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
  • C25D5/60—Electroplating characterised by the structure or texture of the layers
  • C25D5/625—Discontinuous layers, e.g. microcracked layers
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B08—CLEANING
  • B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
  • B08B17/00—Methods preventing fouling
  • B08B17/02—Preventing deposition of fouling or of dust
  • B08B17/06—Preventing deposition of fouling or of dust by giving articles subject to fouling a special shape or arrangement
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B08—CLEANING
  • B08B—CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
  • B08B17/00—Methods preventing fouling
  • B08B17/02—Preventing deposition of fouling or of dust
  • B08B17/06—Preventing deposition of fouling or of dust by giving articles subject to fouling a special shape or arrangement
  • B08B17/065—Preventing deposition of fouling or of dust by giving articles subject to fouling a special shape or arrangement the surface having a microscopic surface pattern to achieve the same effect as a lotus flower
• • 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
  • C25D5/605—Surface topography of the layers, e.g. rough, dendritic or nodular 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

Definitions

• the invention relates to a method for electro-chemical (galvanic) application of a surface coating according to the German application with the file number DE 42 11 881.6-24.
• Such surface structures are more or less well achieved by chemical etching processes following the coating or by mechanical processing methods such as grinding or sandblasting.
• a Ha rtch romschi cht is then applied to the surface structure thus created.
• DE 33 07 748 relates to a method for electrochemical coating, in which a pulse-shaped current is used for the seed formation. If an appropriate current density is used, the resulting nuclei form a dendritic structure. Rough, dendritically structured surfaces can be created in one step.
• the current density is understood to mean the mean current density at the cathode surface.
• the invention has for its object to provide an improved method for the electrochemical application of structural metal layers, which dispenses with mechanical or chemical aftertreatments and with which various structural metal layers can be produced, and an apparatus for carrying out this method.
• the structure layer is applied directly galvanically to the object to be coated.
• this must have an electrically conductive surface, which is usually ground to provide a smooth base for the structural layer.
• the object is cleaned and degreased according to the usual galvanotechnical rules. It is immersed as a cathode in a galvanic bath, which also contains an anode. The distance between the anode and cathode is usually chosen in the range between 1 and 40 cm.
• Chrome electrolyte in particular sulfuric acid, chrome electrolyte, mixed acid chromium electrolyte or fermentation electrolyte, are preferably used as the electrolyte.
• a process voltage can be applied between the anode and the cathode and the flowing current causes an application of material to the object to be coated, which is used as the cathode.
• the invention proposes to apply positive current jumps for the formation of germs.
• the process of structure generation consists of a germination phase and a germ growth phase.
• process voltage and process current are increased in several stages with a predeterminable change in current density of 1 to 6 mA / cm 2 per stage from an initial value to a structural current density.
• the initial value is 0 mA / cm 2 , but this can also be higher if the germination phase directly follows a previous galvanic process phase and the current in between is not reduced to zero.
• the time between two current density increases is about 0.1 to 30 seconds, most often step intervals of about 7 seconds are used. With each jump in current, new germs are formed. In contrast to pulse current coating, the process current does not go back to zero after every positive jump, but is increased further with every current jump. In this way, in particular round and more uniformly shaped germs or bodies can be deposited on the object than is possible with the known pulse current methods.
• the flow stages are applied to the bath in such a number until a structural layer consisting of a precipitate of individual or adjacent, approximately spherical or dendritic bodies is reached on the surface of the object.
• a structural layer thickness of 4 ⁇ m to 10 ⁇ m is preferably aimed for with the germination phase. This usually requires between 10 and 240 current levels, particularly good results are achieved with 50 to 60 levels.
• the current density achieved after completion of the last current stage is the structure current density.
• the nucleation phase the actual formation of the structure, is largely completed.
• the structure of the resulting structure depends on many parameters, above all on the selected structure structure, on the number, the height and the time interval of the current stages, on the bath temperature and on the electrolyte used.
• the change in current density per stage as well as the time between two current density increases can be changed during the germination phase.
• different surface structures can be created, the main ones are characterized by different roughness depths.
• the ideal process parameters can easily be determined empirically. As a rule, it can be said that with a higher bath temperature and a higher acid content of the electrolyte, a higher structure current density is also used.
• This structure current density is usually two to three times the current density used in normal DC coating.
• current densities in the range from 15 to 60 mA / cm 2 are used .
• the value of the current density is dependent on the electrolyte and the bath temperature.
• Current densities in the range from 30 to 180 mA / cm 2 are possible for structure coating.
• a process stream with a current density in the range from 80% to 120% of the current is used during a predeterminable ramp working time
• the ramp working time is usually in a range from 1 to 600 seconds, preferably around 30 seconds.
• the process current is reduced to a final value, often to zero. This lowering of the process stream to the final value can occur suddenly, but it is also possible to lower the ramp. Here too, good results were achieved with a gradual change in the process stream.
• the current levels are preferably in a range from -1 to -8 mA / cm 2 per stage and the time between two current stages is preferably selected in the range from 0.1 to 1 second.
• process steps have been described above: gradually increasing the process current during the germination phase until the structure current density is reached, keeping the process current in the region of the structure current density during the ramp working time (germ growth phase) and then reducing the process current to a final value.
• These process steps represent a structure generation cycle. They can be repeated cyclically. This is particularly advantageous if a stronger structuring of the surface is desired.
• the end value of the previous cycle corresponds to the start value of the following cycle. The number of repetitions depends on the desired surface structure and layer thickness. Good results were achieved with repetitions between two and twenty times.
• the final values of the individual cycles can be of different heights.
• the object to be coated is immersed in the bath for some time, preferably one minute before the start of the process.
• This waiting time is primarily used to adjust the temperature, i.e. the base material assumes the temperature of the electrolyte.
