The influence of butt welding flange process factors on weld formation

Groove size and gap size, the inclination 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 gap

　　When using arc welding to weld butt joints, it is usually based on the thickness of the welded plate to determine whether to reserve a gap, the size of the gap, and the form of the groove. Under certain other conditions, the larger the size of the groove or the gap, the smaller the reinforcement of the welded seam, which is equivalent to the decrease of the weld position, and the fusion ratio decreases at this time. Therefore, leaving a gap or opening a groove can be used to control the size of the excess height and adjust the fusion ratio. Compared with opening groove without leaving gap, the heat dissipation conditions of the two are somewhat different. Generally speaking, the crystallization condition of opening groove is more favorable.

　　2, electrode (welding wire) inclination

　　 In butt welding flange arc welding, according to the relationship between the electrode tilt direction and the welding direction, there are two types of electrode forward tilt and electrode backward tilt. When the welding wire is tilted, the arc axis is also tilted accordingly. When the welding wire is tilted forward, the effect of the arc force on the backward discharge of the molten pool metal is weakened, the liquid metal layer at the bottom of the molten pool thickens, the penetration depth decreases, the depth of arc penetration into the butt welding flange decreases, and the arc spot movement range expands. The melting width increases and the residual height decreases. The smaller the forward angle α of the welding wire, the more obvious this effect. When the wire is tilted backward, the situation is reversed. When electrode arc welding, the electrode backward tilt method is mostly used, and the tilt angle α is between 65° and 80°.

　3, butt welding flange inclination

　　 Butt welding flange tilt is often encountered in actual production, and can be divided into upslope welding and downslope welding. At this time, the molten pool metal has a tendency to flow down the slope under the action of gravity. When uphill welding, gravity helps the molten pool metal to discharge to the end of the molten pool, so the penetration depth is large, the melting width is narrow, and the excess height is large. When the upslope angle α is 6°～12°, the residual height is too large, and undercuts are easily generated on both sides. When downhill welding, this effect prevents the molten pool metal from discharging to the end of the molten pool, and the arc cannot go deep to heat the metal at the bottom of the molten pool. The penetration depth decreases, the arc spot movement range expands, the melting width increases, and the residual height decreases. Excessive inclination of the weldment will result in insufficient penetration and overflow of liquid metal in the molten pool.

　　4, butt welding flange material and thickness

　　 Butt weld flange weld penetration is related to welding current, and also related to the thermal conductivity and volumetric heat capacity of the material. The better the thermal conductivity of the material and the larger the volumetric heat capacity, the more heat is required to melt a unit volume of metal and increase the same temperature. Therefore, under certain conditions such as welding current, the penetration depth and penetration width Just reduce. The greater the density of the material or the viscosity of the liquid, the more difficult it is for the arc to displace the metal in the liquid bath and the shallower the penetration. The thickness of the butt welding flange affects the heat conduction inside the welding flange. When other conditions are the same, the thickness of the weldment increases, the heat dissipation increases, and the melting width and penetration depth are reduced.

　　5, flux, electrode coating and shielding gas

　　The composition of the flux or electrode coating is different, resulting in the difference in the voltage drop of the arc pole area and the potential gradient of the arc column, which will inevitably affect the 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 spot moves in a large range, so the penetration depth is small, the melting width is larger, and the excess height is small. When welding thick parts with high-power arc welding, the use of pumice-like 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 makes the slag poorly breathable, and it is easy to form many pressure pits on the weld surface, and the weld surface shape becomes poor.

The composition of the shielding gas for arc welding (such as Ar, He, N2, CO2) is different, and its thermal conductivity and other physical properties are different, so that the polar region voltage drop of the arc and the potential gradient of the arc column, the conductive section of the arc column, and the plasma flow force , Specific heat flow distribution, etc., all of which affect the formation of the weld.

In short, there are many factors that affect the formation of the weld of the butt welding flange. To obtain a good weld formation, it is necessary to determine the performance of the joint and the weld according to the material and thickness of the butt welding flange, the spatial position of the weld, the joint form, and the working conditions. The size requirements and so on to choose the appropriate welding method and welding conditions for welding. Otherwise, the weld formation and performance may not meet the requirements, and even various welding defects may appear.