Patent Description:
Welding is a process that has become ubiquitous in various industries for a variety of applications. For example, welding is often used in applications such as shipbuilding, offshore platform, construction, pipe mills, and so forth. Certain welding techniques (e.g., Gas Metal Arc Welding (GMAW), Gas-shielded Flux Core Arc Welding (FCAW-G), and Gas Tungsten Arc Welding (GTAW)), typically employ a shielding gas (e.g., argon, carbon dioxide, or oxygen) to provide a particular local atmosphere in and around the welding arc and the weld pool during the welding process, while others (e.g., Flux Core Arc Welding (FCAW), Submerged Arc Welding (SAW), and Shielded Metal Arc Welding (SMAW)) do not. Additionally, certain types of welding may involve a welding electrode in the form of welding wire. Welding wire may generally provide a supply of filler metal for the weld as well as provide a path for the current during the welding process. Furthermore, certain types of welding wire (e.g., tubular welding wire) may include one or more components (e.g., flux, arc stabilizers, or other additives) that may generally alter the welding process and/or the properties of the resulting weld.

From <CIT>, a method as defined in the preamble of claim <NUM> is known. <CIT> discloses a welding wire and method comprising a solid or a cored wire made from metal power only, not containing a flux. In the welding wire an alkaline metal compound is contained. Said wire is used together with inert gases, e.g. an argon atmosphere containing <NUM>% or more argon. <CIT> refers to a welding method for welding zinc-coated plates using pulsed current, however, said method does not use an argon atmosphere nor are any statements made with regard to the used welding wire.

<NPL>, describes positive effects of using DCEP compared to using DCEN. <CIT> discloses a welding wire which is similar to the welding wire used with the present invention, however, it does e.g. not comprise the claimed organic stabilizers. Furthermore, there is no hint to the use of argon shielding gas or pulsed DCEP. Further welding wires for use with gas metal arc welding and pulsed electric arc welding are described in <CIT> and <CIT>.

According to the present invention, a method of forming a weld deposit on a zinc-coated workpiece is provided as defined in claim <NUM>.

Further features are disclosed in the subclaims.

It should be appreciated that, as used herein, the term "tubular welding electrode" or "tubular welding wire" may refer to any welding wire or electrode having a metal sheath and a granular or powdered core, such as metal-cored or flux-cored welding electrodes. It should also be appreciated that the term "stabilizer" or "additive" may be generally used to refer to any component of the tubular welding that improves the quality of the arc, the quality of the weld, or otherwise affect the welding process. Furthermore, as used herein, "approximately" may generally refer to an approximate value that may, in certain embodiments, represent a difference (e.g., higher or lower) of less than <NUM>%, less than <NUM>%, or less than <NUM>% from the actual value. That is, an "approximate" value may, in certain embodiments, be accurate to within (e.g., plus or minus) <NUM>%, within <NUM>%, or within <NUM>% of the stated value.

As mentioned, certain types of welding electrodes (e.g., tubular welding wire) may include one or more components (e.g., flux, arc stabilizers, or other additives) that may generally alter the welding process and the properties of the resulting weld. For example, certain presently disclosed welding electrode embodiments include an organic stabilizer (e.g., a derivatized cellulose-based component) that may generally improve the stability of the arc while providing a reducing atmosphere conducive to welding coated workpieces. For example, presently disclosed welding electrodes and welding conditions may be especially useful for welding zinc (Zn)-coated workpieces (e.g., galvanized, galvannealed, painted with a Zn-based paint) that include a Zn-rich coating layer at the surface of the workpiece. Certain presently disclosed welding electrode embodiments also include a rare earth silicide component that may generally help to control the shape and penetration of the arc during welding. Furthermore, the disclosed welding electrode embodiments includes other components such as, for example, a carbon component (e.g., graphite, carbon black, or other suitable carbon component), and an agglomerated stabilizer component (e.g., a potassium/titanate/manganate agglomerate), as set forth in detail below.

Accordingly, the presently disclosed welding electrodes enhance the weldability of coated (e.g., galvanized, galvannealed, painted, and so forth) workpieces and/or thinner (e.g., <NUM>, <NUM>,<NUM>, <NUM> (<NUM>-, <NUM>-, <NUM>-gauge), or thinner) workpieces, even at high travel speed (e.g., greater than <NUM>,<NUM>/min (<NUM> in/min)). Additionally, the disclosed welding electrodes generally enable acceptable welds under different welding configurations (e.g., direct current electrode negative (DCEN), direct current electrode positive (DCEP), alternating currents (AC), and so forth) and/or different welding methods (e.g., involving circular or serpentine welding electrode movements during welding). Additionally, certain presently disclosed welding electrodes may be drawn to particular diameters (e.g., <NUM>,<NUM> (<NUM> in), <NUM>,<NUM> (<NUM> in), <NUM>,<NUM> (<NUM> in), or other suitable diameters) to provide good heat transfer and deposition rates. Furthermore, various welding conditions (e.g., welding processes, polarities, shielding gases) are disclosed that, in combination with the disclosed welding electrodes, enable exceedingly low spatter rates and sound weld deposits when welding Zn-coated workpieces, even at relatively high travel speeds (e.g., greater than <NUM>,<NUM> (<NUM> inches) per minute).

