Arc characteristics of GMA welding in high-pressure air condition

Gas metal arc （ GMA ） welding process can be fluently executed under the range of 0. 1 - 0. 7 MPa air pressure shielded by C02 and ArS0% ＋ CO220% gases, which were tested by the igniting and exploding experiments using a hyperbaric chamber to simulate the underwater conditions. The arc voltage characteristics of the GMA welding were tested in hyperbaric conditions to discover the law of the welding arc affected by environmental pressure, welding current, stick-out, gas type and gas-flow. The experimental results and related discussion are also given in this paper. Finally, a mathematical model was calculated under high-pressure air condition based on the experimental data with the least square approximation method.

Effects of pulse parameters on arc characteristics and weld penetration in hybrid pulse VP-GTAW of aluminum alloy

A novel ultrafast-convert hybrid pulse variable polarity gas tungsten arc welding process （HPVP-GTAW） is developed. High frequency pulse square-wave current which has a frequency of more than 20 kHz is exactly integrated in the positive polarity current duration. The effects of pulse current parameters on arc characteristics and weld penetration have been studied during the HPVP-GTAW process using Al-5. 8 Mg alloy plates. The arc characteristics studied by arc voltage and its profile, weld penetration noted by the ratio of weld depth to width have been found to be influenced significantly by the pulse current. The experimental results show that the HPVP-GTA W process can improve the arc profile predominantly and obtain the higher weld penetration with lower heat input. The observation may help in understanding the weld characteristics with respect to variation in the pulse current parameters which may be beneficial in using the novel HPVP-GTAW process to produce the better weld quality of aluminum alloy plates.

Analysis of Arc Characteristics and Flow Field in Arc Chamber of High-Voltage SF_6 Auto-Expansion Circuit Breaker

A new magnetic hydro-dynamics model for nozzle arc emphasizing the interaction of arc with PTFE （polytetrafluorethylene） vapour is established based on the conservation equations. The interruption of auto-expansion circuit breaker is simulated numerically by finite element method and the influence of PTFE vapour on the arc is analysed with this model. The results reveal that the flow field inside the arc chamber is determined by the arc current, the arcing time, the nozzle arc and the clogging of its thermal boundary. The establishment of quenching pressure relies on both SF6 gas and PTFE vapour that absorbed arc energy in the nozzle. The PTFE vapour leads to an increase in the pressure of nozzle arc obviously, and a decrease in the temperature of arc. But it enhances the temperature of arc at zero current and slows down the decreasing rate of arc temperature as the current decreases.

Simulation of the Influences of the Pressure Ratio and Cu Vapour on SF_6 Arc Characteristics

The inlet and outlet pressure of the SF6 high voltage circuit-breaker nozzle are of importance in determining the thermal interruption capability of a breaker. Besides, electrode evaporation is inevitable during the arcing process, which may affect the SF6 arc behaviour significantly. In this study a numerical investigation on the arc characteristics of a supersonic nozzle is carried out, by considering the influence of the pressure ratio between the inlet and outlet, and the Cu vapour. It is demonstrated that a lower inlet pressure may result in a higher arc temperature, a lower arc voltage and a smaller mach number, and Cu vapour from electrode evaporation may cool the arc significantly.

Simulation of Vacuum Arc Characteristics at Different Moments Under Power-Frequency Current

In this paper, based on the quasi-stationary magneto-hydrodynamic （MHD） model, vacuum arc characteristics are simulated and analyzed at different moments under power-frequency current. For a vacuum arc with sinusoidal current under a uniform axial magnetic field （AMF）, simulation results show that at the moment of peak value current, maximal values appear in the ion number density, axial current density, heat flux density, electron temperature, plasma pressure and azimuthal magnetic field. At the same time, the distributions of these parameters along the radial position are mostly nonuniform as compared with those at other moments. In the first 1/4 cycle, the ion number density, axial current density and plasma pressure increase with time, but the growth rate decreases with time. Simulation results are partially compared with experimental results published in other papers. Simulations and light intensity near the cathode side is stronger than arcs. experimental results both show that the arc that near the anode side for diffusing vacuum

