Arc Temperature Research Articles

Heat and pressure characteristics in hollow cathode centered negative pressure arc column

Arc characteristics are found greatly changed by the negative pressure from the hollow cathode. These changes affect the distribution of arc pressure, arc plasma flow and temperature along the arc column. The characteristics of HCCNPA (hollow cathode centered negative pressure arc) along the arc column were investigated in this study to understand the changes and influences. It was found that the negative pressure applied to the cathode reduced the arc pressure and the arc radius, and complicated the plasma flow distribution with a clear zero-speed dividing line in the arc column. Above the boundary line, the plasma in the middle of the arc column flowed to the cathode, and the peripheral plasma flowed to the anode, presenting two peak values in the arc pressure distribution. The inner negative pressure also could adjust the total arc force acting on the work-piece. Under the same inner negative pressure conditions, the difference in arc force between GTA (gas tungsten arc) and HCCNPA did not change at varying arc lengths.

Research on Quality Control of Arc Welding Robot Based on Molten Pool Contour extraction

In order to overcome the influence of various uncertainties on the welding quality in robot welding process, this paper proposes a multi-information fusion detection method. At first, in order to obtain the geometrical characteristics of the molten pool image, the adaptive Wiener filtering algorithm was used to denoise the image, and the Otsu threshold method was used to binarize the image. Then the binarized image was co rroded, swelled, removed and small area operation. The complete clear edge information of the weld pool is extracted; then the simple and effective geometric feature parameters are used to describe the shape of the weld pool. According to the characteristics of the arc welding temperature field, the method of radiation temperature measurement and the wavelength selection principle are discussed. From the arc temperature, wavelength and the angle of the thermometer with respect to the molten pool area, the interference of the arc at the temperature measurement point in the near-melting pool area was analyzed; It is proved quantitatively that the radiation temperature measurement method is feasible under the condition of small arc current.

The effects of metal vapour on the fault arc in a closed, air-filled container

The present work is an investigation of the effects of metal vapour on the behavior of a fault arc in a closed, air-filled container. Experiments were performed to measure the pressure, temperature, and energy balance of the fault arc for different metal electrodes. Theoretical results are obtained using a magneto-hydrodynamic model for the fault arc and then compared with the experimental results. It is found that the effects of increased radiation and mass transfer caused by metal vapour considerably cool down the plasma in the central arc, whereas the influence of increased electrical conductivity is relatively small. The simulation of the energy balance suggests that the pressure rise is seriously affected by the metal vapour due to the similarity of heat transport processes of the fault arc. In the case of Cu and Al electrodes, the heating of surrounding gas dominates in the energy dissipation, while for Fe, the radiation does. Huge chemical energy released due to Al vapour results in the maximum pressure rise for Al electrodes, and the strong radiation in the case of Fe electrodes is responsible for its smallest pressure rise.

Preparation and arc erosion properties of Ag/Ti2SnC composites under electric arc discharging

New Ag/Ti2SnC (Ag/TSC) composites with uniform microstructure were prepared by powder metallurgy. The superior wettability between Ag and Ti2SnC was confirmed with a contact angle of 14°. Arc erosion properties of Ag/10wt%Ti2SnC (Ag/10TSC) and Ag/20wt%Ti2SnC (Ag/20TSC) contacts were investigated under 400 V/100 A/AC-3 and compared with Ag/CdO contact. The Ag/10TSC contact exhibited comparable arc erosion property to Ag/CdO contact. The fine arc erosion resistance was attributed to the good wettability between Ti2SnC and Ag, the good heat-conducting property of Ag/10TSC, and the slight decomposition of Ti2SnC that absorbed part of electric arc energy. The excessive Ti2SnC significantly decreased the thermal conducting property of the Ag/20TSC composite, resulting in the severe heat accumulation that decomposed Ti2SnC and deteriorated arc erosion property. The oxidation behavior of Ti2SnC under high electric arc temperature was also studied and then an arc erosion mechanism was proposed to get a comprehensive understanding on the arc erosion property of Ag/TSC composites.

