Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
  • C25F3/00—Electrolytic etching or polishing
  • C25F3/16—Polishing

Definitions

• This invention relates to an electrolyte for the polishing of metal surfaces and more particularly to an electrolytic solution of high mineral acid concentration for use in the anodic treatment of metals to impart thereto a lustrous, mirror-like polish.
• the surfaces exhibit a tendency to "pile, with the result that the polished surfaces so produced are cold worked and strained.
• Such surfaces are characterized by the presence of a layer of amorphous or pseudoamorphous materials.
• the surface will be found to be marked by microscopic scratches.
• Mechanical polishing has the further objection that it involves a considerable amount of comparatively highly paid labor.
• mechanical polishing is one of the most expensive steps in the finishing operations, so that polished stainless steels have heretofore sold for a price which is very high in comparison with the material cost.
• the cost of mechanical polishing is also a major item in the manufacture of chromium plated articles, particularly articles of irregular shape that must first be polished, then nickel plated and finally bufled before the application of the chromium plate.
• an electrolytic solution consisting essentially of a mixture of sulfuric and phosphoric acids provided that the combined concentration of the acid is at least 50% by weight of I the solution.
• Such an electrolytic solution is particularly-applicable in the polishing of stainless steel, nickel, Monel metal, German silver and plain carbon steels, as well as various other metals. in the case of plain carbon steels,
• the method to which this invention pertains involves making the metal to be polished an anode in an electrolytic bath of suitable composition and passing a current of sufllclent density and for a. sufficient length of time to produce a high lustre or polish on the metal.
• the electrolytic solution that I have found to possess the most general applicability comprises a mixture of sulfuric and phosphoric acid in such proportions that the combined acid concentration is at least 50% by weight of the solution, the balance being mainly water.
• Sulfuric and phosphoric acids, particularly ortho phosphoric acid are eminently suitable for the purpose, mainly because of their stability and the ease with which they produce satisfactory polishes.
• the relative proportions of sulfuric to phosphoric acid may, in general, be varied from' 5% of sulfuric and 85% of phosphoric acid to 5% of phosphoric acid and 85%0f sulfuric acid, but the phosphoric acid content is preferably in excess of 50% of the total bath composition. Unless otherwise specified, all percentages referred to herein will be understood to represent percentages by weight, rather than by volume. Also, references to sulfuric and phosphoric acids should be understood to mean the respective.
• the process can be operated with anode current .densities varying from 50 to 1000 amperes per sq. ft. It will be understood that even lower current densities may be employed, but longe'r times of treatment will be required and the process may for that reason he uneconomical. Higher current densities than indicated by the foregoing range may also be used, but in that case the higher cost of electrical energy offsets the saving in time.
• the length of time to effect the desired results depends upon the magnitude of the current densities employed, and to some extent upon the particular metal to be polished and the character of its surface initially. Rough surfaces, of course, require a longer time to polish than relatively smooth ones.
• the same bath will also produce an excellent polish on a gray nickel eleetroplate at current densities of 125 to 250 amperes per sq. ft. within a period of from 2 to 6 minutes.
• similar conditions may be used, but I prefer to operate at an anode current density of about 100 amperes per sq. ft. for a period of 20 minutes at a. temperature of about 40 C.
• EXAMPLE 2 Bath composition, per cent by weight Per cent Sulfuric acid 60 Ortho phosphoric acid 30 Water 10 A bath of this composition produces excellent polishes on 18-8 and 24-12 chromium-nickel 1 stainless steels at current densities of 250 amperes per sq. ft. or more, and on nickel and nickel alloys, such as Monel metal, German silver, and the like, at current densities of 250 amperes per sq. ft.
• the temperatures empoyed may be in the neighborhood of 50 0., although that is not critical.
• EXAMPLE 3 Bath composition, per cent by weight Per cent Sulfuric acid 15 Ortho phosphoric acid 63 Chromic acid 10 Balance water.
• chromic acid greatly increases the polishing effect of the sulfuric-phosphoric acid mixture and is preferably added in amounts up to 20%, the percent of chromic acid, however, being in general not over 10% and therefore less than the percentage of either sulfuric or phosphoric acid.
• An electrolytic solution for use in the anodic polishing of metals selected from the group .consisting of iron and its alloys, nickel and its alloys and German silver, consisting initially of from 15 to 60% of sulfuric acid and from 15 to 70% of ortho phosphoric acid, the combined acid content being between 50 and 90% by weight of said solution and the balance being mainly water.
• the method of electrolytically polishing a metal selected from the group consisting of iron and its alloys, nickel and its alloys and German silver which comprises making the metal the anode in an aqueous solution consisting essentially of from 5 to 85% sulfuric and from 5 to 85% ortho phosphoric acids having a combined acid content in excess of 50% but not over 90% by weight of said solution the balance being mainly water and passing an electric current therethrough of sufficient density and for a sufficient length of time to produce a polish on said metal.
• the method of electrolytically polishing a metal selected from the group consisting of iron and its alloys, nickel and its alloys and German silver which comprises making the metal the anode in an aqueous solution consisting initially of from 15 to 60% of sulfuric and from 15 to 70% of ortho phosphoric acids having a combined acid content in excess of but not over 90% by weight of said solution the balance being mainly water and passing an electric current therethrough of sufficient density and for a suflicient length of time to produce a polish on said metal.
• the method of electrolytically polishing a metal selected from the group consisting of iron and its alloys, nickel and its alloys and German silver which comprises making the metal the anode in an aqueous solution consisting initially of about 15 to 20% of sulfuric and about 63 to 67% of ortho phosphoric acids by weight of said solution and passing an electric current therethrough of sufficient density and for a sumcient length of time to produces polish on said metal.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• ing And Chemical Polishing (AREA)

Priority Applications (6)

Applications Claiming Priority (1)

Publications (1)

Family

ID=22912957

Family Applications (1)

Country Status (5)

Cited By (21)

• 0
  • BE BE478064D patent/BE478064A/xx unknown
  • LU LU28863D patent/LU28863A1/xx unknown
  • NL NL71883D patent/NL71883C/xx active
• 1938
  • 1938-11-23 US US241975A patent/US2334699A/en not_active Expired - Lifetime
• 1947
  • 1947-07-28 CH CH271130D patent/CH271130A/fr unknown

Also Published As

Similar Documents