Straight seam steel tube excitation frequency is inversely proportional to the square root of capacitance and inductance in the excitation circuit, or proportional to the square root of voltage and current. As long as the capacitance, inductance or voltage and current in the loop are changed, the excitation frequency can be changed to achieve control Purpose of welding temperature. In addition, the welding temperature can also be achieved by adjusting the welding speed.

The high frequency induction coil should be as close as possible to the position of the squeeze roller. If the induction ring is far away from the squeeze roller, the effective heating time is longer, the heat affected zone is wider, and the strength of the weld is reduced. On the contrary, the edge of the weld is not heated enough, and the shape is poor after extrusion.

The resistor is one or a group of special magnetic rods for welding pipes. 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 function is to form an electromagnetic induction loop between the induction ring, the edge of the tube blank weld and the magnetic bar, and generate a proximity effect. The eddy current heat is concentrated near the edge of the tube blank weld seam, and the tube blank edge is heated to the welding 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. When starting up, due to the rapid movement of the tube blank, the resistor is greatly worn by the friction of the inner wall of the tube blank, and it needs to be replaced frequently.