Showing papers on "Shielding gas published in 1990"

Effect of rare earth metal oxide additions to tungsten electrodes

Abstract: A comparative study has been made on the operating characteristics of gas-tungsten arc (GTA) welding for several types of electrodes. The work was carried out with a pure tungsten electrode and tungsten electrodes activated with a small quantity of the rare earth metal oxides, La2O3, Y2O3, CeO2, and with ZrO2, ThO2, and MgO. Their behaviors during arcing were analyzed and compared from the points of view of arc starting characteristics, electrode consumption, change in shape due to long-term operation, and incompleteness of insert gas shielding and electrode temperature. The results indicated that W-La2O3 electrodes have superior characteristics among those tested. Metallographic studies of the electrodes indicate that the superiority of operating characteristics strongly depends on the behavior of the rare earth metal oxides during arc burning. It is observed that the rare earth metal oxides form tungstate or oxytungstate during arc burning. These newly formed compounds have low melting points and migrate from the low temperature zones to the high temperature zones throughout the electrode tip, while ThO2 reacts with tungsten, forming pure Th. Also, the investigation demonstrates good stability of La2O3 during arc burning compared with the other oxides. Particular attention was also paid to the electrode temperature measurement and the important phenomena concerning the emissivity of a particular surface as one of the thermal properties. The investigation reveals the effects of temperature and oxide distribution on the spectral emissivity of the electrode in addition to the main different effect of oxides added to tungsten. Observations of the cathode tip microstructure during and after arc burning were made, and important phenomena concerning the formation of a tungsten “rim” at the periphery of the cathode area, which governs the durability of the electrode and the stability of the arc, are discussed theoretically and experimentally based on the temperature measurement of the tip and the oxidation of tungsten.

Energy absorption by metal‐vapor‐dominated plasma during carbon dioxide laser welding of steels

Abstract: During laser welding, the plasma plume affects the amount of energy reaching the weld surface and the composition and properties of the welds. Light emissions during welding were recorded by emission spectroscopy to understand the energy absorption and the nature of the plasma formed during welding of various grades of steels. The flow of gases and the concentrations of the various metal vapors were computed by solving the Navier Stokes equation and the equations of conservation of various species. The variables studied were shielding gas composition and flow rate and the base metal composition. Until now, self‐absorption of emissions arising from species present at high concentrations within the plasma has kept researchers limited to either analyzing ideal situations that are unrelated to the welding process or not accounting for the attenuation of the emissions. It is demonstrated that during welding, the peaks in the emission spectra that are affected by the self‐absorption process can be eliminated on the basis of the initial and the terminal energy levels for electronic transitions. By selectively eliminating the affected transitions and by using the numerically computed local concentrations of metal vapors, the absorption of the laser beam energy by the plasma can be accurately determined.

