Experimental Study on Wire Melting Control Ability of Twin-Body Plasma Arc

The twin-body plasma arc has the decoupling control ability of heat transfer and mass transfer,which is beneficial to shape and property control in wire arc additive manufacturing.In this paper,with the wire feeding speed as a characteristic quantity,the wire melting control ability of twin-body plasma arc was studied by adjusting the current separation ratio(under the condition of a constant total current),the wire current/main current and the position of the wire in the arc axial direction.The results showed that under the premise that the total current remains unchanged(100 A),as the current separation ratio increased,the middle and minimum melting amounts increased approximately synchronously under the effect of anode effect power,the first melting mass range remained constant;the maximum melting amount increased twice as fast as the middle melting amount under the effect of the wire feeding speed,and the second melting mass range was expanded.When the wire current increased,the anode effect power and the plasma arc power were both factors causing the increase in the wire melting amount;however,when the main current increased,the plasma arc power was the only factor causing the increase in the wire melting amount.The average wire melting increment caused by the anode effect power was approximately 2.7 times that caused by the plasma arc power.The minimum melting amount was not affected by the wire-torch distance under any current separation ratio tested.When the current separation ratio increased and reached a threshold,the middle melting amount remained constant with increasing wire-torch distance.When the current separation ratio continued to increase and reached the next threshold,the maximum melting amount remained constant with the increasing wire-torch distance.The effect of the wire-torch distance on the wire melting amount reduced with the increase in the current separation ratio.Through this study,the decoupling mechanism and ability of this innovative arc heat source is more clearly.

采用DC Arc Plasma JetCVD方法沉积微/纳米复合自支撑金刚石膜

在30kW级直流电弧等离子体喷射化学气相沉积(DC Arc P lasm a Jet CVD)设备上,采用Ar-H2-CH4混合气体,通过调节甲烷浓度以及控制其他沉积参数,在Mo衬底上沉积出微/纳米复合自支撑金刚石膜。实验表明,当微米金刚石膜层沉积结束后,在随后的沉积中,随着甲烷浓度的增加,金刚石膜表面的晶粒大小是逐渐减小的。当甲烷浓度达到20%以上时,金刚石膜生长面晶粒呈现菜花状的小晶团,膜体侧面已经没有了粗大的柱状晶,而是呈现出光滑的断口,对该层进行拉曼谱分析显示,位于1145 cm-1附近有一定强度的散射峰出现。这说明所沉积的晶粒全部变为纳米级尺寸。

Investigation on Plasma Jet Flow Phenomena During DC Air Arc Motion in Bridge-Type Contacts

Arc plasma jet flow in the air was investigated under a bridge-type contacts in a DC 270 V resistive circuit. We characterized the arc plasma jet flow appearance at different currents by using high-speed photography, and two polished contacts were used to search for the relationship between roughness and plasma jet flow. Then, to make the nature of arc plasma jet flow phenomena clear, a simplified model based on magnetohydrodynamic （MHD） theory was established and calculated. The simulated DC arc plasma was presented with the temperature distribution and the current density distribution. Furthermore, the calculated arc flow velocity field showed that the circular vortex was an embodiment of the arc plasma jet flow progress. The combined action of volume force and contact surface was the main reason of the arc jet flow.

OES study of the gas phase during diamond films deposition in high power DC arc plasma jet CVD system

This paper used optical emission spectroscopy （OES） to study the gas phase in high power DC arc plasma jet chemical vapour deposition （CVD） during diamond films growth processes. The results show that all the deposition parameters （methane concentration, substrate temperature, gas flow rate and ratio of H2/Ar） could strongly influence the gas phase. C2 is found to be the most sensitive radical to deposition parameters among the radicals in gas phase. Spatially resolved OES implies that a relative high concentration of atomic H exists near the substrate surface, which is beneficial for diamond film growth. The relatively high concentrations of C2 and CH are correlated with high deposition rate of diamond. In our high deposition rate system, C2 is presumed to be the main growth radical, and CH is also believed to contribute the diamond deposition.

