Flash butt welding-flashing, Mechanical Engineering

Assignment Help:

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.


Related Discussions:- Flash butt welding-flashing

Residual stress and deformation in aluminum, deformation and stress in alum...

deformation and stress in aluminum 6061 after extrusion

Dynamically induced emf and statically induced emf, Q. What is meant by dyn...

Q. What is meant by dynamically induced emf and statically induced emf? On what factors do these depend? Derive eq. for these two emfs.   Sol. Dynamically induced emf:

Determine the deflection of the spring, Determine the deflection of the spr...

Determine the deflection of the spring: A close coiled helical spring deflects 25 mm under a certain axial load. Determine the deflection of the second spring under the simila

Pressure vessel materials, Pressure Vessel materials shall be as specified ...

Pressure Vessel materials shall be as specified on the Vessel Data Sheet. All attachments to vessels shall be of the same ‘P Number' material as that for the pressure envelope,

Electromagnetic conversion device with example., Q.  In every electromagne...

Q.  In every electromagnetic conversion device, both generator and motor action take place simultaneously. Explain. The case the output is mechanical as in a motoring mode, th

Array, sorting order of arra

sorting order of arra

Rankine cycle, A cycle stream power plant is to be designed for stream temp...

A cycle stream power plant is to be designed for stream temperature and turbine 350

Potential energy and kinetic energy- thermodynamics, Potential energy (PE) ...

Potential energy (PE) The energy possessed by body or system by virtue of its position above the datum level. The work done is because of its falling on earth's surface. Po

Washing and drying a motorcycle, Washing and Drying a Motorcycle :  It is ...

Washing and Drying a Motorcycle :  It is important to wash and dry the motorcycle before servicing. It would ensure cleanliness during the service and would not allow any dust ent

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd