WELDING RESEARCH Optical and Spectroscopic Study of a Submerged Arc Welding Cavern A combination of highspeed imaging and spatically resolved spectroscopy at 5000 fps was performed on a submerged arc welding process using a thingauge steel tunnel BY G. GÖTT, A. GERICKE, K.-M. HENKEL, AND D. UHRLANDT DECEMBER 2016 / WELDING JOURNAL 491-s Introduction Submerged arc welding (SAW) is a widely used joining process in a great variety of industries. This includes shipbuilding, construction, and the energy sector with the production of pipelines, wind towers, and offshore foundations. While the fundamentals of the process have not changed, there have been improvements in filler materials and power source technologies. However, one basic characteristic of the process is the restricted observability of the wire, arc, and droplet behavior due to the flux covering the cavern and molten bath. This restricted observability affects the process from being well understood, compared to other arc welding processes gas metal arc welding (GMAW) and gas tungsten arc welding (GTAW). The complex chemical reactions leading to specified mechanical properties of the joint, which depend on the droplet transfer and parameters in SAW, have not yet been completely described. The understanding of these mechanisms would support the development of more sophisticated process varieties, as can be seen in other arc welding processes, because modern power sources are capable of a variety of different waveforms and current patterns. In this work, the processes inside the SAW cavern have been recorded at 5000 frames/s (fps). There are only a few preceding papers on high-speed imaging in SAW. Two kinds of approaches to achieve these images can be found in literature. Tybus (Ref. 1) used two-quartz-borosilicat windows on both sides of the process. By welding between those windows, highspeed images could be recorded to analyze the process from the side. This had a strong impact on the process, since it changed the shape of the cavern drastically. In addition, the images were of low quality due to the spatter and smoke residue adhering to the windows. The second approach can be found in the dissertation from Franz (Ref. 2). He used a ceramic tube that he positioned in front of the weld path. By welding over it, he could observe the process with less disturbance. The material of the tube was chosen to match the flux. In addition, he compensated for the loss of pressure inside the cavern by adding a shielding gas. This also kept the tube and the attached window clear of debris. Within these investiga- ABSTRACT For the first time, a combination of highspeed imaging and spatially resolved spectroscopy at 5000 fps was performed on a submerged arc welding process. This was achieved by inserting a thingauge steel tunnel into the flux and aligning the diagnostics accordingly. Four processes were observed; both direct current electrode positive (DCEP) and direct current electrode negative (DCEN), as well as alternating current (AC) at 600 A and DCEP with a higher current at 1000 A. The videos show an erratic droplet transfer with a lot of spatter that was caught by the cavern walls and directed into the weld pool. Additionally, flux was molten at the top of the cavern close to the electrode and merged into the droplet that was still attached to the wire. The cavern walls were a mixture of solid flux that was partially falling into the weld pool and molten flux, which created a smooth wall. The surface properties of the cavern wall behind the process was mostly smooth and merged with the weld pool, which created a solidifying layer of slag on top of the slowly cooling weld joint. The observed processes showed only a slight change in chemical composition of main alloying elements in the solidified weld joint, while the oxygen content varied significantly in the droplet stage and weld joint between the processes. The highspeed images indicated a correlation between dropletflux interaction and oxygen content. The spatially resolved spectra showed intense selfreversed lines of Na, Ca, and Mn. Fe lines suggested that the arc was also dominated by metal vapor. Especially during the AC process, a fluctuating emission of Mn lines was observed, which correlated with the frequency of the shifting polarity. KEYWORDS • Submerged Arc Welding (SAW) • HighSpeed Video • Metal Transfer • Cavern • Spectroscopy • Droplet • Flux • Oxygen Content G. GÖTT (g.goett@inpgreifswald. de) and D. UHRLANDT are with the Leibniz Institute for Plasma and Technology, Greifswald, Germany. A. GERICKE and K.M. HENKEL are with Fraunhofer Application Center Large Structures in Production Engineering, Rostock, Germany.
Welding Journal | December 2016
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