Study on arc characteristics and behavior of metal transfer in pulse current flux-cored arc welding of mild steel

The variation in arc characteristics and behavior of metal transfer with the change in pulse parameters has been studied by high speed video camera during pulse current flux-cored arc weld deposition.A comparative study of similar nature has also been carried out during flux-cored arc weld deposition in globular and spray transfer modes.The effect of pulse parameters has been studied by considering their mean current and arc voltage.The arc characteristics studied by its root diameter,projected diameter and length,and the behavior of metal transfer noted by the metal transfer model and the droplet diameter have been found to vary significantly with the pulse parameters.The observation may help in understanding the arc characteristics with respect to the variation in pulse parameters which may be beneficial in using pulse current FCAW to produce desired weld quality.

Numerical simulation of influence of nozzle structure on arc characteristics of GPCA-TIG welding

This work mainly articulated the effects of nozzle structure on arc characteristics in gas pool coupled activating TIG （GPCA-TIG） welding process by using Fluent Software. Different models were set up to adapt the different torch structure during computer progress. The specific configuration of the welding torch made the gas flow in outer gas passage constrained. The nozzle structure has great influence on outer gas distribution because of the changing of coupling region between the outer active gas and molten pool surface. When the coupling degree is reduced or the outer gas passage become smaller, the oxygen in outer gas penetrates into the arc plasma and spreads to the arc region more easily. Owing to its cooling effects, the morphology of arc is contracted, and the arc temperature is increased. When the inner wall and the outer wall of outer gas passage are not parallel, the wide top and narrow bottom nozzle shape can bring more oxygen into the arc plasma, the arc is contracted and the peak temperature of arc rises a little more comparing to the narrow top and wide bottom one.

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.

Arc characteristics of twin-wire indirect arc gas shielded welding

Twin-wire indirect arc gas shielded welding is a novel welding method. By recording the arc shape and welding parameters, the effects of welding parameters and included angle on arc characteristics are discussed in this paper. The experimental results show increasing welding current can prompt centralized and straight of arc due to increasing plasma force and electric magnetic pinch effect. Increasing arc voltage can increase the size and brightness of the arc, as a result of increasing arc energy. The reducing of included angle increases the electric magnetic pinch effect, the arc becomes slender and supplies higher energy. It is thought the smaller included angle is beneficial to obtain perfect weld bead.

Research on dynamic characteristics of arc under electrode relative motion

The relative motion of the electrodes is a typical feature of sliding electrical contact systems.The system fault caused by the arc is the key problem that restricts the service life of the sliding electrical contact system.In this paper,an arcing experimental platform that can accurately control the relative speed and distance of electrodes is built,and the influence of different electrode speeds and electrode distances on arc motion characteristics is explored.It is found that there are three different modes of arc root motion:single arc root motion mode,single and double arc roots alternating motion mode,and multiple arc roots motion mode.The physical process and influence mechanism of different arc root motion modes are further studied,and the corresponding relationship between arc root motion modes and electrode speed is revealed.In addition,to further explore the distribution characteristics of arc temperature and its influencing factors,an arc magnetohydrodynamic model under the relative motion of electrodes is established,and the variation law of arc temperature under the effect of different electrode speeds and electrode distances is summarized.Finally,the influence mechanism of electrode speed and electrode distance on arc temperature,arc root distance,and arc root speed is clarified.The research results enrich the research system of arc dynamic characteristics in the field of sliding electrical contact,and provide theoretical support for restraining arc erosion and improving the service life of the sliding electrical contact system.

