| Welding arc is the carrier of electrical energy transfer to thermal energy, the characteristics of welding arc will have an important impact on the welding quality. TIG arc is the primary object for studying the arc physics properties because of its strong representation and well applicability. Proper shielding gas could improve efficient and saving cost, mixed shielding gas is widely used in TIG welding. Whereas the traditional research of TIG welding physical property is mainly about measurement of single component arc plasma which is shielded only by pure argon. For mixed shielding gas, because of demixing, it should be treated as multi component arc plasma, the measurement method and experimental system should be improved. There are seldom research on the physical property of multi component arc plasma, and no report on dynamic measurement of multi component arc plasma. In this thesis, the measurement principle of two component arc plasma and double CCD arc image acquisition experimental system were researched for P-TIG welding arc plasma, which solved dynamic measurement problem of physical property for multi component arc plasma.Temperature is a very important parameter of physical characteristic for welding arc plasma. In order to use Fowler-Milne method dynamically measure the physical characteristic of welding arc plasma, the arc image acquisition system was designed and constructed for pure argon arc plasma. Through the study of single component P-TIG welding arc plasma, it indicates that when the frequency is less than 500 Hz, the physical characteristic either in peak period or base period does not change significantly with frequency. The intensity and temperature change periodically with time, and also synchronized with current. During peak current(200A) period, the arc center temperature reached to 20000 K, while, the arc center temperature reached to 18000 K during base current(100A) period. In the transition process between peak current and base current, the time for arc plasma reaches to stable status is less than 1ms. This study laid a good foundation for the measurement of multi component arc plasma and the extension of experimental system.Based on the single component Fowler-Milne method, through the principle and theoretical analysis of two element two component Fowler-Milne method, the experimental system was designed and constructed for the measurement of two components arc plasma physical property. The arc image synchronous acquisition experimental system was proposed which consists of double CCD and narrow band pass filter, this experimental system realized synchronous obtain arc image information with two group spectrums. It also has high time and spatial resolution to obtain dynamic measurement of two component arc plasma physical characteristic. 80%Ar+20%N2 which is commonly used in copper welding was used to study the two components DC-TIG welding arc plasma. Demixing phenomenon is appeared in argon-nitrogen arc plasma, the argon composition is lower than original value in the arc center, and then it elevated to higher than the original composition, finally, the argon composition tend to be equal to original value at the edge of arc plasma. This is caused by the process of N2 dissociation which needs more energy, nitrogen is accumulated to the arc center where both has high temperature and high energy. Through the study of two component Ar-N P-TIG welding arc plasma, it indicates that the intensity, temperature and argon composition change periodically with time, and also synchronized with current. During peak current period, both the intensity of Ar I and NI increase as the distance is away from the cathode, which is associated with temperature and arc diameter. During base current period, the intensity of Ar I and NI are low, and its change is not obvious. Since arc energy increases with current, temperature in peak period is higher than that in base period, the arc center temperature reached to 21000 K in 200 A peak current period, while, the arc center temperature reached to 16500 K during 100 A base current period. In the arc axis positions, argon composition is lower than original composition of shielding gas, N2 dissociated at high temperature area, so argon composition in peak period is lower than that in base period, and demixing phenomenon is more clear in peak period. In the arc center, argon composition reaches 55% during 200 A peak current period, it reaches 65% during 100 A base current period. This realized the experimental measurement in dynamic physical features for two component P-TIG welding arc plasma.Based on the two element two component Fowler-Milne method, measuring principle of single element two component Fowler-Milne method is proposed. This is a new method which use the atomic spectrum and ion spectrum of the same element to measure the temperature and argon composition of two component welding arc plasma, and breaks out the limitation of traditional Fowler-Milne method which demands the temperature must be higher than the normal temperature. Through calculate and compare the theoretical error of single element two component Fowler-Milne method, two line intensity correlation method and Boltzmann method, the error formula were deduced, the error range is calculated, the error distribution and its influencing factor is analyzed. 50%Ar+50%He which is commonly used in stainless steel welding was used to study the two component DC-TIG welding arc plasma. The result of temperature and mole fraction of argon distribution shows that the temperature reaches to 21500 K in the arc center, and the argon composition is lower than 50%. This is caused by temperature gradient and particle collision which increases the helium concentration in high temperature area. Through the study of two component Ar-He P-TIG welding arc plasma, it indicates that the intensity, temperature and argon composition change periodically with time, and also synchronized with current. Because of demixing phenomenon, Ar I intensity in peak period is higher than that in base period, and Ar II intensity has the similar distribution due to its normal temperature is higher than arc temperature. Since arc energy increases with current, temperature in peak period is higher than that in base period, during 200 A peak current period, the arc center temperature reached to 21500 K, while, the arc center temperature reached to 19000 K during 150 A base current period. In the arc axis positions, argon composition is lower than original composition of shielding gas, helium tend to gather at high temperature area since its high ionization energy, so demixing phenomenon is more clear in peak period. In the arc center, argon composition reaches 20% during peak current(200A) period, it reaches 30% during base current(150A) period. |
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