1. The control of the weld gap: the strip steel is sent to the welded pipe unit after rolling by multiple rollers. The strip steel is gradually rolled up to form a circular tube blank with an opening gap. Adjust the reduction of the extrusion roller to control the gap between the welds at 1~3mm and make the two ends of the welds flush. If the gap is too large, the proximity effect will be reduced, the heat of the eddy current will be insufficient, and the welding seam will be poorly bonded, resulting in unfused or cracked. 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 a deep pit after extrusion and rolling, which will affect the appearance of the weld seam.
2. Welding temperature control: According to the formula, the welding temperature is affected by the high-frequency eddy current thermal power. 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, capacitance, and inductance. Inductance = magnetic flux/current In the formula: f-encouragement frequency (HzC-capacitance in the encouragement loop (F capacitance = electricity/voltage; L-inductance in the encouragement loop. The encouragement frequency is inversely proportional to the square root of the capacitance and inductance in the encouragement loop, It may be proportional to the square root of voltage and current, as can be seen from the above formula. Just change the capacitance, inductance, or voltage and current in the circuit to change the size of the excitation frequency, and then achieve the purpose of controlling the welding temperature. For low carbon steel, welding temperature control At 1250~1460°C, 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. The edge of the weld that is heated cannot reach the welding temperature, and when the input heat is insufficient. The metal structure remains solid, forming incomplete fusion or incomplete penetration; when the input heat is insufficient, the edge of the heated weld exceeds the welding temperature, overheating or droplet occurs, and the weld forms a molten hole.
3. Extrusion force control: Under the extrusion of the extrusion roller, the two edges of the tube blank are heated to the welding temperature. The metal grains that form together penetrate and crystallize each other, and finally form a strong weld. If the extrusion force is too small, the number of crystals formed together will be small, the strength of the weld metal will decrease, and cracks will occur after being stressed; if the extrusion force is too large, the molten metal will be squeezed out of the weld, which will not only reduce. The strength of the weld is reduced, a lot of internal and external burrs will occur, and even defects such as weld laps will be formed.
4. Adjustment of the position of the high-frequency induction coil: the effective heating time is longer, and the high-frequency induction coil should be as close as possible to the position of the extrusion roller. If the induction coil is far away from the extrusion roller. The heat-affected zone is wider, and the strength of the weld is reduced; on the contrary, the edge of the weld is insufficiently heated, and the shape is poor after extrusion. The cross-sectional area of the impedance should generally not be less than 70% of the cross-sectional area of the inner diameter of the steel pipe. The proximity effect occurs, and the eddy current heat is concentrated near the edge of the weld of the tube blank, heating the edge of the tube blank to the welding temperature. The resistor is dragged in the tube blank by a steel wire, and the central position should be relatively fixed close to the central position of the extrusion roller. When starting up, due to the rapid movement of the tube blank, the resistor is worn out by the friction of the inner wall of the tube blank and needs to be replaced frequently.
5. Weld scars will occur after welding and extrusion. Rely on the rapid movement of the welded pipe to scrape off the weld scars. The burrs inside the welded pipe are generally not cleaned.
Post time: Apr-20-2023