High-frequency welding originated in the 1950s. It is a new welding process that uses the skin effect and adjacent effect generated by high-frequency current to connect steel plates and other metal materials. The emergence and maturity of high-frequency welding technology has directly promoted the great development of the straight seam welded pipe industry, which is a key process in the production ofERW tubes. The quality of high-frequency welding directly affects the overall strength, quality level and production speed of welded pipe products.
The basic principlehigh frequency welding
The so-called high frequency is relative to the alternating current frequency of 50Hz, generally referring to the high frequency current of 50KHz ~ 400KHz. When a high-frequency current passes through a metallic conductor, two peculiar effects will occur: the skin effect and the proximity effect. High frequency welding uses these two effects towelding steel pipes. So what are these two effects? The skin effect means that when an alternating current of a certain frequency passes through the same conductor, the current density is not evenly distributed in all sections of the conductor, and will be mainly concentrated on the surface of the conductor, that is, the density of The current on the surface of the conductor is high, the density inside the conductor is small, so we call it "skin effect" vividly. The skin effect is generally measured by the depth of current penetration. The smaller the penetration depth value, the more significant the skin effect. This penetration depth is proportional to the square root of the resistivity of the conductor and inversely proportional to the square root of the frequency and permeability. In simple terms, the higher the frequency, the more concentrated the current is on the surface of the steel plate; The lower the frequency, the more dispersed the surface current will be. It should be noted that although steel is a conductor, its permeability will decrease as the temperature increases, that is, when the temperature of the steel plate increases, the permeability will decrease and the skin effect will decrease.
The proximity effect means that when high-frequency current flows in opposite directions in two adjacent conductors, the current will concentrate at the edges of the two conductors that are close to each other. Even if the two conductors have another shorter side, the current will not flow along the shorter path flow, we call this effect: the "proximity effect". The proximity effect is essentially due to the role of inductive reactance, which plays a dominant role in high-frequency currents. The proximity effect increases as the frequency increases and the spacing between adjacent conductors increases. If a magnetic core is added around the adjacent conductors, the high-frequency current will be more concentrated on the surface of the workpiece. These two effects are the basis for performing high frequency metal welding. High-frequency welding uses the skin effect to concentrate high-frequency current energy on the surface of the workpiece; and uses the proximity effect to control the location and range of the high-frequency current flow path. The current speed is very fast, it can heat and melt the edges of adjacent steel plates in a very short time, and realize the butt joint by extrusion.
