US3669855A - Control of integral color anodizing process - Google Patents

Control of integral color anodizing process Download PDF

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Publication number
US3669855A
US3669855A US6516A US3669855DA US3669855A US 3669855 A US3669855 A US 3669855A US 6516 A US6516 A US 6516A US 3669855D A US3669855D A US 3669855DA US 3669855 A US3669855 A US 3669855A
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voltage
color
acid
anodizing
time
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Richard L Smith
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Kaiser Aluminum and Chemical Corp
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Kaiser Aluminum and Chemical Corp
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    • 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
    • C25D11/02—Anodisation
    • C25D11/04—Anodisation of aluminium or alloys based thereon
    • C25D11/14—Producing integrally coloured layers

Definitions

  • ABSTRACT A process for controlling an integral color anodizing process to minimize the effect of variations in electrolyte bath composition, temperature and the like upon the color of the anodic oxide coatings comprising developing a voltage-time relationship to obtain a desired color and controlling the anodizing process in accordance with the developed voltagetime relationship.
  • This resistance characteristic of the integrally colored anodic oxide coatings is to be distinguished from the resistance characteristics of clear or colorless anodizing in sulfuric acid electrolytes and the like which increases up to a certain value and remains substantially at this value or increases just slightly during the remainder of the anodizing process.
  • the oxide coatings produced in chromic acid electrolytes do exhibit a rapidly increasing resistance during the formation thereof but the color density of these coatings, which is very low, is not primarily voltage dependent.
  • chromic acid anodizing is normally not used to anodize aluminum for architectural purposes because of the very limited color range obtainable.
  • the aluminum workpiece is submerged in the electrolyte and subjected, as the anode, to electrolysis.
  • many electrical programs can be employed, only two are presently being commercially used to any extent. The most efficient is a two-step process comprising subjecting the workpiece to a substantially constant current density until a particular voltage is reached and then maintaining this voltage at a substantially constant level until the desired total current quantity has passed through the workpiece.
  • the elapsed time of the constant current density phase is commonly termed "time to peak" -that is, the time to reach peak voltage.
  • the other method comprises maintaining the substantially constant current density until the desired total current quantity has passed through the workpiece.
  • color control from batch to batch has been quite difi'icult due to the problems of controlling all the variables. This is particularly true over long periods of time due to the changes which occur within the controllable limits of bath composition.
  • the aluminum industry has placed stringent controls on the composition and thermal treatment of the aluminum workpiece. Similar controls have been placed on the initial and operating compositions of the electrolyte bath.
  • most anodizing installations have cation exchange devices for the removal of dissolved aluminum and periodically analyze the bath to determine the need of adding other components e.g., sulfuric acid and sulfosalicylic acid.
  • most anodizers attempt to control the temperature of the bath within 1 2 F by suitable refrigerating and heating means. However, due to the heat generation at the anodeelectrolyte interface, temperature gradients exist within the bath. The anodizers agitate the bath either mechanically or with air to minimize these gradients; however, agitation does not ensure a constant temperature at the interface of the electrolyte and the surface of the workpiece-the critical place for color generation.
  • anodizers have installed automatic control devices for maintaining the proper current density and peak voltage to eliminate human error in the operation of the anodizing program.
  • control of color is still technically a difficult task and the reject rate remains quite high.
  • anodizers must visually inspect the workpiece to determine whether the color thereof matches the standard color sought. This is particularly noticeable over long periods of time due to the buildup of decomposition products in the bath. As the decomposition products build up in the bath, the color of the oxide coating will not match the standard color sought. Due to the cost of the electrolyte, frequent replacement would be economically prohibitive.
  • the purpose of this invention is to provide a process for controlling the anodizing process wherein the effect of variations of workpiece composition and surface characteristics, bath composition and temperature and the like on the ultimate color of the anodic oxide coating are minimized.
  • This invention relates to a process for controlling the integral color anodia'ng process wherein reproducibility of the color of the oxide coating from anodizing load to anodizing load is substantially improved.
