Stable Arc Research Articles

Propagation of a stable gaseous detonation in a circular arc configuration

We examine numerically the effect that detonation wavefront curvature has on gaseous detonation cellular structure in a circular arc geometry with rigid walls. For the model considered, a planar detonation is weakly unstable. The detonation curvature is induced by diffraction and flow divergence as the wave sweeps around the arc. We examine the effect of arc thickness, inner arc radius and activation energy on the cellular pattern. A combination of pseudo-Schlieren, pseudo-soot foil records and detonation shock and sonic flow loci are used to explore the observed detonation structures. We find that for sufficiently wide arcs, the detonation wavefront curvature renders the detonation hydrodynamically stable, i.e. laminar flow with no cells. The stable configuration consists of a broadly curved wave originating from the inner arc surface, which is typically connected to the outer arc boundary by a stable Mach stem. The stable detonation is driven by a small region of subsonic flow attached to the inner arc surface, outside of which the flow is supersonic. The initiation dynamics of a stable propagating wave case are explored. The evolution dynamics between an unstable (cellular) and stable arc thickness are also examined. Smaller inner arc radii and lower activation energies increase the range of stable solutions.

Decreasing of the concentration quenching of fluorescent dye in a solution by introducing it to nanoparticles of silicon dioxide

The article presents the results of experimental studies of a double-chamber linear circuit DC electric arc plasmatron in experimental and industrial conditions. The electric arc plasmatron of the VORTEX-200 linear circuit with a rated power of 200 kW is designed for plasma ignition of a pulverized-coal torch, its stabilization and oil-free ignition of pulverized-coal boilers of thermal power plants.The linear circuit plasmatron contains two water-cooled casings isolated from each other, one of which has a hollow cylindrical electrode - a cathode having swirlers of the plasma-forming gas at both ends, and the other has an output electrode - an anode-diffuser having a channel with a cylindrical segment at one end and the exit nozzle in the form of a diffuser at the other end.The power of the plasmatron, depending on the process parameters, can vary from 80 to 230 kW. The plasmatron has a stable powerful air plasma torch. Tests of such plasmatrons showed their high reliability and possibility of their operation in difficult conditions of thermal power plants (high level of dust and humidity, high temperatures near the boilers). Measured volt-ampere characteristics of the plasmatron enabled us to determine the region of stable arc combustion from 350 to 475 A. Parameters of the plasmatron operation at its nominal power of 200 kW and the flow rate of the plasma-forming gas of 1000 l/min are attained at currents not exceeding 450 A. The use of mechanical ignition of the plasmatron with a needle from a refractory material, instead of breakdown the inter electrode gap by an oscillator, increased the reliability of its operation.The device for axial scanning of binding of the cathode spot of the arc, which allows us to increase the surface of cathode erosion many times,was developed. The use of azimuthal and axial scanning of the cathode spot of the arc of the plasma torch makes it possible to increase the service life of the cathode up to 200 hours with a service life of the massive anode exceeding 500 hours.

Calculation of Heat Transfer Characteristics of an Arc in a Gas Stream of Plasma-Arc Furnaces

Within the framework of the heat exchange model of electric arc, the arc characteristics in the gas jet of a melting plasmotron are calculated in the approximation of the interaction of a semi-infinite isothermal jet with a wall. The temperature profile, structure, and values of the heat fluxes of a part of the arc column in the melting space of the plasma arc furnace are determined to a distance from the cathode. For the given power and composition of plasma-forming gas, the electric and thermal characteristics of the plasmotron and its geometry are established. Examples are given of calculation of arc characteristics in argon and argon–hydrogen mixture in the initial period of melting of solid charge with stable arc combustion taking into account the influence of electric circuit parameters. The results on the temperature profile of the arc in a gas jet are presented.

Effect of hydrostatic pressure on protective bubble characteristic and weld quality in underwater flux-cored wire wet welding

The metal transfer and protective bubble images, real-time electric signal data and weld appearance were obtained in different simulated water depth wet flux-cored arc welding. The electric signal results showed that the high hydrostatic environment deteriorated the stability of the wet welding process. The poor weld appearances with porosity were displayed when it was welded in deep water. The weld dilution rate descended from 51% to 40% with increasing water depth from 0.5 m to 90 m because of arc shrinking and heat input reduction. The reduction of protective bubble size and duration caused by high water pressure was unable to maintain a stable burning arc. With increasing water depth, the increase of pores in welds strongly deteriorated the mechanical property of joints. The process of gas generation and its escape from the droplet during the droplet transfer were observed. The rise of pressure compressed gas pores and prevented the gas from escaping, which resulted in the increase of pores.

