Does the extrusion force play a decisive role in the quality of the pipe during the welding process of high-frequency longitudinal seam welded pipe

In simple terms, the force on the squeeze roller consists of two parts: one is the force required to squeeze the open tube until the two edges touch, and the other is the force required to deform the tube when the edges are heated and welded.

The role of extrusion force
High-frequency straight seam welding is a kind of pressure welding. After the two edges of the tube blank are heated to the welding temperature, the two edges need to be pressed together under a certain external force to squeeze the oxide on the heated surface to form a common Metal particles, to achieve welding, here a certain external force is the extrusion force in the production process of welded pipes, which is an important process parameter in the production process of welded pipes.
In essence, the greater the extrusion force, the better, and a suitable extrusion force is the guarantee for obtaining high-quality welds.
When the extrusion force is insufficient, on the one hand, the oxide on the edge of the tube blank is difficult to be extruded, and non-metallic inclusions are formed in the weld, which damages the continuity of the weld and becomes the source of weld cracking during the flaring test. On the one hand, the small extrusion force makes the number of ordinary crystals formed in the weld less, the microstructure is loose and not dense, and the weld is easy to crack after being stressed.
When the extrusion force is too large, most of the high-temperature metal used for crystallization at the edge of the tube blank will be squeezed out of the weld, causing a small amount of high-temperature metal crystals to form a weld, but the metal far away from the edge of the tube blank and at a lower temperature actually forms Weld crystals, resulting in a lower bond strength of the weld.
Matching of Extrusion Force and Welding Form
It is meaningless to discuss whether the extrusion force is appropriate or not apart from the welding temperature. Whether the extrusion force is appropriate depends on whether the welding temperature is appropriate and kept constant. A large extrusion force is suitable for solid-solution welding, but it is too large to match with fusion welding. It is not suitable for solid-phase welding. Matching is not enough.
The method of judging the size of extrusion force
1. The average size method, that is to say, the horizontal "diameter" and vertical "diameter" of the tube blank out of the extrusion roll, and then average them and compare them with the diameter of the extrusion roll pass. If the former is slightly larger than the latter, It is considered that the extrusion force is normal, and if the former is less than the latter, corresponding force reduction adjustments are required.
2. The method of reversing the car is to return the tube 50~80mm from the extrusion roller, and observe whether there are obvious diameter reduction "stretch marks" on the tube billet. If the "stretch marks" are obvious, the extrusion force is too large. If Slight "stretching mark" indicates that the extrusion force is appropriate, and if there is no "stretching mark", it indicates that the extrusion force is insufficient.
3. Dynamometer, usually only for reference.
4. Destructive test, through bending, flaring, flattening and other destructive tests, check the strength of the weld to judge the extrusion force. The test method is a relatively reliable, convincing and authoritative test method among the judgment methods.