In addition to the skin effect, the proximity effect is another characteristic of the current during the operation of the high frequency welded pipe machine. When two adjacent conductors pass alternating current of equal magnitude and opposite direction, the current will flow on the inner surface layer adjacent to the two conductors. The outer surface layer of the conductor flows through. The proximity effect of the current makes the current in the conductor further uneven, and it is this unevenness that makes high-frequency welding.

First, the strength of the proximity effect is related to the following three factors:

(1) Distance. The closer the two conductors are adjacent to each other, the stronger the proximity effect, especially when the distance between the two conductors is very close or even tends to 0, the current in the conductors will almost all converge on the adjacent layers, so that the current on the adjacent planes Sharp increase and thus cause heating of adjacent surfaces. (for example, converging to the position of the extrusion point) This property is of great significance for formulating the welding process of high frequency welded pipes. The closer to the apex of the opening V angle, the closer the distance between the two edges of the strip, the stronger the proximity effect, and the higher the temperature of the strip edge, until it reaches the melting point of the metal, and then the extrusion force of the extrusion roller acts. Weld down. Therefore, the proximity effect requires that the pipe manufacturing process of high frequency pipe machine must pay attention to the size of the V-shaped mouth, that is, the opening angle, which is related to the level of welding heat, the speed of welding and the quality of welding.

(2) Ratio. The strength of the proximity effect is closely related to the ratio of half of the conductor size and thickness to the current penetration depth. The larger the ratio, the stronger the proximity effect; conversely, the smaller the ratio, the weaker the proximity effect. See formula: ratio = conductor thickness / 2 penetration depth

(3) Frequency. The higher the current frequency, the stronger the proximity effect based on the skin effect.

Significance of Proximity Effect on High Frequency Straight Seam Welded Pipe Production

The significance of the proximity effect is that the characteristics of the high-frequency current flow path, location and range can be controlled by using the proximity effect. Guide the production of welded pipes and formulate welding procedures. It is necessary to select the corresponding frequency and opening angle for different specifications of welded pipes, such as the production of large-diameter thick-walled pipes, after comprehensively considering the influence of the skin effect, it is necessary to appropriately reduce the current frequency; by reducing the opening angle to shorten the length of the two edges of the pipe blank to be welded. The proximity distance and current flow path can shorten the heating time and improve the welding efficiency. On the other hand, since the high-frequency current of the induction coil and the induced current on the tube blank to be welded are both high-frequency currents, there is also a proximity effect between them. If they are placed symmetrically, the current on the tube blank to be welded is evenly distributed; placed, the current on the tube blank to be welded will present an uneven distribution. Therefore, in terms of details, the gap between the induction coil of the high frequency pipe machine and the tube blank to be welded should be installed in a small up and down manner, so that more current can be collected at the edge of the tube blank to be welded. 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 blank to be welded should be minimized within the range allowed by the process.