The Research On The Technology Of Ultra-narrow Gap Welding With The Flux Strips Constricting Arc

Ultra-narrow gap welding(UNGW) has more prominent every merits than narrow gap welding(NGW). The researches indicate when the technology of UNGW is adopted, the HAZ softening phenomenon of fine-grained steel can be eliminated, the strength even-matched joint of fine-grained steel can be achieved. In time of welding steel piping with the technology of UNGW, it is possible of compressive stress around the entire circumference in root area of welds to be transformed into tensile stress, so the stress corrosion crack can be resolved completely. However, when UNGW is carrying out, arc can not work on maintaining the stability of arc by self-regulation in the metal arc welding and can climb up along the sidewalls from the bottom of gap because of excessive narrow gap. For the purposes of achiving UNGW, the paper bases on the thought of constricting arc to investigate UNGW in five aspects as follows.Firstly, the UNGW of constricting arc with flux bands is put forward by analysising the action of arc heating sidewalls. The formula of welding parameters matched to predict good welds and the range of voltage and current for good welds are gained by carrying out UNGW. Furthermore, softening of HAZ can be avoided when the UNGW is used to weld fine grained steel. At the same time, the experiment shows that the UNGW can't be applied in industrial manufacture , because the flux bands can be peeled off from sidewalls in time of cleaning up the slag. The UNGW of constricting arc with flux strips(UNGWFS) is brought forward, which is based on the principle of flux bands constricting arc. The corresponding welding torch of UNGW has been designed, the proper technology of producing flux strip has been developed by a series of experimrnts. Accordingly, all of this have established a foundation for the next study of the UNGW with flux strips constricting arc.Secondly, gas shielding experiments of UNGWFS is carried out. By the experiments and analysis, the result shows that bulky flat duct installed lateral of arc has the best shielding effect among three methods of gas shield because it can avoid welding torch is burned out and easing the turbulence of shielding gas, the other two kinds of gas shielding methods are gas spurted out downwards above the arc with thin flat duct and gas spurted out on both sides of arc with thin flat duct. The best flux of shielding gas under different section of duct has been gained with a designed instrument of gas shield.Thirdly, adopting surfacing welding on the plate and adjusting welding parameters to photograph the arc and measure constricting parameters, by which analysis the effect of arc heating flux strip and the change of action length of arc and flux strip(ACL). In addition, under different welding parameters measuring the width and length of arc, width and depth of welds, by which arc morphology and heating characteristic of arc are analysed. Thereby, theoretic gist can be provided to be convenient for understanding the mechanism of flux strips constricting arc. Moreover, the heating characteristic of flux strips constricting arc in Ultra-narrow gap has been analyzed.Fourthly, correlation between position of flux strip in its constricting arc and potential of flux strip has been analyzed by collecting the waveforms of flux strip and voltage. At the same time, the transfer modes of melted flux strips have been also analyzed. Furthermore, the waveforms of flux strip with good constriction and lack constriction have been analysed contrastively.Fifthly, UNGW with flux strips constricting arc is performed. The results shows that UUNGW welds with good fusion on sidewalls can be achieved with flux strips constricting arc. Positional conditions of flux strips in the arc zone that can ensure to constrict arc effectively have been obtained, by analyzing the influence of position of flux strips in the arc zone on constricting arc. Otherwise, the matching range of voltage and velocity of feeding flux strips has also been gained. At the same time, the experiment shows that short circuiting transfer mode is the proper transfer mode of drop, and the proper range of voltage and current in UNGWFS is 21-23 V and 240-260 A. At last, the heating characteristic of flux strips constricting arc in UNGW is studied by analyzing the influence of welding parameters such as voltage, current and velocity of feeding flux strips on the cross sectional sizes of welds. At last, the feasible analysis of UNGWFS applied in manufacture indicates that UNGWFS can be applied in manufacture.