Contribution of metal vapor mass at periphery part of pulsed arc to electromagnetic force in weld pool

AbstractThe arc welding has been used in various welding methods because it is inexpensive and high in strength after welding. However, it is a problem that accidents such as collapse of the bridge occur because of the welding defects. The welding of low cost and high productivity is required without the welding defects. The pulsed TIG welding is inexpensive and capable of high‐quality welding. The electromagnetic force contributing to penetration changes because the transient response of arc temperature and iron vapor generated from anode occurs. However, the analysis of pulsed TIG welding with metal vapor has been elucidated only metal vapor concentration near anode with transient phenomenon and heat flux. Thus, the theoretical elucidation of penetration depth with control factor has not been researched. In this paper, the contribution of metal vapor mass at the periphery part of pulsed arc to the electromagnetic force in the weld pool is elucidated. As a result, the iron vapor mass at periphery part decreased with increasing the frequency. The iron vapor was stagnated at axial center within one cycle. The electromagnetic force to the penetration depth direction in weld pool increased at axial center. Therefore, the metal vapor mass at periphery part plays an important role for the electromagnetic force increment at axial center.

An improved arc model for vacuum arc regarding anode spot modes

This paper introduces an improved arc model for vacuum arcs. In this model, the impact of different high-current anode modes is considered. An existence diagram for different high-current anode modes including footpoint, anode spot type 1 and type 2 is determined using emission spectroscopy, high-speed camera, and electrical measurements. During transition from diffuse to the high-current mode the arc voltage will be affected due to high evaporation rate, which can affect dielectric recovery of vacuum interrupter. Conventional arc models cannot trace the corresponding sudden changes in the arc voltage during the transition to anode spot type 2. Therefore, different areas of discharge modes are determined based on the threshold current and gap length for AC 50 Hz and cylindrical contacts made of CuCr7525. The physical parameters of the arc, e.g. the arc temperature, contact geometry and material is considered as implicit parameters in the existence diagrams. The boundaries of the areas are used as a user-defined library in EMTP-RV for a new electric arc model. The voltage behavior of the arc can be predicted well in a larger range of peak currents by the results. The validity of the model is also investigated for AC 100 Hz and pulsed DC 10 ms.

Numerical investigation of coupled arc and electrode for GTAW with a longitudinal electromagnetic field

Due to the good conductivity of ions and free electrons in the arc column, arc plasma possesses a remarkable magnetic controllability. Thus, a new technique of electromagnetic stirring has been developed which is of great interest during welding process by applying superimposed external magnetic field. However, few researches have focused on arc behavior with a coupled electrode under a magnetic field. In this paper, a three-dimensional plasma arc model coupled cathode was developed, and the distributions of current density, electric potential, magnetic field, pressure, velocity and temperature of plasma arc were obtained by solving the conservation equations of momentum, mass and energy coupled Maxwell’s equations. By applying finite volume method, when the intensity of applied electromagnetic field exceeded a threshold value, it reveals that arc contraction near cathode and arc divergence near anode are induced resulting in mutation phenomenon. The distributions of arc temperature and pressure deviate from the axis of tungsten and exhibit a bimodal shape. This is distinctly different from that of the free arc under natural combustion condition. In addition, the maximum velocity of the plasma flow appears on both sides of the arc symmetry axis. Moreover, arc plasma presents a behavior of heavy reflow and eddy, and a low-temperature area and a negative pressure zone appear in the central axis of arc plasma.

Effect of welding current on arc behavior in tandem GMAW

A three-dimensional numerical model of double-arc in tandem gas metal arc welding (GMAW) was established based on the theory of arc physics, momentum equation, energy equation, continuous equation and Maxwell equations. The effects of different welding current on temperature field, velocity field and pressure field on the surface of workpieces were investigated. The results showed that the maximum values of arc temperature, arc plasma velocity and arc pressure on workpieces surface were increased with the increasing welding current. These maximum values occurred at the tip of double-wire. The current density and axial deflection angle of coupling arc were increased following the increasing welding current.

Effects of the Driving Frequency on Temperature in a Multiphase AC Arc

Effects of the driving frequency on temperature in a multiphase ac arc were successfully clarified. A multiphase ac arc is one of the thermal plasmas, which is suitable for producing functional materials such as nanoparticles, in-flight glass melting, and waste treatment in terms of its large plasma volume, high-energy efficiency, and low flow velocity. The temperature and arc behavior in various driving frequencies were investigated by the observation system consisting of a high-speed video camera and bandpass filters for plasma spectroscopy. The temperature measurement was conducted on the basis of the Boltzmann plot method. The obtained results indicated that the arc behavior and its temperature field were strongly influenced by the driving frequency. An increase of the frequency led to concentrated arc region, higher arc temperature at the center of electrode region and lower arc fluctuation. The temperature and its distribution can be controlled depending on the material properties to be treated and the purpose of the process.

