CA1100087A - Process and apparatus for electrolytic colouration of anodised aluminium - Google Patents
Process and apparatus for electrolytic colouration of anodised aluminiumInfo
- Publication number
- CA1100087A CA1100087A CA220,430A CA220430A CA1100087A CA 1100087 A CA1100087 A CA 1100087A CA 220430 A CA220430 A CA 220430A CA 1100087 A CA1100087 A CA 1100087A
- Authority
- CA
- Canada
- Prior art keywords
- strip
- stage
- colouring
- electrolyte
- anodising
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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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
- C25D11/02—Anodisation
- C25D11/04—Anodisation of aluminium or alloys based thereon
- C25D11/18—After-treatment, e.g. pore-sealing
- C25D11/20—Electrolytic after-treatment
- C25D11/22—Electrolytic after-treatment for colouring layers
-
- 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
- C25D11/005—Apparatus specially adapted for electrolytic conversion coating
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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)
- Electrochemical Coating By Surface Reaction (AREA)
- Eyeglasses (AREA)
- Inorganic Insulating Materials (AREA)
- Rigid Containers With Two Or More Constituent Elements (AREA)
- Electrolytic Production Of Metals (AREA)
- Catalysts (AREA)
- Other Surface Treatments For Metallic Materials (AREA)
Abstract
ABSTRACT
A continuous length of aluminium is anodised during passage through an anodising electrolyte and then coloured during passage through an inorganic colouring electrolyte, in which a counterelectrode s immersed.
In the electrolytic colouring stage alternating current with a superimposed D.C. compound is preferably passed between the anodised aluminium and the counterelectrode when the electrolyte is appropriate for such treatment.
The alternating current circuit for the electrolytic colouring stage is preferably completed via an electrode immersed in the anodising electrolyte at a position facing substantially unanodised aluminium so as to effect a liquid contact.
A continuous length of aluminium is anodised during passage through an anodising electrolyte and then coloured during passage through an inorganic colouring electrolyte, in which a counterelectrode s immersed.
In the electrolytic colouring stage alternating current with a superimposed D.C. compound is preferably passed between the anodised aluminium and the counterelectrode when the electrolyte is appropriate for such treatment.
The alternating current circuit for the electrolytic colouring stage is preferably completed via an electrode immersed in the anodising electrolyte at a position facing substantially unanodised aluminium so as to effect a liquid contact.
Description
~l~QQ87 The present invention relate~ to colouring anodised aluminium b~ an alternating current electro-lytic treatment and in particular to a procedure in which a continuous strip of coloured anodised aluminium ma~ be produced.
It is well know~ that anodised aluminium ma~ ~e coloured by the passage of alternating current between the ~nodised aluminium and a counterelectrode immersed in an electrolyte, containing certain metallic compound~.
~he electrolyte may contain salts of nickel, cobalt, copper, tin, chromium, silver, iron, lead or a manganate, ! solenite or tellurite and is maintatned at an acid pH, dependent on the compound present i~ the bath. In some instances the bath contains salts of two or more metals, such as cobalt and nickel salts.
The operability of the process has always been explained on the a~sumption that, because of the bloc~ing effe¢t of the anodic oxide film, the total charge passin~
during the intervals when the aluminium is cathodic i8 great~r than when the aluminium i5 anodic, BO that the material deposited from the electrolyte during the cathodic intervals is greater than the amount re-dissolved during the anodic intervals. It has long been known that the pas~age of alternating current between anodised aluminium wor~pieces in these electrolytes j leads at best to very faint colours, because in such circumstances the waveform Or the current i8 sym-metrical.
When it i8 desired to colour a moving ~trip of anodised aluminium by the alternating current process~
it i8 obviousl~ desirable that there should bo no contQ¢t between the a~odised aluminium and a stationar~
electrode. It i8 well known in the continuous anodi-sation of aluminium ~trip to employ the bipolar or "liquid contact" s~tem. However, when that ~ystem i8 '~`
`:
I~OQQ87 employ,ed with an alternating current electrolytic colouring process, very little colour is produced.
The almost total lack of colour is believed to be due to the symmetrical nature of the waveform resulting from passing alternating current from a first elec-trode through the electrolyte to the anodised aluminium and from the anodised aluminium through the electrolyte to a second electrode remote from the first - electrode.
In order to overcome this difficulty, according to the present invention all the electrodes out of direct contact with the strip and facing an anodised surface in the electrolytic colouring stage are main-tained at the same polarity. Where the strip is anodised on both surfaces the alternating current circuit is completed either by means of a mechanical contact located at a position in advance of the develop-ment of the anodic film or by means of a liquid contact at a position where the anodic film is at most only partly developed. It follows that, in this procedure, the colouring of the continuous strip is performed in line with the anodic oxidation stage.
