U.S. patent application number 10/390867 was filed with the patent office on 2003-12-25 for method of manufacturing corrosion-resistant welding electrodes made of tungsten or a tungsten alloy.
Invention is credited to Geiger, Ernst, Resch, Joachim, Schintlmeister, Arno.
Application Number | 20030234064 10/390867 |
Document ID | / |
Family ID | 3493905 |
Filed Date | 2003-12-25 |
United States Patent
Application |
20030234064 |
Kind Code |
A1 |
Schintlmeister, Arno ; et
al. |
December 25, 2003 |
Method of manufacturing corrosion-resistant welding electrodes made
of tungsten or a tungsten alloy
Abstract
Corrosion-resistant welding electrodes made of tungsten or a
tungsten alloy are produced. Prefabricated welding electrodes are
heat treated at temperatures of between 300.degree. C. and
500.degree. C. in an oxidizing atmosphere. This results in the
formation of oxide layers on the surface of the welding electrodes;
these layers have good electrical conductivity and prevent the
formation of unwanted corrosion layers with poor conductivity.
Welding electrodes produced in this way demonstrate outstanding
spark ignition and problem-free erosion.
Inventors: |
Schintlmeister, Arno;
(Reutte, AT) ; Resch, Joachim; (Reutte, AT)
; Geiger, Ernst; (Reutte, AT) |
Correspondence
Address: |
LERNER AND GREENBERG, P.A.
POST OFFICE BOX 2480
HOLLYWOOD
FL
33022-2480
US
|
Family ID: |
3493905 |
Appl. No.: |
10/390867 |
Filed: |
March 17, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10390867 |
Mar 17, 2003 |
|
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PCT/AT02/00182 |
Jun 25, 2002 |
|
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Current U.S.
Class: |
148/281 |
Current CPC
Class: |
B23K 35/402 20130101;
C22F 1/18 20130101; C23C 8/10 20130101 |
Class at
Publication: |
148/281 |
International
Class: |
C23C 008/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 25, 2002 |
AT |
GM 563/2001 |
Claims
We claim:
1. A method of producing a corrosion-resistant welding electrode,
which comprises: providing a welding electrode of tungsten or
tungsten alloy; and heat treating the welding electrode at a
temperature of between 300.degree. C. and 500.degree. C. in an
oxidizing atmosphere.
2. The method according to claim 1, which comprises heat treating
at a temperature between 375.degree. C. and 430.degree. C.
3. The method according to claim 1, which comprises heat treating
over a period of between 2 and 8 hours.
4. The method according to claim 1, wherein the oxidizing
atmosphere is air.
5. The method according to claim 1, which comprises adjusting
oxidation conditions to form an oxide layer with a color
corresponding to a color prescribed to identify the electrode
material.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of copending
International Application No. PCT/AT02/00182, filed Jun. 25, 2002,
which designated the United States and which was not published in
English.
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] The invention is for a method for the production of
corrosion-resistant welding electrodes made of tungsten or a
tungsten alloy.
[0003] In situations of high air humidity in particular, and even
at room temperature, tungsten forms corrosion layers consisting of
a combination of tungsten with oxygen and nitrogen. Tungsten and
tungsten alloys, especially those that are alloyed with oxidic
additives, such as thorium oxide, lanthanum oxide, cerium oxide or
zirconium oxide, are also frequently used for the manufacture of
welding electrodes for TIG welding (TIG, tungsten inert gas).
Tungsten welding electrodes have to exhibit a low transfer
resistance, especially to the electrode holder, in order to
guarantee good spark ignition and problem-free operation.
[0004] The layers of corrosion that form on the tungsten and
tungsten alloys as a result of increased air humidity greatly
impair the electrical conductivity and thus increase contact
resistance. Consequently, the spark ignition and erosion of such
corroded welding electrodes present a considerable problem.
SUMMARY OF THE INVENTION
[0005] It is accordingly an object of the invention to provide a
method of producing corrosion-protected welding electrodes of
tungsten or a tungsten alloy which overcomes the above-mentioned
disadvantages of the heretofore-known devices and methods of this
general type and which is aimed at creating a measure that
prevents, to a sufficient extent, the unwanted corrosion of
tungsten or tungsten alloy welding electrodes.
[0006] With the foregoing and other objects in view there is
provided, in accordance with the invention, a method of producing a
corrosion-resistant welding electrode, which comprises:
[0007] providing a welding electrode of tungsten or tungsten alloy;
and
[0008] heat treating the welding electrode at a temperature of
between 300.degree. C. and 500.degree. C. in an oxidizing
atmosphere, and preferably in a temperature range between
375.degree. C. and 430.degree. C.
[0009] That is, the above and other objects of the invention are
achieved by heat-treating the prefabricated welding electrodes at
temperatures of between 300.degree. C. and 500.degree. C. in an
oxidizing atmosphere.
[0010] Such a heat treatment results in the formation of an oxide
layer consisting of WO.sub.3 or WO.sub.3-x on the surfaces of the
welding electrodes.
[0011] The formation of this oxide layer, which exhibits good
electrical conductivity, safely prevents the formation of
undesirable corrosion layers with poor conductivity and the welding
electrodes demonstrate outstanding spark ignition and problem-free
erosion.
[0012] This process is suitable for pure tungsten, as well as for
all tungsten alloys normally used as welding electrodes.
[0013] The process is cost-effective. Before the heat treatment,
which can, for example, take place in a drying cabinet, the welding
electrodes have to be carefully cleaned to remove traces of grease
and dirt.
[0014] Ideally, heating to the oxidation temperature should occur
within a period of approx. 15 to 45 minutes. Cooling to room
temperature should preferably take place within a period of 30 to
60 minutes. The oxidation treatment of this invention has no
negative effects whatsoever on the metallurgical properties of the
welding electrodes. Oxidation treatment within a temperature range
of 375.degree. C. to 430.degree. C. has proved to be particularly
advantageous.
