US3681207A - Metal coating process - Google Patents

Metal coating process Download PDF

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Publication number
US3681207A
US3681207A US101674A US3681207DA US3681207A US 3681207 A US3681207 A US 3681207A US 101674 A US101674 A US 101674A US 3681207D A US3681207D A US 3681207DA US 3681207 A US3681207 A US 3681207A
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Prior art keywords
solution
coating
potential
fluoride
weight
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US101674A
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William S Russell
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Henkel Corp
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Hooker Chemical Corp
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Assigned to HOOKER CHEMICALS & PLASTICS CORP, A CORP OF NY reassignment HOOKER CHEMICALS & PLASTICS CORP, A CORP OF NY ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: OXY METAL INDUSTRIES CORPORATION
Assigned to OXY METAL INDUSTRIES CORPORATION reassignment OXY METAL INDUSTRIES CORPORATION CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). 4-09-74 Assignors: OXY METAL FINISHING CORPORATION
Assigned to OCCIDENTAL CHEMICAL CORPORATION reassignment OCCIDENTAL CHEMICAL CORPORATION CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). EFFECTIVE MARCH 30, 1982. Assignors: HOOKER CHEMICAS & PLASTICS CORP.
Assigned to PARKER CHEMICAL COMPANY, A DE CORP. reassignment PARKER CHEMICAL COMPANY, A DE CORP. ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: OCCIDENTAL CHEMICAL CORPORATION
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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
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/73—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals characterised by the process
    • C23C22/77—Controlling or regulating of the coating process

