The effect of a ledge in outlet electrode on operation efficiency of the two-chamber plasmatorch

Electric and thermal characteristics of the two-chamber plasmatorch with a stepped outlet electrode were studied experimentally. Formulas for determination of arc voltage, plasmatorch efficiency, and length of a narrow part of the outlet electrode were derived. It is shown that such a plasmatorch is more efficient than the plasmatorch with a smooth outlet electrode.     

Investigation of the high-current arc in helium

The secondary and erosion characteristics of the electric-arc plasmatorch were studied experimentally. Formulas for arc voltage calculation depending on helium flow rate, diameter of the inner cavity of cylindrical copper anode, arc current, and distance from the nozzle to metal melt were derived.     

Electric arc plasmatorch for steam heating

A construction arrangement of electric arc plasmatorch with copper tubular electrodes for steam plasma generation was developed and tested. Experimental data on energy curves of this plasmatorch with nominal power of 100 kW are presented.     

强流脉冲电弧作用下石墨电极蒸发特性

气体开关电弧的热侵蚀作用是电极损耗的主要成因。石墨电极在电弧作用下发生蒸发并在多次放电后有明显的质量损耗,改变了开关内的气体环境和电极间距,导致开关动作可靠性降低。为研究石墨电极在脉冲电弧冲击下的侵蚀特征,基于开关电弧瞬态扩散特征和石墨材料参数,在弧根区域建立了电弧-电极能量耦合模型,得到了等离子体-固体区域的传热特性。考虑石墨电极的相变特征,计算瞬态热作用下石墨电极的加热范围以及临界相变点,研究瞬态电弧热冲击作用下的石墨电极相变机制。研究结果表明,电弧-电极界面热流主要集中在电弧接触面中心,电弧沉积的能量密度最高可达109 W/m2,石墨在电流上升初期基本处于加热状态,在能量积聚作用下,石墨转变为升华状态,传热强度随半径急剧衰减,蒸发区域略小于电弧半径。通过实验记录了5种开关工况下石墨电极烧蚀形貌和质量损失情况,结果表明,电极质量损失与电弧沉积在电极表面的能量线性相关,近似为0.015 mg/J。研究了电弧关键参数对电极质量损失速率的影响,为延缓电极损耗提供数据支撑。     

Heat transfer and cold cathode erosion in electric arc heaters

A simple thermophysical model is proposed for cold electrode erosion in electric arc heaters. The model regards erosion as characterized by an effective enthalpy of electrode material ablation, resulting in heat unbalance between heat supply and heat removal by conduction. Replacing the arc spot by a moving surface heat source, the space-time evolution of the electrode surface temperature is studied in coordinates coupled to the source. Applying heat diffusion equations, we show that the erosion problem can be represented by a system of three simple equations. An experimental coaxial setup, with a magnetically driven arc, has been used for the erosion measurements in copper electrodes. Special thermal experiments were carried out for measuring needed arc spot parameters. A comparison of the model with our own and other experimental data demonstrates a reasonable agreement. The present model reveals the relative significance of the different parameters in the erosion process, and permits us to predict the erosion behavior in cold electrode electric arc heaters in a wide range of parameters     

大脉冲电流下钨铜电极水和空气中的烧蚀特性

针对水中、空气中脉冲放电条件下金属电极烧蚀速率及烧蚀机理差异,对脉冲大电流作用下水中、空气中钨铜电极的烧蚀特性进行了对比研究。在保证放电电流波形一致性的前提下,通过采用高精度天平测量并获取了水中、空气中钨铜电极的阴、阳极烧蚀速率及总烧蚀速率,并对电极表面进行了二次电子观察和背散射电子观察分析。结果表明,大脉冲电流作用下,水中钨铜电极烧蚀较空气中更为严重,钨铜电极的烧蚀主要是金属蒸发引起的汽相侵蚀。由于水介质较空气具有不可压缩性,水中放电电弧集中,电极表面电弧斑点处电流密度和电流作用时间较空气中更为严重,同时由于水中脉冲放电时发生的高温物理化学反应,是造成水中电极烧蚀要高于空气中的根本原因。     

