High Temperature Of Arc Research Articles

Investigation of the Mechanism of Powder Pool Coupled Activating TIG Welding

As a highly effective welding method, PPCA-TIG (Powder Pool Coupled Activating Flux–Tungsten Inert Gas) welding aims to achieve automated activation of TIG welding through the use of suitable activating fluxes. However, due to the unique transitional behavior of activating elements, the mechanism of PPCA-TIG is a little bit different from common activating TIG welding. In this research, a two-dimensional model is established to investigate the effect of four activating fluxes (TiO2, SiO2, MnO2, CaF2) on arc morphology and force. A series of welding experiments is performed to study the impact of the different activating elements on the molten pool. The results show that the increase in the penetration of TiO2 is related to the high arc temperature and great arc force and electromagnetic force in the molten pool. The problem of the softening of 3003 aluminum alloy welded joints is solved. Other activating fluxes are less effective than TiO2. The addition of calcium fluoride significantly affects penetration. The use of TiO2, SiO2 and MnO2 changes the molten pool viscosity and affects the molten pool oscillation, thus affecting the weld quality.

Development of Tungsten Electrode for TIG Welding

Tungsten Inert Gas (TIG) welding process is mostly applied to high alloy steel pipes including stainless steels because of superior welding quality and gap bridge-ability than other welding processes. However, it has poor productivity due to low welding speed and deposition rate. In order to improve TIG welding productivity, high performance TIG welding with higher arc temperature, automation and high deposition rate system including hot wire have been developed. Higher arc temperature and longer welding time damage tungsten electrodes of TIG welding. It causes welding defect such as tungsten inclusion and short replacement cycle of tungsten electrodes. Various types of tungsten electrodes containing rare earth metal oxides (thorium, lanthanum, cerium, etc) were introduced to improve electrode erosion resistance and arc stability. In this study, their operation characteristics, arc starting performance, tip development, and electrode consumption were reviewed.

Study of variable range hopping conduction mechanism in nanocrystalline carbon thin films deposited by modified anodic jet carbon arc technique: application to light-dependent resistors

In this study, we report the deposition of nanocrystalline carbon thin films by modified anodic jet carbon arc technique assisted with inert-helium and reactive-nitrogen gaseous environments. The modified anodic jet technique facilitates to generate a very high localized pressure near the arc spot for the growth of nanocrystallites of carbon at high arc temperature and high pressure. The deposited films were analyzed for the growth of nanocrystallites in amorphous carbon structure under high-resolution transmission electron microscopy (HRTEM). The HRTEM studies reveal the distribution of nanocrystallites in the amorphous carbon matrix. The temperature-dependent conduction behavior of the deposited films has also been analyzed under Mott’s variable range hopping conduction mechanism. Both sets of the film are found to follow three-dimensional variable range hopping conduction mechanisms for the transport of charge carriers. The deposited films are also analyzed for their applications to energy-saving light-dependent resistors under an illumination intensity of ~ 100 mW/cm2 of white light. The reasonably high value of detectivity values ~ 1.26 × 106 and 3.12 × 106 Jones and relatively lower values of trap depth 0.6826 and 0.6834 eV for the nanocrystalline films deposited in helium and nitrogen environments suggest trapped state-assisted significantly high power conversion efficiency. This supports the suitability of the deposited films for light-dependent resistor applications.

A more precise unified model to describe comprehensive multiphysics and multiphase phenomena in plasma arc welding

Plasma technology involves complex and coupled electric, magnetic, thermal and hydrodynamical interaction. It’s important to understand all the multiphysics mechanism for a wider industrial application. A 3D unified model was established, which includes a combination of hydrodynamical equations, heat transfer equation and electromagnetic equations, to comprehensively describe the electro-thermal conversion, electromagnetic effect, heat transfer, gas-liquid two-phase flow and solid-liquid phase change in plasma arc welding (PAW). Volume of Fluid method was used to track the gas-liquid interface of plasma arc and liquid metal pool, and an enthalpy-porosity technique was used to deal with the solid-liquid phase change during the welding process. The transient evolutions of temperature field, flow field and keyhole in the entire PAW process were predicted, and the distribution of electric potential and current density was obtained. It is found that there are high potential drop and current density near the electrode tip, which generates very high arc temperature and arc velocity. Plasma arc gradually melts the metal, then pushes the liquid metal to flow upwards along the keyhole surface, and finally penetrates through the workpiece, forming a “reversed bugle-like” configuration. Experiment was conducted with a plasma arc welding system, and it is found that both weld pool and keyhole geometry predicted by the model generally agree with experimental results. The calculated electric potential and full-penetration time also coincide with the experiment. It’s for the first time to give a relatively accurate prediction of electric potential drop and full-penetration time in unified PAW models. The research provides a deep and fundamental understanding of the comprehensive electric-magnetic-thermal-hydrodynamical multiphysics and gas-liquid-solid multiphase interaction in PAW process.

