Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D21/00—Processes for servicing or operating cells for electrolytic coating
  • C25D21/04—Removal of gases or vapours ; Gas or pressure control
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D21/00—Processes for servicing or operating cells for electrolytic coating
• • 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
  • C25D5/003—Electroplating using gases, e.g. pressure influence
• • 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
  • C25D5/04—Electroplating with moving electrodes
• • 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
  • C25D5/08—Electroplating with moving electrolyte e.g. jet electroplating
• • 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
  • C25D5/12—Electroplating with more than one layer of the same or of different metals at least one layer being of nickel or chromium
• • 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
  • C25D5/18—Electroplating using modulated, pulsed or reversing current
• • 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
  • C25D5/60—Electroplating characterised by the structure or texture of the layers
  • C25D5/623—Porosity of the layers
• • 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
  • C25D5/60—Electroplating characterised by the structure or texture of the layers
  • C25D5/625—Discontinuous layers, e.g. microcracked layers
• • 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
  • C25D5/627—Electroplating characterised by the visual appearance of the layers, e.g. colour, brightness or mat appearance
• • 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

Definitions

• the present invention relates to a method for depositing a hard chromium layer on a substrate surface.
• the present invention relates to a method for depositing hard chromium layers at high deposition rates.
• Hard chrome layers are widely used as coatings of engineering components. For example, it is known to provide valve bodies, liners, brake pistons or axle hubs with hard chrome layers.
• the deposited chromium layer serves on the one hand as a corrosion protection layer for the underlying substrate surface, on the other hand, as a tribological wear protection layer, since the deposited hard chrome layers have a high hardness.
• the substrate surfaces to be coated are brought into contact with an electrolyte having at least the metal (chromium) to be deposited after a suitable pretreatment for the surface, wherein a deposition voltage is applied between the cathodically contacted substrate surface and an anode.
• a deposition voltage is applied between the cathodically contacted substrate surface and an anode.
• the layers thus deposited may have tensile or compressive residual stresses. Compressive stresses can cause the deposited layers to be microcracked, which means that the layers are not continuous, but have a network of microcracks.
• Inherent tensile stresses can lead to deep cracks in the deposited layers into which moisture or aggressive substances migrate and thus can lead to corrosion phenomena of the substrate surface located beneath the chromium layer, as a result of which damage to the chromium layer up to its flaking off can occur.
• the coated substrate surfaces in the prior art are mechanically reworked, for example by grinding or honing, in order to break down the inherent tensile stresses occurring in the layers.
• the processing can also lead to a violation of the deposited chromium layers, which ultimately drastically reduces their property as a corrosion protection layer.
• chromium is itself a chemically relatively non-noble metal
• chromium layers have a corrosion-protective effect due to the formation of a thin oxide layer on the surface and the associated very positive potential.
• Corrosion and tarnish protection with precious metals such as gold, silver or platinum shows comparable corrosion protection properties.
• the crack network occurring in the electrodeposited chromium layers due to residual compressive stresses not only has a negative influence on the anticorrosive property of the deposited layer, but also leads to improved mechanical properties of the so coated running parts, since any lubricants to reduce the tribological resistance between moving components in the Microcracks can store the so have a depot effect for the lubricant.
• This ability of the layers is termed oil carrying capacity and is consistently desired for corresponding mechanical components. This is important, for example, in the case of piston rings to maintain the fire stability.
• GB 1 551 340 A discloses the deposition of a hard chromium layer on a substrate surface at a temperature of 60 ° C and a set current density of 80 A / dm 2 in a vacuum chamber through which a chromium deposition electrolyte flows.
• US 2,706,175 A discloses a device for internal coating of hollow cylinders, wherein a chromium layer is deposited under negative pressure.
• EP 1 191 129 A discloses a method for depositing a hard chromium layer under negative pressure, wherein the electrolyte and substrate are moved relative to each other at a relative speed of 0.4 m / s.
• US 2001/054557 A1 discloses a method for the electrodeposition of hard chromium layers, in which the chromium layer is also under reduced pressure at a Current density of 30 to 40 A / dm 2 and a pulse frequency of 5 to 700 Hz is deposited.
• EP 0 024 946 A discloses a process for the deposition of hard chromium layers in vacuum at a current density in the range of 200 A / dm 2 and the generation of a relative movement between the electrolyte and the substrate to be coated.
• US 5,277,785 discloses a method and apparatus for depositing hard chromium layers by brush deposition.
• the pressure difference to be set is in a range from 20 mbar to 200 mbar.
• a second hard chromium layer is deposited on a first deposited hard chrome layer, a pulse current being applied between the substrate surface and counterelectrode for depositing the first hard chrome layer and a direct current being applied to deposit the second hard chrome layer on the first hard chrome layer.
• a first hard chrome layer is deposited, which has no residual stresses due to the applied pulse current and is free of microcracks.
• a direct current between the substrate surface to be coated and the counter electrode is deposited on the already deposited intrinsic and crack-free first hard chrome layer, a second hard chrome layer, which has tensile residual stress and the mechanically desired microcracking.
• the layer composite obtained in this way exhibits excellent corrosion resistance and moreover has excellent mechanical properties as running or sliding surfaces due to the microcracks occurring in the upper chromium layer.
