Key words: high frequency welded pipe welding process
The power of 60Hz is converted to high frequency power, which is used in solid metal welding with efficiency of 90%. In high frequency welding, welding power usually exceeds 100 kW, heating, impedance and roller consume 4/5 of the power. Therefore, the key to reduce power loss is to set reasonable coils, impedance and rolling mill configuration. In most cases, power loss can be reduced by 50% by optimizing welding process, which can improve welding quality, reduce downtime and increase production.


The mechanism of high frequency welding is that the voltage passes through the edge of the opening part of the pipeline and the induction is used to reach the convergence point. As the current flows through the junction, the metal is heated rapidly. By using pressure in the extrusion roll, heat is pressed together by melting metal, and impurities are extruded from the weld.


Technically speaking, impedance is the main consumption of low frequency current through resistance components. With the increase of frequency and magnetic field, induction resistance becomes the main factor of impedance, and increases with the increase of frequency. During welding, the size of induction coil as primary winding should be reduced appropriately. The power supply can be adjusted by electromagnetic coupling. The magnetic loss caused by high frequency is related to the number of coil turns and current. The 60 Hz frequency of welded pipes requires coils with hundreds of turns and thousands of amperes of current; high frequency welding usually involves 7% coils and hundreds of amperes of current. In addition, high frequency welding is also conducive to "skin effect" and "proximity" effect.


The low efficiency of high frequency welding operation is due to the poor position and impedance of induction coil. When the voltage is applied to the edge of the billet, part of the current flows through the V-shaped region along the edge. The steel side is stripped and heated; the other part of the current flows through the inner ring of the open tube and the outer ring surface returns to generate power loss.