Note: Descriptions are shown in the official language in which they were submitted.
7~
The invention relates to the fleld of metal joining, cladding and
surfacing by fusion, generally refsrrecl to by the broad term "welding".
More particularly, the invention relates to electric arc deposition welding
and to the electrodes used in such welding.
Metal welding processes are so well known and widely used as to
require no exhaustive description here. Welding is generally a fusion method
or process in which the workpiece or substrate is at least partially melted
and molten filler metal is deposited thereon. The filler metal may be of
the same composition as the substrate or may be dissimilar in composition.
Work-pieces to be welded together may be of like composition or may be
dissimilar to each other.
The foregoing metal arc fusion processes all utilize concentrated
heat for elevating base metal temperatures and melting *he filler metal.
Other sources of heat, such as gas combustion, radiant energy and pressure-
friction also are known for fusion joinder. However, electric arc welding
is the technique most commonly used. The invention is directed to the
consumable filler metal rods used as electrodes in arc welding, for purposes
of the present description, consumable filler metal electrodes may be steel,
iron, or other ferrous alloy, nickel, nickel-base alloy, or non-ferrous
metal such as aluminum, copperJ etc. or alloys thereof. Bare metal elec-
trodes have a specialized and limited use. They are difficult to operate
and to control, and weld metal quality often is poor. Consequently, elec-
trodes commonly are covered with external coatings of suitable fluxing and/or
deoxidizing compositions to improve operation and weld deposit quality. Such
coatings are applied by dipping the core in a liquid slurry or, more often,
by concentric extrus:ion of a plastic mixture and baking the resultant coating.
Sometimes, an electrode has a primary coating of one composition for a parti-
cular purpose and a second coating of another composition to serve another
purpose. Disclosures of coated and double-coated electrodes appear in
-- 1 --
.,. ~
United States patent Nos. 1,368,287 (Pennington, issued January 15, 1921);
1,669,660 (Green, issued May 15, 1928); 1,669,661 (Green, issued May 15, 1928);
1,931,466 (Notvest, issued October 17, 1933); 2,008,447 (~laglund, issued
July 16, 1935) and 2,870,047 (Kee, issued January ZO, 1959) and are represent-
ative of the state of the art.
Most of the electrode coatings commonly used in the welding art
have a granular, porous structure which is moisture absorbent even under
ambient storage conditions. Absorbed moisture rapidly impairs the coating
and its efficacy and may eventually result in an unusable electrode. Con-
sequently, most coated electrodes have a relatively short shelf life and,
when not used immediately, have progressively impaired performance and weld
deposit characteristics.
The nature of arc welding is such that there are problem areas in
which improvement in welding electrodes is desired and sought. Among these
problems are the relatively high levels of electric current needed to main-
tain adequate arc temperatures and voltages; the inability oE electrodes,
particularly electrodes of relatively small diameter, to perform properly
outside of a narrow range of current values; the overheating of electrodes
with consequent loss of arc drive; the inability to make efficient use of
AC in certain welding applications; and inadequate arc stability and weld
bead control in out-of-position welding operations.
The invention is directed to improving the performance character-
istics of welding electrodes by overcoming or minimizing some of the pre-
viously mentioned problems which exist in arc welding as well as to improving
the shelf life of coated electrodes. Essentially, this is accomplished by
sheathing a welding electrode in an energy-reflective continuum, the most
common form of which is metal. This provides a secondary coating for a
coated electrode, and also may serve as a vapor barrier against the absorp-
tion of moisture into the primary flux coating.
Broadly stated, the present invention provides in a welding elec-
trode, the combination of a consumable core, a modifier-containing coating
~0
;., ~
on said core, and an adjacent sheath providing an energy-refLective
continuLIm substantially surrolmding said coating, said sheath presenting
interiorly directed surfaces having specular reflectivity toward said core.
The metallic sheat}ling which serves as an energy-reflec-tive
coating permits the use of lower and broader ranges o:f electric current
values while maintaining higher arc voltages and higher arc temperatures at
-2a-
7;~;
given amperage values. ~rc stability is enhanced and arc ~rive is main-
tained for substantialLy op-timum electrode performance over a greater length
of the electrode cons~led. The resulting improvement in penetration of the
substrate and the stabilization of current values produces greater wetting
action of the deposit, a flatter and cleaner bead with greater adherence to
the substrate, easier start in striking the arc, and improved joints in
vertical and other out-of-position welding. Improvements in operation and
weld deposit quality are noted particuLarly with welding electrodes of
relatively small diameter, such as those in which the diameter of the core
is 1/8~' or less. Operation on alternating current is enhanced. All the
various types of welding electrodes to which this invention may be applied
exhibit improved performance in one or more aspects which vary with such
factors as electrode composition, electrode diameter, flux coating compos-
ition, arc current and voltage, substrate meta~ and the technique of welding
employed.
