Electric heating – Metal heating – Nonatmospheric environment at hot spot
Patent
1999-01-27
2000-10-03
Ryan, Patrick
Electric heating
Metal heating
Nonatmospheric environment at hot spot
219 73, 228102, B23K 918
Patent
active
06127643&
ABSTRACT:
A process, called Covered Trailing Edge of Weld (CTEW) that can be applied during fusion welding that produces a weld without cracks and porosity and reduced residual stress level, is described. The process eliminates or reduces the need of non-destructive testing, re-work and post weld heat treatments in weld manufacturing. It is known that in a normal unassisted solidification of a weld, numerous cooling gradients from solid-liquid interfaces come into effect, because of numerous and multi-directions of solid crystal faces that promote crystal growth in solidifying metal in different direction. Such micro cooling gradients in molten metal are in various directions also because of varying inclinations of the surface of the cup at each point where solid base of microstructure is exposed for crystal growth. Resultant growth direction of mass of crystals/grains is determined by direction of welding, gun angle, inclination of cup surface on which crystals grow at each point and applied directions of heat conduction. Different directions of neighboring crystals thus grown at the interface, generate complex micro structure which may be dense with several entanglements or with voids which may capture gas. As the temperature falls, stress is generated at each entanglement according to property of the metals involved. In the process described a heat sink is created on the trailing edge of weld (TEW) by depositing a material on it as the welding progresses. Such deposited material absorbs heat from the solidifying metal adjoining it, beneath it, and creates a unidirectional cooling gradient that is stronger than individual micro-cooling gradients at each point at the interface. The deposited material has lower melting point than the temperature at solidification of the metal. Thus, heat conduction is reduced into the base metals, micro-cooling gradients being weaker, as part of heat in the solidifying cup of molten metal is conducted into heat sink on TEW. Thus, in CTEW process easy growth of crystals is assisted by superimposed constant heat flow towards TEW. Such a pattern of growth of crystals creates compact arrangement of crystals, eliminating porosity and voids due to gas which may otherwise be entrapped in complex micro structure during solidification, as temperature falls. The covering formed on TEW insulates the weld metal beneath it so that radiation to atmosphere is reduced and the micro structure is incubated, which provides further means to reduce the stress.
REFERENCES:
patent: 3610868 (1971-10-01), Mantel et al.
patent: 4386727 (1983-06-01), Unde
patent: 5024371 (1991-06-01), Unde
patent: 5211327 (1993-05-01), Clarke et al.
Dey Anjan
Ryan Patrick
LandOfFree
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