U.S. patent application number 11/937639 was filed with the patent office on 2008-05-29 for electropolishing process.
This patent application is currently assigned to POLIGRAT GmBH. Invention is credited to Olaf BOHME, Siegfried PIESSLINGER-SCHWEIGER.
Application Number | 20080121530 11/937639 |
Document ID | / |
Family ID | 38984297 |
Filed Date | 2008-05-29 |
United States Patent
Application |
20080121530 |
Kind Code |
A1 |
PIESSLINGER-SCHWEIGER; Siegfried ;
et al. |
May 29, 2008 |
ELECTROPOLISHING PROCESS
Abstract
The present invention relates to a method for the
electropolishing of surfaces of metals and metal alloys. Said
method is characterized in particular in that it can be applied to
a wide range of metals. Thus, it is suitable for the
electropolishing of metal surfaces comprising iron, tungsten,
magnesium, aluminum or an alloy of these metals. The electrolyte
used in the method comprises methanesulfonic acid and at least one
alcoholic compound selected from aliphatic diols of general formula
C.sub.nH.sub.2n(OH).sub.2 with n=2-6 and alicyclic alcohols of
general formula C.sub.mH.sub.2m-1OH with m=5-8.
Inventors: |
PIESSLINGER-SCHWEIGER;
Siegfried; (Vaterstetten, DE) ; BOHME; Olaf;
(Erding, DE) |
Correspondence
Address: |
BORDEN LADNER GERVAIS LLP;Gail C. Silver
1100-100 QUEEN ST
OTTAWA
ON
K1P 1J9
omitted
|
Assignee: |
POLIGRAT GmBH
Munich
DE
|
Family ID: |
38984297 |
Appl. No.: |
11/937639 |
Filed: |
November 9, 2007 |
Current U.S.
Class: |
205/684 |
Current CPC
Class: |
C25F 3/16 20130101; C25F
3/26 20130101; C25F 3/24 20130101; C25F 3/20 20130101; C25F 3/18
20130101 |
Class at
Publication: |
205/684 |
International
Class: |
C25F 3/18 20060101
C25F003/18 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 14, 2006 |
DE |
10 2006 053 586.3 |
Claims
1. A method for the electropolishing of surfaces of metals,
comprising exposing a metal surface to an electrolyte in the
presence of an electric current, wherein the metal surface is
selected from iron, tungsten, a light metal, and an alloy thereof,
and wherein the electrolyte comprises: methanesulfonic acid, and at
least one alcoholic compound selected from the group comprising
aliphatic diols of general formula C.sub.nH.sub.2n(OH).sub.2 with
n=2-6 and alicyclic alcohols of general formula C.sub.mH.sub.2m-1OH
with m=5-8.
2. The method as claimed in claim 1, wherein the surface comprises
iron or an iron alloy, hardened or unhardened.
3. The method according to claim 2, wherein the iron alloy is
ferro-nickel, special steel, or carbon steel.
4. The method as claimed in claim 1, wherein the surface comprises
tungsten or a tungsten alloy.
5. The method as claimed in claim 1, wherein the surface comprises
magnesium, a magnesium alloy, aluminium, or an aluminum alloy.
6. The method as claimed in claim 1, wherein the surface comprises
an aluminum-silicon alloy.
7. The method as claimed in claim 1, wherein the alcoholic compound
comprises at least one aliphatic diol of general formula
C.sub.nH.sub.2n(OH).sub.2 with n=3-6.
8. The method as claimed in claim 7, wherein the aliphatic diol
comprises 1,2-propanediol and/or 1,2-butanediol.
9. The method as claimed in claim 1, wherein the electrolyte
comprises 5 to 93 wt. % methanesulfonic acid and 95 to 7 wt. % of
the alcoholic compound or compounds.
10. The method as claimed in claim 1, wherein the electrolyte
comprises 10 to 80 wt. % methanesulfonic acid and 90 to 20 wt. % of
the alcoholic compound or compounds.
11. The method as claimed in claim 1, wherein the alcoholic
compound comprises at least one aliphatic diol and at least one
alicyclic alcohol.
12. The method as claimed in claim 1, wherein the alicyclic alcohol
comprises cyclohexanol.
13. The method as claimed in claim 1, wherein the electrolyte does
not contain any chromic acid or chromates.
14. The method as claimed in claim 1, wherein the method is carried
out at a temperature between 40 and 100.degree. C.
15. The method as claimed in claim 1, wherein the method is carried
out at a temperature between 60 and 100.degree. C.