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Thus, according to one feature of the invention there is provided a method of producing a coloured anodised alumin-ium strip which comprises drawing aluminium in strip form successively through an anodic oxidation treatment cell and an electrolytic colouring.cell to carry out electrolysis in said cells to anodize and color the material, characterized in that just prior to the anodizing~stage, a circuit is formed by commonly connecting to the aluminum material a power source for anodizing and a power source for electrolytically colouring, said power source for anodizing being further con-nected to the electrolytic colouring cell; said power source for anodizing being. a current to anodize the aluminum mater-ial in the anodizing cell and said power source for electro-lytically colouring being a current having an alternating wave form to colour the aluminium material in the colouring cell.
According to a further feature of the invention there is provided a method of producing a coloured anodised aluminium strip which comprises drawing aluminium in strip form successively through an anodic oxidation treatment cell and an electrolytic colouring cell to carry out electrolysis in said cells to anodize and color the material, characterized in that just prior to the anodizing stage, a circuit is formed by commonly connecting~to the aluminum material a power source for anodizing and a power source for electrolytically colouring, said power source for anodizing being further connected to the anodizing cell and said power source for electrolytically colouring being further connected to the electrolytic colouring cell; said power source for anodizing being a current to anodize the aluminum material in the anodizing cell and said power source for electrolytically colouring being a current having a~ alternating.wave form to colour the aluminium material in the colouring cell.
-3a-1~9~7 ~here the strip is anodised on one surface only, it is of course possib e tO co~lplete the alternat- ;
in~ current circuit by means of electrodes in direct contact with the unanodised surface of the strip or S facing the unanodised surface, so that the electrolytic colourin~ may be performed iIl line t~ith the anodic oxidation stage or, if desired, an already anodised continuous strip, anodised on one face only, may be coloured.
With certain colouring electrolytes, parti-cularly I~i, Sn and Co salts, it has already been found hi~hly beneficial to superimpose a D.C component on the alternating current in batch processes for 110~7 colouring anodised aluminium articles. With the above electrolytes it has been found that the superimposed D.C. component leads to more rapid colouring. With the other electrolytes listed above, superimposed D.C.
has little or no advantage and may indeed be disad-vantageous.
In one arrangement in accordance with the presont invention the superimposition of a D.C. compon-ent is very conveniently achieved in an apparatus in ; 10 which both faces of the strip are anodised in a preceding D.C. continuous anodising stage.
~ he D.C. component is preferably of such a ~ magnitude that the average current in the portion of '~ the cycle when the strip is cathodic in the electro-lytic colouring bath is 2-10 times, preferably 3-6 times, greater than the average current when the strip i8 anodic. ~he superimposed D.C. component may con-veniently be derived from the rectifier system employed for the anodising stage, where the D.C. current is i introduced into the strip in the anodiæing stage by means of longitudinally ~paced cathodes and anodes, using the "liquid contact" technique.
We have described in Canadian Patent No.
809,640 a method of conti~uously anodising aluminium strip, in which the strip whilst immersed in a turbulent ~tream of sulphuric acid electrolyte first passes one or more anodes to render cathodic that part of the surface facing the anodes and then pas~es a series of Gathodes, longitudinally spaced from the anode or anodes, to render the facing surface anodic in relation to the cathodes. ~he arrangement described ~n that prior patent is very~ conveniently employed for the anodic oxidation ætage in the present invention, when both faces of the strip are to be coloured.
~5 Conveniently the alternating current circuit for the electrolytic colouring is completed via the anodising cell anodes, since this results in a small portion of the direct current flowing from the counterelectrodes in the electrolytic colouring stage through the strip to the anodising cell cathodes.
Referring now to the accompanying drawir,gs :-~igure 1 is a schematic arrangement of an apparatus for continuous production of anodised and coloured aluminium strip, ~igure 2 is a schematic of the D.C. circuit in Figure 1, Figure 3 i8 a schematic of the D.C. circuit of a modification of Figure 1, ~igure 4 is a schematic arrangement for contin-uous anodising and colouring one surface of aluminium strip, and ~igure 5 is a schematic of an alternative arrangement for anodising and colouring both surfaces of an aluminium strip.
In Figure 1 aluminium strip is drawn from a supply reel (~ot shown) into an anodising cell of the type described in Canadian Patent ~o. 809,640, into which a stream of sulphuric acid electrolyte, for example 15%
sulphuric acid, is supplied through inlets 2 and with-drawn through outlets 3 for recirculation. The cell 1 is shown as having five pairs of spaced electrodeæ 4.
For perform~nce of the anodising operation the first two pairs of electrodes 4 are connected to the positive of a rectifier assembly 5 and the remaining three pairs of electrodes 4 are connected to the negative. Other anodising electrolytes, such as oxalic acid or chromic acid, may be employed in the anodising cell in place of sulphuric acid.
After leaving the anodising stage the now ~l~Q~87 anodised strip is passed through a rinsing stage, shown diagrammatically at 6, which serves to remove the 8ul-phuric acid electrolyte. ~he strip then enters the electrolytic colouring cell 7 in which it passes between an array of counterelectrodes 8. ~he counter-;~ electrodes 8 are connected to one terminal of a variable voltage A.C. supply 9, the other terminal of which is connected to the anode electrodes 4 in the cell 1, from which current flows to a substantially unanodised portion of the surface of the aluminium strip.
