The influence of operation on welding quality in the production of high-frequency welded pipe
Abstract: in the production of high-frequency welded pipe, the influencing factors of operation on the quality of welded pipe include input heat, welding pressure, welding speed, opening angle, placement position of inductor and impedance, geometric size and shape of pipe blank, etc. Mastering operation in production is one of the important ways to improve the quality of welded pipe
key words: high frequency welded pipe; Welding quality; Welding pressure; Welding speed
the quality of welded steel pipes refers to the specification and size requirements of products, appearance quality and weld quality. Users often regard weld quality as an important symbol of welded pipe quality, so welding quality is the decisive factor affecting the quality of welded pipe. How to improve the welding quality of welded pipe is a very important problem. The factors that affect the welding quality are external factors - the influence of operation on the welding quality; There are internal factors - the influence of steel quality and steel type on welding. Mastering the process technology and operation in production is one of the important ways to improve the quality of welded pipe. The influence factors of operation on the quality of welded pipe include input heat, welding pressure, welding speed, opening angle, sensor, placement position of impedance and shape of pipe blank The input heat can be expressed by the output power of the oscillator:
n = EP · IP
where n - output power, kW
EP - screen voltage, kV
IP - screen flow, a 
when the oscillator, inductor and impedance are determined, the efficiency of the oscillation pipe channel, output transformer and inductor is also determined, and the change of input power is roughly proportional to the change of input heat
when the input heat is insufficient, the heated edge cannot reach the welding temperature, and the solid structure can not be welded, forming welding cracks; When the input heat is large, the heated edge is easy to overheat or even burn when it exceeds the welding temperature, and cracks will occur after stress; When the input heat is too large, the welding temperature is too high, so that the weld breakdown, resulting in molten metal splash, forming holes. The melting and welding temperature is generally 1350 ~ 1400 ℃
2 welding pressure
welding pressure is one of the main parameters of the welding process. After the two edges of the tube blank are heated to the welding temperature, the extrusion makes meimeike win the favor of some of the domestic first and second tier cell factories. Under the action of the force, common metal grains are formed, that is, mutual crystallization and welding. The welding pressure affects the strength and toughness of the weld. If the applied welding pressure is small, so that the metal welding edge cannot be fully pressed, the residual non-metallic inclusions in the weld are not easy to be discharged due to the small pressure, the weld must be replaced, and the control instrument is reduced, which is easy to crack after being stressed; When the pressure is too high, most of the metal reaching the welding temperature is extruded, which not only reduces the weld strength, but also produces defects such as excessive internal and external burrs or lap welding. Therefore, the best welding pressure should be obtained in practice according to different varieties and specifications. According to practical experience, the unit welding pressure is generally 20~40mpa.
due to the possible tolerances of the width and thickness of the tube blank, as well as the fluctuations of the welding temperature and welding speed, it is possible to involve the changes of the welding extrusion force. The welding extrusion amount is generally controlled by adjusting the distance between the extrusion rollers, or by the circumferential difference between the front and rear tubes of the extrusion rollers
3 welding speed
welding speed is also one of the main parameters of welding process, which is related to heating system, weld deformation speed and mutual crystallization speed. In high-frequency pipe welding, the welding quality improves with the acceleration of welding speed. This is because the shortening of heating time narrows the width of the edge heating zone and shortens the time to form metal oxides. If the welding speed is reduced, not only the heating zone becomes wider, but also the width of the melting zone changes with the change of input heat, resulting in large internal burrs. In low-speed welding, less heat input makes welding difficult, and defects are easy to occur if it does not meet the specified value.
therefore, when welding pipes with high frequency, the appropriate welding speed should be selected according to different specifications and varieties under the maximum speed allowed by the mechanical equipment and welding device of the unit
4 opening angle
opening angle refers to the angle between the two edges of the tube blank in front of the extrusion roll. The size of the opening angle is related to the stability of the burning process and has a great impact on the welding quality.
when the opening angle is reduced, the distance between the edges is also reduced, so that the proximity effect is strengthened. Under the same other conditions, the heating temperature of the edges can be increased, so as to improve the welding speed. If the opening angle is too small, the distance from the junction point to the center line of the extrusion roll will be lengthened, resulting in the edge not being extruded at the highest temperature, which will reduce the welding quality and increase the power consumption. Practical production experience shows that the opening angle can be adjusted by moving the longitudinal position of the guide roller, which usually changes between 2 and 6 °. When the guide roller cannot be adjusted longitudinally, the opening angle can be adjusted by the thickness of the guide ring or pressing the closed pass