Note: Descriptions are shown in the official language in which they were submitted.
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BUS211 ct
METHOD FOR COMPRESSING A COMPONENT MADE OF
ALUMINUM AND/OR AN ALUMINUM ALLOY
The invention relates to a method for densifying a device component
made of aluminum and/or an aluminum alloy, in particular a decorative part
or a functional part, with a very high corrosion stability.
High glazing, mat glazing or, respectively, silk glazing decorative parts,
which are formed from aluminum sheet metal or aluminum profiles, are
disposed in the outer and inner region of many motor vehicles. The
decorative surfaces are produced by polishing and glazing anodizing
treatment. These possibly also colored surfaces are optically demanding and
fulfill a high quality standard. These are surfaces, which exhibit a
completely
uniform layer thickness and have neither waves nor edge superstructures nor
edge alignments. They feel metallic and therewith with a high value, and
there is talk of so-called "cool touch ": The surfaces exhibit in addition a
good corrosion stability based on a combination of cold and hot densification
processes.
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Improvements of the densification method are in particular- directed to
an increase of the corrosion stability of anodized and densified device
components, in particular in the alkaline region. A method is known frorm
the European patent application EP 1 407 935 Al wherein non densified
glazed anodizing treatment surfaces are coated with a transparent "lacquer"
(Aluceram), that is a lacquering method follows to the anodizing treatment. It
is disadvantageous that the non densified or, respectively, part densified
anodized goods cannot be transported as is desired and handled as desired
prior to the layer application with these lacquers, since the capillary action
of
the open pores entails an irreversible soiling of the parts. Furthermore, only
the view sides are coated for reasons of process technology and costs. An
increased tendency to corrosion of the backside results therefrom, in
particular in combination with other metals or working materials containing
free carbon, which stand in direct contact with the non densified or partially
densified backside in the presence of a conductive electrolyte, for example a
salt solution. The thus coated parts corrode at view faces and at non view
faces to a different degree such that an inhomogeneous overall picture can be
generated.
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Furthermore, there existed tests to increase the corrosion stability by
additions during the cold sealing process. Corrosion stability up to pH values
of 13.5 can be obtained with a combination of a.cold sealing process and a hot
water densification process, wherein in the cold sealing process for example
nickel fluoride containing products are added and the cold water densification
is performed with completely desalted water in combination with nickel
acetate and possibly with a further hot water densification step. The -pores
of
the anodizing layer are in this case closed or, respectively, covered by a
covering layer, wherein the covering layer contains nickel containing
compounds in addition to aluminum oxide hydrate (Bohmit). This covering
layer takes care that highly alkaline solutions cannot attack. This nickel
containing covering layer however is little stable, such that a small
mechanical load leads to the elimination of this layer, which then destroys
the
increased corrosion stability and therefore is unsuitable for the application
with construction parts in the motor vehicle region.
The generation of a stabilized, glass like modified oxidized layer is
known from the unpublished German patent application DE 10 2007 057
777.1-45. In this method, construction parts with a very high corrosion
stability relative to acid and alkaline media are obtained, and in particular
an
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alkaline resistance at pH values of 13.5 is accomplished.
Furthermore, a vapor densification is known which can be performed at
temperatures above the boiling point of the water. However, the possibility
does not exist here to bring materials, for example silicates into the
densification layer by way of the vapor, since these substances are not
carried
along in the vapor.
Usually, several densification steps are performed in all known
densification processes for the treatment of device components of aluminum
and/or aluminum alloys with a high densification quality and in particular a
high corrosion resistance. Various flushing vessels and several densification
vessels are furnished, in addition to the anodizing vessel and possibly
various
different vessels for pretreatment, for the treatment of device components in
an anodizing treatment plant. Usually, the longest densification time is
required for a hot water densification such that several hot water
densification
vessels are furnished in an anodizing plant for a continuous flow through of
the products.
It is an object of the invention to furnish a method for densification of
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device components out of aluminum or an aluminum alloy with high
densification quality, in particular good corrosion resistance. It is a
further
object to accelerate the densification process and thus to increase the plant
capacity and to reduce the cost for each piece.
This object is obtained with a method with the features of claim 1. The
new improved densification sealing substitutes the usually employed hot
water densification and in addition leads to a reduction of the necessary
processing time.