旋转电弧对火花间隙开关电极烧蚀的影响

 根据开关间隙放电产生的电弧在自身磁场作用下沿着开关电极表面运动的设想,设计了一个旋转电弧场畸变火花开关，研究了开关电极在大电流情况下的烧蚀情况。实验结果表明,开关的工作电压为6~30kV，开关电感0.07μH，转移电荷量35.2C/shot时，铝电极non RAG结构比RAG结构的开关电极的烧蚀情况要严重得多，黄铜电极比铝电极的烧蚀要小得多。     

Analysis and optimization of gas-thermal spray process in terms of condensed phase velocity and temperature

The paper presents the experimental results for velocity and tempertaure disibutions of the condensed phase in a plasma jet from the plasmatorch PNK-50 (design from ITAM SB RAS, Novosibirsk). The plasma jet is used at different operational modes for thermal spraying of nickel alloy powder PR-NKh16SR3. The measurements for average velocity (230–280 m/s) and temperature (2290–2410 K) of sprayed particles were matched to data on microhardness (630–710 HV) and porosity (1.7–13.5 %) of samples. Results were transferred into coating properties maps plotted in coordinates “arc current vs. torch offset” and “particle velocity vs. particle temperature”. Experiments demonstrated the change in parameters of condensed phase in the jet after performimg of maintenance job for the plasmatorch. We propose the method for adjusting the operational parameters of thermal spraying equipment using optical methods of control for particle velocity and particle temperature. The exemplary apparatus function of the plasmatorch was plotted; an approach is proposed for optimization and transfer of spraying technology of coatings with specified properties between equipment from different manufacturers, different class and power.     

Erosion of tube electrodes in vortex plasmatorches

The stationary modes of the end-face tube electrodes operation are under consideration. The formation of cathode and anode jets which cause dramatic increase in the electrode erosion at the arc current growth has been explained. We have considered the ways to increase the life-time of the continuous operation of tube electrodes. The analysis of the thermophysical interaction of the arc spot and electrode surface has enabled us to choose the optimum metal for the electrode.     

Effect of plasma spraying regimes on structure and properties of Ni<Subscript>3</Subscript>Al coatings

The structure and tribological properties of coatings made of PN85YU15 powder were studied. The coatings were deposited on the mild steel blanks by the technology of air-plasma spraying using a unit of annular input and gas-dynamic powder focusing. Efficiency of heating and acceleration of powder particles was studied preliminarily. Measurement results on temperature and velocity distributions of particles at a certain spraying distance by the method of spectral pyrometry and time-of-flight method are presented. The effect of plasmatorch arc current and amount of propane-butane in the plasma flow on the structure and properties of coatings is analyzed in this paper. It is determined that the phase composition of coatings and initial powder is the same: the main phase is Ni₃Al compound; moreover, the structure contains Ni₅Al₃ phase. It is shown that an increase in the amount of propane-butane increases coatings porosity. The densest coatings (5.77%) were obtained at the plasmatorch arc current of 200 A with the reduced amount of propane-butane. The coatings obtained at the minimal arc current of 100 A with an increased amount of propane-butane are characterized by maximal porosity (20.38%). The results of tribological testing of the coatings under the conditions of sliding friction with a lubricant by the disc-plane scheme are presented. From the standpoint of obtaining the densest coatings with high performance, the optimal regimes of plasma spraying of PN85YU15 powder are the current from 140 A to 200 and using the air and propane-butane mixture only as the shielding gas (anode curtain).     

