US3730758A - Method of protecting ferrous strip in hot-dip processes - Google Patents
Method of protecting ferrous strip in hot-dip processes Download PDFInfo
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- US3730758A US3730758A US00085011A US3730758DA US3730758A US 3730758 A US3730758 A US 3730758A US 00085011 A US00085011 A US 00085011A US 3730758D A US3730758D A US 3730758DA US 3730758 A US3730758 A US 3730758A
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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
- 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
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
- C23C2/06—Zinc or cadmium or alloys based thereon
-
- 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
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
- C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
- C23C2/0222—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating in a reactive atmosphere, e.g. oxidising or reducing atmosphere
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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
- 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
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
- C23C2/026—Deposition of sublayers, e.g. adhesion layers or pre-applied alloying elements or corrosion protection
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S205/00—Electrolysis: processes, compositions used therein, and methods of preparing the compositions
- Y10S205/917—Treatment of workpiece between coating steps
Definitions
- This invention relates to the coating of metal stock, and more particularly to hot-dip coating of steel strip.
- Hot-dipping is the term applied to processes in which a metal base, such as cold-rolled steel strip, is coated by passing a clean strip through a bath of a molten metal.
- the coating metal is zinc
- the process is known as galvanizing.
- the effectiveness of a metal such as zinc as a protective coating for steel strip depends to a considerable extent upon the uniformity and adherence of the coating material.
- the ferrous base must be clean and maintained free of oxide formation immediately prior to the coating step.
- Cold-rolled strip is customarily annealed prior to coating in order to render it more ductile and suitable for various forming operations, and the like, subsequent to coating.
- One widely used method of cleaning and maintaining steel strip free from oxides prior to hot-dip coating is by continuously, in-line annealing the strip before it enters the coating bath. During annealing the strip is raised to, or above, 1200". F. Subjection to this high temperature is effective to burn off all contaminants, and, if accomplished in a reducing atmosphere will also effectively remove all oxides from the surface of the strip.
- the strip may then be passed from the protective reducing, or neutral, atmosphere directly into the hot-dip coating bath without intermediate contact with oxygen in the atmosphere.
- Batch annealed strip therefore, is customarily first cleaned with various acids in pickling or electrolytic cleaning baths and then treated with halide salts known as fluxes.
- halide salts known as fluxes.
- Various other reactive substances in addition to halide salts may also be used as fluxes, but halides are the most popular.
- Fluxing while providing a satisfactory manner of achieving desired cleanliness and strip protection, has the disadvantage of generating corrosive fumes.
- Fluxing due to increased production on continuous galvanizing lines, increases in fume formation have caused rising incidents of equipment corrosion, environmental hazards, and air pollution. Fluxing, furthermore, has had the disadvantage of failing to provide a uniformly tight, adherent coat. Typical defects caused by flux failure include black spots, smear, and uncoated areas.
- Step one comprises a flash coating of metal deposited on a clean steel strip by vacuum deposition, electroplating, or similar processes.
- This first coating step is followed by a conventional hot-dipping operation in which a second coat of the same, or different, metal is applied to the metal strip.
- flash coating I mean a very thin layer of metal coating.
- a first flash zinc coating is applied to a clean steel strip.
- the coated strip is then preferably activated either by the application to the strip of a dilute inorganic acid wash, or other suitable agents, after which the strip is passed through a molten zinc bath.
- the temperature of the molten zinc bath is such that the first flash zinc coat is melted and either (a) forms an alloy with the ferrous strip or (b) is completely removed and replaced by the second hot-dipped zinc coat.
- FIGS. 1 and 1a diagrammatically depict the preferred embodiment of my invention.
- FIG. 1b is an alternate embodiment.
- FIG. 10 shows a further variation of my method.
- the strip proceeds from there to heating unit 26 in which the temperature of the strip is raised from about 400 F. to about 600 F. Leaving heating unit 26 the strip passes through activating unit 28 where the surface is sprayed with 1% aqueous hydrochloric acid to prepare the strip surface for subsequent coating, and from there enters galvanizing bath 30.
- the pot temperature of galvanizing bath 30 is about 850 F. and the bath contains, in addition to molten zinc, about 0.13% aluminum.
- After galvanizing the strip passes through gas wipers 32 to establish the desired thickness of coating.
- An alternate of my preferred method would be to have a second activating unit (not shown) immediately after electroplating tank 22 and before heating unit 26.