16. The method as claimed in claim 1, wherein the method is carried
out at an anodic current density of 3 to 40 A/d m.sup.2.
17. An electrolyte for the electropolishing of surfaces of metals,
which are selected from iron, tungsten and light metals, and from
alloys of these metals, wherein the electrolyte comprises
methanesulfonic acid and at least one alcoholic compound consisting
of an aliphatic diol of general formula C.sub.nH.sub.2n(OH).sub.2
with n=2-6 or an alicyclic alcohol of general formula
C.sub.mH.sub.2m-1OH with m=5-8.
18. The electrolyte as claimed in claim 17, wherein the alcoholic
compound comprises at least one aliphatic diol of general formula
C.sub.nH.sub.2n(OH).sub.2 with n=3-6.
19. The electrolyte as claimed in claim 17, wherein the aliphatic
diol comprises 1,2-propanediol and/or 1,2-butanediol.
20. The electrolyte as claimed in claim 17, wherein the electrolyte
comprises 5 to 93 wt. % methanesulfonic acid and 95 to 7 wt. % of
the alcoholic compound or compounds.
21. The electrolyte as claimed in claim 17, wherein the electrolyte
comprises 10 to 80 wt. % methanesulfonic acid and 90 to 20 wt. % of
the alcoholic compound or compounds.
22. The electrolyte as claimed in claim 17, wherein the alcoholic
compound comprises at least one aliphatic diol and at least one
alicyclic alcohol.
23. The electrolyte as claimed in claim 17, wherein the alicyclic
alcohol comprises cyclohexanol.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method for the
electrochemical polishing of surfaces of metals and metal
alloys.
BACKGROUND OF THE INVENTION
[0002] The purpose of the process of electrochemical polishing or
electropolishing is to produce metal surfaces of high purity, and
to smooth and deburr the metal surfaces. Smoothing in the
micro-range can also produce gloss of the surfaces so treated.
Furthermore, electropolishing can also remove any stresses from the
outer layers of the material.
[0003] There are a great many different electropolishing processes
that can be used for the processing of various metals or metal
alloys. As a rule these processes are based on the use of
electrolytes that comprise a concentrated inorganic acid such as
phosphoric acid or sulfuric acid or a mixture of concentrated
inorganic acids, often with additives for further enhancing the
action of the electrolytes so as to obtain smoother and shinier
metal surfaces. Some examples of such additives are chromic acid,
hydrofluoric acid, amine fluorides or organic additives, such as
alcohols, amines, glycerol, etc.
[0004] However, a feature that is common to all of these existing
electrolytes, which are widely used industrially, is that they can
only be used successfully for certain metals and/or alloys and thus
have a very restricted application profile. For the processing of
various metals or alloys it is therefore often necessary to
maintain a corresponding number of different electrolytes. Often
the individual electrolytes must be kept strictly separate and in
particular must not be mixed, as any mixing may damage them and
make them unusable. Sometimes this can even result in certain
constituents of the electrolytes reacting together and, for
example, releasing substances that are hazardous or injurious to
health. Furthermore, the requirements on execution of the process
and equipment of the electropolishing installations are also often
very varied on account of the different electrolytes, so that
several installations have to be maintained for different
materials.
[0005] The electrolytes usually employed are often hazardous
materials, which depending on their particular toxicity,
flammability and/or danger class are subject to special
requirements and regulations with respect to their storage and use
and require appropriate precautions in connection with
environmental protection and labor safety. This in turn causes
considerable expenditure and the associated costs.
[0006] The ideal solution for these problems would be an
electropolishing process that is equally suitable for the
processing of all metals and metal alloys and is largely harmless
with regard to the associated environmental impact and labor
safety.
[0007] An electrolyte that largely meets the requirements for
universal application has long been known from the state of the
art. This is a mixture of perchloric acid and acetic anhydride.
Often, however, this mixture cannot be used industrially owing to
the associated explosion risk, or can only be used with
considerable expenditure on safety measures.
[0008] Patent application WO 01/71068 A1 discloses electrolytic
polishing processes that can apparently be used for a wide range of
metals or metal alloys. These electropolishing processes use, among
other things, an electrolyte of methanesulfonic acid and methanol.
This electrolyte has, however, the serious drawback that because of
its high proportion of more than 80% of highly volatile methanol it
is a health hazard, and presents a risk of fire and explosion.
Therefore such a process can as a rule only be used at very low
temperatures, for example max. 10.degree. C., or with an expensive
system for trapping the resultant vapors and carrying them away.
