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WELDING RESEARCH OCTOBER 2005-s156 ABSTRACT. A cascade impactor was em- ployed to separate the fume particles in order to det

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Content	WELDING RESEARCH OCTOBER 2005-s156 ABSTRACT. A cascade impactor was em- ployed to separate the fume particles in order to determine the size distribution of welding fume. Clear images of coarse welding fume particles (microspatter) from scanning electron microscopy are presented. The particle size distribution of the welding fume reveals that gas metal arc welding (GMAW) fume consists pre- dominately of particle agglomerates smaller than approximately one microme- ter. Less than 10% of the fume by weight is microspatter, which is larger than a mi- crometer. This fraction of microspatter does not change greatly as the GMAW pa- rameters are changed. Flux cored arc welding (FCAW) fume contains more mi- crospatter, approximately 30% by weight. Introduction Arc welding poses many hazards, in- cluding heat, noise, vibration, and elec- tricity. Radiation from the arc can cause eye and skin damage. Gases and res- pirable particles in the welding environ- ment contain chemicals that can create adverse side effects after inhalation, if de- livered in the appropriate dose and chem- ical state. A major source of respirable particles is welding fume. Aerosol scientists use the term “fume” to describe any airborne metal or metal oxide particles that condense from vapor (Ref. 1), which is indeed the case for most particles formed from welding. However, some airborne particles generated by welding are not formed from vapor con- densation, but from liquid droplet ejec- tion, and thus are not technically fume particles. Welding spatter is formed from liquid droplets and is for the most part too large to remain airborne; droplets small enough to remain airborne have been termed microspatter. The welding com- munity has traditionally labeled all air- borne particles formed during welding as “welding fume,” including microspatter, despite it not technically being fume. This naming convention is used here. Particles smaller than 20 µm in diame- ter can remain airborne (Ref. 2), but not all airborne particles are deposited the same way in the lungs, because airborne particles of different sizes behave differ- ently aerodynamically. Objects greater than a few micrometers in size are trapped on the walls of the human airway before they reach the lungs. They are carried away in the mucus, which is then trans- ported to the digestive tract. Particles smaller than 0.1 µm are inhaled and de- posited in the lungs. The path of entry into the body strongly affects the biological fate of the chemicals present in the in- haled particles. Particles or agglomerates between 0.1 and 1 µm can be exhaled, meaning that only about 30% of particles of this size eventually deposit in the lungs (Ref. 3). Therefore, it is important to mea- sure the size distribution of particles in order to ascertain the respirable fraction thereof. Zimmer and Biswas (Ref. 4) reported the results of using two different airborne particle counters with different size range capabilities to measure the particle size of gas metal arc welding (GMAW) fume. This provided a particle size distribution over all sizes of interest. Three modes of particle sizes can clearly be distinguished: a nucleation mode of individual particles from a few nanometers to ~0.1 µm, an accumulation mode (~0.1 to ~1 µm) of agglomerated, aggregated, and coalesced particles formed from the nucleation mode, and a coarse mode of unagglom- erated particles in the range of ~1 to ~20 µm. Particles in the nucleation mode form by vapor condensation. Because particles in the accumulation mode agglomerate from nucleation mode particles, vapor chemistry also controls accumulation par- ticle composition. The particles formed from nucleation are called primary parti- cles whenever found in fractal-like ag- glomerates or aggregates. Aggregates refer to clumps of primary particles that have fused together. Agglomerates are those particles made up of primary parti- cles that adhere together because of elec- trostatic or van der Waals forces. The nu- cleation and accumulation modes are therefore often grouped together as “fine particles,” which distinguishes them from the coarse mode particles created through liquid ejection (Ref. 5). Coarse particles, or microspatter, in welding fume have been reported earlier (Ref. 6). Because the median diameter of coarse particles is an order of magnitude larger than the median diameter of ag- glomerates (Ref. 2), coarse particles may presumably dominate the bulk chemistry of welding fume, even if these coarse par- ticles are few in number. There seems to be a correlation be- tween fume formation rate (FFR) and spatter formation rate. Some researchers (Refs. 6, 7) have proposed that the forma- tion of additional microspatter explains why processes that create more spatter, such as globular GMAW or flux cored arc welding, have greater fume formation rates. A comparison of the particle size distributions of various welding processes would yield insight into how welding fume forms, which would help determine which process controls are most effective in re- ducing fume formation. Several studies on the size of welding Particle Size Distribution of Gas Metal and Flux Cored Arc Welding Fumes Impactor separation of welding fumes shows at least two size modes, the relative magnitude of which is determined by the welding process BY N. T. JENKINS, W. M.–G. PIERCE, AND T. W. EAGAR KEYWORDS Airborne Particles Arc Welding Flux Cored Arc Welding Fumes Gas Metal Arc Welding Particulate Welding Fume N. T. JENKINS is with the College of Medicine, The Ohio State University, Columbus, Ohio. W. M.–G. PIERCE is with the College of Medicine, Drexel University, Philadelphia, Pa. T. W. EAGAR is with the Department of Materials Science and Engineering, Massachusetts Institute of Technol- ogy, Cambridge, Mass. %Jenkins-10=05corr 9/9/05 11:24 AM Page 156
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Following Datasheets	10-2005-POORHAYDARI-s (7 pages) 10-50TV_IPC-1752 (3 pages) 10-50TV_097_Rev_A (2 pages) 10-50TVC_IPC-1752 (3 pages) 10-50TVC_097_RevA (2 pages) 10-50TVC-S_IPC-1752 (1 pages) 10-50TVC-S_097_RevC (2 pages) 10-50TVR_IPC-1752 (3 pages) 10-50TVR_097_Rev_A (2 pages) 10-appc-11-hb133-final (10 pages)
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