When welding butt joints with arc welding, it is usually determined whether to reserve gaps, the size of gaps, and the form of grooves to be made based on the thickness of the welding plate. When other conditions are constant, the larger the size of the groove or gap, the smaller the residual height of the welded seam, which is equivalent to a decrease in the position of the weld seam, and at this time, the fusion ratio decreases. Therefore, leaving gaps or opening grooves can be used to control the size of the excess height and adjust the fusion ratio. Compared with leaving a gap and opening a groove without a gap, the heat dissipation conditions of the two are slightly different. Generally speaking, the crystallization conditions of opening a groove are more favorable.
When the welding wire tilts forward, the effect of the arc force on the backward discharge of the molten pool metal weakens, the liquid metal layer at the bottom of the molten pool becomes thicker, the melting depth decreases, the depth of the arc penetrating the welding flange decreases, the range of arc spot movement expands, the melting width increases, and the residual height decreases. The smaller the forward tilt angle α of the welding wire, the more pronounced this effect becomes. When the welding wire tilts backwards, the situation is the opposite. When welding with welding rods, the electric backward tilt method is often used, with a tilt angle α between 65 ° and 80 °.