Study Of Radiative Properties:Application To Arc Diagnostics And Photobiological Hazard Assessment For Welding Arc

Radiation is a remarkable feature of welding arc plasma.The radiation carries some information of the arc,such as temperature and species,hence it is possible to diagnose the arc from the radiation.Also,the radiation has strong photobiological effect and can cause serious hazards to welders'eyes and faces.Based on the study of the radiation of welding arc plasma,this thesis focuses on the diagnostics of MAG?metal active gas?arc and the photobiological hazard assessment for GTAW?gas tungsten arc welding?arc.The diagnostics of metal active gas?MAG?welding arc has been a major stumbling block in the filed of welding arc physics.There are two questions in arc diagnostics:a.it is hard to measure the MAG arc due to the fact that the arc is unsteady during welding process;b.The radiation of MAG arc is affected not only by arc temperature but also by the species,especially the metal vapour concentration,because that the MAG welding usually uses gas mixtures?e.g.82%Ar-18%CO₂?as shielding gas and that the metal vapour evaporated from the surface of welding wire and weld pool will enter the arc.As a consequence,there is no effective diagnostic method for the MAG arc.Arc temperature and metal vapour concentration are two most impotant parameters for the diagnostics of the MAG arc.Since all the plasma properties,including thermophysical properties,and transport and radiative properties,depend on these two paramters,it is possible to deduce the mass,electricity and heat transfer in the arc.If the boundary between the arc and the workpiece is well treated,the heat flux into the workpiece can be determined.All of these are of great significance for improving the understanding of the MAG arc.This method has also been validated for a layer of plasma by adopting other existing diagnostics such as Stark broadening,which demonstrates the effectiveness and superiority of this new method.The radiation of UV?180-400 nm?,UVA?315-400 nm?and blue light?300-700 nm?regions emited by welding arcs has received much attention in recent years due to its photobiological hazards on welders'eyes and faces.However,although there are some experimental studies on the effective irradiances for welding arcs,little attention has been paied to the theoretical investigation of these radiations.In this thesis,the radiative properties of argon plasma are calculated for the three spectral regions,and a two-dimensional model of an argon GTAW arc is then developed to determine the local emissions in the arc,the total radiation escaping from the arc and corresponding effective irradiances.Finally,the photobiological hazards posed by the GTAW arc is evaluated by the exposure standard of Directive 2006/25/EC.This study clearly supports the importance of undertaking an effective protection strategy for workers.