EP0950127A1 - Advanced galvanic corrosion protection - Google Patents

Advanced galvanic corrosion protection

Info

Publication number
EP0950127A1
EP0950127A1 EP97945553A EP97945553A EP0950127A1 EP 0950127 A1 EP0950127 A1 EP 0950127A1 EP 97945553 A EP97945553 A EP 97945553A EP 97945553 A EP97945553 A EP 97945553A EP 0950127 A1 EP0950127 A1 EP 0950127A1
Authority
EP
European Patent Office
Prior art keywords
aluminum
recited
less noble
noble metal
consists essentially
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP97945553A
Other languages
German (de)
French (fr)
Other versions
EP0950127B1 (en
Inventor
Thomas J. Garosshen
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Carrier Corp
Original Assignee
Carrier Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US08/734,146 external-priority patent/US6578628B1/en
Application filed by Carrier Corp filed Critical Carrier Corp
Publication of EP0950127A1 publication Critical patent/EP0950127A1/en
Application granted granted Critical
Publication of EP0950127B1 publication Critical patent/EP0950127B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F19/00—Preventing the formation of deposits or corrosion, e.g. by using filters or scrapers
    • F28F19/02—Preventing the formation of deposits or corrosion, e.g. by using filters or scrapers by using coatings, e.g. vitreous or enamel coatings
    • F28F19/06—Preventing the formation of deposits or corrosion, e.g. by using filters or scrapers by using coatings, e.g. vitreous or enamel coatings of metal
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C30/00—Coating with metallic material characterised only by the composition of the metallic material, i.e. not characterised by the coating process

