Classifications

• • 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
  • C23D—ENAMELLING OF, OR APPLYING A VITREOUS LAYER TO, METALS
  • C23D3/00—Chemical treatment of the metal surfaces prior to coating
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/34—Pretreatment of metallic surfaces to be electroplated
  • C25D5/36—Pretreatment of metallic surfaces to be electroplated of iron or steel

Definitions

• the present invention relates to the pickling of steel plates prior to nickel plating and coating.
• a metal protective layer of this kind lies in the complicated aftertreatment which is necessary and which requires the enamelling plant to erect another installation for several stages i.e. degreasing, rinsing, removing the protective layer with corrosives such as acid, e.g. hydrochloric acid, rinsing and neutralization.
• a process for pretreating steel plate (US. Patent Application Serial No. 864,516, filed Oct. 7, 1969) by degreasing, pickling, metallizing, neutralizing and drying, in which the pickling is carried out electrolytically, the plates to be pickled being treated at a current density of from 2 to 20 amperes/dm. for up to about 3 minutes at temperatures of from 40 to C. in an acid sulfatecontaining and/or phosphate-containing solution.
• Another characteristic feature of such baths is the presence of magnesium ions. This process was particularly developed for the direct-on white enamelling of steel plates.
• pickling baths contain, more particularly, from 2 to 25% by weight of S0 ions, calculated in terms of sulfate; from 2 to 20% by weight of POQ- ions, calculated in terms of phosphate; and, preferably, from 1 to 5% by weight of magnesium, calcualted in terms of mag nesium hydrogen phosphate.
• the nickel sulfate-containing baths which have a nickel content of from 6 to 30 g. of nickel per liter of bath liquid are preferably used at pH values of from 3 to 6.
• chlorides are added to the baths in a quantity of from 3 to 20 g. of chlorine per liter of bath liquid, and magnesium ions in a quantity of from about 0.1 to 10 g. of magnesium per liter.
• this coating is carried out either by masking with a water soluble polyphosphate layer or by applying a water-soluble film-forming organic polymer.
• a water soluble polyphosphate layer use is made of watersoluble salts of polyphosphates having the general formula HO[HOPO ],,H, in which n is a larger number of at least 10 and preferably greater than 100.
• polyethylene oxide, polyvinyl alcohol, carboxy methyl cellulose, hydroxyethylene cellulose and mixtures of these polymers may be used as the film-forming organic polymers.
• the organic polymers may also be combined with; the ployphosphates.
• the present invention relates to an improved process for the pretreatment of steel plates for direct-on white enamelling which reliably provides satisfactory enamel finishes of high bond strength and which is suitable not only for open-coil decarbonized steel, but also for all the usual types of steel used in the enamelling industry.
• the invention relates to a process for the pretreatment of steel plates for direct-on white enamelling in which, after they have been electrolytically degreased and pickled, the plates are nickel-plated by electrodeposition and then provided with a Water-soluble protective layer of a poly phosphate and/or an organic film-forming polymer, in which process the electrolytic pickling is carried out at a current density of from about 20 to 40 amperes/dm. in an acid sulfateand/or phosphate-containing solution for periods of from about 0.2 to 3 minutes at temperatures of about 40 to 80 C.
• Electrolytic pickling is preferably followed by a galvanic nickel-plating operation in which nickel is deposited into the surface to be enamelled in a quantity of from about 0.3 to 0.7 g. of nickel per square meter of steel plate.
• the pickling treatment may be carried out by the dip technique, the plate to be pickled being connected as anode.
• the cathode material is not crucial to the success of the process and any plates of iron or other metallic materials may be used. There is never any need for the plates to be pickled for longer than 3 minutes. Pickling times of from about 0.2 to 3 minutes are adequate, depending upon the quanlity of the steel.
• the pickling time is governed by the current density, the composition of the bath and the temperature of the bath, and can thus be varied within certain limits.
• the bath temperature should be in the range from about 40 to 80 C., preferably from about 60 to 70 C.
• the pickling bath should contain sulfate and/or phosphate ions.
• the SO ion concentration, calculated in terms of sulfate, should be from about 2 to 25% by weight, while the PO ion concentration, calculated in terms of phosphate, should be from about 2 to 20% by weight.
• the sulfate ions can be provided as sulfuric acid, alkali sulfates and/ or alkali hydrogen sulfates. In addition to the alkali metals, preferably sodium and/or potassium, it is also possible to use a magnesium sulfate or magnesiurn hydrogen sulfate.
• the PO ions can be provided in the form of phosphoric acid, alkali phosphates, magnesium phosphates, alkali hydrogen phosphates, alkali dihydrogen phosphates, magnesium hydrogen phosphate and/or magnesium dihydrogen phosphate.
