Classifications

• • 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
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/30—Electroplating: Baths therefor from solutions of tin
• • 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
  • C25D5/10—Electroplating with more than one layer of the same or of different metals

Definitions

• This invention relates to a method of making tin plate and, in particular, to the manufacture of electrolytic tin plate having improved corrosion resistance.
• a further object is to provide a method including such pre-oxidation of the steel followed by a light electrotinning thereof from an alkaline bath, then completion of the desired deposit of tin from an acid bath. This latter procedure results in a product having markedly superior properties, particularly in respect to corrosion resistance.
• my method comprises the formation of a film of hydrated iron oxide on cleaned pickled steel sheet, immediately before electrotinning it, by subjecting it to anodic electrolysis in a strong solution of an alkali-metal hydroxide or carbonate.
• the film of oxide (Fe O -H O) should be from 100 to 500 A. thick so it will not be completely removed by the acid electrolyte used for electrotinning the steel base.
• the latter requires no other treatment except water rinsing, before electroplating, but I have found that a surprisingly improved product is obtained by tinning the base first lightly from an alkaline bath and then depositing additional tin to the desired total amount from an acid electrolyte.
• Other alkali-metal hydroxides or alkali-metal carbonates may be used instead of NaOH.
• the strip is in the solution, I make it anode in a circuit including a source of direct current and cause a current to flow therein at a density of from 100 to 300 amperes per square foot. The anodic treatment should continue until at least 200 coulombs per square foot have been delivered.
• the solution should be at a temperature of from 225 to 275 F. Within that range, the desired thickness of film, 100 to 500 A., is formed in from 1.5 to 4 seconds.
• Example 2 The same procedure as described in Example 1 was used except that oxidation-treatment current density was increased to 184 a.s.f. The following results were obtained:
• black plate is cleaned, rinsed, pickled and again rinsed in accordance with conventional electrotinning practice. It is then subjected to oxidation of the surface in any convenient manner, e.g., that described above, viz., in a hot, concentrated caustic solution wherein the steel strip is made the anodic pole.
• This oxidation step results in the formation of a hydrated iron oxide (Fe O -H O) on the surface of the strip having a thickness of from 100 to 500 A.
• the strip is rinsed and then plated with a flash coating of tin (0.05 lb./bb.
• the second stage of this phase of my invention consists of depositing a thin coating of tin from an alkaline tin-plating solution over the oxidized surface of the steel strip without prior removal of the oxide film.
• a conventional alkaline-tin electrolyte consisting of about 70 g./l. Sn++++ and 11 g./l. NaOH, at a temperature of 170 F. and a current density of about 30 a.s.f.
• the plating solution is not limited to sodium stannate-sodium hydroxide, since a bath of potassium stannate-potassium hydroxide or combinations of sodium and potassium salts could also be used.
• the amount of tin deposited from an alkaline bath need be no greater than 0.05 lb./bb. and can range from about 0.005 to 0.05 lb./bb. I prefer that the coating be about 0.03 lb./bb. alkaline tin.
• the weight of the coating is increased to the desired final value.
• Example 3 Aqueous solution g./l. Na'OH-.. 500 Temperature F... 255 Current density a.s.f 200 Time seconds 2.5
• the strip was water rinsed and plated from an alkaline electrotinning bath to a coating weight of 0.05 lb./bb. tin under the following conditions:
• the strip was then water rinsed and plated to a total in coating weight of 1.0 lb./bb. tin in an acid aqueous solution as follows:
• ATC 'alloy tin couple
• Grapefruit-Juice Pack Lite Predicted from ATC Current, weeks AT C, la/cm;
• Untreated Treated Example 4 Black plate was cleaned and pickled as in Example 3, except that the time for cleaning was reduced to 2 seconds.
• the oxidation treatment was carried out in a solution containing 600 g./l. NaOH at 250 F. 3 seconds, at a current density of 100 a.s.f.
• the alkaline tin coating was deposited under the conditions described in Example 3 except that the amount of tin deposited was only 0.005 lb./bb. This was followed by overplating in acid electrolyte (using a solution as in Example 3) to a total coating weight of 1.0 lb./bb. tin.
• the performance of plate so produced as measured by the ATC testis shown below:
• the improvement in predicted pack life was about This demonstrates that an improvement greater than the 70% ordinarily to be expected from using the combination of treatments can be achieved, even under conditions less favorable than the optimum. It will be evident from the foregoing that the invention provides a cheap yet effective method of forming an oxide film of predetermined thickness and composition which materially improves the quality of the finished product made by electrolytically tinning the oxide-filmed black plate. An even higher quality product, from the standpoint of corrosion resistance, is obtained when the oxide-filmed black plate is subjected first to a light tin coating from an alkaline bath andthe balance of the coating from an acid bath.
• a method of making tin plate which comprises treating electrolytically as anode, sheet steel of tin-plate gage, in a water solution at from 225 to 275 F. containing from 400 to 700 grams per liter of an alkali-metal compound selected from the group consisting of hydroxides and carbonates, at a current density of from to 300 amps.

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

Priority Applications (6)

Applications Claiming Priority (1)

Publications (1)

Family

ID=21863224

Family Applications (1)

Country Status (4)

Cited By (5)

Citations (3)

• 0
  • NL NL124778D patent/NL124778C/xx active
  • NL NL265208D patent/NL265208A/xx unknown
• 1960
  • 1960-05-27 US US32123A patent/US3075897A/en not_active Expired - Lifetime
• 1961
  • 1961-05-19 GB GB18438/61A patent/GB917095A/en not_active Expired
  • 1961-05-25 DE DE19611446072 patent/DE1446072A1/de active Pending

Patent Citations (3)

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