10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Emission and Oxidative Potential of Particulates from Alternating Current Tungsten Inert Gas Welding on Aluminum
JUN WANG, Shalayne Sims, Jacob Bartels, Marcio Bezerra, University of Oklahoma
Abstract Number: 1521 Working Group: Workplace Aerosol
Abstract Welding process generates particulates and gaseous pollutants that are potentially hazardous to welders without adequate ventilation and respiratory protection. Past studies on welding were mainly focused on stainless steel and mild steel with constant feeding direct current (DC). Aluminum (Al) is a common lightweight material that can only be welded with tungsten inert gas (TIG) welding. Al metal plate usually has a tenacious oxide film on the surface that requires being removed through the use of alternating current (AC). AC is achieved through switching between electrode positive and electrode negative polarity at more than 50 cycles per minute. Currently, there is a knowledge gap in understanding the emission of particulates (mostly Al compounds) from Al-AC-TIG welding and their health implications. The scope of this study is to examine whether AC parameters have an effect on the production of particulate Al fume and their oxidative potentials. A conical welding chamber was used to collect metal fumes generated from an AC/DC TIG welder. Welding was performed on a 12×12 aluminum plate and 1/8th inch aluminum filler rods and tungsten electrode, under pure argon shielding gas. The TIG welder’s currents vary between 60 and 200 amps. A hurricane high-volume air sampler draws the fume through a 90 mm glass fiber filter. The fume collected on the filter was weighed, and then ultrasonically extracted through water and methanol. The extracts were dried overnight with pure nitrogen flow. The oxidative potentials of extracts were determined using ascorbic acid (AA) assay which showed good sensitivity to transition metal oxides. The rate of AA consumption was calculated using linear regression of the data from a plot of absorbance (265 nm) against concentration gradient/time. The results indicated AC mode can effectively reduce the emission of particulate fume by over 55% comparing to DC mode. Fume emission increased with higher welding currents, with the highest of 335.2 mg/min arc time at 200 A. The consumption of AA showed averaging of 0.2035 nmol of AA/µg of extracts, which is a strong indicator of OP from aluminum oxides. The latter results need to be verified with in-vitro cellular reactive oxygen species assays in future studies.