U.S. patent application number 11/081942 was filed with the patent office on 2006-09-21 for flux cored electrode.
This patent application is currently assigned to LINCOLN GLOBAL, INC.. Invention is credited to Nikhil Karogal.
Application Number | 20060207984 11/081942 |
Document ID | / |
Family ID | 37009232 |
Filed Date | 2006-09-21 |
United States Patent
Application |
20060207984 |
Kind Code |
A1 |
Karogal; Nikhil |
September 21, 2006 |
Flux cored electrode
Abstract
A flux cored electrode including a metal sheath surrounding a
core of particles containing a flux system with dispersed magnesium
particles in generally spherical shape and having a graded size to
pass through a number 30 U.S. Standard sieve.
Inventors: |
Karogal; Nikhil; (Cleveland,
OH) |
Correspondence
Address: |
FAY, SHARPE, FAGAN, MINNICH & MCKEE, LLP
1100 SUPERIOR AVENUE, SEVENTH FLOOR
CLEVELAND
OH
44114
US
|
Assignee: |
LINCOLN GLOBAL, INC.
|
Family ID: |
37009232 |
Appl. No.: |
11/081942 |
Filed: |
March 17, 2005 |
Current U.S.
Class: |
219/145.22 |
Current CPC
Class: |
B23K 35/0266 20130101;
B23K 35/368 20130101; B23K 35/406 20130101; B23K 35/3608
20130101 |
Class at
Publication: |
219/145.22 |
International
Class: |
B23K 35/02 20060101
B23K035/02 |
Claims
1. A flux cored electrode including a metal sheath surrounding a
core of particles containing a flux system with dispersed magnesium
particles in generally spherical shape and having a graded size to
pass through a number 30 U.S. Standard sieve.
2. A flux cored electrode as defined in claim 1 wherein said
magnesium particles are formed by gas atomization of molten
magnesium.
3. A flux cored electrode as defined in claim 2 wherein said
magnesium particles are coated with a layer of organic compound
with a thickness of less than 10 microns.
4. A flux cored electrode as defined in claim 1 wherein said
magnesium particles are coated with a layer of organic compound
with a thickness of less than 10 microns.
5. A flux cored electrode as defined in claim 4 wherein said
fluxing system is based upon titanum dioxide.
6. A flux cored electrode as defined in claim 3 wherein said
fluxing system is based upon titanum dioxide.
7. A flux cored electrode as defined in claim 2 wherein said
fluxing system is based upon titanum dioxide.
8. A flux cored electrode as defined in claim 1 wherein said
fluxing system is based upon titanum dioxide.
9. A flux cored electrode as defined in claim 8 wherein said core
includes particles of alloying agents.
10. A flux cored electrode as defined in claim 7 wherein said core
includes particles of alloying agents.
11. A flux cored electrode as defined in claim 6 wherein said core
includes particles of alloying agents.
12. A flux cored electrode as defined in claim 5 wherein said core
includes particles of alloying agents.
13. A flux cored electrode as defined in claim 4 wherein said core
includes particles of alloying agents.
14. A flux cored electrode as defined in claim 3 wherein said core
includes particles of alloying agents.
15. A flux cored electrode as defined in claim 2 wherein said core
includes particles of alloying agents.
16. A flux cored electrode as defined in claim 1 wherein said core
includes particles of alloying agents.
17. A flux cored electrode as defined in claim 16 wherein said
electrode is self shielding and said core includes aluminum
particles with the weight of said aluminum particles being greater
than the weight of said magnesium particles.
18. A flux cored electrode as defined in claim 8 wherein said
electrode is self shielding and said core includes aluminum
particles with the weight of said aluminum particles being greater
than the weight of said magnesium particles.
19. A flux cored electrode as defined in claim 4 wherein said
electrode is self shielding and said core includes aluminum
particles with the weight of said aluminum particles being greater
than the weight of said magnesium particles.
