Research On The Welding Operation Performance Of Self-shielded Flux Cored Arc Welding For Steel Constructions

Self-shielded flux-cored wires are the most attractive new welding materials with the fastest developing speed in recent years. In order to improve the welding operation performance of Self-shielded flux cored wire, the paper has modified the present flux-core system and developed a new flux-core system for self-shield flux cored wire, i.e. CaF₂-Al₂O₃-MgO-CaO slag system. The paper has carried on systematic research and discussion around fluoride and aluminium magnesium alloy's influences on pore sensitivity droplet, transfer formations, welding arc stability, slag covering ability and detachability of the self-shield flux cored wires.The effects of core components of drugs and welding parameters to sensitivity of weld porosity were investigated by stomatal sensitivity test. The result showed that when the fluoride(CaF₂, Na2SiF6) in the flux-cored is about 42%⁵4%, Al-Mg is more than 16%;welding current is between 220A²80A,arc voltage is between 20V²6V,the sensitivity of weld porosity is lower.The effects of flux-core system composition on droplet transfer formations of flux cored wires and welding spatter were investigated by high-speed photography, by collecting droplets in a water through and test of spatter. The result showed that when the content of Al-Mg alloy is less than 18%, The droplet transfer was steady with relatively small molten droplets and welding spatter was smaller too. Replacing a part of CaF₂ with Na2SiF6 could reduce welding spatter with thinning molten drops. But when the Na2SiF6 was more than 5%, it would increase the welding spatter.The arc voltage and welding current was recorded synchronous with DEWE-TRANS, and then the arc voltage and welding electric current oscillogram were produced according these data. At the same time, the electric arc shape could be observed through the high-speed photography. The effects of flux-core system composition on welding arc stability of the flux cored wire were therefore studied. The results showed that when CaF₂ was about 40%⁴5%, Na2SiF6 was 3%⁵%, Al-Mg alloy was less than 18%, the welding arc stability was well.The paper has investigated the flux-core system composition influences on slag covering ability by slag covering ability evaluating and slag detachability testing.The results showed that the melting point of molten slag and changes in surface tension influence the slag covering ability. When CaF₂ was about 50%, Al-Mg alloy was 14%¹8%, the slag was covered well. In addition, it was benefit for slag detachability when the structure of slag was dense, high density, small coefficient of linear expansion and the weld was thorough deoxidation and contrariwise, the slag detachability became worse.Finally, the paper has acquired the composition for the self-shielded flux cored wire with favorable welding operation performance, i.e.CaF₂ was (45%⁴7%), Na₂SiF₆ was (5%⁷%), Al-Mg was (16%¹8%).