An improved asymmetric plasma spectroscopy method

Abstract

The application discloses an improved asymmetric plasma spectrum analysis method, considers a diatomic dissociation process correction part standard temperature method curve result, and is higher in precision in diatomic gas calculation; adopts radiation intensity calculation instead of an emission coefficient, reduces a process of reconstructing an emission coefficient distribution model, is more convenient in calculation, avoids calculation deviation caused by reconstruction model error, simultaneously expands the application range of the method, and is not limited by an inverse transformation method; converts two relative emission coefficient curve intersection points into a relative emission coefficient ratio to determine plasma composition, and compensates for error caused by radiation intensity instead of the emission coefficient. Meanwhile, the concentration calculation can be extended to the case that the relative emission coefficient of the plasma center is greater than 1.

Description

TECHNICAL FIELD

[0001] The present application relates to an improved asymmetric plasma spectrum analysis method, belonging to the technical field of material processing engineering. BACKGROUND

[0002] The welding plasma is high-temperature plasma, and the higher temperature limits most commonly used contact detection methods. Meanwhile, the interaction between various particles, mass and energy transport processes in the plasma are very complex, making it more difficult to detect. However, the wide application of arc welding and laser welding inevitably requires a deeper understanding of the physical process of plasma. After a large number of researchers' research, the theory and means of plasma detection are also increasingly mature. Among them, the standard temperature method (Fowler-Milne method) can be used for temperature and composition measurement in plasma. Murphy of Australia expanded the standard temperature method, making it applicable to the measurement of temperature and concentration of multi-component arc plasma, and measured the argon-nitrogen arc using this method. However, the application of the standard temperature method requires that the relative emission coefficient be obtained first, and the relative emission coefficient is obtained by Abel inverse transformation of arc intensity, assuming that the emission coefficient in the plasma is uniformly distributed in the radial direction. The radiation intensity measured in a certain direction, i.e. the integral transformation of the emission coefficient, obtains the theoretical emission coefficient distribution curve. The limitations of this method are: 1. Limited by the image acquisition system, if the image is overexposed, the intensity of the center region will reach the peak and no longer increase, which will cause the maximum emission coefficient point to move to the outside of the arc, and the emission coefficient curve obtained by inverse transformation has a large error, so the emission coefficient value of a certain point is also biased. 2. The TIG arc is assumed to be symmetrical, but in fact it is not completely symmetrical, and even the plasma is completely asymmetrical in structure, so it is not possible to obtain the emission coefficient curve by simple transformation, which limits the application of the standard temperature method to welding methods other than arc welding in the vertical direction. 3. Since the plasma is constantly changing, the relative emission coefficient ratio also has a certain error, and cannot solve the abnormal situation when the sum of the relative emission coefficients at the center of the arc exceeds 1.

[0003] At present, many scholars are committed to the research of the automation and adaptability improvement of spectral analysis method. A method for calculating the axisymmetric plasma arc temperature of pulse TIG welding is proposed in patent CN201811119604.2, which is mainly used for automatically calculating the obtained spectral results, but is also limited to axisymmetric plasma. The scholars of Beijing University of Technology (Research on measurement method of transient temperature field of non-axisymmetric arc) optimize the accuracy of transforming the arc image into the emission coefficient distribution by using the CT reconstruction algorithm, and apply it to the measurement of non-axisymmetric arc; the scholars of Osaka University in Japan (Study on temperature measurement of two-electrode TIG arc plasma) observe each angle of the arc by using 6 high-speed cameras, and consider that the temperature field of the inclined arc can be obtained more accurately by reconstructing the images at different angles. However, the above methods have problems such as complex implementation process, high cost, and unsynchronized images, and therefore are difficult to be used for quickly and simply measuring the distribution trend of the components in the plasma. In addition, the method of modeling by using the arc image is more suitable for the welding materials without interfering components, so that the distribution of the plasma components obtained is more regular, and is not limited by the accuracy of the camera acquisition. Since the small concentration difference is difficult to be distinguished on the arc image, the accuracy of the three-dimensional reconstruction result will be affected to a certain extent.

[0004] Based on this, the improved asymmetric plasma spectral analysis method is proposed to measure the regional distribution of mixed components in the asymmetric plasma (inclined arc welding, laser-arc hybrid welding, etc.). SUMMARY

[0005] In view of the above technical problems, the purpose of the present application is to provide an improved analysis method for the problem that the asymmetric plasma is difficult to apply the standard temperature method for measurement.