20. A flux cored electrode as defined in claim 2 wherein said
electrode is self shielding and said core includes aluminum
particles with the weight of said aluminum particles being less
than the weight of said magnesium particles.
21. A flux cored electrode as defined in claim 1 wherein said
electrode is self shielding and said core includes aluminum
particles with the weight of said aluminum particles being less
than the weight of said magnesium particles.
22. A flux cored electrode as defined in claim 21 wherein said
magnesium particles are coated with a layer of a silicon compound
with a thickness of less than 10 microns.
23. A flux cored electrode as defined in claim 16 wherein said
magnesium particles are coated with a layer of a silicon compound
with a thickness of less than 10 microns.
24. A flux cored electrode as defined in claim 8 wherein said
magnesium particles are coated with a layer of a silicon compound
with a thickness of less than 10 microns.
25. A flux cored electrode as defined in claim 2 wherein said
magnesium particles are coated with a layer of a silicon compound
with a thickness of less than 10 microns.
26. A flux cored electrode as defined in claim 1 wherein said
magnesium particles are coated with a layer of a silicon compound
with a thickness of less than 10 microns.
27. A method of electric arc welding on a workpiece, said method
comprising: (a) providing a flux cored electrode with spherical
particles of elemental magnesium having a graded particle size of
less than about 0.025 inches in diameter; (b) passing a current
through said electrode and between said electrode and workpiece to
melt said electrode into molten metal whereby said magnesium
particles are melted and reduce free oxygen in said molten metal;
and, (c) forcing a shielding gas around said molten metal.
28. A gas shielded flux cored electrode with a core comprising:
titanium dioxide ferro alloys magnesium wherein the magnesium is in
the form of particles with a generally spherical shape and a graded
size less than about 0.025 inches in diameter.
29. A self shielded flux cored electrode with a core comprising:
titanium dioxide ferro alloys aluminum magnesium wherein the
magnesium is in the form of particles with a generally spherical
shape and a graded size less than about 0.025 inches in
diameter.
30. A flux cored electrode as defined in claim 29 wherein said
aluminum in particle form is greater in weight than said
magnesium.
31. A flux cored electrode as defined in claim 30 wherein said core
includes MgO.
32. A flux cored electrode as defined in claim 29 wherein said core
includes MgO.
33. A flux cored electrode as defined in claim 28 wherein said core
includes MgO.
34. A flux cored electrode as defined in claim 33 wherein said core
includes less than 0.01 percent hydrated magnesium.
35. A flux cored electrode as defined in claim 32 wherein said core
includes less than 0.01 percent hydrated magnesium.
36. A flux cored electrode as defined in claim 31 wherein said core
includes less than 0.01 percent hydrated magnesium.
37. A flux cored electrode as defined in claim 30 wherein said core
includes less than 0.01 percent hydrated magnesium.
38. A flux cored electrode as defined in claim 29 wherein said core
includes less than 0.01 percent hydrated magnesium.
39. A flux cored electrode as defined in claim 28 wherein said core
includes less than 0.01 percent hydrated magnesium.
40. A magnesium powder particle for use in a flux cored electrode,
said powder particle having a surface tension created smooth outer
surface and a graded size less than about 0.025 inches in
diameter.
41. A magnesium powder particle as defined in claim 40 wherein said
particle as a graded size greater than about 0.002 inches in
diameter.
42. A magnesium powder particle as defined in claim 41 wherein said
particle has a coating of less than about 10 microns.
43. A magnesium powder particle as defined in claim 40 wherein said
particle has a coating of less than about 10 microns.
Description
[0001] The present invention relates to a flux cored electrode used
in electric arc welding and more particularly to the use of a
specific form of magnesium particles in the core of the electrode
or wire.