Turning to the figures, <FIG> illustrates an embodiment of a gas metal arc welding (GMAW) system <NUM> that utilizes a welding electrode (e.g., tubular welding wire) and that may be used with the method according to the present invention. It should be appreciated that, while the present discussion may focus specifically on the GMAW system <NUM> illustrated in <FIG>, the presently disclosed welding electrodes may benefit any arc welding process (e.g., FCAW, FCAW-G, GTAW, SAW, SMAW, or similar arc welding process) that uses a welding electrode. It may be appreciated that, in certain embodiments, the GMAW system <NUM> may be capable of manual welding, semi-automated welding, or fully automated welding operations. The welding system <NUM> includes a welding power source <NUM>, a welding wire feeder <NUM>, a gas supply system <NUM>, and a welding torch <NUM>. The welding power source <NUM> generally supplies power to the welding system <NUM> and may be coupled to the welding wire feeder <NUM> via a cable bundle <NUM> as well as coupled to a workpiece <NUM> using a lead cable <NUM> having a clamp <NUM>. In the illustrated embodiment, the welding wire feeder <NUM> is coupled to the welding torch <NUM> via a cable bundle <NUM> in order to supply consumable, tubular welding wire (i.e., the welding electrode) and power to the welding torch <NUM> during operation of the welding system <NUM>. In another embodiment, the welding power unit <NUM> may couple and directly supply power to the welding torch <NUM>.

The welding power source <NUM> may generally include power conversion circuitry that receives input power from an alternating current power source <NUM> (e.g., an AC power grid, an engine/generator set, or a combination thereof), conditions the input power, and provides DC or AC output power via the cable <NUM>. As such, the welding power source <NUM> may power the welding wire feeder <NUM> that, in turn, powers the welding torch <NUM>, in accordance with demands of the welding system <NUM>. The lead cable <NUM> terminating in the clamp <NUM> couples the welding power source <NUM> to the workpiece <NUM> to close the circuit between the welding power source <NUM>, the workpiece <NUM>, and the welding torch <NUM>. The welding power source <NUM> may include circuit elements (e.g., transformers, rectifiers, switches, and so forth) capable of converting the AC input power to a direct current electrode positive (DCEP) output, direct current electrode negative (DCEN) output, DC variable polarity, pulsed DC, or a variable balance (e.g., balanced or unbalanced) AC output, as dictated by the demands of the welding system <NUM>. It should be appreciated that the presently disclosed welding electrodes (e.g., tubular welding wire) may enable improvements to the welding process (e.g., improved arc stability and/or improved weld quality) for a number of different power configurations. As discussed in greater detail below, in certain embodiments, the use of pulsed DC may enable benefits in terms of low spatter rates and low weld deposit porosity when welding Zn-coated workpieces, especially at high travel speeds.

The illustrated welding system <NUM> includes a gas supply system <NUM> that supplies a shielding gas or shielding gas mixtures from one or more shielding gas sources <NUM> to the welding torch <NUM>. In the depicted embodiment, the gas supply system <NUM> is directly coupled to the welding torch <NUM> via a gas conduit <NUM>. In another embodiment, the gas supply system <NUM> may instead be coupled to the wire feeder <NUM>, and the wire feeder <NUM> may regulate the flow of gas from the gas supply system <NUM> to the welding torch <NUM>. A shielding gas, as used herein, may refer to any gas or mixture of gases that may be provided to the arc and/or weld pool in order to provide a particular local atmosphere (e.g., to shield the arc, improve arc stability, limit the formation of metal oxides, improve wetting of the metal surfaces, alter the chemistry of the weld deposit, and so forth). In certain embodiments, the shielding gas flow may be a shielding gas or shielding gas mixture (e.g., argon (Ar), helium (He), carbon dioxide (COz), oxygen (Oz), nitrogen (N<NUM>), similar suitable shielding gases, or any mixtures thereof). For example, a shielding gas flow (e.g., delivered via the conduit <NUM>) may include Ar, Ar/CO<NUM> mixtures, Ar/CO<NUM>/O<NUM> mixtures, Ar/He mixtures, and so forth. By specific example, in certain embodiments, the shielding gas flow may include <NUM>% Ar and <NUM>% CO<NUM>. As discussed in greater detail below, in certain embodiments, the use of <NUM>% Ar shielding gas may enable benefits in terms of low spatter rates and low weld deposit porosity when welding Zn-coated workpieces, especially at high travel speeds.

Accordingly, the illustrated welding torch <NUM> generally receives the welding electrode (i.e., the tubular welding wire), power from the welding wire feeder <NUM>, and a shielding gas flow from the gas supply system <NUM> in order to perform GMAW of the workpiece <NUM>. During operation, the welding torch <NUM> may be brought near the workpiece <NUM> so that an arc <NUM> may be formed between the consumable welding electrode (i.e., the welding wire exiting a contact tip of the welding torch <NUM>) and the workpiece <NUM>. Additionally, as discussed below, by controlling the composition of the welding electrode (i.e., the tubular welding wire), the chemistry of the arc <NUM> and/or the resulting weld (e.g., composition and physical characteristics) may be varied. For example, the welding electrode may include fluxing or alloying components that may affect the welding process (e.g., act as arc stabilizers) and, further, may become at least partially incorporated into the weld, affecting the mechanical properties of the weld. Furthermore, certain components of the welding electrode (i.e., welding wire) may also provide additional shielding atmosphere near the arc, affect the transfer properties of the arc <NUM>, deoxidize the surface of the workpiece, and so forth.

A cross-section of an embodiment of the presently disclosed welding wire is illustrated in <FIG> illustrates a tubular welding wire <NUM> that includes a metallic sheath <NUM>, which encapsulates a granular core <NUM> (also referred to as filler). In certain embodiments, the tubular welding wire <NUM> may comply with one or more American Welding Society (AWS) standards. For example, in certain embodiments, the tubular welding wire <NUM> may be in accordance with AWS A5. <NUM> ("SPECIFICATION FOR CARBON STEEL ELECTRODES AND RODS FOR GAS SHEILDED ARC WELDING") and/or with AWS A5. <NUM> ("SPECIFICATION FOR CARBON AND LOW-ALLOY STEEL FLUX CORED ELECTRODES FOR FLUX CORED ARC WELDING AND METAL CORED ELECTRODES FOR GAS METAL ARC WELDING").

