DEVICE INTENDED FOR IMPLEMENTING AN ANODIZATION TREATMENT
AND ANODIZATION TREATMENT
Background of the invention
The invention relates to devices for performing
anodizing treatment, preferably micro arc anodizing
treatment, and i,t also relates to associated methods.
It is known to treat alloys based on magnesium,
aluminum, or titanium by micro arc anodizing. That
10 technique serves to make layers with very low porosity
and of hardness·that is much greater than the hardness of
an amorphous oxide that could be obtained by conventional
anodizing such as sulfuric anodic oxidation (SAO),
chromic anodip oxidation (CAO), or phosphoric anodic
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15 oxidation (PAO). Specifically, in micro arc anodizing
treatments, the oxide layer on the surface of the part is
formed as a result of generating microelectric discharges
leading to the formation of micro arcs that have the
ability to raise the temperature of the surface of the
20 part very locally so as to crystallize the amorphous
oxide that forms during the anodizing step. In micro arc
anodizing treatment, the parts may be immersed in an
aqueous electrolyte and they are exposed to oscillating
pulses of electrical energy by a specific electronic
25 generator, and if necessary by a counter-electrode of
shape matching the parts. Microscopic light-emitting
discharges are then visible at the surfaces of such
parts, which discharges are due to dielectric breakdowns
in the hydroxide layer, and they can be considered as
30 being microplasmas.
The main parameters of the treatment (frequency of
the electrical signal, current density, duration for
which the parts are immersed in the bath, temperature,
... ) can be modulated and controlled as a function of the
35 material of the treated part, of its sha~€, and of the
properties desired for the layer of anodizing.
5
2
Nevertheless, making a coating by the present micro
arc anodizing technique in a large vessel (vessel having
a volume of about 0.5 cubic meters (m3)) can present
several limits.
Firstly, that technique can involve using a
generator delivering high value bipolar currents, given
the large surfac~ area of the part(s) for treatment,
which can lead to high levels of electricity consumption.
Furthermore, it can be difficult to obtain a coating by
10 micro arc anodizing on a part of large area because of
the high currents needed for anodizing.
Furthermore, since micro arc anodizing treatment
consumes a large amount of energy, the temperature of the
electrolyte ip ~rior art bath treatments can be difficult
15 to control. Nevertheless, it is necessary to control the
temperature of the bath in order to ensure that the
coating is properly made. The desire to regulate the
temperature of the bath can lead to using an installation
that is relatively complex, thereby significantly
20 increasing the cost of performing the treatment.
Another disadvantage of prior art micro arc
anodizing methods is that it can be difficult to measure
reliably certain parameters of the electrolyte in the
bath while the anodizing treatment is being performed.
25 Reliable measurements of such parameters are nevertheless
desirable, e.g. in order to be able to modify the
anodizing treatment being performed as a function of the
information determined from such measurements.
Finally, in order to perform micro arc anodizing on
30 a part in a well-specified zone, it is possible to use
resists that may be of organic type, e.g. a varnish, or
of inorganic type, e.g. resulting from conventional
anodizing, for the purpose of preventing the micro arc
anodizing layer being formed over the entire surface of
35 the part. Resists serve in particular td-insulate the
surface of the underlying part electrically from the
electrolyte, thereby preventing that surface being
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anodized. Nevertheless, putting resists into place can
be relatively expensive and can make the organization of
fabrication significantly more complex. Furthermore, the
masking step may be difficult to perform and can thus
5 make the treatment significantly more expensive.
There thus exists a need to provide devices that
enable anodizing, ,treatment to be performed in simple and
inexpensive manner, and in particular micro arc anodizing
treatment.
10 There also exists a need to provide devices that
enable the temperature of the electrolyte during
anodizing treatment to be controlled effectively, and in
particular during micro arc anodizing treatment.
There al?O exists a need to provide novel devices , I
15 suitable for performing treatments in addition to
anodizing and making it possible in particular to monitor
reliably the parameters of the electrolyte in use during
the anodizing treatment.
