アーク溶接現象に関する界面張力理論(第4章)

Abstract

The author has proposed the following mechanism of penetration in Chapter 3 of this report.The contact line of a mother drop push-squeezed by the arc force recedes, leaving the base metal surface bare. Near the point where the contact line starts to deviate from the boundary line of the surface of penetration, a strong pulling force to counteract the arc pressure is developed and this is the greater, the larger the value of the angle of penetration θg. When the θg of exposed surface is increased through direct action of arc the exposed surface displaces itself, and a "Peripheral Penetration" is caused at the front portion of the surface of penetration through the joint action of arc and mother drop.The theory was testified in this report through the observation of various patterns of penetration and other evidences. Existence of bare surface of mother metal during welding proved to be true, and the traces of direct action of arc were discovered as small concavities upon it. Although the proposed theory is satisfactory for the peripheral penetration, it is necessary to modify the theory in order to explain the "Central Penetration", which is the result of direct action of arc on the constantly exposed base metal without interference of the mother drop. And at the rearward portion of the peripheral penetration, indirect action of the liquid metal overheated by arc plays a significant role, which is also coupled with the oscillation of the mother drop.It was concluded that the most essential factors to decide the type of penetration are arc force on the one side and interfacial tension and contact angle of the mother drop on the other, because the interaction of these forces determines the size of exposed bare surface and induces its oscillation around the surface of penetration.