The metallic sheath <NUM> of the tubular welding wire <NUM> illustrated in <FIG> may be manufactured from any suitable metal or alloy, such as steel. It should be appreciated that the composition of the metallic sheath <NUM> may affect the composition of the resulting weld and/or the properties of the arc <NUM>. In certain embodiments, the metallic sheath <NUM> may account for between approximately <NUM>% and <NUM>% of the total weight of the tubular welding wire <NUM>. For example, in certain embodiments, the metallic sheath <NUM> may provide approximately <NUM>% or approximately <NUM>% of the total weight of the tubular welding wire <NUM>.

As such, the metallic sheath <NUM> may include certain additives or impurities (e.g., alloying components, carbon, alkali metals, manganese, or similar compounds or elements) that may be selected to provide desired weld properties. In certain embodiments, the metallic sheath <NUM> of the tubular welding wire <NUM> may be a low-carbon strip that includes a relatively small (e.g., lower or reduced) amount of carbon (e.g., less than approximately <NUM>%, less than approximately <NUM>%, or less than approximately <NUM>% carbon by weight). For example, in an embodiment, the metallic sheath <NUM> of the tubular welding wire <NUM> may include between approximately <NUM>% and <NUM>% carbon by weight. Additionally, in certain embodiments, the metallic sheath <NUM> may be made of steel generally having a small number of inclusions. For example, in certain embodiments, the metallic sheath <NUM> may include between approximately <NUM>% and approximately <NUM>%, or approximately <NUM>% manganese by weight. By further example, in certain embodiments, the metallic sheath <NUM> may include less than approximately <NUM>% phosphorus or sulfur by weight. The metallic sheath <NUM>, in certain embodiments, may also include less than approximately <NUM>% silicon by weight, less than approximately <NUM>% aluminum by weight, less than approximately <NUM>% copper by weight, and/or less than approximately <NUM>% tin by weight.

The granular core <NUM> of the illustrated tubular welding wire <NUM> may generally be a compacted powder. In certain embodiments, the granular core <NUM> may account for between approximately <NUM>% and approximately <NUM>%, or between approximately <NUM>% and approximately <NUM>%, of the total weight of the tubular welding wire <NUM>. For example, in certain embodiments, the granular core <NUM> may provide approximately <NUM>%, approximately <NUM>%, or approximately <NUM>% of the total weight of the tubular welding wire <NUM>. Furthermore, in certain embodiments, the components of the granular core <NUM>, discussed below, may be homogenously or non-homogenously (e.g., in clumps or clusters <NUM>) disposed within the granular core <NUM>. For example, the granular core <NUM> of certain welding electrode embodiments (e.g., metal-cored welding electrodes) may include one or more metals (e.g., iron, iron titanium, iron silicon, or other alloys or metals) that may provide at least a portion of the filler metal for the weld. By specific example, in certain embodiments, the granular core <NUM> may include between approximately <NUM>% and approximately <NUM>% iron powder, as well as other alloying components, such as ferro-titanium (e.g., <NUM>% grade), ferro-magnesium-silicon, and ferrosilicon powder (e.g., <NUM>% grade, unstabilized). Other examples of components that may be present within the tubular welding wire <NUM> (i.e., in addition to the one or more carbon sources and the one or more alkali metal and/or alkali earth metal compounds) include other stabilizing, fluxing, and alloying components, such as may be found in METALLOY X-CEL™ welding electrodes available from Illinois Tool Works, Inc.

Additionally, presently disclosed embodiments of the tubular welding wire <NUM> used for the present invention includes an organic stabilizer disposed in the granular core <NUM>. The organic stabilizer is any organic molecule that includes one or more alkali metal ions (e.g., Group I: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs)) or alkali earth metal ions (e.g., Group II: beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), or barium (Ba)). That is, the organic stabilizer includes an organic subcomponent (e.g., an organic molecule or polymer), which includes carbon, hydrogen, and oxygen, and may be chemically (e.g., covalently or ionically) bonded to the alkali metal or alkali earth metal ions. In other embodiments, the organic stabilizer may include an organic sub-component (e.g., an organic molecule or polymer, such as cellulose) that has been mixed with (e.g., not chemically bonded with) the alkali metal and/or alkali earth metal salt (e.g., potassium oxide, potassium sulfate, sodium oxide, etc.).

By specific example, in certain embodiments, the organic stabilizer may be a cellulose-based (e.g., cellulosic) component including a cellulose chain that has been derivatized to form a sodium or potassium salt (e.g., sodium or potassium carboxymethyl cellulose). For example, in certain embodiments, the cellulose-based organic stabilizer may be sodium carboxymethyl cellulose having a degree of substitution (DS) ranging from approximately <NUM> and approximately <NUM>. In general, the DS of a derivatized cellulose may be a real number between <NUM> and <NUM>, representing an average number of substituted hydroxyl moieties in each monomer unit of the polysaccharide. In other embodiments, the organic stabilizer may be other organic molecules that include one or more Group I/Group II ions. For example, in certain embodiments, the organic stabilizer may include derivatized sugars (e.g., derivatized sucrose, glucose, etc.) or polysaccharides having one or more carboxylic acids or sulfate moieties available to form an alkali metal or alkali earth metal salt. In other embodiments, the organic stabilizer may include soap-like molecules (e.g., sodium dodecyl sulfate or sodium stearate) or alginates. Additionally, in certain embodiments, the organic stabilizer may account for less than approximately <NUM>%, between approximately <NUM>% and approximately <NUM>%, between approximately <NUM>% and approximately <NUM>%, between approximately <NUM>% and approximately <NUM>%, between approximately <NUM>% and approximately <NUM>%, or approximately <NUM>% of the granular core <NUM> by weight. Additionally, in certain embodiments, the organic stabilizer may account for less than approximately <NUM>%, between approximately <NUM>% and approximately <NUM>%, between approximately <NUM>% and approximately <NUM>%, between approximately <NUM>% and approximately <NUM>%, or approximately <NUM>% of the tubular welding wire <NUM> by weight.

