Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/38—Chromatising
• • 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
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/12—All metal or with adjacent metals
  • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
  • Y10T428/12535—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.] with additional, spatially distinct nonmetal component
  • Y10T428/12583—Component contains compound of adjacent metal
  • Y10T428/1259—Oxide
• • 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
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/12—All metal or with adjacent metals
  • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
  • Y10T428/12771—Transition metal-base component
  • Y10T428/12806—Refractory [Group IVB, VB, or VIB] metal-base component
  • Y10T428/12826—Group VIB metal-base component
  • Y10T428/12847—Cr-base component
  • Y10T428/12854—Next to Co-, Fe-, or Ni-base component
• • 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
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/12—All metal or with adjacent metals
  • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
  • Y10T428/12771—Transition metal-base component
  • Y10T428/12861—Group VIII or IB metal-base component
  • Y10T428/12951—Fe-base component
  • Y10T428/12958—Next to Fe-base component
  • Y10T428/12965—Both containing 0.01-1.7% carbon [i.e., steel]

Definitions

• a process for surface treating chromium plated steel sheet obtained by applying chromium plating directly on a single sheet or strip of carbon steel which comprises: electrolytically contacting said chromium plated steel as the cathode with an aqueous solution of chromic anhydride as the main ingredient and a hydroxide or carbonate of an alkali metal, calcium, magnesium or strontium to form an almost colorless and transparent chromate film on the chromium plating.
• the film enhances corrosion resistance and does not interfere with any subsequent painting of the plated steel.
• This invention relates to a chromium plated steel sheet which is produced by forming directly on the surface of the steel sheet a plated layer of chromium of a thickness of about 0.00l0.1 and then coating the surface of the chromium layer with an almost colorless and transparent anticorrosive chromate film.
• This invention also relates to a chromate coating process for a chromium plated steel plate in order to form an almost colorless and transparent chromate film.
• the purpose of this invention is to impart to the chromium plated steel sheet improved anticorrosi-ve properties, to retain the fine metallic luster peculiar to chromium, and not inhibiting color effects when painted.
• Chromium plated steel sheet wherein the surface is coated with a thin layer of chromium is described in US. Patent No. 3,113,845 by the present inventors. Such a coating might be deteriorated by the presence of socalled pinholes. Therefore, a chromate coating on the plated layer is desirable. Investigations by the inventors on chromate coating processes, including dipping and electrolysis processes using various treating solutions, revealed that the anticorrosive property was remarkably improved by electrolysis, but much less by the dipping process. Nevertheless the electrolysis process using the conventional chromate coating liquid which contains chromic anhydride as a major constituent produces a colored opaque film on the plated layer of chromium.
• the present invention relates to a method for obtaining such colorless and transparent chromate film. It particularly relates to a method for surface treating a chromium plated steel sheet which is characterized by cathodically treating in an aqueous solution a chromium plated steel plate which has been obtained by applying a thin chromium coating directly on a single sheet or strip of ordinary carbon steel.
• the aqueous solution contains chromic anhydride as main component and one or more compounds selected from hydroxides or carbonates of alkali metals, calcium, magnesium or strontium in an amount greater than 20% by weight of the chromic acid.
• Alkali metal hydroxides employed in this invention include NaOH, KOH and LiOH.
• alkaline earth metal hydroxides includes Ca(OH)
• carbonates which provide these hydroxides when added in the aqueous CrO solution such as Na CO K2C03, Ligcog, Ca CO and SrCO
• the present invention relates to electrolytically treating a chromium plated steel sheet as cathode in an aqueous solution containing chromic anhydride as the main component with the addition of one or more of the above compounds in an amount more than 20% by weight of the chromic acid.
