Welding principle of high frequency welded steel pipe: synergistic effect of skin effect and proximity effect
The welding principle of high frequency welded steel pipe is mainly based on the skin effect and proximity effect of high frequency current. Skin effect means that when high-frequency current passes through a metal conductor, due to electromagnetic induction, the current density is mainly concentrated on the surface of the conductor, while the current density inside the conductor is small. This effect enables high-frequency electric energy to concentrate on the surface of the weldment, thus rapidly heating the weld area. The intensity of skin effect is directly proportional to the current frequency. The higher the frequency, the higher the concentration of current on the conductor surface. Therefore, high-frequency welding usually uses a current with a frequency above 300kHz to achieve efficient heating of the weld area.
Proximity effect means that when high-frequency current flows reversely in two adjacent conductors, due to the interaction of magnetic fields, the current will concentrate on the edge flow of two adjacent conductors. This effect can further control the flow route of high-frequency current, making it more concentrated in the weld area, thus improving the welding efficiency and quality. In the process of high frequency welding, proximity effect is helpful to reduce energy loss, ensure sufficient heat input in the weld area, and realize rapid and uniform heating.
In the process of high-frequency welding, high-frequency current is introduced into the workpiece through the induction coil or contact electrode, which generates heat to locally melt the metal. Induction coil is a device that converts high-frequency current into electromagnetic induction energy. It generates an alternating magnetic field around the workpiece, causing eddy current inside the workpiece, thus heating the metal. The contact electrode is in direct contact with the workpiece, introducing high-frequency current into the workpiece and heating the metal through the thermal effect of resistance. The two methods have their own advantages and disadvantages. Induction welding is suitable for thicker workpieces, while contact welding is suitable for thinner workpieces.
Subsequently, by applying pressure, the molten metal is cooled to form a firm welded joint. In the welding process, the pressure and the application time have an important influence on the weld quality. Proper pressure can ensure that the molten metal flows and fuses fully to form a dense weld, while excessive pressure may lead to weld deformation or defects. High-frequency welding has the advantages of fast heating speed, small heat affected zone and high weld quality. The mechanical properties and sealing performance of weld are excellent, which can meet the requirements of various projects for pipeline performance.