[0006] The technical solution of the present application is realized as follows: an improved asymmetric plasma spectral analysis method, comprising the following steps:

[0007] ①A material without the measured element is used for welding, after the spectral measurement and image acquisition position calibration are performed on both sides of the welding plasma, the measured material, the mixed protective gas to be measured and the pure protective gas for calibration are used for welding and measurement, and the required spectrum and plasma image are obtained;

[0008] ②The plasma spectral line is extracted, the characteristic spectral line that can be used for analysis is selected, the emission coefficient curve and the corresponding temperature-concentration curve are calculated, the Guldberg-Wagge dissociation equation is added for correction for the diatomic gas, the concentration results under different relative emission coefficient ratios are calculated, and the relative emission coefficient ratio-concentration curve is obtained;

[0009] III. Calculate the ratio of the arc radiation intensity under the mixed protective gas to be tested and the arc radiation intensity under the pure protective gas at the corresponding position, i.e. the relative radiation intensity, and then calculate the ratio of the two; use the relative radiation intensity ratio to replace the relative emission coefficient ratio in the relative emission coefficient ratio-concentration curve to obtain the concentration result.

[0010] Preferably, in step I, the mixed protective gas to be tested is mixed by multiple protective gases, and the pure protective gas used for calibration is one of the gases in the mixed protective gas to be tested.

[0011] Preferably, in step II, the diatomic gas is nitrogen N2.

[0012] The Guldberg-Wagge dissociation equation is as follows:

[0013]

[0014] In the formula, Z N (T) is the partition function of nitrogen atom at temperature T, which is obtained from the atomic spectrum database;

[0015] is the partition function of nitrogen molecule at temperature T, which is obtained from the atomic spectrum database;

[0016] N N is the particle number density of nitrogen atom;

[0017] is the particle number density of nitrogen molecule;

[0018] m N is the mass of nitrogen atom (2.325×10 -26 kg);

[0019] is the mass of nitrogen molecule;

[0020] h is the Planck constant (6.62607015×10 -34 J·s or 4.1356676969×10 -15 eV·s);

[0021] k is the Boltzmann constant (1.380649×10 -23 J / K);

[0022] E d is the dissociation energy of nitrogen molecule (9.760eV);

[0023] T is the plasma temperature.

[0024] By means of the technical scheme, the present application has the following advantages compared with the prior art:

[0025] ①The accuracy is higher in the calculation of diatomic gas by considering the correction part of the standard temperature method curve result of diatomic dissociation process.

[0026] ②The radiation intensity calculation is used instead of the emission coefficient, the process of reconstructing the emission coefficient distribution model is reduced, the calculation is more convenient, the calculation deviation caused by the reconstruction model error is avoided, and the application range of the method is expanded and is not limited by the inverse transformation method.

[0027] ③The intersection of the two relative emission coefficient curves is converted into the relative emission coefficient ratio to determine the plasma composition, and the error caused by the radiation intensity instead of the emission coefficient is compensated. Meanwhile, the concentration calculation can be extended to the case that the relative emission coefficient of the plasma center is greater than 1. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the description of the embodiments of the present application will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and all other drawings obtained by those skilled in the art without creative labor based on the contents of the embodiments of the present application also belong to the protection scope of the present application.

[0029] FIG. 1 is a relative emission coefficient ratio and equivalent nitrogen concentration curve diagram of the present application; Figure 1 FIG. 2 is an error analysis result diagram of the two methods in the embodiments of the present application.

[0030] FIG. 3 is a relative emission coefficient ratio and equivalent nitrogen concentration curve diagram of the present application; Figure 2 FIG. 4 is an error analysis result diagram of the two methods in the embodiments of the present application. DETAILED DESCRIPTION

[0031] In order to make the technical problems solved by the present application, the technical scheme adopted and the technical effects achieved more clear, the technical solutions of the embodiments of the present application will be further described in detail below with reference to the drawings. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor also belong to the protection scope of the present application.

[0032] The present application provides an improved asymmetric plasma spectrum analysis method, comprising the following steps:

[0033] ①A material without the measured element is used for welding, after the spectrum measurement and image acquisition position calibration are performed on both sides of the welding plasma, the measured material, the measured mixed protective gas and the pure protective gas for calibration are used for welding and measurement, and the required spectrum and plasma image are obtained.

[0034] ②Extract the plasma spectrum line, select the characteristic spectrum line that can be used for analysis, calculate its emission coefficient curve and the corresponding temperature-concentration curve; for diatomic gas, add Guldberg-Wagge dissociation equation for correction; calculate the concentration results under different relative emission coefficient ratios, and obtain the relative emission coefficient ratio-concentration curve.