Considering Figure 2, the resistances R1, R2, R3 are the resistances of the current path~ between the strip and the counterelectrodes 8, the strip and the ; 15 cathodes 4, the strip and the anodes 4 respectively.
' Because of the growth of the anodic oxide film in the cell 1 and the lower conductivity of the electrolyte in , the colouring stage (as compared with the anodising -I stage), R1~ R2~ R3, and in consequence it will be seen that the D.C. current i1 in the electrol~tic colouring stage will be much smaller than the D.C. cuxrent employed in the anodising stage.
In one example the anodising cell 1 had a length of 12 feet and the colouring cell 7 had a length of 9 feet. ~he strip (2 inch wide) was drawn through at a speed of 12 ft./min. to give a dwell time of 1 minute in the anodising stage and 45 seconds in the colouring stage. Using a 1~/o sulphuric acid electrolyte at 60C, a D.C. voltage of 25 volts was found to produce an ~0 anodic film of 5 microns thickne~s at a total current of 500 amps. It was found possible to provide a desirable dark bronze colour in this film with an A.C.
current of 30 amps in 45 seconds dwell time in the cell 7, which contained the following nickel electrolyte:-Ni~04 7~2 25 gpl (NH4)2S04 15 Mg~o4~7H2o 20 ~3B03 25 pH 5.7 Alternatively other known baths, such as those contain-ing salts of tin or cobalt, for electrolytic colouring of anodic aluminium oxide films by means of alternating current with superimposed direct current may be employed.
~ he counterelectrodes 8 were formed of lead strips and had a dimension in the direction of strip tra~el of two inches. In the system arranged as des-cribed above the ratio of the average cathodic current to the average anodic current in the cell 7 was esti-mated at about 4:1 by measuring the areas under the curve of oscillograms.
In the modified arrangement shown in Figure 3, Rl and R2 have the same signific~lce as in ~igure 2.
R4 and R14 are respectively the resist~nce of the path between the strip and the first pair of electrodes 4 and between the strip and the second pair of elec-trodes 4. In this arrangement the variable resistance R5 is connected in the conductor 10 in Figure 1. As will be seen, this arrangement enables the D.G. current in the cell 7 to be ~aried by appropriate ad3ustment of resistor X5. If conductor 10 is disconnected, the resistance R5 becomes infinite and there is no ~.C.
component superimposed on the alternating current in the electrolytic colouring stage.
In another example the apparatus of Fi~ure 1 is operated with no interco~nection between the two pairs of anodes 4 when e~ploying a copper electrolyte in the electrocolouring stage. The anodisation was performed ~5 under the same conditions as in the precedin~; example, }Q87 but no superimposed D.C. was employed i~ the electro-lytic colouring sta~e. It was found possible to obtain a desirable maroon shade in this film with an A.C.
current of 27 amps at 23 volts in 45 seconds dwell time with a copper-containing electrolyte having the following composition :-~uS04.5~20 35 gpl MgS04.7H20 20 gplp~ brought to 1.3 by addition of sulphuric acid.
One known system for anodisin~ one surface of an aluminium strip is described in U.S. Patent No.
3,296,114. ~n anodising cell 11 operating on that system is illustrated diagrammatically in Figure 4. In the anodising cell 11 the reverse face of the strip is in contact with a carbon brush 12 connected to the positive terminal of a D.C. supply and a cathode 14 is connected to the negative terminal. ~he electrolyte is showered onto the strip through a perforated screen, the streams of electrolyte constituting the current path between the cathode 14 and the strip, which is brought into a somewhat surved ~rofile during it~ passage through the cell so as to avoid much contact between the electrolyte and the reverse surface of the strip.
~he electrolytic colouring is carried out in a similar cell 16. The alternating current circuit for the electrolytic colouring operation is then completed between the electrode 12 and a counterlectrode 15 in the electrolytic colouring bath 17~ It is preferable to superimpose a ~C. component on the current flowing in the ~.C~ circuit thus constituted, when an appro-priate electrolyte is employed in the electrocolouring stage.
In an alternative arran~ement a car~on elec-trode in contact with the unanodised side o~` the strip llQ~7 in the cell 16 may be employed in addition to theelectrode 12. In this case the A.C. circuit is com-pleted through this second carbon electrode. However the arrangement illustrated in Figure 4 is preferred for reasons of economy since these carbon brushes become worn by contact with the strip and require periodic replacement.
Figure 5 illustrates an arrangement for continuous anodisation and electrolytic colouring of aluminium strip where a contact roll is employed for introducing current into the strip in the anodisation stage. In this arrangement the contact roll 21 is connected to the positive terminal of a D.C. supply and cathodes 23 in an anodisation cell 22 are connected to the negative terminal. The roll 21, which is in contact with unanodised aluminium, is connected to one terminal of an A.C. supply having a superimposed D.C.
component, whilst the opposite terminal is connected to the counterelectrodes 8 of the electrolytic colouring 2C cell 7.
