Patent Application
20070051702
The invention relates generally to the field of welding and more particularly directed to fluxes having improved weld bead formation properties, and even more particularly directed to a flux system that can be used with a welding electrode to reduce the occurrence of copper cracking in a formed weld bead.
In the field of arc welding, the main types of welding processes are gas-metal arc welding with solid (GMAW) or metal-cored wires (GMAW-C), gas shielded flux-cored arc welding (FCAW-G), self shielded flux-cored arc welding (FCAW-S), shielded metal arc welding (SMAW) and submerged arc welding (SAW). Of these processes, gas metal arc welding with solid or metal-cored electrodes are increasingly being used for joining or overlaying metallic components. These types of welding processes are becoming increasingly popular because such processes provide increased productivity and versatility. Such increase in productivity and versatility results from the continuous nature of the welding electrodes in gas metal arc welding (GMAW & GMAW-C) which offers substantial productivity gains over shielded metal arc welding (SMAW). Moreover, these electrodes produce very good looking welds with very little slag, thus saving the time and expense associated with cleaning welds and disposing of slag, a problem that is often encountered in the other welding processes.
In gas metal arc welding with solid or cored electrodes, a shielding gas can be used to provide protection for the weld against atmospheric contamination during welding. Solid electrodes are appropriately alloyed with ingredients that, in combination with the shielding gas, provide porosity free welds with the desired physical and mechanical properties. In cored electrodes, these ingredients are on the inside, in the core (fill) of a metallic outer sheath, and provide a similar function as in the case of solid electrodes.
Solid and cored electrodes are designed to provide, under appropriate gas shielding, a solid, substantially porosity free weld with yield strength, tensile strength, ductility and impact strength to perform satisfactorily in the final applications. These electrodes are also designed to minimize the quantity of slag generated during welding. Cored electrodes are used increasingly as an alternative to solid wires because of increased productivity during welding fabrication of structural components. Cored electrodes are composite electrodes consisting of a core (fill) material surrounded by a metallic outer sheath. The core can consist mainly of metal powder. The core may also include fluxing ingredients to help with arc stability, weld wetting and appearance etc., such that the desired physical and mechanical properties are obtained in the weld. Cored electrodes are typically manufactured by mixing up the ingredients of the core material and depositing them inside a formed strip, and then closing and drawing the strip to the final diameter. Cored electrodes can provide increased deposition rates and produce a wider, more consistent weld penetration profile compared to solid electrodes. Moreover, cored electrodes can provide improved arc action, generate less fume and spatter, and provide weld deposits with better wetting compared to solid electrodes.
In the art of welding, much prior effort has been expended in developing flux compositions of the type having predetermined flux components intended to perform in predetermined manners.
A large number of compositions have been developed for use as fluxes in arc welding both for use generally as welding fluxes. Fluxes are utilized in arc welding to control the arc stability, modify the weld metal composition, and provide protection from atmospheric contamination. Arc stability is commonly controlled by modifying the composition of the flux. Fluxes also modify the weld metal composition by rendering impurities in the metal more easily fusible and providing substances with which these impurities may combine, in preference to the metal to form slag. Other materials may be added to lower the slag melting point, to improve slag fluidity, and to serve as binders for the flux particles.
In the welding of pipe sections, it is common practice to use one or more electrodes that are fed to a groove between adjoining pipe sections to join such pipe section together. The groove between the pipe section is typically filled with a granular flux that is used to protect the weld bead from the atmosphere. During the welding process, the molten metal from the melted welding electrode is covered by molten slag formed from the granular flux. The welding electrode, whether a solid wire or cored wire, typically includes a copper outer layer that is used to facilitate in forming an electrical contact between the welding electrode and the power source of the welder. The resistivity of the copper layer is very small so that the current passes from the contact tip of the welding gun to the welding electrode without generating large heat losses. During the feeding of the welding electrode through the welding gun, flakes of copper are often removed from the outer surface of the welding electrode. These flakes or particles of copper commonly commingle with the granular flux during a welding procedure. These flakes or particles of copper can become molten from the heated slag during a welding procedure and then pass through the slag and contact the formed weld bead. The formed welding bead for iron based alloys typically begins to solidify at about 1400-1800° C. The melting point of copper is about 1085° C. As a result, molten copper commonly passes through the molten slag and eventually settles on the upper surface of the solidified weld bead. Molten copper has a low surface tension, thus tends to migrate into the solidified weld bead at the grain boundaries of the weld bead. The migration of molten copper into the grain boundaries can result in “copper cracking”. Cracks of any kind are an unacceptable defect in pipe welds. The incidence of copper cracking becomes more pronounced as the granular flux is recycled and reused since such reused granular flux has an increased copper flake or particle content. The increased amount of copper flakes or particles in the reused granular flux results in the increased incidence of copper cracking in the formed weld bead. To reduce the tendency of copper cracking, it is commonly recommended to only use the granular flux once. This recommendation is both costly and results in a substantial amount of waste of effective granular flux. Another method to reduce the incidence of copper cracking is to reduce the abrasive action of the welding tip on the welding electrode so as to reduce the incidence of the copper flaking from the welding electrode. This arrangement requires frequent attention to the welding equipment which can be both time consuming and result in relatively frequent downtime to replace components of the welding gun. As a result, both of these procedures reduce the incidence of “copper cracking” and require added expense and added time, thus driving up the cost for forming a weld bead and also increasing the amount of time to form a weld bead.