STUDY ON THE CHARACTERISTICS OF UNDER WATER PLASMA ARC

The static and dynamic characteristics of underwater plasma arc, arc shape and heating features to the workpieces, are studied, lt shows that underwater plasma arc has higher energy rate, higher rates of heating and cooling. Furthermore, it reduces the pollutions of noise ,arc light , dust and ozone; strengthens the cooling of nozzle, thus it is advantageous to develop various new technologies of underwater material processing. The static characteristic is rising. The dynamic characteristic is of quasi-cyclic fluctuations whose mechanisms and solving methods are pointed out.

The Dynamic Volt-Ampere Characteristics of a Vacuum Arc at Intermediate-Frequency Under a Transverse Magnetic Field

In this study, the changes of a vacuum arc＇s appearance were observed and the volt-ampere characteristics of the vacuum arc at intermediate frequency were analyzed under a transverse magnetic field （TMF）. The TMF and phase shift time were calculated by using the TMF contact model and the large phase shift of the magnetic field at a higher frequency was conductive to the dispersion process of residual plasma. The arc velocity was higher at 800 Hz than at 400 Hz. It can be inferred that TMF will encourage arc movement at 800 Hz. Moreover, the arc movement has an impact on the arc voltage. Because of the increasing length of the arc column with a high arc velocity, the elongated arc causes the arc voltage to increase. Specifically, the volt-ampere characteristics of the vacuum arc are divided into three stages in this paper. The higher the frequency, the greater the initial rate of rise in the arc voltage and the larger the area surrounded by arc volt-ampere characteristics. The correlations between the arc voltage and the amplitude and frequency of the current are also presented.

Numerical analysis of plasma arc physical characteristics under additional constraint of keyhole

The physical characteristics of a plasma arc affect the stability of the keyhole and weld pool directly during keyhole plasma arc welding （KPAW）. There will be significant change for these characteristics because of the interaction between the keyhole weld pool and plasma arc after penetration. Therefore, in order to obtain the temperature field, flow field, and arc pressure of a plasma arc under the reaction of the keyhole, the physical model of a plasma arc with a pre-set keyhole was established. In addition, the tungsten and base metal were established into the calculated domain, which can reflect the effect of plasma arc to weld pool further. Based on magneto hydrodynamics and Maxwell equations, a twoSdimensional steady state mathematical model was established. Considering the heat production of anode and cathode, the distribution of temperature field, flow field, welding current density, and plasma arc pressure were solved out by the finite difference method. From the calculated results, it is found that the plasma arc was compressed a second time by the keyhole. This additional constraint results in an obvious rise of the plasma arc pressure and flow velocity at the minimum diameter place of the keyhole, while the temperature field is impacted slightly. Finally, the observational and metallographic experiments are conducted, and the shapes of plasma arc and fusion line agree with the simulated results generally.

Preparation and Arc Erosion Characteristics of Ultrafine Crystalline CuCr50 Alloy by MA-SPS

The ultrafine crystalline CuCr50（Cr 50 wt%） alloys were fabricated by a combination of mechanical alloying and spark plasma sintering process. The effects of milling time on crystallite size and solid solubility of the CuCr50 composite powders were investigated. The results showed that crystallite size of powders decreases gradually and solid solubility of Cr in Cu was extended with increasing milling time. The minimal crystallite size about 10 nm and the maximum solid solubility about 8.4 at%（i e, 7 wt%） were obtained at 60 h. The microstructure of ultrafine crystalline CuCr50 alloy was analyzed by SEM and TEM, which contains two kinds of size scale Cr particles of 2 μm and 50-150 nm, distributing homogeneously in matrix, respectively. The arc erosion characteristics of ultrafine crystalline CuCr50 alloy were investigated by the vacuum contact simulation test device in low D.C. voltage and low current（24 V/10 A）. A commercial microcrystalline CuCr50 alloy was also investigated for comparison. Experiments indicate that the cathode mass loss of ultrafine crystalline CuCr50 contact material is higher than that of microcrystalline CuCr50 material, but its eroded surface morphology by the arc is uniform without obvious erosion pits. While the surface of microcrystalline CuCr50 contact is seriously eroded in local area by the arc, an obvious erosion pit occurred in the core part. Therefore, the ability of arc erosion resistance of ultrafine crystalline CuCr50 alloy is improved compared to that of microcrystalline CuCr50 material.

