Welding gap of welded pipe

　　The strip steel is sent to the welded pipe unit, and the strip is rolled by a plurality of rolls, and the strip is gradually rolled up to form a circular tube blank having an open gap, and the pressing amount of the pressing roll is adjusted to control the weld gap to be 1 to 3 mm. And make the ends of the solder joints flush. If the gap is too large, the proximity effect is reduced, the eddy current is insufficient, and the weld intergranular joint is poor to cause unmelting or cracking. If the gap is too small, the proximity effect is increased, the welding heat is too large, and the weld is burnt; or the weld is pressed and rolled to form a deep pit, which affects the surface quality of the weld.

　　1, Welding temperature control

　　The welding temperature is mainly affected by the high-frequency eddy current thermal power. According to the relevant formula, the high-frequency eddy current thermal power is mainly affected by the current frequency. 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 capacitance, inductance.

　　2, The control of the pressing force

　　After the two edges of the tube are heated to the soldering temperature, under the extrusion of the pressing roller, common metal crystal grains are mutually infiltrated and crystallized, and finally a firm weld seam is formed. If the pressing force is too small, the number of common crystals formed will be small, the strength of the weld metal will decrease, and cracking will occur after the force is applied; if the pressing force is too large, the molten metal will be extruded out of the weld, not only will it be lowered. The weld strength, but also a large number of internal and external burrs, and even caused by welding seams and other defects.

　　3. Regulation of the position of the high frequency induction coil

　　The high frequency induction coil should be as close as possible to the position of the squeeze roller. If the induction coil is far away from the squeeze roller, the effective heating time is longer, the heat affected zone is wider, and the weld strength is decreased; otherwise, the weld edge is insufficiently heated, and the extrusion is poorly formed.

　　4. The resistor is one or a set of special magnetic rods for the welded pipe.

　　The cross-sectional area of the resistor is usually not less than 70% of the cross-sectional area of the inner diameter of the steel pipe. The function is to form an electromagnetic induction circuit between the induction ring and the edge of the tube blank and the magnetic rod to genera
te a proximity effect. The eddy current is concentrated in the tube blank weld. Near the edge, the edge of the tube blank is heated to the soldering temperature. The resistor is dragged in the tube blank with a wire, and its center position should be relatively fixed near the center of the squeeze roller. When starting up, due to the rapid movement of the tube blank, the resistor is greatly damaged by the friction of the inner wall of the tube blank and needs to be replaced frequently.

　　5. After the weld is welded and extruded, it will produce a weld bead and need to be removed.

　　The cleaning method is to fix the tool on the frame and smooth the welding bead by the rapid movement of the welded pipe. The burrs inside the welded pipe are generally not removed.