Figure 1 is a view in elevation of an arc welding electrode
; embodying the invention, a portion thereof being broken away to show its
cross-section.
Figure 2 is a transverse cross-sectional view, ~aken as indicated
on line 2-2 of Figure 1.
Figure 3 is a photomicrograph, at a magnification of about 2X of a
conventional arc-welded butt joint in a sheet steel substrate 3/32" thick.
Figure 4 is a photomicrograph comparable to Figure 3, but using
a metallic sheathed electrode under like operating conditions.
Figure 5 is a photomicrograph, at a magnification of about 2X~ of
two conventional arc welded deposits made on a cast iron plate at two
different electrical current levels.
~ igure 6 is a photomicrograph comparable to Figure 5, but using
a metallic sheathed electrode under like operating conditions.
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7~;
Figure 7 is a photomicrograph, a~ a magnification of about 3X,
of a conventional arc welded deposit made on an aluminum plate ~" thick
using an aluminum welding electrode.
Figure 8 is a photomicrograph comparable to Pigure 7, but using
a metallic sheathed aluminum electrode under like operating conditions.
Figure 9 is a photograph, enlarged about 2X, of a conventional
fillet weld made between adjacent steel plates using a consumable arc welding
electrode.
Figure 10 is a photograph comparable to Figure 9, but using a
metallic sheathed electrode under like operating conditions.
Figure 11, which is located on the same drawing sheet as Figure 1,
is a cross-sectional view similar to Figure 2, but showing a modified form
of the invention.
Figure 12, which is located on the same drawing sheet as Figure 1,
is a graph showing values of moisture absorption for conventional flux-coated
electrodes and the comparative values for metallic sheathed electrodes embody-
~ing the invention.
;Figures 1 and 2 show a representative form of sheathed electrode
10 having a metal core 11 of wire or rod and a circumferentially extending !
adherent primary coating 12 of a fluxing composition. Conventionally, theprimary coating 12 extends and covers substantially the entire length of the
core 11, except for a short terminal portion 13 which is left bare for
electro-conductive contact with the electrode holder (not shown) used in
electric arc welding. Circumferential to the flux coating 12 is a secondary
coating in the form of an energy-reflective metallic continuum or sheath 14.
The sheath 14 may have a variety of formulations and may be applied to the
electrode by a variety of techniques.
Basically, the sheath 14 comprises an energy-reflective layer of
non-ferrous metal or alloys thereof, a ferrous metal or alloys thereof, or
mixtures thereof, which is deposited on or applied to the electrode as an
adherent continuum. The metal may constitute 100% of the sheath or it may
--4--
7~6
cons-titute only a portion of the composition of the sheath, the remainder
being in the Eorm of a suitable vehicle, binder or matrix for the meta:L
continuum. Essentially, the minimum metal content of the metallic sheath
is that which will provide a substantia~Lly continuous energy-reflective
face or surface or continuum adjacent to the primary flux coating 12, In
practice it has been found that it is desirable, to achieve an effective
continuum~ that the metal content of the sheath preferably be at least 10%
by volume and not less than ~% by volume as a minimum in situ on the elec-
trode.
The metal of the metallic sheath may be in the form of thin sheet,
foil or film, or it may be in the form of a continuum of reflective particles,
such as metal flake particles. Additionally, a film of a reflective metal
having a low melting point may be applied in the molten condition to produce
an adherent cast film upon subsequent cooling, or suitable films may be
applied by deposition from the vapor phase as, for example, an evaporated
film of reflective metal. The manner of application depends upon the
physical state of the sheath composition which is to be utilized.
The non-metallic portion, if any, of the sheath 14, is primarily
intended as a vehicle for the metallic portion and may, for example, consist
of one or more organic resins, inorganic binders or combinations thereof.
However, the invention does not preclude the minor additions of other
metallic or non-metallic ingredients having particuLar functions or desired
characteristics, such as deoxidizers, for example, provided that such
- additions do not substantially reduce or diminish the reflective ability of
the sheath.
The thiclmess of the sheath 14 may depend upon the field of use of
the particu~Lar electrode involved. Although even an extremely thin contin-
uous reflective film may be shown to have some beneficial eEfect on elec-
trode performance and weld quality, in general it has been found that the
, ., ,.. ~ : ~
7~6
wall thickness o~ the annular sheath should be at least .0001". The
beneficial advantages of the sheath 14 do not appear to be enhanced when the
thickness of-the sheath is increased beyond about .005" although thicker
sheaths may be operable. For most arc welding applications, the thickness
of the sheath is preferably from .0005 to .0003". Excessive thickness of
the sheath is not only lmnecessary and wasteful, but if carried to extremes,
can be counter-productive and have a deleterious effect on weld deposit
; quality.
Although the described sheath is a metallic continuum with
lo ~ respect to its ability to serve as an energy-reflective coating surrounding
the electrode, it is not necessary -that the sheath be an electrical conduc-
tor. Preferably, electrical conductance of the sheath should be sufficiently
small so as not to detract from the main stream of arc current carried by the
core of filler metal 11. Owing to the minimal thickness and composition of
the sheath, this generally will be the case.