Ultrahigh-Pressure Nitrogen Arcs Burning Inside Cylindrical Tubes

When the pressure and temperature of a fluid exceed a critical point, the fluid enters into the supercritical (SC) region. In this region, the physical properties are believed to be in favor of a good current interruption medium. This paper focuses on the arc voltage characteristics of nitrogen arcs burning inside cylindrical tubes at different filling pressures: 1, 20, 40, and 80 bar, thus covering the SC region. Two different tube materials have been used in the experiments, alumina and polytetrafluoroethylene. Arc voltages are measured for arcs burning inside tubes of 2, 4, 8, and 15 mm inner diameters. In addition, free-burning arcs have been investigated at the same filling pressures. The arc current was 150 A at 350 Hz throughout the study. The arc voltage is found to increase with decreasing inner diameter of the tube at atmospheric pressure. At higher filling pressures (i.e., 20, 40, and 80 bar), however, such a simple relationship is not observed. The arc temperature and radius have been calculated based on the “simple theory of free-burning arcs” and the “two-zone ablation arc model.” The calculated arc radius decreases with increasing gas pressure. Furthermore, due to increased absorption of radiation at high filling pressures, ablation is found less significant for ultrahigh-pressure nitrogen arcs compared to atmospheric pressure arcs. This is in line with the observations from optical micrographs of the inner surfaces of the tubes exposed to arcs at different filling pressures.

Numerical simulation of mixture gas arc of Ar-O<sub>2</sub>

Mixture gas arcs are used extensively in welding manufacturing. A two-dimensional steady mathematical model for Ar-O<sub>2</sub> mixture gas arc is developed to understand further the heat and mass transfer of the mixture gas arc. The model is based on the assumption of local thermodynamic equilibrium, and the thermodynamic parameters and transport coefficients are dependent on both the temperature and the oxygen content. In the present model, the diffusion between the argon species and oxygen species is depicted by the approach of the combined diffusion coefficient, i. e. the mixture gas arc is simplified into two different species, and the diffusion between them is formulated by combined ordinary diffusion coefficient and combined temperature diffusion coefficient; the oxygen distribution and its influence on the temperature and flow field of the arc are investigated for two different current conditions. It is shown that the oxygen species presents significant non-uniform distribution for argon gas mixed with 5% oxygen; the oxygen content is higher than that in mixed shielding gas in the regions close to the electrodes and arc axis, while its content is lower than that of the mixed shielding gas in other regions. For high current, oxygen concentrates more to the flat anode, while it concentrates more to tungsten cathode for low current. For both cases, oxygen content is inhomogeneous in the region 0.1 mm above the anode. The 5% oxygen mixed in argon constricts the arc plasma to some extent and thus raises the arc temperature as well as the plasma flow velocity.

Ablation mechanism and morphology evolution of the HfC-SiC coating for C/C composites deposited by supersonic atmospheric plasma spraying

HfC-SiC protective coating was deposited on the surface of SiC-coated carbon/carbon composites by supersonic atmospheric plasma spraying due to the high arc temperature and the efficient deposition rate. The morphology and microstructure of the HfC-SiC coating were analyzed by X-ray diffraction and scanning electron microscopy. The results showed that Hf and Si elements distributed uniformly in the coating and the coating was dense without crack. Ablation resistance test was processed by oxyacetylene torch. During the ablation process, the sintering rate of HfO2 was slow, and more oxygen diffused into the internal coating, which caused the oxidation of the internal coating and damaged the structure of internal coating in the ablation center region. In addition, during cooling process, a new phase HfSiO4 was generated by the reaction between HfO2 and SiO2, which acted as a pinning agent to prevent the further expansion of the crack.