• the pulse current is applied at a pulse frequency of 5 Hz to 5000 Hz, preferably 50 Hz to 1000 Hz.
• a current density between 25 A / dm 2 and 1000 A / dm 2 , preferably 50 A / dm 2 to 500 A / dm 2 is set.
• a direct current with a current density in the range between 25 A / dm 2 and 1000 A / dm 2 , also with a preferred range between 50 A / dm 2 and 500 A / dm 2 is set.
• the substrate surface to be coated can with the chromium-containing electrolyte.
• the electrolyte may have a pH in the range ⁇ pH 3, preferably ⁇ pH 1.
• the chromium-containing electrolyte has a conductivity K of from 200 mS / cm to 550 mS / cm (at 20 ° C.).
• the process can be carried out with only one electrolyte in a single coating cell.
• the relative speed here is in a range between 0.1 m / s and 5.0 m / s.
• the substrate surfaces can be moved or the electrolyte can be conveyed accordingly.
• agitators or pumps are suitable for conveying the electrolyte.
• the substrate surface to be coated is contacted with the electrolyte in a cell in which the chromium-containing electrolyte flows from below and can flow off via an overflow, with a sufficient flow rate is adjusted to the peeling to support the resulting hydrogen bubbles.
• a coating reactor is particularly suitable, which is cylindrical and is equipped with a cylindrical inner anode made of platinized metal such as platinum-plated titanium, niobium or tantalum. At the top and bottom of the coating reactor can be recordings for the component to be chromed.
• a coating reactor designed in this way is particularly suitable for coating cylindrical components. At least one of the two receptacles serves to supply power to the component to be coated and is accordingly designed as an electrical contact.
• an electrolyte is sucked from a reservoir through the reactor to the upper part of the reactor by means of a suitable pump and conveyed by this back into the reservoir.
• the electrolyte can be degassed by means of suitable facilities.
• the gas mixture to be separated off is discharged to the outside via a mist eliminator.
• a separate degassing container may be provided.
• means for controlling the temperature of the electrolyte ie heaters and / or cooling can be provided.
• the reservoir can be connected via metering with other reservoirs, which receive compositions for supplementing the electrolyte contained in the reservoir, if a re-dosing of the electrolyte is necessary.
• electrolyte can be passed through an evaporator unit, wherein the electrolyte is deprived of water and this is cooled simultaneously.
• such a reactor designed according to the invention is equipped with at least one movable end face, which facilitates the supply and removal of the component to be coated.
• conventional handling systems and seals may be provided to automate the process.
• the coated component can be rinsed in the reactor with rinsing water or steam or at least pre-rinsed.
• the electrolyte supply to the reactor can be interrupted and replaced by rinsing water or steam.
• the final rinse can take place in a second reactor, which is essentially identical in construction to the first reactor, but has no anode and power supply.
• a work piece to be chromium plated (CK 45 steel piston rods) was contacted in a reactor constructed in accordance with the invention with an electrolyte for depositing a hard chromium layer comprising 370 g / l chromic acid and 5.3 g / l sulfuric acid, the electrolyte from below in the corresponding reactor flowed in and was discharged via an upper course at the top of the reactor.
• the relative velocity set here between the substrate surface of the workpiece to be coated and the electrolyte was 4 m / s.
• the electrolyte had a temperature of 70 ° C.
• a pressure of 50 mbar was set within the reactor.
• a hard chrome layer was subsequently deposited by setting a current density of 235 A / dm 2 within 300 seconds. Subsequently, the substrate was rinsed.
• the chromium layer obtained had a layer thickness of 11 microns, showed about 40 cracks / cm and had a corrosion resistance in the neutral salt spray test of less than 100 h.
• a workpiece to be chrome plated was contacted with an electrolyte as in Example 1 in a reactor constructed according to the invention, which had 370 g / l chromic acid, 5.3 g / l sulfuric acid and 6 g / l methanesulfonic acid.
• the deposition conditions corresponded to Example 1.
• a shiny chromium layer was obtained with a layer thickness of 11 microns, which showed about 250 cracks / cm and a corrosion resistance in the neutral salt spray test less than 100 h.
• a workpiece to be chromium plated was contacted with the electrolyte according to Example 2 under the conditions mentioned in Example 2, wherein a pulse current with a current density during the pulse of 235 A / dm 2 , a frequency of 1000 Hz and a duty cycle of 50% for 400 seconds was created.
• a bright, crack-free chromium layer with a layer thickness of 11 ⁇ m was obtained which showed 0 cracks / cm and a corrosion resistance in the neutral salt spray test of greater than 500 h.
• a work piece to be chrome plated was coated under the deposition conditions of Example 1 except that first a pulse current with a current density of 235 A / dm 2 was applied during the pulse, a frequency of 1000 Hz and a duty cycle of 50% for 400 seconds and then in the same electrolyte under otherwise identical conditions, a direct current with a current density of 235 A / dm 2 was applied for 100 seconds.
• the obtained shiny chromium layer showed a layer thickness of 17 ⁇ m and had about 25 cracks / cm, the layer having a corrosion resistance in the neutral salt spray test of greater than 500 h.

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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)

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• 2008
  • 2008-10-22 PL PL08018462T patent/PL2180088T5/pl unknown
  • 2008-10-22 ES ES08018462T patent/ES2363566T5/es active Active
  • 2008-10-22 EP EP08018462.5A patent/EP2180088B2/de active Active
• 2009
  • 2009-10-22 JP JP2011533333A patent/JP5739341B2/ja active Active
  • 2009-10-22 BR BRPI0920600-0A patent/BRPI0920600B1/pt active IP Right Grant
  • 2009-10-22 KR KR1020117011605A patent/KR101658254B1/ko active Active
  • 2009-10-22 WO PCT/US2009/061683 patent/WO2010048404A1/en not_active Ceased
  • 2009-10-22 US US13/125,622 patent/US20110198226A1/en not_active Abandoned
  • 2009-10-22 CN CN200980151479.6A patent/CN102257184B/zh active Active

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