Definitions

  • This invention relates generally to protecting metals from a corrosive environment, and more specifically to protecting copper-aluminum heat exchangers for use in air conditioners.
  • Galvanic corrosion occurs when two dissimilar metals make contact with one another in the presence of an electrolyte thereby forming a galvanic couple.
  • the more noble metal (higher on the galvanic series) provides the surface area for the reduction reaction and the less noble metal (lower on the galvanic series) corrodes in an oxidation process.
  • the oxidation occurs in the greatest amount at the interface of the two metals but may also occur at some distance away from the actual interface.
  • the most common electrolyte is salt water in the air. A fine salt water mist may be blown inland for up to fifty miles from the coast. Sulfur dioxide from industrial pollution also creates an electrolyte when it combines with moisture in the air.
  • a common method of preventing galvanic corrosion has been to coat the exposed surfaces cf the metals with various types of paint.
  • These protective coatings have met with only limited success for a number of reasons.
  • the main problem with coatings is that their effectiveness at preventing corrosion is degraded by exposure to the environment such as ultraviolet light and acid rain.
  • Another common problem is that the coating materials often do not adhere well to the metal substrates and eventually flake off or erode away exposing the metal substrates.
  • such protective coatings are somewhat porous and allow the electrolyte to penetrate the surface of the substrates and connect the galvanic couple.
  • the application of protective coatings to the surfaces of certain articles can negatively affect their performance.
  • the present invention provides an advanced galvanic corrosion protection method.
  • the outer surface of the more noble metal is treated with a metal which is galvanically compatible with the less noble metal to form a protective layer between the two dissimilar metals which prevents the reduction reaction of the galvanic couple from occurring.
  • the invention greatly reduces the oxidation reduction process which occurs when two dissimilar metals are in contact with one another in the presence of an electrolyte.
  • FIG. 1 is a perspective view of a heat exchanger incorporating heat exchanger tubes treated in accordance with the present invention.
  • the present invention will be described in to providing for galvanic corrosion protection of a copper-aluminum heat exchanger.
  • the present invention is not limited to this specific example and could be used in connection with a number of arrangements where dissimilar metals are in contact with one another in the presence of an electrolyte.
  • FIG. 1 illustrates a fin/tube heat exchanger 10 of the type typically used in air conditioning units.
  • the heat exchanger includes one or more flow circuits for carrying refrigerant through the heat exchanger unit.
  • the heat exchanger 10 contains a single flow circuit tube 2 consisting of an inlet line 3 and an outlet line 4 which are connected at one end of the heat exchanger 10 by means of a 90° tube bend 5. It should be evident, however, that more circuits may be added to the unit depending upon the demands of the system.
  • the unit further includes a series of fins 6 comprising radial disposed plate like elements spaced along the length of the flow circuit. The fins 6 are supported in the assembly between a pair of end plates 7 and 8 to define a gas flow passage through which a gas passes over the extension of the tube 2 and between the spaced fins 6.
  • heat exchangers of this type are commonly exposed in use to corrosive environments.
  • heat exchangers of this type are fabricated utilizing copper tubes for the circuit flow tubes and aluminum for the fins.
  • the fins are disposed in contact with the tubes and draw heat away from the tubes through conductive heat transfer and then dissipate the heat through convective heat transfer to the gas (commonly air) flowing over the tubes.
  • Copper is utilized in tube construction because of its good heat transfer properties, general resistance to corrosion, and ease of repair.
  • the fins are fabricated from aluminum because of its good heat transfer properties, ease of fabrication, and low cost. Heat exchangers fabricated entirely from copper, as well as entirely from aluminum, are utilized in certain applications to avoid the problems of galvanic corrosion but at the cost of trades characterized above.
  • Aluminum is significantly lower on the galvanic series, i.e. less noble, than copper. It is for this reason that the aluminum oxidizes or corrodes when it is in contact with copper in the presence of an electrolyte.
  • the interface of the tube and fin is where the galvanic couple is made and where the corrosion of the aluminum fins occurs. Once the fin has corroded at the intersection the fin is no longer in contact with the tube and thus the heat exchanger efficiency is greatly reduced because the fin loses its ability to conduct heat away from the tube.
  • the exposed surfaces of the tubes 2 are coated or enriched with aluminum or a metal more galvanically compatible with aluminum.
  • Aluminum is the best candidate material since a galvanic couple will not form between the aluminum coating and the aluminum fins 6.
  • active metals such as zinc, tin magnesium, gallium, cadmium and lead will also reduce the extent of the galvanic couple and thus the rate of oxidation of the fin material.
  • the coating or surface enrichment of the copper tubes 12 with aluminum is accomplished prior to the assembly of the heat exchanger 10.
  • the aluminizing of copper is a well known practice and can be accomplished to a degree precision so as to virtually eliminate the above cited problems with conventional coating for corrosion protection.
  • the coating processes include hot dipping, electroplating, aluminum filled painting and slurries, and thermal spraying.
  • the surface enrichment processes include ion vapor deposition, chemical vapor deposition, and physical vapor deposition.
  • the critical aspect of the present invention is the production of a uniform coating of aluminum over the entire surface of the flow circuit tubes 2. Regardless of the process contemplated the variables of tube surface preparation, tube preheat temperature, coating composition, and coating thickness must be carefully controlled to achieve the proper results of the present invention.
  • the preparation of the exposed surfaces of the tube is preferred to remove the surface oxide layer from the copper to ensure that the coating material will adhere well to the tube.
  • a number of surface preparation processes are known in industry and include the use of reducing gases, fluxes and shot blasting.
  • the tube preheat temperatures should be controlled between 24 C and 600 C to prevent the dissolution of copper and to limit intermetallic growth during the coating process.
  • the coating have high ductility to allow for the subsequent assembly of the heat exchanger without damaging the coating.
  • the ductility of the coating is determined in part by the coating composition and the thickness of the coating.
  • any metallic composition more galvanically compatible with the fin material than the tube material would slow the oxidation rate of the fins 6, while the ideal coating material would exactly match the fin material.
  • Certain aluminum alloys are considered for use in the present invention and they comprise aluminum combined with silicon and aluminum combined with zinc.
  • the coating must be thick enough to prevent the penetration of the electrolyte. However, as any coating has a somewhat negative effect on the heat transfer of the unit, excessively thick protective layer should be avoided.
  • the optimal range of thickness contemplated by the present invention is .1 mils to 2 mils.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Organic Chemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Other Surface Treatments For Metallic Materials (AREA)
  • Prevention Of Electric Corrosion (AREA)
  • Electroplating Methods And Accessories (AREA)

Abstract

A method for reducing the galvanic corrosion of dissimilar metals in contact with one another wherein the exposed surface of the more noble metal is coated with a metal more galvanically compatible with the less noble metal.