- FIGS. 1 and 1b Another embodiment of my method is shown in FIGS. 1 and 1b.
- the strip cleaning process as shown in FIG. 1 is performed, as described above, but instead of the electroplating as shown in the FIG. 1a, a vapor deposition process is employed.
- the strip leaves rinse tank 20, shown in FIG. 1, enters drying unit 33 followed by vapor deposition unit 34, as shown in FIG. 1b where the strip is coated with zinc from a molecular dispersion of vaporized zinc. Leaving vapor deposition tank 34, the strip enters heating unit 36, and from there passes through tank 38 which contains a suitable non-fuming, activating fluid such a molten sodium or potassium halide or the like. The activating fluid floats upon the surface of molten zinc 39 in the area under tank 38.
- FIGS. 1, c and 1c Another alternative method by which my invention may be practiced is shown in FIGS. 1, c and 1c.
- the strip cleaning process as shown in FIG. 1, and previously explained, is performed, after which the strip enters electroplating unit 22 in which a flash metal coat is applied, as in FIG. 1a and previously described.
- the strip emerges from electroplating unit 22 and enters heating unit 44 as shown in FIG. 10.
- heating unit 44 the temperature of the strip is raised from about 400 F. to about 600 F.
- a reducing atmosphere may be formed by adjusting the gases in the heating unit to provide products of combustion such as carbon monoxide, carbon dioxide, hydrogen and water vapor.
- chlorine or hydrogen chloride may be used to activate the surface of the strip preparatory to further coating.
- the strip preferably remains in the protective reducing atmosphere until passing into, and through, galvanizing pot 46.
- the emerging strip then passes through wipers 48.
- the initial flash coating applied to the strip is designed only to provide short terms or temporary protection to the strip surface, it does not need to be as thick as would be necessary for more permanent protection.
- the flash coating can thus be applied relatively cheaply in a simple coating apparatus having only a feW electroplating cells or vapor deposition units.
- any process which applies a thin metallic protective coat is applicable.
- An example of this would be sherardizing, a process in which particulate metal particles of dust-like fineness are used as the coating medium. Passage through a fluidized bed of a particulate metallic coating material might also be taken advantage of to apply the first flash protective layer.
- any oxide reducing treatment which accomplishes this activation function is applicable in my method.
- electroplating which is performed in a halide bath such as zinc chloride would permit elimination of activation altogether as a separate step.
- the halide salts remaining on the strip after the strip leaves the electroplating unit would in this case perform the activation in situ as the strip passes through the preheater 26 as shown in FIG. In.
- My method is especially applicable to galvanizing because of the magnitude of the corrosion problem caused by fluxing fumes in continuous galvanizing lines. It would be equally applicable, however, to hot-dip aluminum or tin coating lines. Also, while it is preferable in many, or perhap most, cases to have the initial flash protective coating consist of the same metal as the desired final hotdip metal coating, to prevent the coating bath from contamination by the protective coating as it melts or merges with the final hot-dip coating, the two coatings may be dissimilar but compatibile metals. Examples of the latter are: tin as coat one, with tin or zinc as coat two; or zinc as coat one with terne as coat two.
- a first flash protective coating of aluminum may in some cases be particularly useful in gelvanizing since an aluminum addition is normally made to galvanizing baths in order to decrease interface alloy formation of the zinc with the surface of the strip.
- the protective coating furthermore, is so thin, about .001 inch to about .000001 inch, that only a very minor amount will enter the body of the molten coating bath.
- the method of my invention has many advantages over prior art hot-dip processes. First and most importantly, flux, with its inherent corrosion and environmental problems, may be eliminated as a step in hotdip processes, especially galvanizing. My method retains, however, the advantages afforded by a fluxing process. These advantages include applicability to batch annealed steel strip, economy of installation and upkeep, and the production of a superior product. Steel strip galvanized in accordance with my method shows a bright, well-defined spangle pattern.
- My process is dilferent from conventional two-coat metal coating processes in which one layer of metal is applied to a strip, followed by a second layer applied to the first layer in order to form a plurality of final coating layers on the strip surface.
- the first flash metal coating acts as a temporary protective coating only, and is melted or alloyed and replaced by the second hot-dipped coat.
- the present invention is likewise not similar to certain reclaiming operations wherein defective tin plated sheets, otherwise unsuitable for sale, have been dipped either in a hot tin bath to make tin plate or a lead-tin mixture to make terne plate. In these latter instances, the first coat is initially defective and serves no function, protective or otherwise; the only object of redipping being to recoat and thus reclaim an initially defective sheet.