Physical Characteristics of Welding Arc Ignition Process

The existing research of welding arc mainly focuses on the stable combustion state and the research on the mechanism of welding arc ignition process is quite lack.The tungsten inert gas（TIG） touch arc ignition process is observed via a high speed camera and the high time resolution spectral diagnosis system.The changing phenomenon of main ionized element provided the electrons in the arc ignition is found.The metallic element is the main contributor to provide the electrons at the beginning of the discharging,and then the excitated shielding gas element replaces the function of the metallic element.The electron density during the period of the arc ignition is calculated by the Stark-broadened lines of Hα.Through the discussion with the repeatability in relaxation phenomenon,the statistical regularity in the arc ignition process is analyzed.The similar rules as above are observed through the comparison with the laser-assisted arc ignition experiments and the metal inert gas（MIG） arc ignition experiments.This research is helpful to further understanding on the generation mechanism of welding arc ignition and also has a certain academic and practical significance on enriching the welding physical theoretical foundation and improving the precise monitoring on automatic arc welding process.

Characteristics of Resistance Triggering of a Pulsed Vacuum Arc Ion Source

Triggering scheme is a significant factor that may influence the process of vacuum arc initiation. In this work, the characteristics of resistance triggering of a pulsed vacuum arc ion source are investigated and compared with the independent pulse generator triggering. The results show that although the resistance triggering method is capable of triggering a vacuum arc ion source by properly choosing the resistance and electric parameters, it inevitably increases the rise time of the arc current. A high speed multiframe camera is used to reveal the transition process o~ arc initiation during one shot. From the images it is conjectured that the lower voltage between the cathode and the anode may be the reason that leads to the lower transition speed of discharge at the moment of arc initiation.

Large scale characteristic distance between strong earthquake

The global seismicity shows a characteristic distance of about 23°. The middle deep and deep earthquakes in the European and Asian blocks concentrate on several zones which separate about 23° away from earch other. The shallow strong earthquakes ( M S≥7) form belts of over 20°, the ends of these belts are near the concentration points of middle deep and deep earthuakes. The Circular Pacific island arcs, volcanoes, shallow earthquakes, middle deep and deep earthquakes also show the characteristic distance of about 23°.

Coupling model of AC filter branch in SF6 circuit breaker during the break process

In this paper, a coupling model of the AC filter branch circuit with the arc plasma in the circuit breaker was built to investigate the arcing process considering the harmonic current. The comparisons among the current at power frequency(50 Hz), power frequency combining the 11 th harmonic and power frequency combining the 24 th harmonic show that the high-order harmonic current would lead to higher decreasing rate of current before current-zero period. In addition, the influence of arc on the amplitude of high-order harmonic current is not negligible. Thus, the coupling of arc with AC filter branch circuit is quite necessary in the numerical modeling of the circuit breaker in the AC filter branch at the high voltage direct current converter station.

Multi-variable Dependent Forecast Algorithm for Predicting Secondary Arc

Hybrid reactive power compensation(HRPC)combines step-controlled shunt reactors and series compensation,and will be employed in ultra-high-voltage(UHV)power systems.The single-phase auto-reclosure characteristics of secondary arcs in systems with HRPC require further investigation.In this paper,both the arc-recalling voltage and subsidiary variations in arc current are investigated with and without HRPC.The frequency components of the secondary arc current and variations in arcing time are analyzed for various influential factors,such as the neutral reactor,arc resistance,fault location,degrees of compensation of HRPC,and the length of the transmission line.The non-dominated sorting genetic algorithm II(NSGA-II)and support vector machine regression are combined to create a multi-variable dependent forecasting algorithm to predict the characteristics of the secondary arc in UHV systems with HRPC.This paper provides a theoretical reference for optimizing the parameters of HRPC,and for developing adaptive auto-reclosure schemes and protection equipment.