Numerical Simulation of Fluid Flow and Heat Transfer in a DC Non-Transferred Arc Plasma Torch Operating Under Laminar and Turbulent Conditions

In this work, a magnetic fluid dynamics （MHD） model is used to simulate the electromagnetic field, heat transfer and fluid flow in a DC non-transferred arc plasma torch under laminar and turbulent conditions. The electric current density, temperature and velocity distributions in the torch are obtained through the coupled iterative calculation about the electromagnetic equations described in a magnetic vector potential format and the modified fluid dynamics equations. The fluid-solid coupled calculation method is applied to guarantee the continuity of the electric current and heat transfer at the interface between the electrodes and fluid. The predicted location of the anodic arc root attachment and the arc voltage of the torch are consistent with corresponding experimental results. Through a specific analysis of the influence of mass flow rates and electric current on the torch outlet parameters, the total thermal efficiency, thermal loss of each part, and the laws of the variation of outlet parameters with the variation of mass flow rates and electric current was obtained. It is found that operation under a laminar condition with a limited area of the anode could increase the total thermal efficiency of the torch.

Energy Balance in DC Arc Plasma Melting Furnace

In order to treat hazardous municipal solid waste incinerator＇s （MSWI） fly ash, a new DC arc plasma furnace was developed. Taking an arc of 100 V/1000 A DC as an example, the heat transfer characteristics of the DC arc plasma, ablation of electrodes, heat properties of the fly ash during melting, heat transfer characteristics of the flue gas, and heat loss of the furnace were analyzed based on the energy conservation law, so as to achieve the total heat information and energy balance during plasma processing, and to provide a theoretical basis for an optimized design of the structure and to improve energy efficiency.

Comparison of Reynolds average Navier-Stokes turbulence models in numerical simulations of the DC arc plasma torch

Five turbulence models of Reynolds average Navier-Stokes(RANS),including the standard k-ω model,the RNG k-e model taking into account the low Reynolds number effect,the realizable k-ω model,the SST k-ω model,and the Reynolds stress model(RSM),are employed in the numerical simulations of direct current(DC)arc plasma torches in the range of arc current from 80 A to 240 A and air gas flow rate from 10 m^3 h^-1 to 50 m^3 h^-1.The calculated voltage,electric field intensity,and the heat loss in the arc chamber are compared with the experiments.The results indicate that the arc voltage,the electric field,and the heat loss in the arc chamber calculated by using the standard k-ω model,the RNG k-ωmodel taking into account the low Reynolds number effect,and the realizable k-ω model are much larger than those in the experiments.The RSM predicts relatively close results to the experiments,but fails in the trend of heat loss varying with the gas flow rate.The calculated results of the SST k-ω model are in the best agreement with the experiments,which may be attributed to the reasonable predictions of the turbulence as well as its distribution.

Fluid Flow Modeling of Arc Plasma and Bath Circulation in DC Electric Arc Furnace

A mathematical model describing the flow field, heat transfer and the electromagnetic phenomenon in a DC electric arc furnace has been developed. First the governing equations in the arc plasma region are solved and the calculated results of heat transfer, current density and shear stresses on the anode surface are used as boundary conditions in a model of molten bath. Then a two-dimensional time-dependent model is used to describe the flow field and electromagnetic phenomenon in the molten bath. Moreover, the effect of bottom electrode diameter on the circulation of molten bath is studied.

3D Numerical Analysis of the Arc Plasma Behavior in a Submerged DC Electric Arc Furnace for the Production of Fused MgO

A three dimensional steady-state magnetohydrodynamic model is developed for the arc plasma in a DC submerged electric arc furnace for the production of fused MgO. The arc is generated in a small semi-enclosed space formed by the graphite electrode, the molten bath and unmelted raw materials. The model is first used to solve a similar problem in a steel making furnace, and the calculated results are found to be in good agreement with the published measurements. The behavior of arcs with different arc lengths is also studied in the furnace for MgO production. From the distribution of the arc pressure on the bath surface it is shown that the arc plasma impingement is large enough to cause a crater-like depression on the surface of the MgO bath. The circulation of the high temperature air under the electrode may enhance the arc efficiency, especially for a shorter arc.

Effects of deposition parameters on microstructure and thermal conductivity of diamond films deposited by DC arc plasma jet chemical vapor deposition

The uniform diamond films with 60 mm in diameter were deposited by improved DC arc plasma jet chemical vapor deposition technique. The structure of the film was characterized by scanning electronic microcopy(SEM) and laser Raman spectrometry. The thermal conductivity was measured by a photo thermal deflection technique. The effects of main deposition parameters on microstructure and thermal conductivity of the films were investigated. The results show that high thermal conductivity, 10.0 W/(K·cm), can be obtained at a CH4 concentration of 1.5% (volume fraction) and the substrate temperatures of 880-920 ℃ due to the high density and high purity of the film. A low pressure difference between nozzle and vacuum chamber is also beneficial to the high thermal conductivity.

