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How to control welding gap for carbon steel pipe

The strip is into the welded pipe unit and by the multi-channel roll rolling, gradually rolled strip steel, formed with an opening gap round tube, adjust the amount of reduction squeeze rollers, so that the weld gap control for carbon steel pipe in 1 ~ 3mm, and to weld ends flush. If the gap is too large and will result in reduced proximity effect, eddy current lack of heat, poor weld joint between grain yield incomplete fusion or cracking. If the gap is too small, causing the proximity effect increases, excessive soldering heat, causing the weld burning; or weld by extrusion, rolling to form a pit, affecting the quality of the weld surface .

1, welding temperature control, soldering temperature is mainly affected by the impact of high-frequency eddy current heating power, high-frequency eddy current frequency heating power is mainly affected by the impact of thermal power and eddy current excitation frequency is proportional to the square; while current excitation frequency but also by the excitation voltage, current and capacitance, inductance. excitation frequency of the excitation circuit of the capacitance and inductance is inversely proportional to the square root, or the voltage and current proportional to the square, as long as the change in the circuit capacitance, inductance, or voltage and current can change the excitation frequency size , so as to control the welding temperature. For low carbon steel , welding temperature control in the 1250 ~ 1460 ℃, can meet the pipe wall thickness 3 ~ 5mm penetration requirements. In addition, the soldering temperature can be achieved by adjusting the welding speed. When the heat input is low, the heated soldering temperatures reach the edge of the weld metal structure remains solid, forming incomplete fusion or penetration; when the input is hot enough, over the edge of the heated seam welding temperature, resulting in burnt or droplet formation of the weld Cave.

2, the extrusion pressure control, both edges of the heating tube to the welding temperature in the extrusion press roll, a common mutual penetration of the metal grains, crystals, and ultimately form a strong weld. If the pressing force is too small, a common number of crystals is small, the weld metal strength decreases, the force will produce cracks; if the extrusion pressure is excessive, the molten weld metal is extruded, not only reduces the the weld strength, and will generate a lot of internal and external burrs , and even cause defects such as seam welding ride.

3, high-frequency induction loop position control
High-frequency induction loop should be as close to the squeeze roller position. If the nip roll farther away from the induction coil, the effective heating time is longer, wider heat affected zone, weld strength decreases; contrary, insufficient heating of the weld edge, after extrusion molding failure.

4, the impedance is a magnet or a group of dedicated pipe, the impedance is a cross-sectional area is usually not less than pipe inner cross-sectional area of ​​70%, its role is the induction coil, tube weld edge to form an electromagnetic induction magnet circuit, resulting in the proximity effect, eddy current weld heat concentrated in the tube near the edge, the edge of the tube is heated to soldering temperature. Used impedance dragging a wire within the tube, fixed to its central position should be relatively close to the center of the press roller. Boot, because tube fast motion, the impedance is affected by tube wall friction loss is large, require frequent replacement.

5, the weld after welding and extrusion welding scars will produce, which need to be cleared. Removal method is on the rack cutter, pipe by the rapid movement will burr gelling. Pipe inside burr is generally not cleared.





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