In this paper the thermal stress distribution, its time effect and the character of the residual stress of welded thin mild steel plates during and after welding is studied. The plate is heated suddenly till melting temperature during welding and cooled rapidly after welding, therefore, authors treat as unstationary state. It has been already approved by many literatures that there is a stress function φ as the necessary and the sufficient condition in plane thermal elastic stress. So authors try to find the stress function to satisfy the condition of welding thin mild steel plate, and can extress the following equation, ∅=-me-a2t∫∞ea2tΘdt+e-a2t∅′∞, from which authors can calcurate the stress distribution relate to arbitrary Orthogonal Cartesian co-ordinate (x.y) by following equations, xx=∂∅/∂y2, yy=∂∅/∂x2, xy=∂∅/∂x∂y where m =E.a.k E : young's modulus a : Coefficient of thermal expansion k : thermal diffusibility of the plate a7 : Coefficient of cooling Θ: temperature distribution t: time after the welding is finished φ∞: arbitrary constant xx, yy : normal stress. xy : shearing stress Authors take.the plug welding (point thermal source) as applied practical example. As the result under consideration of the plastic flow in beyond 700°C zone besides pure elastic treatise, authors can solve the thermal stress and the residual stress distribution. This results are a good fit to experimental results in Germany and to our experimental results in regard to the radius of Luders line zone.
This flash butt welder has an ability joining large sections up to 7620 mm2 cross sectional area corresponding to 60 kg heavy rail, the capacity of which is 700 kVA. The tech nical features of this machine are its large welding capacity, thorough automatic control from preheating to upsetting process and the vertical type clamps with a power motor, having adjustable methanisms against small gaps between both materials to be welded. The machine by this design is succesfully employed and the welded rail joints show satis factory mechanical properties.