~ xamples of sheathed welding electrodes embodying the invention and
the improved results attained, are given below.
Example 1: The electrode selected for test comprised a mild
steel core wire 1/16" in diameter coated with a primary layer of heat-cured,
inorganic deoxidizing flux composition. Sample electrodes were sheathed
by dipping in a liquid composition comprising aluminum flake particles and
a silicone-modified alkyd resin in an organic solvent medium, then allowing
to dry during which process the aluminum flake pigment leafed to form a
reflective continuum about 'J002" in thickness as a resin-bonded sheath ad-
herent to the primary flux coating. This sheath, when dry, comprised about
45% by volume of aluminum flake particles in the resin matrix. Both
sheathed and comparison unsheathed electrodes were used to make welded butt
joints between adjacent mild steel sheets 3/32" in thickness by means of a
single, horizontal weld pass along the juncture. The current used was
-- 6 --
7~
45 amperes AC. ~nder -these conditions, the conventional, unsheathed elec-
trode produced a high-crowned bead at the juncture with only partial pene-
tration of the juncture interface as seen in Figure 3, whereas the sheated
electrode produced a substantially flatter, wider bead with complete
penetration of the juncture and a solid weld joint, as shown in Figure ~.
- Example 2: The electrode type selected for test and the conditions
of sample electrode sheathing were similar to those of Example 1, the only
significant difference being tha-t, for this test, electrocles having cores
of 1/8" diameter wire were used. Weld tests were performed using both
sheathed and conventional unsheathed electrodes at a current of 90 amperes
AC to make vertical-up fillet welds between 3/16" mild steel plates meeting
at a juncture angle of 90 . In this test, the beneficial effect of the
sheathing was pronounced; as compared to the unsheathed electrode under the
same conditions, -the sheathed electrode produced a much flatter, more uni-
form fillet weld joint and with a much better we-tting of the substrate by
the weld deposit as evidenced by a lower contact angle between the weld
bead and the substrate.
~c~mple 3: The electrode type selected for test was similar
; to that of Example 2. Samples were dip-coated in a composition comprising
equal parts by weight of aluminum flake particles, stainless steel flake
particles and a coumarone-indene resin together with organic solvents. The
thickness of the air-dried sheath layer was ~`003'l. Tests of comparative
welding ability of sheathed and unsheathed electrodes were made using a welding
current of 110 amperes DC reverse polarity (electrode positive) to deposit
horizontal stringer beads on the surface of a mild steel plate 1/4~ thick.
It was noted that, under the same welding conditions, the sheathed elec-
trodes gave a much smoother operation and a flatter weld deposit, or bead.
Better wetting of the substrate by the weld deposit was evidenced by the low
contact angle between the edge of the weld bead and the surface of the sub-
strate plate in the case of the weld deposited by the sheathed electrode.
Example 4: The electrode type selected for test comprised a mildsteel core wire of 3/32" diameter coated with a primary layer of a cellulosic
flux composition. This type of electrode is widely used in welding practice
for the joining of low-carbon steel members. Samples were coated with a
leafed, reflective sheathing of aluminum flake particles in a silicone-
modified alkyd resin matrix according to the practice described in Example
1. Welding tests were made by depositing horizontal stringer beads on 1/4"
mild steel plate using a current of approximately 75 amperes AC. Under the
same welding conditions, the sheathed electrodes appear~d to offer the
operator a better control of the weld deposit and a more stable arc current
than the unsheathed electrode. The improved stability of the arc current
was observed through the use of current measuring devices to meter the
welding current in the conductor from welding generator to electrode holder
and to verify a significant decrease in the range of fluctuation of welding
current during the course of the welding operation.
Example 5: The electrode type selected for test was similar to
that of Example 2. Samples were coated with a slurry prepared by suspending
15% by weight of aluminum flake particles in a solution of inorganic binder
material made by diluting 40 Beaume sodium silicate solution with water in
about 1-1 ratio. For general tests of the reflective sheath effect, this
mixture was simply brushed onto sample electrodes, allowed to air dry, and
then the electrodes were baked at elevated temperatures to thoroughly dry
the coating. For tests of out-of-position welding ability, the previously
described slurry was further diluted with water to form a medium having the
consistency of light cream into which sample electrodes were dipped, with-
drawn, air-dried, and baked at 200 C for 12 hours. Thickness of the reflec-
tive sheath of aluminum flake particles in inorganic binder was .003". To
further protect against moisture absorption, coated electrodes were given a
7~'~
light overcoating about .0003" thick, of a flim consisting of 12% by volume
of copper flake in an acrylic resin binder, and applied by spraying followed
by air drying. The weld performance of both sheathed and unsheathed elec-
trodes was measured by making vertical-up fillet welds between 1~" mild steel
plates adjacent at 90 , using a welding current of 115 amperes AC. Under
these conditions, the unsheathed control electrodes produced very high-
crowned, round beads with poor wetting of the steel substrate plates whereas
the sheathed electrodes produced excellent flat beads with good wetting of
the substrate plates.