20 Object and summary of the invention
To this end, in a first aspect, the invention
provides a device for performing anodizing treatment on a
part, the device comprising:
· a treatment chamber comprising a part to be
25 treated and a counter-electrode situated facing the part
to be treated, the part to be treated constituting a
first wall of the treatment chamber;
· a generator, a first terminal of the generator
being electrically connected to the part to be treated
30 and a second terminal of the generator being electrically
connected to the counter-electrode; and
· a system for storing and circulating an
electrolyte, the system comprising:
· a storage vessel, different from the
35 treatment chamber, for containing the ele'ctrolyte; and
4
· a circuit for circulating the electrolyte in
order to enable the electrolyte to flow between the
storage vessel and the treatment chamber.
The invention relies on the principle of using a
5 treatment chamber that is "remote" from the electrolyte
storage vessel, the part to be treated forming a wall of
the treatment ch~mber. Unlike anodizing devices known in
the prior art, the part to be treated is not immersed in
the electrolyte, but only the surface of the part that is
10 to be treated is in contact with the electrolyte during
the anodizing treatment. Naturally, the surface of the
part to be treated is electrically conductive, the part
being constituted for example by a metal, e.g. aluminum,
15
magnesium, an?l?r titanium.
The invention advantageously enables the anodizing
treatment to be "concentrated" in a limited volume in the
treatment chamber and makes it possible to use a
treatment chamber of volume that is significantly smaller
than that of a vessel used in prior art anodizing methods
20 in which the part to be treated is immersed. Thus, in
the invention, a treatment chamber is used that has a
volume that matches the dimensions of the surface to be
treated, and this presents.several advantages.
Specifically, the invention makes it possible to
25 achieve savings in terms of energy consumption compared
with prior art methods since, while using the device of
the invention, the power delivered by the generator is
specifically proportional to the dimensions of the
surface area to be treated. In addition, a part of large
30
35
dimensions of the kind frequently encountered in the
field of aviation, e.g. a part made of aluminum, can
advantageously be anodized without having recourse to a
vessel in which it can be totally immersed, as is
required in known prior art methods, thus making it
possible to achieve a saving in terms of.Ehe quantity of
electrolyte that is used during the anodizing treatment.
5
It is thus possible to use a current and a quantity
of electrolyte that match the dimensions of the surface
area to be treated, as a result of using a treatment
chamber of volume and of shape matching the surface to be
5 treated. In addition, the use of such a treatment
chamber advantageously makes expensive steps of
installing resista or masks superfluous.
The invention thus provides devices enabling
anodizing treatment to be performed in simple and
10 inexpensive manner, and preferably micro arc oxidation
treatment.
The device of the invention is preferably for use in
performing micro arc oxidation treatment.
Devices .9f,the invention also make it possible to
15 have better control over the effects of heat being
produced in the treated zone by enabling the electrolyte
to be renewed effectively in the treatment chamber and by
maintaining the treatment chamber under good mixture
conditions. This renewal is made possible by the system
20 for storing and circulating the electrolyte that enables
the electrolyte to flow from the storage vessel to the
treatment chamber and the electrolyte to return from the
treatment chamber to the storage vessel. Such a system
contributes to having better control over the anodizing
25 treatment and leads to coatings that are easier to make
so that they comply with the required specifications.
30
35
Advantageously, the system for storing and
circulating the electrolyte may further include a pump
for driving circulation of the electrolyte through said
system.
In an embodiment, the device may be such that the
circuit for circulating the electrolyte comprises:
a first channel for enabling the electrolyte
coming from the storage vessel to flow to the treatment
chamber; and
· a second channel for enabling the electrolyte to
flow from the treatment chamber to the storage vessel.
6
Advantageously, the treatment chamber may have a
volume that is less than the volume of the storage
vessel. The volume of the storage vessel and the volume
of the treatment chamber correspond respectively to the
5 inside volumes of said storage vessel and of said
treatment chamber (i.e. not including the volumes of the
walls). In part~cular, the ratio (volume of the
treatment chamber)/(volume of the storage vessel) is less
than or equal to l, preferably less than or equal to 0.2.
10 In an embodiment, the devic.e may include at least
one sealing gasket constituting a second wall of the
treatment chamber, the second wall being different from
the first wall. In particular, the device advantageously
includes two ~e~ling gaskets situated facing each other
15 and constituting two distinct walls of the treatment
chamber.