In a first step of the invention densification method, the porous oxide
layer obtained by the anodization, wherein the oxide layer usually exhibits a
layer thickness of from 2 to 30 micrometers, preferably a layer thickness of
from 5 to 7 micrometers in case of naturally colored parts, and with colored
parts exhibits a layer thickness of from 12 to 15 micrometers, is subjected to
a
known cold sealing step. Preferably, sealing products with nickel fluoride are
here added.
In the following, a hot water densification is performed after multiple
flushing in fully desalted water. This new hot water densification according
to the present invention is performed at increased temperatures and under
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application of over pressure in a closed chamber. The temperatures lie in the
region above 100 degrees centigrade, preferably in a region above of from
100 degrees centigrade to 140 degrees centigrade. The increased temperature
serves for increasing the reaction speed. The over pressure amounts
preferably to from 1 bar to 2 bar. In case of a lower over pressure than 1
bar,
the shortening of the hot water densification time is not such significant
that
the additional plant expenditure for the pressure generation would pay off.
Over pressures of more than 2 bar are associated with the disadvantage that
the plant technical expenditure through the high effective forces unreasonably
increases. The optimum operating pressure has to be determined depending
on the employed chemicals, substrates and layer thicknesses.
The hot water densification can be performed in different pH regions.
According to a preferred embodiment, the pH values are situated in the region
from 6.0 to 7Ø In contrast, pH values resulted in the basic region with a
silicate densification, since the dissolved silicates are basic.
The densification bath contains fully desalinated water. Known
surfactants can be added. Additionally, glass like substances of one or
several
such alkaline silicates can be brought into the covering layer for increasing
the
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stability in the alkaline region. The glass like substances are preferably
entered as an aqueous solution in concentrations of from 5 to 20 grams per
liter into the hot water densification bath. The thus densified parts show in
this case no attack in a test in an acid medium with a pH value of 1.0 for ten
minutes and in a following test in an alkaline medium at a pH value of 13.5
for
ten minutes.
The densification time amounts to between 0.5 and 3 minutes in a hot
water densification according to the invention at 1 bar over pressure and
temperatures of 120 degrees centigrade per 1 micrometer layer thickness of
the anodization layer. The reduction of the densification time becomes clear
when comparing this result with the known hot water densification without
pressure application, where the densification time per 1 micrometer layer
thickness of the anodization layer amounts to between 2 and 6 minutes.
The hot water densification according to the present invention is
performed in place of a known hot water densification. As already described,
the flow through time of device components in an anodization treatment plant
are reduced and simultaneously the quality of the densification is improved.
The densification layer obtained by the invention method is without a gap and
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reaches up to the floor of the pores of the anodization layer. A very
homogeneous sealing of the pores with aluminum oxide hydrate is
accomplished with the process of the present invention. The conventional
known hot water densification does not or not always achieve this goal,
amongst others based on process inherent residual amounts of chemicals, for
example acids from the bright bath, which can collect in the capillary floors
of
the pores and which are not displaced, but more likely included in the layer.
According to the invention method, the densification media, for example fully
desalinated water or in case of addition of alkali silicates also these
silicates, -
are improved entered into the pores through the pressure. Residual amounts
of treatment substances, deposited in the pores, which have not been removed
by the various flushing processes, are displaced or assimilated. In addition
the
reaction speed and the reaction completeness is increased by the possible
increased processing temperature above 100 degrees centigrade, which
represents the usual boiling temperature of the water under normal pressure.
This way the densification times of about 1 to 3 minutes per micrometer can
be achieved, which corresponds to a shortening of time of up to 50 percent.
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Comparison example 1 a :
A piece of aluminum sheet metal with the dimensions 40 by 100 by 2 mm of
an Al 91.9MgO.8 alloy is mechanically polished and chemically pretreated in
a known fashion. Then an anodically generated oxide layer is generated on
this piece during a direct current sulfuric acid treatment. The layer
thickness
is about 7 micrometers. After the flushing of device component A, the porous
oxide layer is subjected to a cold sealing step.