In view of the current state of the art of welding, there is a need for a granular welding flux that can reduce the incidence of the “copper cracking” while enabling the granular welding flux to be reused.
The present invention pertains to slag systems for welding and more particularly to a granular flux system that is used with a welding electrode and which is formulated to reduce the incidence of “copper cracking” in a formed weld bead. The granular flux system is formulated for particular application in submerged arc welding process and will be described with particular reference thereto; however, it will be appreciated that the granular flux system can be used in other types of welding processes. The granular flux system is also particularly formulated for welding together pipe sections by a submerged arc welding process and will be described with particular reference thereto; however, it will be appreciated that other types of workpieces can be welded together using the granular flux system of the present invention. The granular flux system is formulated to reduce the incidence of “copper cracking” during a welding procedure. Copper cracking occurs when molten copper migrates to a solidified weld bead. The source of copper is typically from copper flakes that drop into the granular flux as a copper coated welding electrode passes through the welding gun during a welding operation. Some of the copper flakes in the granular flux become molten from the heat generated by the welding arc and migrate through the granular flux and molten slag that is formed during the welding process. Due to the low surface tension of the molten copper, the molten copper that eventually migrates through the slag and into contact with the recently solidified weld bead continues into the grain boundaries of the solid weld bead that forms as the weld bead continues to cool. The copper migration into the grains of the weld bead can result in cracking. The granular flux system of the present invention is formulated to reduce the incidence of molten copper interacting with the recently solidified weld bead by increasing the rate at which the molten slag freezes, and/or creating a solidified slag with a higher degree of crystalline structure. It has been found that by increasing the rate at which the molten slag freezes or solidifies, the amount of molten copper that contacts the recently solidified weld bead can be reduced. The rate at which the molten slag freezes can be increased by increasing the melting temperature of the slag. As the melting temperature of the slag is increased, the time it takes the molten slag to cool to a temperature below its melting point decreases, thus increasing the rate at which the molten slag freezes. When the slag is in a molten state, it is easier for the molten copper particles to migrate through the slag and come into contact with the weld bead. Once the slag freezes, the rate of migration of the molten copper through the solidified slag significantly decreases or ceases. By terminating the rate at which the molten copper passes through the solid slag, the amount of molten copper that penetrates the molten slag and gains contact with the weld bead is reduced, thereby reducing the incidence of copper cracking. The impeded movement of the molten copper in the solid slag results in the copper eventually solidifying in the slag before the copper can come in contact with the weld bead, thereby eliminating the chance that such copper can cause copper cracking in the weld bead. Terminating the rate at which the molten copper migrates through the molten slag results in a reduced amount of molten copper that contacts the solidified weld bead. As previously stated, once the molten slag solidifies, the rate at which the molten copper can migrate through the solidified slag is significantly reduced or terminated. It has been further found that by formulating the granular flux so as to form a solid slag that has increased crystalline structures, the rate at which molten copper can migrate through the solid slag decreases. Certain slag components have a tendency to form a glass-type structure when cooled to a solid form, whereas other slag components form a crystalline structure when solidified. The glass-type structure is a more fluid structure and allows the molten copper to migrate through the solid slag. A crystalline structure has been found to essentially bar any migration of the molten copper. As such, by increasing the percentage of slag components that form a crystalline structure once the slag has solidified, the migration of molten copper through the solid slag is significantly impeded.
In accordance with one aspect of the present invention, there is provided a granular flux system that includes an enhanced amount of magnesium oxide and/or calcium oxide. The increase in the amount of magnesium oxide and/or calcium oxide in the granular flux system results in raising the melting point of the molten slag and promotes the formation of a more crystalline slag. In one embodiment of the invention, the weight percentage of calcium oxide in the granular flux system is at least about 3 weight percent, more typically about 3.5-8 weight percent, and even more typically about 5-6 weight percent. In another and/or alternative embodiment of the invention, the weight percentage of magnesium oxide in the granular flux system is at least about 10 weight percent, more typically about 12-20 weight percent, and even more typically about 15.75-17 weight percent. In still another and/or alternative embodiment of the invention, the weight percent of calcium oxide and magnesium oxide in the granular flux system is at least about 15 weight percent, more typically about 18-28 weight percent, and even more typically about 20.7-23.5 weight percent.