BACKGROUND OF INVENTION
[0002] Flux cored electrodes have been used for many years and
include an outer metal sheath sized around an inner core of
particles forming a flux system. To control the composition of the
weld metal formed by using the electrode in an electric arc welding
process, the core generally includes a number of metal particles to
be melted and alloyed into the weld metal resulting from the
welding process. It is common practice to use magnesium particles
in the core of the electrode so these particles are evenly
dispersed with the other core particles to produce a flux cored
electrode. The use of small magnesium particles in flux cored
electrodes is common.
[0003] The flux in a cored electrode that produces high impact
welds while welding vertically up or overhead and has high melt off
rates is disclosed in Amata U.S. Pat. No. 4,551,610. Particles of
lithium oxide, iron oxide, silicon dioxide, lithium carbonates,
magnesium and aluminum are used in the core. This patent is
incorporated by reference herein to illustrate a representative
flux cored electrode using magnesium. The magnesium particles can
be particles employing the present invention. This patent also
combines a large amount of elemental aluminum with a smaller amount
of elemental magnesium to provide the oxidizing agents in the weld
metal for a self shielded electrode. The present invention is
primarily used for gas shielded electrodes, but also relates to the
concept of using a combination of magnesium with standard aluminum
particles. Thus, this patent teaches a type of electrode in which
the present invention can be implemented.
[0004] In Sakai U.S. Pat. No. 4,571,480, another flux cored
electrode using aluminum and magnesium particles is disclosed. This
flux cored electrode patent discusses the function of magnesium
particles and the combination of aluminum and magnesium in the core
of the electrode. However, there is an indication that the
magnesium leads to an increase in fume generation. Thus, it is
suggested that magnesium particles should be in an amount not more
than 10%. The magnesium vaporizes into an explosive substance upon
exposure to heat of the arc. The explosive nature of the magnesium
causes formation of a large number of spatter events. Thus, it is
preferable that magnesium particles are in the form of a magnesium
alloy, such as aluminum-magnesium, magnesium-silicon,
magnesium-silicon calcium, nickel-magnesium or lithium-magnesium.
Disadvantages of using magnesium particles, as discussed in the
Sakai patent, are overcome by the formation of magnesium powder in
accordance with the present invention. However, this patent does
illustrate the problems to which the present invention is directed
and the function of magnesium and the function of a magnesium oxide
which prevents magnesium from being a deoxidizing or
denitrification material in the molten weld metal. Thus, this
patent teaches the reasons for elemental magnesium and slag forming
magnesium oxide, together with some of the difficulties associated
with using the elemental magnesium particles in the flux cored
electrode. Indeed, the solution suggested in this prior art is the
use of aluminum as an alloy with elemental magnesium metal. By
using the present invention, modification of magnesium into an
alloy particle before inclusion into the core of the electrode is
not required. Another background flux cored electrode is described
in Sakai U.S. Pat. No. 5,580,475 which again discusses the
advantage of magnesium particles wherein cracking of the metal is
reduced, together with the improved slag removability using
magnesium oxide or magnesium particles in an amount of about 0.2%.
This use of deoxidizing magnesium or slag forming magnesium oxide
causes deterioration of the bead shape, but adds to the improved
slag removability. Thus, there is a need to reduce both the amount
of magnesium in the flux core and the amount of resultant magnesium
oxide formed from magnesium during or before the welding process.
Magnesium acts to reduce oxygen in the weld metal. MgO also removes
free oxygen. These two magnesium sources are effective to improve
toughness and blow hole resistance. The preferred source of
magnesium is metal or elemental magnesium particles even though, as
described, metal alloys of magnesium can be employed. In this
patent, the magnesium oxide is incorporated into the flux core as a
separate oxide so it performs its function in the welding process
as the magnesium particles react actively as a deoxidizing agent.
The magnesium and magnesium oxide improve the slag removability.
Thus, there is a need to provide both magnesium in the metal form
without requiring an alloy and magnesium as magnesium oxide. These
two Sakai patents are incorporated by reference herein as
illustrating electrodes which can employ advantageously magnesium
particles of the present invention.