The influence of TIG-Arc physical characteristics on the penetration and weld width under different Ar and He supply conditions

Abstract In the paper, the 5A03 aluminium alloy was employed to study the influence of TIG arc on the penetration and the weld width. And the split anode method with water-cooled copper plate was used to measure and record the distribution of arc current, under different flow ratio of argon and helium conditions. And a gas supply device controlled by a solenoid valve was employed to obtain the stable TIG welding arc of gas supply alternately at the frequency of 1 Hz and 4 Hz, and then collected the phenomenon of arc alternate by the high-speed camera. The experimental results indicated that the current density at the arc anode center of argon and helium supply alternately with different mixing ratio is lower than that of the pure argon-arc center. Nonetheless, the former is more uniform in current density within 2 mm from the arc center. Furthermore, it presented as a component arc of argon-arc and helium-arc switched, with the condition of argon and helium supply alternately at a frequency of 1 Hz and the arc power density is greater and concentrated, leading to the wider and deeper weld.

Energy efficient dry reforming process using low temperature arcs

An energy efficient dry reforming process using a rotating arc plasma is introduced. By virtue of an elongated stable arc state in a rotating arc, a thermal energy efficiency of up to 76% and a reduction of the process costs to 9.4 and 5.52 kJ L−1 for reactant conversion and syngas production, respectively, are realized. The effects of the CH4/CO2 molar ratio on the energy cost were also investigated. The lowest energy costs were obtained at molar ratios of 3/7 and 1 for the reactant conversion and syngas production, respectively. Moreover, we found that a specific energy input (SEI) of 11.2kJ L−1 could maximize the conversion of both CO2 and CH4 to almost 100%. The results presented herein successfully demonstrate the commercial feasibility of using low‐temperature arcs for the dry reforming of methane.

The Development of Low-Current Surface Arcs Under Clean and Salt-Fog Conditions in Electricity Distribution Networks

Electricity distribution networks are built to deliver increasing amount of electricity from distributed energy resources (DERs) such as offshore and onshore wind and solar farms. Aging of network assets through low-current surface discharges is becoming a great concern for the security and reliability of the distributed energy supply. In particular coastal conditions can present a challenge for overhead line insulators through the environment of salt fog. Also, onshore areas may expose power lines to clean fog and agricultural or industrial pollution. In this paper, experimental studies are conducted to investigate electrical arc formation and growth on insulators, following the testing standards in accordance with IEC 61109. Dry-band arcs in both clean-fog and salt-fog environments are compared. It is identified that arcs are much faster to develop and have greater energy in salt-fog environments, due to the lower surface resistance and resulting higher leakage current. The time from a first arc to strike, to the situation where the arc is stable on the insulator surface is identified as a potentially critical parameter in controlling aging of an insulation surface. The time from initial appearance of an arc to full stability is eight times shorter in a salt fog of 16,000 $\mu \text{S}$ /cm compared to a clean fog of $600~\mu \text{S}$ /cm. This means the very existence of a stable low-current arc is much more likely in polluted conditions. Accumulated arc energy and heat dissipation have been calculated for both fog conditions. It is concluded that aging by low-current electrical arcs tends to be more severe in salt-fog environments, so that great care needs to be taken when designing overhead lines and insulators in such areas.

The mechanisms of arc coupling and rotation in cable-type welding wire CO2 welding

In the cable-type welding wire CO2 welding process, the arc coupling and rotation behaviors are greatly different from those in typical single-wire CO2 welding. A deflection length model is proposed to explain the phenomenon of arc shape interaction and coupling, which is considered to be caused by a concentration of forces at the central wire resulting from the electromagnetic forces generated by the currents running through the individual wires. The arc rotation is influenced by the compositional characteristics of the cable-type welding wire as the wire is fed, resulting in self-rotation as the wire melts. The arc stability, the droplet transfer behavior and the weld pool are affected by the balance of the forces during the welding process and cause the arcs from the cable-type welding wire to couple together, resulting in a stable arc and stable droplet transfer. The combined forces acting on the weld pool are beneficial for the transfer of arc heat and droplet heat to the side and bottom of the molten pool, affecting the weld pool and weld formation.

