Constricted Arc Research Articles

Experimental Investigation of Drawing Vacuum Arc Under Different TMF Contacts in Vacuum Interrupter

Vacuum interrupter is widely used in the medium-voltage power system. Controlling the arc by the magnetic field is an effective method to improve the breaking capacity. The transverse magnetic field (TMF) forces the constricted arc to rotate to reduce local overheating. In this paper, three kinds of TMF contacts, which are Swastika-type contact, cup-shaped contact, and double-TMF contact that combines Swastika-type and cup-shaped contacts coaxially, are investigated in a demountable vacuum chamber with a high-speed camera. The arc voltage and current are also recorded. The experiments were conducted with circuit currents from 5 to 20 kA (root mean square) with a frequency of 50 Hz. There are four current levels in the experiment, which are 5, 10, 15, and 20 kA, and at least three tests are taken for each current level. The results showed that under low current (I = 10 kA), the arc of the three TMF contacts did not rotate. Under high current (I = 20 kA), it was observed that the arc of Swastika-type and double-TMF contacts rotated in the gap. The arc speed of double-TMF contacts is higher than that of Swastika-type contacts. The cup-shaped contacts have the highest arc voltage and noise among the three TMF contacts. The Swastika-type contacts were eroded most seriously. The simulation results show the force distribution of the arc on different locations. The resultant force makes the arc rotate counterclockwise.

TENSILE PROPERTIES OF GAS TUNGSTEN CONSTRICTED ARC WELDED TI-6AL-4V ALLOY JOINTS

Titanium and its alloys have been considered as one of the best engineering materials for industrial applications. Excellent combination of properties such as high strength to weight ratio, excellent resistance to corrosion makes them attractive materials for many industrial applications. Recently, considerable research has been performed on Gas Tungsten Constricted Arc welding (GTCAW) process and reported advantages include, lower heat input, reduced residual stresses and distortion. In this investigation, tensile properties of GTCA welded Ti-6Al-4V alloy joints were evaluated. Single pass, autogeneous welds free from volumetric defects were fabricated using optimized GTCAW parameters. The joints were characterized using optical microscopy, scanning electron microscopy and microhardness, survey. Tensile properties of the joints were overmatching with the base metal. The alpha and granular beta grains in the base metal were changed into short acicular alpha martensitic structure in the fusion zone as a result of GTCAW

Structure-property Interaction in Flux Assisted Tungsten Inert Gas Welding of Austenitic Stainless Steel

Austenitic stainless steel SS304 grade was welded with active Tungsten Inert Gas (TIG) welding process by applying a flux paste made of SiO2 powder and acetone. SiO2 flux application improves the weld bead depth with a simultaneous reduction in weld bead width. The improvement in penetration results from arc constriction and reversal of Marangoni convection. Experimental studies revealed that the SiO2 flux assisted TIG welding can enhance the weld bead penetration by more than 100%. Full depth welds up to 6mm were obtained by applying SiO2 flux. Microstructure reveals a reduction in ferrite formation in fusion zone by applying SiO2 flux. Samples welded with flux exhibits reduction in tensile strength and improvement in impact strength. Fractography of the tensile test specimens reveals the presence of oxide inclusions in the samples welded with flux. The relation of ferrite content and mechanical properties are presented in this paper.

Electrostatic Probe Differential Analysis for Temperature Distribution Diagnostics of Constricted Arc Current-carrying Region in Sheet Slanting Tungsten Electrode with Insulating Solid Wall

Electrostatic Probe Differential Analysis for Temperature Distribution Diagnostics of Constricted Arc Current-carrying Region in Sheet Slanting Tungsten Electrode with Insulating Solid Wall

Formation of the Properties of the Working Surfaces of Important Parts by Plasma Surfacing and Surface Heat Treatment by a Reversed-Polarity Current

The properties of surface layers can be formed by changing their structure using heat treatment and their composition and structure via the supply of an additional material to a treatment zone. The structural and phase transformations in the near-surface layer are determined by the thermal cycle in a treatment zone. To control the heating spot area at a uniform energy distribution and a high energy concentration is a challenging problem for surface heat treatment and deposition (surfacing). The results of studying plasma surface heat treatment and surfacing with a reversed-polarity current are presented. The contribution of the heat transfer from nonstationary cathode spots to an article during plasma surface treatment using a reversed-polarity current is separated. The advantages of surface heat treatment of medium- and high-alloy steels and the deposition of similar and dissimilar alloys using a reversed-polarity current constricted direct arc are presented.