It may be appreciated that the organic stabilizer component of the tubular welding wire <NUM> may be maintained at a suitable level such that a reducing environment (e.g., hydrogen-rich) may be provided near the welding arc, but without introducing substantial porosity into the weld. It should further be appreciated that utilizing an organic molecule as a delivery vehicle for at least a portion of the Group I/Group II ions to the welding arc, as presently disclosed, may not be widely used since organic molecules may generate hydrogen under the conditions of the arc, which may result in porous and/or weak welds for mild steels. However, as set forth below, using the presently disclosed organic stabilizers afford quality welds (e.g., low-porosity welds), even when welding at high travel speed on coated (e.g., galvanized) and/or thin workpieces.

According to the present invention, the tubular welding wire <NUM> also includes a carbon component disposed in the granular core <NUM>. For example, the carbon source present in the granular core <NUM> and/or the metal sheath <NUM> may be in a number of forms and may stabilize the arc <NUM> and/or increase the carbon content of the weld. For example, in certain embodiments, graphite, graphene, nanotubes, fullerenes and/or similar substantially sp<NUM>-hybridized carbon sources may be utilized as the carbon source in the tubular welding wire <NUM>. Furthermore, in certain embodiments, graphene or graphite may be used to also provide other components (e.g., moisture, gases, metals, and so forth) that may be present in the interstitial space between the sheets of carbon. In other embodiments, substantially sp<NUM>-hybridized carbon sources (e.g., micro- or nano-diamond, carbon nanotubes, buckyballs) may be used as the carbon source. In still other embodiments, substantially amorphous carbon (e.g., carbon black, lamp black, soot, and/or similar amorphous carbon sources) may be used as the carbon source. Furthermore, while the present disclosure may refer to this component as a "carbon source," it should be appreciated that the carbon source may be a chemically modified carbon source that may contain elements other than carbon (e.g., oxygen, halogens, metals, and so forth). For example, in certain embodiments, the tubular welding wire <NUM> may include a carbon black component in the granular core <NUM> that may contain a manganese content of approximately <NUM>%. In certain embodiments, the carbon component of the tubular welding wire <NUM> may be powdered or granular graphite. Additionally, in certain embodiments, the carbon component may account for less than approximately <NUM>%, between approximately <NUM>% and approximately <NUM>%, between approximately <NUM>% and approximately <NUM>%, between approximately <NUM>% and approximately <NUM>%, or approximately <NUM>% of the granular core <NUM> by weight. In certain embodiments, the carbon component may account for less than approximately <NUM>%, between approximately <NUM>% and approximately <NUM>%, between approximately <NUM>% and approximately <NUM>%, or approximately <NUM>% of the tubular welding wire <NUM> by weight.

Furthermore, in addition to the organic stabilizer discussed above, the tubular welding wire <NUM> may also include one or more inorganic stabilizers to further stabilize the arc <NUM>. That is, the granular core <NUM> of the tubular welding wire <NUM> may include one or more compounds of the Group <NUM> and Group <NUM> elements (e.g., Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba). A non-limiting list of example compounds include: Group <NUM> (i.e., alkali metal) and Group <NUM> (i.e., alkaline earth metal) silicates, titanates, carbonates, halides, phosphates, sulfides, hydroxides, oxides, permanganates, silicohalides, feldspars, pollucites, molybdenites, and molybdates. For example, in an embodiment, the granular core <NUM> of the tubular welding wire <NUM> may include potassium manganese titanate, potassium sulfate, sodium feldspar, potassium feldspar, and/or lithium carbonate. By specific example, the granular core <NUM> may include potassium silicate, potassium titanate, potassium alginate, potassium carbonate, potassium fluoride, potassium phosphate, potassium sulfide, potassium hydroxide, potassium oxide, potassium permanganate, potassium silicofluoride, potassium feldspar, potassium molybdates, or a combination thereof as the potassium source. Similar examples of stabilizing compounds that may be used are described in <CIT>, entitled "STRAIGHT POLARITY METAL CORED WIRES," and <CIT>, entitled "STRAIGHT POLARITY METAL CORED WIRE".

Furthermore, one or more inorganic stabilizers are included in the granular core <NUM> in the form of an agglomerate or frit. That is, certain embodiments of the tubular welding wire <NUM> may include one or more of the inorganic stabilizers described above in an agglomerate or frit that may stabilize the arc during welding. The term "agglomerate" or "frit," as used herein, refers to a mixture of compounds that have been fired or heated in a calciner or oven such that the components of the mixture are in intimate contact with one another. It should be appreciated that the agglomerate may have subtly or substantially different chemical and/or physical properties than the individual components of the mixture used to form the agglomerate. For example, agglomerating, as presently disclosed, may provide a frit that is better suited for the weld environment than the non-agglomerated materials.

According to the present invention, the granular core <NUM> of the tubular welding wire <NUM> includes an agglomerate of a mixture of alkali metal or alkaline earth metal compound and other oxides (e.g., silicon dioxide, titanium dioxide, manganese dioxide, or other suitable metal oxides). For example, one embodiment of a tubular welding wire <NUM> may include an agglomerated potassium source including of a mixture of potassium oxide, silica, and titania. By further example, another embodiment of a tubular welding wire <NUM> may include in the granular core <NUM> another stabilizing agglomerate having a mixture of potassium oxide (e.g., between approximately <NUM>% and <NUM>% by weight), silicon oxide (e.g., between approximately <NUM>% and <NUM>% by weight), titanium dioxide (e.g., between approximately <NUM>% and <NUM>% by weight), and manganese oxide or manganese dioxide (e.g., between approximately <NUM>% and <NUM>% by weight). In certain embodiments, an agglomerate may include between approximately <NUM>% and <NUM>% alkali metal and/or alkaline earth metal compound (e.g., potassium oxide, calcium oxide, magnesium oxide, or other suitable alkali metal and/or alkaline earth metal compound) by weight, or between approximately <NUM>% and <NUM>% alkali metal and/or alkaline earth metal (e.g., potassium, sodium, calcium, magnesium, or other suitable alkali metal and/or alkaline earth metal) by weight. Furthermore, in certain embodiments, other chemical and/or physical factors (e.g., maximizing alkali metal and/or alkaline earth metal loading, acidity, stability, and/or hygroscopicity of the agglomerate) may be considered when selecting the relative amounts of each component present in the agglomerate mixture. Additionally, in certain embodiments, the agglomerate may account for less than approximately <NUM>%, between approximately <NUM>% and approximately <NUM>%, between approximately <NUM>% and approximately <NUM>%, between approximately <NUM>% and approximately <NUM>%, or approximately <NUM>% of the granular core <NUM> by weight. In certain embodiments, the agglomerate may account for less than approximately <NUM>%, between approximately <NUM>% and approximately <NUM>%, between approximately <NUM>% and approximately <NUM>%, or approximately <NUM>% of the tubular welding wire <NUM> by weight.

