Interfacial Tension Theory on the Phenomena of Arc Welding (Chapter 5)

Solidification of Mother Drop

Abstract

The author discussed various phenomena of solidification of a molten metal droplet with a certain contact angle on the solid surface of the same metal. It was concluded as follows.
(1) If the solidifying layer of a droplet is always flat and horizontal, the contact line of the remaining droplet must move inward to maintain the contact angle. If the droplet is very small and spherical, the final solidified body obtained must be a cone of which the base angle φ is calculated to be 70% of the contact angle θ₀.
(2) First assumption is satisfied in the case of very rapid solidification of welding spatter, and the fact that the beautiful conical bodies, 'Ishizaki's cones', were obtained experimentally is considered to support the theory.
(3) The base angle of conical spatters obtained with lime type coated electrode was found to be 45 degrees, therfore its contact angle should be 64 degrees.
(4) Staircase-like solidification found on small metal spatter was explained to be the result of oscillation of remaining molten droplet confined at the edge of each solidified layer.
(5) Three types of bead solidification, that is, slipping, confined and overlapping type, were defined.
(6) Under-cut of weld bead is caused by the simillar mechanism to that of the above-mentioned phenomenon.