[0005] As described in the various prior art patents, magnesium
particles are used in the core of flux cored electrodes to
deoxidize the weld metal during the welding process. However,
magnesium forms hydrides due to the inherent reactivity of
magnesium. Consequently, as the cored electrode is manufactured by
being extruded to size and then baked to a temperature of
400-700.degree. F., the reactive magnesium particles tend to be
hydrated. Furthermore, hydration occurs as the reactive particles
are stored awaiting filling into the metal sheath prior to the
extrusion and baking. Since the procedure for forming flux cored
electrodes involves exposure to the atmosphere and high heat, the
magnesium small particles in the core are also oxidized into MgO.
This conversion changes the reactivity of the magnesium and
decreases its oxidizing capability in the molten weld metal.
[0006] The baking process is required to remove drawing lubricants
from the extruded electrode. By hydration of the magnesium
particles and oxidation of the magnesium particles, the magnesium
particles in the core material has a reduced amount of active
magnesium available for its primary function of deoxidation in the
weld metal. In other words, the amount of available magnesium for
deoxidation prior to the electrode manufacturing process is
substantially greater than the actual magnesium available in the
final flux cored electrode. Some of the magnesium is converted to
MgO or is hydrated by hydrophilic action of the very reactive,
small magnesium particles. Hydration of the magnesium powder during
storage and baking, reduces the amount of magnesium available for
oxidation by producing a certain amount of MgH.sub.2. This hydrogen
compound decomposes in the molten metal to increase the amount of
diffusible hydrogen in the weld. Thus, the formation of MgH.sub.2
during processing or storage increases the tendency of the
magnesium powder itself to cause higher levels of diffusible
hydrogen. Furthermore, the oxidation of the magnesium particles
into MgO reduces the amount of deoxidation potential of the
particles in the core. Thus, the use of small magnesium particles
in the past has involved balancing the advantage of magnesium to
deoxidize the molten metal with the disadvantage of hydrogen
pick-up of the magnesium powder. The hydrogen pick-up, together
with oxidation of the magnesium powder during processing, reduces
the deoxidation potential of the magnesium particles. The present
invention reduces these disadvantages of using small magnesium
powder in the flux core of an electrode. When the electrode is gas
shielded, the magnesium particles are normally less than about 25%
and there is no added aluminum powder. On the other hand, when the
flux cored electrode is used for self shielding, the core includes
small aluminum particles together with small magnesium particles,
with the aluminum particles being greater in weight. The aluminum
and magnesium particles form the deoxidation component of the core
for self shielded electrodes. The present invention is primarily
directed to gas shielded electrodes wherein the core merely
includes small magnesium particles for deoxidation. However, the
invention is also capable of being employed in self shielded flux
cored electrodes where small aluminum and small magnesium powders
are used for deoxidation. The term small means less than about
0.025 inches in major dimension. This particle size allows better
distribution in the core.
THE INVENTION
[0007] In the past, magnesium particles were crushed and ground
into small particles. These particles had a tremendously high ratio
of surface area to total volume of the particles. Consequently, the
magnesium particles have high exposed reactivity. This is in
proportion to the ratio of exposed surface area to weight. The
surface reactivity is different than the mass reactivity. To
decrease the effect of the extreme surface reactivity of the
otherwise high mass reactive magnesium material, it was suggested
that a coating of silicon oxide be applied in some manner over the
small particles. Coating of the small particles with a thin layer
does not encompass the many crevices on the surface of the
magnesium particles and, thus, was easily dislodged during the
storage, pressure extrusion and baking. Furthermore, thin coating
of the small magnesium particles was a delicate and expensive
process. It could be done only in a batch procedure. Consequently,
the thin coating of the otherwise high mass reactive magnesium
particles with the extreme high surface reactivity, engendered by
the large surface ratio, was only theoretical and not practical.