In an embodiment, the treatment chamber may define a
single compartment.
The present invention also provides a method of
20 anodizing a part, the method comprising the following
steps:
forming a coating on a surface of the part by
anodizing treatment using a device as defined above, an
electrolyte being present in the treatment chamber during
25 the anodizing treatment, and the electrolyte flowing in
the electrolyte circulation circuit during the anodizing
treatment.
30
The anodizing treatments of the invention present
the advantages as described above.
Preferably, the anodizing treatment is micro arc
oxidation treatment.
In an implementation, the electrolyte may flow in
the electrolyte circulation circuit at a flow rate lying
in the range 0.1 times to 10 times the volume of the
35 treatment chamber, per minute.
' ' ' _____ ,,_,_,
7
Advantageously, the electrolyte present in the
treatment chamber is continuously renewed during the
anodizing treatment.
In an implementation, during the anodizing
5 treatment:
· the electrolyte coming from the storage vessel may
flow to the treatment chamber through the first channel;
and
· the electrolyte may flow from the treatment
10 chamber to the storage vessel through the second channel.
In an implementation, the method may also further
include a step of filtering the electrolyte flowing in
the second channel prior to its return into the storage
vessel. ·'
15 In an implementation, the method may also further
include the following steps:
· determining at least information relating to the
electrolyte flowing in the first channel and/or in the
second channel; and
20 modifying at least one characteristic of the
anodizing treatment, this modification being performed as
a function of the information determined about the
electrolyte.
25 Brief description of the drawings
Other characteristics and advantages of the
invention appear from the following description of
particular embodiments of the invention, given as nonlimiting
examples, and with reference to the accompanying
30 drawings, in which:
35
· Figure 1 shows an embodiment of a device of the
invention; and
Figures 2 and 3 show other embodiments of devices
of the invention.
Detailed description of embodiments
Figure 1 shows an embodiment of a device 1 of the
8
invention. The device 1 comprises the part to be treated
3 and a generator 5. The part to be treated 3 is for
being subjected to anodizing treatment, preferably micro
arc oxidation. The generator 5 serves to perform this
5 anodizing. As shown, a first terminal of the generator 5
is electrically connected to the part 3, and a second
terminal of the generator 5 is electrically connected to
a counter-electrode 7 situated facing the part 3. The
generator 5 is advantageously configured to apply
10 alternating current (AC) .
The counter-electrode 7 is preferably made of
stainless steel. More generally, it is possible to use
any electrically-conductive material for the counterelectrode
7 proyiding it is compatible with performing
15 anodizing treatment.
The device 1 has a treatment chamber 10 in which the
anodizing treatment is to be performed, the part 3 to be
treated constituting a first wall of the treatment
chamber 10 and the counter-electrode 7 constituting a
20 wall of the treatment chamber that is situated facing the
first wall. An electrolyte 11 is present in the
treatment chamber 10 between the part 3 and the counterelectrode
7. The electrolyte 11 has a chemical
composition that enables the part 3 to be subjected to
25 anodizing treatment. As shown, the counter-electrode 7
is not immersed in the electrolyte 11. The counterelectrode
7 forms a wall of the treatment chamber 10.
Thus, as shown, the part 3 to be treated is not
immersed in the electrolyte 11 present in the treatment
30 chamber 10. The part 3 constitutes a wall of the
treatment chamber 10 so that only the surface S to be
treated of the part 3 is in contact with the electrolyte
11. In the example shown, the part 3 is treated over its
entire length, i.e. over its entire longest dimension.
35 Naturally, it would not be beyond the ambit of the
present invention for the part to be treated over a
fraction only of its length. In the ambit of the
• ·~ -
9
invention, it is thus equally possible to perform
anodizing treatment over a fraction only of a surface of
a part or over an entire surface of a part.
In addition, the treatment chamber 10 comprises two
5 sealing gaskets 13a and 13b situated facing each other
and forming two distinct walls of the treatment chamber.
