Electrode Erosion Rate Research Articles

LOW ELECTRODE EROSION RATE OF NANOCRYSTALLINE CuCr-50 ALLOY IN VACUUM

The CuCr-50 alloy with grain size of less than 50 nm was prepared by the mechanical alloy and hot pressing technique. Its microstructure was examined by XRD, SEM and TEM. The electrode erosion rates of nanocrystalline and microcrystalline CuCr-50 were investigated. It is found that the electrode erosion rate of nanocrystalline CuCr-50 is 24.8 μg/C, much lower than that of microcrystalline CuCr-50 . The main cause is that the vacuum arc shows diffusional features on the nanocrystalline electrode, decreasing the heat flux, current density and the dimensions of the droplets emmited from the cathode.

A user-friendly fuzzy-based system for the selection of electro discharge machining process parameters

This paper introduces a user-friendly intelligent system for the selection of electro discharge machining (EDM) parameters. In this system, a compact selection method based on expert rules, which were obtained from experimental results and extracted from the knowledge of skilled operators, is presented. Expert rules are evaluated by the fuzzy set theory. The developed fuzzy model uses fuzzy-expert rules, triangular membership functions for fuzzification and centroid area method for defuzzification processes. The system was developed on a PC using MATLAB Fuzzy Logic Toolbox. Inevitably, there are many machining parameters (discharge current, pulse duration, pulse interval, gap control, flushing rate, etc.) that should be considered in EDM processes. Selection of these parameters is still an ill-defined problem and generally relies on heuristics, which are not easy to model, and based on the experiences of specialists. In this system, discharge current, pulse duration and pulse interval are the inputs while the outputs are electrode wear, surface roughness and erosion rate. The remaining parameters are considered at constant rate during machining. The system is a compact and homemade tool that can be easily used by an average operator and provides the EDM parameters which lead to less electrode wear, better surface quality and more erosion rate according to the selected operation (finishing, roughing, etc.).

Low-pressure switching plasmas with axial magnetic field stabilization

Low pressure gas discharge switches of the usual pseudospark design are known to have rather large electrode erosion rates when operated at high current levels and long switching times. In order to improve the plasma confinement and to reduce the electrode erosion in high-current applications, an axial magnetic field has been used in a low-pressure pulsed switching device. For a pulse duration of 28 /spl mu/s and current amplitudes of up to 50 kA the plasma expands quickly, leading to a diffuse discharge mode. The radial expansion velocity increases with current amplitude and reaches up to 10 km/s at a peak current of 53 kA. With a further increase in current, a constricted plasma is superimposed onto the expanded diffuse part. These findings are compared with the case in which no magnetic field is applied.

Effects of silicone impregnant viscosity on metallised layer of polypropylene capacitor film under partial discharges

The authors present results of testing the metallised layer of polypropylene (PP) capacitor film for destruction from partial discharges (PD) and from arcing with impregnated silicone fluids of different viscosity. A special method of testing is presented. The testing was carried out on specimens which modelled a capacitor dielectric system containing the metallised PP film and silicone impregnating fluid. The characteristics of PDs were measured by means of a pulse-height analyser with a detection level of 10-13 C. The arcing voltage between the high-voltage electrode and measuring electrode was measured by means of a disconnecting device whose disconnect time is ≤ 20 µs. In both specimens the object under test was the metallised 8 µm PP film, with an Al metallised layer of 4 Ω surface resistance. The time dependence of destroyed length, the frequency dependence of electrode erosion rate and the relationship between electrode gap distance and arcing voltage are given.

Electrode erosion and coating properties in pulsed air arc deosition of WC-based hard alloys

WC-based hard alloys were deposited from a slab source anode on to low carbon steel and pure Ti substrates using a pulsed air arc. The depositions were conducted with a series of pulses with current amplitudes of 75 A, 300 A, and 500 A, a pulse duration of 150 μs, and a pulse repetition rate of 100 Hz. The influence of the electrode material, discharge energy and deposition time on the electrode erosion rate, mass transfer direction, and the wear resistance and friction coefficient of the coatings was investigated. Anodic and cathodic mass change characteristics depended on both the anode and cathode materials. Using a steel cathode and a WC anode, depositions of the anode material always formed on the cathode. For the same WC anode but a Ti cathode, coatings only formed locally in the craters of the eroded cathode. The anodic mass loss when using the steel cathodes was about a factor of 3 larger than when using the Ti cathodes. The microhardness of the coated substrates was larger by factors of 5–12 than the uncoated Ti and low carbon steel substrates. The coatings increased the wear resistance of the steel and Ti substrates by factors of 4.3 and 1.4, respectively. The poorer performance of the coated Ti substrates is attributed to the intensive erosion of the Ti cathodes (compared to the steel cathodes) and the discontinuous nature of the coatings (i.e. only in the erosion caters).

