I. Resistance butt welding
The two workpieces are always pressed together at the end, heated to a plastic state by resistance heat, and then quickly apply the top forging pressure (or in the absence of top forging pressure to maintain welding pressure) is called resistance butt welding.
Resistance butt welding process parameters are mainly the following three.
(1) outstretched length: in determining the length of the workpiece from the clamp electrode end face outstretched, should take into account the stability of the workpiece during the top forging and heat dissipation of the clamp.
(2) Welding time and welding current. In resistance butt welding there are two decisive factors, welding time and welding current, both can be adjusted accordingly within a certain range. Large current, short time can be used; can also use small current and long time. However, when the difference is too large, affecting the strength of the welded joints, prone to joint oxidation, coarse grain and other defects.
(3) top forging pressure, welding pressure. Heating is appropriate to use a smaller top forging pressure, with a larger welding pressure top forging.
- Flash butt welding
Usually flash butt welding can be divided into preheating flash butt welding, continuous flash butt welding (continuous flash butt welding is divided into the top forging stage and flash stage two parts).
1, flash stage
In the flash stage, the electricity is turned on first, the main function is to heat the workpiece, and then make the two workpieces slightly contact with the end surface, forming many contacts. When heat is generated by the passage of electric current, the contacts are melted and turned into a liquid metal over-beam connecting the two ends. The liquid metal in the over-beam evaporates and the over-beam bursts due to the extremely high current density in the liquid metal beam. The operation of the moving clamp is slowly advanced, the process of over-beam will still continue to generate the burst. Under the action of electromagnetic force, the liquid metal particles continue to form sparks, sprayed from the interface, that is, flash.
2, top forging stage
After the end of the flash stage, you need to immediately carry out the top forging pressure on the workpiece, the interface gap is rapidly reduced, it stops over the beam blast, into the top forging stage. The role of the top forging is to squeeze the liquid metal and oxidation inclusions on the end face, close the gap between the end face of the workpiece, while making the clean plastic metal in close contact to form a solid joint.