Activated flux TIG welding of Inconel 718 super alloy in presence of tri-component flux

ABSTRACTIn this study, we have explored the influence of newly developed tri-component oxide flux (Cr2O3, FeO, and MoO3) on weldability, bead geometry, weld pool temperature variation, and mechanical strength of Inconel 718 welded joints. Moreover, the influence of used flux on weld pool, the surface morphology of electrode and penetration capability of tungsten inert gas (TIG) welding on Inconel 718 plates have been well elucidated. Results indicate that the flux mixture significantly increases the penetration depth as well as aspect ratio almost 200% as compared to conventional TIG welding. The arc constriction caused by newly developed oxide flux upsurges the heat density and the weld pool temperature of joints. The alloying effect caused by entrapped oxide particles greatly improves the hardness as well as the tensile strength of joints. The reported reinforcement in the welding performance may increase potential utility of the developed methods for real-world applications.

Identification of Optimized Gas Tungsten Constricted Arc Welding Parameters to Attain Minimum Fusion Zone Area in Ti–6Al–4V Alloy Sheets Used in Aero Engine Components

Identification of Optimized Gas Tungsten Constricted Arc Welding Parameters to Attain Minimum Fusion Zone Area in Ti–6Al–4V Alloy Sheets Used in Aero Engine Components

Studies on the weldability, mechanical properties and microstructural characterization of activated flux TIG welding of AISI 321 austenitic stainless steel

The presence of titanium in AISI 321 austenitic stainless steel, mitigates the corrosion when deployed in specific applications such as boiler shells, aircraft exhaust manifolds and process equipment. Using Commercial flux purchased from Edison Welding Institute (EWI), studies were conducted to note the effect of Activated Tungsten Inert gas (A-TIG) welding on the surface morphology of type 321 austenitic stainless steel welds and compared with conventional TIG welding. A thin flux layer was applied to the surface of the 6 mm thick plate, followed by a conventional TIG welding process. The bead on trial results shows that compared with the TIG welding process, the flux causes the weld depth to increase, weld bead width to decrease and weld area to increase. This incredible depth of penetration (DOP) has been accomplished by the mechanisms of reversal of Marangoni flow and Arc constriction. From various experimental trials, arc length of 3 mm, welding current of 220 Amps and welding speed of 120 mm min−1 were found to be optimal and subsequently used as input parameters to produce a good quality A-TIG welded butt joint. The welded joint is subjected to transverse and longitudinal tensile and bend tests, charpy impact toughness tests, microhardness, optical microscope, x-ray diffraction analysis, ferrite number measurement and Scanned electron fractography. The welded joint exhibited improved tensile strength, bend and charpy impact toughness and hardness. The weld metal microstructure was observed to be austenite, delta-ferrite and TiC intermetallic compounds (Titanium carbides). The XRD pattern indicates that austenite and ferrite phases are present in both base and weld metal. The results of Fischer Feritscope FMP30 (ferrite measurement) show that the content of delta-ferrite in the weld metal (5.9 FN) is much higher than the parent metal (1.2 FN) and shows excellent mechanical properties in the A-TIG welded joint. Scanned electron fractography indicates that the failure of weld metal and base metal occurs in the ductile mode of fracture.

