Research on Arc Cathodic Vacuum Arc Spectrum

The spectral characteristics of the arc under the same current conditions provide directions for the study of hollow cathode vacuum welding arcs.

Different types of arcs have been widely used in welding, such as: melting and non-melting arc arcs, submerged arc arcs, plasma arcs, and pulsed arcs. These arcs stabilize the combustion pressure is generally in the 1330 ~ 26600Pa. Hollow cathode The vacuum arc can be stably burned at a pressure of 0.133130 Pa. The initial application of the hollow cathode discharge is mainly to provide an ion source, which is now widely used in the welding and metallurgical industries.

The so-called hollow cathode, in a broad sense, refers to a cavity geometry in which the walls that make up the cavity confine the plasma, leaving a small vent opening to the outside. Inert gas (such as Ar, He, etc.) enters the arc region via the hollow cathode. The wall of the chamber maintains the cathode potential. Not only electrons can be emitted, but also electrons are emitted from the wall. The electrons cannot easily escape from the cathode chamber, so the discharge is easily maintained. Is the basic characteristics of hollow cathode. Due to its high process capability, hollow cathode arc welding has been widely used in industrial enterprises in the former Soviet Union since 1972. Since the 1980s, the United States, China, and other countries have competed to begin research on hollow cathode vacuum arc welding technology.

This article will provide the first measurement of the spectral distribution of a hollow cathode vacuum arc.

1 Principles of Spectral Measurement and Test Methods To determine the spectral characteristics of HCVAW welding arcs, a measuring device was set up as shown. The multi-channel spectral analysis system consists of an optical path, a silica optical fiber transmission beam, spectral analysis SP-556 and its controller ST-133. The spectrometer has a focal length of 500mm, and incorporates three gratings, 150g/mm, 1 and 2400g/mm, respectively. The spectral acceptance device is an array-enhanced UV-enhanced CCD with a pixel array of 1 024x128. The main features of this spectral analysis system are: Yes: 1 Simultaneous ingestion of multiple emission spectra. 2 Spectral data reading speed is fast, the sampling frequency is 100kHz, and multiple spectra can be acquired continuously in time series.

Spectral analysis is concerned with two parameters of the spectral line: the wavelength of the spectral line and the intensity of the spectral line. The wavelength of the line is used to identify different atoms (or ions), and for certain excitation conditions, the line intensity can measure how much the element mass fraction in the measured object. The factors that affect the intensity of the spectral line can be considered from two aspects. On the one hand, it is the evaporation characteristic of the sample, which is determined by the mass fraction of the elements in the sample and the number of plasmas that the element enters into the light source; on the other hand, it is the excitation characteristic of the line, which is the temperature of the light source, the excitation potential, Statistical weight, transition probability, radiation frequency (or photon energy), partition function, etc. The distribution function is also affected by statistical weights and the temperature of the light source. The generation of spectral lines is a very complicated process. The dissociation, ionization, excitation, radiation, and self-absorption processes in high-temperature plasma all affect the spectral line intensity.

The purpose of the spectral analysis in this paper is to determine the distribution of the arc spectrum in the visible and near visible range, and to study the spatial distribution of the spectral lines of the main components in the arc.

The test uses hollow coiled tubes and water-cooled copper anodes as electrodes.

Since the water-cooled copper anode does not form a molten pool, it can provide a stable arc for a long time, and the arc composition is also stable. Therefore, multi-point sampling can be realized.

In this paper, Hollow Cathode Vacuum Arc is studied by using integral arc spectrum analysis and local area arc spectral analysis. The so-called global arc spectrum analysis is to use a spectrometer to receive the arc emitted by the whole arc, requiring the arc to be an electric light source with respect to the spectrometer; the arc local area spectral analysis is to detect a thin layer of the arc, and by adjusting the drive device of the combination platform, the Arc detection at all levels.

2 Test parameters and test results 2.1 Welding process parameters for the overall arc spectrum test of hollow cathode vacuum arc under different welding current conditions are shown in Table 1. Grating selection 150g/mm, each spectrum read range is 200~1 2~4 is the overall arc spectrum of HCVAW welding arc under water-cooled copper anode conditions, from the near ultraviolet to the infrared spectrum (200 to 1 vertical axis is the relative of the spectrum Intensity, expressed as /SP, the horizontal axis is the wavelength of the spectrum, in Table A; gK. Table 1 Test process parameters Test 1 Test 2 Test 3 Current / / A gas flow rate g / (ml cathode diameter (wall thickness M cathode extension Length//mm arc length L/mm Arc spectrum distribution under 100A current conditions 2.2 Spatial distribution of hollow cathode vacuum arc Spectrographic analysis of different sections along the axial direction of the arc was carried out using local area arc spectral analysis. A direction represents each section. The length of the hollow cathode outlet.

The spatial distribution of the arc spectrum at 100A is discussed. 2.3 Discussion From the spectral distribution of the hollow cathode arc light obtained from the above test, it can be seen that the basic law of the overall arc spectrum is superposed on the lower continuum in the measured spectral range. Many line spectra and high-radiance lines are distributed in the 350-550nm and 600-900nm bands. Therefore, the spectrum of the HCVAW arc is composed of the basic radiation spectrum.

Among the recorded lines, there are mainly an argon ion line and an argon atom stimulated line, and the plasma is not contaminated by the cathode material. The result shows that the impurity content in the hollow cathode vacuum arc is lower than one thousandth. . The high spectral intensity of the low-current hollow cathode vacuum arc is mainly concentrated in the spectral range greater than 700 nm. The line spectrum intensity in the visible light range is very low, so the arc is not visible to the naked eye. Its arc spectrum is mainly affected by the argon atom. The composition of the laser line; the high-current arc spectrum is mainly composed of a primary argon ion spectrum and an argon atom excited spectrum line (,), and the primary argon ion spectrum line is mainly located in the visible blue spectrum, so the arc at this time looks like A bunch of columnar, blue arcs.

From the spatial distribution of the spectrum of the hollow cathode vacuum arc, the arc is the strongest at the cathode exit region of the arc, indicating that the degree and frequency of the gas atoms being excited and ionized are high in this region. According to t2, the ionization of the gas is mainly concentrated on the cathode. Export area. In the direction toward the anode, the intensity of each spectral line decreases almost proportionally due to the enhanced diffusion of the plasma into the surrounding environment and the reduction of the internal collision effect of the plasma.

The above distribution characteristics of the hollow cathode vacuum arc spectrum provide favorable conditions for carrying out research on its physical properties. Since the line spectrum has the corresponding distinguishability of the elements and the state of the atoms, the arc can be used to understand the arc. The composition of the internal components and the transport process inside the arc plasma.

3 Conclusions In this paper, the characteristics of the spectral distribution of hollow cathode vacuum welding arc were studied. The following conclusions and conclusions were obtained: The spectral distribution of hollow cathode vacuum welding arc is a line spectral structure on a continuous radiation background, the presence of line spectral characteristics This makes it possible to study the selectivity of arc components.

In the high-current vacuum arc spectrum, a large number of primary argon ion lines appear in the blue spectrum, so the arc color is blue. The low current arc spectrum is because the line intensity in the visible range is low and the arc pattern is invisible to the naked eye.

The spatial distribution characteristics of the vacuum arc spectrum show that the internal composition of the arc and the internal transport process of the arc plasma can be understood by using the line spectra corresponding to the arc.

The research results of this paper have established the understanding of the arc arc spectrum of hollow cathode vacuum welding for the first time, pointing out the direction for the study of low pressure welding arc.

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