Effect of the welding direction on the microstructural characterization in fiber laser-GMAW hybrid welding of 5083 aluminum alloy

Thick plates of 5083 aluminum alloy are welded with double-side hybrid welding method, and the effects of different heat source positioning arrangement on porosity formation, microstructure and mechanical property of the welding joints are studied. The results show that relative stable arc and stable process can be obtained in laser-arc hybrid welding (LAHW) process, and the weld bead with lower porosity level can be achieved. Fewer air involved in the weld pool, better stability of the keyhole and the easier escape of bubbles from the weld pool are the three ways to suppress the porosity. In both arc-laser hybrid welding (ALHW) and LAHW processes, the columnar grains are found in the fusion boundary, while equiaxed grains are observed in the weld center. In LAHW process, although the grain size is larger, the strength of the joint is higher, which is attributed to less porosity formation, the slight loss of Mg, more second-phase particles with uniform distribution, and the formation of dislocation with higher density in the joints.

Effect of TIG current on microstructural and mechanical properties of 6061-T6 aluminium alloy joints by TIG–CMT hybrid welding

In order to expand the direct current-cold metal transfer (DC-CMT) method to include large-thickness plate welding, a tungsten inert gas–CMT (TIG–CMT) hybrid welding process was employed in this work. Adding a stable TIG arc can increase the total heat input on the workpiece and the penetration capacity of the DC-CMT welding process. Al6061 plates 4mm thick were welded successfully by this method. As the TIG current increased, the heat input of the welding process increased. The effect of TIG current on the microstructure and mechanical properties of the joints was investigated. The hardening phase in Al6061 was sensitive to the heat input provided by the welding process. Because of microstructural transformation, a decrease in the mechanical properties (softening phenomenon) invariably appeared in the heat-affected zone (HAZ). With increasing TIG current, the microstructures of the joints coarsened, and the width of the partially melted zone (PMZ) and HAZ of the joints broadened. A precipitation strengthening phase of Mg2Si appeared in HAZ. The hardness curve of the joint presented roughly W-type distribution. The hardness obtained in the softened zone was approximately 50% that of the base metal (BM). The joints demonstrated good deformation capability before fracture. As compared to the base material, the strength and the elongation of the joints decreased approximately 40% and 50%, respectively.

Multiple Types of Topological Fermions in Transition Metal Silicides.

Exotic massless fermionic excitations with nonzero Berry flux, other than the Dirac and Weyl fermions, could exist in condensed matter systems under the protection of crystalline symmetries, such as spin-1 excitations with threefold degeneracy and spin-3/2 Rarita-Schwinger-Weyl fermions. Herein, by using the abinitio density functional theory, we show that these unconventional quasiparticles coexist with type-I and type-II Weyl fermions in a family of transition metal silicides, including CoSi, RhSi, RhGe, and CoGe, when spin-orbit coupling is considered. Their nontrivial topology results in a series of extensive Fermi arcs connecting projections of these bulk excitations on the side surface, which is confirmed by (001) surface electronic spectra of CoSi. In addition, these stable arc states exist within a wide energy window around the Fermi level, which makes them readily accessible in angle-resolved photoemission spectroscopy measurements.

Evaluation of the Effect of the Water in the Contact Tip on Arc Stability and Weld Bead Geometry in Underwater Wet FCAW

Abstract: Underwater wet flux cored arc welding – FCAW – is an important process employed to repair marine structures with the advantages of not handling the components off the water and offers higher productivity in comparison to other conventional welding process. Under the water, wet welding activities are performed with lower stability, due to the pressure of the water surrounding the arc column and the presence of water in the gap between the contact tip and the electrode, which promotes poor electrical contact. In the present work, to compare the process stability of underwater wet FCAW with self-shielded electrode, welds were carried out using a special torch, which keeps the contact tip dry under the water. A two-level factorial design was used for experimentation and an Analysis of Variance was conducted to validate the results. Current coefficient of variation was used as the stability index. Welds performed with the torch have shown better-shaped beads and more stable arc in comparison to beads deposited with no mechanical barrier between water and the contact tip.