Additionally, the granular core <NUM> of the tubular welding wire <NUM> may also include other components to control the welding process. For example, rare earth elements may generally affect the stability and heat transfer characteristics of the arc <NUM>. As such, in certain embodiments, the tubular welding wire <NUM> may include a rare earth component, such as the Rare Earth Silicide (e.g., available from Miller and Company of Rosemont, Illinois), which may include rare earth elements (e.g., cerium and lanthanum) and other non-rare earth elements (e.g., iron and silicon). In other embodiments, any material including cerium or lanthanum (e.g., nickel lanthanum alloys) may be used in an amount that does not spoil the effect of the present approach. By specific example, in certain embodiments, the rare earth component may account for less than approximately <NUM>%, between approximately <NUM>% and approximately <NUM>%, between approximately <NUM>% and approximately <NUM>%, between approximately <NUM>% and approximately <NUM>%, between approximately <NUM>% and approximately <NUM>%, between approximately <NUM>% and approximately <NUM>%, or approximately <NUM>% of the granular core <NUM> by weight. In certain embodiments, the rare earth component may account for less than approximately <NUM>%, between approximately <NUM>% and approximately <NUM>%, between approximately <NUM>% and approximately <NUM>%, or approximately <NUM>% of the tubular welding wire <NUM> by weight.

Furthermore, the tubular welding wire <NUM> may, additionally or alternatively, include other elements and/or minerals to provide arc stability and to control the chemistry of the resulting weld. For example, in certain embodiments, the granular core <NUM> and/or the metallic sheath <NUM> of the tubular welding wire <NUM> may include certain elements (e.g., titanium, manganese, zirconium, fluorine, or other elements) and/or minerals (e.g., pyrite, magnetite, and so forth). By specific example, certain embodiments may include zirconium silicide, nickel zirconium, or alloys of titanium, aluminum, and/or zirconium in the granular core <NUM>. In particular, sulfur containing compounds, including various sulfide, sulfate, and/or sulfite compounds (e.g., such as molybdenum disulfide, iron sulfide, manganese sulfite, barium sulfate, calcium sulfate, or potassium sulfate) or sulfur-containing compounds or minerals (e.g., pyrite, gypsum, or similar sulfur-containing species) may be included in the granular core <NUM> to improve the quality of the resulting weld by improving bead shape and facilitating slag detachment, which may be especially useful when welding galvanized workpieces, as discussed below. Furthermore, in certain embodiments, the granular core <NUM> of the tubular welding wire <NUM> may include multiple sulfur sources (e.g., manganese sulfite, barium sulfate, and pyrite), while other embodiments of the tubular welding wire <NUM> may include only a single sulfur source (e.g., potassium sulfate) without including a substantial amount of another sulfur source (e.g., pyrite or iron sulfide). For example, in an embodiment, the granular core <NUM> of the tubular welding wire <NUM> may include between approximately <NUM> % and approximately <NUM>%, or approximately <NUM>% potassium sulfate.

Generally speaking, the tubular welding wire <NUM> may generally stabilize the formation of the arc <NUM> to the workpiece <NUM>. As such, the disclosed tubular welding wire <NUM> may improve more than one aspect of the welding process (e.g., deposition rate, travel speed, splatter, bead shape, weld quality, etc.). It should further be appreciated that the improved stability of the arc <NUM> may generally enable and improve the welding of coated metal workpieces and thinner workpieces. For example, in certain embodiments, the coated metal workpieces may include galvanized, galvanealed (e.g., a combination of galvanization and annealing), or similar zinc-coated workpieces. A non-limiting list of example coated workpieces further includes dipped, plated (e.g., nickel-plated, copper-plated, tin-plated, or electroplated or chemically plated using a similar metal), chromed, nitrite-coated, aluminized, or carburized workpieces. For example, in the case of galvanized workpieces, the presently disclosed tubular welding wire <NUM> may generally improve the stability and control the penetration of the arc <NUM> such that a good weld may be achieved despite the zinc coating on the outside of the workpiece <NUM>. Additionally, by improving the stability of the arc <NUM>, the disclosed tubular welding wire <NUM> may generally enable the welding of thinner workpieces than may be possible using other welding electrodes. For example, in certain embodiments, the disclosed tubular welding wire <NUM> may be used to weld metal having an approximately <NUM>, <NUM>, <NUM>, <NUM>, <NUM>,<NUM>, <NUM> (<NUM>-, <NUM>-, <NUM>-, <NUM>-, <NUM>-, <NUM>-gauge), or even thinner workpieces. For example, in certain embodiments, the disclosed tubular welding wire <NUM> may enable welding workpieces having a thickness less than approximately <NUM>, less than <NUM>, or even less than approximately <NUM>.

