Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K9/00—Arc welding or cutting
  • B23K9/0026—Arc welding or cutting specially adapted for particular articles or work
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
  • F28D9/00—Heat-exchange apparatus having stationary plate-like or laminated conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall
  • F28D9/0062—Heat-exchange apparatus having stationary plate-like or laminated conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall the conduits for one heat-exchange medium being formed by spaced plates with inserted elements
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F21/00—Constructions of heat-exchange apparatus characterised by the selection of particular materials
  • F28F21/08—Constructions of heat-exchange apparatus characterised by the selection of particular materials of metal
  • F28F21/081—Heat exchange elements made from metals or metal alloys
  • F28F21/085—Heat exchange elements made from metals or metal alloys from copper or copper alloys
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F9/00—Casings; Header boxes; Auxiliary supports for elements; Auxiliary members within casings
  • F28F9/02—Header boxes; End plates
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K2101/00—Articles made by soldering, welding or cutting
  • B23K2101/04—Tubular or hollow articles
  • B23K2101/14—Heat exchangers
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F2275/00—Fastening; Joining
  • F28F2275/04—Fastening; Joining by brazing
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F2275/00—Fastening; Joining
  • F28F2275/06—Fastening; Joining by welding

Definitions

• the invention relates to a method for welding brazed copper heat exchangers, a method for manufacturing by welding heat exchangers, the exchangers obtained by such a method and their use for the separation of gases, in particular air.
• Copper heat exchangers or heat exchangers are usually manufactured first by stacking plates and fins which are brazed together to form a matrix, then by adding one or more fluid collecting chambers used to collect and distribute fluids treated in the equipment.
• fluid collecting enclosure or enclosures also called collectors
• collectors are attached and fixed to the brazed matrix of the exchanger by welding.
• the bonding weld uniting the fluid collector with the matrix necessarily crosses the interstices filled with solder which connect between them the plates and fins constituting this part of the exchanger.
• brazing alloys are used for brazing copper, namely copper-silver alloys which are very expensive and copper-phosphorus alloys which are much cheaper but generally contain an amount of phosphorus of between approximately 5%. and about 8% by weight. Indeed, the addition of silver or phosphorus makes it possible to significantly lower the melting temperature of the alloy compared to pure copper, typically by several hundred degrees Celsius, which is essential in order to be able to perform a brazing operation. .
• the object of the invention is therefore to propose an improved welding process applicable to the manufacture of brazed copper heat exchangers making it possible to overcome the above-mentioned problems, as well as improved exchangers obtained by this process, which do not present any problems of leak or poor seal.
• the problem is to be able to efficiently weld copper parts of heat exchangers without the formation of fragile zones rich in phosphorus and therefore to propose a method of welding heat exchangers leading to obtaining exchangers having a resistance greater than that of the exchangers whose sub-parts which constitute them have been welded by implementing traditional methods.
• the invention therefore relates to a method of arc welding at least one metal part on a matrix comprising at least one brazed zone, the brazing of which contains copper and phosphorus, in which the following steps are carried out: (a) a deposit of at least one layer of pure copper or of a copper alloy for which the phosphorus solubility limit is between approximately 0.1 and 3.5% is applied to at least part of the brazed zone. the solidification temperature, and (b) a metal part is welded to said at least one layer of copper deposited in step (a).
• the percentages (%) are percentages by weight.
• the method of the invention may include one or more of the following technical characteristics:
• the copper alloy has a phosphorus solubility limit of between approximately 0.5 and 3.5% at the solidification temperature, preferably between approximately 1 and 3.5%.
• step (a) a deposit is made of several copper-based layers which are at least partially superposed on each other.
• the brazed matrix also contains at least one brazing element chosen from Sn, Ag and Zn.
• the copper or copper alloy constituting the layer or layers deposited in step (a) additionally contain at least one additional element chosen from tin, silicon, manganese, iron and nickel.
• the brazing contains from 3 to 10% of phosphorus, from 0 to 15% of silver and from 0 to 1% of nickel and / or the layer or layers deposited in step (a) contain less than 1% of tin, less than 0.5% manganese, less than 0.5% silicon and less than 0.05% iron.
• the deposition of at least one layer of copper from step (a) is carried out by:
• step (ii) supply of copper and deposit on the zone preheated in step (i) of copper melted by an electric arc.
• the preheating of the zone to be coated with copper of step (i) is effected by the use of one or more electric arcs, preferably at least one arc generated by a TIG or plasma welding torch.
• step (ii) the supply of copper is in the form of a copper wire and the electric arc used to melt said copper wire is generated by at least one MIG welding torch.
