Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D7/00—Electroplating characterised by the article coated
  • C25D7/10—Bearings
• • 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

Definitions

• the present invention relates to the electroplating of bimetal bearings containing aluminum alloys. More particularly, the present invention relates to an immersion bath solution for pretreatment of a composite bearing structure which has one surface composed of an aluminum base metal (i.e., aluminum or an alloy of aluminum) and another surface composed of a ferrous base metal) (i.e., iron or an alloy of iron) prior to the electroplating thereof and to an improved process for electroplating utilizing said immersion hath solution.
• an aluminum base metal i.e., aluminum or an alloy of aluminum
• a ferrous base metal i.e., iron or an alloy of iron
• Immersion plating baths are either alkaline or acidic. While both types of baths can be used to deposit on the surface of aluminum or aluminum alluy, none of the heretofore known baths can be used to satisfactorily apply a thin coating to a composite structure having one surface composed of an aluminum base metal and another surface composed of a ferrous base metal. Specifically, alkaline immersion baths do not coat both the aluminum and ferrous base metals, but only the aluminum base metal.
• a process for the electroplating of a bimetal bearing having one portion thereof composed of an aluminum base metal and another portion of the surface thereof composed of a ferrous base metal comprising the pre- treatment step of immersing said bearing, prior to the electroplating thereof, in a solution having an acidic pH and containing nickel and halogen ions, whereby said bearing is provided with a coating from said solution without the use of an external source of electricity, which coating can then be coated with an electroplated deposit without any further intermediary steps.
• said electroplated deposit is obtained from the lead fluoborate/tin fiuoborate/copper fluoborate baths typically used in the bearing industry and which are collectively known as 'Babit' solutions.
• said electroplated deposit is obtained from lead. lead-tin, tin-lead, nickel, copper, brass, silver, tin, zinc, cadmium. or chromium plating solutions typically used in the metal finishing industry.
• U.S. Patent 3,612,964 discloses a process for plating aluminum with an adherent nickel coating by contact with an aqueous solution of hydrofluoric acid and a soluble metal salt such as nickel salt;
• U.S. Patent 2,746,136 discloses treatment of aluminum and its alloys prior to electro-plating, wherein aluminum or aluminum base alloys are initially treated by pickling and subsequently coated with a nickel layer by treating in a solution containing a nickel salt and finally electroplated with lead coating;
• U.S. Patent 2.580.773 discloses immersing cleaned aluminum or aluminum alloy articles in an aqueous bath containing a water soluble zinc salt and a water soluble fluoride.
• the electroless metal coating provides a base for receiving a subsequently deposited electrolytic metal layer;
• U.S. Patent 2,694,017 discloses nickel plating of aluminum or aluminum alloy materials by immersion in an acetic solution including nickel ions, fluoride ions, phosphite ions and nitrate ions; and
• U.S. Patent 3.726.771 discloses a process for chemical nickel plating of aluminum and aluminum alloys wherein the base is electrolessly plated with nickel without extensive pretreatments wherein the nickel is characterized by good adhesion to the aluminum base and which is sufficiently active to allow for direct electrolytic plating without extensive chemical treatments to activate the nickel.
• the electroless plating solution has an acetic pH and includes nickel ions and fluoride ions.
• said bearing is subjected to alkaline cleaning and etching followed by neutralization and desmutting prior to immersion in said solution as described hereinafter.
• the present invention also provides an immersion solution for the pretreatment of a bimetal bearing having one portion thereof composed of an aluminum base metal and another portion of the surface thereof composed of a ferrous base metal, comprising the pretreatment step of immersing said bearing, prior to the electroplating thereof, comprising nickel and halogen ions, said solution having an acidic pH.
• Said solution preferably comprises an acid, such as HC1 or H 2 SO 4 , to bring the pH of the solution within a range of about 6 to about -0.2 and a solution having a pH range of about 3 to about 0 is especially preferred.
• an acid such as HC1 or H 2 SO 4
• said solution contains halogen ions, such as F - , Cl - , BR - , I - , either individually or in combination, and in individual concentrations up to 160 g/L. and solutions containing chloride or fluorideions and especially solutions containing both fluoride and chloride are preferred.
• Said halogen ions are obtained in the solution from readily soluble salts such as NaCl, KCl, LiCl, RbCC1, NH 4 C1, KF, KHF 2 , NH 4 HF 2 , HF, NaF and especially preferred are solutions, wherein said halogen ions are derived from an ammonium salt thereof.
• Another preferred source of halogen atoms and or the acidic nature of the solution can be the nickel salt which serves as the source of the nickel ions in the solution and thus a solution comprising about 10 to 800 g/1 especially 150 to about 600 g/1 NiCl 2 .6H 2 O, NiSO 4 6H 2 O or a combination thereof, is preferred.
• the solution can ⁇ contain between about 0.2 g/1 and 180 g/1 of nickel ions that are provided from nickel salts other than those mentioned above and produced by dissolving nickel metal in an acid or other solution.
• An additional preferred component of the solutions of the present invention is an aluminum oxidizing material.
• Said oxidising materials are typically from the following groups: F +++ , MnO 4 , IO 3 - , IO 4 - , NO 3 - , ClO - , etc. They can be in the form of simple ions, such as FeCl 3 , or complex ions, such as K 3 Fe(CN) 6 , especially preferred is an aluminum oxidizing material selected from the group consisting of ferric and permanganate salts.
• said oxidizing material acts as a promoter to achieve an effective replacement of the aluminum alloy with nickel, thus providing an adherent conversion coating, that is primarily nickel-based and on which an effective and adherent lead-tin coating can be deposited to the required thickness.