Thermodynamic of Liquid Iron Ore Reduction by Hydrogen Thermal Plasma

The production of iron using hydrogen as a reducing agent is an alternative to conventional iron- and steel-making processes, with an associated decrease in CO2 emissions. Hydrogen plasma smelting reduction (HPSR) of iron ore is the process of using hydrogen in a plasma state to reduce iron oxides. A hydrogen plasma arc is generated between a hollow graphite electrode and liquid iron oxide. In the present study, the thermodynamics of hydrogen thermal plasma and the reduction of iron oxide using hydrogen at plasma temperatures were studied. Thermodynamics calculations show that hydrogen at high temperatures is atomized, ionized, or excited. The Gibbs free energy changes of iron oxide reductions indicate that activated hydrogen particles are stronger reducing agents than molecular hydrogen. Temperature is the main influencing parameter on the atomization and ionization degree of hydrogen particles. Therefore, to increase the hydrogen ionization degree and, consequently, increase of the reduction rate of iron ore particles, the reduction reactions should take place in the plasma arc zone due to the high temperature of the plasma arc in HPSR. Moreover, the solubility of hydrogen in slag and molten metal are studied and the sequence of hematite reduction reactions is presented.

Use of radiative properties to determine temperature and vapours concentration in MAG welding arc (Ar–CO2–Fe plasmas)

This paper introduces a method allowing a fast determination of space- and time-resolved plasma temperature and iron concentration in MAG arcs during the high-current phase. This method consists of measuring the plasma spectral radiation of a 82%Ar–18%CO2 plasma with iron vapours using a high-speed camera filtered by narrow band filters in the spectral intervals of 570–590 nm and 606–627 nm respectively; calculating theoretically the dependence of the absolute emissivity ε570–590 nm and relative emissivity ε570–590 nm/ε607–627 nm versus the plasma temperature and the iron concentration, and comparing the two results in order to deduce the plasma temperature (T) and iron concentration (YFe) fields of the experimental measurements. The evolution of their profile in time and space are coupled to arc recorded images. This method has also been validated for three layers of plasma at the positions of 0.5 mm, 1.5 mm and 2.5 mm above the workpiece by using a high-resolution spectrometer and adopting other existing diagnostics such as Stark broadening. The plasma temperature and iron concentration show good agreement throughout the different methods, which demonstrates the effectiveness of this new method.

Investigation on volt-ampere characteristic of secondary arc burning in atmospheric air

The secondary arc, as a common phenomenon in a high voltage power transmission system, is an essence of an electric arc. It not only damages the electrical power equipment but also threatens the safety of the power system. A series of experiments on the secondary arc have been conducted in this work. The volt-ampere curves are measured, the motion trajectories are captured, and the centroid of the secondary arc body is calculated by means of image processing. The experimental results indicate that the secondary arc length can reach several meters, and its volt-ampere curve is completely different from that of short-gap arcs and others operated in some special dielectrics such as vacuum. The evolution of the secondary arc can be generally divided into two stages. In the early stage, the arc column performs a vertical motion and has an upward trend due to thermal buoyancy. Basically, the volt-ampere curve has a shape of a regular hysteresis loop. The impacts of the frequent short-circuit behavior of the arc column on the volt-ampere curve and arcing time are investigated. At the later stage, the secondary arc temperature drops and the zero-off behavior becomes obvious. The volt-ampere curve is inevitably affected. The zero-off duration is obtained, and the key factors are discussed. The dynamics of charged particles in the zero-off interval are analyzed. Furthermore, under the effect of strong wind, it has been found that the secondary arc current is occasionally forced to zero and preceded by the voltage. The mechanism for such a phenomenon is first elucidated from the perspective of energy balance. The results lay a theoretical basis for secondary arc physics.

UPDATED VERSION OF THE SIMPLIFIED MODEL OF INTENSIVELY BLASTED ELECTRIC ARC

The article deals with an improvement of a simplified model of intensively blasted electric arc burning in argon in an anode channel of a modular-type arc heater. Gradually gained experience in the application of the model with various input data has revealed that some refinement is needed. The contribution focuses especially on the process of searching for an optimum combination of the state variables, which are the exponent determining the arc radius development along the anode channel axis, the current density at the cathode, and the arc temperature at the end of the near-cathode layer. The limiting relations for the state variables are set and discussed. Three constituent parts of the used objective function are analysed and compared. The procedure is demonstrated on a chosen set of experimental data. Further computations with many sets of measured data are necessary to test the designed procedure and to confirm the determination of the state variables’ range.