• step (b) the part (1) is welded by an MIG, TIG, plasma process or a combination of these processes, preferably a pulsed MIG process.
• the brazed matrix is carried by a stack of several plates separated by fins forming spacers between said plates, said fins and said plates being based with each other so as to form said brazed matrix.
• the part is a constituent part of a collecting container and / or fluid distributor forming part of a heat exchanger, preferably said part is made of copper or stainless steel.
• the layer deposited on the matrix has a sufficient width to allow a welding joint to be produced between the part and said layer without incorporation in said joint of additional elements coming from the brazed zone of the matrix.
• the invention also relates to a method of manufacturing a copper brazed heat exchanger in which the welding method according to the invention is used to weld at least one container, preferably made of copper, collector and fluid distributor of the exchanger on a stack of plates separated by fins forming spacers between said plates and carrying at least one brazed matrix.
• the invention also relates to a copper heat exchanger comprising at least one collecting container and fluid distributor welded on a brazed matrix carried by a stack of several plates separated by fins forming spacers between said plates, characterized in that said container is soldered onto at least one layer of pure copper or a copper alloy for which the phosphorus solubility limit is between approximately 0.1 and 3.5% at solidification temperature, said at least one layer of copper being deposited on said matrix brazed.
• the welded fluid collecting and distributing container is made of copper or stainless steel.
• the invention also relates to a fluid separation installation, in particular of gas mixtures, comprising at least one exchanger according to the invention, preferably said installation is a cryogenic air separation unit.
• the invention relates to a process for the separation of fluid, in particular of gas mixtures in which at least one heat exchanger according to the invention is used, preferably the fluid is air. More generally, the invention also relates to a process for coating a matrix comprising at least one brazed zone, the brazing of which contains copper and phosphorus, in which the following steps are carried out:
• preheating of the zone to be coated by exposing said zone to at least a first electric arc (2) supply of copper in the form of a fusible wire and progressive melting of said copper wire by means of at least a second arc electric with deposition on the area preheated by the first electric arc of step (1) of copper melted by the second electric arc, said copper wire being made of pure copper or a copper alloy for which the solubility limit phosphorus is between approximately 0.1 and 3.5% at the solidification temperature, and
• the copper constituting the filler wire contains at most 2% by weight of at least one additional element chosen from tin, silicon, manganese, phosphorus, iron and nickel, preferably copper. constituting the filler wire is almost free of phosphorus.
• FIG. 1 the principle of the invention is shown applicable to the welding of a part 1, for example a fluid collection and distribution enclosure for heat exchanger, on a brazed matrix 2, such as the brazed matrix 3 d 'a heat exchanger formed by brazing a stack of plates 11 separated by fins 12 forming spacers, as detailed in FIG. 2.
• a brazed matrix 2 such as the brazed matrix 3 d 'a heat exchanger formed by brazing a stack of plates 11 separated by fins 12 forming spacers, as detailed in FIG. 2.
• the part 1 is not welded directly to the matrix 2 comprising the brazed zone 3 formed of a copper alloy generally containing less than 10% phosphorus and possibly other compounds, as commonly operated in the prior art.
• the inventors of the present invention have demonstrated that the phosphorus is that which is at the origin of the cracking problems arising in the prior art if the local concentration of phosphorus exceeds the limit of solubility in "l 'local alloy' resulting from the non-homogeneous mixture of the deposited metal, the copper of the exchanger and the solder.
• the invention to avoid this cracking problem due to phosphorus, first depositing one or more layers 5, 6, 7, 5 superimposed of pure copper or a copper alloy on the face of the matrix 2 comprising brazing 3 so as to constitute a seat on which the part 1 is then welded; these 5,6,7 superimposed layers of copper covering the brazed surface 3 are called “buttering" layers.
• the deposition of layers 5, 6, 7 of "buttering" copper operated on the surface on which the brazed interstices 3 of the matrix 2 end, constitutes an insulating barrier making it possible to avoid any possible contamination of the joint 4 of welding by resurgences of harmful elements from the solder 3, during the subsequent welding of the part 1 on the layers 5 to 7 of buttering.
• the layers 5 to 7 of copper thus formed can admit a significant quantity of pollutants, in dilution, ranging up to about 3.5% by weight in the case of phosphorus for example, without being greatly deteriorated.
• the maximum value of 3.5% corresponds to the solubility limit of phosphorus in pure copper at the solidification temperature of the alloy thus obtained, the solubility limit of one element (phosphorus) in another element (copper) being defined in metallurgy as being the maximum content of the first element which can be combined with the second without the appearance of a second phase; see Dr. M. Hansen, Constitution of binary alloys, McGraw-Hill Book Company, Inc.