One means for generating ~.C. with an 8sym-metrical waveform (equivalent to A.C. with a superimposed D.C. component) is shown in Figure 5 and is comprised of a transformer 24 connected with diodes 25 as shown.
Since there is a voltage drop of the order of 2 volts across each diode 25, more current can be caused to flow in the half cycle in which the strip is cathodic in cell 7 than in the half cycle in which it is anodic.
In some circumstances it may be desirable to operate the electrolytic colouring stage with pure D.C.
current. In such case the A.C. component may be elimin-ated and the ratio of D.C. to A.C. becomes infinite.
It is well know~ that anodised aluminium ma~ ~e coloured by the passage of alternating current between the ~nodised aluminium and a counterelectrode immersed in an electrolyte, containing certain metallic compound~.
~he electrolyte may contain salts of nickel, cobalt, copper, tin, chromium, silver, iron, lead or a manganate, ! solenite or tellurite and is maintatned at an acid pH, dependent on the compound present i~ the bath. In some instances the bath contains salts of two or more metals, such as cobalt and nickel salts.
The operability of the process has always been explained on the a~sumption that, because of the bloc~ing effe¢t of the anodic oxide film, the total charge passin~
during the intervals when the aluminium is cathodic i8 great~r than when the aluminium i5 anodic, BO that the material deposited from the electrolyte during the cathodic intervals is greater than the amount re-dissolved during the anodic intervals. It has long been known that the pas~age of alternating current between anodised aluminium wor~pieces in these electrolytes j leads at best to very faint colours, because in such circumstances the waveform Or the current i8 sym-metrical.
When it i8 desired to colour a moving ~trip of anodised aluminium by the alternating current process~
it i8 obviousl~ desirable that there should bo no contQ¢t between the a~odised aluminium and a stationar~
electrode. It i8 well known in the continuous anodi-sation of aluminium ~trip to employ the bipolar or "liquid contact" s~tem. However, when that ~ystem i8 '~`
`:
I~OQQ87 employ,ed with an alternating current electrolytic colouring process, very little colour is produced.
The almost total lack of colour is believed to be due to the symmetrical nature of the waveform resulting from passing alternating current from a first elec-trode through the electrolyte to the anodised aluminium and from the anodised aluminium through the electrolyte to a second electrode remote from the first - electrode.
In order to overcome this difficulty, according to the present invention all the electrodes out of direct contact with the strip and facing an anodised surface in the electrolytic colouring stage are main-tained at the same polarity. Where the strip is anodised on both surfaces the alternating current circuit is completed either by means of a mechanical contact located at a position in advance of the develop-ment of the anodic film or by means of a liquid contact at a position where the anodic film is at most only partly developed. It follows that, in this procedure, the colouring of the continuous strip is performed in line with the anodic oxidation stage.
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Thus, according to one feature of the invention there is provided a method of producing a coloured anodised alumin-ium strip which comprises drawing aluminium in strip form successively through an anodic oxidation treatment cell and an electrolytic colouring.cell to carry out electrolysis in said cells to anodize and color the material, characterized in that just prior to the anodizing~stage, a circuit is formed by commonly connecting to the aluminum material a power source for anodizing and a power source for electrolytically colouring, said power source for anodizing being further con-nected to the electrolytic colouring cell; said power source for anodizing being. a current to anodize the aluminum mater-ial in the anodizing cell and said power source for electro-lytically colouring being a current having an alternating wave form to colour the aluminium material in the colouring cell.
According to a further feature of the invention there is provided a method of producing a coloured anodised aluminium strip which comprises drawing aluminium in strip form successively through an anodic oxidation treatment cell and an electrolytic colouring cell to carry out electrolysis in said cells to anodize and color the material, characterized in that just prior to the anodizing stage, a circuit is formed by commonly connecting~to the aluminum material a power source for anodizing and a power source for electrolytically colouring, said power source for anodizing being further connected to the anodizing cell and said power source for electrolytically colouring being further connected to the electrolytic colouring cell; said power source for anodizing being a current to anodize the aluminum material in the anodizing cell and said power source for electrolytically colouring being a current having a~ alternating.wave form to colour the aluminium material in the colouring cell.
-3a-1~9~7 ~here the strip is anodised on one surface only, it is of course possib e tO co~lplete the alternat- ;
in~ current circuit by means of electrodes in direct contact with the unanodised surface of the strip or S facing the unanodised surface, so that the electrolytic colourin~ may be performed iIl line t~ith the anodic oxidation stage or, if desired, an already anodised continuous strip, anodised on one face only, may be coloured.
With certain colouring electrolytes, parti-cularly I~i, Sn and Co salts, it has already been found hi~hly beneficial to superimpose a D.C component on the alternating current in batch processes for 110~7 colouring anodised aluminium articles. With the above electrolytes it has been found that the superimposed D.C. component leads to more rapid colouring. With the other electrolytes listed above, superimposed D.C.
has little or no advantage and may indeed be disad-vantageous.