- a method of hot-dip coating ferrous comprising:
- a method of hot-dip coating according to claim 1 wherein the oxide reducing treatment comprises subjecting the heated strip to a reducing gas.
- both the protective metal coating and the molten metal bath are substantially comprised of zinc.
Abstract
A METHOD FOR COATING BATCH ANNEALED FERROUS STRIP WITH MOLTEN METAL BY A HOT-DIP PROCESS IN WHICH FLUXING IS ELIMINATED. THE STRIP IS INITIALLY COATED WITH A VERY THIN METALLIC LAYER BY ELECTROPLATING OR VAPOR DEPOSITION AND THEN, AFTER SUITABLE ACTIVATION OF THE SURFACE, PASSED THROUGH A MOLTEN METAL COATING BATH.
Description
May 1, 1973 J. N. LAIDMAN METHOD OF PROTECTING FERROUS STRIP 1N HOT-DIP PROCESSES 2 Sheets-Sheet l Filed Oct. 29, 1970 INVENTOR L/O/I)? /V. lo/oman 0w ATTORNEY ECO May 1, 1973 J. N. LAIDMAN METHOD OF PROTECTING FERROUS STRIP [N HOT-DIP PROCESSES 2 Sheets-Shet 2 Filed Oct. 29, 1970 INVENTOR Jo/m 1V Zak/man United States Patent Ofiice 3,730,758 METHOD OF PROTECTING FERROUS STRIP IN HOT-DIP PROCESSES John N. Laidman, Coopersburg, Pa., assignor to Bethlehem Steel Corporation Filed Oct. 29, 1970, Ser. No. 85,011 Int. Cl. C23c 1 US. Cl. 117-51 5 Claims ABSTRACT OF THE DISCLOSURE A method for coating batch annealed ferrous strip with molten metal by a hot-dip process in which fluxing is eliminated. The strip is initially coated with a very thin metallic layer by electroplating or vapor deposition and then, after suitable activation of the surface, passed through a molten metal coating bath.
BACKGROUND OF THE INVENTION This invention relates to the coating of metal stock, and more particularly to hot-dip coating of steel strip.
Hot-dipping is the term applied to processes in which a metal base, such as cold-rolled steel strip, is coated by passing a clean strip through a bath of a molten metal. When the coating metal is zinc, the process is known as galvanizing. The effectiveness of a metal such as zinc as a protective coating for steel strip depends to a considerable extent upon the uniformity and adherence of the coating material. To achieve uniformity and adherence of a metal coat, the ferrous base must be clean and maintained free of oxide formation immediately prior to the coating step.
Cold-rolled strip is customarily annealed prior to coating in order to render it more ductile and suitable for various forming operations, and the like, subsequent to coating. One widely used method of cleaning and maintaining steel strip free from oxides prior to hot-dip coating is by continuously, in-line annealing the strip before it enters the coating bath. During annealing the strip is raised to, or above, 1200". F. Subjection to this high temperature is effective to burn off all contaminants, and, if accomplished in a reducing atmosphere will also effectively remove all oxides from the surface of the strip. The strip may then be passed from the protective reducing, or neutral, atmosphere directly into the hot-dip coating bath without intermediate contact with oxygen in the atmosphere.
Steel strip which has to withstand various deep drawing or other severe forming operations, such as that encountered in the forming of fenders for automobiles, must be exposed to the heat of the annealing operation for periods ranging from up to several hours or even days. It is impractical to perform this type of annealing in an in-line operation. Such strip is, therefore, batch annealed. While the strip could, after batch annealing, be directed Through a conventional in-line annealing and coating line to further clean and then coat the strip, such a procedure is impractical because the high temperature necessary to assure cleaning impairs the mechanical properties obtained by batch annealing. Batch annealed strip, therefore, is customarily first cleaned with various acids in pickling or electrolytic cleaning baths and then treated with halide salts known as fluxes. Various other reactive substances in addition to halide salts may also be used as fluxes, but halides are the most popular. The =flux layer serves to protect the strip surface from oxidation by the atmosphere as the strip passes from the cleaning tanks to Patented May 1., 1973 the molten bath, and particularly at the point where the strip is preheated several hundred degrees prior to entrance into the coating bath. Preheating of the strip is customary in continuous operations to attain a satisfactory adherence of the coating and prevent excessive cooling of the coating bath.