Simulation and Experimental Investigation on a New Type of Cup-Shaped Contacts With Iron Cores

Vacuum interrupters, with the advantages of high breaking ability, small volume, low weight, and little pollution, are widely used in medium voltage circuit breakers. The transverse magnetic field (TMF), generated by spiral-type or cup-type contact, moves the constricted arc over the contact surface, which avoid excessive heating on the contact and reduce the erosion of a fixed area. The TMF contacts are slotted to cause current flow diversion, and a radial magnetic field is produced. In this paper, we propose an improved cup-type contact with iron cores. The magnetic field distribution of this new contact was simulated, and the magnetic force acted on arc column was calculated. It was found that the optimized contacts could effectively enhance the radial magnetic field between contacts and reduce the radial force of the arc column. In addition, two different kinds of cup-type TMF contacts were investigated in a demountable vacuum chamber using a high-speed charge-coupled device video camera. The experimental results suggested that compared with the traditional cup-shaped contacts, the new contacts could effectively improve the arc speed and duration of arc movement, accompanied by a more evenly surface ablation and an improved surface utilization.

Arc characteristics during the instability stage on transverse magnetic field contacts

The arcing process greatly affects the breaking ability after current zero. The instability stage is the transition stage from the ignition to the movement stage, which affects the arc movement characteristics. In this paper, the arc characteristics during the instability stage on spiral-type contacts were investigated using a high-speed video camera. A multi-column parallel instability mode and a single-column instability mode were found during the instability stage. The arc appearance and constriction degree changed rapidly. The arc voltage usually increased accompanied by fluctuations. In addition, it was found that the current significantly influenced the arc mode and duration in the instability stage. With increased peak current, the probability of a single-column instability mode increased, and the fluctuation range and average time decreased.

Rotation Characteristics of Vacuum Arcs Driven by Transverse Magnetic Fields

The objective of this paper is to propose a new method to quantitatively determine the arcing rotation characteristics of the constricted vacuum arc driven by the transverse magnetic field (TMF). This method is based on a split-anode TMF contacts’ system, including a split-anode TMF and a spiral TMF cathode. Experiments were carried out in a demountable vacuum chamber. Both contacts had a diameter of 60 mm. The anode surface was divided into four areas: one central area and three symmetrically peripheral annular areas. The currents of the four split-anode areas were measured using four Rogowski coils situated outside the vacuum chamber. The observed arc behavior was recorded by a high-speed charge-coupled device video camera. This experiment proposes a new method to quantitatively determine the arcing rotation velocity of the TMF vacuum arcs by the current waveforms of the four split-anode areas. After some comparison to the new method, the rotation velocity of the TMF vacuum arcs estimated in the traditional method by the arc photographs seems underestimated. The experimental results indicate that the constricted vacuum arc driven by the TMF should be higher than 471 m/s with the arc current of 16-kA rms. The results also reveal the corresponding anode current distribution characteristics under the TMF in different arc stages during the arcing period.

Microstructure and mechanical properties of similar and dissimilar metal gas tungsten constricted arc welds: Maraging steel to 13-8 Mo stainless steel

Abstract Maraging steel (250) and 13-8 Mo stainless steel plates were joined by gas tungsten constricted arc welding (GTCAW) process in similar and dissimilar metal combinations using 13-8 Mo stainless steel filler wire. The similar and dissimilar metal welds made in solutionized condition were subjected to standard post weld hardening treatments direct ageing at 485 °C, soaking for 3½ hours followed by air cooling (ageing treatment of maraging steel) and direct ageing at 510 °C, soaking for 4 h followed by air cooling (ageing treatment of 13-8 Mo stainless steel). The joint characterization studies include microstructure examination, microhardness survey across the weldments and transverse weld tensile test. Similar and dissimilar metal weldments responded to both the post weld ageing treatment. After post weld aging, increase in yield strength, UTS and slight reduction in % elongation of similar and dissimilar metal were observed. The observed tensile properties were correlated with microstructure and hardness distribution across the welds.

