Steel strip is feeding into square pipe machine, gradually rolled by continuously located rollers, shaped to tube blank with opening gap. Adjust the depth of squeeze roller to control the welding seam gap between 1-3mm and straight two ends. If the gap is larger, it will cause less proximity effect, less vortex heat, not completely connection between weld intergranulars, so that there will be un-fusion or cracking. If the gap is too small, it will cause larger proximity effect, high welding heat will destroy the welding seam; or welding pit will be shaped after squeezing and rolling, so that the welding surface quality is lower.
The welding temperature of square pipe machine is effected by high frequency eddy thermal power, which is effected by current frequency. Eddy thermal power is in proportion to square of current excitation frequency. While current excitation frequency is effected by excitation voltage, current, capacity and inductance.
Straight square pipe machine, excitation frequency is in inverse proportion to the square of capacity and inductance in excitation circuit, or in proportion to the square of voltage and current. If the capacity, inductance, voltage, current is changed ,the excitation frequency is changed to control the welding temperature. For low carbon steel, welding temperature will be controlled between 1250~1460℃ to meet the welding requirement for thickness 3-5mm。 In additional, welding temperature will be controlled by adjusting the welding speed。
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