Temperature: 28-32 degrees centigrade
pH value: 6.2-7.0
sealing time: 4-8 minutes
addition 4-8 g per liter densification agent (sealing salt with nickel
fluoride)
an after densification is performed through a hot water densification
temperature: 95-100 degrees centigrade
pH value : 6.25 0.2
sealing time: 21 minutes
densification bath: fully desalinated water
2-3 ml/1 deposit prevention agent
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Comparison example lb:
an equal piece of aluminum sheet metal is treated as in the comparison
example 1 a, wherein only the hot water densification is different,
namely a first hot water densification under the following conditions:
temperature: 70 - 80 degrees centigrade
pH value : 5.7 0.3
sealing time: 3 minutes
densification bath: fully desalinated water
15 - 20 grams per liter nickel acetate
and a second hot water densification for after densifying under the following
conditions:
temperature: 95 to 100 degrees centigrade
pH value: 6.2 + 0.2
sealing time: 21 minutes
densification bath: fully desalinated water
2 -,3 milliliter per liter of deposit prevention agent
Embodiment example 1 according to the present invention
a like piece of aluminum sheet metal as present in the comparison example 1
was treated, wherein only the hot water densification is different. This is
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followed by the new hot water densification, which is performed under the
following conditions:
temperature: 120 degrees centigrade
pressure: 1 bar over pressure
pH value: 6.2 0.2
sealing time: 14 minutes
densification bath: fully desalinated water
2 - 3 milliliters per liter surfactant mixture (deposit prevention agent)
If one compares the hot water densification times, then the advantageous
reduction of the treatment time from 21 minutes or, respectively, 24 minutes
to 14 minutes becomes clear.
Embodiment example 2:
A piece of aluminum sheet metal with the dimensions 40 x 100 x 2 mm of an
A199.9Mg 0.8 alloy is mechanically polished and in a known way chemically
pretreated. Then an anodically generated oxide layer is generated on this
piece during a direct current-sulfuric acid treatment. The device component B
is additionally led to an electrolytic and adsorptive coloring method. The
layer thickness lies at 15 micrometers. After the flushing of the device
component, the porous oxide layer is subjected to a cold sealing step as
recited
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in the comparison example 1.
An after densification is performed by way of a hot water densification.
Temperature: 95 - 100 degrees centigrade
pH value: 6.2 + 0.2
sealing time: 45 minutes
densification bath: fully desalinated water
2 - 3 milliliter deposit prevention agent per liter
Embodiment example 2 according to the present invention
A like piece of aluminum sheet metal is treated as in the comparison example
3, wherein only the hot water densification is different.
The new hot water densification follows, which is performed under the
following conditions:
temperature: 120 degrees centigrade
pressure: 1 bar over pressure
pH value 6.2 + 0.2
sealing time: 60 minutes
densification bath: fully desalinated water
8 grams per liter sodium silicate and potassium silicate mixture
0.2 - 0.3 milliliter per liter surfactant mixture
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If one compares the hot water densification times, then the advantageous
reduction of the treatment time from 45 minutes to 30 minutes becomes clear.
Comparison example 3
A piece of aluminum sheet metal with the dimensions 40 x 100 x 2 mm
of an A199.9MgO.8 alloy is mechanically polished and chemically pretreated
in a known fashion. Then an anodic generated oxide layer is generated on this
piece during a direct current sulfuric acid treatment. The layer thickness
lies
at 7 micrometers. After the flushing of the device component, the porous
oxide layer is subjected to a cold sealing step as performed in the comparison
example 1.
An after densification is performed through a hot water densification.
temperature: 94 - 100 degrees centigrade
pH value: 10.4 - 10.8
sealing time: 21 minutes
densification bath: fully desalinated water
8 g per liter sodium silicate
0.2 - 0.3 milliliters surfactant mixture per liter
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Embodiment example 3 according to the present invention:
a like piece of aluminum sheet metal is treated as in the comparison example
4,
wherein only the hot water densification is different.
The new hot water densification follows, which is undertaken under the
following conditions:
temperature: 120 degrees centigrade
pressure: 1 bar over pressure
pH value: 10.4 - 10.8
sealing time: 14 minutes
densification bath: fully desalinated water
8 g per liter sodium and potassium silicate mixture
2 - 3 ml per liter surfactant mixture
If the hot water densification times are compared, then the advantageous
reduction in treatment time from 21 minutes to 14 minutes becomes clear.
The porous oxide layer is densified under pressure at the device
component densified according to the present invention. Since water as is
known has a higher boiling point under pressure as compared with under
standard conditions, the densification according to the present invention. can
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be performed at temperatures of 100 degrees centigrade or higher, whereby
the reaction speed is increased, whereby the reaction, on which the
densification is based, runs quicker and in addition more completely. An
improved and more homogeneous densification results based on the applied
pressure. The residues of the treatment media possibly remaining in the pores
of the anodizing layer are better displaced and represent no local microscopic
densification errors in the finished product, which- act as weak positions
with
respect to the corrosion stability. In the example 3 according to the present
invention of the silicatic densification, the glass like substance added
during
the hot water densification is better entered into the pores of the oxide
layer
and/or built on the surface layer through the pressure and the temperature.
