| Vacuum metallurgy is an important technique for metal smelting and manufacture. It can be used for the production of die steels, bearing steels, rare metals and high performance special alloys. Composition analysis is an indispensable step in vacuum metallurgy. The most widely used composition analysis methods are off-line, which need taking sample under vacuum, delivering sample to the laboratory, performing sample treatment and then analyzing the composition. The procedure has complicated operation and poor real-time capability, and can hardly satisfy the need of high-efficiency and accurate composition control in modern metallurgy. Online rapid component detection can help realizing the precise composition control and metallurgic process automation. Besides, shortening the measurement time can reduce the energy consumption. So it is important to develop the technique that is in-situ, online and rapid quantitative analysis for the metallurgy industry.Laser induced plasma spectroscopy (LIPS) is a typical emission spectrometric analysis method. Compared with other techniques used in metallurgical analysis, the method has several key advantages:no sample pretreatment, remote measurement and rapid multi-element quantitative analysis.The paper focuses on the research of the rapid quantitative analytical methods based on LIPS, as well as the design and improvement of the relevant systems of LIPS equipment, which is applied for online composition analysis of molten metals under vacuum. The main results are summarized as follows:1. An experimental LIPS system for online component detection of the molten metal under vacuum was designed and built. The system can simulate the general industrial conditions with high-temperature and different pressure from atmosphere to vacuum. It provides us a tool which can perform LIPS experiment of molten metals under vacuum. The system was installed and tested, and the results indicated that the vacuum of the system can reach1×10-4Pa without heating, and the heating temperature could be about1600℃The system can be used for LIPS experiments with melting metal samples such as steel and aluminum, etc. Utilizing this system, LIPS experiments have been conducted using standard steel samples under different vacuum or high-temperature conditions. Comparison between LIPS spectra of solid steel samples under different vacuum were achieved, and so were the spectra of molten and solid steel samples under vacuum environment. The experiments proved that the system functions well and is ready for LIPS measurement with molten metal under vacuum environment. The software for LIPS system control and LIPS spectra pre-process were developed simultaneously, which laid the foundation of the rapid quantitative analysis.2. A multi-line internal standard calibration (MLISC) method based on internal standard calibration method was proposed. The method uses multiple analytical and reference lines to construct the calibration model. The proposed method can reduce the matrix effect and the signal fluctuations in the experimental process. The results show that the method has improved the stability and accuracy of the calibration model. A method used to automatically select the best analytical lines and reference lines for calibration model construction was proposed as well. This method can eliminate the errors during the spectral lines selection process. It can quickly find the best analytical and reference lines among thousands of spectral signal. Combining MLISC method with the automatic spectral line selection process, we can improve the efficiency and accuracy of the LIPS quantitative analysis process. LIPS experiments were performed with solid steels in air and molten steels under vacuum, and the quantitative analysis was conducted with the MLISC method and the automatic selection process. Elements such as C, Cr, Cu, Mn, Ni, P, S, and Si in the samples were detected and the corresponding calibration models were obtained. The results proved the reliability of the MLISC method and automatic spectral line selection process, and the feasibility of LIPS application in composition analysis of molten steel under vacuum was verified.3. The laser source and the optical system used for laser focusing and spectral signal collection were improved. Due to the harsh metallurgy field environment condition, we modified the laser source and the optical system in order to obtain better plasma spectral signals. The technique to generate multiple laser pulse with a single laser is realized by using multiple high-voltage pulse to trigger the Q-switched crystal of the laser. The number of pulses and the delay time between each laser pulse are adjustable. Experiments with solid steels using the modified laser system were performed, and the results showed that the multi-pulse LIPS can improve the spectral signal intensity and the detection limit. The auto-focus remote detection optical system was modified in order to apply in vacuum metallurgy. The modified Schwarzschild telescope system is more compact, efficient and convenient to connect to furnace. Meanwhile, a technical solution for in-situ LIPS system application in vacuum metallurgy was proposed. The solution combined mechanical shutter and gate valve with LIPS system, and brought them into sequential control. The solution realized physical isolation from high-temperature radiation and dust pollution with precise timing control. In this way, the limitation of the spectral range from the protection windows is eliminated, and the spectral transmission efficiency and the spectral range avaliable are improved. |
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