  • the invention is predicated upon the discovery of controlling the voltage across the electrolytic cell with respect to time in accordance with a preselected voltage-time relationship to obtain a particular color and thereby obtaining integrally colored anodic oxide coatings that will match from anodizing load to anodizing load despite variations in the workpiece composition and surface characteristics, the bath composition and temperature, and the like.
  • control process of the present invention eliminates the need for determining the surface area of the workpiece because the control program is based upon voltage which is not surface area dependent.
  • the prior art color anodizing technique required surface area determinations because the control was based on current density (amps/ft of workpiece surface).
  • current density amps/ft of workpiece surface.
  • the total current quantity should not vary from batch to batch, because the thickness of the oxide coating is dependent upon the total current quantity and the thickness of the coating affected the color.
  • the present invention was developed from the belief that the color generation of integral color anodizing processes is primarily dependent upon a dark band of anodic oxide immediately adjacent to the metallic substrate and below a relatively colorless oxide layer which is exposed to the atmosphere.
  • a slight golden or brownish hue permeates the entire oxide coating, but this hue has very little effect on the colored appearance of the anodized workpiece.
  • the colored appearance of the workpiece is a function of the color density and the thickness of the dark-band layer; however, the color density is primarily the color determinant.
  • the dark-band formation occurs only after a threshold voltage is reached, the level of which varies depending upon the bath composition, temperature, etc.
  • the color density, i.e., the lightness or darkness per unit thickness, of the dark band is primarily a function of voltage the higher the voltage the higher the color density (i.e., the darker becomes the oxide layer).
  • the total current quantity passed through the workpiece after the threshold voltage is reached determines the thickness of the dark-band layer, and thus to a certain extent the color of the workpiece, the effect of the total current quantity during that period is not as great as the effect of the voltage. Therefore, by controlling the voltage with respect to time, the color density is very reproducible and, although the current density and total current quantity will change from load to load, the change is insufi'icient magnitude to noticeably change the colored appearance of the anodized workpiece.
  • control process of the present invention avoids this problem allowing aluminum workpieces of all shapes and sizes to be anodized by the same control program to give identical colored oxide coatings.
  • This control of the present invention is advantageously obtained by developing a voltage-time relationship for a given bath composition and temperature and particular workpiece composition to give an anodic oxide coating with the desired color; transferring said relationship as data to a data storage means; retrieving said voltage-time data in the form of a signal and controlling the voltage impressed across the electrolytic cell with respect to time by means responsive to said signal.
  • F IG. 1 illustrates typical voltage-time and current densitytime relationships characteristics of a prior art two-step, constant current density-constant voltage, integral color anodizing program.
  • FIG. 2 illustrates typical voltage-time, current density time relationships characteristics of a prior art single-step, constant current density, integral color anodizing program.
  • FIG. 3 is a schematic diagram of a control system for controlling the integral color anodizing in accordance with the present invention.
  • FIG. 4 is a diagramatic view of an advantageous device for storing and retrieving voltage-time data.
  • a voltage-time relationship is developed for a particular aluminum alloy by anodizing an aluminum workpiece having the alloy composition, in accordance with known constant current density-constant voltage or constant current density programs for the particular alloy and bath composition to obtain the anodic oxide coating of the desired color and texture.
  • the voltage with respect to time is noted, either continually by automatic means, or periodically by manually noting the voltage at particular intervals oftime.
  • the voltage-time data is scribed on a Mylar card 1 coated with a conductive material.
  • the scribing removes the conductive material from the card, dividing the card into two electrically isolated conductive planes. in operation the two isolated planes are separately charged by oppositely phased AC voltages, by circuitry 2 establishing an electrostatic voltage gradient across the scribed voltage-time curve.
  • a probe 2 adjacent to, but specially disposed from, the card scans the card at a particular time based speed.
  • the prove picks up from the electrostatic field an error signal having a magnitude proportional to the probes deviation from the center of the program line.
  • a servo system comprising a servo amplifier 4 and a servo motor 5 responds to an error signal to correct the probe s deviation by rotating the shaft of an output potentiometer 6 which is mechanically connected to the probe by cable 7 and pulleys 8, 9 and 10.
  • the rotational movement of the potentiometer shaft varies the position of the wiper 11 thus varying the output of the potentiometer which is directly related to the voltage-time curve scribed on the conductive surfaces as measured from a base coordinate.