Example_6: The electrode type selected for test was a nickel-base
core wire 3/16" in diameter coated with primary flux composition containing
graphite as an ingredient to control weld quality in the joining and repair
of cast iron. To provide an energy-reflective sheath according to the inven-
tion, sample electrodes were tightly wrapped with a single layer of commercial
aluminum foil .OOB" thick. Electrodes so sheathed were compared with conven-
tional unsheathed electrodes by welding horizontal stringer beads on cast
iron plates 3/8" thick using a welding current of 140 amperes DC reverse
polarity (electrode positive). As compared with the unsheathed electrodes
under the same conditions, the sheathed electrodes gave flatter weld deposits
à~d better wetting of the substrate by the weld metal as evidenced by a low-
er contact angle between the weld bead and the substrate.
Example 7: The electrode type selected for test was similar to
that of Example 6 except that the diameter of the nickel-base core wire was
1/8". Sample electrodes were sheathed by dipping in a mixture of aluminum
flake particles and silicone resin (Dow-Cor~ing #806A) in organic solvent
medium, drying in air, and baking 12 hours at 220 C. to cure the silicone
resin matrix. The cured sheath film comprised 67% aluminum flake by volume and
was .002" thick. Sheathed electrodes were tested by making horizontal
stringer beads on cast iron plates at a current of 105 amperes DC reverse
polarity. The sheathed e:Lectrodes produced excellent weld beads, smooth,
with good wetting of the subs-tra-te and no porosity in the weld bead. Similar
results were observed in testing electrodes of the same type and manner of
sheathing but having core wire diameters of 5/32" and 3/16". At welding
currents of 120 amperes AC, and under test conditions as described above,
both of these samples produced weld deposits superior to those produced by
unsheathed electrodes of the same diameters.
Weld deposits made on cast iron plates with sheathed and un-
sheathed electrodes of this general type have been examined by transversely
fracturing the test plates across the weld deposits. By such examination it
is evident that although the weld bead deposited with a sheathed electrode
has a lower profile than that deposited by an unsheathed electrode operating
under the same conditions, the penetration of the weld into the substrate
metal is greater in depth and extent with the sheathed electrode.
Example 8: The electrode type selected was similar to that of
~xample 6 except that the core wire had a diameter of 3/32l'. Sample elec-
trodes were sheathed by dipping in a medium comprising 10 grams of aluminum
flake particles suspended in a solution of 5 grams of diammonium phosphate
in 30 grams of water to apply a layer which became approximately .005"
thick when dry, followed by air drying, baking for 12 hours at 250 C to
bond the inorganic matrix, then applying a thin overlayer 15 of copper
bronze flake in acrylic matrix by spraying to stabilize the reflective sheath
as described in Example S and illustrated in Figure 11 of the drawings.
Welding tests were made using 85 amperes AC welding current to deposit
horizontal stringer beads on cast iron plates. Sheathed test electrodes
produced excellent Elat beads with good wetting of the substrate. Electrodes
; maintained arc drive to complete consumption of the electrode in welding even
though the rods became visibly bright red under passage of the relatively high
welding current through the small diameter, highly-resistive core material.
-- 10 --
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7'~6
Weld beads exhibited no porosity. Under similar conditions, unsheathed
electrodes produced beads with higher crown and lesser wetting of the sub-
strate and, owing to high operating temperatures, such electrodes generally
lost arc drive abrup-tly well before the electrode was completely consumed.
_xam~le 9: The electrode type selected for test was a chrome-nickel-
iron alloy core wire of 3/32" diameter coated with a primary flux coating
comprising inorganic oxides in a silicate binder matrix. Sample rods were
sheathed by dipping in 2 slurry of aluminum flake particles in silicone-
modified alkyd resin similar to that described in Example 1, followed by air
drying. The particular purpose of this test was to determine -the effect of
the sheathing on arc strikeability under difficult welding conditions. The
substrate used was mild steel plate 3/16~ thick, and the welding current was
set at 80 amperes AC. The test comprised striking an arc, drawing a hori-
zontal stringer bead on the substrate plate for 2 seconds, breaking the arc
completely for 2 seconds, then restriking and holding for 2 seconds, and so
forth in like manner for a total of 20 strikes. Under the relatively
unfavorable conditions of low amperage alternating current in this test, it
was found difficult to strike and maintain stable welding arcs with unsheathed
electrodes which sporadically missed initiation of arcing on striking. Under
the same conditions, the sheathed electrodes were definitely superior, and
consistently initiated stable arc on every strike.