Attempts have been to eliminate the use of flux. These attempts have included the use of protective atmospheres and the like through which the strip passes between the cleaning tanks and the hot-dip bath. One of these prior attempts has included the use of hydrochloric acid fumes to try to protect the strip as it passes from the pickling or cleaning tank to the molten galvanizing bath. This expedient has, however, not proven practical.
Fluxing, while providing a satisfactory manner of achieving desired cleanliness and strip protection, has the disadvantage of generating corrosive fumes. In recent years, due to increased production on continuous galvanizing lines, increases in fume formation have caused rising incidents of equipment corrosion, environmental hazards, and air pollution. Fluxing, furthermore, has had the disadvantage of failing to provide a uniformly tight, adherent coat. Typical defects caused by flux failure include black spots, smear, and uncoated areas.
None of the prior art methods afford a method of protection for ferrous strip in hot-dip processes which has. the advantages of fluxing, e.g. adaptability to batch annealed strip, but none of the disadvantages, such as corrosion and air pollution.
SUMMARY OF THE INVENTION 1 have discovered that the aforementioned problems of the prior art may be obviated by the two step coating process of this invention. Step one comprises a flash coating of metal deposited on a clean steel strip by vacuum deposition, electroplating, or similar processes. This first coating step is followed by a conventional hot-dipping operation in which a second coat of the same, or different, metal is applied to the metal strip. By flash coating, I mean a very thin layer of metal coating. In the example of galvanizing, a first flash zinc coating is applied to a clean steel strip. The coated strip is then preferably activated either by the application to the strip of a dilute inorganic acid wash, or other suitable agents, after which the strip is passed through a molten zinc bath. The temperature of the molten zinc bath is such that the first flash zinc coat is melted and either (a) forms an alloy with the ferrous strip or (b) is completely removed and replaced by the second hot-dipped zinc coat.
BRIEF DESCRIPTION OF THE DRAWING FIGS. 1 and 1a diagrammatically depict the preferred embodiment of my invention.
FIG. 1b is an alternate embodiment.
FIG. 10 shows a further variation of my method.
DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, 36 inch wide, 26 gage batch annealed, cold-rolled rimmed steel strip enters a cleaning bath 10, which contains a suitable alkali cleaner of the type well known in the art, followed by scrubbing unit 12 and rinse tank 14. The strip continues through pickling bath 16, which contains an acid such as 10-14% aqueous hydrochloric acid. After pickling, the strip is scrubbed in scrubbing unit 18 and rinsed in tank 20. After leaving tank 20, and referring now to FIG. la, the strip enters electroplating tank 22 Where the strip is plated with zinc from an ionic dispersion of zinc in a zinc cyanide bath to a depth of .02 oz. per sq. ft. (.01 oz. of zinc/sq. ft. on each side). Emerging from electroplating tank 22 the strip proceeds from there to heating unit 26 in which the temperature of the strip is raised from about 400 F. to about 600 F. Leaving heating unit 26 the strip passes through activating unit 28 where the surface is sprayed with 1% aqueous hydrochloric acid to prepare the strip surface for subsequent coating, and from there enters galvanizing bath 30. The pot temperature of galvanizing bath 30 is about 850 F. and the bath contains, in addition to molten zinc, about 0.13% aluminum. After galvanizing the strip passes through gas wipers 32 to establish the desired thickness of coating. An alternate of my preferred method would be to have a second activating unit (not shown) immediately after electroplating tank 22 and before heating unit 26.
Another embodiment of my method is shown in FIGS. 1 and 1b. The strip cleaning process as shown in FIG. 1 is performed, as described above, but instead of the electroplating as shown in the FIG. 1a, a vapor deposition process is employed. The strip leaves rinse tank 20, shown in FIG. 1, enters drying unit 33 followed by vapor deposition unit 34, as shown in FIG. 1b where the strip is coated with zinc from a molecular dispersion of vaporized zinc. Leaving vapor deposition tank 34, the strip enters heating unit 36, and from there passes through tank 38 which contains a suitable non-fuming, activating fluid such a molten sodium or potassium halide or the like. The activating fluid floats upon the surface of molten zinc 39 in the area under tank 38. Thank 38 is positioned directly over galvanizing pot 40 and the strip passes directly into galvanizing pot 40 from tank 38. After emerging from galvanizing pot 40, the coated strip passes through wipers 42. The flash metal coating protects the strip in place of the conventional flux coating and the molten halide bath activates the strip surface and melts the first coat just prior to immersion of the strip in the metal coating bath. The molten halide activating fluid operates without the generation of any noxious or corrosive fumes.
