Effects of electrode polarity on the droplet transfer mode in self-shielded flux-cored arc welding

Self-shielded flux-cored wires (AWS E71 T FCW) are widely applied in the fields of construction. In this study, the effect of the electrode polarity on the mode of droplet transfer and arc stability in self-shielded flux-cored arc welding was investigated by the high-speed video camera system and electric signal. The results showed that the change of electrode polarity determined different mode of droplet transfer. In direct current electrode positive (DCEP), droplet transfer mode presented the globular repelled transfer. And the area of the arc root decreased at the bottom of the droplet because of the metallurgical reaction effect of the flux core, it resulted in the relatively lager electromagnetic force acting on the droplet, which hindered the droplet transfer. Moreover, when the droplet was separated from the welding wire, the droplet was kept rotation state under the action of the resultant force couple. In the direct current electrode negative (DCEN), the electromagnetic force promoted the droplet transfer and droplet transfer mode shown spray transfer mode. Due to the particularity of the composition and distribution of the molten slag, the conductive path was generated easily at the connection between the droplet and the wire, it made the arc root climb up and wrap the droplet, the necking phenomenon appeared obviously. In DCEN or DCEP, arc voltage and arc current have little effect on the droplet transfer mode. At the same time, compared with the welding process in DCEP, the welding process in DCEN had the advantages of higher arc stability, fewer welding spatter.