In addition to the skin effect, the proximity effect is another feature of current. When alternating currents of equal magnitude and opposite directions pass through two adjacent conductors, the current will flow through the adjacent inner surface layers of the two conductors, and when the two conductors pass When alternating currents of the same size and direction, the current will flow through the outer surface layers of the two conductors. The proximity effect of the current makes the current in the conductors further uneven. It is this unevenness that makes the high-frequency straight seam welded pipe(ERW welded pipe).
The strength of the proximity effect is related to the following three factors:
1. distance
The closer the adjacent distance between two conductors, the stronger the proximity effect, especially when the distance between the two conductors is close to or tends to zero, the current in the conductors almost all converge to the adjacent layer, making the adjacent surface The sharp increase of the current on the surface leads to heating of adjacent surfaces, such as converging to the position of the extrusion point, which is of great significance for the formulation of the high-frequency welded pipe process. The closer to the apex of the V angle of the opening, the closer the distance between the two edges of the strip, and therefore the proximity The stronger the effect, the higher the temperature of the strip edge, until it is close to the melting point of the metal, and the welding is realized under the squeezing force of the subsequent squeeze roller. Therefore, the proximity effect requires that the welded pipe process needs to pay attention to the size of the V-shaped opening. Welding heat, speed and quality are related.
2. Ratio
The strength of the proximity effect is closely related to the ratio of the half of the conductor size and thickness to the current penetration. The larger the ratio, the stronger the proximity effect; on the contrary, the smaller the ratio, the weaker the proximity effect. Refer to the formula: ratio = conductor thickness/2 penetration degree.
3. Frequency
The higher the current frequency, the stronger the proximity effect based on the skin effect.
Significance of proximity effect to the production of high-frequency straight seam welded pipes:
The significance of the proximity effect is that it can control the flow path, position and range of the high-frequency current, guide the production of welded pipes, and formulate the welding process. For welded pipes of different specifications, such as the production of large-diameter thick-walled pipes, the corresponding frequency and opening need to be selected. After considering the effect of the skin effect, it is necessary to appropriately reduce the current frequency. By reducing the opening angle, the distance between the two edges of the blank to be welded and the current flow path are shortened, thereby shortening the heating time and increasing Improved welding efficiency.
On the other hand, because the high-frequency current of the induction coil and the induced current on the tube to be welded are both high-frequency currents, there is also a proximity effect between them. If placed symmetrically, the current on the tube to be welded will be evenly distributed. If placed asymmetrically, the current on the tube blank to be welded will be unevenly distributed. Therefore, specifically, the gap between the induction coil and the tube blank to be welded should be installed in a small top-down manner, so as to The edges of the billet to be welded collect more current. At the same time, in order to strengthen the proximity effect, the gap between the inner diameter of the induction coil and the outer diameter of the tube to be welded should be minimized within the range allowed by the process.
