| Metal surface cleaning is the precondition and preparation process for modern industry production, and the proper choice of cleaning technology is valuable for improving the quality and performance of metallic products. The atmospheric plasma jet cleaning is an emerging cleaning technology and has received tremendous attention in recent years. Compared with traditional cleaning technology, the atmospheric plasma jet cleaning has many advantages such as high efficiency and environmental protection. Besides, compared with other atmospheric plasma cleaning technologies, the atmospheric plasma jet cleaning is the spatial separation of their generation from their cleaning regions, with many advantages such as simple operation, low cost and excellent controllability. Therefore, the atmospheric plasma jet has extensive developing space and a wonderful prospect in the field of oil cleaning.Considering the requirement of large-scale industrial production, it is necessary for the atmospheric plasma jet cleaning to be quantitatively calculated and to be improved by adjusting the discharge parameters. The theory and technology research in the atmospheric plasma jet cleaning have important theoretical and practical significances. Accordingly, this paper carries out the following studies:1. Atmospheric pressure Ar and O2/Ar plasma jets are generated in a discharge device with single quartz tube powered by double high voltage to remove lubricant on the surface of metal. A study of optimization of plasma jet parameters (the input power, the electron density, the oxygen atom concentration, the excitation electron temperature and gas temperature) by changing the power frequency is carried out, upon which the improvement of cleaning effect is investigated. The results show that the power frequency has the influence to the plasma parameters, and, the variation of plasma jet parameters with the power frequency is also influenced by length of discharging area. The plasma parameters increase as the power frequency increases from 17 kHz to 35 kHz, howerver, when the length of discharging area changed, the increasing trend of plasma jet parameters with the power frequency is somewhat different when the length of discharging area changes.. When the length of discharging area is 6 cm, and the power frequency increases from 17 kHz to 23 kHz, there is a steady increase of plasma jet parameters. While once the power frequency exceeds a certain value of about 23 kHz, the discharge becomes intense abruptly and the corresponding plasma jet parameters increase drastically with the power frequency. When the power frequency further increases to 35 kHz, the corresponding plasma jet parameters continue maintaining a steady growth. The above results show that, there is a critical frequency about 23 kHz for plasma jet parameters. While when the length of discharging area is 10 cm, with the power frequency increasing from 17 kHz to 35 kHz, there is a steady increase of plasma jet parameters without critical frequency. Furthermore, when the power frequency is fixed, compared with the discharging area lengh of 6 cm, the plasma jet parameters are higher for the discharging area length of 10 cm compared with the discharging area length of 6 cm. The contact angle and lubricant removal percentage are performed to assess the effect of plasma jet cleaning as a function of power frequency. The results show that the effects of cleaning are not only influenced by the power frequency, but also by the length of discharging area. When the length of discharging area is 6 cm, with the power frequency increasing from 17 kHz to 23 kHz, there is a steady decline of the contact angle and a steady increase of lubricant removal percentage. While once the power frequency exceeds a certain value of about 23 kHz, there are also sudden changes in the contact angle and lubricant removal percentage, which means that there is also a critical frequency for plasma jet cleaning when the length of discharging area is 6 cm, in this case, about 23 kHz. However, when the length of discharging area is 10 cm, with the power frequency increasing from 17 kHz to 35 kHz, there is a steady decline of the contact angle and a steady increase of lubricant removal percentage, while there is no critical frequency, and furthermore, when the power frequency is fixed, compared with the discharging length of 6 cm, the effect of cleaning is better for the discharging length of 10 cm. This study suggests that the match between the power frequency and the discharging area length have a great influence on the effect of cleaning, which provides a foundation for further optimize the design of discharge device.2. Atmospheric pressure O2/Ar plasma jet genenrated in a discharge device with two quartz tube powered by double high voltage with a metal as ground electrode is studied, and the improvement of cleaning effect by changing the oxygen mixing ratio is investigated. The results show that there is an optimum mixture ratio in the cleaning process. At the optimum mixture ratio, the electron density and oxygen atom concentration achieve their peak value, and furthermore, the cleaning effect has been improved greatly. While once the mixture ratio exceeds optimum value and further increases, the electron density and oxygen atom concentration no longer increases, and the cleaning effect no longer continuously improved. Therefore, the electron density and oxygen atom concentration play vital roles in plasma jet cleaning, and when using oxygen to improve the effect of cleaning, the optimal oxygen mixing ratio must be analyzed.3. Basing on this discharge device with two quartz tube powered by double high voltage, a new discharge device with outer quartz tube as ground electrode is designed, which is no limit to the shape and volumn of the surface. At different oxygen mixing ratios and input powers, atmospheric pressure O2/He and O2/Ar plasma jets are generated in this discharge device to remove lubricant on the surface of metal and a comparative study of their effects on the lubricant removal are carried out. The results show that at the constant oxygen mixing ratio and input power, the electron density and oxygen atom concentration are higher in O2/Ar plasma jet than in 02/He, and furthermore, the effect of cleaning is better for O2/Ar plasma jet, therefore, O2/Ar plasma jet is preferable to the contaminations removal. In addition, the results also show that with the input power increasing, except that the cleaning effects of 02/He and O2/Ar plasma jets are improved, the optimum oxygen mixture ratio also increase. It implies that increasing input power permit more oxygen molecules to participate in discharge, so that more oxygen atoms can be generated that further assist in improving the plasma jet cleaning performance. The effect on the lubricant removal is also studied at different discharge voltage and gas flux rate. The results show that the effect of cleaning is improved obviously with discharge voltage increasing, while the gas flux rate is inversely proportional to the effect of cleaning, that is, the effect of cleaning cannot be improved effectively. These results further improve the parameters affecting the effect of cleaning, which provides a possible route to precise control of plasma jet cleaning.4. On basis of reactive dynamics equation combined with Arrhenius law, the parameters (pre-exponential factor and activation energy) of the reactive dynamics equations for the three plasma jet devices are obtained, and then the reactive dynamics equations for the three plasma jet devices are established for calculating the lubricant removal percentage at any cleaning time. Moreover, the accuracy of three reactive dynamics equations is verified by experiment, which shows that the theoretical value coincides with experimental value. From the comparative study of the three reactive dynamics equations, it can be found that in the discharge device with two quartz tube powered by double high voltage with a metal as ground electrode, rate of lubricant removal is fastest, in the discharge device with two quartz tube powered by double high voltage with outer quartz tube as ground electrode second, and in the discharge device with single quartz tube powered by double high voltage slowest. The three reactive dynamics equations provide theoretical backgrounds and good quantum method for quantitatively control in the surface cleaning process for modern industry production. |
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