METHOD OF RETARDING DEFECT FORMATION DURING THERMITE WELDING OF RAILWAY RAILS

摘要

"Preventing or reducing defects" improves "endurance limit" and "fatigue resistance" of alumino thermit welding of railway rails. The regions of two rails present just beside mould wall on both sides of mould are heated to a temperature between 200° C to 1200° C, preferably between 500° C to 900° C using any heat energy sources like burners that are used in gas-pressure welding in time span between start of pre-heating process up to completion of solidification of weld collar. Heating of regions of two rails just beside mould wall to a high temperature causes: a) Prevents thermal contraction of "heated and thermally expanded regions of two rails" during "solidification phase of welding" and thereby prevents occurrence of "tearing apart tensile stresses" and thereby prevents "hot tearing" and formation of"centerline defect"; b) Reduces thermal gradient and thereby reduces conductive heat flux from weld cavity to two rails and thereby: i) Causes "increase in depth of melt-back of stick-out rail ends", which prevents "cold-lap defect formation", ii) Demotes "progression of parallel dendritic solidification fronts of rails 41 and 42 towards each other along longitudinal axis of rails", which prevents formation of liquid weld metal pool locked amidst nascent solidus and thereby prevents "shrinkage cavity defect formation", iii) Reduces criticality of "quantity of heat energy that is tapped into weld-cavity" for achieving proper fusion and thereby reduces quantity of dissolved gases in fused liquid metal present in weld-cavity and thereby reduces severity of microporosity defect. c) during solidification phase of welding increases conductive heat flux to the bottom of mould due to dissipation of heat energy via surfaces of heat dissipating fins present at the bottom of mould-assembly and thereby promotes vertically upward directional solidification of fused liquid metal present in weld-cavity and thereby prevents shrinkage cavity defect formation.