• the present inventors found that there is a large difference in corrosion resistance between a chromium plated steel sheet which has been cathodically treated in an aqueous solution of Na Cr O or Kgcl'zoq and a chromium plated steel sheet which has been cathodically treated in an aqueous chromic anhydride solution with the addition of NaOH or KOH.
• the latter has superior corrosion resistance.
• the present inventors have also confirmed that this quality shows a similar relation in case of addition of hydroxides etc. of other alkali metals and alkali earth metals.
• the aqueous solution containing chromic anhydride as main component may contain only chromic anhydride.
• trivalent chromium is formed by the reduction of hexavalent chromium ion as the cathodic treatment process. Usually, this trivalent chromium ion is present within a range of 0.2 to g./l.
• the cathodic treatment can be accelerate-d by adding to the aqueous solution of chromic anhydride the following compounds as subsidiary additives which act as catalyst for accelerating the cathodic treatment.
• Soluble compounds containing halogen NaCl, H010 Na SiF (NHQ TiF CrCl etc.).
• Soluble salts of metals sodium stannate, sodium aluminate etc.
• the electrolytical chromate coating process is carried out under the following condition.
• the smallest possible concentration of chromic anhydride is about 5 g./l., because the anticorrosive property is decreased at too small a concentration.
• the anticorrosive property can not be substantially improved, therefore the upper limit of the concentration of chromic anhydride is decided from the point of economy.
• the chromate treatment of the present invention is not substantially influenced by temperature. But at higher temperatures where the aqueous solution is gradually concentrated by evaporation difficulties are often encountered in maintaining the constant temperature and composition of the liquid in which the electrolysis takes place. Consequently the range from room temperature up to approximately C. is considered to be adequate.
• composition, structure and the process of formation of the almost colorless and transparent chromate coating film of this invention are not known. Nonetheless the electrolysis of the chromium plated steel sheet as cathode using the chromate coating liquid of this invention can give a colorless and transparent chromate coating film of excellent anticorrosive property, in contrast with the colored chromate films which are formed when conventional chromate coating solutions are used as electrolyte. Thus the almost colorless and transparent product of this invention provides high anticorrosive properties and remarkably enhanced commercial value.
• Advantages of the present invention are that the fine metallic luster, peculiar to chromium, of the base is not spoiled and that, when the plate is painted, the bright color of the paint is not deleteriously affected.
• the single operation of painting improves the working efficiency and the thin layer of paint costs less.
• the chromate coating of a steel plate covered with a thin layer of plated chromium by the electrolysis process as cathode was comparatively examined relative to the coating by the dipping process.
• the chromate coating of the latter process allowed rust to appear usually in several hours, while with the coating of the former process it took well over ten hours. More particularly rust developed in spots where the pinholes existed in the latter process, while in the former where the chromate coating film was worn out. This fact suggested that the former process produced much stronger and more compact chromate coating films. This is the reason why the thickness of the plated layer of chromium can be reduced, in case of coating by electrolysis, down to 0.00m as the lower limit. The upper limit of thickness may be about 0.1/L for the ease of working.
• the other process No. 1 is not effective for preventing coloring of the chromate film when NaOH is in an amount of 10% by weight of tion, but almost colorless and transparent chromate film CrO in case of 20 g./l. to 60 g./l. of CrO concentrais obtained when NaOH is in an amount of 22% by weight of CrO as shown in Example No. 10 of the present invention.
• Example No. 19 the chromate film is almost colorless and transparent in case the CrO concentration is less than 20 g./l. even when the amount of NaOH is 12% by weight of CrO But in this case, as shown in Example No. of the electrolytical colored chromate treatment, it is not effective for preventing coloring of the chromate film when the amount of NaOH is 5% by weight of CTO3.
