Significance of Proximity Effect on High Frequency Longitudinal Welded Pipe Production

In addition to the skin effect, the proximity effect is another characteristic of electric 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 through When the alternating current is equal in size and in the same 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 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 conductor is almost all gathered to the adjacent layer, making the adjacent surface The sharp increase of the current on the wire leads to heating on the adjacent surface, such as converging to the extrusion point, which is of great significance for the formulation of the high-frequency welded pipe process. The closer to the V-angle vertex of the opening, the closer the distance between the two edges of the strip, so the adjacent The stronger the effect, the higher the temperature of the edge of the strip until it is close to the melting point of the metal, and the welding is realized under the extrusion force of the subsequent extrusion roller. Therefore, the proximity effect requires that the welded pipe process needs to pay attention to the size of the V-shaped opening, which is the same as Welding heat, speed and quality are related.
2. Ratio
The strength of the proximity effect is closely related to the ratio of half the thickness of the conductor size 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. See the formula: ratio = conductor thickness / 2 penetration Spend.
3. Frequency
The higher the current frequency, the stronger the proximity effect based on the skin effect.
Significance of Proximity Effect on High Frequency Longitudinal Welded Pipe Production
The significance of the proximity effect is that it can control the flow path, position and range of 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, it is necessary to select the corresponding frequency and opening. After comprehensively considering the influence of the skin effect, the current frequency needs to be appropriately reduced. 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 the 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 is evenly distributed, If it is placed asymmetrically, the current on the tube to be welded will be unevenly distributed. Therefore, specifically, the gap between the induction coil and the tube to be welded should be installed in a small way from top to bottom, so that The edges of the tube blanks 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 pipe blank to be welded should be reduced as much as possible within the range allowed by the process.