Effects of different activating fluxes on the surface tension of molten metal in gas tungsten arc welding

Surface tension is an important factor in arc welding and affects weld microstructure and flow mode in the weld pool. A novel surface tension measurement method based on the principle of weld pool oscillation is proposed to sense the surface tension of the weld pool without and with TiO2, NaCl, and CaF2 activating fluxes during tungsten inert gas welding process. Experimental results reveal that the TiO2 activating flux can convert the surface tension gradient from negative to positive but exerts minimal effect on arc behavior. The surface tension gradient is mainly controlled by the oxygen content in the weld pool, which determines the Marangoni convection and penetration depth. High oxygen content decreases the surface tension gradient and weakens the Marangoni convection in the weld pool. The NaCl and CaF2 activating fluxes can reduce the absolute value of average surface tension but exert negligible effects on the sign of surface tension gradient. The varied surface tension and increased penetration depth with NaCl and CaF2 activating fluxes are caused by arc constriction and increased arc temperature, respectively.

Effect of Welding Process on Microstructure, Mechanical and Pitting Corrosion Behaviour of 2205 Duplex Stainless Steel Welds

An attempt has been made to weld 2205 Duplex stainless steel of 6mm thick plate using conventional gas tungsten arc welding (GTAW) and activated gas tungsten arc welding (A- GTAW) process using silica powder as activated flux. Present work is aimed at studying the effect of welding process on depth of penetration, width of weld zone of 2205 duplex stainless steel. It also aims to observe the microstructural changes and its effect on mechanical properties and pitting corrosion resistance of 2205 duplex stainless steel welds. Metallography is done to observe the microstructural changes of the welds using image analyzer attached to the optical microscopy. Hardness studies, tensile and ductility bend tests were evaluated for mechanical properties. Potentio-dynamic polarization studies were carried out using a basic GillAC electro-chemical system in 3.5% NaCl solution to observe the pitting corrosion behaviour. Results of the present investigation established that increased depth of penetration and reduction of weld width in a single pass by activated GTAW with the application of SiO2 flux was observed when compared with conventional GTAW process. It may be attributed to the arc constriction effect. Microstructure of the weld zones for both the welds is observed to be having combination of austenite and delta ferrite. Grain boundary austenite (GBA) with Widmanstatten-type austenite (WA) of plate-like feature was nucleated from the grain boundaries in the weld zone of A-GTAW process. Mechanical properties are relatively low in activated GTAW process and are attributed to changes in microstructural morphology of austenite. Improved pitting corrosion resistance was observed for the welds made with A-GTAW process.

Effect of high-speed welding with a constricted arc on changes in the structure of the weld metal of 1201 aluminium alloy

The results of investigation of the special features of changes in the structure of welded joints in 1201 aluminium alloy at different speeds of welding with a constricted arc are presented. It is shown that the reduction of the holding time of liquid metal in the appropriate temperature ranges determines the solidification rate of metal and the extent of diffusion processes of alloying elements and impurities and also the nature of structural changes.

Evaluation of MIG welding process parameter using Activated Flux on SS316L by AHP-MOORA method

In this research work an attempt to investigate the influence of different single component oxide flux in Activated Metal Inert gas (MIG) welding of AISI 316L. Two different fluxes SiO2, Cr2O3 were used to bead on plate welding. 6 mm thick plate of stainless steel weld with MIG welding, Carried out under some process parameter. The process parameters such as welding speed, current, Arc voltage and response are welding dimension such as depth of penetration, Bead width were studied. The Welding experiments were conducted with L9 orthogonal array using minitab 16 softwere. A Same Nine set of parameter used for the without flux, With Sio2 and with Cr2O3 flux. Total 27 experimentshad done at work. AHP-MOORA and ASRS method was applied to optimizing the MIG welding process parameters and result indicated the enhanced penetration in weld achieved with use of fluxes Sio2, Cr2O3. On the basis of present result it is considered that the centripetal Marangoni convection & Constricted arc as a mechanism in increasing the penetration of activated MIG welding. The metallurgical characteristic Hardness of weldment was evaluated using Vickers-Hardness. The purpose of this work to investigate the effect of oxide fluxes on weld morphology & welding parameter. The optimization of Parameter with using AHP-MOORA and ASRS method.

