穿孔等离子弧焊的熔深检测

在小孔等离子弧焊接过程中，首次利用鞘层电压获知等离子云喷封角，从而获知熔深情况。从以往研究只停留在实时检测小孔是否穿透的状态信息，前进到通过等离子云喷射角来检测熔池熔深的状态。设计了无源探针检测等离子云装置，该装置简单、可靠，具有较好的工业应用前景。     

Analysis of the acoustic safety of narrow-jet metal-cutting plasma torches

Two types of plasma torch for cutting of metals, working with narrow-jet (exact or constricted) plasma, are described. Methods of modernizing the plasma torches proposed taking into account the principles and design methods developed by the authors are outlined. The efficiency of design is analysed using acoustic safety criteria. The results of comparative analysis of the noise characteristics of Russian and foreign plasma torches for cutting in sound and ultrasonic noise emission ranges are presented. The advantages of the new narrow-jet plasma torch determined on the basis of the acoustic safety criterion in comparison with both the basic model and other investigated plasma torches are discussed.     

Real-time imaging of the plasma spray process—Work in progress

A LaserStrobe Control Vision system was employed to examine water-stabilized plasma (WSP), gas-sta-bilized plasma (GSP), and single-wire arc plasma (SWAP) technologies. Visualization of the plasma spray process in each of these technologies has been made possible, in some instances, for the first time. Parame-ter optimization for the three processes was accomplished. This technology has significantly added to the theoretical and scientific knowledge of plasma diagnostics and plasma processing. This summary of work in progress was presented at the NSF Design, Manufacturing and Industrial Innovation Grantees Meeting, San Di-ego, January 4–6,1995.     

Comparative study of the structure of gas-stabilized and water-stabilized plasma jets

The near-field structures of a gas- stabilized plasma jet and a water-stabilized plasma jet were investigated using a nano-pulsed laser probe and stroboscopic focusing schlieren techniques. The high exit temof the gas caused laminar flow conditions at the exit of the jet, producing instability waves in the region. Significant heat conduction to the ambient fluid and volumetric expansion of the ambient gases in the near- field were observed in the schlieren images of these jets. Considerable asymmetry in the mixing and entrainment region of the water- stabilized plasma jet was also visible, whereas no significant asymmetry occurred in the luminous core of the jet. The particles injected into the plasma jet, which were visualized by the pulsed- laser technique, were confined to a narrow central core of the jet in the near- field of the jet. The combination of the two visualization techniques used in the present study allowed nonintrusive monitoring of the plasma spray process in an effort to enhance the quality of the processed deposits.     

等离子弧焊中小孔检测的研究

在小孔等离子弧熔透焊接中，利用等离子云电压能够检测小孔的成形。本文首次应用等离子鞘层理论，指出尾焰电压和等离子云电压的本质特点，提出计算尾焰电压和等离子云电压公式。为用简单方法检测小孔成形奠定了基础。     

Study of the Active Screen Plasma Nitriding

Active screen plasma nitriding (ASPN) is a novel nitriding process, which overcomes many of the practical problems associated with the conventional DC plasma nitriding (DCPN). Experimental results showed that the metallurgical characteristics and hardening effect of 722M24 steel nitrided by ASPN at both floating potential and anodic (zero) potential were similar to those nitrided by DCPN. XRD and high-resolution SEM analysis indicated that iron nitride particles with sizes in sub-micron scale were deposited on the specimen surface in AS plasma nitriding. These indicate that the neutral iron nitride particles, which are sputtered from the active screen and transferred through plasma to specimen surface, are considered to be the dominant nitrogen carder in ASPN. The OES results show that NH could not be a critical species in plasma nitriding.     

放电通道振荡特性分析及其蚀除机理的研究

从理论上对单脉冲放电通道的等离子体振荡特性进行了分析,发现其振荡频谱包含了金属晶格振动的本征频率.由此提出了受激原子共振的观点:在放电电流上升阶段,因放电通道中等离子体振荡频率可覆盖金属晶格振动频率,会使电极材料表面晶格原子产生共振或接近共振,加剧放电的热作用,使电极表面材料以"共振"形式去除;而在放电电流趋于平稳后,等离子体振荡频率则远远小于晶格振动频率,电极材料表面晶格原子不具备共振的必要条件,此时材料主要是以"碰撞"形式去除.从这个观点出发,说明了放电电流初始阶段和短脉冲加工是对电极消耗影响较大的原因.     