Furthermore, suitability of this process for carbon steels,
magnesium, magnesium alloys or aluminum-silicon alloys has not been
disclosed.
[0009] The method disclosed in patent application U.S. 2005/0045491
A1 also appears to have a relatively wide range of applications,
but once again, suitability for magnesium-containing metal surfaces
or those comprising aluminum-silicon alloys is not disclosed. The
electrolyte used contains at least 75 wt. % of an alkylene glycol,
the remainder comprising a chloride salt of alkali metals and/or
alkaline-earth metals.
SUMMARY OF THE INVENTION
[0010] The present invention relates to an electropolishing process
that can be used successfully for a wide range of metals and metal
alloys and is substantially harmless with respect to labor safety
and environmental protection. The electrolyte used for this
comprises methanesulfonic acid and at least one alcoholic compound,
which is selected from aliphatic diols and alicyclic alcohols.
[0011] The method is suitable for the electropolishing of surfaces
of such diverse metals as iron, tungsten and light metals, and of
surfaces of alloys of these metals. In particular it is suitable
for surfaces of iron or an iron alloy, such as ferronickel, special
steel (stainless steels) or carbon steel, which can be
electropolished according to the present process both in the
hardened and in the unhardened form; of tungsten or a tungsten
alloy, of magnesium, a magnesium alloy, aluminum or an aluminum
alloy, as well as an aluminum-silicon alloy. An alloy of a
particular metal means alloys in which this metal is the main
constituent of the alloy, based on the weight of the constituents
of the alloy. Often said metal (or metals) comprises more than 50
wt. % of the alloy.
[0012] The electrolyte used in the electropolishing process
according to the present invention is a solution comprising
methanesulfonic acid and at least one alcoholic compound, the at
least one alcoholic compound being selected from the group
comprising aliphatic diols of general formula
C.sub.nH.sub.2n(OH).sub.2 with n=2-6 and alicyclic alcohols of
general formula C.sub.mH.sub.2m-1OH with m=5-8. In particular, the
alcoholic compound can comprise at least one aliphatic diol of
general formula C.sub.nH.sub.2n(OH).sub.2, with n=3, 4, 5 or 6.
Moreover, all isomers of these aliphatic diols can be used,
provided the two hydroxyl groups are bound to different carbon
atoms. Examples that may be mentioned are the compounds
1,2-propanediol, 1,2-butanediol or 1,4-butanediol.
[0013] In a special embodiment, the electrolyte contains, as
alcoholic compounds, both at least one aliphatic diol of general
formula C.sub.nH.sub.2n(OH).sub.2 and at least one alicyclic
alcohol of general formula C.sub.mH.sub.2m-1OH, where n=2-6 and
m=5-8.
[0014] The alicyclic alcohols of the present invention also
comprise all isomers satisfying the general formula
C.sub.mH.sub.2m-1OH with m=5-8. All carbon atoms can form the ring
structure, such as in cyclopentanol, cyclohexanol, cycloheptanol
and cyclooctanol; it is also possible, however, for one or more
carbon atoms to form a hydroxyalkyl and/or one or more alkyl side
chain(s). Electrolyte solutions comprising cyclohexanol are
especially preferred.
[0015] In a preferred embodiment, the electrolyte according to the
method for electropolishing of the present invention comprises a
mixture comprising 5-93% methanesulfonic acid and 95-7% of the at
least one alcoholic compound. These percentages and all others in
the present application relate, unless stated otherwise, to the
weight of the respective substances and solutions. It is especially
preferred for the electrolyte to comprise 10-80% methanesulfonic
acid and 90-20% of the at least one alcoholic compound. Thus, the
electrolyte can comprise for example 20-50% methanesulfonic acid
and 50-80% of the at least one alcoholic compound.
[0016] In particular, the method for electropolishing according to
the present invention is characterized in that apart from
methanesulfonic acid and alcoholic compounds, no other additives
are required for the electrolyte. It should be mentioned in
particular that the electrolyte used in this method contains
neither chromic acid or chromates, nor perchloric acid or its
salts. Moreover, the method does not use any highly volatile
additives such as methanol, ethanol or esters, the high vapor
pressure of which presents a particular challenge for labor safety
both with respect to their flammability and their toxicity. In
addition, the electrolyte does not contain any hydrofluoric acid
and also on this basis is largely problem-free in operation.
[0017] Preferably, the electrolyte used in the method according to
the present invention contains no water or only small amounts of
water. Thus, the water content of the electrolyte should not exceed
a proportion of 10% water. Furthermore, the electrolyte does not
require any addition of salts to increase its conductivity.