• a DC base layer is applied before the application of the structural layer under the conditions customary for normal chrome plating. This is achieved by applying a basic pulse (voltage or current pulse) at the beginning of the coating. A current density of 15 to 60 mA / cm 2 is used, which corresponds to the current values customary in normal chrome plating. This basic pulse has a duration of approximately 600 seconds. Concentration changes due to the upstream DC treatment in the
• Chromium-plated tools can be used in forming technology to give the workpiece a structured surface.
• the surface of sheet metal can be structured by rolling with chrome-plated rollers.
• the device for performing the described method consists of a galvanic bath, which is a
• Chrome electrolyte are preferred as electrolyte, in particular sulfuric acid chrome electrolyte, mixed acid
• Ch rome le kt ro lyte or alloying lect ro lyte is a preferred one
• Electrolyte has a concentration of 180 to 300 grams
• a preferred electrolyte contains 1 to 3.5
• the temperature of the electrolyte is preferably 30 to 55 degrees Celsius.
• An anode and a cathode are immersed in the electrolytic bath solution, the object to be coated forming the cathode or at least being the cathode's egg. If a chrome electrolyte is used, platinum-plated platinum or PbSn7 are preferably used as the anode material.
• Anode and cathode are connected to a device for feeding a process current.
• the process current can be increased from the initial value to the structure current density in several stages, each with a predeterminable change in the current density of 1 to 6 mA / cm 2 per stage.
• the time intervals between two current increases can be set between 0.1 and 30 seconds.
• a process current with a current density in the range of 80% to 120% of the structure current density can be applied for a predeterminable ramp working time.
• the device can be equipped with a rotary drive for continuously rotating the object.
• the distance between the anode and the object to be coated is selected in the range from 1 to 40 cm, preferably at 25 cm.
• FIG. 1 shows a schematic representation of a device for the galvanic application of structural layers
• FIG. 2 shows a graphical representation of a temporal current density profile when generating a structure layer
• FIG. 4 photographic illustration on a scale of 500: 1 of the surface structure shown in FIG. 3 and
• FIG. 7 shows a graphical representation of a temporal current density profile when generating a structure layer.
• a container filled with electrolytic liquid 1 forms the galvanic bath.
• An object 2 to be coated and an anode 3 are immersed in the galvanic bath.
• the object to be coated forms the cathode 2.
• the anode and cathode are connected to a controlled electrical energy source 4.
• the energy source can be a current or a voltage source. Since the current or the current density at the cathode is decisive for the coating as far as the electrical influences are concerned, the process can be controlled more precisely with a current source. In contrast, the use of a voltage source has the advantage of less electrical circuit complexity. As long as other parameters, such as. B. not the bath temperature and the concentration of the electrolyte change significantly, the process can also be easily controlled with a voltage source.
• the electrical energy source 4 is controlled by a programmable control unit 5.
• the control unit can be used to specify any desired voltage or current profiles, which are then automatically applied to the electrodes via energy source 4.
• FIG. 2 shows the graphic representation of the time course of the process current density when generating a structure layer.
• the 'horizontal axis of Fig. 2 is the time axis, on the vertical axis y the current density is shown.
• This is an exemplary embodiment of a possible process sequence, which is described in more detail below.
• FIGS. 3 and 4 show photographic representations of the structural layer produced using this method.
• a sulfuric acid chromium electrolyte with 200 grams of chromic acid CrO and 2 grams of sulfuric acid H SO is used as the galvanic bath
• the workpiece to be coated is a rotationally symmetrical component, a dampening device for the printing industry.
• the cylinder consisting of St52 is first finely ground, with a roughness depth of Rz ⁇ 3 ⁇ m.
• a 30 ⁇ m thick nickel layer and then a 10 ⁇ m thick, low-crack chrome layer are then applied according to the conditions customary in electroplating.
• the workpiece prepared in this way is rotated for structural chrome plating in the galvanic bath in order to achieve a coating that is as uniform as possible.
• the workpiece forms the cathode, platinum-plated titanium or PbSn7 is used as the anode.
• the anode / cathode electrode spacing is set to 25 cm.
• the process stream switches off. This phase serves to acclimatize the workpiece to the galvanic bath. The workpiece takes on the temperature of the electrolyte. After about a minute, a direct current between the anode and cathode is switched on. This remains switched on during phase 8, which lasts about 600 seconds.
• a chrome DC base layer is applied to the workpiece. The current density used is also common for standard chrome, here 20 mA / cm 2 . After the application of the DC base layer, a second phase 9 follows without current.
• the current density is increased in steps to the structure current density 14.
• the characteristic data of the stages are varied during the ascent.
• the current is increased in 16 steps to 40 mA / cm 2 . This corresponds to a change in the current density of 2.5 mA / cm 2 per stage.
• the time 28 between two current stages is 5 seconds.
• the current density during phase 11 is then increased in 62 further steps to the structure current density of 100 mA / cm 2 , the time between two current stages is 6 seconds (the current density curve shown in the graph in FIG. 2 is not to scale, the same applies to that 5 and 6 graphs).
• Chrome structure layer applied a 4 to 8 ⁇ m thick micro-cracked chrome layer. This is done under the direct current conditions common in electroplating and is not explained in more detail here.
• FIG. 3 and 4 show microscopic images of the chromium structure layer which was produced by the method described for FIG. 2.
• the structural layer consists predominantly of spherical, individual and partly also adjacent bodies. The one shown
• the "Tragantei l” is also defined as “Materialantei l” according to DIN 4762.
• a direct current pulse 18 follows, which in its nature is the direct current pulse 8 in Fig. 2 corresponds.
• a seed phase 19 in which the current density is gradually increased to the structure current density 24.
• the current density is then kept at the structure current density during the ramp working time 20 and is then ramped down to an end value 26 during the phase 21.
• a germination phase 23 with a gradual increase in the current density up to the new structure current density 25.
• the initial current density of the germination phase 23 is equal to the end value 26 to which the current density was reduced at the end of the previous structure generation cycle.
• the current density is then kept at the structure current density 25 during the ramp working time 27 and subsequently abruptly reduced to the new final value of 0 mA / cm 2 .
• Process sections 7 to 9 have already been discussed in relation to FIG. 2.
• the process stream is then gradually increased to the structure current density 30 during phase 29.
• a process current with a current density value of 80% of the structure current density 30 is then applied during the ramp working time 32. In between there is a current-free rest time 31.
• the process current is reduced to a final value during phase 33. This final value serves as an initial value for a second structure generation cycle, starting with the gradual current increase in phase 35.
• a process current with a current density value of 120% of the structure stomp density 36 is applied during the ramp working time 38. In between there is again a current-free rest 37.

