Influence of production operation of high frequency welded pipe equipment on welding quality of carbon steel pipe
Author： Source：TENYES ELECTROTHERMAL EQUIPMENT CO.,LTD. Date：2020-09-29
First, the principle and process of high-frequency pipe welding machine
The production process of high-frequency welded pipe mill, high-frequency welded pipe mill, is trusted by pipe-making and other industries for its advantages of energy saving, environmental protection, safe use, long service life and excellent welding quality, and it is also the replacement product of high-frequency welded pipe, which is also a great change in China's high-frequency market.
The production process of high-frequency pipe welding machine mainly depends on the product variety, and a series of processes are needed from raw materials to finished products. To complete these processes, various mechanical equipment and welding, electrical control and testing devices are needed. These equipment and devices are reasonably arranged according to different process requirements. The typical process of high-frequency pipe welding is uncoiling-strip leveling-head-tail cutting-strip butt welding-looper storage-forming-welding-burr removal-sizing-flaw detection.
Second, the impact on welding quality
1 input heat
Because one of the main parameters of welding process, i.e. welding current (or welding temperature), is difficult to measure, it is replaced by input heat, which can be expressed by oscillator output power: n = output power in EP IP formula, kW; ? ? Ep—— screen voltage, kV; ? ? Ip-screen flow, a . When the oscillator, inductor and impedance are determined, the efficiency of tank circuit, output transformer and inductor is 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 can not reach the welding temperature, and still keeps the solid structure and 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 after being stressed; When the input heat is too large, the welding temperature is too high, which makes the weld break down, causing the molten metal to splash and form holes. The melting welding temperature is generally 1350 ~ 1400℃.
2 welding pressure
Welding pressure is one of the main parameters of welding process. After the two edges of pipe blank are heated to welding temperature, common metal grains are formed under the action of extrusion pressure, that is, mutual crystallization leads to welding. The welding pressure affects the strength and toughness of the weld. If the applied welding pressure is small, the metal welding edge can not be fully pressed, and the residual non-metallic inclusions in the weld are difficult to discharge due to the small pressure, the weld strength is reduced, and it 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, according to different varieties and specifications, the best welding pressure should be obtained in practice. According to practical experience, the unit welding pressure is generally 20~40MPa. The variation of welding extrusion force may be involved due to the possible tolerance of tube blank width and thickness, and the fluctuation of welding temperature and welding speed. The welding extrusion amount is generally controlled by adjusting the distance between the extrusion rollers, and can also be controlled by the tube circumference difference before and after 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. When welding high-frequency pipes, the welding quality is improved with the acceleration of welding speed. This is because the shortening of heating time narrows the width of edge heating zone and shortens the time of forming metal oxide. If the welding speed decreases, not only the heating zone widens, but also the width of melting zone changes with the change of input heat, resulting in larger internal burrs. In low-speed welding, less input heat makes welding difficult, and defects are easy to occur if it does not conform to the specified value.
Therefore, when welding high-frequency pipes, the welding speed should be selected according to different specifications and varieties at the maximum speed allowed by the mechanical welding equipment and welding device of the unit.