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What are the temperature control of straight seam welded pipe unit?
Release time:
2018-12-06 11:46
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 pipe blank with an opening gap. The pressing amount of the squeezing roller is adjusted to control the weld gap at 1~3mm, and both ends of the welded joint are flush. If the gap is too large, the proximity effect will be reduced, the eddy current heat will be insufficient, and the joint between the weld grains will be poor, resulting in incomplete fusion or cracking.
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 pipe blank with an opening gap. The pressing amount of the squeezing roller is adjusted to control the weld gap at 1~3mm, and both ends of the welded joint are flush. If the gap is too large, the proximity effect will be reduced, the eddy current heat will be insufficient, and the joint between the weld grains will be poor, resulting in incomplete fusion or cracking. If the gap is too small, the proximity effect will increase, the welding heat will be too large, resulting in weld burning; or the weld will form deep pits after extrusion and rolling, affecting the surface quality of the weld.
The welding temperature is mainly affected by the high-frequency eddy current thermal power. According to the formula (2), the high-frequency eddy current thermal power is mainly affected by the current frequency, which is proportional to the square of the current excitation frequency, while the current excitation frequency is affected by the excitation voltage, current, capacitance and inductance. The excitation frequency formula is:
F=1/[2pi(CL)1/2].
where: f-excitation frequency (Hz);C-capacitance (F) in excitation loop, capacitance = electricity/voltage; L-inductance in excitation loop, inductance = magnetic flux/current
The above formula shows that the 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 circuit are changed, the excitation frequency can be changed 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 requirements of 3~5mm pipe wall thickness. 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 heat input of the straight welded pipe unit is insufficient, the edge of the heated weld exceeds the welding temperature, resulting in over-burning or molten droplets, causing the weld to form a molten hole.
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