Control of weld seam clearance The strip is fed into the welded pipe unit, rolled by multiple rollers, the strip is rolled up gradually, and a round tube billet with open gap is formed, the pressure of the extrusion roll is adjusted, the weld clearance is controlled in the 1~3mm, and the welding ends are flush. If the gap is too large, the proximity effect is reduced, the vortex heat is insufficient, the weld crystal is not fused or cracked.
If the gap is too small, the proximity effect increases, welding heat is too large, resulting in weld burning loss, or weld after extrusion, rolling formation of deep pits, affecting the surface quality of welds.
5.2 Welding Temperature Control Welding temperature is mainly affected by 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, eddy current heat power and current excitation frequency of the square is directly proportional to the current excitation frequency is stimulated by the voltage, current and capacitance, inductance.
The excitation frequency formula is: f=1/[2π (CL) 1/2] ...
Type: F-excitation frequency (Hz), C-excitation circuit capacitance (f), capacitance = electricity/voltage; inductance in L-excitation circuit, inductance = flux/current On the formula, the excitation frequency and the excitation circuit in the capacitor, inductance square root is inversely proportional to the voltage and current square root, as long as the change in the circuit of the capacitor, inductance or voltage, current can change the size of the excitation frequency, so as to achieve the purpose of controlling the welding temperature. For low carbon steel, welding temperature control in 1250~1460℃, can meet the thickness of pipe wall 3~5mm penetration requirements.
In addition, the welding temperature can be achieved by adjusting the welding speed.
When the input of heat is insufficient, the weld edge of the heating is not up to the weld temperature, the metal tissue remains solid, the formation is not fused or not welded, and when the input heat is insufficient, the weld edge of the heated seam exceeds the welding temperature, and the weld seam is formed by burning or droplet.
5.3 Control of extrusion pressure After the two edges of the tube are heated to the welding temperature, the common metal grains are infiltrated and crystallized in the extrusion rolls, forming a solid weld.
If the squeeze pressure is too small, the number of common crystals is small, weld metal strength decreases, after the force will produce cracking; if the squeeze pressure is too large, it will make the molten metal extrusion weld, not only reduce the weld strength, but also produce a large number of internal and external burrs, and even welded joints and other defects.
5.4 High frequency induction coil position regulation The high frequency induction coil should be as close as possible to the extrusion 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, the weld strength decreases, whereas the weld edge is not heated enough and the forming is poor after extrusion. 5.5 Impedance device is one or a group of special magnet for welded pipe, the section area of the impedance is usually not less than 70% of the inner diameter section of the steel pipe, its function is to make the induction ring, the weld edge of the tube billet and the magnet to form an electromagnetic induction circuit, which produces proximity effect, and the eddy current heat is concentrated near the edge of the weld seam, which heats The impedance is driven by a wire in the Tube billet, and its central position should be relatively fixed at the center of the extrusion roll.
When the boot, because the rapid movement of the tube, the impedance of the tube billet inside the wall friction and loss of large, need to change frequently. 5.6 Weld after welding and extrusion will produce weld scar, need to clear. The removal method is to fix the tool on the rack, and rely on the quick movement of the welded pipe to scrape the weld scar flat.
The internal burr of welded pipe is generally not cleared.
5.7 Process examples are the welding of φ32x2mm straight seam welded pipe, for example, the technical parameters:
Strip specification: 2x98mm bandwidth by medium diameter expansion plus a small amount of molding allowance
Steel Material: q235a
Input excitation voltage: 150V excitation current: 1.5A frequency: 50Hz
Output DC voltage: 11.5kV DC current: 4A frequency: 120000Hz Welding speed: 50 m/min