Example 10: The electrode type selected or test and the sheathing
composition were similar to those used in Example 9, except that the core
wire diameter was 1/16". Comparative welding tests were made of sheathed and
unsheathed electrodes of this type b~ depositing horizontal stringer beads
on thin, mild steel plates 3/32" thick using a welding current of 40 amperes
DG reverse polarity. It was noted that the thin substrate plate became much
hotter when welds were made with a sheathed electrode as compared to welding
an unsheathed electrode. Performance of the unsheathed electrode was marginal
- 11 -
a-t this low current, giving a high-crownecl, poorly-wetting bead with a dark,
oxidized surface. 'I'he sheathed electrode under the same conditions gave a
satisfactory bead, flat and with good wetting of the substrate and, after
slag removal, the bead produced by the sheathed electrode was bright and
shiny.
; Example 11: The electrode selected for test comprised a 3/32"
diameter core wire of a ferrous composition of the type known generally as
"high-speed" tool steel alloy, said core being coated with a primary layer
of conventional inorganic fluxing and deoxidizing materials, Samples were
sheathed as in Example 1. Weld performance testing comprised the deposition
of a single stringer bead along the edge of a steel plate 3/16" thick using
a welding current of 70 amperes direct current, reverse polarity. As compared
to an unsheathed electrode under the same conditions, a sheathed electrode
gave better wetting and a flatter weld deposit.
Example 12: The electrode type selected for test comprised hard
metal carbides enclosed in a tubular mild steel container or envelope, the
composite being coated externally with a primary flux layer of inorganic
oxides. Samples of this type of electrode were sheathed with an energy-
reflective film .002" thick comprising about 30% by volume of aluminum flake
particles in a matrix of silicone-modified alkyd resin applied according to
the technique described in Example 1. Comparative tests were made of
sheathed and unsheathed electrodes using a welding current of 160 amperes DC
reverse polarity to deposit horizontal weld beads on the edge of mild steel
plate 3~16" thick so as to simulate the hard-facing of cutting tool edges.
Under these conditions, the sheathed electrode gave a more stable arc,
better control of the weld deposition, operation and a noticeably flatter,
better-wetting bead on the edge of the steel plate than did the unsheathed
electrode.
Example_13: The electrode type selected for test comprised an
~ 12 ~
alunun~ core wire 1/8" in diamete r coated with a -primary flux layer of
ino-rganic halides and oxides. Sample electrodes were sheathed with an energy-
reflective layer by wiping the surface of the flux layer with a paste of
rolled al~inum flalce powder of the so-called standard lining grade in a
medium of 30% by weight of mineral spirits. Eollowing air drying to evaporate
the mineral spirits, the resulting sheath comprised an overlay of .0005" of
mechanically adherent aluminum flake particles. Welding tests were made by
depositing horizontal stringer beads on aluminum sheet 1/4" thick using
welding current of 95 amperes direct ourrent reverse polarity. Under these
conditions, an electrode with the wiped-on reflective layer produced a weld
bead that was noticeably flatter and with better wetting of the substrate
plate than did an unsheathed electrode of the same type.
Example 14: The electrode type selected for test was similar to
that of Example 13. Sample electrodes were provided with energy-reflective
sheathing according to the method described in ~xample 5 except that elec-
trodes to be coated first were wet with water before the sheath composition
was brushed onto the primary flux layer. Sheathed electrodes were air dried,
heated 48 hours at 120 C. then 1 hour at 220 C. Welding tests were made
using a welding current of 85 amperes DC reverse polarity to deposit hori~on-
tal stringer beads on 1/4" thick aluminum substrate plates. Under theseconditions, the sheathed electrodes gave much flatter, better-wetting beads
; with noticeable improvement in substrate penetration by the weld deposit.
In addition, the sheathed electrodes gave smoother running arc with better arc
and weld control as compared to untreated control electrode.
Example 15: The electrode type selected for test comprised a
1/8" diameter copper-base alloy core surrounded by a primary flux coating of
inorganic constituents. Samples were sheathed with a reflective of aluminum
using the materials and method described in Example 1. Weld brazing tests
were made using a current of 120 amperes AC to braze steel shims and brass
- 13 -
i3~ G
shims to a mild steel subs-trate plate with a continuous pass, horizontal
fillet weld. As compared to a conventional unsheathed electrode, a sheathed
electrode gave a somewhat hotter arc and a better wetting of the substrate
and shim metals by the weld deposit. Similar results in favor of the
sheathed electrode were noted in a similar test made using a welding current
of 120 amperes DC reverse polarity.
xample 16: The electrode -type selected for test was similar to
that of Example 9 except that core wire cliameter was 1/8". Sample electrodes
were provided with an energy-reflective sheath by applying two light coatings
of copper bronze flake particles in acrylic resin binder according to the
method described in Example 5, allowing a sufficient period for drying
between sprayings. Total thickness of sheath was .0004". Welding tests
were made by depositing horizontal stringer beads on mild steel plates 3/16"
thick using a current of approximately 105 amperes AC. Whereas at this
current level, the arc voltage of an unsheathed control electrode averaged
approximately 21 volts the arc voltage of a sheathed electrode averaged
about 10% higher. In addition, the sheathed electrode provided a smoother,
quieter arc with less weld spatter, and the resulting weld bead exhibited
evidence of better wetting of the substrate metal by the deposited weld metal.