In one arrangement in accordance with the presont invention the superimposition of a D.C. compon-ent is very conveniently achieved in an apparatus in ; 10 which both faces of the strip are anodised in a preceding D.C. continuous anodising stage.
~ he D.C. component is preferably of such a ~ magnitude that the average current in the portion of '~ the cycle when the strip is cathodic in the electro-lytic colouring bath is 2-10 times, preferably 3-6 times, greater than the average current when the strip i8 anodic. ~he superimposed D.C. component may con-veniently be derived from the rectifier system employed for the anodising stage, where the D.C. current is i introduced into the strip in the anodiæing stage by means of longitudinally ~paced cathodes and anodes, using the "liquid contact" technique.
We have described in Canadian Patent No.
809,640 a method of conti~uously anodising aluminium strip, in which the strip whilst immersed in a turbulent ~tream of sulphuric acid electrolyte first passes one or more anodes to render cathodic that part of the surface facing the anodes and then pas~es a series of Gathodes, longitudinally spaced from the anode or anodes, to render the facing surface anodic in relation to the cathodes. ~he arrangement described ~n that prior patent is very~ conveniently employed for the anodic oxidation ætage in the present invention, when both faces of the strip are to be coloured.
~5 Conveniently the alternating current circuit for the electrolytic colouring is completed via the anodising cell anodes, since this results in a small portion of the direct current flowing from the counterelectrodes in the electrolytic colouring stage through the strip to the anodising cell cathodes.
Referring now to the accompanying drawir,gs :-~igure 1 is a schematic arrangement of an apparatus for continuous production of anodised and coloured aluminium strip, ~igure 2 is a schematic of the D.C. circuit in Figure 1, Figure 3 i8 a schematic of the D.C. circuit of a modification of Figure 1, ~igure 4 is a schematic arrangement for contin-uous anodising and colouring one surface of aluminium strip, and ~igure 5 is a schematic of an alternative arrangement for anodising and colouring both surfaces of an aluminium strip.
In Figure 1 aluminium strip is drawn from a supply reel (~ot shown) into an anodising cell of the type described in Canadian Patent ~o. 809,640, into which a stream of sulphuric acid electrolyte, for example 15%
sulphuric acid, is supplied through inlets 2 and with-drawn through outlets 3 for recirculation. The cell 1 is shown as having five pairs of spaced electrodeæ 4.
For perform~nce of the anodising operation the first two pairs of electrodes 4 are connected to the positive of a rectifier assembly 5 and the remaining three pairs of electrodes 4 are connected to the negative. Other anodising electrolytes, such as oxalic acid or chromic acid, may be employed in the anodising cell in place of sulphuric acid.
After leaving the anodising stage the now ~l~Q~87 anodised strip is passed through a rinsing stage, shown diagrammatically at 6, which serves to remove the 8ul-phuric acid electrolyte. ~he strip then enters the electrolytic colouring cell 7 in which it passes between an array of counterelectrodes 8. ~he counter-;~ electrodes 8 are connected to one terminal of a variable voltage A.C. supply 9, the other terminal of which is connected to the anode electrodes 4 in the cell 1, from which current flows to a substantially unanodised portion of the surface of the aluminium strip.
Considering Figure 2, the resistances R1, R2, R3 are the resistances of the current path~ between the strip and the counterelectrodes 8, the strip and the ; 15 cathodes 4, the strip and the anodes 4 respectively.
' Because of the growth of the anodic oxide film in the cell 1 and the lower conductivity of the electrolyte in , the colouring stage (as compared with the anodising -I stage), R1~ R2~ R3, and in consequence it will be seen that the D.C. current i1 in the electrol~tic colouring stage will be much smaller than the D.C. cuxrent employed in the anodising stage.
In one example the anodising cell 1 had a length of 12 feet and the colouring cell 7 had a length of 9 feet. ~he strip (2 inch wide) was drawn through at a speed of 12 ft./min. to give a dwell time of 1 minute in the anodising stage and 45 seconds in the colouring stage. Using a 1~/o sulphuric acid electrolyte at 60C, a D.C. voltage of 25 volts was found to produce an ~0 anodic film of 5 microns thickne~s at a total current of 500 amps. It was found possible to provide a desirable dark bronze colour in this film with an A.C.
current of 30 amps in 45 seconds dwell time in the cell 7, which contained the following nickel electrolyte:-Ni~04 7~2 25 gpl (NH4)2S04 15 Mg~o4~7H2o 20 ~3B03 25 pH 5.7 Alternatively other known baths, such as those contain-ing salts of tin or cobalt, for electrolytic colouring of anodic aluminium oxide films by means of alternating current with superimposed direct current may be employed.
~ he counterelectrodes 8 were formed of lead strips and had a dimension in the direction of strip tra~el of two inches. In the system arranged as des-cribed above the ratio of the average cathodic current to the average anodic current in the cell 7 was esti-mated at about 4:1 by measuring the areas under the curve of oscillograms.