• the part 1 is therefore welded according to the weld joint 4, on the layer or layers 5 to 7 of buttering copper previously deposited on the brazed matrix 3, and not directly on the brazed zone 3, as conventionally made in the prior art.
• the difficulty of soldering copper with a copper filler product comes from the fact that the copper melts and solidifies at a fixed temperature and not in a temperature range like most alloys.
• the weld pool is very difficult to handle for a welder and the beads obtained are generally poorly "wet", that is to say have a poor connection of the sides of the bead to the base metal, and in addition, often have defects of the bonding type, that is to say that the filler metal is "placed" on the base metal without fusion of this detnier.
• Another satisfactory solution consists in using a hybrid plasma-MIG torch which is characterized by a plasma arc which surrounds the filler wire and the MIG arc.
• the buttering layers 5 to 7 have a sufficient width and will be produced with pure copper or possibly a copper alloy for which the limit of phosphorus solubility is still sufficiently high at the solidification temperature, for example 0, 5 to 1%, so that the phosphorus coming from the solder and introduced into the buttering layer 5 can be diluted sufficiently to avoid the formation of cracks and that an additional weld 4 can be produced without risk for the integrity of the structure.
• This process is particularly well suited to the manufacture of brazed heat exchangers which can be used to separate gases, in particular cryogenically within cryogenic distillation columns.
• FIGS. 2 and 3 The detailed structure of the brazed zone of a copper exchanger 10 of this type, seen in cross section, is shown diagrammatically in FIGS. 2 and 3 where it can be seen that it comprises a stack of metal plates or sheets 11 separated by from each other by fins 12 forming spacers between said plates 11. Said fins 12 are brazed at the ends of the plates 11 so as to form therein a brazed die 2 3 (see also Figure 1) on which must be welded one or structures or enclosures 1 used to collect and distribute the fluids in the exchanger 10.
• the layers 5 to 7 of "buttering" are produced on the external surface of this brazed zone 3 of the matrix 2 of the exchanger 10, as explained above in relation to FIG. 1, before welding of said structure or enclosure for collecting and distributing fluid on this or these layers 5 to 7 of "buttering" of pure copper which may contain alloying elements or unavoidable impurities.
• a localized preheating of the zone to be coated is first carried out, then a deposit of molten copper on this preheated zone, said copper being brought in the form of '' a copper-based fuse wire, the fusion of which is obtained by implementing an electric arc, in particular by means of a MIG torch.
• the MIG process is preferred because this welding process generates movements of the molten metal liquid bath more important than the TIG process, which leads to avoid a localized concentration of certain harmful elements, such as phosphorus, in particular in the areas of the "buttering" bead 5 at the crossing of the solder.
• an arc welding torch such as a MIG (Metal Inert Gas), TIG (Tungsten Inert Gas) torch, plasma or combinations of such torches, for example a plasma-MIG torch or M1G-TIG torches.
• MIG Metal Inert Gas
• TIG Tungsten Inert Gas
• plasma or combinations of such torches for example a plasma-MIG torch or M1G-TIG torches.
• a filler product of the copper / nickel or copper / aluminum type can be brought in, or, when it is desired to provide a connection between the zone covered with copper and a piece of stainless steel, such as a collector of fluid, it may be necessary to use other filler products of the nickel or nickel alloy type.
• a piece of stainless steel such as a collector of fluid
• the welding process of the invention is particularly well suited to the manufacture of brazed heat exchangers which can be used to separate gases from the air, in particular cryogenically within cryogenic distillation columns, because these exchangers will be more resistant to cracking problems than conventional exchangers.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Mechanical Engineering (AREA)
• Thermal Sciences (AREA)
• General Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• Arc Welding In General (AREA)

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• 2001
  • 2001-11-22 FR FR0115118A patent/FR2832336B1/fr not_active Expired - Fee Related
• 2002
  • 2002-10-14 US US10/496,721 patent/US20050029242A1/en not_active Abandoned
  • 2002-10-14 CN CNB028259459A patent/CN1296167C/zh not_active Expired - Fee Related
  • 2002-10-14 WO PCT/FR2002/003509 patent/WO2003043771A1/fr active Application Filing
  • 2002-10-14 EP EP02785546A patent/EP1450980A1/de not_active Withdrawn
  • 2002-10-14 JP JP2003545436A patent/JP4680502B2/ja not_active Expired - Fee Related

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