region is heated by means of a laser which emits light having a wavelength of less than 600 nm, taking-off of the welded hollow profile from the welding region, selective introduction of sections having corrugation into the welded hollow profile determining of the tensile force on the flat strip of the nonferrous metal and/or the welded hollow profile, regulating a drive which supplies the flat strip and/or a drive which supplies the welded hollow profile to forming, and/or a drive which supplies the welded hollow profile to welding and/or a drive which supplies the welded hollow profile to taking-up in an uptake apparatus, and taking-up of the welded hollow profile in an uptake device wherein a beam of the laser is focussed onto the surface of the hollow profile in accordance with a profile, which profile has a central focus point of high intensity and an annular region of lower intensity surrounding the central focus point.

2. The process according to claim 1, wherein an inert protective gas flows around or blankets at least the welding region on the inside and/or outside the hollow profile during heating.

3. The process according to claim 1, additionally comprising: cutting to size of one or two edges of the flat strip of the nonferrous metal before forming.

4. The process according to claim 3, additionally comprising: measuring the width of the strip of the nonferrous metal which has been cut to size before welding and/or measuring at least one dimension of the hollow profile after welding and providing a cut width and control of the cutting to size as a function of the measurement result and a prescribed value.

5. The process according to claim 1, additionally comprising: measuring a temperature profile transverse to the welding seam and control of the energy introduced into the welding region as a function of a comparison of the temperature profile with a prescribed profile.

6. The process according to claim 1, additionally comprising: checking of the welding seam by means of ultrasound, eddy current measurement and/or X-rays.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention will be illustrated below by way of example with the aid of an embodiment with reference to the accompanying figures. All figures are purely schematic and not true to scale. The figures show:

(2) FIG. 1 an illustrative example of the process of the invention for the continuous production of thin-walled, radially closed hollow profiles which are corrugated in sections,

(3) FIG. 2 an illustrative example of an apparatus according to the invention for the continuous production of thin-walled, radially closed hollow profiles which are corrugated in sections,

(4) FIG. 3 pictures of a welding seam of a hollow profile produced by the process of the invention,

(5) FIG. 4 a schematic depiction of a process known from the prior art for reducing the wall thickness and the diameter of a tube,

(6) FIG. 5 a schematic depiction of a tube which is corrugated in sections and

(7) FIG. 6 an illustrative schematic depiction of a heat exchanger comprising a tube which is corrugated in sections and has been produced by the process of the invention.

(8) Identical or similar elements are denoted by identical or similar reference numerals in the figures.

DETAILED DESCRIPTION

(9) FIG. 1 shows steps of a process 100 for producing thin-walled, radially closed hollow profiles which are corrugated in sections according to one aspect of the invention. In step 102 of the process a flat strip composed of nonferrous metal is fed at a first supply speed to a forming apparatus. For example, a flat copper strip is rolled off from a coil. In the forming apparatus, the flat strip supplied is formed in step 108 to give a shape corresponding to the desired hollow profile, for example a round tube. Forming can, for example, be carried out by means of a roll-forming tool.

(10) Before forming, an optional step 106 in which one or both edges of the strip of nonferrous metal are cut or prepared in another way can be carried out in a cutting device. In this way, the width of the strip can be set uniformly and precisely even in the case of poor edge quality of the strip of nonferrous metal and the edges can optionally be prepared for the subsequent welding operation.

(11) The cutting device can be supplied with measured values from a measurement apparatus which determines the width of the nonferrous metal strip after cutting to size.

(12) In the forming operation, the edges of the strip are conveyed by means of guide elements so that twisting before welding is prevented and the flush adjacent edges are conveyed in a defined position and at a defined spacing past a welding apparatus. The guide elements can, for example, comprise one or more guide swords and guide bushings which are matched to the hollow geometry to be manufactured. The closing of the geometry can, for example, be carried out by means of drawing dies.