Thus, a suggestion to reduce the surface reactivity of magnesium
particles for use in flux cored electrodes was not commercially
viable or physically effective.
[0008] The present invention recognizes the problems of providing
the highly explosive, magnesium particles having a small size
necessary for even distribution in the core of a flux cored
electrode. This technical difficulty of providing small magnesium
particles has been overcome by using gas atomized magnesium powders
produced by atomizing metal magnesium with high velocity inert gas,
such as argon. Such particles are generally spherical due to the
surface tension associated with each particle during the gas
atomized procedure. To provide the necessary small dimension for
uniform distribution in the core of an electrode, the individually
atomized particles of magnesium are sized or graded by a screen or
sieve process. The spherical particles pass through a US Standard
screen of 30 or 40 mesh, but not through a screen of about 325
mesh. Thus, the particles have a small size in the general range of
about 0.025 to 0.002 inches in diameter. This small size allows the
individual particles to be evenly dispersed through the core
material of the electrode. Since the sizing is done by a screen
procedure not crushing, the diminution of the particle size of the
magnesium does not increase the ratio of surface area to volume or
mass of the small magnesium powder or particles. Each particle is
generally spherical caused by surface tension during the molten
metal forming process and a gradation procedure is employed for
producing the desired small size of particles for the flux cored
electrode manufacturing procedure. The atomizing process is quite
expensive; however, the advantageous end result is economically
justified. The particles have a low surface reactivity, but retain
the same level of mass reactivity.
[0009] The spherical particles having small size minimizes the
surface area ratio to thereby reduce the effective exposure
reactivity of the magnesium particles. Consequently, during storage
and processing of the core material or magnesium particles, there
is a less tendency for the magnesium to oxidize. Indeed, during the
baking action, very little MgO is formed due to the oxidation of
the reduced reactive nature of the inventive particles.
Furthermore, during storage of the reduced surface reactivity
magnesium particle, there is a lesser tendency to form MgH.sub.2 or
MgOH.sub.2 so there is a lesser tendency for the magnesium powder
to attract hydrogen. Such hydration of a core material constitutes
a source of diffusible hydrogen in the weld metal of the welding
process. Consequently, by using the present invention, the tendency
of the weld metal to crack is reduced without the necessity for
highly expensive procedures to avoid hydrodration of the magnesium
during storage and processing. The present invention reduces the
diffusible hydrogen in localized areas of the resulting weld metal
and substantially improves the cracking characteristics of the weld
metal, without drastically increasing the expense associated with
reducing the hydrogen pick-up of magnesium during the manufacturing
process. The advantages of the invention greatly offsets the higher
costs of producing the small magnesium particles before they are
shipped to the manufacturing line for the cored electrode. In the
invention, it is preferred that the spherical particles with lower
surface area are produced by a gas atomized process. Such process
has heretofore been employed to produce large particles primarily
for military use in flares. The military magnesium particles are
graded, preferably through a 40 mesh screen. Thus, the magnesium
powders are separated into a small size for even distribution in
the core of an electrode. Standard military gas atomized magnesium
powders has the magnesium droplets frozen while in an unrestrained
molten state. They are in a substantially spherical shape, which is
defined as the shape caused by surface tension on freezing instead
of crushing of large particles. Although a 40 mesh screen size is
preferred, it has been found that the invention is applicable with
a larger sized magnesium particle, such as particles passing
through a 30 mesh screen. Thus, the small particles are formed
without crushing and results in a smooth surface. The relative size
of the surface area reduces the surface reactivity of the
individual particles. These individual gas atomized particles may
be treated with hydrophobic fumed silica or caruba wax. This
coating procedure further reduces the surface reactivity of the
otherwise smooth surface formed by the gas atomizing process. Thus,
the present invention utilizes small magnesium particles with a low
surface reactivity caused by a decrease in the ratio of surface
area to mass or weight.