• the chromate film is almost colorless and transparent, as shown in Example No. 12 of the present invention, even when the amount of NaOH is 12% by weight of CrO in case the CrO concentration is more than 60 g./l. In this case also, when the amount of NaOH is less than 5% by weight of CrO coloration takes place, as shown in Example No. 6 of the electrolytical colored chromate treatment.
• Example No. 2 of the other process a chromium plated steel sheet which has been cathodically treated in an aqueous solution of Na Cr O has inferior corrosion resistance, whereas in case of Ex ample No. 12 of the present invention where NaOH and CrO are in a chemical equivalent relation, the corrosion resistance is good showing more than 20 hours by the salt spray testing.
• the process of this invention forms a colorless and transparent chromate coating film without any loss in the anticorrosive property on a steel plate covered with a thin layer of plated chromium.
• the advantages of the colorless and transparent coating film are that the appearance can be remarkably improved by the metallic luster peculiar to chromium, and that, when a white coating is applied with an epoxy paint, a single application can produce a satisfactory color effect, while in contrast a colored chromate coating film requires more than two applications for good color effect.
• the advantages of course, considerably enhance the commercial value of the product.
• the working efficiency can be improved owing to the single application and the consequent thin layer of paint is economical.
• a process for surface treating chromium plated steel sheet which has been obtained by applying chromium plating directly on a single sheet or strip of carbon steel which comprises: electrolytically contacting said chromium plated steel as the cathode with an aqueous solution of chromic anhydride in a concentration of 5 grams per liter to 300 grams per liter of said solution, said solution further containing hydroxides, or carbonates which convert to hydroxides in said solution, of an alkali metal, calcium, magnesium or strontium, and wherein said solution contains (a) greater than 20% of said hydroxide or carbonate, based on the quantity of chromic anhydride,
• concentration of chromic anhydride when the concentration of chromic anhydride is in the range of 20 to grams per liter of solution, or (b) at least 10% of said hydroxide or carbonate, based on the quantity of chromic anhydride, when the concentration of chromic anhydride is below 20 grams per liter or above 60 grams per liter of said solution.
• aqueous solution further contains one or more ions selected from the group consisting of Cl, C10 1 SiF TiFy, N0 1 C H SO H, C H (SO H) Sn(OH) and A1 0.
• a process of claim 1 wherein the concentration of chromic anhydride is from 20 to 60 grams per liter of the aqueous solution and the amount of said hydroxide or carbonate is over 20% by weight of the chromic anhydride.
• concentration of chromic anhydride is (a) below 20 grams per liter or (b) above 60 grams per liter of said aqueous solution, and said solution contains at least 10% of said hydroxide or carbonate, based on the quantity of chromic anhydride.
• a process of claim 1 wherein the electrolytic contact of the chromium plated steel with said solution is effected at a current density of 1 to 45 A per dm. for 0.1 to 15 seconds and wherein the temperature of said solution is from room temperature to C.
• a process for surface treating chromium plated steel sheet which has been obtained by applying chromium plating directly on a single sheet or strip of carbon steel which comprises: electrolytically contacting said chromium plated steel as the cathode with an aqueous solution of chromic anhydride containing (a) chromic anhydride in a concentration of from 20 to 60 grams per liter and (b) a hydroxide or carbonate of an alkali metal or calcium, magnesium or strontium in a concentration of from above 20% to based on the weight of said chromic anhydride and wherein said electrolytic contact is effected at a current density of 1 to 20 A per dm. for 0.1 to 7 seconds at a solution temperature of 40 to 65 C.
• said aqueous solution further contains from 0.1 to 5 grams per liter of SiF and the alkali metal is sodium.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemical Treatment Of Metals (AREA)
• Electroplating And Plating Baths Therefor (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=26352594

Family Applications (1)

Country Status (5)

Cited By (5)

Citations (2)

• 1967
  • 1967-03-23 US US625306A patent/US3479162A/en not_active Expired - Lifetime
  • 1967-03-24 FR FR100284A patent/FR1515611A/fr not_active Expired
  • 1967-03-28 BE BE696127D patent/BE696127A/xx unknown
  • 1967-03-28 GB GB04085/67A patent/GB1188591A/en not_active Expired
  • 1967-03-28 NL NL6704415A patent/NL6704415A/xx unknown

Patent Citations (2)

Also Published As

Similar Documents