As shown, the se~ling gaskets 13a and 13b are present at
the top and bottom ends of the treatment chamber 10. The
gaskets 13a and 13b may be made of flexible material.
10 Thus, in the embodiment shown of the device 1 the
electrolyte 11 used for anodizing is contained between
the part 3 and the counter-electrode 7 by static sealing
making use of the flexible gaskets 13a and 13b. The
treatment ch~~byr 10 thus constitutes a tank of
15 electrolyte 11 for coating the surface S of the part 3.
As mentioned above, the treatment chamber 10 has a volume
and dimensions that are adapted to the dimensions and to
the shape of the surface S to be treated of the part 3.
In the example shown, the treatment chamber 10 defines a
20 single compartment.
In addition, the device 1 includes a system 20 for
storing and circulating the electrolyte 11. The system
20 comprises a storage vessel 21 in which the electrolyte
11 is stored, with the temperature of the electrolyte 11
25 stored in the storage vessel being maintained at a value
that is determined by a cooling system (not shown) . The
pH of the electrolyte 11 present in the storage vessel 10
is also maintained at a fixed value. During anodizing
treatment, the electrolyte 11 coming from the storage
30 vessel 21 flows along a first channel 23 to the treatment
chamber 10. The system 20 also has a second channel 25
enabling the electrolyte 11 to flow from the treatment
chamber 10 to the storage vessel 21. The second channel
25 enables the electrolyte 11 present in the treatment
35 chamber 10 to be discharged and returned to the storage
vessel 21 where it can be cooled. The electrolyte 11 is
caused to circulate through the system 20 by a pump 27.
10
By way of example, the pump 27 may be a pump that is sold
under the name YB1-25 by the supplier TKEN.
Figure 1 includes arrows showing the flow direction
of the electrolyte 11. The flow rate of the electrolyte
5 11 determined by the pump 27 enables the electrolyte 11
in the treatment chamber 10 to be renewed appropriately
so as to enable. t,he desired coating to be made by
anodizing. It may be advantageous for the pump 27 to
cause the electrolyte 11 to flow at a rate that is equal
10 to about one volume of the treatment chamber 10 per
minute. More generally, the pump 27 may advantageously
cause the electrolyte 11 to flow at a rate lying in the
range 0.1 times to 10 times the volume of the treatment
chamber 10 pef minute.
. I
15 Advantageously, the flow of electrolyte 11 from the
storage vessel 21 to the treatment chamber 10 and from
the treatment chamber 10 to the storage vessel 21 is not
interrupted throughout the duration of the anodizing
treatment. In other words, it is preferred to renew the
20 electrolyte 11 present in the treatment chamber 10
continuously throughout the anodizing treatment.
The first channel 23 may have a diameter d1 over all
or part of its length that is less than or equal to
10 centimeters (em), e.g. lying in the range 1 em to
25 3 em. The second channel 25 may present a diameter d 2
over all or part of its length that is less than 10 em,
e.g. lying in the range 1 em to 3 em. The treatment
chamber 10 may have a volume that is less than or equal
to 0.5 m3, e.g. lying in the range 10 cubic decimeters
30 (dm3) to 40 dm3. The storage vessel 21 may have a volume
greater than or equal to 0.5 m3, e.g. lying in the range
0. 5 m3 to 2 m3.
The materials forming the gaskets 13a and 13b, the
first channel 23, and the second channel 25 are selected
35 so as to ensure that electricity does not·-pass between
the counter-electrode 7 and the part 3.
11
The device 1 shown in Figure 1 serves to perform
anodizing treatment on a part by part basis. As shown,
the method performed by the device 1 shown in Figure 1
advantageously does not include a step of masking a
5 portion of the surface S of the part 3 or of putting into
place
to be
at least
treated.
one resist on the surface S of the part 3
'''
The final thickness of the coating formed after
anodizing treatment measured perpendicularly to the
10 surface of the underlying part may lie in the range
2 micrometers (~m) to 200 pm.