In accordance with still another and/or alternative aspect of the present invention, there is provided a granular flux system that includes a reduced amount of sodium oxide, silicon dioxide and/or zirconium oxide. The sodium oxide, silicon dioxide and/or zirconium oxide in the granular flux system results causes the melting point of the slag to lower and/or promotes the formation of a more glass-type slag. The reduction of sodium oxide, silicon dioxide and/or zirconium oxide in the granular flux system can be used to increase the melting point of the slag and/or to cause the slag to form more crystalline structures. In one embodiment of the invention, the weight percentage of sodium oxide in the granular flux system is less than about 6 weight percent, more typically about 0-4 weight percent, and even more typically about 1.5-3 weight percent. In another and/or alternative embodiment of the invention, the weight percentage of silicon dioxide in the granular flux system is less than about 30 weight percent, more typically about 10-25 weight percent, and even more typically about 15-20 weight percent. In still another and/or alternative embodiment of the invention, the weight percentage of zirconium oxide in the granular flux system is less than about 6 weight percent, more typically about 0-3 weight percent, and even more typically about 0-1 weight percent. In yet another and/or alternative embodiment of the invention, the weight percent of sodium oxide, silicon dioxide and/or zirconium oxide in the granular flux system is less than about 40 weight percent, more typically about 10-25 weight percent, and even more typically about 15-24.2 weight percent.
In accordance with still yet another and/or alternative aspect of the present invention, there is provided a granular flux system having the following compositions in weight percent:
In accordance with a further and/or alternative aspect of the present invention, the metal electrode used with the granular flux in a submerged arc welding process is typically a solid metal wire or a metal wire that includes metal power in the core of the wire. When the metal electrode is a metal wire having a core, the metal sheath of the wire is typically formed primarily from iron (e.g., carbon steel, low carbon steel, stainless steel, low alloy steel, etc.); however, the metal sheath can be primarily formed of other materials. The fill composition typically constitutes at least about 1 weight percent of the total electrode weight, and not more than about 80 weight percent of the total electrode weight, and typically about 8-60 weight percent of the total electrode weight, and more typically about 10-40 weight percent of the total electrode weight. The fill composition includes one or more metal alloying agents that are selected to at least closely match the desired weld metal composition and/or to obtain the desired properties of the formed weld bead. Non-limiting examples of such alloying metals include aluminum, antimony, bismuth, boron, calcium, carbon, chromium, cobalt, copper, iron, lead, manganese, molybdenum, nickel, niobium, silicon, tin, titanium, tungsten, vanadium, zinc, zirconium, etc.
In accordance with yet a further and/or alternative aspect of the present invention, a shielding gas is used in conjunction with the welding electrode and granular flux system to provide protection to the weld bead from elements and/or compounds in the atmosphere. The shielding gas generally includes one or more gases. These one or more gases are generally inert or substantially inert with respect to the composition of the weld bead. In one embodiment, argon, carbon dioxide or mixtures thereof are at least partially used as a shielding gas. In one aspect of this embodiment, the shielding gas includes about 2-40 percent by volume carbon dioxide and the balance of argon. In another and/or alternative aspect of this embodiment, the shielding gas includes about 5-25 percent by volume carbon dioxide and the balance of argon. As can be appreciated, other and/or additional inert or substantially inert gases can be used.
It is a primary object of the invention to provide a welding process that results in a reduction of copper cracking in the weld bead.
Another and/or alternative object of the present invention is the provision of granular flux that reduces copper cracking in the weld bead.
Still another and/or alternative object of the present invention is the provision of a granular flux system that forms a slag that solidifies or freezes at a higher temperature and/or forms a solid slag having a higher degree of crystalline structure.
Yet another and/or alternative object of the present invention is the provision of granular flux that can be reused without causing a substantial increase in the incidence of copper cracking in the weld bead.
These and other objects and advantages will become apparent from the discussion of the distinction between the invention and the prior art and when considering the preferred embodiment as shown in the accompanying drawings.
Referring now in greater detail to the drawings, wherein the showings are for the purpose of illustrating preferred embodiments of the invention only, and not for the purpose of limiting the invention,
The submerged arc welding process is illustrated in more detail in
During a welding procedure, copper flakes or particles 70 are scraped offofthe outer surface of the welding wire W as the welding wire passes through the welding gun. These copper flakes or particles 70 can be relatively large and in some instances accumulate as globules in granular flux 62 as shown schematically in
Referring now to
The granular flux of the present invention is formulated to reduce the incidence of copper cracking, even when the granular flux is recycled more than once. The components in the granular flux are selected to 1) increase the melt point temperature of the molten slag so that the slag freezes more quickly, and/or 2) form a solid slag that is more crystalline in structure. The granular flux is an improvement of prior flux systems that had lower melting points for the molten slag and formed a glassy type slag. A comparison of one prior art granular flux system to one non-limiting example of the new granular flux system is set forth below in weight percent of the flux system:
The new formulation of the granular flux system overcomes many of the past problems associated with copper cracking in the weld bead. The new formulation forms a slag having a substantially crystalline structure whereas the prior art glass forms a glassy type slag. As a result of these features of the new formulation, significantly less amounts of molten copper migrate through the slag during a welding process, thus significant reductions in the amount of copper entering into the grains of the solidified weld bead during the cooling of the welding occurs. The effect of reducing the amount of molten copper migrating through the slag is illustrated in
These and other modifications of the discussed embodiments, as well as other embodiments of the invention, will be obvious and suggested to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the present invention and not as a limitation thereof.