INFLUENCE OF STRUCTURAL PARAMETERS OF LOW-CARBON STEEL ON ELECTRIC ARC BURNING

Purpose. The article is aimed to evaluate the influence of structural parameters of low-carbon steel on arcing process. Methodology. The values of the micro- and substructure characteristics of the electrode wire metal were changed by varying the parameters of heat treatment and cold deformation by drawing. The degree of plastic deformation was obtained by drawing blanks from different initial diameter to final dimension of 1 mm. The thermal treatment was carried out in electric chamber furnace of the SNOL-1,6.2,5.1/11-IZ type. The temperature was measured by chromel-alumel thermocouple and the electromotive force was determined using the DC potentiometer. In order to obtain the substructure of different dispersion degree the steel (after quenching from temperatures and tempering at 650°C for 1 hour) was subjected to cold drawing to reduction 17 – 80%. To form structure with different ferrite grain size the steel after drawing was annealed at 680°C for 1 hour. The microstructure was examined under a light and electron transmission microscope UEMV-100K at the accelerating voltage 100 kV. The grain and subgrain sizes were evaluated using the methodologies of quantitative metallography. A welding converter of the PSG-500 type was used to study the arc welding process of direct and reverse polarities. Findings. The experimentally detected value of the welding current, which depends on the degree of deformation during wire drawing, under conditions of stable arc burning of direct polarity is about an order of magnitude lower than the calculated value. Similar difference was found for the arc of reverse polarity: the experimental value of the welding current is 5...6 times less than the calculated value. Dependence analysis shows that, regardless of the polarity of the welding arc, a good enough agreement between the calculated and experimental values of the welding current is limited to deformations of 60%. For deformation degrees of more than 60%, the differences are explained by qualitative changes in the dislocation cell structure. Originality. In the conditions of stable arcing of different polarity for the electrode of low-carbon steel, an extreme dependence of welding current on the degree of cold plastic deformation was observed. Practical value. Influence of ferrite grain size of electrode wire on the value of welding current is much greater than that from substructure presence.

Electric Arc Furnace Modeling with Artificial Neural Networks and Arc Length with Variable Voltage Gradient

Electric arc furnaces (EAFs) contribute to almost one third of the global steel production. Arc furnaces use a large amount of electrical energy to process scrap or reduced iron and are relevant to study because small improvements in their efficiency account for significant energy savings. Optimal controllers need to be designed and proposed to enhance both process performance and energy consumption. Due to the random and chaotic nature of the electric arcs, neural networks and other soft computing techniques have been used for modeling EAFs. This study proposes a methodology for modeling EAFs that considers the time varying arc length as a relevant input parameter to the arc furnace model. Based on actual voltages and current measurements taken from an arc furnace, it was possible to estimate an arc length suitable for modeling the arc furnace using neural networks. The obtained results show that the model reproduces not only the stable arc conditions but also the unstable arc conditions, which are difficult to identify in a real heat process. The presented model can be applied for the development and testing of control systems to improve furnace energy efficiency and productivity.

Study of Oblique Shock Wave Control by Surface Arc Discharge Plasma

The mechanism of oblique shock wave control by surface arc discharge plasma is explored through a combined numerical and experimental study. The experiments are conducted in a supersonic wind tunnel with Mach number of 2.5, total pressure of 3.5–6.4 bar, and total temperature of 300 K. An oblique shock is formed by a compression ramp with an angle of 7 deg mounted on the lower wall of the wind tunnel. Six electrodes are arranged equally in the spanwise direction and upstream of the compression ramp. The schlieren images show that the angle of the original oblique shock is increased, and the surface pressure measurements indicate that the oblique shock is weakened by the addition of the stable discharge arc. The reason is that the arc heating decreases the Mach number upstream of the oblique shock; thus, the oblique shock is weakened and the shock angle is increased. A three-dimensional numerical simulation is performed using experimental configuration. Results show that the static pressure increases in front of the oblique shock and decreases after the shock, which is in good agreement with the experimental measurements. This validates that the numerical model presents a reasonable approach for the arc discharge plasma and further confirms the predominant role of the thermal effects of plasma on shock manipulation.

Using Mathematical Modeling to Develop Electrode Coating Composition for Stable Arcing and Arc Restarting

This paper proposes a method to optimize electrode coating using the desirability function for such stick electrode quality assessment criteria as stable arcing while ensuring sustainable restarting of the arc. Based on the mathematical apparatus of the experiment design theory, we derived a regression equation that describes the joint effect of electrode coating components on the arcing and arc restarting stability when using coated electrodes for welding. We have also analyzed the mathematical apparatus for experimental data processing for optimizing based on a generalized criterion. This method enables an assessment of responses that differ in their physical meaning and dimension. This experience helped optimize the electrode coating.

