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
  • C25D11/36—Phosphatising

Definitions

• the invention relates to a method for preparing workpieces made of titanium or titanium alloys for sliding operations and its use for preparing the workpieces for cold forming.
• titanium or titanium alloys are also subjected to cold forming in various processes, such as tube drawing, wire drawing, cold extrusion, and cold rolling of sheet metal.
• titanium and titanium alloys tend to seize to a much greater extent, since their chemical resistance is greater and, accordingly, suitable lubricant carrier layers are difficult to apply. It is therefore the current state of the art to apply lubricating oil to incandescent scale or to a resin coating as a lubricant carrier in the pipe drawing. As far as conversion coatings are concerned, the investigations are limited to fluoride coatings.
• the object of the invention is to provide a method for preparing workpieces made of titanium or titanium alloys for sliding processes that does not have the known, in particular the aforementioned disadvantages, which in particular enables cold forming without gassing even with a large reduction in cross section and is of constant quality over a long period of time.
• the object is achieved by designing the method of the type mentioned at the outset in accordance with the invention in such a way that the workpieces are immersed in an aqueous phosphate solution containing acidic zinc phosphate and a zinc phosphate coating is produced on their surface by cathodic electroysis.
• the acidic zinc phosphate solution to be used in the process according to the invention contains primary zinc phosphate as the main constituent.
• the zinc content is in the range from 1 to 50 g / l, preferably in the range from 5 to 20 g / l.
• the phosphate content is usually 3 to 140 g per liter (calculated as PO4), preferably 10 to 60 g per liter.
• ions other than zinc, such as calcium, manganese or iron is possible and allows modified phosphate coatings to be obtained.
• the phosphating solution usually contains oxidizing agents, which can be organic or inorganic. Examples include nitrate, nitrite, hydrogen peroxide, nitrobenzenesulfonate and para-nitrophenol compounds.
• the pH of the phosphating solution is generally in the range from 0 to 5, preferably in the range from 1.5 to 3.5. He can e.g. be adjusted with the help of sodium hydroxide solution or sodium carbonate.
• the phosphating solution is generally used at a temperature of 30 to 80 ° C, preferably 40 to 60 ° C.
• the workpiece is switched as a cathode, while e.g. a zinc plate serves as an anode.
• a cathode e.g. a zinc plate serves as an anode.
• suitable anode materials are graphite, platinum sheets, stainless steel sheets and the like.
• the conditions with regard to electrode spacing, current density and duration of treatment should be selected in such a way that the required coating properties are obtained.
• the electrode spacing is about 5 to 30 cm
• the current density is 0.2 to 30 A / dm2, preferably 0.5 to 5 A / dm2
• the electrolysis time is 10 seconds to 5 min. An excessively high current density and an excessively long electrolysis time can lead to blackening of the coating produced or reduced adhesion of the coating.
• the zinc phosphate coating which is obtained by the process according to the invention generally has a layer weight of 2 to 20 g / m2.
• Known lubricants such as sodium soap from fatty acids, mineral oil and solid lubricants are applied to it.
• the workpieces are pretreated with an aqueous conditioning agent based on a colloidal titanium compound before immersion in the phosphating solution.
• the conditioning agents known per se for the phosphating of metal surfaces serve as the aqueous conditioning solution. They generally contain 10 to 200 ppm titanium, 200 to 3000 ppm phosphate, 30 to 600 ppm pyrophosphate and have a pH of 7.5 to 9.5. Titanium sulfate, titanyl sulfate or titanium oxide or phosphoric acid or alkali or ammonium phosphate or alkali or ammonium pyrophosphate can serve as sources for the individual components.
• the activation agent is produced in a simple manner by mixing the above-mentioned substances with water.
• the task of the conditioning agent is to apply adherent, colloidal titanium compounds to the surfaces of the titanium or titanium alloys, which improve the layer formation and the layer quality during the subsequent coating formation. As a result, lower titanium concentrations than those given above result in poorer coating formation. Higher titanium concentrations have no additional effect. Differing concentrations of phosphate and pyrophosphate have a similar effect.
• the subsequent coating formation is hindered at lower values than those mentioned. The same is the case when the pH is higher.
• the workpieces are immersed in the aqueous zinc phosphate solution for cathodic electrolysis.
• the conditions regarding the zinc phosphate solution and the cathodic electrolysis are the same as mentioned above.
• the lubricants known per se already mentioned are also used.
• a zinc phosphate coating can be applied to the workpiece by dipping it in an acidic one Zinc phosphate solution can be obtained in the simplest way, whereas in the case of the treatment of titanium or titanium alloys which have a dense oxide coating on the surface, the pickling reaction by phosphoric acid does not take place and consequently a phosphate coating is difficult to form.