(13) After forming, two opposite edges of the flat strip are located flush against one another in a contact region. In step 110, the flush adjoining edges in the contact region are welded to one another continuously. Welding is carried out by means of a laser which emits light having a wavelength of less than 600 nm. Blanketing of the welding seam by protective gas can optionally be carried out from the outside and/or inside of the hollow profile, depending on the required welding seam quality.

(14) After welding, the now radially closed hollow profile is taken off from the welding region, step 114, and in step 122 selectively corrugated in sections by means of a corrugator before being fed to an uptake device for accommodation in step 124. Taking-off is effected by means of a transport device, for example by means of a clamping tong offtake, cleat offtake or belt offtake.

(15) To monitor the quality of the welding seam, the temperature profile transverse to the welding seam can be determined in an optional step 112. The temperature profile determined can be supplied to a control device for the laser and other elements of an apparatus implementing the process, in particular one or more drives which regulate the supply speed of the strip of nonferrous metal or the speed at which the welded hollow profile is taken off from the welding region.

(16) The process can optionally also comprise a determination of the tensile force on the strip before forming, step 104, and/or on the hollow profile after welding, step 120. The tensile force determined can likewise be supplied to the one or more drives as measured parameter for regulation.

(17) The process can additionally comprise an optional step 116 in which one or more dimensions of the welded hollow profile are determined. The dimensions determined can first and foremost be supplied as input variables for regulating the forming operation and the cutting operation for adjusting the width of the strip.

(18) The process can additionally comprise an optional step 118 in which the quality of the welded seam and/or the welded material is checked for material defects in a non-destructive manner, for example by means of eddy current testing, ultrasound or X-rays.

(19) FIG. 2 shows an illustrative example of an apparatus according to the invention for the continuous production of thin-walled, radially closed hollow profiles which are corrugated in sections. A thin strip 204 of nonferrous metal, for example a copper strip, is rolled off from a roll or unwinder 202. The strip 204 is fed to a roll-forming tool 212 by means of which it is brought to the shape of the desired hollow profile, for example shaped to give a longitudinally slitted round or quadrilateral tube. A cutting apparatus 208 which cuts the strip 204 to a required width or cuts one or both edges of the strip 204 to give clean and smooth edges can be provided between the roll or unwinder 202 and the roll-forming tool 212. An uptake apparatus 205 can be provided for accommodating offcuts of the strip 204. The width of the strip 204 which has been cut to size can be checked in a strip width measurement apparatus 210. The measured results can be supplied to the cutting device 208 for the purposes of regulation. In addition, a measurement apparatus 206 for determining the tensile force, the measured values from which can, for example, be used for regulating drives of the apparatus, can be arranged between the roll or unwinder 202 and the roll-forming tool 212. The edges of the strip located next to one another after forming of the hollow profile can be conveyed by means of one or more guide elements 214 before the laser welding apparatus 216 in such a way that twisting of the hollow profile before welding is prevented and the distance underneath optics of the laser welding apparatus 216 is adhered to. The guide elements can comprise one or more guide swords and guide bushings matched to the hollow profile. The geometry of the hollow profile to be welded is closed by means of drawing dies or guide bushings 218, so that the edges of the strip 204 which has been shaped to give the hollow profile rest against one another in the region of the laser welding apparatus 216. The laser welding apparatus 216 emits high-energy light at a wavelength of less than 600 nm, preferably in a range from 550 to 450 nm. Wavelengths in a range below 450 nm can also be advantageously used according to the invention. The welding region can be blanketed with a protective gas, for example argon, within or outside the hollow profile via a protective gas facility, which is not shown in the figure, in order to prevent reactions of the material being welded with the atmosphere. The advance of the welded hollow profile 224 is effected by means of a transport device 219. The transport device 219 can, for example, comprise one or more clamping tong offtakes, cleat offtakes, disc offtakes or belt offtakes, or combinations thereof. After taking off from the welding region, one or more dimensions of the hollow profile 224 can be determined by means of a measurement instrument 220, preferably in a contactless manner, before the welded hollow profile 224 is fed to a corrugator 225 and then to a winder 226. To determine the tensile forces acting on the hollow profile 224, a further tensile force measurement apparatus 222 can be provided before the corrugator 225 and the winder 226. The corrugator 225 arranged upstream of the winder 226 has a corrugating tool 225a and is configured for introducing a parallel or helical corrugation into the hollow profile selectively in sections.