Effects of welding flux additions on 4340 steel weld metal composition

Abstract: The effects of CaF2, CaO and FeO additions on weld metal chemistry were evaluated for the manganese — silicate flux system. Comparisons were made between AISI 4340 steel and lowcarbon steel welds to understand the weld metal chemistry. The results show that the elemental transfer from the slag to the weld metal and vice versa cannot be consistently explained using thermodynamic data; e.g., the carbon/oxygen partition is apparently controlled by a CO reaction in the 1010 steel welds, but the AISI 1020 and 4340 steel welds show constant carbon contents despite increasing oxygen levels. In addition, data are reported as a resource for future analytical and comparative purposes. Introduction Submerged arc welding of high integrity can be achieved through proper selection of the wire and flux combination for the specific base metal and welding parameters. Small amounts of alloying elements such as nickel, chromium and molybdenum are added to steels to increase strength, hardness or toughness, as is the case with AISI 4340 steel. Generally, welding low-alloy steels requires more careful control of procedures and selection of consumables than welding the carbon steels. Moreover, the oxygen potential of the flux influences the loss or gain of alloying elements during welding, the weld-deposit oxygen content, and the type, size and distribution of oxide inclusions in the solidified weld metal. The effective application of the submerged arc welding process for joining high-strength, low-alloy steels depends heavily upon understanding the behavior of the flux. Understanding the elemental P. A. BURCK and D. L. OLSON are with the Center for Welding and joining Research, Colorado School of Mines, Golden, Colo. J £ INDACOCHEA is with the University of Illinois at Chicago, Chicago, III. transfer mechanisms between the flux and the weld metal can be attained by studying the influence of each chemical additive on the flux behavior. To determine the many slag/weld metal chemical reactions occurring simultaneously during welding, a state of thermodynamic equilibrium has been assumed to be attained. The basis for this assumption is that the high temperatures and high surface-to-volume ratio associated with the welding process counteract the short time available for a reaction to be completed (Ref. 1). Chai and Eagar (Ref. 2) reported that the very short times and the large thermal gradients involved in the process prevent overall slag-metal equilibrium from being reached. They also reported that an understanding of kinetics, in combination with the thermodynamic limits of the process, would be necessary to determine the final weld metal composition. Blander and Olson (Ref. 3) also discussed the influence of kinetics, the role of interfacial reaction, and the degree to which equilibrium is approached. This paper is a part of the systematic investigation undertaken by the Colorado School of Mines (Refs. 3-7) to better understand the behavior of different flux additions to the manganese-silicate and lime-silicate flux systems. The influence of FeO, CaO and CaF2 additions to a manganese-silicate flux on AISI 4340 steel weld metal chemistry is reported here. In addiKEY W O R D S Welding Flux Effects Flux Additions 4340 Steel Weld Metal Weld Composition Submerged Arc Fluxes 1020 Steel Weld Metal Ca2/CaO/FeO Addition Mn-Silicate Fluxes SAW Flux Systems tion, a comparison of the effects of CaF2 and FeO additions to a manganese-silicate flux on welds on AIS11020 and 4340 steels was made in an effort to understand the effect of alloying elements on weld metal chemistry. The results presented in this paper should be a useful database for future analytical modeling and comparisons. Materials and Procedure Single pass, bead-on-plate welds were made using the submerged arc welding process on AIS11010,1020 and 4340 steel base plates. The dimensions of the plates were 73 X 203 X 13 mm (2.9 X 8 X 0.5 in.). The welding wires used were AWS Type E70S-3 for welds produced on AISI 1010 and 1020 steels, and Type EM12K for AISI 4340 steel welds. Compositions of the base plates and welding wires are given in Table 1. The submerged arc welding process was performed using direct current, electrode positive. The welding parameters were maintained constant at 30 V, a travel speed of 8 mm/s (19 in./min), and the wire speed was varied to give 500 A. All welds were made with a heat input of 1.9 kj /mm (48 kj/in.). Three different flux systems were used in this investigation: Si02"MnO-FeO, Si02" MnO-CaO and Si02-MnO-CaF2. The fluxes were prepared using reagent grade chemical powders. The flux compositions were reported as wt-% MnO because M n 0 2 decomposes to form MnO during the melting operation used to produce the fused flux. The iron ion in the fused flux was determined to be in the Fe + state and is reported as wt-% FeO (Ref. 10). The reagent-grade powders were weighed and mixed prior to induction melting. The powders were then placed in a graphite crucible for the melting operation. All fluxes were brought to 1773 K. The crucible was then removed from the furnace and the flux poured onto a stainless steel plate to solidify. After cooling, the fused fluxes were crushed and sized. Fluxes sized 14 to 100 mesh were used for WELDING RESEARCH SUPPLEMENT 1115-s

Method of laser welding

Abstract: First and second metallic components are joined along a weld path by providing a beam of coherent electromagnetic energy having sufficient power to melt the first and second components and providing a low turbulent flow of an inert shielding gas over a weld region along a portion of the weld path. The beam is focussed on the weld region such that the beam energy is linearly distributed in the direction of the weld path with an intensity sufficient to form a pool of molten metal in the weld region. Relative motion is then established between the components and the beam to cause the weld region to move along the weld path, thereby joining the first and second components along the weld path.

Manual keyhole plasma arc welding system

Abstract: A manual keyhole plasma arc welding system including a power source; a manual arc welding torch assembly which includes, a) a hollow shield cup, b) a orifice subassembly concentrically disposed within the shield cup, and c) an electrode concentrically disposed within the orifice subassembly; a shield gas source; and a plasma gas source. A shield gas discharge annulus is formed between a terminal edge of the shield cup and the terminal end of the orifice subassembly. The terminal edge of the shield cup is extended beyond the terminal end of the orifice subassembly to produce a laminar shield gas discharge flow through the discharge annulus, providing cooling of the orifice subassembly. A plasma gas discharge annulus is formed between the terminal end of the orifice subassembly and a terminus of the electrode. A first terminal of the power source is connected to the electrode and a second terminal of the power source is connected to the workpiece. The power source provides a sinewave alternating current. A transferred arc is formed between the electrode and the workpiece. The power density is sufficient to provide keyhole welding, the reversing sinewave polarities providing simultaneous keyhole penetration and cathodic cleaning, eliminating the requirement of substantial workpiece surface preparation and/or removal of internal workpiece defects.