  • the output signal may then be conveniently employed as a reference signal for controlling the voltage impressed across the electrolytic cell because it is directly related to the voltage-time data stored on the card 1 measured from a base coordinate.
  • the system comprises a direct current source 20, a voltmeter 21, programmer or function generator 22, a comparator 23 and a control means 24 responsive to any error signal produced by the comparator 23 in conjunction with an electrolytic cell 30 with an anode 3i and cathode 32.
  • the DC source 20 normally comprises a rectifier and a suitable transforming device for converting alternating current to a relatively stable DC output.
  • the voltmeter 21 senses the voltage across the anode and cathode of the anodizing cell.
  • the comparator compares the measured cell voltage with the desired voltage represented by the signal from the programming or function generating means 22 and generates an error signal if the cell voltage does not correspond to the signal from programmer 22. Should an error signal exist, the controller 24 will adjust the DC source to provide the programmed voltage across the cell.
  • the voltmeter measures the voltage between the anode and an auxiliary electrode spaced a short distance from the anode. In this manner several anodizing tanks can be controlled by the same voltage-time program if the anode-electrode spacing is kept the same in each tank because the voltage drops in the bus bars, splines and the like are not included in the voltagetime program.
  • a 5005 aluminum alloy sheet was cut up to provide specimens for the integral color anodizing tests.
  • Three separate aqueous electrolytic baths were prepared having the compositions set forth in Table I.
  • EXAMPLE 1 To develop the required voltage-time relationship, a 5005 alloy specimen was subjected to anodizing in Bath No. 1 at a temperature of 25 C in accordance with a program known to give a light-amber color to this alloy.
  • the program comprised subjecting the specimen to a constant current density of 30 amps/ft until a voltage of 62 volts was obtained and then maintaining this voltage at a substantially constant level until a total current quantity of 10 amps-hours/ft passed through the specimen and the anodic oxide coating was 0.88 mils thick.
  • the anodizing the cell voltage was noted at short periodic intervals.
  • the voltage-time relationship obtained was scribed on a Data-Trak card.
  • EXAMPLE 2 Another 500$ specimen was subjected to anodization in Bath No. 2 at 20 C.
  • the anodizing program was the voltagetime relationship previously developed and stored on the Data-Trak card in Example I.
  • the anodizing was controlled by placing the previously scribed card into a model 5300 Data-Trak programmer, the output potentiometer of which controlled the cell voltage.
  • the color of the anodic oxide coating was a light amber which acceptably matched" the first 5005 specimen anodized to obtain the voltage-time relationship.
  • the oxide coating thickness was 0.70 mil.
  • EXAMPLE 3 A separate 5005 specimen was subjected to anodization in Bath No. 2 at a temperature of 25" C and controlled by the same Data-Trak card used in Example 1. The color of the anodic oxide coating "matched" both previously anodized samples. The oxide coating was 0.79 mil thick.
  • EXAMPLE 4 Another of the 5005 specimens was subjected to anodization in Bath No. 2 at a temperature of 30 C and controlled by the same Data-Trak card used in previous examples.
  • the color of the anodic oxide coating "matched the previously anodized samples.
  • the oxide thickness was 0.84 mil.
  • EXAMPLE 5 The test described in Example 2 was repeated using Bath No. 3 and resulting color of the anodized specimen matched" the other specimens. The oxide thickness was 0.78 mil.
  • EXAMPLE 6 The test described in Example 3 was repeated using Bath No. 3 and again the anodic oxide coating matched the other specimens. The oxide thickness was 0.82 mil.
  • EXAMPLE 7 The test described in Example 4 was repeated using Bath No. 3 and again the anodic oxide coating matched the others. The oxide thickness was 0.93 mil.
  • the instrumental color determinations of each of the abovementioned specimens are set forth in Table ll.
  • the Green Reflectance values generally indicate the lightness and dark ness of the specimen-the higher the value the lighter the color. An untrained eye usually cannot distinguish colors having a difference of Green Reflectance values of less than 2 reflectance units. For most architectural applications a variance of up to 3 units is acceptable.
  • the Green Reflectance values are obtained by measuring the reflectance of green light from the sample (a standard green filter is placed between the light source and the specimen), utilizing a standard tristimulus colorimeter. This system of color measurement is commonly termed the CIE system.
  • aluminum as used herein includes pure aluminum and aluminum base alloys containing more than 50 percent aluminum.
  • the electrolyte comprises an aqueous solution of 0.l to 2.0 percent sulfuric acid and a compound selected from the group consisting between about 5 and 30 percent by weight of an organic acid selected from the group consisting of sulfosalicylic acid, sulfophthalic acid, lignosulfonic acid, sulforesorcinol, oxalic acid, maleic acid, succinic acid and combinations thereof; and between 0.03 to 0.50 gram-mo! per liter of polyacid species selected from the group consisting of dichromates, molybdates, tungstates and vanadates.