Description

ADVANCED GALVANIC CORROSION PROTECTION
This invention relates generally to protecting metals from a corrosive environment, and more specifically to protecting copper-aluminum heat exchangers for use in air conditioners.
Galvanic corrosion occurs when two dissimilar metals make contact with one another in the presence of an electrolyte thereby forming a galvanic couple. The more noble metal (higher on the galvanic series) provides the surface area for the reduction reaction and the less noble metal (lower on the galvanic series) corrodes in an oxidation process. The oxidation occurs in the greatest amount at the interface of the two metals but may also occur at some distance away from the actual interface. In coastal regions, the most common electrolyte is salt water in the air. A fine salt water mist may be blown inland for up to fifty miles from the coast. Sulfur dioxide from industrial pollution also creates an electrolyte when it combines with moisture in the air.
A common method of preventing galvanic corrosion has been to coat the exposed surfaces cf the metals with various types of paint. These protective coatings have met with only limited success for a number of reasons. The main problem with coatings is that their effectiveness at preventing corrosion is degraded by exposure to the environment such as ultraviolet light and acid rain. Another common problem is that the coating materials often do not adhere well to the metal substrates and eventually flake off or erode away exposing the metal substrates. Moreover, such protective coatings are somewhat porous and allow the electrolyte to penetrate the surface of the substrates and connect the galvanic couple. In addition, the application of protective coatings to the surfaces of certain articles can negatively affect their performance.
Attempts have been made, with varying degrees of success, to coat conventional copper-aluminum heat exchangers with various materials in an effort to extend the useful life of the unit. These coating materials oftentimes reduce the heat transfer capability of the unit, exhibit poor adhesion properties and fail to penetrate into all the areas that might be exposed to a hostile environment.
In general the present invention provides an advanced galvanic corrosion protection method. In accordance with the present invention, in an article made of two metals, one being more noble than the other, the outer surface of the more noble metal is treated with a metal which is galvanically compatible with the less noble metal to form a protective layer between the two dissimilar metals which prevents the reduction reaction of the galvanic couple from occurring. The invention greatly reduces the oxidation reduction process which occurs when two dissimilar metals are in contact with one another in the presence of an electrolyte.
FIG. 1 is a perspective view of a heat exchanger incorporating heat exchanger tubes treated in accordance with the present invention.
As will be described in detail below the present invention will be described in to providing for galvanic corrosion protection of a copper-aluminum heat exchanger. However, it should be evident to one skilled in the art that the present invention is not limited to this specific example and could be used in connection with a number of arrangements where dissimilar metals are in contact with one another in the presence of an electrolyte.
FIG. 1 illustrates a fin/tube heat exchanger 10 of the type typically used in air conditioning units. The heat exchanger includes one or more flow circuits for carrying refrigerant through the heat exchanger unit. For the purposes of explanation, the heat exchanger 10 contains a single flow circuit tube 2 consisting of an inlet line 3 and an outlet line 4 which are connected at one end of the heat exchanger 10 by means of a 90° tube bend 5. It should be evident, however, that more circuits may be added to the unit depending upon the demands of the system. The unit further includes a series of fins 6 comprising radial disposed plate like elements spaced along the length of the flow circuit. The fins 6 are supported in the assembly between a pair of end plates 7 and 8 to define a gas flow passage through which a gas passes over the extension of the tube 2 and between the spaced fins 6.
As noted above, heat exchangers of this type are commonly exposed in use to corrosive environments. In a typical arrangement heat exchangers of this type are fabricated utilizing copper tubes for the circuit flow tubes and aluminum for the fins. The fins are disposed in contact with the tubes and draw heat away from the tubes through conductive heat transfer and then dissipate the heat through convective heat transfer to the gas (commonly air) flowing over the tubes. Copper is utilized in tube construction because of its good heat transfer properties, general resistance to corrosion, and ease of repair. The fins are fabricated from aluminum because of its good heat transfer properties, ease of fabrication, and low cost. Heat exchangers fabricated entirely from copper, as well as entirely from aluminum, are utilized in certain applications to avoid the problems of galvanic corrosion but at the cost of trades characterized above.
Aluminum is significantly lower on the galvanic series, i.e. less noble, than copper. It is for this reason that the aluminum oxidizes or corrodes when it is in contact with copper in the presence of an electrolyte. In the arrangement shown in FIG. 1, the interface of the tube and fin is where the galvanic couple is made and where the corrosion of the aluminum fins occurs. Once the fin has corroded at the intersection the fin is no longer in contact with the tube and thus the heat exchanger efficiency is greatly reduced because the fin loses its ability to conduct heat away from the tube.
As will be explained in greater detail below, in accordance with the present invention the exposed surfaces of the tubes 2 are coated or enriched with aluminum or a metal more galvanically compatible with aluminum. Aluminum is the best candidate material since a galvanic couple will not form between the aluminum coating and the aluminum fins 6. However, such active metals such as zinc, tin magnesium, gallium, cadmium and lead will also reduce the extent of the galvanic couple and thus the rate of oxidation of the fin material. The coating or surface enrichment of the copper tubes 12 with aluminum is accomplished prior to the assembly of the heat exchanger 10. The aluminizing of copper is a well known practice and can be accomplished to a degree precision so as to virtually eliminate the above cited problems with conventional coating for corrosion protection. Several processes for aluminizing the copper tubes are known in industry and contemplated by the present invention. The coating processes include hot dipping, electroplating, aluminum filled painting and slurries, and thermal spraying. The surface enrichment processes include ion vapor deposition, chemical vapor deposition, and physical vapor deposition.
The critical aspect of the present invention is the production of a uniform coating of aluminum over the entire surface of the flow circuit tubes 2. Regardless of the process contemplated the variables of tube surface preparation, tube preheat temperature, coating composition, and coating thickness must be carefully controlled to achieve the proper results of the present invention. The preparation of the exposed surfaces of the tube is preferred to remove the surface oxide layer from the copper to ensure that the coating material will adhere well to the tube. A number of surface preparation processes are known in industry and include the use of reducing gases, fluxes and shot blasting. The tube preheat temperatures should be controlled between 24 C and 600 C to prevent the dissolution of copper and to limit intermetallic growth during the coating process.
It is preferred that the coating have high ductility to allow for the subsequent assembly of the heat exchanger without damaging the coating. The ductility of the coating is determined in part by the coating composition and the thickness of the coating. As mentioned above any metallic composition more galvanically compatible with the fin material than the tube material would slow the oxidation rate of the fins 6, while the ideal coating material would exactly match the fin material. Certain aluminum alloys are considered for use in the present invention and they comprise aluminum combined with silicon and aluminum combined with zinc. The coating must be thick enough to prevent the penetration of the electrolyte. However, as any coating has a somewhat negative effect on the heat transfer of the unit, excessively thick protective layer should be avoided. The optimal range of thickness contemplated by the present invention is .1 mils to 2 mils.