大功率电弧加热器起弧过程流场特性研究

电弧等离子体是通过电极之间击穿放电,产生热电弧,实现对冷态介质加热,目前大功率的电弧等离子体发生器在航空航天领域有重要的应用,是国内外开展飞行器防热材料筛选和考核研究最重要的地面模拟试验设备.本研究基于发展的高焓气流非接触式光谱诊断方法,开展对10 MW量级大功率长分段电弧加热器起弧过程流场特性的定量、定性研究,在线测...     

高库仑量大电流两电极气体火花开关研究

 设计了一个两电极气体火花开关，开关的主体部分仅包括阴极、阳极两个主电极，以及金属外壳和绝缘支撑外壳，两电极结构取消了触发极，消除了由于触发极烧蚀影响开关寿命的问题。开关设计工作电压23 kV，单脉冲能量1.2 MJ，峰值电流300 kA，单次脉冲电荷转移量110 C。初步试验阶段开关工作电压达到15 kV，开关的通流180 kA，电荷转移量为47.85 C。开关触发性能可靠，电极烧蚀均匀。     

100kA微秒级气体火花开关电极材料熔蚀研究

 电极材料是影响气体火花开关性能和寿命的关键因素之一。基于热传导方程分析了电弧作用下电极表层的温度场分布，得出了电极材料以及电弧属性参数对温度场分布的影响，并对黄铜、不锈钢、钨铜合金和高密度石墨4种电极材料进行了电极熔蚀实验，其质量亏损率分别为：黄铜6.39mg/C，不锈钢6.38mg/C, WCu合金4.19mg/C，高密度石墨1.19mg/C，与理论计算基本一致。     

Arc spot scanning of tube electrodes in gas-vortex plasmatorches

The peculiarities of cooling of stationary working hot and cold cathodes are under consideration. Scientific premises of the advisability of the tube electrodes arc-spot scanning are presented. The classification of the scanning methods is given. The assumption has been made that the phenomena of auto-electron emission of electrons in vacuum discharge tubes and in arc chambers of plasmatorches under the pressure equal or above atmospheric are somehow similar. The optimum scanning frequency and achievable values of the end-face tube cathode life-time have been estimated. Owing to the magnetic scanning, the area of the electrode surface, which is swept by the arc spot, increases one order or more, resulting in better cooling and reduced specific erosion. The continuous electrode lifetime becomes several orders longer than it is during the work without scanning.     

A Review of Anode Phenomena in Vacuum Arcs

This paper discusses arc modes at the anode, anode temperature measurments, anode ions, transitions of the arc into various modes (principally the anode-spot mode), and theoretical explanations of anode phenomena. A vacuum arc can exhibit five anode discharge modes: 1) a low-current mode in which the anode is basically passive, acting only as a collector of particles emitted from the cathode; 2) a second low-current mode that can occur if the electrode material is readily sputtered (a flux of sputtered atoms will be emitted by the anode); 3) a footpoint mode, characterized by the appearance of one or more luminous spots on the anode (footpoints are much cooler than the true anode spots present in the last two modes); 4) an anode-spot mode in which one large or several small anode spots are present (such spots are very luminous, have a temperature near the atmospheric boiling point of the anode material, and are a copious source of vapor and ions); and 5) an intense-arc mode where an anode spot is present, but accompanied by severe cathode erosion. The arc voltage is relatively low and quiet in the two low-current modes and the intense-arc mode. It is usually high and noisy in the footpoint mode, and it can be either in the anode-spot mode. Anode erosion is low, indeed negative, in the two low-current modes, and it is low to moderate in the footpoint mode. Severe anode erosion occurs in both the anode-spot and intense-arc modes.     

