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1.
E. Moreau C. Chazelas G. Mariaux A. Vardelle 《Journal of Thermal Spray Technology》2006,15(4):524-530
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. 相似文献
2.
A numerical model for the calculation of hydro and thermo dynamical gas flow in a three electric arc torch, considering electromagnetic influences on gas flow behaviour was described and developed. The modelling results were compared with experimentally determined temperatures, obtained by computer tomography. A characteristic threefold symmetrical distribution of temperature on the torch nozzle outlet was obtained numerically as well as experimentally. Calculated and tomographic temperature contours and their rotations were compared and showed good agreement. In the second step, a model for the free jet was used for the evolution of thermal conditions into plasma jet outside the torch. The comparison of the calculated temperature distributions and those determined by tomography exhibit good agreement. 相似文献
3.
Arc instabilities in a plasma spray torch 总被引:2,自引:1,他引:2
The control over coating quality in plasma spraying is partly dependent on the arc and jet instabilities of the plasma torch.
Different forms of instabilities have been observed with different effects on the coating quality. We report on an investigation
of these instabilities based on high-speed end-on observation of the arc. The framing rate of 40,500 frames per second has
allowed the visualization of the anode attachment movement and the determination of the thickness of the cold-gas boundary
layer surrounding the arc. The images have been synchronized with voltage traces. Data have been obtained for a range of arc
currents, and mass flow rates for different gas injectors and for anodes displaying different amounts of wear. The analysis
of the data has led to quantitative correlations between the cold-gas boundary layer thickness and the instability mode for
the range of operating parameters. The arc instabilities can be seen to enhance the plasma jet instabilities and the cold-gas
entrainment. These results are particularly useful for guiding plasma torch design and operation in minimizing the influence
of plasma jet instabilities on coating properties. 相似文献
4.
基于局域热力学平衡假设,建立了三维非稳态等离子电弧的湍流模型,运用计算流体力学软件ANSYS CFX系统地模拟了电弧电流、氩气流量和氢气流量对氩/氢等离子喷枪内电弧波动的影响.结果表明,当电流小于600 A时,增大电流,电弧柱缩短,平均电弧电压和电压波动幅度减小,波动频率升高.当电流大于600 A时,增大电流对电弧波动基本没有影响.增加氩气流量或氢气流量均使得电弧柱增长,平均电弧电压和电压波动幅度增大,波动频率降低.三种工艺参数相比,氢气流量对电弧波动的影响最大,氩气流量次之,电弧电流影响最小. 相似文献
5.
Integrated fabrication process for solid oxide fuel cells in a triple torch plasma reactor 总被引:2,自引:0,他引:2
This paper describes an approach for an integrated manufacturing process for solid oxide fuel cells. The approach is based
on successively depositing the different layers of the cell using plasma deposition processes in a controlled-atmosphere chamber.
Cells have been manufactured following this approach with minimal changes in process conditions for the different processes.
The cells have been evaluated with regard to their materials characteristics and with regard to their electrical performance.
The cell performance has been acceptable, with open circuit voltages of about 1 V and power densities between 325 and 460
mW/cm2. Process modifications to improve the performance further are possible. The described process has the potential for being
easily automated. 相似文献
6.
In spite of the fact that plasma spraying is a commonly used technique for coating elaboration, it remains important to follow in time the characteristics of the arc jet delivered by the plasma torch. Arc voltage and heat loss measurement could be used, together with the control parameters such as arc current and plasma gas flow rate, to investigate the global behavior of the torch in association with a simple analytical model. It is shown that the specific enthalpy and the isentropic coefficient of the plasma gas have a strong influence on the jet velocity, this latter being also significantly modified by the drift of the torch performance. This work is completed by the analysis of the plasma jet instabilities that are responsible for the discrepancy in particle thermal histories. The rear part of the torch is involved in self sustained oscillations, so that the torch shows the characteristics of a Helmholtz resonator, giving rise to periodic variations of the torch voltage, higher in amplitude than the commonly admitted restrike mode. It is also evoked, that the generated acoustic waves are interacting with the solvent vaporization. 相似文献
7.
8.
N. A. Rudenskaya M. V. Rudenskaya N. V. Sokolova G. P. Shveikin 《Welding International》2013,27(10):810-813
Results of investigations of the process of dissipation of polydisperse particles in low-temperature plasma flow with the formation of ultrafine, including nanosized, particles are presented. A special method is proposed that can be used for producing polydisperse powders, including ultrafine and nanosized powders, with spherical particles and the amorphous, crystalline, or amorphous, crystalline structure. 相似文献
9.
Yang Gao Lian-Tong An Cheng-Qi Sun Zhi-Jun Yan 《Journal of Thermal Spray Technology》2004,13(4):521-525
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. 相似文献
10.
Plasma spraying of yttria-stabilized zirconia was carried out under chamber pressures ranging from low (30 kPa) to high pressure
(300 kPa) to investigate pressure effects on the plasma jet and to clarify the potential of high-pressure plasma spraying
(HPPS) as a high performance coating tool. Plasma flame length and velocity of the particles were measured in situ, and the
coating characteristics including its microstructure, density, and hardness were studied. A condensed plasma flame under high
pressure facilitated sufficient melting of zirconia particles, resulting in high deposition efficiency and a dense coating
with improved hardness, in spite of reduced particle velocity. High-pressure plasma spraying was found to be suitable for
thermal spraying of high-melting-point materials such as zirconia. 相似文献
11.