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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)
  • Recording Measured Values (AREA)
  • Other Surface Treatments For Metallic Materials (AREA)
  • Electroplating And Plating Baths Therefor (AREA)
US6516A 1970-01-28 1970-01-28 Control of integral color anodizing process Expired - Lifetime US3669855A (en)

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US (1) US3669855A (en, 2012)
BE (1) BE762147A (en, 2012)
CA (1) CA921861A (en, 2012)
CH (1) CH545858A (en, 2012)
DE (1) DE2103980A1 (en, 2012)
FR (1) FR2077377B1 (en, 2012)
GB (1) GB1344192A (en, 2012)
NL (1) NL150857B (en, 2012)
ZA (1) ZA708645B (en, 2012)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3996125A (en) * 1974-05-02 1976-12-07 Riken Keikinzoku Kogyo Kabushiki Kaisha Apparatus for electrolytically processing aluminium material
US4478689A (en) * 1981-07-31 1984-10-23 The Boeing Company Automated alternating polarity direct current pulse electrolytic processing of metals
US4517059A (en) * 1981-07-31 1985-05-14 The Boeing Company Automated alternating polarity direct current pulse electrolytic processing of metals
US4666567A (en) * 1981-07-31 1987-05-19 The Boeing Company Automated alternating polarity pulse electrolytic processing of electrically conductive substances
US5066368A (en) * 1990-08-17 1991-11-19 Olin Corporation Process for producing black integrally colored anodized aluminum components
US9139926B2 (en) 2011-08-05 2015-09-22 Calphalon Corporation Process for making heat stable color anodized aluminum and articles formed thereby

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2324764A1 (fr) * 1975-09-19 1977-04-15 Kimura Shozo Procede de coloration par traitement anodique de l'aluminium et de ses alliages en un temps tres court
US5288372A (en) * 1992-07-07 1994-02-22 Alumax Inc. Altering a metal body surface

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US25566A (en) * 1859-09-27 Apparatus for washing- gas
US3098018A (en) * 1958-04-14 1963-07-16 Kaiser Aluminium Chem Corp Sealing anodized aluminum
CA736458A (en) * 1966-06-14 R. W. Smith Peter Anodising of aluminium and its alloys
US3280013A (en) * 1964-06-02 1966-10-18 Aluminum Co Of America Anodizing electrolyte and process
US3328274A (en) * 1966-11-25 1967-06-27 Kaiser Aluminium Chem Corp Method of anodizing aluminum
US3384561A (en) * 1965-02-15 1968-05-21 Olin Mathieson Process and electrolyte for coloring aluminum
US3486991A (en) * 1965-12-27 1969-12-30 Sumitomo Chemical Co Method of producing a colored anodic oxide film on aluminum

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US25566A (en) * 1859-09-27 Apparatus for washing- gas
CA736458A (en) * 1966-06-14 R. W. Smith Peter Anodising of aluminium and its alloys
US3098018A (en) * 1958-04-14 1963-07-16 Kaiser Aluminium Chem Corp Sealing anodized aluminum
US3280013A (en) * 1964-06-02 1966-10-18 Aluminum Co Of America Anodizing electrolyte and process
US3384561A (en) * 1965-02-15 1968-05-21 Olin Mathieson Process and electrolyte for coloring aluminum
US3486991A (en) * 1965-12-27 1969-12-30 Sumitomo Chemical Co Method of producing a colored anodic oxide film on aluminum
US3328274A (en) * 1966-11-25 1967-06-27 Kaiser Aluminium Chem Corp Method of anodizing aluminum

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
Appearance Control of Architectural Anodized Finishes by Bushey & Kissin, Jan. 31, 1968, pages 7, 10. *
The Surface Treatment and Finishing of Aluminum by Wernick et al., 1964, pages 351 352. *

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3996125A (en) * 1974-05-02 1976-12-07 Riken Keikinzoku Kogyo Kabushiki Kaisha Apparatus for electrolytically processing aluminium material
US4478689A (en) * 1981-07-31 1984-10-23 The Boeing Company Automated alternating polarity direct current pulse electrolytic processing of metals
US4517059A (en) * 1981-07-31 1985-05-14 The Boeing Company Automated alternating polarity direct current pulse electrolytic processing of metals
US4666567A (en) * 1981-07-31 1987-05-19 The Boeing Company Automated alternating polarity pulse electrolytic processing of electrically conductive substances
US5066368A (en) * 1990-08-17 1991-11-19 Olin Corporation Process for producing black integrally colored anodized aluminum components
WO1992003846A1 (en) * 1990-08-17 1992-03-05 Olin Corporation Anodized aluminum electronic package components
US5403975A (en) * 1990-08-17 1995-04-04 Olin Corporation Anodized aluminum electronic package components
US9139926B2 (en) 2011-08-05 2015-09-22 Calphalon Corporation Process for making heat stable color anodized aluminum and articles formed thereby

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ZA708645B (en) 1971-09-29
NL7101114A (en, 2012) 1971-07-30
GB1344192A (en) 1974-01-16
CA921861A (en) 1973-02-27
FR2077377B1 (en, 2012) 1975-01-17
CH545858A (en, 2012) 1974-02-15
DE2103980A1 (de) 1971-08-05
FR2077377A1 (en, 2012) 1971-10-22
NL150857B (nl) 1976-09-15
BE762147A (fr) 1971-07-27

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