Furthermore, the presently disclosed tubular welding wire <NUM> enables welding (e.g., welding of thin gauge galvanized steels) at travel speeds in excess of <NUM>,<NUM> or even <NUM>,<NUM> (<NUM> or even <NUM> inches) per minute. For example, the tubular welding wire <NUM> readily enables high quality fillet welds at travel speeds above <NUM>,<NUM> (<NUM> inches) per minute (e.g., <NUM>,<NUM> or <NUM>,<NUM> (<NUM> or <NUM> inches) per minute) with low weld porosity. That is, the presently disclosed tubular welding wire <NUM> may enable higher (e.g., <NUM>% to <NUM>% higher) travel speeds than other solid-cored, metal-cored, or flux-cored welding wires. It should be appreciated that higher travel speeds may enable higher production rates (e.g., on a production line) and reduce costs. Additionally, the presently disclosed tubular welding wire <NUM> exhibits good gap handling and provides excellent weld properties (e.g., strength, ductility, appearance, and so forth) using a wide operating process window. Further, the tubular welding wire <NUM> generally produces less smoke and spatter than other solid-cored, metal-cored, or flux-cored welding wires.

Furthermore, the disclosed tubular welding wire <NUM> may also be combined with certain welding methods or techniques (e.g., techniques in which the welding electrode moves in a particular manner during the weld operation) that may further increase the robustness of the welding system <NUM> for particular types of workpieces. For example, in certain embodiments, the welding torch <NUM> may be configured to cyclically or periodically move the electrode in a desired pattern (e.g., a circular, spin arc, or serpentine pattern) within the welding torch <NUM> in order to maintain an arc <NUM> between the tubular welding wire <NUM> and the workpiece <NUM> (e.g., only between the sheath <NUM> of the tubular welding wire <NUM> and the workpiece <NUM>). By specific example, in certain embodiments, the disclosed tubular welding wire <NUM> may be utilized with welding methods such as those described in <CIT>, entitled "DC ELECTRODE NEGATIVE ROTATING ARC WELDING METHOD AND SYSTEM,"; in <CIT>, entitled "DC ELECTRODE NEGATIVE ROTATING ARC WELDING METHOD AND SYSTEM"; and in <CIT>, entitled "ADAPTABLE ROTATING ARC WELDING METHOD AND SYSTEM". It should be appreciated that such welding techniques may be especially useful when welding thin workpieces (e.g., having <NUM>, <NUM>,<NUM>, <NUM> (<NUM>-, <NUM>-, or <NUM>-gauge) thickness), as mentioned above.

<FIG> illustrates an embodiment of a process <NUM> by which a workpiece <NUM> may be welded using the disclosed welding system <NUM> and tubular welding wire <NUM>. The illustrated process <NUM> begins with feeding (block <NUM>) the tubular welding electrode <NUM> (i.e., the tubular welding wire <NUM>) to a welding apparatus (e.g., welding torch <NUM>). As set forth above, in certain embodiments, the tubular welding wire <NUM> includes one or more organic stabilizer components (e.g., sodium carboxymethyl cellulose), one or more carbon components (e.g., graphite powder), and one or more rare earth components (e.g., rare earth silicide). Further, the tubular welding wire <NUM> may have an outer diameter between approximately <NUM>,<NUM> (<NUM> in) and approximately <NUM>,<NUM> (<NUM> in), between approximately <NUM>,<NUM> /<NUM> in) and approximately <NUM>,<NUM> (<NUM> in), between <NUM>,<NUM> (<NUM> in) and approximately <NUM>,<NUM> (<NUM> in), or approximately <NUM>,<NUM> (<NUM> in). It may also be appreciated that, in certain embodiments, the welding system <NUM> may feed the tubular welding wire <NUM> at a suitable rate to enable a travel speed greater than <NUM>,<NUM>/min (<NUM> in/min) or greater than <NUM>,<NUM>/min (<NUM> in/min).

Additionally, the process <NUM> includes providing (block <NUM>) a shielding gas flow (e.g., <NUM>% argon (Ar), <NUM>% Ar / <NUM>% CO<NUM>, <NUM>% Ar / <NUM>% CO<NUM>, or similar shielding gas flow) near the contact tip of the welding apparatus (e.g., the contact tip of the torch <NUM>). According to the present invention, the shielding gas flow includes at least <NUM>% (e.g., at least <NUM>%, at least <NUM>%, at least <NUM>%) Ar. In other, not claimed embodiments, welding systems may be used that do not use a gas supply system (e.g., such as the gas supply system <NUM> illustrated in <FIG>) and one or more components (e.g., potassium carbonate) of the tubular welding wire <NUM> may decompose to provide a shielding gas component (e.g., carbon dioxide).

Next, the tubular welding wire <NUM> is brought near (block <NUM>) the workpiece <NUM> to strike and sustain an arc <NUM> between the tubular welding wire <NUM> and the workpiece <NUM>. It should be appreciated that the arc <NUM> may be produced using, for example, a DCEP, DCEN, DC variable polarity, pulsed DC, balanced or unbalanced AC power configuration for the GMAW system <NUM>. Once the arc <NUM> has been established to the workpiece <NUM>, a portion of the tubular welding wire <NUM> (e.g., filler metals and alloying components) may be transferred (block <NUM>) into the weld pool on the surface of the workpiece <NUM> to form a weld bead of a weld deposit. Meanwhile, the remainder of the components of the tubular welding wire <NUM> may be released (block <NUM>) from the tubular welding wire <NUM> to serve as arc stabilizers, slag formers, and/or deoxidizers to control the electrical characteristics of the arc and the resulting chemical and mechanical properties of the weld deposit.

