The size of the groove and the size of the gap, the Angle of the electrode and the butt welding flange, and the spatial position of the joint can also affect the weld formation and weld size.
1, groove and clearance
When welding butt joints with electric arc welding, it is usually determined whether the gap is reserved, the size of the gap and the form of the groove according to the thickness of the welding plate. When other conditions are certain, the larger the size of the groove or gap, the smaller the residual height of the welded seam, which is equivalent to the position of the weld decreases, and the fusion ratio decreases at this time. Therefore, the gap or groove can be used to control the size of the residual height and adjust the fusion ratio. Compared with the open groove with no gap, the heat dissipation conditions of the two are somewhat different, and the crystallization conditions of the open groove are generally more favorable.
2, electrode (wire) Angle
When welding flange, according to the relationship between the electrode tilt direction and the welding direction, it is divided into two kinds of electrode forward tilt and electrode backward tilt. When the welding wire is tilted, the arc axis is tilted accordingly. When the welding wire is tilted forward, the effect of arc force on the backward discharge of molten pool metal is weakened, the liquid metal layer at the bottom of the molten pool becomes thicker, the penetration depth decreases, the arc diving depth decreases, the arc spot moving range expands, the melting width increases, and the residual height decreases. The smaller the α Angle of wire forward tilt is, the more obvious the effect is. When the wire is tilted back, the opposite is true. When the electrode arc welding, the electrode backward tilt method is used, and the inclination Angle α is between 65° and 80°.
Butt welded flange
3, butt welding flange Angle
Butt welding flange tilt is often encountered in actual production, can be divided into uphill welding and downhill welding. At this time, the molten pool metal has a tendency to flow down the slope under the action of gravity. In upslope welding, gravity helps the molten pool metal to flow towards the end of the molten pool, so the melting depth is large, the melting width is narrow, and the residual is tall. When the slope Angle α is 6° ~ 12°, the residual height is too large, and the two sides are easy to produce biting edges. In downslope welding, this effect prevents the molten pool metal from discharging to the end of the molten pool, and the arc cannot penetrate into the metal at the bottom of the molten pool, so the melting depth decreases, the arc spot moving range expands, the melting width increases, and the residual height decreases. Excessive inclination of weldment will lead to insufficient penetration and liquid metal overflow of molten pool.
4, butt welding flange material and thickness
The weld penetration of butt welded flange is related to welding current, thermal conductivity and volumetric heat capacity of the material. The better the thermal conductivity of the material and the greater the volume heat capacity, the more heat is required to melt the unit volume of the metal and raise the same temperature, so under certain conditions such as welding current, the depth and width of the melting will be reduced. The higher the density of the material or the viscosity of the liquid, the more difficult it is for the arc to displace the metal of the liquid molten pool, and the shallower the melting depth. The thickness of the welded flange affects the heat conduction inside the welded flange. When other conditions are the same, the thickness of the welded part increases, the heat dissipation increases, and the melting width and depth decrease.
5. Flux, electrode cover and protective gas
Different composition of flux or electrode cover leads to different electrode pressure drop and arc column potential gradient, which will inevitably affect weld formation. When the flux density is small, the particle size is large or the accumulation height is small, the pressure around the arc is low, the arc column expands, and the arc spots move in a large range, so the melting depth is small, the melting width is large, and the remaining height is small. When welding thick parts with high power arc welding, pumice flux can reduce the arc pressure, reduce the penetration depth and increase the penetration width. In addition, the welding slag should have a suitable viscosity and melting temperature, too high viscosity or high melting temperature make the slag poor permeability, easy to form many pits on the weld surface, and the weld surface deformation is poor.
The composition of the protective gas used in arc welding (such as Ar, He, N2, CO2) is different, and its thermal conductivity and other physical properties are different, so that the electrode pressure drop of the arc and the arc column potential gradient, arc column conductive cross section, equal ion current force, specific heat flow distribution are different, which affect the formation of the weld.
In short, there are many factors affecting the weld formation of the welding flange, in order to obtain a good weld formation, it is necessary to select the appropriate welding method and welding conditions according to the material and thickness of the welding flange, the spatial position of the weld, the joint form, the working conditions of the joint performance and the requirements of the weld size. Otherwise, the weld formation and its performance may not meet the requirements, and even various welding defects may occur.
From: Chongqing Giant Pipe Fittings Co., LTD