Electrode phenomena and measurements of the erosion rate in high-current pseudospark switches

For microsecond pulses and peak currents up to 105 kA, the erosion rate, electrode profile, and electrode surface of molybdenum electrodes were investigated. The direction of electrode material transport was verified. The discharge behavior of molybdenum electrodes was studied by streak photography. A contraction of the plasma column occurs at the cathode for peak currents above 20 kA. A bright luminous anode flare appears at a peak current of about 40 kA, correlated with an evident anode melting. A further constriction of the anode flare was observed for currents exceeding 90 kA. Opposite to lower currents, an increase in the weight of the cathode was noticed as well.

Erosion rate evaluation of plasma torch electrodes from measurements of the emitted metal vapour radiation

Spectroscopic observation of copper vapour density in 100 A arc columns simulating plasma torches is reported. These densities are compared with electrode erosion rate values for two operating conditions inducing different erosion conditions at the cathode. It is found that the evolution of copper vapour in the arc column away from the electrode source correlates with the electrode erosion rate. The possibility of real time monitoring of electrode erosion rate is suggested.

Characteristics and electrode erosion rates of a D.C. plasma torch operating with TiCl4 plasma gas

A stable TiCl4 plasma was produced using a simplified d.c. torch. The arc was struck between two concentric ring electrodes, d mm apart, and rotated using a magnetic coil. The electrode material was a new TaC composite. The arc was operated at 100 A for up to I h using plasma gas containing 0–30% TiCl4. The voltage was 24–60 V, depending on the TiCl4 concentration. The electrode erosion rate was of the order of 20μg/C. It is shown that the erosion rate is a function of the aerodynamic drag of the are column.

State-of-the-art insulator and electrode materials for use in high current high energy switching

An investigation into the failure of ceramic insulators that are used in a surface discharge switch (SDS) was conducted. The materials analyzed are Al/sub 2/O/sub 3/-25% SiC, MTF (modified alumina titanate), and CZA 500 (zirconia-alumina composite) ceramics. These insulators were subjected to high-current ( approximately 300 kA) surface discharges in atmospheric air and nitrogen. Energy-dispersive X-ray surface analysis was performed on the insulator surfaces in order to determine the contaminants that are present and the possible failure modes associated with the plasma arc environments mentioned above. Electrode erosion rates have been measured as a function of total charge transfer (up to 50 C/shot) for several in-situ materials including Cu-Nb, Cu-Nb+LaB/sub 6/, and Cu-Ta. Results from comparisons with standard Cu and CuW materials indicate that the in-situ materials represent an efficient method of retaining the copper in the bulk until it vaporizes and thus yield significantly lower erosion rates at high Coulomb transfer rates. >

Multichannel, high-energy railgap switch

A low-inductance, multichannel railgap switch has been developed which is capable of switching 20 kJ at 500 kA. The switch has low jitter, a wide operating voltage range and low electrode erosion rate.

Laser-Initiated Vacuum ARC for Heavy Ion Sources

Laser-triggered discharges have been considered for some time both for electron[1] and ion[2] sources. It has been recently shown that conventionally triggered metal-vapor vacuum arcs[3] can sustain even higher ion currents. In this paper, we point out that laser initiation permits arc operation in a high-current regime, and with geometry attractive for heavy ion sources. We present preliminary data on laser-initiated vacuum arcs [4] using carbon, copper, and tungsten cathode electrodes. Discharge current pulses of over 104 amperes with durations of up to 1 msec were employed to yield fully ionized source plasmas of liters volume with ion densities greater than 1013 cm-3. Electrode erosion rates were in the range of 10-4gm/C (the same order as in vacuum arcs) corresponding to ion injection currents in the range of 103 amperes.

Spectrochemical analysis of iron, copper and silicon in high purity aluminum

For improvement of analytical sensitivity using quantrecorder or vacuum quantrecorder, iron, copper and silicon in high purity aluminum were analyzed under argon atmosphere by low voltage spark discharge.The electrode erosion rate under argon atmosphere is higher than under nitrogen or oxygen atmosphere. The electrode erosion rate has a linear relation with the integrated value of discharge current ∫idt. Spectral line intensity depends mainly on the electrode erosion rate. Therefore, 50 μF, 50 pH, 10 Ω, 900 V and argon atmosphere may be better analytical condition rather than the now routin work conditions.

Spectral analysis by low voltage impulse discharge observation of spectra by a time-resolved technique and erosion rate of electrodes

A time-resolved technique was applied to investigate characteristics of spectra excited by a low voltage impulse discharge. Ion spectra of the gases in the atmosphere surrounding the spark and of some elements in the electrodes appeared in the first 10 msec of the discharge. Atom lines had lifetimes of about 30 msec, and resonance lines showed high absorption effects in air or in helium, especially in the later stages of the discharge. The absorption effect in a helium atmosphere was divided into two steps, the first caused by the initial breakdown energy and the next by the metastable state of helium. Further, a relation between the errosion rate of the electrodes and spectral line intensity was found in argon and in helium discharges.