Claims

CLAIMSWhat is claimed is:
1. A method of preventing galvanic corrosion of a surface of a first member to be disposed in contact with a second member, the first member being formed of a metal less noble than the second member, the first member having a surface adapted to be in contact with a surface of the second metal, comprising the step of: treating the exposed surface of the second member with a less noble metal.
2. The method as recited in claim 1 wherein the treating step comprises coating the exposed surface of the second member with the less noble metal to form a layer of the less noble metal on the exposed surface of the second member.
3. The method as recited in claim 2 wherein the layer of less noble metal is of a thickness of about between .0001 and .002 inches.
4. The method as recited in claim 3 wherein the coating process is a hot dipping process, an electroplating process, a painting process or a diffusion coating process.
5. The method as recited in claim 1 wherein the treatment step is a surface enrichment process.
6. The method as recited in claim 5 wherein the treatment step is an ion vapor deposition process, a chemical vapor deposition process or a physical vapor deposition process.
7. The method as recited in claim 1 wherein the second member consists essentially of copper, the first member consists essentially of aluminum and the less noble metal consists essentially of aluminum or aluminum alloy including either silicon or zinc.
8. The method as recited in claim 1 wherein the second member consists essentially of copper, the first member consists essentially of aluminum and the less noble metal comprises an element less noble than aluminum selected from the group consisting of zinc, tin, magnesium, gallium, cadmium, lead and combinations thereof.
9. A heat exchanger manufactured in accordance with the method of claim 1.
10. A heat exchanger as recited in claim 9 wherein the first member is a fin comprised of aluminum and the second member is a tube comprised of copper, and the less noble metal is selected from the group consisting of aluminum, silicon aluminum alloy, zinc aluminum alloy, zinc, tin, magnesium, gallium, cadium, lead and combinations thereof.
EP97945553A 1996-10-21 1997-09-30 Advanced galvanic corrosion protection Expired - Lifetime EP0950127B1 (en)

Applications Claiming Priority (5)

Application Number Priority Date Filing Date Title
US73414596A 1996-10-21 1996-10-21
US734145 1996-10-21
US734146 1996-10-21
US08/734,146 US6578628B1 (en) 1996-10-21 1996-10-21 Article exhibiting increased resistance to galvanic corrosion
PCT/US1997/018122 WO1998017841A1 (en) 1996-10-21 1997-09-30 Advanced galvanic corrosion protection

Publications (2)

Publication Number Publication Date
EP0950127A1 true EP0950127A1 (en) 1999-10-20
EP0950127B1 EP0950127B1 (en) 2005-05-18

Family

ID=27112678

Family Applications (1)