Effect of electrochemical reactions on submerged arc weld metal compositions

Abstract: The purpose of this work is to investigate the relative influence of electrochemical and thermochemical reactions on the weld metal chemistry in a direct current submerged arc welding process. Chemical analyses were carried out on the melted electrode tips, the detached droplets and the weld metal for both electrode-positive (reverse) polarity where the welding wire is anodic and electrode-negative (straight) polarity where the welding wire is cathodic

Gas metal arc welding of aluminum-based workpieces

Abstract: Method of welding aligned aluminum torque tube components, comprising (i) defining a stepped square-butt joint to be welded by preforming the ends of said torque tubes and assembling such ends together in the nested condition; (ii) establishing an electrical direct current arc between a positive consumable aluminum-based electrode and said joint as cathode, the arc being shrouded in a shielding gas consisting, by volume, of 2-5% oxygen and the remainder inert gas, the current to the arc being pulsed at a frequency of 40-60 cycles per second while maintaining an average current of at least 200 amps; and (iii) while holding the pulsed arc in a predetermined orientation (i.e., position angle 45-60°, lead angle 5-15°, transverse angle 12°) to the joint, moving the arc along the joint in a single pass at a relative speed of at least 60 inches per minute.

The Energy Transfer Efficiency in Laser Welding Process

Abstract: The process efficiency of laser beam welding was measured as a function of travel speed Temperature measurements were carried out during the bead‐on‐plate laser welding of mild steel with a focused 2KW CO2 laser beam at various welding travel speeds The laser welding process efficiency (power delivered to work/power in the beam) was calculated from the ratio of the heat content of the welded the specimen to the available laser beam energy (power × time) In the deep penetration welding region at intermediate travel speeds, the laser beam welding process efficiency (equal to the beam absorptance) was about 65%; but it was only about 28% in the shallow penetration region at high travel speeds In deep penetration welding, multiple reflections within the penetration cavity enhance absorptance A calculation based on four reflections within the cavity can account for the observed process efficiency

Keyhole and weld shapes for plasma arc welding under normal and zero gravity

Abstract: A first order study of the interfacial (keyhole) shape between a penetrating argon plasma arc jet and a stationary liquid metal weld pool is presented The interface is determined using the Young-Laplace equation by assuming that the plasma jet behaves as a one-dimensional ideal gas flow and by neglecting flow within the weld pool The solution for the keyhole shape allows an approximate determination of the liquid-solid metal phase boundary location based on the assumption that the liquid melt is a stagnant thermal boundary layer Parametric studies examine the effect of plasma mass flow rate, initial plasma enthalpy, liquid metal surface tension, and jet shear on weldment shape under both normal and zero gravity Among the more important findings of this study is that keyhole and weld geometries are minimally affected by gravity, suggesting that data gathered under gravity can be used in planning in-space welding

The Physics of Arc Welding Processes

Abstract: Welding is an extremely complex process; however, due to its commercial importance, it is essential that a more thorough study of the various processes be undertaken. Three examples of areas requiring greater understanding of arc physics are presented. The first discusses heating or cooling of the metal at the cathode; the second describes variations in heat transfer using various shielding gases and the last describes droplet formation in gas metal arc welding.

Electrode melting and plate melting efficiencies of submerged arc welding and gas metal arc welding

Abstract: The effect of process variables such as current, voltage, electrode extension, electrode diameter, etc., on the electrode melting and plate melting efficiencies of submerged arc welding (SAW) and gas metal arc welding (GMAW) has been studied. It has been shown that there is an increase in the electrode extension or a decrease in the voltage and electrode diameter. For the same welding parameters, the electrode melting efficiency is higher when the electrode is negative. A similar relationship was observed for GMAW. The results also indicated that the shielding gas in GMAW also had an effect on the electrode melting efficiency. The plate melting efficiency of GMAW increases with an increase in the welding current, voltage, and electrode diameter, and decreases with an increase in the electrode extension. For the same welding parameters, the plate melting efficiency is lower when the electrode is negative. For SAW there is an increase in the plate melting efficiency with an increase in the welding c...