[0010] In accordance with the present invention there is provided a
flux cored electrode including a metal sheath surrounding a core of
particles containing a flux system with dispersed small magnesium
particles having generally spherical shape and having a size to
pass through a 30 U.S. Standard sieve.
[0011] In accordance with another aspect of the invention, the flux
cored electrode as defined above also includes particles of
alloying agents as well as a fluxing system based upon titanium
dioxide.
[0012] In accordance with another aspect of the present invention
there is provided a method of electric arc welding on a workpiece.
This method comprises providing a flux cored electrode with
spherical particles of elemental magnesium having a particle size
of less than about 0.025 inches in diameter, passing a current
through the electrode and between the electrode and the workpiece
to melt the electrode into molten metal wherein the magnesium
particles are melted and reduce free oxygen in the molten metal,
and forcing a shielding gas around the molten metal. When the
welding method is to use a flux cored electrode that this self
shielding, it is normally advantageous to provide small aluminum
particles to act with the small magnesium particles wherein the
aluminum particles have a greater weight than the magnesium
particles.
[0013] Yet another aspect of the present invention is the graded
magnesium particles themselves. These particles are used for flux
cored electrodes and each has a surface tension created smooth
outer surface and are graded to a size of less than about 0.025
inches in diameter.
[0014] The primary object of the present invention is the provision
of magnesium particles for use in a flux cored electrode, which
magnesium particles have a reduced surface reactivity to prevent
oxidation and hydrogen reaction during the storage and
manufacturing of the electrode.
[0015] Another object of the present invention is the provision of
magnesium particles, as defined above, which particles have an
outer surface formed by surface tension as contrasted to forming a
jagged surface by a mechanical crushing action.
[0016] Still a further object of the present invention is the
provision of powdered magnesium particles, as defined above, which
particles have a graded size less than about 0.025 inches in
diameter and a minimum size normally greater than about 0.002
inches in diameter.
[0017] These and other objects and advantages will become apparent
from the following description taken together with the accompanying
drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0018] FIG. 1 is a schematic diagram of a process for forming air
atomized magnesium particles having a variety of spherical
sizes;
[0019] FIG. 2 is an enlarged partial view taken generally along
line 2-2 of FIG. 1;
[0020] FIG. 3 is a distribution and gradation curve used in
practicing the preferred embodiment of the present invention;
[0021] FIG. 4 is a schematic pictorial view illustrating the first
step of filling the sheath in manufacturing a flux cored
electrode;
[0022] FIG. 5 is a cross-sectional view of a flux cored electrode
during the manufacturing process preparatory to being drawn through
a die and heated in a furnace;
[0023] FIG. 6 is a cross-sectional view of a finished flux cored
electrode illustrating the final baking procedure;
[0024] FIG. 7 is an enlarged, generally cross-sectioned view of the
preferred embodiment of a flux cored electrode used in an electric
arc welding process; and,
[0025] FIG. 8 is a schematic view illustrating a thin coating over
a small particle of magnesium produced by the procedure
schematically illustrated in FIGS. 1-3.
PREFERRED EMBODIMENT
[0026] To minimize the oxidation of small magnesium particles and
the ability of magnesium particles to attract hydrogen, the present
invention involves the use of a specially produced magnesium
particle, which particles are graded for a selected range of
particle sizes. This concept is schematically illustrated in FIGS.
1-3 wherein an air atomizing system 10 includes a molten metal
nozzle 20 receiving molten magnesium from supply 22 maintained in a
molten condition by heat source 24. Nozzle 20 causes droplets of
magnesium to fall by gravity past one or more gas jets 30 having a
high velocity spray of gas G directed toward the downwardly
traveling individual droplets. These droplets are particles which
translate from molten particles P1 to partially solidified
particles P2 into fully solid particles P3 as the particles P pass
downwardly through gas G from one or more high pressure jet 30.
This process is used for producing atomizing magnesium powder for
military use and is produced by Hart Metals, Inc. Of Tamaqua, Pa.
