TWI Industrial Member Report Summary 289/1985
By G J Carter
Fume emission rate and composition have been examined for a number of commercially available and experimental MMA electrodes using the Swedish Fume Box technique. Emphasis has been placed on rutile electrodes, although results for some basic and cellulosic electrodes are included. As far as possible, test parameters except coating composition were kept constant, thus making observed differences in emission rate and composition attributable to effects arising only from the coating. Work was divided into three phases. In Phase 1, commercial electrodes were used to examine the applicability of reported fume emission mechanisms to MMA welding, and for preliminary assessment of coating constituents affecting fume emission rate. Phase 2 examined fume emission rates from commercially available low fume electrodes, and compared them with their standard counterparts, whilst Phase 3 was conducted using experimental electrodes designed so that the effect of specific coating constituents on fume emission rate could be identified and quantified. From the results, fume emission rate was increased by coatings giving higher working arc voltage range. Compounds producing hydrogen in the arc atmosphere or containing sodium were found to increase fume emission rate significantly for rutile electrodes, but the effects of carbon dioxide, iron powder and potassium were less important. For many elements, a direct relationship existed between the quantity of an element in the coating and its concentration in the fume. Generally, more volatile elements concentrated into the fume.