Factors Affecting The Weld Gap Of Square Steel Hollow Section

1. Soldering temperature

The welding temperature of the square steel hollow section is mainly affected by the high-frequency eddy current thermal power, the high-frequency eddy current thermal power is mainly affected by the current frequency, the eddy current thermal power is proportional to the square of the current excitation frequency; and the current excitation frequency is affected by the excitation voltage, current and the influence of capacitance and inductance. The excitation frequency is inversely proportional to the square root of the capacitance and inductance in the excitation circuit or proportional to the square root of the voltage and current. As long as the capacitance, inductance, or voltage and current in the circuit are changed, the excitation frequency can be changed, so as to achieve the control of welding temperature. Purpose. For low carbon steel, the welding temperature is controlled at 1250-1460°C, which can meet the penetration requirements of the pipe wall thickness of 3-5mm. In addition, the welding temperature can also be achieved by adjusting the welding speed. When the input heat is insufficient, the edge of the heated weld cannot reach the welding temperature, and the metal structure remains solid, forming incomplete fusion or incomplete penetration; when the input heat is insufficient, the heated edge of the weld exceeds the welding temperature, resulting in overburning or dripping causes the weld to form a molten hole.

2. Position of high frequency induction coil

The high-frequency induction coil should be as close as possible to the squeeze roller position. If the induction coil is far away from the extrusion roller, the effective heating time is longer, the heat-affected zone is wider, and the strength of the weld seam decreases; otherwise, the edge of the weld seam of the square steel hollow section is insufficiently heated, and the shape after extrusion is poor.

3. Weld scars

After the weld has been welded and squeezed, there will be weld scars that need to be removed. The method of removing the weld scar of the square steel hollow section is to fix the tool on the frame, and rely on the rapid movement of the welded pipe to scrape the weld scar flat, while the burr inside the square steel hollow section is generally not removed.

4. Squeeze roll reduction

The square steel hollow section strip is sent to the welded pipe unit, rolled up by multiple rollers, and the strip is gradually rolled up to form a round pipe billet with an opening gap. Adjust the reduction of the extrusion roller to control the weld seam gap at 1 －3mm, and make both ends of the welding joint flush. If the gap is too large, the proximity effect will be reduced, the heat of the eddy current will be insufficient, and the intergranular bonding of the weld will be poor, resulting in lack of fusion or cracking. If the gap is too small, the proximity effect will increase, and the welding heat will be too large, causing the weld to burn; or the weld will form deep pits after extrusion and rolling, which will affect the surface quality of the weld.

5. Resistor

The impedance is one or a group of special magnetic rods for welded pipes. The cross-sectional area of the impedance should generally not be less than 70% of the inner diameter cross-sectional area of the square steel hollow section. The circuit produces a proximity effect, and the eddy current heat is concentrated near the edge of the weld of the tube blank, heating the edge of the tube blank to the welding temperature. The impedance is dragged in the tube blank by a steel wire, and its central position should be relatively fixed close to the center of the extrusion roller. When starting up, due to the rapid movement of the tube blank, the resistor is worn out by the friction of the inner wall of the tube blank and needs to be replaced frequently.