In addition, the bead deposited by the sheathed electrode appeared smoother
with less ripple.
Example 1~: The electrode type selected for test was similar to
that of Example 16. Samples were provided with a reflective sheath of
aluminum flake particles in organic binder according to the method and
materials described in Fxample 1 except that, by thinning the medium with
solvent, the thickness of the resulting sheath was reduced to approximately
.0009~'. Following this, a second overlayer of copper bronze pigment in
acrylic matrix was provided by spraying followed by air drying as described
in Example 5. The thickness of the overlay film was .0003". Samples of
- 14 -
~ ~ ~ 1 3 7 ~ 1~
~msheathed and sheathe(l electrodes were weighed, then placed in an enclosed
h~idity chc~ber and held for a period of ~0 hours at a relative humidity of
100% at a temperature of 70 F. During this exposure, the unsheathed elec-
trodes absorbed a quantity of water into the t`lux coating equivalent to 5.1
grams of water per pound of electrodes whereas the sheathed electrodes
absorbed less than 0.2 grams of moisture per pound of electrodes. Further,
whereas the slight amount of moisture absorbed by the sheathed electrodes
was loosely held and was readily removed by heating at 150 F for an hour,
the moisture absorbed by the unsheathed electrodes was more tightly held and
its removal required an extended time at temperatures about 400 F. Figure
12 depicts the relative absorption of moisture by conventional and sheathed
electrodes as a f~mction of time.
EXample 18: The electrode type selected was similar to that of
Example 6 except that the diameter of the nickel-alloy core wire was 1/8".
Sample electrodes were sheathed by dipping into a suitable mixture of alum-
- inum flake pigment and silicone-modified alkyd resin binder in organic solvent
to leave, after drying, a reflective sheath .001" in thickness comprising 33%
; by volume of metallic aluminum. Welding tests were conducted by depositing
pairs of horizontal stringer beads on cast iron plates 3/8" thick using
welding currents of 85 amperes AC for one bead and 120 amperes AC for the
other. Separate substrate plates were used for deposition of the test beads
from sheathed electrodes and from conventional unsheathed electrodes. At
either current level3 the sheathed electrodes provided flatter beads exhibit-
ing better wetting of the substrate and with greater depth of penetration
thereof. Figure 5 is a cross-sectional view of the test beads deposited by
the unsheathed electrode at the two different current levels, while F~gure 6
is a similar view of the test beads produced under the same conditions by
the electrodes sheathed according to the invention. In both cases, the
smaller bead was deposited at 85 amperes AC, the larger bead at 120 amperes
7~
~c.
Example 19: The electrode selected for test was similar to that of
Example 13. Samples were coated with a mixture of aluminum f:Lake in poly-
urethane resin matrix prepared by mixing 48 grams of base resin in a solvent
marketed by the Sherwin-Williams Company under the trade name P~lane, 8
grams of isocyanate catalyst, 16 grams of additional solvent thinner, and 30
grams of a paste of aluminum flake pigment in mineral spirits cornprising 75%
by weight of aluminum. This mixture was wiped onto the test electrode to
leave a sheath which, when allowed to dry and polymerize, had a thickness o-f
.002". Welding tests were made by depositing horizontal stringer beads on
alurninum substrate plates 1/4" thick at a current of 90 amperes DC reverse
polarity (electrode positive). A cross-section of the bead deposited by the
conventional unsheathed electrode under these conditions is shown in Figure 7.
The bead deposited by the sheathed electrode under the same conditions is
shown in Figure 8. As will be apparent from these microphotographs, the
electrode sheathed according to the invention produced a weld deposit
noticeably Matter and with better wetting of the substrate as evidenced by
the relatively low contact angle between the edge of the weld deposit and
the substrate plate in Figure 8.
Exa ple 20: The electrode selected for test was representative of
.
the type known as "low hydrogen" common~Ly used for high-performance welding ~ -
in critical applications, and comprising a ferrous metal core wire 3/32" in ~-
diameter coated with a primary layer of inorganic fluxing and deoxidizing
materials. Sample electrodes were sheathed by dipping into a mixture of
alurninum flake pigment and silicone-modified alkyd resin in a solvent med-
ium followed by drying in air. The resuLting reflective sheath comprised 33%
`by volume of aluminum flake in a .001" layer circumferential and adherent
; to the primary flux coating. Comparative tests of welding performance were
made by depositing weld beads by the so-called "vertical up" technique in the
- 16 -
,.
