1. Welding temperature control of
thick-walled steel pipe:
The welding temperature is affected by the high-frequency eddy current thermal power. According to the formula, the high-frequency eddy current thermal power is affected by the current frequency, and the eddy current thermal power is proportional to the square of the current encouraging frequency; and the current encouraging frequency is affected by the encouraging voltage, current, and the influence of capacitance and inductance. The formula for encouraging frequency is: f=1/[2π(CL)1/2]... where: f-encouraging frequency (Hz); C-encouraging capacitance (F) in the circuit, capacitance=electricity/voltage; L-encouraging The inductance in the loop, inductance = magnetic flux / current The above formula shows that the excitation frequency is inversely proportional to the square root of the capacitance and inductance in the excitation loop, or directly proportional to the square root of the voltage and current. It only needs to change the capacitance, inductance, or voltage in the loop, The current can change the size of the excitation frequency, to achieve the purpose of controlling the welding temperature. For low-carbon steel, the welding temperature is controlled at 1250~1460℃, 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, resulting in incomplete fusion or incomplete penetration; when the input heat is insufficient, the edge of the heated weld exceeds the welding temperature, resulting in Overburning or dripping makes the weld form a molten hole.
2. Control of weld gap of thick-walled steel pipe:
The strip steel is sent to the welded pipe unit, rolled by multiple rollers, and the strip steel is gradually rolled up to form a round tube blank with an opening gap. Adjust the reduction of the kneading roller to control the weld seam gap at 1~3mm. And make the two 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 unfused 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 kneading and rolling, which will affect the weld seam surface.