15
20
There follows an example of operating conditions
that may be implemented in order to perform micro arc
oxidation tre9t~ent with a device 1 as described above:
imposed current: 40 amps per square decimeter
(A/dm2 ) to 400 A/dm2 ;
voltage: 180 volts (V) to 600 V;
pulse frequency: 10 hertz (Hz) to 500 Hz;
duration of treatment: 10 minutes (min) to 90 min;
temperature of the electrolyte in the storage
vessel: 17°C to 30°C.
· pH of the electrolyte in the storage vessel: 6 to
12; and
· conductivity of the electrolyte in the storage
25 vessel: 200 millisiemens per meter (mS/m) to 500 mS/m.
30
In particular, for performing micro arc oxidation
treatment, it is possible to use an electrolyte 11 having
the following composition:
demineralized water;
potassium hydroxide (KOH) at a concentration lying
in the range 5 grams per liter (g/L) to 50 g/L;
sodium silicate (Na2Si03 ) at a concentration lying
in the range 5 g/L to 50 g/L; and
potassium phosphate (K3P04 ) at a concentration
35 lying in the range 5 g/L to 50 g/L.
Nevertheless, the invention is not limited to
performing a micro arc oxidation method. A device of the
j
12
invention may be used for performing any type of
anodizing, such as for example sulfuric anodic oxidation
(SAO), chromic anodic oxidation (CAO), sulfotartric
anodic oxidation (STAO), or sulfa-phosphoric anodic
5 oxidation (SPAO).
By way of example, the treated part may be a blade,
e.g. made of titBnium, or a pump body. It is also
possible to use a device of the invention to repair a
layer of anodizing that has been damaged, the device
10 making it possible to perform localized repair with a
coating being formed by anodizing solely in the damaged
zone.
In a variant that is not shown, it is possible to
treat a plura+ity of distinct parts using a plurality of , I
15 devices of the invention optionally connected to the same
generator. The parts may optionally be treated
simultaneously.
The storage vessel 21 is dedicated to storing and
renewing the electrolyte and no anodizing treatment is
20 performed therein. By separating the storage vessel 21
from the treatment chamber 10, it is possible to
configure devices of the invention so as to perform
treatments additional to anodizing, as described in
detail below. So far as the inventors are aware, these
25 treatments additional to anodizing are not performed or
are not performed in satisfactory manner in methods known
in the state of the art.
Figure 2 shows a variant of the device 1 of the
invention. In this example, the device 1 also has a
30 filter device 52 situated between the treatment chamber
10 and the storage vessel 21. The electrolyte present in
the second channel 25 flows through the filter device 52
and is returned to the storage vessel 21 after being
filtered via the channel 25a. By way of example, using
35 such a filter device 52 advantageously maRes it possible
to eliminate particles that have not become attached to
the anodic layer being formed, thereby purifying the
13
electrolyte 11 before returning it to the treatment
chamber 10.
Figure 3 shows a variant of the device 1 of the
invention. The device 1 includes a sensor 60 for
5 determining information about the electrolyte 11 flowing
in the first channel 23. As a function of the
information it d\",termines, this sensor 60 makes it
possible to act on the generator 5 in such a manner as to
modify at least one characteristic of the anodizing
10 treatment being performed. In a variant, the sensor may
determine information about the electrolyte flowing in
the second channel, or indeed it may determine both
information about the electrolyte flowing in the first
channel and ir;f9rmation about the electrolyte flowing in
15 the second channel, so as to modify the anodizing
treatment that is being performed as a function of this
information. By taking measurements upstream and/or
downstream of the treatment chamber 10, this embodiment
of the device 1 of the invention advantageously makes it
20 possible to obtain information that is more reliable than
the information that can be observed in the reaction
chamber, thus making it possible to control the anodizing
performed in the treatment chamber in satisfactory manner
as a function of the information that has been
25 determined. Typically, the information about the
electrolyte that is determined by the sensor may concern
one or more of the following parameters: the
concentration of metallic species, e.g. aluminum, within
the electrolyte, the pH, and the conductivity of the
30 electrolyte. The electrolyte can become laden with
metallic species progressively as the anodizing
progresses, and this parameter, like the pH or the
conductivity of the electrolyte, makes it possible to
have an influence on the anodizing treatment that is
35 performed. Direct control over the anodi~z-ing being
performed may be advantageous in particular for
performing anodizing treatments on parts that are to be
ii
il,
II
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14
used in the field of aviation and/or when performing
anodizing treatments that are relatively lengthy.