Pulsed Electron Source with Grid Plasma Cathode and Longitudinal Magnetic Field for Modification of Material and Product Surfaces

The description and the main characteristics of the pulsed electron source “SOLO” developed on the basis of the plasma cathode with grid stabilization of the emission plasma boundary are presented. Тhe emission plasma is generated by a low-pressure arc discharge, and that allows to form the dense low-energy electron beam with a wide range of independently adjustable parameters of beam current pulses (pulse duration of 20–250 μs, pulse repetition rate of 1–10 s–1, amplitude of beam current pulses of 20–300 A, and energy of beam electrons of 5–25 keV). Тhe special features of generation of emission plasma by constricted low-pressure arc discharge in the grid plasma cathode partially dipped into a non-uniform magnetic field and of formation and transportation of the electron beam in a longitudinal magnetic field are considered. The application area of the electron source and technologies realized with its help are specified.

A Perspective Review on Estimation of Keyhole Profile during Plasma Arc Welding Process

Plasma arc welding uses a highly constricted arc to get a keyhole inside the molten pool. Hence, process efficiency of plasma arc welding process is much higher compared to the traditional gas tungsten arc welding process. In plasma arc welding process, keyhole stability, heat transfer and fluid flow behavior, process sensing and control methods are the significant issues for deeper understanding of the process and weld joint quality. The present work provides a critical review on plasma arc welding process with respect to the recent advances in plasma arc keyhole process models such as estimation of keyhole profile using two dimensional and three dimensional numerical models. Also, this paper provides sensing, controlling methods during plasma arc welding process.

Investigation of the short argon arc with hot anode. I. Numerical simulations of non-equilibrium effects in the near-electrode regions

The atmospheric pressure arcs have recently found application in the production of nanoparticles. The distinguishing features of such arcs are small length and hot ablating anode characterized by intensive electron emission and radiation from its surface. We performed a one-dimensional modeling of argon arc, which shows that near-electrode effects of thermal and ionization non-equilibrium play an important role in the operation of a short arc, because the non-equilibrium regions are up to several millimeters long and are comparable to the arc length. The near-anode region is typically longer than the near-cathode region and its length depends more strongly on the current density. The model was extensively verified and validated against previous simulation results and experimental data. The Volt-Ampere characteristic (VAC) of the near-anode region depends on the anode cooling mechanism. The anode voltage is negative. In the case of strong anode cooling (water-cooled anode) when the anode is cold, temperature and plasma density gradients increase with current density, resulting in a decrease of the anode voltage (the absolute value increases). Falling VAC of the near-anode region suggests the arc constriction near the anode. Without anode cooling, the anode temperature increases significantly with the current density, leading to a drastic increase in the thermionic emission current from the anode. Correspondingly, the anode voltage increases to suppress the emission, and the opposite trend in the VAC is observed. The results of simulations were found to be independent of sheath model used: collisional (fluid) or collisionless model gave the same plasma profiles for both near-anode and near-cathode regions.

Modeling and numerical simulation of anode activity and arc motion in a transverse magnetic field

Vacuum interrupters based on transverse magnetic field contacts now are widely used in medium voltage circuit breakers. The arc motion under the transverse magnetic field (TMF) plays a decisive role in the interruption. In this paper, we focus on the movement of vacuum arc driven by TMF and anode thermal process during the arcing. Then, based on the principle of conservation, a transient two-dimensional anode activity model (subjected to TMF constricted arc) is established. The state change of material, evaporation from contacts and motion of molten pool are also considered in our model. By considering the arc motion in the anode activity model, the transient anode thermal process and the movement of constrict arc under TMF are studied, respectively. The simulation predicted that average speed of arc is not higher than 200m/s. In the simulation, the anode surface is completely melted near the current peak with 200 μm molten layer. In addition, the influence of movement of molten pool on the arc speed is analyzed, finding that the movement of the bath accelerates arc speed, but weakens the surface melting at the same time.