By specific example, it is believed that, for certain embodiments, the Group I or Group II metals (e.g., potassium and sodium ions) of the organic stabilizer may generally separate from the organic stabilizer and provide a stabilization effect to the arc. Meanwhile, it is believed that the organic portion (e.g., comprising at least carbon and hydrogen, but possibly including oxygen) may decompose under the conditions of the arc to provide a reducing (e.g., rich in hydrogen) atmosphere at or near the welding site. Accordingly, while not desiring to be bound by theory, it is believed that the resulting reducing atmosphere, and in potential combination with the Group I/Group II stabilizing metals, the rare earth components, cyclical motion, and so forth, presently disclosed, provides a welding solution enabling high travel speeds and low-porosity, even when welding coated workpieces or performing gap fills. For example, in certain embodiments, the tubular welding wire <NUM> may generally enable the welding of thinner workpieces as well as painted, galvanized, galvannealed, plated, aluminized, chromed, carburized, or other similar coated workpieces. For example, certain embodiments of the presently disclosed tubular welding wire <NUM> may enable welding workpieces having thicknesses less than <NUM> or less than <NUM>, or workpieces having thicknesses of approximately <NUM> or <NUM>, while maintaining high travel speed (e.g., in excess of <NUM>,<NUM>/min (<NUM> in/min)) and low-porosity, even when performing gap fills (e.g., <NUM>-<NUM> gap fills).

Results for an example all-weld metal welding experiment using two embodiments of the disclosed tubular welding wire <NUM> (i.e., FabCOR® F6 and FabCOR® F6 LS, both available from Hobart Brothers Company, Troy, OH) according to the process <NUM> is set forth below in Table <NUM>. It should be appreciated that the weld chemistry illustrated in Table <NUM> accounts for certain components of the weld metal (e.g., approximately <NUM>% of the total weld metal) with the remaining percentage provided by iron. As shown in Table <NUM>, the Charpy-V-Notch values for the resulting weld is at least approximately <NUM> J (<NUM> ft. ) (e.g., at least approximately <NUM> J (<NUM> ft. ), at least approximately <NUM> J (<NUM> ft lbs. ), at least approximately <NUM> J (<NUM> ft. )) at approximately -<NUM> and/or at approximately -<NUM>. In certain embodiments, the Charpy-V-Notch values of a weld formed using the disclosed tubular welding wire <NUM> may generally range between approximately <NUM> J (<NUM> ft. ) and approximately <NUM> J (<NUM> ft. Additionally, for the experiment illustrated in Table <NUM>, the resulting weld afforded an ultimate tensile strength (UTS) of at least approximately <NUM> N/mm<NUM> (<NUM> kilopounds per square inch (kpsi)) (e.g., greater than <NUM> N/mm<NUM> (<NUM> kpsi), greater than <NUM> N/mm<NUM> (<NUM> kpsi), greater than <NUM> N/mm<NUM> (<NUM> kpsi)), a yield strength (YS) of at least approximately <NUM> N/mm<NUM> (<NUM> kpsi) (e.g., greater than <NUM> N/mm<NUM> (<NUM> kpsi), greater than <NUM> N/mm<NUM> (<NUM> kpsi), greater than <NUM> N/mm<NUM> (<NUM> kpsi)), and an elongation of at least approximately <NUM>% (e.g., between approximately <NUM>% and approximately <NUM>%). For example, in other embodiments, the elongation of the weld deposit may be at least <NUM>%. In general, the FabCOR® F6 welding wire demonstrated lower spatter and superior wetting compared to FabCOR® F6 LS, when performing a welding operation according to the process <NUM>.

Furthermore, it may be appreciated that the present approach enables low-porosity (e.g., a low surface porosity and/or low total porosity) welds to be attained at high travel speed (e.g., in excess of <NUM>,<NUM>/min or <NUM>/min. (<NUM> in/min or <NUM> in/min)), even when welding coated workpieces. In certain embodiments, the low-porosity enabled by the presently disclosed tubular welding wire <NUM> may provide a weld that is substantially non-porous. In other embodiments, the disclosed tubular welding wire <NUM> may provide a low-porosity weld having only small voids or pores (e.g., less than approximately <NUM> in diameter) that are separated from one another by a distance greater than or equal to the respective diameter of each pore. Further, in certain embodiments, the porosity may be represented as a sum of the diameters of the pores encountered per distance of the weld in a direction (e.g., along the weld axis). For such embodiments, the weld may have a porosity less than approximately <NUM>,<NUM> per <NUM>,<NUM> (<NUM> inches per inch) of weld, less than approximately <NUM>,<NUM> per <NUM>,<NUM> (<NUM> inches per inch) of weld, less than approximately <NUM>,<NUM> per <NUM>,<NUM> (<NUM> inches per inch) of weld, or less than approximately <NUM>,<NUM> per <NUM>,<NUM> (<NUM> inches per inch) of weld. It may be appreciated that the porosity of the weld may be measured using an X-ray analysis, microscope analysis, or another suitable method.

Tables <NUM> and <NUM> present the results of example welding operations of Zn-coated workpieces using an embodiment of the tubular welding wire <NUM> at relatively high travel speeds (i.e., <NUM>,<NUM> (<NUM> inches) per minute) using different welding conditions. The varied welding conditions of the indicated examples include: welding polarity (e.g., DCEN or DCEP), welding process (e.g., constant voltage (CV) or pulsed, such as Miller AccuPulse™), and shielding gas (e.g., <NUM>% Ar / <NUM>% CO<NUM> or <NUM>% Ar). Length porosity and area porosity measurements of Table <NUM> are provided as a percentage of the porosity that would cause the weld deposit to fail radiographic (e.g., X-ray) acceptable standards based on the minimum size of circular indications and the minimum weld viewing area, in accordance with AWS A5. <NUM> Radiographic Acceptance Standards.

