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
  • C25F3/22—Polishing of heavy metals

Definitions

• This invention relates to improvements in the electrolytic polishing of metal surfaces wherein an electrolyte of sulphuric acid or of a mixture of sulphuric acid and phosphoric acid, the electrolyte being of high acid concentration, is employed and the. article to be polished is made the anode.
• the generally accepted theory is that an anodic film is formed on the surface of the metal being polished, through which film the high spots project and are dissolved away resulting in the formation of a smooth surface.
• the method of polishing metals and metal alloys byimmersing them in an electrolyte and passing an electric current therethrough, utilising the article to be polished as the anode and employing as the cathode either the tank containing the electrolyte or an independent or conforming cathode, has in general, as is wellknown, many advantages over the mechanical methods of polishing. It utilises non-skilled labour, is quicker and cleaner than the mechanical method, articles once they have been introduced into the solution can be left unattended until it is time to withdraw them from the electrolyte, in most cases one electrolytic treatment is suflicient to obtain the required degree of polish and the process lends itself to the mass production of polishing of large outputs.
• Treatment times require to be prolonged. Treatment times can be shortened by -increasing operating temperatures e. g. C.
• the object of the present invention is to provide a method for the electrolytic polishing of metals employing an electrolyte which will be less expensive than those which it has hitherto been found possible to work on a commercial scale, which can be regenerated, which will in general give faster working at given current densities and which can be employed within a temperature range of 45 C. to 60 C. A temperature within this range will not burn the operative and has many other practical advantages.
• the electrolyte is primarily intended for the electrolytic polishing of stainless steels but they can be employed for polishing some other metals and alloys by suitable adjustment of the operating condition.
• the electrolyte according to the invention consists of an aqueous solution of sulphuric acid and phosphoric acid with a relatively small amount of an additive consisting of aniline.
• the acid concentration should be between 50% and 80% by weight of the solution and the ratio of sulphuric acid to phosphoric acid in the case of a. mixed solution should be greater than :3. Suitable ranges of sulphuric acid are 4.0% to 70% by weight and of phosphoric acid 0 to 30% by weight.
• Aniline is effective at concentrations of from 0.3% to 3% by weight.
• Suitable current densities when using an electrolyte according to the invention are between 0.5 amp. and 1.5 amps. per square inch of the surface of the metal forming theanode and the voltage in general lies between 3 volts and volts..
• a satisfactory electrolyte working temperature is 50 C. to 60 C. which is a very convenient range from a commercial standpoint.
• the time of treatment varies according to different factors and the initial condition of the surface of the metal and may be between a-few minutes and half an hour.
• the sulphuric acid is commercial sulphuric acid (95% H2SO4 specific gravity 1.84) and the phosphoric acid is commercial ortho-phosphoric acid (85% H3PO4 specific gravity 1.7). It is of course possible to replace ortho-phosphoric acid by suitable proportions of meta-phosphoric acid or pyro-phosphoric acid. The percentage of the additive is the pure chemical.
• the invention has been mainly described in its application for the electrolytic polishing of stainless steel, it can be used for polishing other ferrous base metals and alloys, and nickel and its alloys.
• the invention has the following advantages over other known processes for polishing stainless steel and other metals.
• salts When salts are formed due to dissolution of the metal undergoing treatment depending to some extent on the composition of the electrolyte, they begin to precipitate out after a time and can be filtered off.
• the electrolytic solution can be regenerated by filtration and fortification with fresh acid or .wate'r; f' l 6.
• The, solutions are of relatively low viscosity and the use of the additive does not rely for its bcneficial' feifect on increasing the viscosity of the body of the electrolyte although it induces desirablegcliaracteristics in the anodic layer.
• the electrolyte can be used commercially in tanks holding up to 5 tons and articles with areas as great as 20 square feet can be satisfactorily polished.
• metals employing an electrolyte consisting essentially of an aqueous solution of sulphuric acid and phosphoric acid, which comprises immersing the article to be polished as the anode in the acid solution having an acid concentration of between 50% and 80% by weight of the solution and a ratio of sulphuric acid to phosphoric acid greater 6 than 5 to 3, and which contains an additive or between 0.3% and 5% by weight of the solution and consisting of aniline.

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)
• Electrolytic Production Of Metals (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=10153033

Family Applications (1)

Country Status (4)

Cited By (7)

Citations (3)

• 0
  • BE BE494749D patent/BE494749A/xx unknown
• 1946
  • 1946-09-12 GB GB20865/46A patent/GB622118A/en not_active Expired
• 1947
  • 1947-09-02 US US771591A patent/US2594124A/en not_active Expired - Lifetime
• 1950
  • 1950-04-01 DE DEC746A patent/DE829391C/de not_active Expired

Patent Citations (3)

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