(20) FIG. 3 shows pictures of a welding seam of a hollow profile produced by the process of the invention. The hollow profile is a copper tube which has a diameter of 2 mm and a wall thickness of 0.1 mm and has been formed and welded continuously at an advance speed of 6 m/m in from a copper strip. The welding position has been blanketed with argon on the inside and outside. FIG. 3a) shows the welding seam on the outside of the hollow profile, which has a width in the range from 140 to 150 μm. FIG. 3b) shows a photograph of the inside of the hollow profile, in which the welding seam has a width of about 242 μm. It can readily be seen that the welding seams are very uniform both on the inside and the outside, so that after-working would not be necessary for most applications. A section of the tube produced by the process was subjected to a pressure test and withstood pressures of more than 200 bar.

(21) FIG. 4, which shows a schematic depiction of a process known from the prior art for reducing the wall thickness and the diameter of a tube, has been described further above in relation to the prior art.

(22) FIG. 5 shows a schematic depiction of a tube 500 which is corrugated in sections. Tube 500 has two corrugated regions 502 between which a noncorrugated region 504 is located.

(23) FIG. 6 shows an illustrative schematic depiction of a heat exchanger 600 comprising a tube 500 which is corrugated in sections and has been produced by the process of the invention. The example depicted in the figure shows a cross-flow heat exchanger, but other flow regimes such as cocurrent, countercurrent, etc., can also be realized using the tube which is corrugated in sections and has been produced according to the invention. A partly corrugated tube 500 produced according to the invention in a continuous process is laid in the dividing plane of a two-part housing 602. Noncorrugated sections 504 are mounted in openings in the housing wall which are matched to the diameter of the tube 500, for example in a bushing. Sealing between tube and housing can also be effected in this noncorrugated region. Between the mounting points, corrugated tube regions 502 can be utilized to increase the area available for heat exchange between a hot medium flowing through inlets 604 into the housing 602 and a cold medium flowing through the tube 500. In addition, the corrugation promotes the formation of turbulences in the flowing media, which likewise improves heat exchange. The tube 500 is conveyed a number of times through the housing 602 in a plurality of loops arranged in a serpentine manner. For this purpose, it is appropriately bent in corrugated regions 502. The medium to be cooled flows out of the housing through outlets 606. The flow direction of the media is indicated by the arrows at the inlets and outlets of the housing 602 and the tube 500. Efficient cooling of the medium to be cooled can be achieved by the one-piece construction according to the invention of the tube 500 with the smooth and corrugated sections, without joins between the smooth tube sections and the corrugated tube sections being necessary.

(24) TABLE-US-00001 List of reference numerals  1 Tube  2 Die  3 Plug 100 Process 102 Supply of strip 104 Determination of tensile force 106 Cutting of edges 108 Shaping of hollow profile 110 Welding 112 Determination of temperature profile 114 Taking-off of hollow profile 116 Determination of dimensions 118 Determination of quality 120 Determination of tensile force 122 Corrugating 124 Feeding to uptake device 200 Apparatus 202 Roll/unwinder 204 Strip of nonferrous metal 205 Uptake apparatus for cutting scrap 206 Tensile force measurement apparatus 208 Cutting device 210 Strip width measurement apparatus 212 Roll-forming tool 214 Guide element 216 Laser welding apparatus 218 Drawing die/guide bushing 219 Transport device 220 Measuring instrument 222 Tensile force measurement apparatus 224 Welded hollow profile 225 Corrugator  225a Corrugating tool 226 Winder 500 Tube 502 Corrugated region 504 Noncorrugated region 600 Heat exchanger 602 Housing 604 Inlet 606 Outlet