Stable synthesis of few-layered boron nitride nanotubes by anodic arc discharge

Boron nitride nanotubes (BNNTs) were successfully synthesized by a dc arc discharge using a boron-rich anode as synthesis feedstock in a nitrogen gas environment at near atmospheric pressure. The synthesis was achieved independent of the cathode material suggesting that under such conditions the arc operates in so-called anodic mode with the anode material being consumed by evaporation due to the arc heating. To sustain the arc current by thermionic electron emission, the cathode has to be at sufficiently high temperature, which for a typical arc current density of ~100 A/cm2, is above the boron melting point (2350 K). With both electrodes made from the same boron-rich alloy, we found that the arc operation unstable due to frequent sticking between two molten electrodes and formation of molten droplets. Stable and reliable arc operation and arc synthesis were achieved with the boron-rich anode and the cathode made from a refractory metal which has a melting temperature above the melting point of boron. Ex-situ characterization of synthesized BNNTs with electron microscopy and Raman spectroscopy revealed that independent of the cathode material, the tubes are primarily single and double walled. The results also show evidence of root-growth of BNNTs produced in the arc discharge.

Microscopic structure and property of double-electrode gas metal arc welding of AZ31B magnesium alloy

This paper focuses on the research on double-electrode gas metal arc welding (DE-GMAW) of AZ31B magnesium alloy sheet with 2mm thickness. During the welding process, stable hybrid arc of metal inert gas (MIG) and tungsten inert gas (TIG) is employed as welding heat source. Optical and electron microscopes are used to observe the microstructures of the weld joint. X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) are employed to identify the components in fusion zone. Microhardness is also tested. When the MIG current is 80A, the perfect weld joint is obtained, though figures of fish scales are observed in all joints in the research. The fusion zone is formed by dendrites, where β-Mg17(Al, Zn)12 is dispersed. The hardness in fusion zone and heat affected zone (HAZ) is lower than that in base metal (BM). The average Vickers hardness of fusion zone and HAZ is about 58 and 56 respectively, while the Vickers hardness of BM is about 63.

Global instability of low-density jets

The global stability of laminar axisymmetric low-density jets is investigated in the low Mach number approximation. The linear modal dynamics is found to be characterised by two features: a stable arc branch of eigenmodes and an isolated eigenmode. Both features are studied in detail, revealing that, whereas the former is highly sensitive to numerical domain size and its existence can be linked to spurious feedback from the outflow boundary, the latter is the physical eigenmode that is responsible for the appearance of self-sustained oscillations in low-density jets observed in experiments at low Mach numbers. In contrast to previous local spatio-temporal stability analyses, the present global analysis permits, for the first time, the determination of the critical conditions for the onset of global instability, as well the frequency of the associated oscillations, without additional hypotheses, yielding predictions in fair agreement with previous experimental observations. It is shown that under the conditions of those experiments, viscosity variation with composition, as well as buoyancy, only have a small effect on the onset of instability.

Feasibility of narrow gap welding using the cold-wire gas metal arc welding (CW-GMAW) process

This article evaluates the performance of the cold-wire gas metal arc welding (CW-GMAW) process for narrow gap girth welding. The CW-GMAW process is characterized by the introduction of a continuously fed non-energized wire (cold-wire) into the electric arc/weld pool region. The cold-wire is melted by using the surplus heat available at the arc and molten metal at the weld pool. Narrow grooves 5 mm wide were prepared in 16 mm thick ASTM A131 grade A steel plates and filled using the CW-GMAW process. The feasibility of the process for narrow gap welding was assessed by analysing the joint cross section, microstructure and Vickers hardness. The mechanism by which the cold-wire prevents groove sidewall erosion is identified by using high speed imaging. It was found that for the CW-GMAW, the electric arc attaches to the cold-wire instead of the weld pool leading to a more stable arc, preventing the arc from attaching to the groove sidewall. The additional weld metal deposited by the cold wire, allowed complete filling of the groove with only three passes, demonstrating the productivity potential of the CW-GMAW process for narrow groove welding.