Test on thermal crack stability :
- All construction components both of the comparison examples as well
as also of the embodiment examples according to the present invention are
stored at 100 degrees centigrade for 60 minutes. All construction parts do not
show optically any heat cracks.
Test for acid resistance and combined acid-/heat-/alkali loading:
All construction parts are subjected to 5 cycles of the Kesternich test
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according to standard DIN 50018 KFW 2.OS. Thereafter no part shows
optical changes. The construction parts according to the present invention
show also no changes in a test according to the standard TL 182 of the
Volkswagen AG, that is a treatment over a ten minute time period in an acid
medium, which exhibits a pH value of 1.0, a following heat dislocation aging
and a ten minute submerging in a medium with a pH value of 13.5. Also the
construction parts of the comparison examples 1 b and 3 meet the test.
requirements, however not if previously also an abrasion test had been
performed. The protective effect on the construction parts treated according
to the present invention remains present in contrast thereto also where
previously an abrasion test had been performed, since here the protective
effect is not only associated with the surface, but is also built in the
pores. The
construction parts of the comparison examples 1 a and 2 fail in this test
completely.
Test of resistance versus salt containing media :
All construction parts are subjected to a salt spray test according to DIN
50017 SS over 480 hours. Thereafter, no part exhibits optical changes.
Test of resistance to alkali:
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All construction parts are stored in an alkaline test solution with a
stochiometrically set pH value of 13.5 at temperatures from 18 - 20 degrees
centigrade for ten minutes. The alkaline test solution comprises a 0.317 molar
solution, wherein one liter solution contains
12.7 gram sodium hydroxide
4.64 gram sodium phosphate dodeca hydrate (corresponds to 2 gram sodium
phosphate)
0.33 gram sodium chloride
and the balance contains distilled water.
The construction parts according to the present invention and the
construction parts from the comparison examples lb and 3 show after 10
minutes no changes or changes removable by polishing. The anodizing layer
is not damaged relative to the starting state with the layer thickness
practically
unchanged.
The construction part of the comparison example 1 a changes after 4
minutes and the construction part of the comparison example 2 changes after
3 - 4 minutes. The transparent densification layer becomes cloudy, and part of
the anodizing treatment layer is completely removed after the overall test
duration of ten minutes.
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Test of alkali resistance after a preceding mechanical loading:
The construction parts from the comparison example 3 and of the
embodiment examples 1, 2, and 3 are led through a device according to
Amtec-Kistler, which represents a washing road simulation. Here, ten double
strokes are exerted on the surface of each construction part. In the
following,
the construction parts are stored in the above described alkaline test
solution
with a measured pH value of 13.5 at temperatures of 18 - 20 degrees
centigrade for ten minutes.
The construction part of the comparison example 3 and the construction
parts out of the embodiment examples 1 and 3 according to the present
invention show after ten minutes a slight change nearly completely reversible
by polishing. The construction part of the embodiment example 2 according
to the present invention meets the test at a pH value of 12.5, whereas the
comparison example 2 meets the test at a pH value of 11.5.
All construction parts can be employed as decorative parts or as
functional parts, since they exhibit a heat crack stable and corrosion
resistant
surface. The construction parts treated according to the present invention
show equally good or better properties as the construction parts treated in
the
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comparison methods. The in part better properties of the construction parts
according to the present invention are obtained based on the improved
densification. The construction parts treated according to the present
invention are obtained in a significantly shorter process time.
The construction parts treated according to the invention method
represent and make available decorative parts with a high densification
quality, in particular with a high corrosion resistance and simultaneously
shortened process time of the anodizing treatment process.
The invention is not limited to the process conditions described in the
embodiment example. These conditions can be varied corresponding to the
application purpose of the construction part. For example the layer thickness
of the anodization layer of a decorative part can lie between 2 and 30
micrometers, whereby the treatment times are changed.
The capacity of an anodizing treatment plant can be increased by faster
flow through times of the construction parts to be treated through the
improved densification quality at a reduced process time. The hot water
densification step is usually the step of longest duration in the overall
process
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such that several hot water densification vessels are furnished in anodizing
treatment plants constructed according to the known method. A lesser
number of hot water densification vessels can be furnished in an anodizing
treatment plant with the faster hot water densification according to the
present
invention method. This is opposed by the higher plant technical expenditure
for a densification under increased temperature. The energy balance is
favorable with the method according to the present invention based on the
reduced flow through times despite the increased entry of used energy.
