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1. ERW steel pipe weld gap control
The strip steel is sent to the welded pipe unit, and after rolling through multiple rolls, the strip is gradually rolled up to form a circular tube blank with an open gap, and the pressing amount of the pressing roll is adjusted, so that the weld gap is controlled at 1 to 3 mm. And make the ends of the solder joints flush. If the gap is too large, the proximity effect is reduced, the eddy current heat is insufficient, and the weld intergranular joint is poor to cause unmelting or cracking. If the gap is too small, the proximity effect is increased, the welding heat is too large, and the weld is burnt; or the weld is pressed and rolled to form a deep pit, which affects the surface quality of the weld.

2. Welding temperature control
The welding temperature is mainly affected by the high-frequency eddy current thermal power. According to formula (2), the high-frequency eddy current thermal power is mainly affected by the current frequency, and the eddy current thermal power is proportional to the square of the current excitation frequency; and the current excitation frequency is stimulated. The effects of voltage, current, and capacitance, and inductance. The excitation frequency formula is:
f=1/[2π(CL)1/2]…(1)
Where: f-excitation frequency (Hz); capacitance in C-excitation loop (F), capacitance = electricity / voltage; inductance in L-excitation loop, inductance = magnetic flux / current

The above formula shows that the excitation frequency is inversely proportional to the square of the capacitance and inductance of the excitation loop, or proportional to the square root of the voltage and current. As long as the capacitance, inductance or voltage and current in the loop are changed, the excitation frequency can be changed. The purpose of controlling the soldering temperature. For low carbon steel, the welding temperature is controlled at 1250~1460 °C, which can meet the welding requirements of 3~5mm wall thickness. In addition, the welding temperature can also be achieved by adjusting the welding speed.

When the input heat is insufficient, the heated weld edge does not reach the welding temperature, the metal structure remains solid, forming unfused or not welded; when the input heat is insufficient, the heated weld edge exceeds the welding temperature, resulting in Over-burning or dripping, causing the weld to form a melt hole.

3. Control of the pressing force
After the two edges of the tube are heated to the soldering temperature, under the extrusion of the pressing roller, a common metal grain is formed to infiltrate and crystallize, thereby finally forming a firm weld. If the pressing force is too small, the number of common crystals formed will be small, the strength of the weld metal will decrease, and cracking will occur after the force is applied; if the pressing force is too large, the molten metal will be extruded out of the weld, not only will it be lowered. The weld strength, and a large number of internal and external burrs, and even weld sews and other defects.

4. Regulation of the position of the high frequency induction coil
The high frequency induction coil should be as close as possible to the position of the squeeze roller. If the induction coil is far away from the squeeze roller, the effective heating time is longer, the heat affected zone is wider, and the weld strength is decreased; otherwise, the weld edge is insufficiently heated, and the extrusion is poorly formed.

5. Impedance is one or a set of special magnetic rods for welded pipes. The cross-sectional area of ​​the impeder is usually not less than 70% of the cross-sectional area of ​​the inner diameter of the steel pipe. Its function is to form an electromagnetic induction circuit between the induction ring and the edge of the blank of the tube blank and the magnetic bar. , creating a proximity effect, vortex heat is concentrated near the edge of the tube blank weld, heating the edge of the tube blank to the soldering temperature. The resistor is dragged in the tube blank with a wire, and its center position should be relatively fixed near the center of the squeeze roller. At the time of starting up, due to the rapid movement of the tube blank, the resistor is greatly damaged by the friction of the inner wall of the tube blank, and needs to be replaced frequently.

6. Welds are produced after welding and extrusion and need to be removed. The cleaning method is to fix the tool on the frame and smooth the welding bead by the rapid movement of the welded pipe. The burrs inside the welded pipe are generally not removed.

7. Process example
Taking the welded φ32×2mm straight seam welded pipe as an example, the process parameters are briefly described:
Strip specification: 2×98mm The bandwidth is expanded by the medium diameter plus a small amount of molding allowance;
Steel material: Q235A;
Input Excitation voltage: 150V Excitation current: 1.5A Frequency: 50Hz;
Output DC voltage: 11.5kV DC current: 4A Frequency: 120000Hz;
Welding speed: 50 m / min;
Parameter adjustment: The output voltage and welding speed are adjusted in time according to the change of welding line energy. After the parameters are fixed, there is generally no adjustment.