Interfacial Tension Theory on the Phenomena of Arc Welding (Chapter 1)

1.Surface of Penetrarion and Mother Drop

Abstract

This is an attempt at interpretting arc welding as a kind of wetting phenomenon, i.e., a mechanical phenomenon which is governed by three kinds of interfacial tension taking part in it. Fundamental and general behaviour of a liquid drop confined within a solid surface was discussed first, and the findings were applied to explain the welding phenomena. The results were as follows.
(1) "Mother Drop", the molten weld metal phase, should be considered as a single liquid drop, surrounded by an interface between molten metal and slag or gas phase, stressed by interfacial tension.
(2) Mother Drop is confined within a concave "Surface of Penetration", which is composed of the melting surface of mother plate and the solidifying surface of a weld bead."Confinement" means that the contact line of a liquid drop can not leave the intersecting line of two surfaces until the liquid surface takes the equilibrium contact angle against the adjoining surface.
(3) Internal pressure of a liquid drop kept within a concave conical surface upon a horizontal plate is minimum when its contact line reaches the boundary line and its contact angle is equilibrium value. Mother drop on the surface of penetration seems to be in a similar condition.
(4) Generally there are two types of drop, "Convex" and "Flat", in a single V-groove. If the inclination of groove face is too small as compared with the contact angle of the drop, there emerges flat to convex transition with an increasing volume of the drop. Mother drop of normal weld bead must be a flat type.