1. Position of the sensor
The placement of the inductor of the erw steel pipe (distance from the center line of the pressing roll) has a great influence on the quality of the welding. When it is far away from the center line of the squeezing roller, the effective heating time is long, the heat-affected zone is wide, and the weld strength is lowered; otherwise, the edge heating is insufficient, and the weld strength is also lowered. The sensor should be placed concentrically with the tube, and the distance between the front end and the center line of the squeeze roller is approximately equal to or smaller than the pipe diameter (1.5 times the diameter of the small pipe).
2. Placement of the resistor
The placement of the resistor (magnetic bar) not only has a great influence on the welding speed, but also has an influence on the welding quality. Practice has proved that the flaring strength and the crushing strength are best when the front end of the impeder is positioned just at the center line of the squeezing roller. When the center line of the squeezing roller is extended to the side of the sizing machine, the flaring strength and the biasing strength are significantly lowered. When the center line is not in the center of the molding machine, the welding strength is also lowered.
The best position is that the impeder is placed in the blank under the inductor, and the head is coincident with the center line of the squeeze roller or adjusted to 20~40mm in the forming direction, which can increase the back impedance of the tube, reduce the circulating current loss, and improve the welding voltage. . When using a single-turn sensor, a small resistor is placed on each of the left and right sides of the inductor, which increases the weld magnetic field and enhances the adjacent effect of the edge of the blank, and the welding speed can be increased by 4 to 5 m per minute.
Billet geometry and shape requirements
1. The geometry of the welded pipe blank
Unlike seamless steel pipes, the tube blank width and thickness deviation of the electric resistance welded pipe is large, which changes the heating temperature and the extrusion amount of the edge. The qualified product must require the width and thickness of the tube blank to be within the tolerance range.
2. Tube shape and joint form
If the edge of the tube blank has deflection, boring and wrinkling, it will deviate from the center of the hole when passing through the forming machine, causing the strip to bend on both sides. Poor roll adjustment can also cause defects such as strip deviation or tube blank distortion, which may affect the quality of the weld or the inability to weld at all.
When welding both ends of the tube blank, all the thicknesses of the two ends are required to be connected, and the two edges of the tube blank are not only straight but also parallel. When the strip is cut longitudinally, the gap between the cutting edge of the disc is too large or the edge of the blade is seriously worn, causing the burr on the edge of the strip to be too large, and it is easy to cause cracks after welding.
Strip edge quality
The quality of the edge of the strip will affect the heating result of the high frequency induction, thus affecting the quality of the weld. After the tube blank is formed, it should be ensured that the two edges of the strip are parallel, otherwise the sharp corner effect will occur, which will affect the weld quality.
For more: https://www.permanentsteel.com/newsshow/seamless-steel-tube-capillary-extension-process.html