• the preferred expanded process of the present invention involves the following process sequence for electroplating of a bi-metal bearing:
• the innovative method of coating bi-metal bearing materials of iron/aluminum alloys and aluminum and its alloys prior to further or nickel electrolytic plating in lead-tin / solutions also includes the pretereatment steps of cleaning and etching the parts, which produces a smut on the aluminum alloy surface. This smut is then removed in the acid solution, which typically contains nitric acid, with or without additives depending on the aluminum alloy being employed.
• the alkaline solution used for cleaning and etching includes up to 150 g/L of NaOH and up to 200 g/L of proprietary additives and complexors from the groups of EDTA, NTA, DTPA.
• AGPTA ethylene diamines, methylene diamines and their derivatives, and also organic acids or their derivatives such as citric acid, tartaric acid, amino acids, gluconic acids, oxalic acids, mallic acids, etc. and salts of acids that are the products of oxidation of carbohydrides, especially the oxidation of the end groups of carbohydrides, such as the aldehyde group and the alcohol group.
• organic acid salts are contained in concentrations up to 250 g/L and preferably in concentrations up to 100 g/l.
• the cleaning and etching solution also contains a wetting agent or surfactant, which is typically non-ionic or anionic and in concentration up to 5%, with a preferred range up to 1.5%.
• the neutralisation and desmutting solution typically contains nitric acid in concentrations of between 5% and 100%, with a preferred range of 50% to 100%, the lower range being only limited by the time required to remove the resultant smut from the alkaline cleaning and etching solution. This process is designed to leave the aluminum surface clean and active prior to processing in the innovating immersion solution of the present inventions. If the aluminum alloy contains silicon, it is preferable to also add to the acid neutralisation and desmutting solution salts of the halogen groups, such as F - , Cl-, Br - , I - , either individually or in combination, and in individual concentrations up to 160 g/L, preferably 2 to 60 g/l.
• the halogen groups such as F - , Cl-, Br - , I -
• the solution also preferably can contain all the metal salts of the metals contained in the bimetals being processed, such as iron salt, aluminum salt, nickel salt, tin salt, copper salt, etc.
• the purpose of this was found from experiments which clearly showed the solution, which did not initially contain these metal salts, performed better after ageing due to the replacement process.
• said solution preferably contains bivalent iron salts, bivalent ion salts and combinations thereof such as FeCl 2 , Fe 2 (SO 4 ) 3 , PeSO., FeCl 3 etc, preferably in amounts of up to about 150 g/1 iron ions.
• the solution preferably also contains a non-ionic wetting agent or surfactant.
• composition of example 6 represents an especially preferred and commercial immersion solution according to the present invention further components can be added thereto to meet customer specifications and to further improve the properties thereof.
• said solution can also preferably contain metallic brighteners from the group, such Zn, Cd, Pb, and Thalium in the form of one of their salts of complexes, and in concentration up to 5 grams of metal per liter.
• metallic brighteners from the group, such Zn, Cd, Pb, and Thalium in the form of one of their salts of complexes, and in concentration up to 5 grams of metal per liter.
• the solution can also preferably contain organic brighteners which can also be included to provide stress-relieving, said brighteners including imide derivatives such as ortho-benzoic sulphonimide, benzene sulphonimide, bi-dibenzene sulfonimide, heterocyclic sulphonic acids such as thiophen-2- sulphonic acid, aromatic sulphinic acids such as benzene sulphinic acid, ethylenic aliphatic sulphonic acids such as allyl sulphonic acid. aromatic sulphonic acids such as benzene suphonic acid, aromatic sulphonamides such as paratoluene sulphonamide.in concentrations up to 10 g/L.
• imide derivatives such as ortho-benzoic sulphonimide, benzene sulphonimide, bi-dibenzene sulfonimide, heterocyclic sulphonic acids such as thiophen-2- s
• Example 13 Of the following compositions, that of Example 13, is especially preferred.
• An aluminum alloy bearing conforming to SAE standard J460e and containing 78.3% aluminum and 20% tin is first placed in an alkaline bath for 1 to 3 minutes at a temperature of between 25 to 50°C for cleaning and surface activation. The bearing is then removed and washed with water.
• the bearing After rinsing the bearing is placed in a nitric acid bath for 20 to 90 seconds at room temperature (20 - 30°C). The nitric acid bath desmutes the surface of the bearing and leaves it clean and active.
• the bearing is then once again rinsed in a water bath for 1-2 minutes.
• the rinsed bearing is then placed in a solution according to the present invention for 1 to 3 minutes at room temperature.
• the bearing is then rinsed again in water and placed in an electroplating bath containing lead fluoborate.
• tin fluoborate, copper fluoborate and fluoboric acid having a preferred ratio of 90% lead fluoborate : 92 tin fluoborate : 1 % copper fluoborate.
• the current density of the electroplating bath is up to about 6 amper/dm 2 and the voltage is about 0.4-6 volts.
• the electroplating is carried out at 20 - 60 °C for up to 30 minutes using a lead tin anode (90% Pb : 10% Sn) using direct or preferably pulsed current.
• the resulting bearing has a uniform plating of about 12-50 microns.
• the bearing can alternatively be plated with nickel from a Wattes Nickel bath containing 300-330 g/1 nickel sulphate. 60-80 g/1 nickel chloride and 35-45 g/1 Boric acid, or other nickel bathes.
• the current density used is up to 10 ampers/dm 2 , the voltage is about 6-8 volts, the temperature is preferably about 40 0- 60 0 C and the anode is made of nickel.

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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 Methods And Accessories (AREA)
• Electroplating And Plating Baths Therefor (AREA)

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Citations (4)

• 1987
  • 1987-01-27 EP EP87300675A patent/EP0234738A1/de not_active Withdrawn

Patent Citations (4)

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