The method of laser-sustained arc ignition

The method of laser-assisted vacuum arc deposition (laser-arc) was developed to effectively produce high-quality coatings, especially multilayer coatings with a reduced number of droplets. The efficiency of this method depends mainly on the ignition probability of the vacuum arc discharges. In the present work, the process of arc initiation by laser irradiation is studied and the influencing factors such as power density of laser irradiation, target material, and electrode configuration are discussed. It is shown that a high ignition probability (ρ>50%) on such coating materials at Ti, TiC, TiN, and C can be guaranteed with a laser power density of about 10⁸ W/cm², which can be achieved with a low-cost Nd-YAG pulse laser. Measurements of the plasma current preceding the arc ignition and microscopic investigations of the erosion pattern caused by the laser irradiation suggest that the process of plasma-sustained are ignition (unipolar arcing) plays an important role during the buildup phase of the vacuum arc discharge     

Influence of the anode material on an argon arc

The interaction between the arc and the anode was experimentally studied by means of a transferred arc burning in argon with copper, iron, or steel anodes. Depending on the rate of anode cooling, a stable plasma was obtained just above the anode, established either in pure argon (strong cooling) or in a mixture of argon with metal vapor. Temperature and metal concentration fields were deduced from spectroscopic measurements. Two important results were reached: the arc radius near the anode depends on the nature of the electrode, even without anode erosion; and the presence of metal vapor leads to a cooling of the plasma. The same arc configurations were theoretically simulated by a two-dimensional model. The comparison between experimental and numerical results allows a large proportion of the observed phenomena to be interpreted, in spite of partial discrepancies between predicted and measured values. The dimension of the arc root at the anode depends on the thermal conductivity of the solid metal, whereas the cooling effect due to metal vapor in the plasma is explained by the increases of electrical conductivity and of radiative losses in the presence of the vapor     

Experimental investigations into the arc properties of vacuuminterrupters with horseshoe electrode, four pole electrode, and theirapplications

By using ferromagnetic material around electrodes to generate strong nonuniform magnetic fields, vacuum arcs can be kept in well-defined diffuse mode or multiple arc mode. As a result, the arc voltage is low and stable, the current is confined in certain areas, and high interrupting ability and small size are achieved. The different arc modes for different electrodes, the arc voltage versus arc current for flat electrodes, horseshoe, and four-pole electrode, and the vacuum arc distribution are measured. The criteria of choice of electrode diameter and electrode distance are given     

Arc root dynamics in high power plasma torches — Evidence of chaotic behavior

Although plasma torches have been commercially available for about 50 years, areas such as plasma gun design, process efficiency, reproducibility, plasma stability, torch lives etc. have remained mostly unattended. Recent torch developments have been focusing on the basic understanding of the plasma column and its dynamics inside the plasma torch, the interaction of plasma jet and the powders, the interaction of the plasma jet with surroundings and the impingement of the jet on the substrate. Two of the major causes of erratic and poor performance of a variety of thermal plasma processes are currently identified as the fluctuations arising out of the arc root movement on the electrodes inside the plasma torch and the fluid dynamic instabilities arising out of entrainment of the air into the plasma jet. This paper reviews the current state of understanding of these fluctuations as well as the dynamics of arc root movement in plasma torches. The work done at the author’s laboratory on studying the fluctuations in arc voltage, arc current, acoustic emissions and optical emissions are also presented. These fluctuations are observed to be chaotic and interrelated. Real time monitoring and controlling the arc instabilities through chaos characterization parameters can greatly contribute to the understanding of electrode erosion as well as improvement of plasma torch lifetime.     

On the Electrode Damage and Current Densities of Carbon Arcs

Arc damage on carbon electrodes has been examined as a function of the charge passing through each arc in the range from 10-6 to 10-1 coloumb. Two forms of arcing damage were observed: that due to the so-called vapor arc, which has a very high current density (~6 × 107 A/cm2) and low erosion rate, and that due to the so-called thermionic arc with a lower current density (~2 × 103 A/cm2) and higher erosion rate. Unlike damage observed on metallic electrodes raised rims were not formed around the carbon craters. The vapor mode damage is compared with two known models of cathode erosion. Differences between the vapor and thermionic modes and the transition between them are discussed. A whitish-gray deposit observed on the arced electrodes appears to be a form of graphite.