WELDING RESEARCH DECEMBER 2016 / WELDING JOURNAL 495-s Fig. 7 — Side view shows the flux falling on the righthand side (Ref. 16, SOM5). The inner cavern surface consists of solid flux grains, molten slag, and solid particles merging into a molten stage (Ref. 16, SOM5). Within a short time of exposure to the heat source, the surface of the flux grains starts melting with visible outgassing or even boiling on the surface. The overexposed region at the center is the arc with the hot wire tip. The emitted light illuminates the whole cavern. The arc contains mostly metal vapor and nonmetallic elements, like calcium (Ca), according to the recorded spectra. On the right-hand side in each frame, the front wall can be seen because this is a side view of the process. Flux grains in different sizes are falling through the cavern or along the cavern wall. These grains with a melting surface appear in the rear part of the cavern relative to welding direction as well, which is supposed to be the coldest part because of its maximum distance to the burning arc. The flux used was agglomerated and fluoride-basic. These fluxes typically start melting at around 1200°– 1400°C depending on chemical composition and the relation of mineral constituents (Refs. 17–19). There is the possibility of reactions and forming of different compounds or crystal phases before melting of the flux grains. One has to be aware that these compounds have different, usually lower, melting and solidification points compared to the separate components listed in Table 3 (Ref. 17). For a first approximation of the internal cavern temperature close to the surface, these effects were disregarded. Since the fusing process of the flux grains is visible in the high-speed images, the cavern surface must rapidly exceed the melting temperature of the flux. This is possible due to the temperatures of the arc and the liquid Table 3 — Main Chemical Composition of Used Welding Flux and Melting Temperature Tmelt (Values in wt% and C, respectively) Chem. Comp. SiO2 MnO MgO CaF2 Na2O Al2O3 CaO K2O TiO2 Metal Alloys CONCN in % 13 1 30 24 2 19 8 1 1 1 Tmelt in C 1713 1650 2852 1423 1275 2050 2575 ± 5 2575 ± 5 1855 –
Welding Journal | December 2016
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