Effect of shielding gas oxygen activity on weld metal microstructure of GMA welded microalloyed HSLA steel

Abstract: The nucleation and growth phenomena that characterize the transformation of austenite in the weld metal of microalloyed HSLA steels are influenced by both cooling rate and composition. An important part of the compositional influence is the oxide particle nucleants that form during the welding process. The compositions of welding wire and shielding gas in GMA welds of microalloyed HSLA steels determine the oxide particle formation; consequently, the welding wire and shielding gas combination is more important than the choice of either wire or gas alone. In this investigation, the wire composition, oxygen activity of the shielding gas, and heat input were varied to study the effects of each. Several mixtures of argon plus oxygen or argon plus carbon dioxide were used

Process and device for welding by laser beam

Abstract: Process for welding by laser beam or similar high-energy radiation, in which two contiguous workpieces have a coating between them, the vaporization point of which is lower than the melting point of the material of the workpieces, and in which a gas flow is directed onto the weld. To improve this process so that coated workpieces can be welded without gaps and so that gas can escape through the vapour capillaries of the weld, a current of gas which promotes degasification of the vaporized coating through the vapour capillaries of the weld is used in addition to the current of protective or working gas which flows around the weld.

Aluminium welding process - uses direct current, tungsten electrode and a shielding gas contg. helium and argon

Abstract: In a welding process for Al, using direct current and a W electrode, a shielding gas is used contg. at least 75%, pref. 90% He with the remainder Ar. The tip of the W electrode is rounded to promote the elimination of the oxide layer on the Al. Electrode is negative. USE/ADVANTAGE - Manual welding, giving port-free welds with low crack susceptibility.

Titanium nitride laser-beam surface-alloying treatment on carbon tool steel

Abstract: In order to improve the wear resistance of tool steel, a study of TiN surface-alloying treatment on 1% carbon steel by irradiation with a CO2 laser beam was performed. Argon and nitrogen were used as shielding gases, and their effects on the formation of the surface-alloyed layer were investigated. The effect of cobalt additions to the TiN powder on the hardness of the alloyed layer was also investigated. When argon was used as shielding gas, the depth of the alloyed layer was increased compared with the depth when nitrogen was used as a shielding gas. A portion of the TiN decomposed into titanium in the argon environment, the nitrogen apparently being lost as a gas. The structure of the surface-alloyed layer was composed of a ferritic phase without martensitic structure even at high cooling rates. When this layer was annealed at 1000 ° C for 3 h, part of the titanium precipitated as TiC particles. The hardness of the annealed alloyed layer increased to about 500 Hv. This increase in hardness was accompanied by the appearance of martensite. When nitrogen was used as shielding gas, decomposition of TiN was suppressed and the hardness of the alloyed layer reached 850 Hv. These layers had a martensitic structure. Thus, nitrogen is preferable to argon as a shielding gas if a martensitic structure is desired in this system. When 5% cobalt was added to the TiN powder, the hardness of the alloyed layer increased to 1100 Hv. This increased hardness is caused by stabilization of the martensitic structure caused by an increase in theMs temperature.

PC-based arc ignition and arc length control system for gas tungsten arc welding

Abstract: A PC-based digital control system for gas tungsten arc welding (GTAW) is presented. This system controls the arc ignition process, the arc length, and the process of welding termination. A DT2818 made by Data Translation is used for interface and A/D and D/A conversions. The digital I/O ports of the DT2818 are used for control of wirefeed, shield gas, cooling water, welding power supply, etc. The DT2818 is housed in a PC. The welding signals and status are displayed on the screen for in-process monitoring. A user can control the welding process by the keyboard. >

Gas shield for welding

Abstract: Disclosed is an improvement in a process of arc welding a work piece involving feeding a consumable electrode through a current-carrying sleeve to the arc to form a weld pool on the work piece. The improvement involves passing a stream of shielding gas inside the sleeve toward the weld pool.

Hydrogen cracking in duplex stainless steel weldments

Abstract: The restraint weld cracking test was conducted to investigate the hydrogen cracking in duplex stainless steels which contain various ferrite/austenite ratio. The gas tungsten arc (GTA) welding was applied with the argon shielding gas containing 10% hydrogen. The effects of preheating or post weld heat treatment (PWHT) on the hydrogen cracking were also tested.The hydrogen cracking occurred in the weld metal with the ferrite ratio higher than 60% using the 10% hydrogen containing shielding gas under the severe restraint condition. The higher ferrite ratio of weld metal produced larger amount of diffusible hydrogen bacause the hydrogen can dissolve in the austenite phase. It was effective for the prevention of cracking to apply the preheating at 473K of the solution treatment at 1373K or to reduce the ferrite ratio by the adjusting the nickel and nitrogen content in the weld metal.