Study of Ablation of Arc Contacts and Dynamic Contact Resistance in High Current Breaker

The fault of power circuit breaker (PCB) can lead very serious problems, especially in high voltage–power grid. The structure of contacts may be composed of main contacts and arc contacts, and this structure can avoid ablation of main contacts efficiently. It is necessary to study the eroded state of the arc contacts and the dynamic contact resistance of arc contacts to estimate the operating state of the PCB. The wear of contacts contains arc ablation and mechanical wear through the characteristics of contacts. The arc ablation is caused by the high temperature of the arc and the mechanical wear is caused by the mechanical friction of static and movable contacts. Some experiments have been done under different size of contacts and different current through them. The results show that the mechanical wear increases, sometimes heavier, with the increase of the size of fixed contacts and the decrease of the size of movable ones because the force between fixed and movable contacts becomes larger. The results also show that the ablation of arc contacts increases with the increase of current, especially when the current is up to 20 kA. With the high temperature of arc reaching the hardness point of copper, the arc ablation and mechanical erosion are increasing obviously since the contacts become soft and easy to wear. Another result of the study shows it is important to choose the material of contacts and the force between movable and fixed contacts. The harder and less resistance the material of contacts, the better the operating situation. To monitor the operating situation of the breaker, the dynamic contact resistance was measured 25 times. As a result, the dynamic contact resistance is sensitive to the current and increasing with the increase of continuous experiment time because of the increasing of metal ions. Furthermore, if the SF6 in the PCB is changes, the dynamic contact resistance would be changed. The dynamic contact resistance in this experiment varies substantially within the range of 80–250 μΩ at the current of 20 kA.

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.

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.

An experimental study on the thermal characteristics and heating effect of arc-fault from Cu core in residential electrical wiring fires.

The characteristics of a series direct current (DC) arc-fault including both electrical and thermal parameters were investigated based on an arc-fault simulator to provide references for multi-parameter electrical fire detection method. Tests on arc fault behavior with three different initial circuit voltages, resistances and arc gaps were conducted, respectively. The influences of circuit conditions on arc dynamic image, voltage, current or power were interpreted. Also, the temperature rises of electrode surface and ambient air were studied. The results showed that, first, significant variations of arc structure and light emitting were observed under different conditions. A thin outer burning layer of vapor generated from electrodes with orange light was found due to the extremely high arc temperature. Second, with the increasing electrode gap in discharging, the arc power was shown to have a non monotonic relationship with arc length for constant initial circuit voltage and resistance. Finally, the temperature rises of electrode surface caused by heat transfer from arc were found to be not sensitive with increasing arc length due to special heat transfer mechanism. In addition, temperature of ambient air showed a large gradient in radial direction of arc.

Numerical analysis of arc characteristics in two-electrode GTAW

A two-dimensional numerical model is developed to describe the arc characteristics in two-electrode gas tungsten arc welding. The influence of different welding current, shielding gas, and shielding gas flow rate is investigated. The arc characteristics are analyzed by studying the distributions of physical quantities including arc temperature, electric potential, and total heat flux on the workpiece. The simulated results reveal that a higher arc temperature value is obtained in helium arc than in argon arc. For obtaining high arc temperature, there is an optimum range for shielding gas flow rate and too high or too low is not appropriate. In addition, the increase of welding current results in the increase of the maximum arc temperature, electric potential, and total heat flux. To validate the accuracy of simulated results, welding experiments are performed and the arc temperature is calculated by the spectral signal of arc plasma. The simulated results are compared with the experimental ones and there is a good agreement.

Mechanical properties and microstructures of 6082-T6 joint welded by twin wire metal inert gas arc welding with the SiO2 flux

Twin wire MIG (metal inert gas arc welding) arc welding was employed on 6-mm thick 6082-T6 Al-alloy plate partially with SiO2 activating flux. The micro-structural characteristics of the weld joint were investigated using optical, scanning microscopy and energy dispersive spectroscopy. Mechanical properties were studied with micro-hardness and tensile test. Results show that no obvious difference from the microstructures of the joints prepared with and without SiO2 flux, the joint HAZ (heat affected zone) with SiO2 flux was observed to be slightly wider than the one without the flux. The weld joint penetration with SiO2 flux was about 26% deeper than what without SiO2 flux. The arc constriction and higher arc temperature were the main reasons for deeper penetration on twin wire MIG weld joint. The tensile test specimens prepared with and without the flux all showed plastic dimple fracture surfaces, SiO2 flux did not have any obvious effect on the micro-hardness and strength of the weld joint.

Simulation of the Influences of the Pressure Ratio and Cu Vapour on SF6 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.

Gas tungsten arc welding of titanium using flux cored wire with magnesium fluoride

Grade 2 Ti–CP was gas tungsten arc welded using flux cored (FC) wires and flux pastes that contained various MgF2 contents. The effects of MgF2 on bead morphology, chemical composition and hardness of weld bead were investigated and interpreted. With an increase of MgF2 content in the flux paste, depth/width ratio of weld bead increased gradually with little variation in interstitial element contents and hardness. Weld bead made with cold FC wire feed showed even deeper and narrower bead, indicating the greater effectiveness of wire feed than flux paste on weld penetration. While the 50% MgF2 FC wire produced complete slag coverage and smooth weld bead surface, 85% MgF2 wire resulted in incomplete slag coverage and rough weld surface. Arc spectroscopy revealed that the 50% MgF2 FC wire produced plasma spectrum with atomic and ionised titanium peaks, which is an indication of a high temperature arc and a larger amount of flux vapours in the arc. Therefore, it is believed that deep weld penetration associated with high MgF2 fluxes in this experiment is caused by arc constriction, resulting from the greater amount of flux vapours owing to high arc temperature.

The Influence of Matrix Anion on Characteristics of the Arc Plasma and on Spectrochemical Determinations

The influence of the matrix anion in CdO and CdCl2 was studied. Radial distributions of temperature and electron density in the arc plasma were measured. For CdCl2 matrix, a higher arc temperature and electron density as well as higher radial gradients of these values have been observed. Spectral line intensities (with background corrections) of trace elements were investigated in both matrices. Elements evaporate faster from chloride matrix. This causes in the beginning an intensity increase of lines compared with CdO matrix. But in determinations with exposure time long enough to ensure complete vaporization of traces from oxide matrix, an enhancement of integral line intensities of traces in CdO, compared with CdCl2 matrix, has been observed.