US3024183A - Sacrificial zinc anodes - Google Patents

Sacrificial zinc anodes Download PDF

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Publication number
US3024183A
US3024183A US859378A US85937859A US3024183A US 3024183 A US3024183 A US 3024183A US 859378 A US859378 A US 859378A US 85937859 A US85937859 A US 85937859A US 3024183 A US3024183 A US 3024183A
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United States
Prior art keywords
zinc
aluminum
core
billet
anodes
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Expired - Lifetime
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US859378A
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English (en)
Inventor
John R Macewan
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Teck Metals Ltd
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Teck Metals Ltd
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Priority to US859378A priority Critical patent/US3024183A/en
Priority to BE604986A priority patent/BE604986A/fr
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Publication of US3024183A publication Critical patent/US3024183A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • 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
    • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F13/00—Inhibiting corrosion of metals by anodic or cathodic protection
    • C23F13/02—Inhibiting corrosion of metals by anodic or cathodic protection cathodic; Selection of conditions, parameters or procedures for cathodic protection, e.g. of electrical conditions
    • C23F13/06—Constructional parts, or assemblies of cathodic-protection apparatus
    • C23F13/08—Electrodes specially adapted for inhibiting corrosion by cathodic protection; Manufacture thereof; Conducting electric current thereto
    • 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
    • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
    • C23F13/00—Inhibiting corrosion of metals by anodic or cathodic protection
    • C23F13/02—Inhibiting corrosion of metals by anodic or cathodic protection cathodic; Selection of conditions, parameters or procedures for cathodic protection, e.g. of electrical conditions
    • C23F13/06—Constructional parts, or assemblies of cathodic-protection apparatus
    • C23F13/08—Electrodes specially adapted for inhibiting corrosion by cathodic protection; Manufacture thereof; Conducting electric current thereto
    • C23F13/10—Electrodes characterised by the structure