A computational model of gas tungsten arc welding of stainless steel: the importance of considering the different metal vapours simultaneously

A 2D computational model of the mixing of multiple metal vapours into a helium arc in gas tungsten arc welding of stainless steel is presented. The combined diffusion coefficient method, extended to three-gas mixtures, is used to treat helium–chromium–iron and helium–manganese–iron plasmas. It is found that all metal vapours penetrate to the arc centre and reach the cathode, with iron vapour confined near the cathode tip, while chromium and manganese vapours accumulate about 1.5 mm above the tip. The predicted distributions of chromium, manganese and iron show reasonable agreement with published photographic images and radial distributions of atomic line emission intensities. The results are also consistent with published measurements of the deposition of the metals on the cathode surface. A detailed examination of the influence of the different diffusion coefficients, net emission coefficients and vapour pressures of the metals on the metal vapour transport in the arc plasma is presented. It is shown that cataphoresis (diffusion due to applied electric fields) leads to the penetration of the metal vapours into the arc. The different distribution of iron vapour from those of chromium and manganese vapours near the cathode is strongly influenced by the lower ordinary diffusion coefficients of iron at low temperatures. Radiative emission is found to be important since it leads to cooling of the arc, which decreases the influence of cataphoresis. The vapour pressure only influences the concentration of the metal vapour close to the workpiece. Results for the two-gas helium–chromium and helium–iron systems are compared to those for the three-gas helium–chromium–iron system. It is shown that it is important to consider the different metal vapours simultaneously to obtain an accurate calculation of the metal vapour and arc temperature distributions.

Tomographic measurement of temperature in non-axisymmetric arc plasma by single camera multi-view imaging system.

In this paper, we introduce a method for dynamic and three-dimensional (3D) arc temperature measurement in non-axisymmetric arc plasma. Optical filters with narrow spectral bands are used to gain 696.5 nm line spectral information of a free-burning Argon (Ar) arc. A measuring system with a setup of mirrors allows a single camera chip to image multi-views of identical welding arc onto one monochromatic image. And based on the underlying characteristics of the arc plasma, we present a modified maximum likelihood expectation maximum (ML-EM) algorithm to reconstruct the emission coefficients from the line intensities. To verify the accuracy of our algorithm, two models of arc plasma have been established to simulate the reconstruction process. Simulation results demonstrated that the modified ML-EM can be utilized to improve the performance of 3D reconstruction compared to common ML-EM methods. To obtain the optimal scheme of the measuring system with limited view directions, the reconstruction quality with different directions is presented and discussed. In the experiment, asymmetric 3D plasma temperature distribution was determined at a direct current (DC) of 80 A and 100A. The results proved the feasibility of the 3D temperature measure method to characterize an asymmetric arc.

Numerical Study of Influence of Frequency and Eddy Currents on Arc Motion in Low-Voltage Circuit Breaker

The air circuit breaker used for permanent magnet wind power generation systems should switch OFF the short-circuit current of variable frequencies. This paper focuses on the influence of frequency on the behavior of air arc. A 3-D magnetohydrodynamic (MHD) model of air arc plasma was developed to investigate the arc motion process at variable frequencies. In this model, the eddy currents in the whole calculation domains including the electrodes, the splitter plate, and the arc column were considered, and the magnetic vector potential approach was adopted to calculate the electromagnetic field produced by the current loop. A thin layer of elements with a nonlinear voltage–current density characteristic surrounding the splitter plate was employed to represent the formation of new arc roots and electrodes voltage drop. Based on this model, the evolutions of arc voltage, temperature, normalized time, and current density were obtained and compared among variable frequencies. The simulation results reveal that the normalized time, the eddy current density peak in splitter plate, and the arc voltage peak increase at a higher frequency.

Influence of helium content on a ternary-gas-shielded GMAW process

Helium was added to the shielding gas for mild-steel gas metal arc welding. The influence of helium content in a ternary shielding gas (Ar–CO2–He) mixture on arc properties, metal transfer process, and weld bead profile was investigated by numerical simulation and experimental study. As the helium content increases, the arc temperature field becomes more constricted but the central high-temperature zone expands. The current density on the arc axis increases with increasing helium content. The heat flux density on the cathode increases as the helium content increases. The changes in the arc properties lead to the changes in the metal transfer. With increasing helium content, the droplet size increases and the transfer frequency decreases, with approximately linear dependence on helium content. When the helium content is increased from 0 to 25 vol%, the droplet diameter increases by about 80% and the transfer frequency decreases by about 77%, compared to the zero-helium case; this is attributed to changes in the forces on the detaching droplets. With the addition of helium, the base metal fusion area increases and has a more rounded profile; this is attributed to the increased droplet diameter and decreased droplet frequency.