[0015] A period of between two and eight hours has proved to be
particularly effective for the oxidation treatment. During this
period, the oxide layers on the surface form with thicknesses
between 10 nm and 50 nm. On the one hand, this guarantees good
adhesive properties and, on the other hand, that the oxide layers
thus formed are sufficiently resistant to abrasion.
[0016] It is especially easy and economical to perform the
oxidation treatment using air as the oxidizing atmosphere.
[0017] Depending on the temperature attained during the oxidation
treatment, it is possible to obtain different colors; at relatively
low temperature deviations of 10.degree. C. to 15.degree. C., clear
changes in color are visible. Different colors are the result of
the formation of surface oxide layers of different densities. In
particular, by varying the temperature, the colors gold, blue,
violet and brown, with the appropriate gradations, can be obtained
during the oxidation treatment.
[0018] Depending on the composition of the material used for the
electrode, welding electrodes must be color-coded for
identification of the electrode material.
[0019] For example, according to EN 26848 and ISO 6848, the
following color markings are prescribed for the following
alloys:
1 Pure T green T with 0.35-0.55% ThO.sub.2 blue T with 0.80-1.20%
ThO.sub.2 yellow T with 1.70-2.20% ThO.sub.2 red T with 2.80-3.20%
ThO.sub.2 violet T with 3.80-4.20% ThO.sub.2 orange T with
0.15-0.50% ZrO.sub.2 brown T with 0.70-0.90% ZrO.sub.2 white T with
1.80-2.20% CeO grey T with 0.90-1.20% La.sub.2O.sub.3 black T with
1.3-1.7% La.sub.2O.sub.3 gold
[0020] The color-coding markings are generally applied in the form
of stripes of paint that are applied to the end of the electrode
that is inserted into the electrode holder. This method results in
the repeated abrasion of the color-coding marking and the paint is
thus distributed over the contact zone with the electrode holder.
This means that the layer of paint can impair the contact between
the electrode holder and the electrode.
[0021] A particularly favorable side-effect of the procedure
described by this invention occurs when the oxidation conditions
are such that the color of the oxide layer formed is the same as
that prescribed for the identification of the electrode material
used. Thus, the formation of the oxide layer serves simultaneously
as oxidation protection and color-coding; this means that no
additional color-coding is required.
[0022] Such a procedure is technically feasible for the following
in particular:
[0023] Welding electrodes made of tungsten alloy with 1.3-1.7%
La.sub.2O.sub.3; gold is the prescribed color-coding.
[0024] Welding electrodes made of tungsten alloy with 0.35-0.55%
ThO.sub.2, blue is the prescribed color-coding.
[0025] Welding electrodes made of tungsten alloy with 2.8-3.2%
ThO.sub.2; violet is the prescribed color-coding.
[0026] Welding electrodes made of tungsten alloy with 0.15-0.50%
ZrO.sub.2; brown is the prescribed color-coding.
[0027] If these colors can be produced clearly by the appropriate
control of the oxidation treatment, additional color-coding using
paint is no longer necessary. There is, consequently, no
deterioration in the contact resistance between the welding
electrode and electrode holder.
[0028] In the following, the invention is described using
manufacturing examples with two different materials for welding
electrodes.
EXAMPLE 1
[0029] Welding electrodes of length 150 mm and diameter 2.4 mm made
from a tungsten alloy with 1.3 to 1.7% La.sub.2O.sub.3 and produced
by wire-drawing were cleaned with acetone in an ultrasonic
bath.
[0030] The electrodes were then heated in air in a muffle furnace
for about 40 minutes to a temperature of 400.degree. C. and
oxidized over a period of 75 minutes.
[0031] After the completion of the heat treatment, the welding
electrodes were removed from the furnace and cooled to room
temperature.
[0032] After the oxidation treatment, the welding electrodes were
gold-colored.
EXAMPLE 2
[0033] Apart from the treatment time, welding electrodes as per
example 1 were treated under the same conditions as described in
example 1.
[0034] In this case, the treatment time was 120 minutes.
[0035] After the oxidation treatment, the welding electrodes were
violet-colored.
EXAMPLE 3
[0036] Apart from the treatment temperature and the treatment time,
welding electrodes as per example 1 were treated under the same
conditions as described in example 1.
[0037] In this case, the treatment temperature was 450.degree. C.
and the treatment time was 10 hours.
[0038] After the oxidation treatment, the welding electrodes were
blue-colored.
EXAMPLE 4
[0039] Welding electrodes of length 150 mm and diameter 2.4 mm made
from pure tungsten were produced and cleaned as described in
example 1.
[0040] Apart from the treatment time, the further oxidation
treatment was in accordance with example 1. In this case, the
treatment time was 45 minutes.
[0041] After the oxidation treatment, the welding electrodes were
gold-colored.
[0042] In order to investigate the corrosion resistance, the
welding electrodes produced as per the examples were stored
together with welding electrodes produced with no oxidation
treatment in a climatic chamber for 90 hours at 70.degree. C. and
98% air humidity.
[0043] After storage, the welding electrodes produced in accordance
with the invention exhibit no visibly discernible surface changes,
which would indicate the formation of a corrosion layer. In a
subsequent welding test, the welding electrodes demonstrate a good
spark ignition and outstanding erosion.
[0044] In contrast, the welding electrodes that were produced
without any oxidation treatment show clearly visible black patches
that indicate the formation of a corrosion layer. In the subsequent
welding test, the spark ignition and the erosion were much worse
than the welding electrodes produced in accordance with the
invention.
* * * * *