Particles P have over 99% free metallic magnesium and minor traces
of other compounds, such as less than 0.030 iron oxide. The maximum
amount of carbides is 0.002%. Essentially, particles P1, P2 and P3
dropping downwardly by gravity from nozzle 20 are pure metal
magnesium starting in a molten state. This process produces
particles P of various sizes as shown in a lower tray or hopper 40.
These particles have a size distribution as schematically
illustrated in FIG. 2 and graphically in FIG. 3. Particles P are
illustrated as particles 50 that are large and particles 52 that
are small. In between the large and small particles there are
different sized particles, such as medium sized particles 54 and
56. Indeed, the distribution of the particles in the process
performed by system 10 are in the form of a common bell curve 100.
In accordance with the invention, the particle size used in a cored
electrode is a particle size greater than a number 30 sieve as
indicated by point 102 and point 104. The particles used in
practicing the invention are generally greater than 0.25 inches in
diameter. To prevent the existence of minute finds, which are
highly explosive, the invention involves a minimum diameter of
about 0.02 inches indicated as a number 325 sieve by point 106,
108. Thus, the present invention involves small gas atomized
magnesium particles distributed in areas 110, 112 of bell curve
100, as shown in FIG. 3. In practice, the magnesium particles P
pass through a number 40 mesh screen with 98% of the particles
passing through a number 60 screen. A very small amount of
particles can pass through a number 325 screen. In practice, this
small amount is drastically less than about 5%. Thus, less than 2%
of the particles are smaller than 20 microns. The particles include
99% magnesium with only a trace amount of impurities. As shown in
FIG. 1, particles P1 are molten and dropped downwardly. These
molten particles use surface tension to assume a generally
spherical configuration, with a smooth outer surface. When exposed
to inert gas G, the outer surfaces of particles P1 are partially
solidified as indicated by particles P2. Full solidification is
effected as particles P drop downwardly into receptacle 40, which
receptacle can be filled with a liquid cooling bath to finalize
solidification of particles P. In the vertical direction, a
plurality of vertically aligned jets 30 can successively solidify
the particles dropping from nozzle 20. Thus, particles P have an
outer surface which is defined in this application as being
generally spherical and has a graded size in the general range of
0.25-0.002 inches in diameter. These particles are then placed in
containers and shipped to a manufacturing facility where they are
stored for a period of time. During transportation and storage, the
spherical smooth outer surface of particles P prevents the
particles from oxidizing or hydrating. This phenomenon maintains
the elemental magnesium composition of particles P, even though
they are reduced to a small size. The surface shape does not allow
the particles to absorb hydrogen for subsequent adverse effect in
the weld metal.
[0027] In accordance with the present invention, particles P
produced in accordance with the procedure described in FIGS. 1-3
are used in the core of flux cored electrode E by a standard
procedure for making flux cored electrodes, as shown in FIGS. 4-6.
Particle dispenser 120 has a nozzle 122 for directing small
particulate core material C, i.e. core C, into the trough of sheath
130 formed of a mild steel. Particles of core C generally include a
fluxing system, metal alloying particles and deoxidizing particles,
such as magnesium particles P. When the flux cored electrode is gas
shielded, a certain amount of aluminum particles is included in
core C. In accordance with standard technology particle storage
bins 150, 152 and 154 direct magnesium particles P, alloying
particles and flux particles, such as titanium dioxide with other
additives, into dispenser 120 by way of solid mixer 140 so that the
particles are all evenly distributed through core material C. By
providing small graded particles, such as described in relationship
to FIG. 3, magnesium particles P can be evenly distributed through
core material C. After depositing core material C into the trough
of sheath 130, the sheath is closed into a cylindrical
configuration as generally illustrated in FIG. 5. In this manner,
core material C is compacted by sheath 130. The compact core
material C is then sized through a drawing die which involves
drawing compounds, that are removed by a subsequent baking
procedure, as schematically illustrated in FIG. 6. The extruded,
sized electrode E is passed through a heating oven at a temperature
between 400-700.degree. F. During this heating process, the
physical surface characteristics of novel, small particle P prevent
oxidation of the particles by ambient oxygen captured within sheath
130. Particles P remain elemental magnesium with the natural mass
reactivity characteristic of magnesium metal itself, but not the
overreactive physical surface reactivity characteristics heretofore
obtained by crushed small particles of magnesium. After electrode E
has been formed into a flux cored electrode having an indeterminate
length, it is stored on a reel or in a box or drum for subsequent
use in an electric arc welding process schematically illustrated in
FIG. 7.