• a bath containing from about 1 to 5% by weight of magnesium dihydrogen phosphate has proved to be particularly suitable.
• Phosphate-containing baths are generally advantageous because they have a favorable effect upon subsequent metallization of the plates to be enamelled, especially nickel-plating.
• Another advantage of phosphate-containing baths is that the iron which enters into solution during pickling is cathodically deposited. In this way, the service life of the baths is considerably lengthened.
• the process according to the invention is suitable for all the usual types of steel used in the enamelling industry. In any event, firmly adhering direct-on enamel finishes are obtained by the pickling treatment according to the invention in combination with other necessary pretreatment stages.
• the prolonged service life of the baths alfords ancobalt ions, the conditions being adjusted so that approximately 0.3 to 0.7 g. of nickel and/or cobalt are deposited per square meter of steel surface.
• the plate to be pretreated is connected as cathode in the known manner, while pure nickel or cobalt alloys thereof are used as anodes.
• the bath is operated at average current densities of from about 0.3 to 0.8. amperes/dm. although, in special cases where particularly quick deposition is required, higher current densities may also be used but in such cases precautions must be taken to ensure that the workpieces do not catch fire. It is best to use either moving electrolytes or moving electrodes.
• the baths are preferably prepared with water-soluble nickel and/or cobalt salts, such as the sulfates and/or chlorides.
• concentration calculated in terms of the metal, should be from about 8 to 30 g./ liter of bath liquid. It is preferable not to add any complex forming reagents to the baths. However, it may be of advantage to add boric acid or another bulfer substance, although such addition should be such that the pH value of the baths does not exceed about 7.
• the baths can be operated at pH values of from about 7 to 1, pH values of from about 3.5 to 6 being preferred. Most of the metals should be present in the form of their sulfates.
• the baths advantageously contain chlorides, from about 3 to 20 g. of Cl/ liter of bath liquid being a preferred chloride content.
• the chloride ions may be introduced in the form of the metal chlorides or in the form of alkali chlorides, including ammonium chloride.
• the presence of magnesium ions in the baths is also recommended to ensure suitable deposition of the nickel and/or cobalt. Extremely small quantitles of from about 0.1 to 10 mg./liter are suificient. Larger quantities are not harmful because the magnesium is not deposited with the nickel and/or cobalt and only indirectly influences the way in which the nickel and/or cobalt is deposited.
• the magnesium is introduced in the form of its Water soluble salts, preferably the sulfate and/ or chloride.
• the metallizing baths remain stable almost indefinitely providing impurities are not entrained in the bath upon the introduction of the workpieces. There is no need for regeneration because the nickel or cobalt concentration is automatically adjusted to the required level because as much nickel dissolves into the bath from the electrodes as is deposited onto the metal surfaces to be treated.
• the pretreatment time is considerably reduced compared with conventional processes. In many cases,
• Electrolytic pickling (40 -a./dm. 70 C.; 77 g.
• H 'PO /1+106 g. H SO 1 Cold rinsing l
• Electrolytic nickel plating (0.6 -a./dm. 20 C.; 80 g. NiSO -7 H O/ 1; 10 g. NH Cl/ 1; 20 g. MgSO -7 H O/ 1; 5 g. H 'BO 1) 1 Cold rinsing 1' Drying.
• the improvement which comprises employing steel having a carbon content of about 0.043% and effecting the electrolytic pickling treatment at 'a current density of about 40 amperes/d-m. in an acid solution containing at least one of sulfate and phosphate ions for about 0.2 to 3 minutes at a temperature of about 40 to C.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electrochemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Electroplating Methods And Accessories (AREA)
• Chemical Treatment Of Metals (AREA)

Applications Claiming Priority (1)

Publications (1)

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ID=5814969

Family Applications (1)

Country Status (12)

Cited By (7)

Families Citing this family (3)

Family Cites Families (3)

• 0
  • BE BE786737D patent/BE786737A/xx unknown
• 1971
  • 1971-07-27 DE DE2137551A patent/DE2137551A1/de active Pending
• 1972
  • 1972-07-14 US US00271898A patent/US3840441A/en not_active Expired - Lifetime
  • 1972-07-20 GB GB3402772A patent/GB1396191A/en not_active Expired
  • 1972-07-25 LU LU65789D patent/LU65789A1/xx unknown
  • 1972-07-25 NL NL7210242A patent/NL7210242A/xx unknown
  • 1972-07-25 IT IT51737/72A patent/IT961683B/it active
  • 1972-07-25 AT AT639172A patent/AT321059B/de not_active IP Right Cessation
  • 1972-07-26 BR BR005015/72A patent/BR7205015D0/pt unknown
  • 1972-07-26 SE SE7209782A patent/SE382472B/xx unknown
  • 1972-07-27 FR FR7227149A patent/FR2147274B1/fr not_active Expired
  • 1972-07-27 ES ES405199A patent/ES405199A1/es not_active Expired

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