Definitions

  • Electrodes are then used to contactga second fluoride accelerated aqueous chromating solution, the composition of which is known, as well as the weight of chromium containing conversion coating that will be formed by it and the total potential between the two elec-- trodes in the second solution is measured. Thedilference between these two potential measurements is determined and this difference is maintained at a value which will consistently produce the desired weight of coating by the first chromating solution by the selected addition of solution components to this chromating solution.
  • This invention relates to a method for operating fluoride-accelerated aqueous conversion coating solutions and more particularly it relates to an improved method for controlling the weight of chromium-containing conversion coating formed on a metal surface which is treated by a fluoride accelerated aqueous chromating bath.
  • a further object of the present invention is to provide an improved method for controlling the weight of C01]: version coating produced on metal surface by a fluorideaccelerated aqueous conversion coating solution.
  • Another object of the present invention is to provide an improved process as described above, wherein repeated standardizations of the control equipment are not necessary.
  • the present invention includes a method for controlling the weight ofconversion coating formed on a metal surface by a fluorideaccelerated aqueous conversion coating solution which comprises contacting a reference electrode and a fluoridesensitive electrode of the potentiometric type with a first fluoride accelerated aqueous conversion coating solution, measuring the total potential between said two electrodes in said solution, contacting said two electrodes with a second fluoride-accelerated aqueous conversion coating solu tion, the composition of which and the weight of conversion coating formed by which is known, measuring'the total potential between said two electrodes in said second solution, determining the difference between said two potential measurements and maintaining this difference at a value which will consistently produce the desired weight of conversion coating by said first solution by the selected addition'of solution components to said first conversion coating solution.
  • fluoride-accelerator conversion coating solutions with which the method of the present invention may be used include fluoride accelerated phosphate conversion coating solutions, such as those containing zinc, iron, manganese, alkali metal, and/or alkaline earth metal phosphates, phosphoric acid, and the like, fluorideaccelerated chromate conversion coating solutions, such as those containing chromic acid and/or other sources of hexavalent chromium, as well as those containing both phosphates and hexavalent chromium.
  • fluoride accelerated phosphate conversion coating solutions such as those containing zinc, iron, manganese, alkali metal, and/or alkaline earth metal phosphates, phosphoric acid, and the like
  • fluorideaccelerated chromate conversion coating solutions such as those containing chromic acid and/or other sources of hexavalent chromium, as well as those containing both phosphates and hexavalent chromium.
  • such conversion coating solutions may also contain other
  • Such treating solutions may be used for forming conversion coatings on a variety of metal surfaces, such as zinc, aluminum and ferrous metal surfaces, as well as surfaces of the various zinc, aluminum and ferrous metal alloys.
  • the present method has been found to be particularly suitable for controlling the weight of coating produced on aluminum and aluminum alloy surfaces by a fluoride accelerated conversion coating solution containing both phosphate and hexavalent chromium, typically as a mixture of phosphoric acid and chromic acid, as is described in US. Pat. 2,928,763, issued Mar. 15, 1960. Accordingly, hereinafter, particular reference will be made to such aqueous conversion coating solutions although it is to be understood that these are merely exemplary of the solutions which may be utilized.
  • the metal surface to be treated is contacted with the aqueous conversion coating solutions for a period sufficient to form the desired coating on the metal surface.
  • Typical of a preferred solution for coating aluminum is an aqueous solution containing from about to 150 grams per liter P0 ions, from about 2.5 to 62 grams per liter, CrO from about 1 to 55 grams per liter of aluminum ions and from about 2.5 to 123 grams per liter fluoride ions.
  • the contact between the metal surface to be treated and the aqueous conversion coating solution may be effected using a variety of application techniques, such as spraying, flooding, immersion, brushing, roll coating, and the like. In many instances, the preferred application techniques are spray or immersion. Using these techniques, the conversion coating solution may be applied to metal in the form of sheet or strip, as well as to formed metal articles, such as, for example in the case of aluminum, formed aluminum cans.
  • these coating solutions are contacted with a reference electrode and a fluoride sensitive electrode of the potentiometric type and the total potential between these electrodes in this solution is measured.
  • This contact of the electrodes and the coating solution may be made in any convenient manner, such as in the actual coating bath or holding tank of the coating solution as it is being used, as well as in a sample portion or stream of the coating solution removed from the main body of the coating solution for purposes of making the measurements.
  • the specific manner in which these measurements are made will depend upon the particular type of operation involved, i.e., whether it is a spray, immersion, roller coating or the like application, as well as on the particular type of equipment which is used.
  • the fluoride sensitive electrode of the potentiometric type which is used has, as its ion-sensitive element, a membrane of a substantially imporous, solid, ionic fluoride which is substantially insoluble in the solution. Electrodes of this type are described in US. Pat. 3,431,182 which issued Mar. 4, 1969. As described in this patent, the ion-sensitive crystalline fluoride of which the imporous membrane of the electrode is formed is selected from lead fluoride and the trifluoride of bismuth, scandium, yttrium, and the lanthanide series of rare earth metals. Of these, the preferred electrodes for use in the method of the present invention are those in which the membrane is formed of monocrystalline lanthanum trifluoride, although electrodes utilizing the other ion-sensitive crystalline fluorides disclosed in this patent are also suitable.
  • the reference electrode which is used in the present method may be any of the commonly used reference electrodes, as are well known to those in the art. Such electrodes include the standard calomel electrode, the standard Ag-AgCl electrode and the like. Both the reference electrode and the fluoride-sensitive electrode are electrically connected to the respective inputs of a suitable electrometric device for measuring the potential between the two electrodes when they are in contact with the coating solutions. Suitable electrometric devices which may be used include various volt meters, particularly the high-input impedience type, expanded millivolt scale pH meters, and the like.
  • a similar measurement of the potential between these two electrodes is also taken in a second or control aqueous conversion coating solution.
  • This second aqueous conversion coating solution is one in which the composition, i.e., the concentration of each of the components of the solution is known, and where it is also known what weight of conversion coating will be formed by this solution.
  • the maintenance of the desired difference in potential is effected by the selected addition of one or more of the various solution components to the aqueous conversion coating solution which is being used to treat the metal surface, i.e., the first conversion coating solution.
  • additions of fluoride and/or the other solution components, such as the chromate or phosphate, or additions of Al, e.g. by processing metal, may be made to the coating solution so as to maintain the value of the potential difference at the level which will consistently provide the desired coating weight on the metal surface treated.
  • a plot or graph is first developed of the coating weights produced versus potential difference. Thereafter, by reference to this plot, it can be determined what the potential difference should be to produce the coating weight that is desired.
  • a series of conversion coating solutions is prepared, containing varying, but known amounts of the solution components. For ex ample, a series of chromate-phosphate coating solutions, each containing different amounts of the fluoride accelerating ions, would be formulated. Each of these standard solutions would then be used to coat the metal surface and then the coating weight produced by each would be determined.
  • determinations may be carried out using conventional and well known techniques, such as by weighing the coated samples, stripping the coating from the sample with nitric acid or a molten salt bath, such as molten caustic soda, and then reweighing the metal sample.
  • a measurement of the potential of each of these standard coating solutions, using the reference electrode and fluoride-sensitive electrode as described above is also made. Thereafter, one of the standard coating solutions is taken as the zero point and the difference between the electrical potential of this solution and each of the other standard solutions is then determined and these differences are ploted against the coating-weight which is produced by each of the solutions. This plot will then be used, as indicated above, to determine the potential difference which should be maintained in order to consistently obtain the desired coating weight on the metal surface being treated.
  • the concentration of solution components used should be chosen such that the coating weights produced by these solutions will bracket the coating weight which it is desired to obtain on the actual processing line.
  • the standard conversion coating solutions prepared will be selected so that they will produce coating weights of from about 10 milligrams per square foot to about 30 milligrams per square foot.
  • the particular standard which is then used as'the'zero point for the preparation of the potential difference versus coating weight curve will then be used as the control or second conversion coating solution from which the difference in potential with the operating coating solution is determined.
  • the solution giving thecoating weight 30 milligrams.
  • control coating solution which produces 30 milligrams perfsquare foot of coating weight has "an actual potential reading of '25 millivolts on one day and "an actual potential reading of 30 millivolts on another day, due to shifts or changes in the measuring apparatus, and it is known that a potential difference of millivolts between the control solution and the operating solution is-necessary to produce the desired-coating weight of 20 milligrams per square foot, restandardization ofv the equipment on the second day so that the control reading is 25 millivolts is unnecessary, since the operating solution potential will also have increased by 5 millivolts on the second day.
  • control solution and the operating solution have a potential of 25 millivolts and millivolets respectively, i.e., a potential difference of 10 millivolts, or a potential of 30 millivolts and millivolts respectively, since the potential difference between the two is still the same, i.e. 1-0 millivolts.
  • the measurement, determinations, and controls effected in the present method may be carried out either manually or by means of various automatic sensing and control equipment, as is familiar to those in the art.
  • Such equipment may include various measuring and sensing devices, with suitable switches and relays whereby the potential of the operating coating bath may be continuously monitored so that upon a deviation from the desired difference in potential between this bath and the control bath, suitable pumps are activated to supply the desired solution components to the operating solution to reestablish the desired difference in potential.
  • This automatic control equipment may also include similar equipment for monitoring the concentrations of the other components in the coating solution, such as by electrical conductivity, pH, and the like. Typical of equipment of this type which may suitably be used for these purposes is that set forth in US. 'Pat. 3,515,094 issued June 2, 1970 and US. Pat. 3,312,189, issued Apr. 4, 1967. It is believed that those skilled in the art will readily be able to determine other suitable equipment of this or similar type which may also be used.
  • this bath When applied to an aluminum sheet, by spraying for 5 seconds, this bath produced a coating weight of 18 milligrams/ftr.
  • the operating bath used had the following composition:
  • a method for controlling the weight of conversion coatings produced upon a metal surface by a fluorideaccelerated aqueous conversion coating solution which comprises contacting a reference electrode and a fluoridesensitive electrode of the potentiometric type with a first fluoride-accelerated aqueous conversion coating solution, measuring the total potential between said two electrodes in said solution, contacting said two electrodes with a second fluoride-accelerated aqueous conversion. coating solution, the composition of which" and the weight of conversion coating formed by which 'is known, measuring the total potential between said two electrodes in said second solution, determiningthe difference between saidtwo potentials, and maintaining this difference at a value which will consistently produce the desired weight of conversion coating by said first solution by the selected addition, of solution components to said first conversion coating solution.