The term "including/containing/comprising a" should
be understood as "including/containing/comprising at
5 least one".
The term "in the range ... to
understood as in9Juding the limits .
. '
" should be

CLAIMS
1. A device (1} for performing anodizing treatment on a
part (3}, the device (1} comprising:
· a treatment chamber (10} comprising a part (3} to
5 be treated and a counter-electrode (7} situated facing
the part to be treated, the part (3} to be treated
constituting a f~rst wall of the treatment chamber (10}
and the counter-electrode (7} constituting a wall of the
treatment chamber (10} situated facing the first wall;
10 ·a generator (5}, a first terminal of the generator
being electrically connected to the part (3} to be
treated and a second terminal of the generator being
electrically connected to the counter-electrode (7}; and
· a system (20} for storing and circulating an
. ' I
15 electrolyte (11}, the system (20} comprising:
20
·a storage vessel (21}, different from the
treatment chamber (10}, for containing the electrolyte
(11}, the treatment chamber (10} having a volume that is
less than the volume of the storage vessel (21}; and
a circuit (23; 25} for circulating the
electrolyte in order to enable the electrolyte to flow
between the storage vessel (21} and the treatment chamber
( 10} .
25 2. A device (1} according to claim 1, characterized in
that it includes at least one sealing gasket (13a; 13b}
constituting a second wall of the treatment chamber (10},
the second wall being different from the first wall.
30
35
3. A device (1} according to claim 1 or claim 2,
characterized in that the system (20} for storing and
circulating the electrolyte further includes a pump (27}
for driving circulation of the electrolyte (11} through
said system (20}.
4. A device (10} according to any one of claims 1 to 3,
characterized in that the ratio (volume of the treatment
16
chamber)/(volume of the storage vessel) is less than or
equal to 0.2.
5. A device (10) according to any one of claims 1 to 4,
5 characterized in that the circuit (23; 25) for
circulating the electrolyte comprises:
10
· a first c0~nnel (23) for enabling the electrolyte
(11) coming from the storage vessel (21) to flow to the
treatment chamber (10); and
· a second channel (25) for enabling the electrolyte
(11) to flow from the treatment chamber (10) to the
storage vessel (21).
6. A method of ?nodizing a part (3), the method
15 comprising the following steps:
· forming a coating on a surface (S) of the part (3)
by anodizing treatment using a device (1) according to
any one of claims 1 to 5, an electrolyte (11) being
present in the treatment chamber (10) during the
20 anodizing treatment, and the electrolyte flowing in the
electrolyte circulation circuit (23; 25) during the
anodizing treatment.
7. A method according to claim 6, characterized in that
25 the anodizing treatment is micro arc oxidation treatment.
8. A method according to claim 6 or claim 7,
characterized in that during the anodizing treatment:
the electrolyte (11) coming from the storage
30 vessel (21) flows to the treatment chamber (10) through
the first channel (23); and
35
· the electrolyte (11) flows from the treatment
chamber (10) to the storage vessel (21) through the
second channel (25).
9. A method according to any one of claims 6 to 8,
characterized in that the electrolyte (11) present in the
I
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17
treatment chamber (10) is continuously renewed during the
anodizing treatment.
10. A method according to any one of claims 6 to 9,
5 characterized in that the electrolyte (11) flows in the
electrolyte circulation circuit (23; 25) at a flow rate
lying in the range 0.1 times to 10 times the volume of
the treatment ch''a mber (10), per minute.
10 11. A method according to any one of claims 8 to 10,
characterized in that it further includes a step of
filtering the electrolyte (11) flowing in the second
channel (25) prior to its return into the storage vessel
(21) .
15 , ; I
12. A method according to any one of claims 8 to 11,
characterized in that it further includes the following
steps:
determining at least information relating to the
20 electrolyte (11) flowing in the first channel (23) and/or
in the second channel (25); and
modifying at least one characteristic of the
anodizing treatment, this :nodificatio'n 'being performed as
a function of the information determined about the
25 electrolyte.