In the modified arrangement shown in Figure 3, Rl and R2 have the same signific~lce as in ~igure 2.
R4 and R14 are respectively the resist~nce of the path between the strip and the first pair of electrodes 4 and between the strip and the second pair of elec-trodes 4. In this arrangement the variable resistance R5 is connected in the conductor 10 in Figure 1. As will be seen, this arrangement enables the D.G. current in the cell 7 to be ~aried by appropriate ad3ustment of resistor X5. If conductor 10 is disconnected, the resistance R5 becomes infinite and there is no ~.C.
component superimposed on the alternating current in the electrolytic colouring stage.
In another example the apparatus of Fi~ure 1 is operated with no interco~nection between the two pairs of anodes 4 when e~ploying a copper electrolyte in the electrocolouring stage. The anodisation was performed ~5 under the same conditions as in the precedin~; example, }Q87 but no superimposed D.C. was employed i~ the electro-lytic colouring sta~e. It was found possible to obtain a desirable maroon shade in this film with an A.C.
current of 27 amps at 23 volts in 45 seconds dwell time with a copper-containing electrolyte having the following composition :-~uS04.5~20 35 gpl MgS04.7H20 20 gplp~ brought to 1.3 by addition of sulphuric acid.
One known system for anodisin~ one surface of an aluminium strip is described in U.S. Patent No.
3,296,114. ~n anodising cell 11 operating on that system is illustrated diagrammatically in Figure 4. In the anodising cell 11 the reverse face of the strip is in contact with a carbon brush 12 connected to the positive terminal of a D.C. supply and a cathode 14 is connected to the negative terminal. ~he electrolyte is showered onto the strip through a perforated screen, the streams of electrolyte constituting the current path between the cathode 14 and the strip, which is brought into a somewhat surved ~rofile during it~ passage through the cell so as to avoid much contact between the electrolyte and the reverse surface of the strip.
~he electrolytic colouring is carried out in a similar cell 16. The alternating current circuit for the electrolytic colouring operation is then completed between the electrode 12 and a counterlectrode 15 in the electrolytic colouring bath 17~ It is preferable to superimpose a ~C. component on the current flowing in the ~.C~ circuit thus constituted, when an appro-priate electrolyte is employed in the electrocolouring stage.
In an alternative arran~ement a car~on elec-trode in contact with the unanodised side o~` the strip llQ~7 in the cell 16 may be employed in addition to theelectrode 12. In this case the A.C. circuit is com-pleted through this second carbon electrode. However the arrangement illustrated in Figure 4 is preferred for reasons of economy since these carbon brushes become worn by contact with the strip and require periodic replacement.
Figure 5 illustrates an arrangement for continuous anodisation and electrolytic colouring of aluminium strip where a contact roll is employed for introducing current into the strip in the anodisation stage. In this arrangement the contact roll 21 is connected to the positive terminal of a D.C. supply and cathodes 23 in an anodisation cell 22 are connected to the negative terminal. The roll 21, which is in contact with unanodised aluminium, is connected to one terminal of an A.C. supply having a superimposed D.C.
component, whilst the opposite terminal is connected to the counterelectrodes 8 of the electrolytic colouring 2C cell 7.
One means for generating ~.C. with an 8sym-metrical waveform (equivalent to A.C. with a superimposed D.C. component) is shown in Figure 5 and is comprised of a transformer 24 connected with diodes 25 as shown.
Since there is a voltage drop of the order of 2 volts across each diode 25, more current can be caused to flow in the half cycle in which the strip is cathodic in cell 7 than in the half cycle in which it is anodic.
In some circumstances it may be desirable to operate the electrolytic colouring stage with pure D.C.
current. In such case the A.C. component may be elimin-ated and the ratio of D.C. to A.C. becomes infinite.
Claims (14)
1. A method of producing a coloured anodised aluminium strip which comprises drawing aluminium in strip form successively through an anodising electrolyte and an acidic colouring electrolyte containing a material selected from a salt of at least one of copper, tin, cobalt, nickel, chromium, iron, silver or lead or a manganate, tellurite or selenite, passing direct current between said strip and at least one cathode immersed in said anodising electrolyte, direct current being introduced into said strip from a positive electrode at a location where said strip is substantially unanodised and passing alternating current between the anodised strip and at least one electrode immersed in the colouring electrolyte, the circuit for the alternating current being completed by contact with a substantially unanodised area of the surface of the aluminium strip.
2. A method of producing a coloured anodised aluminium strip according to claim 1 in which a direct current component is superimposed on the alternating current in the electrolytic colouring stage.