Atmospheric pressure pulsed modulated arc discharge plasma

Direct-current(DC)arc plasma has great application values in the field of the chemical industry,but it has the problem of low energy efficiency.Facing the requirement for improving the energy efficiency of the arc,this paper proposes a unique method of pulsed modulated arc(PMA).This method uses high-frequency pulses and reduces the arc current to improve the control of electron temperature.The electrical characteristics,optical characteristics and products are tested.The test results show that during the PMA process,all of the experimental results which include voltage,current and light will significantly increase.These results are analyzed from the perspective of functionality,repeatability and energy conversion.The analysis results show that although the PMA method does not show good parameter consistency,it has potential application prospects because it increases the energy conversion rate by 4.5%and 8%from the perspective of light and products,respectively.

Arc Voltage Fluctuation in DC Laminar and Turbulent Plasma Jets Generation

Arc voltage fluctuations in a direct current （DC） non-transferred arc plasma generator are experimentally studied, in generating a jet in the laminar, transitional and turbulent regimes. The study is with a view toward elucidating the mechanism of the fluctuations and their relationship with the generating parameters, arc root movement and flow regimes. Results indicate that the existence of a 300 Hz alternating current （AC） component in the power supply ripples does not cause the transition of the laminar plasma jet into a turbulent state. There exists a high frequency fluctuation at 4 kHz in the turbulent jet regime. It may be related to the rapid movement of the anode attachment point of the arc.

DC Arc Plasma Disposal of Printed Circuit Board

A new solid waste disposal technology setup with DC are plasma is presented. Being different from conventional combustion or burning such as incineration, it is based on a process called controlled high-temperature pyrolysis, the thermal destruction and recovery process. The results of vitrification of the circuit board is presented. The properties of vitrified product including hardness and leaching test results are presented. The final product (vitrified material) and air emission from the plasma treatment is environmentally acceptable.

Dynamic physical characteristics of DC arc on arcing horn for HVDC grounding electrode line

The dynamic physical characteristics of a DC arc on an arcing horn for a high voltage direct current(HVDC)grounding electrode line are significantly different from those of the switching device arc,secondary arc,AC fault arc and pantograph-catenary arc.In this work,an experimental platform for the DC arc on the arcing horn was built,and mechanisms of the arc column short circuit and arc root movement were studied.This work further analyzes the characteristics and mechanisms of the arc motion when wind speed and direction,magnetic field and the expansion angle of the electrode are varied.Arc root movement is more likely to occur at the upper electrode.There is a competitive relationship between arc expansion and the transferring effect.The effect of wind on the arc column is greater than the effect on the arc root.The magnetic field has a significant driving effect on both the arc column and the arc root.The research results provide a comprehensive experimental basis for forther probing the method of DC arc suppression,and the improvement of the arcing horn.

Comparative Observation of Ar,Ar-H_2 and Ar-N_2 DC Arc Plasma Jets and Their Arc Root Behaviour at Reduced Pressure

Results observed experimentally are presented, about the DC arc plasma jets and their arc-root behaviour generated at reduced gas pressure without or with an applied magnetic field. Pure argon, argon-hydrogen or argon-nitrogen mixture was used as the plasma-forming gas. A specially designed copper mirror was used for a better observation of the arc-root behaviour on the anode surface of the DC non-transferred arc plasma torch. It was found that in the cases without an applied magnetic field, the laminar plasma jets were stable and approximately axisymmetrical. The arc-root attachment on the anode surface was completely diffusive when argon was used as the plasma-forming gas, while the arc-root attachment often became constrictive when hydrogen or nitrogen was added into the argon. As an external magnetic field was applied, the arc root tended to rotate along the anode surface of the non-transferred arc plasma torch.

