How to Control the Position of High-frequency Induction Coil of High Frequency Straight Seam Welded:
1.The excitation frequency of the high-frequency straight seam welded pipe is inversely proportional to the square root of the capacitance and inductance in the excitation circuit, or to the square root of the voltage and current, and the magnitude of the excitation frequency can be changed by changing the capacitance, inductance or voltage in the circuit. to achieve the purpose of controlling the welding temperature. For mild steel, welding temperature control in 1250 ~ 1460 ℃, to meet the pipe wall thickness of 3 ~ 5mm penetration requirements. In addition, the welding temperature can also be achieved by adjusting the welding speed.
2,High-frequency induction coil should be close to squeeze roller position. If the induction coil is located farther away from the squeeze roller, the effective heating time is longer, the heat affected zone is wider, and the weld strength is decreased. On the contrary, the edge of the weld is heated insufficiently and the forming is bad after extrusion. The impedance of a special pipe or tube, the cross-sectional area of the impedance should normally not be less than 70% of the cross-sectional area of the inner diameter of the tube, its role is to induction coil, tube weld edge and the magnetic bar form an electromagnetic induction circuit, Produces the proximity effect, the eddy current heat concentrates in the tube blank weld nearby the edge, causes the tube blank edge to heat to the welding temperature. Impedance with a wire drag in the tube blank, the center position should be relatively fixed in close to the squeeze roll center position. Boot, due to rapid movement of the tube, the tube wall by the friction of the friction loss and larger, need to be replaced frequently.
3.After the two edges of the tube are heated to the welding temperature, the oil casing is squeezed by the squeeze roll to form a common metal grain to penetrate and crystallize, forming a solid weld. If the squeeze pressure is too small, the formation of the number of common crystals on the weld metal strength decreased, the force will produce cracking; welding and extrusion by welding will produce scar, need to be removed. Removal method is fixed in the rack tool, by the rapid movement of the pipe, the scab scraping. The burrs inside the pipe are generally not removed. If the extrusion pressure is too large, will make the molten metal is squeezed out of the weld, not only reduces the strength of the weld, and will produce a lot of internal and external burrs, and even welding seam and other defects.
4.When the input heat is insufficient, the edge of the heated weld can not reach the welding temperature, the metal structure is still solid, forming not fusion or not penetration; when the input heat is insufficient, the heated edge of the weld over the welding temperature, Burning or droplet, making the formation of welding seam hole. The eddy current thermal power is directly proportional to the square of the current excitation frequency, and the current excitation frequency is affected by the excitation voltage and the frequency of the high frequency eddy current.