Another alternative method by which my invention may be practiced is shown in FIGS. 1, c and 1c. The strip cleaning process as shown in FIG. 1, and previously explained, is performed, after which the strip enters electroplating unit 22 in which a flash metal coat is applied, as in FIG. 1a and previously described. The strip emerges from electroplating unit 22 and enters heating unit 44 as shown in FIG. 10. In heating unit 44 the temperature of the strip is raised from about 400 F. to about 600 F. While the strip is simultaneously subjected to a reducing atmosphere. Such an atmosphere may be formed by adjusting the gases in the heating unit to provide products of combustion such as carbon monoxide, carbon dioxide, hydrogen and water vapor. Alternatively chlorine or hydrogen chloride may be used to activate the surface of the strip preparatory to further coating. The strip preferably remains in the protective reducing atmosphere until passing into, and through, galvanizing pot 46. The emerging strip then passes through wipers 48.
Since the initial flash coating applied to the strip is designed only to provide short terms or temporary protection to the strip surface, it does not need to be as thick as would be necessary for more permanent protection. The flash coating can thus be applied relatively cheaply in a simple coating apparatus having only a feW electroplating cells or vapor deposition units.
Many variations are possible within the scope of my invention. Since the Primary purpose of the first thin coat is strip protection, any process which applies a thin metallic protective coat is applicable. An example of this would be sherardizing, a process in which particulate metal particles of dust-like fineness are used as the coating medium. Passage through a fluidized bed of a particulate metallic coating material might also be taken advantage of to apply the first flash protective layer.
Further, since the heating and activating process steps performed between the coating steps are all directed to preventing strip surface oxidation, overcoming the effects of such oxidation, and/or preparing the surface for the hot dip coating, any oxide reducing treatment which accomplishes this activation function is applicable in my method. For example, electroplating which is performed in a halide bath such as zinc chloride would permit elimination of activation altogether as a separate step. The halide salts remaining on the strip after the strip leaves the electroplating unit would in this case perform the activation in situ as the strip passes through the preheater 26 as shown in FIG. In.
My method is especially applicable to galvanizing because of the magnitude of the corrosion problem caused by fluxing fumes in continuous galvanizing lines. It would be equally applicable, however, to hot-dip aluminum or tin coating lines. Also, while it is preferable in many, or perhap most, cases to have the initial flash protective coating consist of the same metal as the desired final hotdip metal coating, to prevent the coating bath from contamination by the protective coating as it melts or merges with the final hot-dip coating, the two coatings may be dissimilar but compatibile metals. Examples of the latter are: tin as coat one, with tin or zinc as coat two; or zinc as coat one with terne as coat two.
A first flash protective coating of aluminum, for in stance, may in some cases be particularly useful in gelvanizing since an aluminum addition is normally made to galvanizing baths in order to decrease interface alloy formation of the zinc with the surface of the strip. The protective coating, furthermore, is so thin, about .001 inch to about .000001 inch, that only a very minor amount will enter the body of the molten coating bath.
The method of my invention has many advantages over prior art hot-dip processes. First and most importantly, flux, with its inherent corrosion and environmental problems, may be eliminated as a step in hotdip processes, especially galvanizing. My method retains, however, the advantages afforded by a fluxing process. These advantages include applicability to batch annealed steel strip, economy of installation and upkeep, and the production of a superior product. Steel strip galvanized in accordance with my method shows a bright, well-defined spangle pattern.
My process is dilferent from conventional two-coat metal coating processes in which one layer of metal is applied to a strip, followed by a second layer applied to the first layer in order to form a plurality of final coating layers on the strip surface. In the process of my invention, the first flash metal coating acts as a temporary protective coating only, and is melted or alloyed and replaced by the second hot-dipped coat. The present invention is likewise not similar to certain reclaiming operations wherein defective tin plated sheets, otherwise unsuitable for sale, have been dipped either in a hot tin bath to make tin plate or a lead-tin mixture to make terne plate. In these latter instances, the first coat is initially defective and serves no function, protective or otherwise; the only object of redipping being to recoat and thus reclaim an initially defective sheet.