3. A method of producing a coloured anodised aluminium strip which comprises drawing aluminium in strip form successively through an anodising stage and an electrolytic colouring stage comprising in the anodising stage moving the strip successively past one or more anodes immersed in a sulphuric acid anodising electrolyte and past one or more cathodes and passing direct current between said cathodes and said anodes through the strip so as to render the strip initially cathodic and subsequently anodic to develop an anodic oxide film on the surface thereof, the thus anodised strip being then passed through, in said electrolytic colouring stage, an acidic electrolyte containing a material selected from a salt of at least one of copper, tin, cobalt, nickel, chromium, iron, silver or lead or a manganate, tellurite or selenite, and passing alternating current between at least one electrode immersed in said acidic electrolyte and said anodised strip,the circuit for said alternating current being completed through an electrode immersed in the electrolyte of the direct current anodising stage.
4. A method according to claim 3 in which a direct current component is superimposed on the alternating current in the electrolytic colouring stage.
5. A method according to claim 4 in which an alternating current source is connected between an anode of the anodising stage and the electrode in the electrolytic colouring stage whereby a direct current component is superimposed on the alternating current in the electrolytic colouring stage.
6. A method according to claim 1 in which the unanodised strip is, before entry into the anodisation stage, in contact with a contact roll connected to the positive terminal of said direct current supply and an alternating current source is connected between said contact roll and the electrode n the colouring electrolyte.
7. A method according to claim 6 in which in the connection between the contact roll and the colouring electrolyte electrode there are included diode branches in parallel, the diodes in said branches being conductive in opposite directions, the voltage drops across said diode branches when conductive being unequal whereby to generate an asymmetrical alternating current.
8. A method according to claim 1 wherein the circuits for both the alternating current and the direct current are completed by contact with the same substantially unanodised area of the strip surface, and wherein the density of said alternating current is a minor fraction of the density of said direct current.
9. A method of producing a coloured anodised aluminium strip which comprises drawing aluminium in strip form through an anodising stage, contacting the strip with a sulphuric acid electrolyte in said anodising stage, said strip being drawn successively past at least one anode electrode and at least one cathode electrode, a D.C.
power source being established between said anode electrode and said cathode electrode whereby said strip is rendered initially cathodic and subsequently anodic during its passage through said anodising stage, advancing the thus anodised strip to and through an electrolytic colouring stage, contacting said strip with an acidic electrolyte containing a material selected from a salt of at least one of copper, tin, cobalt, nickel, chromium, iron, silver or lead or a manganate, tellurite or selenite and establishing an A.C. power source between said anode electrode in said anodising stage and a counterelectrode in contact with the electrolyte in the electrocolouring stage there-by to establish alternating current with a superimposed D.C. current component flowing between said anodised strip and said counterelectrode in the electrocolouring stage.
power source being established between said anode electrode and said cathode electrode whereby said strip is rendered initially cathodic and subsequently anodic during its passage through said anodising stage, advancing the thus anodised strip to and through an electrolytic colouring stage, contacting said strip with an acidic electrolyte containing a material selected from a salt of at least one of copper, tin, cobalt, nickel, chromium, iron, silver or lead or a manganate, tellurite or selenite and establishing an A.C. power source between said anode electrode in said anodising stage and a counterelectrode in contact with the electrolyte in the electrocolouring stage there-by to establish alternating current with a superimposed D.C. current component flowing between said anodised strip and said counterelectrode in the electrocolouring stage.
10. A method according to claim 9 in which said strip successively passes a first anode and a second anode longitudinally spaced from said first anode in the anodising stage, said anodes being connected in parallel to said A.C. power source, further including establishing a higher resistance path between said A.C. power source and said second anode than the path between said A.C. power source and said first anode.
11. A method according to claim 1, wherein the alternating-current-passing step comprises passing alternating current through the strip between at least one electrode immersed in the colouring electrolyte and out of contact with said strip and at least one electrode immersed in the anodising electrolyte and facing a substantially unanodised area of said strip.
12. A method of producing a coloured anodised aluminium strip which comprises drawing aluminium in strip form successively through an anodic oxidation treatment cell and an electrolytic colouring cell to carry out electrolysis in said cells to anodize and color the material, characterized in that just prior to the anodiz-ing stage, a circuit is formed by commonly connecting to the aluminum material a power source for anodizing and a power source for electrolytically colouring, said power source for anodizing being further connected to the anodizing cell and said power source for electrolytically colouring being further connected to the electrolytic colouring cell; said power source for anodizing being a current to anodize the aluminum material in the anodizing cell and said power source for electrolytically colouring being a current having an alternating wave form to colour the aluminium material in the colouring cell.
13. The method according to claim 12 wherein a direct current voltage is applied between an electric power supply element outside the anodic oxidation treatment cell and an electrode plate within said cell and an alternating current voltage is applied between said element and an electrode plate within the electrolytic colouring cell.