[0018] In a special embodiment of the present invention the method
is carried out at a temperature between 40.degree. C. and
100.degree. C. It is especially preferred for the method to be
carried out at a temperature between 60.degree. C. and 100.degree.
C. Since the electrolyte of the present method does not contain any
highly volatile constituents, higher temperatures can be used, for
example temperatures up to 80.degree. C., up to 90.degree. C., up
to 100.degree. C. or even higher, without the need for special
precautions, for example for reliable capture and removal of vapors
that form. The possibility that the method can also be carried out
at higher temperatures makes it possible, on the one hand, for the
electropolishing process to be carried out if necessary in a
relatively short time, and on the other hand it means that
expensive removal of the heat released in the electropolishing
process becomes unnecessary. Accordingly, expensive cooling becomes
largely or completely unnecessary. If cooling is used, it therefore
does not have to satisfy high performance requirements.
[0019] There is also considerable freedom in the choice of anodic
current density in the method presented here. Depending on the
particular metal, values between 3 and 40 A/dm.sup.2 of the surface
to be polished are preferred, and values in the range 5-30
A/dm.sup.2 are especially preferred. Tungsten or tungsten alloys in
particular permit the use of higher anodic current densities of for
example about 30-40 A/dm.sup.2. However, the other materials
described here can also be electropolished successfully at higher
anodic current densities. For surfaces containing iron, aluminum
and magnesium, however, anodic current densities of about 5-20
A/dm.sup.2 are generally entirely sufficient.
[0020] The duration of the electropolishing operation depends of
course on the metal being processed, the roughness of the workpiece
to be polished, the desired amount of metal removal and the desired
smoothing of the workpiece surfaces, and the temperature and the
current density.
[0021] In addition to its wide applications, the method according
to the invention possesses other important advantages over the
existing electropolishing processes. Thus, the electrolyte used is
not chemically aggressive and therefore after switching off the
electropolishing current, as well as during the subsequent rinsing
operations, it remains substantially inert with respect to the
surfaces being electropolished. The surfaces are not chemically
attacked and etched, so that the quality of the electropolished
surfaces is maintained and no special measures are required for
removing the electrolyte as quickly as possible from the treated
workpiece. This is particularly important in the processing of
workpieces with low corrosion resistance, for instance ordinary
steel, magnesium, aluminum and their alloys.
[0022] In addition to the method itself in all its aspects
presented here, a further aspect of the present invention relates
to the electrolytes described above that are used in this
method.
[0023] The invention is explained in more detail in the following
examples. These examples only represent possible embodiments of the
electropolishing process described here and of the electrolytes
used therein, and do not in any way imply a restriction to the
conditions used here.
EXAMPLES
1
[0024] Treated surface: Special steel, Material No. 1.4301
Electrolyte: 37% methanesulfonic acid+63% 1,2-propanediol
Temperature: 80.degree. C.
[0025] Anodic current density: 10 A/dm.sup.2
Duration: 15 min
Result: Mirror finish
2
[0026] Treated surface: tool steel (carbon steel)
Electrolyte: 37% methanesulfonic acid+63% 1,2-pentanediol
Temperature: 80.degree. C.
Anodic current density; 20 A/dm.sup.2
Duration: 10 min
Result: highly polished
3
[0027] Treated surface: tungsten
Electrolyte: 50% methanesulfonic acid+50% 1,2-propanediol
Temperature: 80.degree. C.
[0028] Anodic current density: 40 A/dm.sup.2
Result: highly polished
4
[0029] Treated surface: magnesium
Electrolyte: 20% methanesulfonic acid+40% 1,2-propanediol+40%
cyclohexanol
Temperature: 60.degree. C.
[0030] Anodic current density: 10 A/dm.sup.2
Duration: 8 minutes
Result: highly polished
5
[0031] Treated surface: aluminum-silicon alloy AlSi.sub.2O
Electrolyte: 20% methanesulfonic acid+80% 1,2-butanediol
Temperature: 80.degree. C.
Anodic current density; 10 A/dm.sup.2
Duration: 12 min
Result: highly polished
6
[0032] Treated surface: aluminum-magnesium alloy AlMg.sub.1
Electrolyte: 50% methanesulfonic acid+50% 1,2-propanediol
Temperature: 80.degree. C.
[0033] Anodic current density: 10 A/dm.sup.2
Duration: 10 min
[0034] Result: highly polished
* * * * *