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
  • 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
  • C23C22/05—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 using aqueous solutions
  • C23C22/06—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 using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/24—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 using aqueous solutions using aqueous acidic solutions with pH less than 6 containing hexavalent chromium compounds
  • C23C22/33—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 using aqueous solutions using aqueous acidic solutions with pH less than 6 containing hexavalent chromium compounds containing also phosphates

Definitions

• This invention relates the production of paint-holding and corrosion-retarding coatings on ferrous surfaces, and relates more especially to producing such coatings by a simpler and more flexible method than is used at the present time in the rustprooflng art.
• the usual method of rustprooflng articles, preparatory to painting, involves reacting the sur-.
• One function of the chromic acid rinse is to dissolve out a part of the zinc phosphate, leaving a coating that is comparatively richer in iron phosphate because this is the more insoluble of the two.
• the final chromic acid rinse therefore, results in a film on the ferrous articlewhich contains iron phosphate, zinc phosphate, hexavalent chromium, and some trivalent chromium resulting from reduction of some chromic acid caused by its dissolving action.
• phosphate solutions Before a ferrous article can be processed in phosphate solutions it must be cleaned. This is usually done commercially by washing the surface with a hot alkaline solution followed by a water rinse. The strength of the cleaner as well as the time of washing must be carefully regulated, otherwise the phosphate coatingwill be the coating as the articles pass along on a conveyor.
• the object of the present invention is to provide a novel method of treating ferrous surfaues by a simplermeans than used with the common phosphate method.
• the phosphoric acid and chromic acid should be present under conditions where a definite etching of the metal surface will occur. It is essential that the solution applied be retained permanently on the surface and be not rinsed off or otherwise removed. Whether or not the solution will etch the metal surface depends both on the concentration of the phosphoric acid and the hexavalent chromium, and on the ratio existing between the two.
• the objects of the invention could not formed of objectionably large crystals which are V be attained, but if this ratio is reduced to .25 to 1 a definite reaction with the metal occurs resulting in a protective film of iron phosphate, trivalent chromium, and possibly some hexavalent chromium which has not been reduced. Any ratio of .25 to 1 or less will therefore result in etching and the formation of the desired products of the reaction.
• the metal to be treated is first cleaned by any suitable means. Such methods as solvent wiping, or vapor degreasing are usually employed for small articles or where there is a limited amount of production. Alkali cleaning is ordinarily adopted for production lines where auto bodies or sheet metal parts, or similar large objects are to be treated. In this case, the cleaning operation is followed by a water rinse to remove the alkali.
• a wettin agent there is a wide selection of these materials suitable for the purpose.
• Sodium lauryl sulfate known commercially as Gardinol or Duponol (trade names) is very effective.
• sodium lauryl benzene sulphonate and certain of the free sulphonic acids one of which is known commercially as Novonacco NN (trade name) are effective.
• a cold rolled steel article is this also must be removed. After the cleaned of oil and grease by wiping with naphtha and then drying the surface with clean cloths. A formula containing 10.0% phosphoric acid, 1.5% chromic acid, and .5% Duponol WA paste wetting agent is then applied to the surface by means of a brush. When the surface has been uniformly wetted the article is placed in an oven and dried for 3 minutes at 300 F. It is then removed and allowed to cool and is ready for the application of any desired paint finish without further treatment of the article.
• the metal, the'solution, or both may be heated prior to the rustprooflng operation in order to facilitate the chemical action and hasten the drYi 8..
• any of the phosphorous acids may be substituted for the ortho-phosphoric acid.
• those are phosphorous acid, meta and pyro phosphoric acid, and hypo-phosphorous acid.
• the anhydrides, such as phosphorous pentoxide, can be substituted for the ortho-phosphoric acid.
• the materials may be in concentrated form and diluted to the proper strength before use.
• a wetting. agent or alcohol it is best to add these after dilution since they will react with the chromic acid when in concentrated form.
• suiiicient amounts up to 5% or over may be required.
• the solution may be applied with a brush "or by means of a spraygumor the article canbemomentarily dipped in a quantity of the solution.
• the solution is allowed to dry upon the treated surface.
• the resulting film will contain iron phosphate, trivalent chromium an possibly some hexavalent chromium.
• a ferrous metal object having on a surface thereof an integral coating having a'composition resulting from drying onto said surface an aqueous solution containing phosphoric acid and chromic acid which will visibly etch the ferrous 2.
• a ferrousmetal object having on. 9. surface thereof an integral coating having a composition resulting from drying onto the said surface an aqueous solution containing chromic acid and phosphoric acid, the ratio between them being not more than .15 part of chromic for each part of phosphoric.

Landscapes

• 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)

Priority Applications (4)

Applications Claiming Priority (1)

Publications (1)

Family

ID=22910526

Family Applications (1)

Country Status (4)

Cited By (11)

Families Citing this family (1)

• 0
  • NL NL60167D patent/NL60167C/xx active
• 1938
  • 1938-11-19 US US241393A patent/US2303242A/en not_active Expired - Lifetime
• 1939
  • 1939-11-19 DE DEM146502D patent/DE718317C/de not_active Expired
  • 1939-11-20 GB GB30411/39A patent/GB534883A/en not_active Expired

Also Published As

Similar Documents