Influence of Metal Transfer Stability and Shielding Gas Composition on CO and CO sub(2) Emissions during Short-circuiting MIG/MAG Welding

Several studies have demonstrated the influence of parameters and shielding gas on metal transfer stability or on the generation of fumes in MIG/MAG welding, but little or nothing has been discussed regarding the emission of toxic and asphyxiating gases, particularly as it pertains to parameterization of the process. The purpose of this study was to analyze and evaluate the effect of manufacturing aspects of welding processes (short-circuit metal transfer stability and shielding gas composition) on the gas emission levels during MIG/MAG welding (occupational health and environmental aspects). Using mixtures of Argon with CO sub(2) and O sub(2) and maintaining the same average current and the same weld bead volume, short-circuit welding was performed with carbon steel welding wire in open (welder's breathing zone) and confined environments. The welding voltage was adjusted to gradually vary the transfer stability. It was found that the richer the composition of the shielding gas is in CO sub(2), the more CO and CO sub(2) are generated by the arc. However, unlike fume emission, voltage and transfer stability had no effect on the generation of these gases. It was also found that despite the large quantity of CO and CO sub(2) emitted by the arc, especially when using pure CO sub(2) shielding gas, there was no high level residual concentration of CO and CO sub(2) in or near the worker's breathing zone, even in confined work cells.Original Abstract: Varios estudos tem demonstrado a influencia dos parametros e protecao gasosa sobre a estabilidade de transferencia metalica ou sobre a geracao de fumos em soldagem MIG/MAG, mas pouco ou nada tem sido discutido sobre a emissao de gases toxicos e asfixiantes, particularmente no que tange a parametrizacao do processo. O objetivo deste estudo foi analisar e avaliar o efeito de aspectos operacionais dos processos de soldagem (estabilidade da transferencia metalica e composicao do gas de protecao) sobre os niveis de emissao gasosa de durante a soldagem MIG/MAG (aspectos ambientais e de saude ocupacional). Utilizando-se misturas de argonio com CO sub(2) e O sub(2) e mantendo-se a mesma corrente media e o mesmo volume de cordao de solda, soldagens com transferencia por curto-circuito foram realizadas com arame de aco carbono em ambientes aberto (zona de respiracao do soldador) e confinados. A tensao de soldagem foi ajustada gradualmente para modificar a estabilidade da transferencia. Verificou-se que quanto mais rica a compo