I claim:
1. A method of hot-dip coating ferrous comprising:
(a) depositing a protective metal coating on a ferrous strip from a particulate dispersion of the coating metal,
(b) heating the strip to from about 400 F. to about (c) activating the protective surface by means of an oxide reducing treatment,
((1) passing the strip through a molten metal bath to melt the protective metal coating and apply to the strip a single metal layer comprising metal from the molten bath.
strip 2. A method of hot-dip coating according to claim 1 wherein the oxide reducing treatment comprises subjecting the heated strip to a reducing gas.
3. A method of hot-dip coating according to claim 2 in which the reducing gas is chlorine.
4. A method of hot-dip coating according to claim 2 in which the reducing gas is hydrogen chloride.
5. A method according to claim 1 wherein both the protective metal coating and the molten metal bath are substantially comprised of zinc. 10
References Cited UNITED STATES PATENTS 936,637 00/1909 Kirk 11771 M X 15 2,374,926 5/1945 Fink 1171 14 A X 6 1,816,617 7/1931 Schueler 204-38.5 1,133,628 3/1915 Field et al. 204-385 FOREIGN PATENTS 350,469 6/1931 Great Britain 20438.5
OTHER REFERENCES Handbook of Chemistry & Physics, 32nd ed., 1950, Chemical Rubber Publishing C0., pp. 598-599.
General Chemistry, by 'Sisler et al., 1949, pp. 413-414.
ALFRED L. LEAVITI, Primary Examiner J. R. BATTEN, 111., Assistant Examiner US. Cl. X.R.
l17-22, 71 M, 114 A, 114 B, 114 C, 114 R; 204-38 S
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US8501170A | 1970-10-29 | 1970-10-29 |
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Cited By (12)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3875896A (en) * | 1973-03-29 | 1975-04-08 | Siemens Ag | Wire tinning system |
US3907611A (en) * | 1972-11-10 | 1975-09-23 | Toyo Kogyo Co | Method for making ferrous metal having highly improved resistances to corrosion at elevated temperatures and to oxidization |
US3936548A (en) * | 1973-02-28 | 1976-02-03 | Perstorp Ab | Method for the production of material for printed circuits and material for printed circuits |
US3945423A (en) * | 1973-09-06 | 1976-03-23 | Mahle Gmbh | Method for the manufacture of a compound casting |
US3957086A (en) * | 1973-06-29 | 1976-05-18 | Bundy Corporation | Corrosion resistant tubing |
US4120997A (en) * | 1976-05-11 | 1978-10-17 | Inland Steel Company | Process for producing one-side galvanized sheet material |
US4202921A (en) * | 1976-02-24 | 1980-05-13 | Aktiebolaget Garphytte Bruk | Process for the preparation of rope and spring wire of carbon steel with an improved corrosion resistance |
US4390377A (en) * | 1981-01-12 | 1983-06-28 | Hogg James W | Novel continuous, high speed method of galvanizing and annealing a continuously travelling low carbon ferrous wire |
US4505958A (en) * | 1981-05-22 | 1985-03-19 | Hermann Huster Gmbh & Co. | Method for hot dip galvanizing metallic workpieces |
US4738758A (en) * | 1985-05-07 | 1988-04-19 | International Lead Zinc Research Organization, Inc. | Process for continuous deposition of a zinc-aluminum coating on a ferrous product, by immersion in a bath of molten metal |
US20080283157A1 (en) * | 2005-03-30 | 2008-11-20 | Makoto Katsube | Method of Production of Hot Dipped Hot Rolled Steel Strip |
US20090200174A1 (en) * | 2005-04-20 | 2009-08-13 | Nippon Steel Corporation | Method for hot-dip galvanizing a steel sheet |
-
1970
- 1970-10-29 US US00085011A patent/US3730758A/en not_active Expired - Lifetime
Cited By (13)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3907611A (en) * | 1972-11-10 | 1975-09-23 | Toyo Kogyo Co | Method for making ferrous metal having highly improved resistances to corrosion at elevated temperatures and to oxidization |
US3936548A (en) * | 1973-02-28 | 1976-02-03 | Perstorp Ab | Method for the production of material for printed circuits and material for printed circuits |
US3875896A (en) * | 1973-03-29 | 1975-04-08 | Siemens Ag | Wire tinning system |
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US9512511B2 (en) * | 2005-04-20 | 2016-12-06 | Nippon Steel & Sumitomo Metal Corporation | Method for hot-dip galvanizing a steel sheet |
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