37~
interstices between adjacent steel plates 3/16" thick held at right angles
to each other using a welding current of 115 amperes AC. Figure 9 is a photo-
graph of the t~eld bead deposited by the unsheathed electrode under these
conditions, while Figure 10 is a photograph of the weld bead deposited under
the same conditions by an electrode sheathed as described above. It will be
apparent that the electrode sheathed according to the invention produced a
; flatter, more adherent weld deposit than the unsheathed electrode.
In addition to the various techniques of dipping, brushing, spraying,
wiping on, wrapping or casting the sheath onto the electrode, there are
sheath compositions which can be applied by dry powder fluidized bed or
electrostatic spraying application, or more exotic techniques such as elec-
troplating or vacuum evaporation-condensation and the like The invention is
not limited to any particular method of applying the sheath to the welding
electrode, although it is expected that the simpler and less costly techniques
of dipping, spraying and the like will most frequently be utilized. It will
be understood that, at the time the sheath is applied, the electrode should
ordinarily be moisture-free insofar as practicable.
In the representative electrode examples set forth above, the energy-
reflective sheathing is in all instances metal-based or metal-bearing and
has the additional common characteristic of the metal being disposed as an
effective continuum regardless of the method of applying the sheath to the
electrode. Inifact, this latter characteristic is salient to the invention
and establishes the ultimate lower li~it for the metal content of the sheath,
other factors being preliminarily ignored. In other words, whatever other
requirements may dictate as to the metal content of the sheath, it is necess-
ary that the metal~content be sufficient and of such nature and disposition
as to establish the sheath as an effective reflective continuum around the
usable length of the electrode. The other requirements may lead to an
increased metal content or volume, but not to a significantly lower one. The
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~ 7 b~6
improved performance of the sheathed welding electrode is in great part the
result of the energy reflectivity of the metal continuum of the sheath,
therefore such continuum must be substantially maintained to obtain the
advantages of the invention. Although this description has emphasized the
use of metallic sheathing, it will be apparent to those skilled in the art
that substances other than metals col~d be utili3ed for the sheath provided
that such substances have or can be applied in a manner tohavc ~substantial
energy-reflectivity characteristic. ~xamples of such non-metallic sheathing
materials or substances are heat-stable inorganic or ceramic compositions
o applied in a form which provides an adequate degree of specular reflection
In some applications, such as where the electrode is used at
relatively high arc temperatures, the selected metal of the sheath may be a
relatively low-melting metal, such as aluminum, which will be vapori3ed or
dissipated during the welding operation without significantly entering into
or contaminating the filler metal deposited by the electrode core 11.
- Examples of such a sheath are, inter alia, described in Example Nos. 1, 6,
9, 11 and 12 above. In other applications, the metal for the sheath 14 may
be selected to contribute some desirable property to the filler metal or to
be similar in whole or in part thereto, as in Examples Nos. 3 and 13 above.
Some of the sheath metals which have been utilized are aluminum, stainless
steel, copper-bronze, and combinations thereof. It will be recogni3ed by
those skilled in the art that certain metals which otherwise might be used
to provide the energy-reflective sheath, such as cadmium or beryllium for
example, are not practicable for such purpose because of the toxicity of
the metals and their vapors.
Suitable vehicles in the form of liquids, slurries~ pastes and the
like are indicated in the examples listed above. Organic resins appear to
be the most suitable, although inorganic binder compositions have also been
successfully utili3ed, as in Example Nos. 5 and 14. These sheathings have
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'
an additional advant;lge in reinforcing and protecting the underlying
primary fll~ coating ~hich often is a brittle composition which is easily
damaged in handling and in shipping.
It has ~een fo~md -that an additional reflective film or very thin
layer, about .0001-.0005" thick, applied over the basic sheath composition in
the form of an overspray, as in Example Nos. 5, 8 and 17, may serve to effec-
tively further improve the performance of the welding electrode after lengthy
periods of storage and particl~arly at higher operating current values at
which the electrode attains red heat in operation. This overlayer or
stabilizing film 15, illustrated in Figure 11 of the drawings, further main-
tains the integrity of the underlying first reflective sheath, as well as
enhancing the maintenance of arc drive. In fact, a multiplicity of thin
layers of reflective overlay 14 will, for an equivalent total sheath thick-
ness, be more effective than a single thick layer owing to such factors as
promotion of reflectivity through a higher degree of flake pigment leafing
and decreased thermal conductance. In addition, a sheath carrying a plur
ality of very thin layers may, under certain conditions, be a more effective
barrier to moisture absorption by the electrode.
