Parametric study of the electrical to thermal power conversion in an inductively coupledrf plasma torch

An inductively coupled (ic) radio-frequency (rf) stabilized argon plasma was generated in a quartz tube using a 7 MHzrf generator. The electrical and thermal powers were measured and the efficiency of energy conversion was computed. The results indicate that for a constant power input, there is an optimum argon flow rate for which maximum energy conversion efficiency occurs.     

等离子-MIG焊接设备的设计与研制

采用双电源供电和双电弧共枪体等技术，成功地完成了等离子-MIG焊接设备的研制。在设计中还采用了焊接参数专家库管理和等离子枪体计算机辅助优化设计等技术，并将该焊接方法应用于三峡电站大型开关断路器的制造过程。     

几何约束下TIG焊焊枪姿态研究

火箭发动机关键部件自动TIG焊中，因一些焊缝周围有特殊结构，为避免相碰，只能使焊枪偏转一个角度进行焊接，且此焊枪姿态与表征电弧电压的弧长和钨极伸出长度等有一定的关系，为了易于离线编程，必须对焊枪姿态进行深入分析。以火箭发动机典型的几何约束焊缝为例，提出了通用的求解思路。实际应用表明，此方法结果正确，可应用到各种几何约束焊缝的焊枪姿态分析中。     

Modeling of axis-symmetric steam plasma flow in a non-transferred torch

This paper discusses the numerical modeling of steam plasma in a DC non-transferred torch equipped with well-type cathode, where the non-trivial azimuthal velocity component and turbulent effect are both taken into account. In order to investigate the complicated flow characteristics of thermal plasma due to the interaction between steam and electric arc, the flow filed inside the plasma torch is modeled by the magnetic–hydrodynamic (MHD) equations. The governing equations are then solved numerically using a non-staggered finite volume discretization based on Cartesian grid system. The anode location and maximum current density at cathode are fixed by the corresponding experimental measurement at a given flow rate. The predicted result suggests that the steam plasma can be accelerated to a mean velocity of 1500 m/s at torch outlet with the mass flow rate of 5 g/s and the system current of 180 A. A strong vortex flow structure is found inside the torch due to the introduction of azimuthal velocity at the gas inlet, which should help to stabilize the rotating arc during the torch operation.     

大气压直流双阳极等离子弧脉动特性研究

等离子弧的脉动特性是表征等离子体物理状态和过程的重要参数之一,等离子体射流的非稳定性和阳极斑点在电极上的运动是引起等离子弧脉动的主要原因,是等离子体技术的实际应用和进一步发展的关键。该文介绍了一种大气压直流双阳极等离子发生器,通过对等离子弧电信号进行时域和频域分析,研究了载气成分、载气流量和弧电流等参数的变化对等离子弧脉动特性的影响,结果表明在文中的实验条件下等离子弧的伏安特性呈上升趋势,纯氩气作为载气时等离子弧的脉动特性主要和电源的交流分量有关,氩氮混合气体作为载气时等离子弧的脉动特性除了和电源的交流分量有关,还和弧室内存在的赫姆霍茨共振有关,其共振频率独立于气体流量和弧电流的变化。     

电感耦合等离子体质谱法测定钽粉中的磷

介绍了采用电感耦合等离子体质谱法（ICP—MS）对钽粉中微量杂质磷进行测定的方法。通过使用耐氢氟酸的惰性进样系统、屏蔽炬（shned torch）和冷等离子体技术，以及对测试条件的探讨，成功地运用标准加入法测量了金属钽粉中微量磷的含量。     

Development of a new hybrid plasma torch for materials processing

The main objectives of this study were to construct a plasma generator device and to investigate its applications in welding, cutting, and surface hardening. The device was derived from the union of two plasma-generating technologies, non-transferred-arc plasma and magnetoplasmadynamic thruster (MPDT), and characterised by the simultaneous formation of two plasma arcs in one device, generating a plasma jet with high energy density. Initially, trials were conducted to analyse the influence of the physical variables (gas flow rate and electric current intensities – primary and secondary) on the plasma jet, for which the thruster and the length of the plasma jet expulsed from the chamber were determined. The relevant parameters for welding, cutting and surface hardening were determined by trial and error, in which the trials were conducted using various plate thicknesses and materials. The results have shown that this device can be used for welding, cutting and surface hardening.     

Morphology and anti-ablation properties of PIP Cf/C–SiC composites with different CVI carbon content under 4.2 MW/m2 heat flux oxy-acetylene test

In this work, the needled carbon fiber preforms were used to make seven groups of carbon/carbon composite billets with different matrix carbon contents by controlling the processing time of chemical vapor infiltration (CVI). C_f/C–SiC composites were prepared by infiltration of SiC into these C/C composites billets using polycarbosilane (PCS) through precursor infiltration and pyrolysis (PIP). After oxy-acetylene torch testing (heat flux of 4.2 MW/m²) for 200s, 300s and 400s, respectively, it revealed that the anti-ablation properties of the C_f/C–SiC composite samples were enhanced by a higher content of SiC matrix. Additionally, specimens bearing longer duration tests showed a trend of lower average ablation rates. The lowest linear ablation rate is 0.008 mm/s and the mass ablation rate is 0.0019 g/s for those high SiC content samples tested for 400s. The SEM images of the tested samples showed the mechanism and the non-linear process of ablation resistance progression.     

Laser and GTAW torch processing of Fe–Cr–B coatings on steel

A comparison has been made of the relationship between microstructure and microhardness developed by surface melting Nanosteel SHS 7170 Fe–Cr–B alloy powder onto a plain carbon steel surface. This powder was initially developed as a high velocity oxyfuel sprayed coating, giving a strength 10 times that of mild steel, and is particularly suitable for surface protection against wear and corrosion. In the present study, the alloy powder was injected into the laser melted surface, while a preplaced powder was melted using the gas tungsten arc welding (GTAW) technique. The laser track consisted of fine dendrites and needle-like microstructures, which produced a maximum hardness value of over 800 HV, while the GTAW track produced a mixture of equiaxed and columnar grain microstructures with a maximum hardness value of 670 HV. The lower hardness values are considered to be associated with dilution and grain size.     

UHTC-based matrix as protection for Cf/C composites: Original manufacturing,microstructural characterisation and oxidation behaviour at temperature above 2000 °C

In space propulsion applications, the development of new ceramic matrix composites with improved resistance to oxidation and ablation at high temperature is needed and ultra-high temperature ceramics-based ones appear the most suitable. Combination of both powder impregnation (ZrB₂, C) and liquid silicon infiltration enabled manufacturing of UHTC based matrices in C_f/C preforms with less than 10 vol% open porosity and various proportions and homogeneous distribution of C, ZrB₂, SiC and Si. Oxidation behaviour was evaluated on composite structures using an oxyacetylene torch at temperatures higher than 2000 °C. Chemical analyses and microstructural observations before and after oxidation testing evidenced the protection ability of ZrB₂-SiC-Si matrices thanks to the formation of multi-oxide scales which resisted even tested durations of 6 min and pointed the unharmful presence of residual 12 vol% silicon on the composite for use at high temperature under high gas flows.