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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.
Explain the uses of Residual soils Residual soils may be underlain by sloping rock which may contain weathered seams. The possibility of foundations sliding on these seams have
SHIELDING GAS The primary function of the shielding gas is to exclude the atmospheric air from the arc zone. However, the shielding gas has significant influence on the arc cha
How to drill 500 sheets paper ?in 4 mm dia , holes are same distance as its dia (4mm) in one line.
torque
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An inside cylinder locomotive has its cylinder centre lines 0.70 m apart and has a stroke of 0.60 m. The rotating mass per cylinder is similar to 150 Kg. and the reciprocating mass
#Double action dies
The tapered, two-cell beam is subjected to a pure torque of 50,000 in-lb counter clockwise. The length of the beam (normal to the figure) is 100 in. The flange areas are 1 sq in an
Charpy impact tests, when required shall comply. Impact tests shall be conducted at the minimum design metal temperature or at a lower temperature and shall meet or exceed energ
Disadvantages of two stroke engine: The following are some of the disadvantages of two stroke engine when compared with four stroke engine: 1. As firing takes place in ever
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