Study on the active screen plasma nitriding and its nitriding mechanism

The active screen plasma and DC plasma nitriding of the low alloy steel 722M24 are investigated. Experimental results showed that the metallurgical characteristics and hardening effect on 722M24 steel nitrided by AS plasma nitriding at both floating potential and grounded potential were similar to those nitrided by DC plasma nitriding. Particles sputtered from the active screen and deposited on the specimen surface play the role of the nitrogen carrier in AS plasma nitriding. XRD and high-resolution SEM analysis indicated that the particles with sizes in sub-micron scale were Fe_xN (x > 2). Based on metallurgical analysis and Optical Emission Spectrometer (OES) experimental results, an AS plasma nitriding model has been proposed considering that AS plasma nitriding is a multi-stage process, involving sputtering, physical adsorption, desorption, diffusion and deposition.     

反极性等离子切割的流场及温度场数值模拟

通过建立反极性等离子切割的数值模型,模拟了不同参数下的等离子体热力学和动力学特征。结果表明,等离子体在枪体内被加热加速并在压缩孔道内达到峰值,而在扩散区域和工件切割腔内等离子体的温度和速度基本保持恒定;等离子枪体的几何尺寸(喷嘴直径和压缩孔道长度)和工艺参数(电流、离子气流量和喷嘴高度)对等离子体的温度和速度具有重要的影响。     

宝钢1450板坯连铸中间包钢液等离子加热

本文介绍了等离子系统工作的基本原理及系统构成,分析了等离子枪使用过程中能源介质和用电量的消耗,以及对中间包耐火材料的影响,最终找出枪体功率和枪位高度的最佳匹配关系等.利用等离子枪初步实现了特殊钢种的低温恒温浇注,铸坯晶粒细化效果明显.     

Determination of arc pressure and current density on the molten pool surface in plasma arc welding

A unified numerical model is developed to couple the plasma arc, weld pool and keyhole in a self consistent way. The plasma arc/anode interface and the melt/solid interface are treated specially, the VOF method is used to trace the moving keyhole wall, and the fluid flow and heat transfer in both the plasma arc and weld pool are numerically simulated. The distributions of current density and arc pressure on the weld pool surface during the keyhole formation process are analyzed using the coupled model. The predicted arc pressure and current density are compared with the experimentally measured results, and both are in good agreement.     

论等离子体在表面技术中的应用

介绍了表面技术领域中应用等离子技术的诸种现代工艺及其工作原理；讨论了等离子体在这些工艺过程中的行为作用，由其引发形成的工艺与产品的特点，以及这些工艺的应用发展前景。     

离子渗氮新技术的研究现状

为了克服传统离子渗氮的一些固有缺点，近些年来出现一些新的离子渗氮技术，如活性屏离子渗氮、等离子体源离子渗氮、离子注入离子渗氮等，本文简要介绍了这些新技术及其原理、特点，总结了这类技术的共性模型。其中，活性屏离子渗氮技术和等离子体源离子渗氮技术有着明显的设备和工艺优势，可能成为离子渗氮技术的发展方向。     

Modeling the restrike mode operation of a DC plasma spray torch

A key aspect of the operation of conventional non-transferred direct current (dc) plasma torches is the random motion of the arc inside the nozzle. Various plasma gun designs have been developed to limit the arc fluctuations without increasing the heat load to the anode wall that results in surface erosion and anode wear. However, construction of these plasma torches is highly complex, while the conventional dc plasma torch consists of a small number of elements and is simple to manufacture and maintain. A better understanding of the behavior of the arc-anode attachment and how it depends on operating conditions may help in the design and operation of conventional plasma torches so that the fluctuation of the time-voltage, and therefore the time-enthalpy variation, is as low as possible with a fluctuation frequency adapted to the time characteristic of the powder particles in the plasma jet. This study deals with a three-dimensional (3D) time-dependent modeling of the arc and plasma generation in such a torch operating under the so-called “restrike” mode. The latter is characterized by rather large voltage fluctuations, corresponding to a broad range of conditions used in the manufacturing of plasma coatings. The mathematical model is based on the simultaneous solution of the conservation equations of mass, momentum, energy, electric current, and electromagnetic equations. These make it possible to predict the effect of operating parameters of the plasma torch on the motion of the anode root attachment over the anode surface and the time-evolution of arc voltage and flow fields in the nozzle. This article was originally published inBuilding on 100 Years of Success: Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