[0028] Referring now in more detail to the arc welding process
schematically illustrated in FIG. 7, electrode E is moved downward
to workpiece WP while arc A is formed between the metal sheath 130
and workpiece WP. The welding process involves formation of a
molten metal ball M on the end of advancing electrode E. Core
material C includes alloying metal with particles that are melted
with sheath 130 to form ball B. Particles P are oxidized in ball B
to attract oxygen and form magnesium oxide. This MgO is removed as
slag S formed on the top of molten metal M deposited by the welding
process. Magnesium particles P are reactive in proportion to the
molten mass and not to the pre-melted surface area. The magnesium
deoxidizing constituents of core material C retain that ability to
reduce the oxygen while being melted by the welding process in
molten metal ball B. Thus, there is no contamination and diminution
of the primary deoxidation function of particles P by previous
surface attraction of oxygen and/or hydrogen. Consequently,
particles P perform their primary function without the deleterious
physical properties of prior crushed magnesium particles, coated or
uncoated. To reduce further the surface activity of particles P,
the particles can be coated with a small layer of protective
material 200, as shown in FIG. 8. This protective material can be
an organic compound or a silicon compound according to the ability
to use such coatings economically. The coating is not required in
practicing the invention; however, the coating is a physical
barrier that can reduce the surface reactivity of the particles P
prior to melting in molten metal ball B as shown in FIG. 7. The
present invention is primarily employed for flux cored electrodes
that are gas shielded gas. A specification for core material C of a
gas shielding electrode using the present invention is set forth in
Table I. TABLE-US-00001 TABLE I Core Percentage Weight Titanium
Dioxide 0-100% Ferro Manganese 0-50% Ferro Silicon 0-50% FerroBoron
0-50% Ferro Molybdenum 0-50% Nickel 0-50% Sodium Aluminum Fluoride
0-50% Potassium Silicon Fluoride 0-50% Ferro Titanium 0-50% Alumina
0-50% Magnesium 0-25%
[0029] Magnesium particles P are also useful for gas shielded
electrodes. An example of the core material for such electrode is
set forth in Table II. TABLE-US-00002 TABLE II Core Percentage
Weight Titanium Dioxide 0-100% Ferro Manganese 0-50% Ferro Silicon
0-50% FerroBoron 0-50% Ferro Molybdenum 0-50% Nickel 0-50% Sodium
Aluminum Fluoride 0-50% Potassium Silicon Fluoride 0-50% Ferro
Titanium 0-50% Aluminum 0-100% Barium Fluoride 0-100% Magnesium
Oxide 0-75% Lithium Fluoride 0-75% Magnesium 0-75% Cerium 0-75%
Barium Oxide 0-75%
[0030] The invention overcomes the disadvantage of prior magnesium
particles that were formed into small sizes by being crushed and
ground into a fine powder. The effect of the crushing action is to
increase surface area drastically and this surface reactivity
defect can not be corrected by merely a thin coating. The invention
involves not only the flux cored electrodes using particles P;
however, involves the process of using such electrodes for welding
and the small magnesium particles themselves. Other procedures can
be used for producing the generally spherical shape, which is the
shape caused by surface tension as contrasted with a crushing or
grinding action.
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