Application Number Title Priority Date Filing Date
EP97945553A Expired - Lifetime EP0950127B1 (en) 1996-10-21 1997-09-30 Advanced galvanic corrosion protection

Country Status (12)

Country Link
EP (1) EP0950127B1 (en)
JP (1) JP2001502757A (en)
KR (1) KR100334213B1 (en)
CN (2) CN101063206A (en)
BR (1) BR9712540A (en)
DE (1) DE69733317T2 (en)
EG (1) EG22317A (en)
ES (1) ES2238731T3 (en)
ID (1) ID18594A (en)
SA (1) SA97180556B1 (en)
WO (1) WO1998017841A1 (en)
ZA (1) ZA978931B (en)

Families Citing this family (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6325138B1 (en) * 1996-10-21 2001-12-04 Carrier Corporation Article exhibiting improved resistance to galvanic corrosion
SE524615C2 (en) 1999-06-30 2004-09-07 Volvo Personvagnar Ab Arrangements for reducing galvanic corrosion between metal components
KR100567801B1 (en) * 2004-11-01 2006-04-05 엘지전자 주식회사 Heat exchanger for refrigerator and method for anufacturing refrigerant tube of the same
DK2836783T3 (en) 2012-04-12 2019-09-02 Carrier Corp NON-RECYCLABLE ALUMINUM FINDER FOR ERROR STATE PROTECTION OF AN ALUMINUM HEAT EXCHANGER.
KR101462150B1 (en) * 2013-09-03 2014-11-14 주식회사 안성에이치이산업 Preventing damage and protection apparatus for heat exchanger using dual plate
KR101400170B1 (en) * 2013-09-03 2014-05-28 주식회사 안성에이치이산업 Preventing damage and protection apparatus for heat exchanger using plate
US10473411B2 (en) 2014-12-17 2019-11-12 Carrier Corporation Aluminum alloy finned heat exchanger
US20210348859A1 (en) * 2018-12-19 2021-11-11 Carrier Corporation Heat exchanger with aluminum alloy clad tube and method of manufacture
WO2020132237A1 (en) * 2018-12-19 2020-06-25 Carrier Corporation Heat exchanger with sacrificial turbulator
JP6923099B1 (en) * 2021-03-23 2021-08-18 秋田県 Dissimilar metal joints and their manufacturing methods

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FR2179317A5 (en) * 1972-04-06 1973-11-16 Chausson Usines Sa
JPS53132449A (en) * 1977-04-25 1978-11-18 Showa Aluminium Co Ltd Preparation of aluminium finnloaded iron pipe
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JPS5849898A (en) * 1981-09-18 1983-03-24 Mitsubishi Heavy Ind Ltd Manufacture of heat exchanger
JPS5995397A (en) * 1982-11-20 1984-06-01 Nippon Radiator Co Ltd Core of heat exchanger made of aluminum
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JPS60121264A (en) * 1983-12-06 1985-06-28 Nippon Mining Co Ltd Manufacture of radiator having fin with superior corrosion resistance
JPS60194291A (en) * 1984-03-16 1985-10-02 Hitachi Plant Eng & Constr Co Ltd Heat exchanger
JPS60245787A (en) * 1984-05-18 1985-12-05 Matsushita Electric Ind Co Ltd Heat exchanger
JPS6334495A (en) * 1986-07-29 1988-02-15 Nippon Denso Co Ltd Aluminum heat exchanger
JPS6363567A (en) * 1986-09-04 1988-03-19 Showa Alum Corp Production of heat exchanger having excellent corrosion resistance
JPH03255895A (en) * 1990-03-02 1991-11-14 Hitachi Cable Ltd Manufacture of heat exchanger for vehicle
JPH04190096A (en) * 1990-11-24 1992-07-08 Sky Alum Co Ltd Heat exchanger
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Also Published As

Publication number Publication date
SA97180556B1 (en) 2006-08-06
EG22317A (en) 2002-12-31
JP2001502757A (en) 2001-02-27
BR9712540A (en) 1999-10-19
DE69733317D1 (en) 2005-06-23
KR100334213B1 (en) 2002-05-02
ZA978931B (en) 1998-04-17
DE69733317T2 (en) 2006-01-19
KR20000052682A (en) 2000-08-25
CN101063206A (en) 2007-10-31
ID18594A (en) 1998-04-23
EP0950127B1 (en) 2005-05-18
ES2238731T3 (en) 2005-09-01
WO1998017841A1 (en) 1998-04-30
CN1234079A (en) 1999-11-03

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