14. The method according to claim 12 wherein the aluminum material is charged with a current having an alternating wave form rich in cathodic component in the electrolytic colouring cell.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB780774A GB1434701A (en) | 1974-02-20 | 1974-02-20 | Process and apparatus for electrolytic colouration of anodised aluminium |
| GB7807/74 | 1974-02-20 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1100087A true CA1100087A (en) | 1981-04-28 |
Family
ID=9840126
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA220,430A Expired CA1100087A (en) | 1974-02-20 | 1975-02-19 | Process and apparatus for electrolytic colouration of anodised aluminium |
Country Status (15)
| Country | Link |
|---|---|
| JP (1) | JPS5629759B2 (en) |
| BE (1) | BE825619A (en) |
| BR (1) | BR7501022A (en) |
| CA (1) | CA1100087A (en) |
| CH (1) | CH597375A5 (en) |
| DE (1) | DE2507063C3 (en) |
| DK (1) | DK61175A (en) |
| ES (1) | ES434852A1 (en) |
| FR (1) | FR2261353B1 (en) |
| GB (1) | GB1434701A (en) |
| IT (1) | IT1031829B (en) |
| NL (1) | NL168889C (en) |
| NO (1) | NO139447C (en) |
| SE (1) | SE408310B (en) |
| ZA (1) | ZA75855B (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1518979A (en) * | 1974-11-19 | 1978-07-26 | Sumitomo Aluminium Smelting Co | Process for continuous electrolytic colouring of almuminium or aluminum base alloy strip and wire |
| FR2542766B1 (en) * | 1983-03-16 | 1987-07-03 | Cegedur | METHOD AND DEVICE FOR ELECTROCHEMICAL TREATMENT OF THE SURFACE OF METALLIC PRODUCTS OF ELONGATE FORM |
| JPS59219669A (en) * | 1983-05-27 | 1984-12-11 | 松下精工株式会社 | Heat pump air conditioner |
| CN107268057B (en) * | 2017-06-14 | 2023-07-04 | 江苏昊科汽车空调有限公司 | Maintenance method for aluminum alloy hard anodic oxidation electrolyte |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR901105A (en) * | 1943-06-11 | 1945-07-18 | Alais & Froges & Camarque Cie | Process for the continuous electrolytic oxidation of metal wires, bands and the like |
| US2755238A (en) * | 1955-03-25 | 1956-07-17 | Sprague Electric Co | Electrolytic etching and oxidizing of aluminum |
| DE1902983C3 (en) * | 1968-06-21 | 1978-06-22 | Keller, Eberhard, 7121 Freudental | Process for the electrolytic coloring of anodic oxide layers on aluminum or aluminum alloys |
-
1974
- 1974-02-20 GB GB780774A patent/GB1434701A/en not_active Expired
-
1975
- 1975-02-11 ZA ZA00750855A patent/ZA75855B/en unknown
- 1975-02-17 BE BE153424A patent/BE825619A/en not_active IP Right Cessation
- 1975-02-18 FR FR7504963A patent/FR2261353B1/fr not_active Expired
- 1975-02-18 IT IT20383/75A patent/IT1031829B/en active
- 1975-02-19 NO NO750565A patent/NO139447C/en unknown
- 1975-02-19 SE SE7501837A patent/SE408310B/en not_active IP Right Cessation
- 1975-02-19 DK DK61175*#A patent/DK61175A/da not_active Application Discontinuation
- 1975-02-19 CH CH207575A patent/CH597375A5/xx not_active IP Right Cessation
- 1975-02-19 DE DE2507063A patent/DE2507063C3/en not_active Expired
- 1975-02-19 CA CA220,430A patent/CA1100087A/en not_active Expired
- 1975-02-19 BR BR1022/75A patent/BR7501022A/en unknown
- 1975-02-19 ES ES434852A patent/ES434852A1/en not_active Expired
- 1975-02-19 JP JP2078975A patent/JPS5629759B2/ja not_active Expired
- 1975-02-20 NL NLAANVRAGE7502023,A patent/NL168889C/en active
Also Published As
| Publication number | Publication date |
|---|---|
| AU7813275A (en) | 1976-08-12 |
| ES434852A1 (en) | 1977-03-01 |
| CH597375A5 (en) | 1978-03-31 |
| NO139447C (en) | 1979-03-14 |
| DE2507063A1 (en) | 1975-08-21 |
| JPS50119735A (en) | 1975-09-19 |
| DE2507063C3 (en) | 1984-08-23 |
| NO750565L (en) | 1975-08-21 |
| NL168889C (en) | 1982-05-17 |
| SE408310B (en) | 1979-06-05 |
| ZA75855B (en) | 1976-01-28 |
| DE2507063B2 (en) | 1978-03-30 |
| DK61175A (en) | 1975-10-20 |
| BR7501022A (en) | 1975-12-02 |
| JPS5629759B2 (en) | 1981-07-10 |
| NO139447B (en) | 1978-12-04 |
| BE825619A (en) | 1975-08-18 |
| IT1031829B (en) | 1979-05-10 |
| NL7502023A (en) | 1975-08-22 |
| SE7501837L (en) | 1975-08-21 |
| FR2261353B1 (en) | 1982-03-19 |
| FR2261353A1 (en) | 1975-09-12 |
| GB1434701A (en) | 1976-05-05 |
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