Flux Strips Development And Processing Experiments Of Ultra-narrow Gap Welding

Ultra-narrow gap welding is an important welding technique and has good prospects for industrial applications. Not only does it have high production efficiency in the manufacture, but also it has the merits of lower residual stress and distortion, and superior mechanical properties of welded joint. Arc constrained by flux strips can improve the fusion of sidewalls, especially gap roots in ultra-narrow gap welding. For the purposes of achieving UNGW,the paper bases on the thought of flux strips development, the effect of the welding voltage and the flux strips thickness on the weld profile and processing experiments to investigate UNGW.Firstly, in order to produce the flux strips, an arch form rolling mould was designed. This mould basically has the following advantages. On one hand, it can fix wire gauze in working face so as to smear flux; on the other hand, it can basically control the thickness of flux strips. Main influence factors of producing flux strips are the mesh number of wire gauze, the concentration of silica sol, the flux size, the roller extrusion force and the thickness of black tape on steel belt.Secondly, in the ultra-narrow gap welding, interaction between arc and flux strip have direct effects on the stability of the welding process and weld formation. By changing the flux strip thickness and welding voltage, a series of experiments for the ultra-narrow gap welding were conducted, with I-groove width of 4mm, and the cross sections of weld profile were analyzed. The results show that the weld profile should be good if the flux strip thickness exceeds 0.566mm with appropriate welding voltage. The thicker flux strip could get the better weld profile, and a larger welding voltage range could be selected. It was indicated that constraining arc could be improved by increasing the welding voltage and the flux strip thickness, and then heating effect of arc to the sidewall root was increased.Finally, with 4mm wide square groove of the 30mm thick steel plate, a series of multi-layer and single-pass ultra-narrow gap welding experiments were conducted. The welded joint was completed by root welding and filling welding and cover welding, their welding parameters were obtained from the experimental analysis. The energy input of this processing was low and about 0.6k J/mm. The width of heat-affected zone of welded joint was narrow and about 1.3mm. Using H08Mn2Si wire of carbon-dioxide arc welding, the hardness in weld bead could increase about 60% by adopting ultra-narrow gap welding compared with that of adopting carbon-dioxide arc welding.