在磁流体动力学模型的基础上,引入阳极鞘层区简化模型,对直流等离子体电弧流动与传热进行了模拟研究.为研究阳极鞘层区对直流等离子体电弧存在的影响,进行了四组不同条件的模拟计算,并对引入和未引入阳极简化模型的模拟结果进行统计分析.结果表明,电弧阳极鞘层区的存在虽然对电弧最高温度及其温度云图没有明显影响,但对阳极热通量影响较大,使阳极热通量明显降低,并且增大了阳极界面所受剪切力.因此,电弧阳极鞘层区不仅降低电弧热传递效率,而且会导致阳极熔池界面不稳定性增强. 相似文献
12.
以5 mm厚的5A06铝镁合金板材为主要研究对象,焊缝的正面熔宽和背面熔宽为成形特征参数,通过正交试验确定焊枪行走角变化对焊缝成形影响的显著性,从能量传递的角度研究了焊枪行走角的变化对等离子弧穿孔立焊焊缝成形产生影响的机理.结果表明,焊枪行走角对焊缝成形的影响在焊接电流和离子气体流量之间;焊枪与试板垂直时正面熔宽最大,而随着行走角的减小,焊缝背面熔宽逐渐增大.焊枪行走角的改变使熔池正面的能量密度以及背面最高温度截面和最大熔宽截面的相对位置发生变化,对焊缝背面熔宽的影响可归结于厚度方向不同截面热源位置的偏离与工件厚度导致的传热滞后之间相互作用的结果. 相似文献
13.
A new concept has been verified for a plasma spray electrode system that improves plasma plume uniformity over that of a single
arc torch. A six-electrode, circular, arc-cascade discharge was formed by mounting seven tungsten-rod electrodes radially
around a stream of argon gas. To maintain the plasma plume, the cascade-arc discharge was repetitively triggered using a cascaded
high-voltage spark initiated by a secondary spark gap. The typical cascade arc voltage and current were 130 V and 20 A. Results
show that the cascaded arc array system can create a ring-shaped plasma plume having near-uniform electrical energy in the
circular direction. This feature suggests that the configuration may have future use in plasma torch systems requiring uniform
circular symmetry. In such a system, spray particles can be injected into the center of the plasma ring. At the same time,
such an arrangement also could provide a lower-cost alternative to systems that use multiple two-electrode plasma torches
arranged in a circular configuration. In the latter system, each two-electrode plasma torch is fed by a separate power supply. 相似文献
14.
15.
Richard Thomas Lermen Ivan Guerra Machado 《Journal of Materials Processing Technology》2012,212(11):2371-2379
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. 相似文献
16.
Aninvestigationonplasmasprayingwithartificialbonepowderandbondingcharacteristicsofcoating¥TianLi;LiJinglongandLinQiansheng(No... 相似文献
17.
轴向送粉式等离子喷涂陶瓷涂层工艺性能研究 总被引:1,自引:1,他引:0
对比研究了新型轴向送粉等离子涂枪和普通等离子喷涂枪的喷涂工艺参数和制备涂层的性能及其组织。试验结果表明:轴向送粉式等离子喷涂枪的功率明显低于普通等离子喷涂枪,其喷的陶瓷涂层的性能优于普通等离子喷涂。 相似文献
18.
A new design is proposed for direct current plasma spray gas-shroud attachments. It has curvilinearly shaped internal walls
aimed toward elimination of the cold air entrainment, recorded for commercially available conical designs of the shrouded
nozzle. The curvilinear nozzle design was tested; it proved to be capable of withstanding high plasma temperatures and enabled
satisfactory particle injection. Parallel measurements with an enthalpy probe were performed on the jet emerging from two
different nozzles. Also, corresponding calculations were made to predict the plasma flow parameters and the particle parameters.
Adequate spray tests were performed by spraying iron-aluminum and MCrAlY coatings onto stainless steel substrates. Coating
analyses were performed, and coating qualities, such as microstructure, open porosity, and adhesion strength, were determined.
The results indicate that the coatings sprayed with a curvilinear nozzle exhibited lower porosity, higher adhesion strength,
and an enhanced microstructure. 相似文献
19.
20.
Y. Tsunekawa M. Okumiya T. Kobayashi M. Okuda M. Fukumoto 《Journal of Thermal Spray Technology》1996,5(2):139-144
Nitrides of transition metals have good wear- and corrosion-resistant properties because of their high hardness and chemical
stability. Chromium-nitride coatings can be deposited by ion plating; however, the thin thickness due to the slow deposition
rate must be improved for severe wear-resistant applications. The main objective in this paper is to realize good structural
control in the processing of chromiumnitride in situ composite coatings formed at a high deposition rate. They were synthesized
by reactive low-pressure plasma spraying using elemental chromium powder as a spray material. The transferred arc between
the gun electrode and the substrate was used to accelerate the nitriding reaction. The sprayed coatings consist of chromium,
Cr2N, and CrN, which have a composition gradient from the substrate interface to the surface. The volume fraction of Cr2N increases with transferred arc current, and nonreacted chromium concurrently decreases, except close to the substrate. The
CrN phase, however, only exists as a surface layer of 20 to 30 μm because it is decomposed to Cr2N above 1420 K. The hardness of the composite coatings depends on the volume fraction of Cr2N, and it increases to 1300 HV at a Cr2N volume fraction of 0.98. The seizure stress with lubricant depends on the coating hardness. The maximum seizure stress of
24.9 MPa is obtained at a hardness of 1300 HV. The composite coatings also show a superior wear resistance. Hence, the Cr2N in situ composite coatings synthesized by reactive plasma spraying with transferred arc are expected to be good candidates
for wear-resistant applications. 相似文献