Plasma diagnosis of tetrahedral amorphous carbon films by filtered cathodic vacuum arc deposition

Filtered cathodic vacuum arc(FCVA)deposition is regarded as an important technique for the synthesis of tetrahedral amorphous carbon(ta-C)films due to its high ionization rate,high deposition rate and effective filtration of macroparticles.Probing the plasma characteristics of arc discharge contributes to understanding the deposition mechanism of ta-C films on a microscopic level.This work focuses on the plasma diagnosis of an FCVA discharge using a Langmuir dualprobe system with a discrete Fourier transform smoothing method.During the ta-C film deposition,the arc current of graphite cathodes and deposition pressure vary from 30 to 90 A and from 0.3 to 0.9 Pa,respectively.The plasma density increases with arc current but decreases with pressure.The carbon plasma density generated by the arc discharge is around the order of10^(10)cm^(-3).The electron temperature varies in the range of 2-3.5 eV.As the number of cathodic arc sources and the current of the focused magnetic coil increase,the plasma density increases.The ratio of the intensity of the D-Raman peak and G-Raman peak(I_(D)/I_(G))of the ta-C films increases with increasing plasma density,resulting in a decrease in film hardness.It is indicated that the mechanical properties of ta-C films depend not only on the ion energy but also on the carbon plasma density.

Numerical simulation and analysis of lithium plasma during low-pressure DC arc discharge

Alkali metal DC arc discharge has the characteristics of easy ionization,low power consumption,high plasma temperature and ionization degree,etc,which can be applied in aerospace vehicles in various ways.In this paper,we calculate the physical property parameters of lithium vapor,one of the major alkali metals,and analyze the discharge characteristics of lithium plasma with the magnetohydrodynamic(MHD)model.The discharge effects between constant current and voltage sources are also compared.It is shown that the lithium plasma of DC arc discharge has relatively high temperature and current density.The peak temperature can reach tens of thousands of K,and the current density reaches 6 x 107 A m 2.Under the same rated power,the plasma parameters of the constant voltage source discharge are much higher than those of the constant current source discharge,which can be used as the preferred discharge mode for aerospace applications.

Study on the formation of arc plasma on the resistive wall liquid metal current limiter

Due to its significant attributes,the liquid metal current limiter(LMCL)is considered a new strategy for limiting short-circuit current in the power grid.A resistive wall liquid metal current limiter(RWLMCL)is designed to advance the starting current-limiting time.Experiments are performed to investigate the dynamic behaviors of liquid metal,and the influence of different currents on the liquid metal self-shrinkage effect is compared and analyzed.Furthermore,the liquid metal self-shrinkage effect is mathematically modeled,and the reason for the formation of arc plasma is obtained by simulation.The laws of arc plasma formation and the current transfer in the cavity are revealed,and the motion mechanisms are explained by physical principles.The simulations are in accordance with the test data.It is demonstrated that the sudden change of the current density at both ends of the wall causes the liquid metal to shrink and depress under the electromagnetic force,and the current starts to transfer from the liquid metal path to the wall resistance path.The RWLMCL can effectively advance the starting current-limiting time.

Three-dimensional non-equilibrium modeling of a DC multi-cathode arc plasma torch

In this paper,a three-dimensional non-equilibrium steady arc model is used to investigate the temperature,velocity and electromagnetic field in multi-cathode arc torch,and the formation mechanism of a large-area,uniform and diffused arc plasma is analyzed.The numerical simulation results show that a large volume plasma region can be formed in the central region of the generator during discharge.During this process,the maximum electron temperature appears near the cathode and in the central convergence region,while the maximum heavy particle temperature only appears in the central convergence region.This phenomenon is consistent with the experimental arc images.Near the cathode tip,the arc column is in a contraction state.In the area slightly away from the cathode,the six arc columns begin to join together.In the plasma generator,there is a large-scale current distribution in all directions of X,Y and Z,forming a stable arc plasma with a wide range of diffusion.The calculated electron temperature distribution is in good agreement with the measured electron temperature.The results suggest that the largearea diffused arc plasma in the multi-cathode arc torch is the combined effect of current distribution,convection heat transfer and heat conduction.

Diagnosis of gas phase near the substrate surface in diamond film deposition by high-power DC arc plasma jet CVD

Optical emission spectroscopy （OES） was used to study the gas phase composition near the substrate surface during diamond deposition by high-power DC arc plasma jet chemical vapor deposition （CVD）. C2 radical was determined as the main carbon radical in this plasma atmosphere. The deposition parameters, such as substrate temperature, anode-substrate distance, methane concentration, and gas flow rate, were inspected to find out the influence on the gas phase. A strong dependence of the concentrations and distribution of radicals on substrate temperature was confirmed by the design of experiments （DOE）. An explanation for this dependence could be that radicals near the substrate surface may have additional ionization or dissociation and also have recombination, or are consumed on the substrate surface where chemical reactions occur.