For the examples indicated in Table <NUM>, when the welding process is CV, then a <NUM>% Ar / <NUM>% CO<NUM> shielding gas generally enables a lower spatter rate than <NUM>% Ar. Similarly, for the examples of Table <NUM>, when the welding process is pulsed DCEN, a <NUM>% Ar / <NUM>% CO<NUM> shielding gas generally enables lower spatter than <NUM>% Ar. However, the trend unexpectedly reverses when the welding process is pulsed DCEP, and a <NUM>% Ar shielding gas not only enables a lower spatter rate than a <NUM>% Ar / <NUM>% CO<NUM> shielding gas, but also results in less spatter than all of the other welding conditions listed on Table <NUM>. In particular, for embodiments in which the combination of welding conditions include <NUM>% Ar and pulsed DCEP, spatter levels may be between approximately <NUM>% and approximately <NUM>% lower (e.g., between approximately <NUM>% and approximately <NUM>% lower) when compared to the other welding conditions listed in Table <NUM>. Accordingly, such embodiments enable welding operations in which less than approximately <NUM> wt% (e.g., less than approximately <NUM> wt%, less than approximately <NUM> wt%, less than approximately <NUM> wt%, approximately <NUM> wt%) of the wire <NUM> is converted to spatter while welding the Zn-coated workpiece, even at a relatively high travel rate (e.g., <NUM>,<NUM> (<NUM> inches) per minute).

As indicated in Table <NUM>, when the welding polarity is DCEN, then a <NUM>% Ar / <NUM>% CO<NUM> shielding gas generally enables lower length porosity than <NUM>% Ar. When the welding polarity/process is CV DCEP, a <NUM>% Ar / <NUM>% CO<NUM> shielding gas generally enables a lower length porosity than <NUM>% Ar. However, the trend unexpectedly reverses when the welding process is pulsed DCEP, and a <NUM>% Ar shielding gas enables lower length porosity than a <NUM>% Ar / <NUM>% CO<NUM> shielding gas. In general, Table <NUM> indicates that, for embodiments in which the combination of welding conditions include <NUM>% Ar and pulsed DCEP, both the length and area porosity are acceptably low, which is indicative of a sound weld deposit. Such embodiments enable the formation of weld deposits having a length porosity less than approximately <NUM>% (e.g., less than approximately <NUM>%, less than approximately <NUM>%, less than approximately <NUM>%, less than approximately <NUM>% or approximately <NUM>%) and an area porosity less than approximately <NUM>% (e.g., less than approximately <NUM>%, less than approximately <NUM>%, less than approximately <NUM>%, or approximately <NUM>%). Further, visual inspection of the weld deposits indicate that, for such embodiments, silicon (Si) islands were distributed toward the toe of the weld deposit rather than distributed throughout the surface of the weld deposit.

<FIG> illustrates an embodiment of a process <NUM> by which the tubular welding wire <NUM> may be manufactured. It may be appreciated that the process <NUM> merely provides an example of manufacturing a tubular welding wire <NUM>; however, in other embodiments, other methods of manufacturing may be used to produce the tubular welding wire <NUM> without spoiling the effect of the present approach. That is, for example, in certain embodiments, the tubular welding wire <NUM> may be formed via a roll-forming method or via packing the core composition into a hollow metallic sheath. The process <NUM> illustrated in <FIG> begins with a flat metal strip being fed (block <NUM>) through a number of dies that shape the strip into a partially circular metal sheath <NUM> (e.g., producing a semicircle or trough). After the metal strip has been at least partially shaped into the metal sheath <NUM>, it may be filled (block <NUM>) with the filler (e.g., the granular core <NUM>). That is, the partially shaped metal sheath <NUM> may be filled with various powdered alloying, arc stabilizing, slag forming, deoxidizing, and/or filling components. For example, among the various fluxing and alloying components, one or more organic stabilizer components (e.g., sodium carboxymethyl cellulose), one or more carbon components (e.g., graphite powder), and one or more rare earth components (e.g., rare earth silicide) may be added to the metal sheath <NUM>. Furthermore, in certain embodiments, other components (e.g., rare earth silicide, magnetite, titanate, pyrite, iron powders, and/or other similar components) may also be added to the partially shaped metal sheath <NUM>.

Next in the illustrated process <NUM>, once the components of the granular core material <NUM> have been added to the partially shaped metal sheath <NUM>, the partially shaped metal sheath <NUM> may then be fed through (block <NUM>) one or more devices (e.g., drawing dies or other suitable closing devices) that may generally close the metal sheath <NUM> such that it substantially surrounds the granular core material <NUM> (e.g., forming a seam <NUM>). Additionally, the closed metal sheath <NUM> may subsequently be fed through (block <NUM>) a number of devices (e.g., drawing dies or other suitable devices) to reduce the circumference of the tubular welding wire <NUM> by compressing the granular core material <NUM>. In certain embodiments, the tubular welding wire <NUM> may subsequently be heated to between approximately <NUM> °F and approximately <NUM> °F for approximately <NUM> to <NUM> hours prior to packaging the tubular welding wire onto a spool, reel, or drum for transport, while, in other embodiments, the tubular welding wire <NUM> may be packaged without this baking step.

Claim 1:
A method of forming a weld deposit on a zinc-coated workpiece, comprising:
- feeding a tubular welding wire (<NUM>) toward a surface of a zinc-coated workpiece;
- directing a flow of shielding gas toward the surface of the zinc-coated workpiece near the tubular welding wire (<NUM>),
wherein the flow of shielding gas is at least <NUM>% argon (Ar);
and
wherein the welding wire (<NUM>) is a tubular welding wire (<NUM>) comprising a granular core (<NUM>) disposed inside of a metallic sheath (<NUM>), wherein the granular core (<NUM>) comprises a stabilizer component bound to one or more Group I or Group II metals;
a carbon component comprising graphite, graphene, carbon black, lamp black, carbon nanotubes, diamond, or a combination thereof; and
an agglomerate comprising Group I or Group II metal oxides, titanium oxide, and manganese oxides,
characterized in that
the welding wire (<NUM>) is electrified with pulsed electropositive direct current (DCEP), and wherein the stabilizer component is an organic component comprising one or more organic molecules or organic polymers bound to the one or more Group I or Group II metals;
the method further comprises:
forming the weld deposit on the zinc-coated workpiece using the tubular welding wire (<NUM>) while providing the flow of shielding gas near the weld deposit, wherein less than <NUM> wt% of the tubular welding wire (<NUM>) is converted to spatter while forming the weld deposit on the zinc-coated workpiece.