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  • Chemical & Material Sciences (AREA)
  • General Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Chemical Treatment Of Metals (AREA)
  • Application Of Or Painting With Fluid Materials (AREA)
US101674A 1970-12-28 1970-12-28 Metal coating process Expired - Lifetime US3681207A (en)

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US10167470A 1970-12-28 1970-12-28

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US (1) US3681207A (fr)
JP (1) JPS5137621B1 (fr)
BE (1) BE772995A (fr)
CA (1) CA960555A (fr)
DE (1) DE2157043A1 (fr)
ES (1) ES398409A1 (fr)
FR (1) FR2120644A5 (fr)
IT (1) IT955084B (fr)
NL (1) NL7117992A (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4849031A (en) * 1986-09-17 1989-07-18 Metallgesellschaft Aktiengesellschaft Process of producing phosphate coatings on metal surfaces
US5456810A (en) * 1993-02-12 1995-10-10 Nippon Paint Co., Ltd. Methods of measuring and controlling activity of zinc phosphate treatment solution

Families Citing this family (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS52136241U (fr) * 1976-04-12 1977-10-17
JPS52145632U (fr) * 1976-04-30 1977-11-04
JPS534414U (fr) * 1976-06-30 1978-01-17
JPS534420U (fr) * 1976-06-30 1978-01-17
JPS534415U (fr) * 1976-06-30 1978-01-17
JPS534413U (fr) * 1976-06-30 1978-01-17
JPS5327232U (fr) * 1976-08-14 1978-03-08
JPS5335422U (fr) * 1976-08-31 1978-03-28
JPS5335423U (fr) * 1976-08-31 1978-03-28
JPS5335421U (fr) * 1976-08-31 1978-03-28
DE3413905A1 (de) * 1984-04-13 1985-10-24 Metallgesellschaft Ag, 6000 Frankfurt Verfahren zur ueberwachung fluoridhaltiger baeder zur oberflaechenbehandlung von metallen

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4849031A (en) * 1986-09-17 1989-07-18 Metallgesellschaft Aktiengesellschaft Process of producing phosphate coatings on metal surfaces
US5456810A (en) * 1993-02-12 1995-10-10 Nippon Paint Co., Ltd. Methods of measuring and controlling activity of zinc phosphate treatment solution

Also Published As

Publication number Publication date
ES398409A1 (es) 1974-09-16
IT955084B (it) 1973-09-29
CA960555A (en) 1975-01-07
FR2120644A5 (fr) 1972-08-18
DE2157043A1 (de) 1972-07-06
BE772995A (fr) 1972-01-17
NL7117992A (fr) 1972-06-30
JPS5137621B1 (fr) 1976-10-16

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Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:OXY METAL INDUSTRIES CORPORATION;REEL/FRAME:003942/0016

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