[0035] ③Calculate the ratio of the arc radiation intensity under the mixed protective gas to be tested and the arc radiation intensity under the pure protective gas at the corresponding position, that is, the relative radiation intensity, and then calculate the ratio of the two; use the relative radiation intensity ratio instead of the relative emission coefficient ratio to substitute into the relative emission coefficient ratio-concentration curve to obtain the concentration result.

[0036] Among them, the laser can use CO2 gas laser, YAG solid laser, semiconductor laser during welding; the welding machine can use Fornes TIG, MIG / CMT welding machine; 1 KUKA robot, the adjustment of the process parameters of laser and arc in the welding process is realized through KUKA robot programming.

[0037] The mixed protective gas to be tested is mixed by a plurality of protective gases, and the pure protective gas for calibration is one of the mixed protective gases to be tested.

[0038] For the commonly used Ar-H2, Ar-N2, Ar-He mixed gas in engineering, for monatomic gas, the original temperature-concentration curve can be used. For diatomic gas (N2, H2), the dissociation process is added to correct the particle number density. Taking nitrogen as an example, the Guldberg-Wagge equation is as follows:

[0039]

[0040] In the formula, Z N (T) is the partition function of nitrogen atom at temperature T, which is obtained from atomic spectrum database;

[0041] is the partition function of nitrogen molecule at temperature T, which is obtained from atomic spectrum database;

[0042] N N is the particle number density of nitrogen atom;

[0043] is the particle number density of nitrogen molecule;

[0044] m N is the mass of nitrogen atom (2.325×10 -26 kg);

[0045] is the mass of nitrogen molecule;

[0046] h is the Planck constant (6.62607015 x 10 -34 J s or 4.1356676969 x 10 -15 eV s);

[0047] k is the Boltzmann constant (1.380649 x 10 -23 J / K);

[0048] E d is the dissociation energy of nitrogen molecule (9.760 eV);

[0049] T is the plasma temperature.

[0050] The present scheme converts the temperature-concentration curve used in the standard temperature method into a relative emission coefficient-nitrogen concentration curve relationship, as shown in FIG. 1, which is the relative emission coefficient-concentration curve of Ar-N2 mixed gas in the high-temperature region (exceeding the standard temperature region). When the relative emission coefficient of nitrogen Figure 1 ε Ar exceeds 0.35-0.4, the relative emission coefficient ratio of the two components has a stable corresponding relationship with the concentration. The nitrogen concentration at the same ratio can be calculated according to the mean value or obtained by least squares fitting. The error of several ratios in the figure is not more than ±0.15% according to the mean value. Since the radiation intensity and the emission coefficient are related to the particle density, the corresponding concentration can be determined from the ratio of the emission coefficients, and it can also be extended to the case where the sum is greater than 1 to avoid the appearance of outliers. The present scheme uses a conventional method to collect plasma spectrum and image. The standard temperature position where the maximum emission coefficient is located is determined by using the plasma image. For the high-temperature region, the relative radiation intensity of Ar I and N I spectral lines under mixed gas conditions is calculated, and the relative radiation intensity under pure argon or pure nitrogen protection is calculated, and then the ratio of the relative radiation intensity of N I to Ar I is calculated to replace the relative emission coefficient ratio, and the corresponding nitrogen concentration is determined in the relative coefficient-nitrogen concentration curve. For the low-temperature region of the plasma edge, the same calculation method can be used, or the relative radiation intensity can be directly used to replace the relative emission coefficient to obtain the concentration result in the temperature-concentration curve.

[0051] For the measurement results of plasma with too high temperature, they can also be compared with the measurement results of other methods under certain parameters to correct the systematic error.

[0052] The following uses the conventional standard temperature method and the method of the present scheme to measure the TIG arc under different nitrogen concentrations and currents under the condition of vertical welding for comparison.

[0053]

[0054] ​The specific test method is as follows:

[0055] 1. The vertical TIG arc under different concentrations and currents is measured by a conventional standard temperature method:

[0056] ①First, a material without a measurement element is used for welding, after spectral measurement and image acquisition position calibration are performed on both sides of the welding plasma, 45# steel and nitrogen argon mixed shielding gas with nitrogen concentration of 25%, 50%, and 75% and pure argon and nitrogen are used for welding and measurement, and the required spectrum and plasma image are obtained;

[0057] ②The plasma spectral line is extracted, the characteristic spectral line that can be used for analysis is selected, the emission coefficient curve and the corresponding temperature-concentration curve are calculated;

[0058] ③The arc image is converted into an emission coefficient distribution curve through Abel inverse transformation, the ratio of the emission coefficient of the mixed gas to the emission coefficient under pure shielding gas, i.e., the relative emission coefficient, is calculated at the corresponding position, and the concentration result is obtained by substituting the temperature-concentration curve.