• reaction (1) takes place and, consequently, the pH increases in the immediate vicinity of the metal surface, reaction (2) takes place and tertiary metal phosphate separates out to form a coating. Without the reaction according to (1), the coating cannot be formed.
• reaction (1) does not take place and, consequently, no coating is formed.
• cathodic electrolysis a reaction proceeds analogously to relationship (1) 2H+ + 2e ⁇ H2 ⁇ (3) from.
• This reaction also increases the pH in the vicinity of the metal surface, so that the reaction can take place according to the relationship (2).
• zinc ions in the treatment solution due to the presence of zinc ions in the treatment solution, a deposition of metallic zinc as a result of the cathodic electrolysis can be determined.
• the zinc phosphate layers produced with the aid of the method according to the invention are aftertreated with a lubricant known per se, so that the workpieces have excellent properties for a subsequent sliding operation.
• the smear layer can be made uniform over a long period of time without e.g. comes to fretting during the subsequent cold forming.
• the method according to the invention is intended for the treatment of all workpieces which are at least temporarily exposed to any sliding processes. These are in particular gear parts, bearings and the like, but also, for example, objects used for fastening, such as bolts, screw threads and the like. However, the greatest importance of the process lies in its application for the preparation of workpieces for cold forming.
• Cleaned sheets of pure titanium (JIS grade 1) with the dimensions 100 x 50 x 0.8 mm were electrolytically phosphated with a phosphating solution of the following quality: 9.6 g / l zinc 36.3 g / l phosphoric acid (calculated as PO4) 2 g / l nitric acid 0.5 g / l sulfuric acid 0.03 g / l nickel pH approx. 3.0.
• the electrolysis conditions were: Anode, a zinc plate, Electrode spacing 15 cm Layer weight about 10 g / m2 Current density 3 A / dm2 Treatment duration 1 min. Treatment solution temperature 45 ° C.
• the phosphated sheets were then treated with a lubricant (Palube 235, a product of Nihon Parkerizing Co., Ltd., with sodium stearate as the main component).
• a lubricant Palube 235, a product of Nihon Parkerizing Co., Ltd., with sodium stearate as the main component.
• the concentration of the Lubricant was 70 g / l, its temperature 75 ° C and the treatment time 3 min.
• the sheets were provided with the aid of 111 QD (product from Hangstafer), the main component of which is a rubber resin, with a plastic coating of 10 ⁇ m thickness, over which a lubricant containing an organic chlorine compound (Jl, product from Hangstafer) was added in an amount of 10 g / m2 was applied.
• 111 QD product from Hangstafer
• Jl organic chlorine compound
• a lubricant containing an organic chlorine compound (Jl, product from Hangstafer) was applied in an amount of 10 g / m 2 over the glow scale produced by treatment at 700 ° C. for 1 hour.
• Example 2 The palube 235 mentioned in Example 1, which was applied under the same conditions, served as the lubricant.
• the test was evaluated both by determining the number of sliding movements up to a friction coefficient of 0.25 (occurrence of contact marks) and by determining the friction coefficient.
• the table shows that the titanium sheet treated according to Example 1 permits a considerably higher number of sliding movements until seizure occurs and also has a lower friction coefficient than the titanium sheet treated according to Comparative Examples 1 to 3.
• the titanium sheet defined in Example 2 received the following treatment.
• the sheets of the individual tests were rolled with the aid of a duofin sheet mill (testing device) using rolling oil (Finerol 704-3 from Nihon Parkerizing) at a concentration of 10% and 40 ° C.
• Rolling mill rolls 100 mm in diameter
• Rolling speed 10 m / min Cross-section reduction 20% each for the 1st to 3rd stitch, 10% each for the 4th to 6th stitch.
• ⁇ (% / T) was determined for each of the sheet series obtained according to Example 2 or Comparative Examples 4 to 6. It stands for the sum of the quotients from cross-section reduction (in%) per pass divided by rolling force (in t / mm2).
• Comparative example 6 leads to values that are close to that according to the present invention. However, due to the short life of the treatment baths, this method (fluoride method) has not been successful in practice.
• Example 1 corresponds to Example 1 in terms of sheet quality, electrolytic phosphating and aftertreatment. It was only preceded by a conditioning treatment by immersing for 10 seconds in an aqueous conditioning agent at room temperature containing 3 g / l titanium compound (Prepalene Z from Nihon Parkerizing).
• Example 3 illustrates that, as a result of the additional activation carried out, even better results are obtained than in the case of Example 1.

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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)
• Lubricants (AREA)
• Chemical Treatment Of Metals (AREA)

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• 1987
  • 1987-04-20 JP JP62097216A patent/JPS63262500A/ja active Pending
• 1988
  • 1988-04-16 DE DE3812692A patent/DE3812692A1/de not_active Withdrawn
  • 1988-04-16 EP EP88106110A patent/EP0288853B1/fr not_active Expired - Lifetime
  • 1988-04-16 DE DE8888106110T patent/DE3863577D1/de not_active Expired - Fee Related
  • 1988-04-16 ES ES88106110T patent/ES2023681B3/es not_active Expired - Lifetime
  • 1988-04-20 US US07/184,548 patent/US4874480A/en not_active Expired - Fee Related

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