It will be understood that7 as applied to mechanically adherent
sheath compositions, such as that of Example No. 13, the overlayer need not
- necessarily be reflective per se or contain or comprise metal to serve
effectively as a reinforcement for the underlying reflective sheath, but can
~ be a protective film such as, for example, an acrylic resin or the like. This
- protective function is accomplished by the binder or matrix in sheath com-
positions such as those of Example Nos. 1, 5 and 6. Further, binder-rein-
forced metallic particle sheaths or continuous film metallic sheaths,
regardless of how applied, serve to maintain useful arc or weld deposit
modifying components within the primary flux coating by preventing or
minimizing loss, such as by evaporation or oxidation, of such valuable flux
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l 376~
layer components during high--temperaturc operation of the electrode. Thus,
an additional advantage of the invention is that it enables the retention of
uset`uL and desirable modifyers in fl~ layer compositions, which are not
possible or feasible with conventional e~Lectrode coating processes and
materials.
Figures 3 and 4, previously referred to in Example 1, are compara-
tive photomicrographs of the cross-section of an arc welded butt joint of
mild steel sheaths 3/32" thick. Figure 3 shows the joint obtained using a
horizontal weld pass at an operation current of 45 amperes AC using a 1/16"
diameter commercial mild steel electrode having an inorganic flux coating.
Figure 4 shows the butt joint obtained on the same substrate sheath and ~mder
the same operating conditions using the same commercial electrode modified
by the addition of a sheath approximately .002" thick comprising aluminum
flake particles in a binder of silicone-modified alkyd resin as described
in Example No. 1. It will be noted in comparing Figures 3 and 4 that in the
joint obtained by use of the metal sheathed electrode~ the filler metal bead
is much flatter and wider than in Figure 3. ALso that penetration of the
joint is much greater in Figure 4 than in Figure 3. This resu~Lts from the
energy-reflective characteristic of the metal continuum of the sheath which
produces significantly increased arc drive, improved arc stability, higher
arc voltage and temperature at a given operating current value, and the
maintenance of uniformity in the characteristics of the arc as the electrode
is consumed. Better wetting action and penetration are achieved, as indicated
in the photomicrographs.
Also of importance, as indicated in Example 1~, is the fact that
the metal continuum of the sheath 14 substantially lengthens the shelf life
of the electrode by minimizing the absorption of moisture by the primary
flux coating with its consequent degradation of electrode performance and
weld deposit quality.
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96
In -the graph of Figure 12, comparative moisture absorption~of
like sheathed and unsheathed electrodes is illustrated by plotting the per-
centage by weight of water or moisture absorbed by the electrode flux coating
against the number of hours of exposure of the electrode to 100% humidity at
65 F. The test results for the unsheathed electrode are shown by the curve
indicated by the reference numeral 16 and the test results for the sheathed
electrode are sho~ by bhe curve indicated by the reference numeral 17. The
dramatic difference in moisture absorption between the sheathed and unsheathed
electrodes is evident and is translated into minimal deterioration of per-
formance for the sheathed electrode as well as substantially longer shelfl~fe.
Although the improved shelf life obtained from sheathed electrodes
is a significant advantage, the primary attribute of the sheathed electrode is
its characteristic of energy-re Mectivity. The metal or other energy-reflec-
tive component of the sheath is in a form or configuration which presents
interiorly-directed surfaces toward the core of the electrode. These surfaces
serve to reflect or direct back toward the core and its point of arc attach-
ment, radiant energy which would otherwise radiate from the rod in a manner
known to the art. This loss of energy, both by radiation and convection,
occurs throughout the length of the electrode with a major portion of the loss
occurring at the point of arc attachment. The specular effect of the sheath
results in a containment of energy in the electrode, which would otherwise
be lost and unavailable for use in the welding process. Thereby, the sheathed
electrode in effect increases the available welding energy with a consequent
higher core temperature which, in turn, increases the electrical resistance
of the core and results in a greater I R heating effect and a higher level of
energy in the arc itself.
The improved heating effect increases the rate of melt of the core
at the point of arc attachment which is believed to result in a more pro-
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.
.
:
nouncecl eup eft`ect at the arc end oE the electrode. This cwp effect may be
further enhanced by the mechanical reinEorcement of the flux coating by the
sheath at the arc end of the electrode. The deeper or more pronounced cup
immediately surro~mding the arc end of the electrode provides an additional
containment against energy losses at this critical terminal portion of the
rod.
Thc consequence of this containment and concentration of available
energy in the electrode is a higher energy level in the arc itself, a greater
concentration and direction of the arc stream, a significant increase in arc
voltage drop at a given welding current level, as discussed in ~cample 16,
with higher arc temperature and greater arc drive, and improved penetration
of-the substrate.
There is also reason to believe that with certain types of elec- -
trodes, the sheath 14 promotes improved spray transfer of filler metal from
the core to the substrate, thus affording better control of the arc and the
deposition of the weld metal, particularly in difficult welding situations
in which the less desirable globular transfer mechanism may interfere with
arc control and weld deposit quality.
It is to be understood that the forms of our invention, herewith
shownc,anddescribed, are to be taken as preferred examples of the same and
that various changes in the shape, si~e and arrangement of the parts may be
resorted to without departing from the spirit of our invention or the scope
of the subjoined claims.
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