The molten pool refers to the part of the base metal that is melted into a pool due to the heat of the welding arc. The geometrical liquid metal part formed on the weldment during welding is called the molten pool. The temperature of the liquid metal in the molten pool is higher than that of ordinary molten steel. The temperature is much higher. The average temperature of the transitional droplets is about 2300°C, and the average temperature of the molten pool is about 1700°C, up to 2900°C. Therefore, the liquid metal in the molten pool is overheated.
In the welding operation, defects such as flash, burn-through, incomplete penetration, recession, slag inclusion, and poor forming often occur. The main reason for these defects is that they are not good at observing the changes in the temperature of the molten pool during the welding operation. The above defects are caused by the lack of control of the temperature of the molten pool. The temperature of the molten pool directly affects the welding quality. The temperature of the molten pool is high, the molten pool is larger, the molten iron has good fluidity, and is easy to fuse. The back side of welding double-sided forming is easy to burn through, forming flash, and the forming is difficult to control, the plasticity of the joint is reduced, and the bending is easy to crack. When the temperature of the molten pool is low, the molten pool is smaller, the molten iron is darker, and the fluidity is poor. Defects such as lack of penetration, lack of fusion, slag inclusion, etc. appear.
During welding, the current flowing back through the weldment is called the welding current. The diameter of the electrode refers to the cross-sectional size of the filler metal rod. In simple terms, the proper melting of the electrode is determined by the current passed. If the current is too small, it is difficult to draw Arc, the welding rod is easy to stick to the weldment, the scales are thick, and the two sides are not well integrated. If the current is too large, the welding spatter and smoke will be large, the welding rod will be red, the surface of the molten pool is very bright, easy to burn through, and undercut.
The current is suitable, easy to ignite and the arc is stable, the splash is small, the uniform crackling sound can be heard, the two sides of the welding seam transition to the base metal smoothly, the surface has fine scales, the welding slag is easy to knock, and in its application, There is a complicated relationship. In the vertical, horizontal, and upright positions, the current is correspondingly smaller than that of the flat welding, and usually should be about 10% less than the current of the flat welding. Also in the vertical, horizontal, and upright positions, the current of the electrode The diameter is usually smaller than in flat welding.
After the electrode is fed along the axis to the molten pool to melt the electrode, the arc length can remain unchanged. Therefore, the speed at which the electrode is fed into the molten pool is equal to the speed at which the electrode melts. If the speed at which the electrode is fed is less than the speed at which the electrode melts, the arc length will be reduced. The gradual increase will cause the arc to break. If the electrode is fed too fast, the arc length will be shortened rapidly, and the end of the electrode will be short-circuited in contact with the weldment, which will also extinguish the arc.
Crescent-shaped transport method: the end of the electrode swings left and right in the welding direction to form a crescent shape. The middle action should be fast, and the two sides should stay a little. This method can control the temperature of the molten pool. The molten pool is shallow. It is necessary to prevent undercut on both sides. , Crescent-shaped transporting strip is one of the main transporting methods of single-sided welding and double-sided forming continuous arc welding.
Zigzag moving method: the end of the electrode swings forward in a zigzag manner, and stops on both sides to prevent undercut. This method is simple to operate and is suitable for the welding of each layer of the butt weld in the flat, vertical and upward welding positions. The temperature of the molten pool of the shaped transport bar is higher than the temperature of the crescent-shaped transport bar, and the temperature of the crescent-shaped transport bar is higher than that of the zigzag transport bar. The zigzag-shaped transport bar is used, and the swing amplitude and the pause on both sides of the groove are used. , The temperature of the molten pool is controlled, the size of the molten hole is basically the same, and the probability of no weld formation and burn through at the root of the groove is reduced, and the lack of penetration is improved, so that the single-sided welding of butt flat welding can not form on both sides. Then there is the difficulty.
Welding rod angle:
When the welding rod is at a 90 degree angle to the welding direction, the arc is concentrated, the temperature of the molten pool is high, the angle is small, the arc is scattered, the temperature of the molten pool is low, the arc burning time, the arc burning time is used to control the temperature of the molten pool, if the temperature of the molten pool is Too high and large melting holes can reduce the arc burning time and lower the temperature of the molten pool. At this time, the melting holes become smaller and the internal forming height is moderate to avoid excessively high internal weld seams or weld bead formation in the pipe.
Tips: High-frequency straight seam resistance welded steel pipe(ERW pipe) is a hot-rolled coil that is formed by a forming machine and uses the skin effect and proximity effect of high-frequency current to heat and melt the edge of the tube blank. Pressure welding is carried out under the action of squeeze rollers to realize the products produced.