Definitions

  • This invention relates to a method of producing sacrificial or consumable zinc anodes for use in inhibiting corrosion by galvanic action, and sacrificial zinc anodes produced thereby.
  • anodes are well known for the protection of metal structures and equipment such as heat exchangers, pipe lines, ship hulls, storage tanks and the like.
  • anodes are made in the form of cast blocks, or slabs, with steel inserts to provide electrical contact between the anode and the metal structure to be protected, and also to provide means for fastening the anode to the metal structure to be protected.
  • long, narrow anodes are required or preferred because of their particular characteristics such as high current output per unit of volume, ease of installation and more streamlined design.
  • Such long, narrow anodes are also made by casting methods in which molten zinc is poured into moulds around a metal core, or insert.
  • the core extends the length of the anode and provides the necessary electrical contact and also the means for attaching the anode to the structure.
  • Casting methods are not completely satisfactory for the production of long, narrow zinc anodes.
  • the cast anodes are not flexible and therefore they are not easily adapted to types of service in which curved or coiled anodes are desired.
  • Anodes are required to be made in a number of different sizes which means that the manufacturer must maintain a large supply of suitable moulds.
  • casting in moulds is not practical for lengths greater than about 5 or 6 feet.
  • the core member must extend the length of the anode as otherwise the anode would break as it became corroded in service, thereby severing the electrical connection between anode and protected structure, and the anode would cease to function.
  • I form zinc anodes by extruding a composite billet comprised of a cylindrical block of zinc with an aluminum core.
  • the required positive and permanent bond between zinc anode metal and core material can be obtained by applying a thin prime coating of molten zinc to an aluminum core, and thereafter, casting molten zinc around the zinc-coated aluminum core to form the composite zinc-aluminum billet.
  • This composite billet which is in the form of a thick zinc sheath around an aluminum core, can then be extruded to form elongated stock of desired cross-sectional shape for use, when cut into suitable lengths, as sacrificial or consumable zinc anodes with aluminum cores.
  • the aluminum core is treated to ensure proper bonding between zinc and aluminum before the zinc sheath is cast around it.
  • This treatment involves the steps of fluxing and dipping the core.
  • a clean, degreased aluminum core is coated with a suitable flux for aluminum surfaces and is then heated to melt the flux to form a continuous film of flux on the surface of the core. Excess flux can be removed by wiping.
  • Suitable fluxes for aluminum surfaces include those based on zinc chloride and containing fluorides, such as those used in normal aluminum fluxing operations.
  • the flux should not be allowed to absorb water. Melting of the flux can be eflected by heating the flux-coated core in a gas flame or in an oven at a temperature between about 1000 F. and 1050 F.
  • the hot, fluxed core is dipped in a bath of molten zinc maintained at a temperature above the melting point of zinc, preferably between 900 F. and 950 F.
  • This dipping step ensures the formation of a continuous, uniform coating of zinc on the aluminum core with a zinc-aluminum alloy at the interface between the aluminum and the zinc.
  • the freshly dipped, hot core is placed in a billet mould and molten zinc is poured around it to form a composite billet.
  • the zinc is cast into the mould at a relatively high temperature, preferably between 1000 F. and 1050 F.
  • the aluminum core should not be allowed to cool between the clipping and casting steps, and it should not be exposed to the air for more than a few minutes.
  • FIGURE 1 is an elevation in section
  • FIGURE 2 is a top plan View.
  • the vertical cylindrical mould 10 is formed of conventional material such as cast iron or graphite.
  • a recess 11 is formed in the base of the mould. This recess is preferably concentrically positioned, and is adapted to receive the lower end of the rod-shaped aluminum core 12.
  • a supporting frame 13 extends from the top of the mould and is adapted to engage the upper part of the aluminum core and thus hold the core firmly in a vertical position while the molten zinc is poured into the mould through access ports 14.
  • the composite billet is withdrawn from the mould after the zinc has cooled and solidified, and can be stored, if desired, before subsequent treatment.
  • Sacrificial zinc anodes in accordance with my invention are produced from such billets by extrusion.
  • the extrusion step is effected with conventional extruding appanatus which involves a chamber adapted to receive the billet, a piston or ram adapted toapply pressure against the base of the billet and a die of dmired shape at the forward end of the billet through which the metal is extruded.
  • the extruded metal is cut into desired lengths for use as anodes. Usually the first few and the last few inches of the composite extrusion are cut off and discarded as the core diameter may not be uniform at the extreme ends.
  • the core diameter is consistently uniform throughout the remainder of the stock, and that the reduction in diameter of the aluminum core in the composite billet to form the aluminum core in the extruded anode stock is substantially the same in proportion as the reduction in diameter of the billet to form the anode stock.
  • the invention is illustrated by the following example: A cylindrical aluminum core 14 inches long and 1 /2 inches in diameter was cleaned, degreased with trichlorethylene, and coated with a flux paste made up of 70% of a zinc chloride soldering flux and 30% normal propyl alcohol.
  • the flux was a commercial product sold as Alcoa Soldering Flux No. 66.
  • the core was dried to remove the alcohol and heated in a gas flame to melt the flux and form a continuous film of flux on the surface of the core.
  • the hot, flux-coated .core was then dipped in a bath of molten zinc maintained at a temperature of about 930 F. When the core was immersed in the molten zinc, fuming and bubbling occurred. The reaction subsided in about 30 seconds and the core was then withdrawn. This dipping step provided a continuous adherent film or coating of zinc on the aluminum core.
  • the hot, zinc-coated core was placed in a billet mould of the type illustrated in the accompanying drawing, and molten zinc at a temperature of about 1025" F. was poured into the mould. After the billet had cooled and solidified, it was removed from the mould and trimmed to remove protruding ends of the aluminum core.
  • the resulting composite billet was 12 inches long and 4 inches in diameter.
  • the billet was extruded through a conventional cylindrical die at 500 F. and 370 to 420 tons pressure to produce cylindrical anode stock 0.84 inch in diameter with an aluminum core 0.3 inch in diameter.
  • the extrusion was about 20 feet long and the core diameter was consistently uniform throughout the length of the extrusion, except for about 12 inches at each end. The first and last 12 inches of the extrusion were cut off and discarded. The remaining 18 feet of anode stock was cut into lengths of 6 feet for use as sacrificial or consumable zinc anodes.
  • the aluminum used was the commercial grade of about 99.9% purity and the zinc used was Special High Grade (99.99%) alloyed with about 0.4% aluminum.
  • other suitable compositions can also be used.
  • high purity zinc which contains less than 0,0015% iron is generally satisfactory and other zinc alloys are also known in the art.
  • other grades of aluminum can also be used.
  • the bond between the zinc and the core in the anodes of the present invention has been tested physically and examined under a microscope.
  • the microscopic examination revealed that the zinc and aluminum were alloyed at the junction or interface of the core and anode metal, the alloy blending into the Zinc on the outer side and into the aluminum on the inner side of the interface.
  • the physical tests showed that the bond between the core and anode metal was strong and adherent, and was impervious when subjected to dye penetrant tests, such as the Zyglo test.
  • the bond between the aluminum core and the zinc is essential for satisfactory operation of the anode, and it is also essential for satisfactory extrusion of the composite billet. Unless a bond is obtained over the whole interface between the aluminum rod and zinc metal sheath of the composite billet, the extrusion step will not produce a continuous core of uniform diameter.
  • a composite billet was prepared by drilling a hole in a solid zinc cylinder and casting aluminum into the resulting cavity. When this billet was extruded, it was found that the aluminum core was discontinuous, and that extrusion lubricant had been forced between the aluminum and zinc, thus preventing metal to metal contact. Also, unsatisfactory results were obtained with composite billets formed by casting molten zinc around dipped aluminum rods which had not been fluxed or around fiuxed rods which had not been dipped.
  • the sacrificial or consumable zinc anode produced by the present invention possesses several important advantages. It can be produced relatively inexpensively from readily available materials. It can be used with advantage to protect steel structures such as ships hulls, storage tanks, hot water tanks, underground installations, and the like, and also for protecting aluminum structures.
  • An aluminum core has important advantages over a steel core when zinc anodes are used for the protection of aluminum from corrosion as steel would be cathodic to aluminum and it would be essential to remove steel cores before all the zinc was consumed. Otherwise, the aluminum structure would corrode when the zinc had been consumed as the aluminum would act as a sacrificial anode for the steel core. When using zinc anodes with aluminum cores, this problem with aluminum structures does not arise.
  • an aluminum core is preferable to a steel core as a composite billet of zinc and aluminum can be easily extruded. Furthermore, extruded zinc anodes are ductile, and can be bent or coiled, if desired, for ease of installation or to meet particular service requirements.
  • the method is particularly advantageous for making long, narrow anodes, but can be used also with any extrudable cross section.
  • the anodes and the cores, or inserts can be made any desired shape by selection of suitable extrusion dies, and by the use of suitably shaped aluminum cores when preparing the composite billet.
  • the anode stock can be cut into any desired length, usually from a few inches to 12 feet or more, depending on the required service.-
  • the improved method of producing sacrificial zinc anodes which comprises the steps of coating an aluminum core with a film of Zinc to form a zinc-aluminum alloy at the interface, casting molten zinc around the zinccoated aluminum core to form a composite zincaluminum billet, cooling said billet below the melting temperature of zinc, and thereafter extruding said billet to form sacrificial zinc anode stock with an aluminum core.
  • the improved method of producing sacrificial zinc anodes which comprises the steps of coating an aluminum core with a flux for aluminum surfaces, coating said fluxcoated core with an adherent film of zinc to form a zincaluminum alloy at the interface thereof, casting molten zinc around the zinc-coated aluminum core to form a composite zinc-aluminum billet, cooling said billet below the melting temperature of zinc, and thereafter extruding said billet to form sacrificial zinc anode stock with an aluminum core.
  • the improved method of producing sacrifical zinc anodes which comprises the steps of coating an aluminum core with a flux for aluminum surfaces, dipping said fluxcoated core in a bath of molten zinc and withdrawing said core therefrom whereby said core is coated with an adherent film of zinc to form a zinc-aluminum alloy at the interface thereof, casting molten zinc around the zinccoated core while the core is still hot from the dipping step to form a composite zinc-aluminum billet with a zinc-aluminum alloy at the interface, and thereafter extruding said billet to form sacrificial zinc anode stock with an aluminum core.
  • a sacrificial zinc anode which comprises a zinc extrusion having an aluminum core extending throughout the length thereof, said extrusion having a zinc-aluminum alloy at the interface of the aluminum and the zinc.
  • a sacrificial zinc anode which comprises a zinc extrusion bonded to an aluminum core, the bond at the interface of the zinc and the aluminum being in the form of a zinc-aluminum alloy.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Prevention Of Electric Corrosion (AREA)
US859378A 1959-12-14 1959-12-14 Sacrificial zinc anodes Expired - Lifetime US3024183A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
US859378A US3024183A (en) 1959-12-14 1959-12-14 Sacrificial zinc anodes
BE604986A BE604986A (fr) 1959-12-14 1961-06-14 Anodes de zinc à consommer

