Views: 182 Author: Site Editor Publish Time: 2023-03-07 Origin: Site
The straight seam welded pipe unit sends the strip steel into the welded pipe unit, and after rolling by multiple rollers, the strip steel is gradually rolled up to form a round tube 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 port 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, the welding heat will be too large, and the weld seam will be burned; or the weld seam will form deep pits after extrusion and rolling, which will affect the surface quality of the weld seam.
The welding temperature is mainly affected by the high-frequency eddy current thermal power. According to the formula, 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 affected by the excitation voltage, current and the influence of capacitance and inductance.
The excitation frequency formula is:
In the formula: f-excitation frequency (Hz); C-capacitance (F) in the excitation circuit, capacitance = electricity/voltage; L-inductance in the excitation circuit, inductance = magnetic flux/current.
It can be seen from the formula above that 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. Size, so as to achieve the purpose of controlling the welding temperature. 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 heated weld edge cannot reach the welding temperature, and the metal structure remains solid, forming incomplete fusion or incomplete penetration; when the input heat of the straight seam welded pipe unit is insufficient, the heated weld edge exceeds Welding temperature, resulting in overheating or molten droplets, so that the weld forms a molten hole.