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High-frequency welding technology of submerged arc steel pipe
Date:2020-11-02      Views:244Time      Label:High-frequency welding technology of submerged arc steel pipe

1. Control of the weld gap: After rolling by multiple rollers, the strip steel is sent to the welded pipe unit. The strip steel is gradually rolled up to form a round tube blank with a tooth gap. Adjust the pressing amount of the squeeze roller to control the weld gap between 1 and 3 mm and make the weld ends flush. If the gap is too large, the proximity effect will be reduced, the eddy current is lacking, and the weld crystals will be directly connected poorly and unfused or cracked. If the gap is too small, the proximity effect will increase, the welding heat will be too large, and the weld will be burnt; perhaps the weld will form a deep pit after extrusion and rolling, which will affect the appearance of the weld.

 

2. Welding temperature control: According to the formula, the welding temperature is affected by the high-frequency eddy current heat power. The high-frequency eddy current heating power is affected by the current frequency, and the eddy current heating power is proportional to the square of the current encouragement frequency; and the current encouragement frequency is influenced by the encouraging voltage, current, capacitance, and inductance. Inductance = magnetic flux/current In the formula: f-encourage frequency (Hz-encourage the capacitance in the loop (F capacitance = electricity/voltage; L-encourage the inductance in the loop. The encouragement frequency is inversely proportional to the capacitance and the square root of the inductance in the encouragement loop). It may be proportional to the square root of voltage and current. Just change the capacitance, inductance, or voltage and current in the loop to change the size of the encouraging frequency, and then reach the goal of controlling the welding temperature. Regarding low carbon steel, the welding temperature is controlled at 1250~1460 ℃, it can meet the requirements of the pipe wall thickness of 3~5mm penetration. The welding temperature can also be adjusted by adjusting the welding speed. The edge of the heated welding seam cannot reach the welding temperature. When the input heat is lacking, the metal structure remains solid and constitutes Insufficient fusion or incomplete penetration; when the input heat is lacking, the edge of the heated weld will exceed the welding temperature, causing overburning or droplets, causing the weld to form a molten hole.

 

3. Control of squeezing force: under the squeeze of the squeeze roller, the two edges of the tube blank are heated to the welding temperature. The metal crystal grains that makeup together penetrate and crystallize each other, and finally form a strong weld. If the extrusion force is too small, the number of crystals will be small, and the strength of the weld metal will decrease, and cracks will occur after the force is applied; if the extrusion force is too large, the molten metal will be squeezed out of the weld, not only reduced The strength of the weld is improved, and a lot of surfaces and interior burrs will occur, and even defects such as weld lap joints will be formed.

 

Fourth, the adjustment of the position of the high-frequency induction coil: the effective heating time is longer, and the high-frequency induction coil should be as close as possible to the position of the squeeze roller. If the induction loop is far away from the squeeze roller. The heat-affected zone is wider and the strength of the weld is reduced; on the contrary, the edge of the weld is lacks heating, resulting in poor molding after extrusion. The cross-sectional area of the resistor should not be less than 70% of the cross-sectional area of the inner diameter of the steel pipe. Its effect is to make the induction coil, the edge of the pipe blank weld, and the magnetic rod form an electromagnetic induction loop. The 5.5 resistor is one or a group of special magnetic rods for welded pipes. . The proximity effect occurs, and the eddy current heat is concentrated near the edge of the weld of the tube blank so that the edge of the tube blank is heated to the welding temperature. The resistor is dragged inside the tube with a steel wire, and the center position should be relatively fixed near the middle of the squeeze roller. When starting up, due to the rapid movement of the tube blank, the resistance device is greatly worn out by the friction of the inner wall of the tube blank and needs to be changed frequently.

 

6. Weld scars will occur after welding and extrusion. Relying on the rapid movement of the welded pipe, the weld scar will be flattened. The burrs inside the welded pipe are generally not cleaned. 

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