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3226314A (en) * 1962-08-09 1965-12-28 Cons Mining & Smelting Co Sacrificial zinc anode
US5293923A (en) * 1992-07-13 1994-03-15 Alabi Muftau M Process for metallurgically bonding aluminum-base inserts within an aluminum casting
US20160131445A1 (en) * 2013-10-31 2016-05-12 Mitsubishi Electric Corporation Lifetime diagnosis component for anticorrosive coating, heat exchanger, refrigeration-and-air-conditioning apparatus

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2478479A (en) * 1947-02-03 1949-08-09 Dow Chemical Co Cored magnesium anode in galvanic protection
US2478478A (en) * 1947-02-03 1949-08-09 Dow Chemical Co Potential gradient anode for galvanic protection
US2735163A (en) * 1956-02-21 Composite magnesium-iron articles
US2841546A (en) * 1952-12-03 1958-07-01 Dow Chemical Co Extruded magnesium anodes with aluminum-coated steel core wires

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2735163A (en) * 1956-02-21 Composite magnesium-iron articles
US2478479A (en) * 1947-02-03 1949-08-09 Dow Chemical Co Cored magnesium anode in galvanic protection
US2478478A (en) * 1947-02-03 1949-08-09 Dow Chemical Co Potential gradient anode for galvanic protection
US2841546A (en) * 1952-12-03 1958-07-01 Dow Chemical Co Extruded magnesium anodes with aluminum-coated steel core wires

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3226314A (en) * 1962-08-09 1965-12-28 Cons Mining & Smelting Co Sacrificial zinc anode
US5293923A (en) * 1992-07-13 1994-03-15 Alabi Muftau M Process for metallurgically bonding aluminum-base inserts within an aluminum casting
US20160131445A1 (en) * 2013-10-31 2016-05-12 Mitsubishi Electric Corporation Lifetime diagnosis component for anticorrosive coating, heat exchanger, refrigeration-and-air-conditioning apparatus
US9964367B2 (en) * 2013-10-31 2018-05-08 Mitsubishi Electric Corporation Lifetime diagnosis component for anticorrosive coating, heat exchanger, refrigeration-and-air-conditioning apparatus

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Publication number Publication date
BE604986A (fr) 1961-10-02

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