[0059] 2. The TIG arc under different concentrations and currents is measured by the method of the present scheme:

[0060] ①First, a material without a measurement element is used for welding, after spectral measurement and image acquisition position calibration are performed on both sides of the welding plasma, 45# steel and nitrogen argon mixed shielding gas with nitrogen concentration of 25%, 50%, and 75% and pure argon and nitrogen are used for welding and measurement, and the required spectrum and plasma image are obtained;

[0061] ②The plasma spectral line is extracted, the characteristic spectral line that can be used for analysis is selected, the emission coefficient curve and the corresponding temperature-concentration curve are calculated. For nitrogen, the Guldberg-Wagge dissociation equation is added for particle density correction; the concentration result under different relative emission coefficient ratios is calculated, and the relative emission coefficient ratio-concentration curve is obtained.

[0062] ③The ratio of the arc radiation intensity of the mixed shielding gas to be measured to the arc radiation intensity under pure shielding gas is calculated at the corresponding position, and the ratio of the two is calculated. The relative radiation intensity ratio is used instead of the relative emission coefficient ratio to substitute the relative emission coefficient ratio-concentration curve, and the concentration result is obtained.

[0063] Reference Figure 2The error analysis of the results obtained by the conventional standard temperature method and the present method. Because of the different analysis methods, the results are not exactly the same. The conventional standard temperature method measures the nitrogen content at a certain point, while the present method measures the weighted average of a certain range of the area, and the higher the temperature, the greater the weight of the area, so there should be a certain gap between the theoretical concentration of a certain point calculated by the conventional standard temperature method and the present method. According to the average error, the nitrogen content measured by the two methods is approximately the same, and the average gap is not more than 10%, and the maximum error point is in the high temperature area, which shows that the calculation accuracy of the present method is sufficient to meet the quantitative analysis of different areas of the electric arc, and further used for the analysis of other asymmetric plasma spectra. At the same time, the measurement results under different temperature areas and welding parameters can be corrected, and the corrected results can be used for calculation under specific points or other conditions.

[0064] The above examples are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the spirit and essence of the present application should be covered within the protection scope of the present application.

Claims

1. An improved asymmetric plasma spectroscopic analysis method, characterized in that, Includes the following steps: ① Welding is performed using materials that do not contain the elements to be measured. After spectral measurement and image acquisition position calibration are performed on both sides of the welding plasma, welding and measurement are performed using the material to be measured, the mixed protective gas to be measured, and the pure protective gas for calibration to obtain the required spectrum and plasma image. The protective gas mixture to be tested is composed of two protective gases, and the pure protective gas used for calibration is one of the protective gases in the protective gas mixture to be tested. ② Extract plasma spectral lines, select characteristic spectral lines that can be used for analysis, and calculate their emission coefficient curves and corresponding temperature-concentration curves; for diatomic gases, add the Guldberg-Wagge dissociation equation for correction; calculate the concentration results at the relative emission coefficient ratio of the two different components, and obtain the relative emission coefficient ratio-concentration curve; ③ Calculate the ratio of the arc radiation intensity under the mixed protective gas to the arc radiation intensity under the two pure protective gases at the corresponding positions to obtain two sets of relative radiation intensities. Then calculate the ratio of the two sets of relative radiation intensities to obtain the relative radiation intensity ratio. Use the relative radiation intensity ratio to replace the relative emission coefficient ratio and substitute it into the relative emission coefficient ratio-concentration curve to obtain the concentration result.

2. The improved asymmetric plasma spectroscopy method according to claim 1, characterized in that: In step ②, the diatomic gas is nitrogen (N2). The Guldberg-Wagge dissociation equation is as follows: ； In the formula, The partition function of nitrogen atoms at temperature T is obtained from an atomic spectral database; The partition function of nitrogen molecules at temperature T is obtained from an atomic spectral database. N N The number density of nitrogen atoms; The number density of nitrogen molecules; The atomic mass of nitrogen is (2.325 × 10⁻⁶). -26 kg); The molecular weight of nitrogen; h is Planck's constant (6.62607015 × 10⁻⁶). -34 J·s or 4.1356676969×10 -15 eV·s); k is the Boltzmann constant (1.380649 × 10⁻⁶). -23 J / K); The decomposition energy of nitrogen molecules is 9.760 eV. T represents the plasma temperature.

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