Exhaust extraction system for welding site

Abstract: An exhaust extraction system for use in a welding work station is provided which operates to exhaust the noxious fumes from the welding site when the welding operation is being carried out and for a limited period thereafter. A supply of an inert shielding gas is delivered under pressure to both the welding side and the damper control mechanism. In response to changes in pressure in the supply line of the inert shielding gas, the damper control mechanism is operable to close the damper when the welding machine is deactivated and to open the damper when the welding machine is activated.

Process for welding coated thin sheets, especially zinc coated sheets

Abstract: A process is disclosed for welding coated thin sheets, especially zinc-coated sheets. Carrying out the welding with the plasma arc welding process in which, in addition to argon as centre gas, an argon/oxygen mixture containing 87 to 97% by volume of argon and 3 to 13% by volume of oxygen is used as outer or protective gas yields, surprisingly, a very good welding result, and consequently this process is an alternative to the known MAG fusion welding process.

Coated electrode for use in ARC welding of Cr-Mo type low alloy steels

Abstract: Described herein is a covered electrode for use in arc welding of Cr-Mo type low alloy steel, the covered electrode having a composition determined in consideration of the yield of each additive element as well as the relationship between the contents of certain key component elements, and permitting to form a weld metal with excellent high temperature strength and toughness along with appropriate room temperature strength.

Gas mixture and welding method

Abstract: Gas mixture suitable for MAG welding at a high current using a rod filled with non-alloyed or low alloy steels, comprises 20 to 65% argon, 5 to 20% helium, and at least 30% CO 2 .

Method and apparatus for electric arc welding a circular joint or the like with a horizontal axis

Abstract: The pressure of the back shielding gas is kept constant and the pressure of the welding gas is varied as a function of the angular position of the rotating electrode (13). Application to the butt-weld assembly of the tubes to the tube plate of a heat exchanger.

The Oxygen and Nitrogen Absorption of Iron Weld Metal during Arc Welding

Abstract: Using thermodynamic data, the free energy changes for dissociation reactions of several gases are obtained at high temperature. The relationship between the partial pressures of several gases and temperature is shown under 0.1 MPa (1 atm) atmosphere. Oxygen and nitrogen absorptions into liquid iron in equilibrium state are discussed thermodynamically. The effects of the welding condition and the oxidizing gas partial pressure in the welding atmospheres of Ar — O2 and Ar — CO2 on the oxygen content of the purified iron weld metals during gas metal arc welding are showed. The effects of the welding condition and the nitrogen partial pressure in the welding atmospheres of several gas mixtures on the nitrogen content of the iron weld metals during gas tungsten arc welding and gas metal arc welding are showed. Using those results and thermodynamic data, the behavior of the oxygen and nitrogen absorptions into the iron weld metal during arc welding is discussed.

Method for build-up welding of filling material to engine valve or the like

Abstract: PURPOSE: To abolish a machining stage and to improve productivity by removing the black skin layers of the annular recessed grooves of a work, etc., simultaneously with a build-up welding stage. CONSTITUTION: The lobe part 1c of an engine valve 1 having the annular recessed grooves 2 in a valve face part 1a formed by forging is first imposed on an inclined turn table 4 of a plasma welding device W. The valve is kept rotated in a fixed direction by rotation of the turn table 4 and while an inert shielding gas is injected in this state from the tip of a torch 5 disposed to face right above the valve face part 1a, only the plasma arc 6 is generated and the oxide scale or black skin layers, etc., formed on the surface of the annular recessed grooves at the time of forging are burned way and peeled by arc heat. The work 1 makes one turn and after all the black skin layers, etc., in the annular recessed grooves 2 are removed, the work 1 is rotated one turn in succession and the plasma arc 6 is generated. The build-up material 7 is simultaneously supplied from the tip of the torch 5 toward the plasma arc 6 and the filling material 7 and the annular recessed grooves 2 are melted by the arc heat, by which the grooves are built up 8. COPYRIGHT: (C)1992,JPO&Japio