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• Chemical & Material Sciences (AREA)
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• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electroplating Methods And Accessories (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Electroplating And Plating Baths Therefor (AREA)

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Cited By (4)

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Citations (4)

• 1994
  • 1994-10-01 EP EP94928407A patent/EP0722515B1/de not_active Expired - Lifetime
  • 1994-10-01 CN CN94190766A patent/CN1044395C/zh not_active Expired - Lifetime
  • 1994-10-01 WO PCT/EP1994/003314 patent/WO1995009938A1/de active IP Right Grant
  • 1994-10-01 SK SK861-95A patent/SK281999B6/sk unknown
  • 1994-10-01 DE DE59405190T patent/DE59405190D1/de not_active Expired - Lifetime
  • 1994-10-01 BR BR9405631-5A patent/BR9405631A/pt not_active IP Right Cessation
  • 1994-10-01 JP JP51061895A patent/JP3293828B2/ja not_active Expired - Lifetime
  • 1994-10-01 KR KR1019950702238A patent/KR100332077B1/ko active IP Right Grant
  • 1994-10-01 ES ES94928407T patent/ES2114703T3/es not_active Expired - Lifetime
  • 1994-10-01 CH CH01713/95A patent/CH690273A5/de not_active IP Right Cessation
  • 1994-10-01 CA CA002172613A patent/CA2172613C/en not_active Expired - Fee Related
  • 1994-10-01 PL PL94309286A patent/PL177073B1/pl not_active IP Right Cessation
  • 1994-10-01 SI SI9420006A patent/SI9420006B/sl not_active IP Right Cessation
  • 1994-10-01 AU AU77847/94A patent/AU7784794A/en not_active Abandoned
  • 1994-10-01 CZ CZ19951447A patent/CZ286909B6/cs not_active IP Right Cessation
• 1995
  • 1995-06-06 FI FI952774A patent/FI103674B/fi active
• 1998
  • 1998-04-21 GR GR980400886T patent/GR3026689T3/el unknown

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