YAG—MIG复合焊接条件下复合等离子体动态特征

利用高速摄像,对单YAG、单MIG、YAG—MIG激光电弧复合焊接铝锂合金5A90时的等离子体动态过程进行了深入研究。结果表明：①YAG—MIG复合焊的等离子体在MIG孤存在阶段,与MIG弧具有相近之处,其周期性与MIG相似,但在MIG弧熄灭阶段与MIG焊和YAG焊都有明显的区别;②在强MIG等离子体复合强YAG等离子体时,复合焊的等离子体强度和形状发生明显变化,且不是二者的简单叠加结果。它呈现一种不规则的弧,充分说明尽管在单激光焊接时等离子体较弱,但在复合焊时,它对MIG孤的影响不容忽视;③在MIG微弧复合强YAG金属蒸气／等离子体时,发现其等离子体的强度高于单一激光焊,且形状也有较大差别,表明此时虽然MIG电弧仅为微弧,但它对YAG金属蒸气／等离子体有显著的影响。     

The characteristics of a low-power-consumption plasma jet and ceramic coatings

The effects of the composition of plasma gases (Ar-N₂, Ar-H₂), arc current, and voltage on the temperature and velocity of a low-power (5 kW) plasma torch in the arc field free region has been investigated using an enthalpy probe. Coatings of Al₂O₃-13TiO₂ were deposited under different conditions. The results show that in the Ar-N₂ plasma, the enthalpy, temperature, and velocity change little with arc current and voltage when regulating the nitrogen proportion in the plasma gas. The hardness of the resulting coatings is 800 to 900 kg/mm² HV.300. For Ar-H₂ plasma, however, increases in the H₂ content in the mixture of the gases remarkably enhanced the velocity and heat transfer ability of the plasma jet, with the result that the coatings showed high hardness up to 1200 HV.     

Investigation of the energy characteristics of a plasma torch with an expanding channel for the output electrode

The results of experimental and theoretical investigations of low-temperature plasma generators with an expanding channel of the output electrode are presented. Experimental equipment with a sectioned output electrode has been constructed. The distribution of electric current in the section for different values of the consumption of gas and current is determined.     

穿孔等离子弧焊接中等离子云的检测

应用天体物理等离子鞘层理论的知识，分析金属板测量尾馅时产生电压和探针测量等离子云时产生电压的原因。当把探针放置在等离子云中，由于等离子体的特殊性，将在探针上产生了负电位，与工件电位差就是鞘层电压，并给出鞘层电压的计算公式，通过分析发现，鞘层电压大小仅仅与检测处等离子体温度和成分有关。提出了一种用无电源探针检测等离子云的新方法，通过检测等离子云中探针上产生的鞘层电压是否为零来判断小孔是否形成。试验验证了鞘层理论在等离子弧焊接中应用的正确性，同时给出了探针放置的最佳位置。     

PAW受控脉冲穿孔状态的检测与控制

根据受控脉冲穿孔的控制策略,研制出等离子弧焊接(PAW)小孔状态的检测与控制系统,采用等离子弧尾焰电压作为表征小孔状态的传感检测信号,对不同焊接电流作用下的焊接过程进行实时监测,系统可以同时采集焊接电流和尾焰电压信号,并对信号进行分析、处理,建立了焊接电流、尾焰电压和背面熔宽三者之间的定量关系曲线.结果表明,尾焰电压信号能够迅速准确地反映出小孔状态和焊缝背面熔宽.根据检测试验得到的数据,建立穿孔型PAW焊接闭环控制系统,通过对普通平板和改变散热条件工件进行闭环控制焊接试验,获得了适当的焊缝背面熔宽及良好的焊缝质量,证明了该系统运行稳定、可靠.     

等离子弧焊小孔行为的反翘电压检测

在穿孔等离子弧焊接过程中,小孔稳定性对焊接过程的稳定和优质的焊缝成形是非常关键的。文中采用无源探针对由等离子弧梯度电压和等离子鞘层电压构成的等离子反翘(等离子云)电压进行检测。根据等离子鞘层理论,随等离子反翘长度和角度变化的反翘电压可以反映小孔的状态信息及其形成、坍塌过程。文中讨论了检测信号的特征,以及材料、探针位置、焊接电流,等离子气流等因素对检测信号的影响。试验证明,该方法可以有效的预测小孔信息和焊缝熔透情况。