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The importance of convective heat transfer in the weld pool has been widely recognized in relation to the penetration shapes of base metal.The main causes that associate streaming in molten pool are the electro magnetic force, buoyancy force, surface tension and aero dynamic drag force. But, the mechanism of heat transfer has not yet been clarified well. Therefore, in this work, they have paid special attension on the importance of convectional heat transfer in the weld pool and the anode size or heat source size under the same heat input, or same current value. A finite difference method was employed to solve above-mentioned mechanism. The results obwere tained as follows.1) When arc length is short, the velocity field induced by outward surface shear strss consists of two flow loops of opposite directions in the molten pool, which lead to comparatively deep weld shape.2) In case of short arc length and positive temperature coefficient of surface tension, surface tension is predominant. Accordingly, penetration shape is deep.3) In case of long arc length aero dynamic drag force is predominant, which leads to the 'shallow' center and 'deep' peripheral penetration. |
