Flash butt welding-flashing, Mechanical Engineering

Flash Butt Welding-Flashing

The phenomenon of flashing is of extreme importance in achieving satisfactory welds. Flashing can begin only after a molten bridge has been formed somewhere along the interface. If the parts fit accurately, difficulty in initiating the process may be experienced and it may be necessary to level the butting surfaces to give local contact. This procedure is much different from that for resistance pressure welding where a good fit is desirable to exclude the atmosphere and prevent surface contamination. In the flash welding, surface contamination is removed in the spatter during flashing and molten metal is expelled in the final upset or forging operation.

Once a molten bridge has been formed it is set in motion over the interface by the electrodynamic forces resulting from the distortion of the current path through the work pieces. While it traverses over interface at a speed of 10 cm / s, more heat is generated in the bridge by the joule effect and is lost to the colder metal at each end. Assuming the bridge does not freeze, it will be broken in one of two ways. It may either explode because of the combined influence of overheating and the pinch effect or it may race to the edge of the work piece where it becomes extended in the form of an arc between the work faces until it ruptures. In either event, much of the metal contained in the bridge is propelled out of the joint as spatter.

Because, there is inevitably considerable inductance in the secondary circuit, collapsing of the electrical field at rupture results in a voltage surge which is capable to initiate an arc, although the open circuit voltage cannot sustain it and it is rapidly extinguished.

The Considerable heat is generated in these brief arcing periods which accounts for the efficiency of the process compared with resistance butt welding.

Posted Date: 9/17/2012 3:56:23 AM | Location : United States

Related Discussions:- Flash butt welding-flashing, Assignment Help, Ask Question on Flash butt welding-flashing, Get Answer, Expert's Help, Flash butt welding-flashing Discussions

Write discussion on Flash butt welding-flashing
Your posts are moderated
Related Questions
SURFACE HARDENING: In many conditions surface hardening instead of throughout hardening only is enough to serve the reasons. Gears are illustrations. Surface hardening is atta

Evaluate total extraction: The steel tie rod 50mm in diameter and 2.5m long is subjected to pull of 100 KN . To what length the rod must be bored centrally so that total ext

A hermite curve passes through the points (1,0), (0.866, 0.5), (0.5, 0.866), (0,1) which are parameterized at u=0,0.25,0.75,1 respectively. determine geometric coefficient of the c

The crank shaft of a high speed pump has a parallel shaft of 2.5 cm diameter and 48 cm in length. It carries three eccentrics each of 6 cm in diameter and uniform thickness of 1.8


Working Principle of Carburettor : All carburettors work on one basic principle, the venturi. A venturi is a very simple device that changes air pressure by changing the velocity

example on operation sheet?

A centrifugal clutch is to be prepared to transmit 15 KW at 900 r.p.m. The shoes are four in number. The speed at which the engagement begins is 3/4 th of the running speed. The in