Abstract
A new underwater plasma welding process has been developed. In this process, viscous liquid is used in place of shielding gas to protect the part being welded from the surrounding water and to stabilize plasma arc.
Welding experiments are done by using steel for welded structure of 6 mm in thickness and it is ascertained that this process can be put to practical use.
Main results are summarized as follows:
(1) Water glass is used as a typical viscous liquid.
(2) Water glass shielding for the part being welded has a marked effect on stabilization of underwater plasma arc.
(3) Water glass shielding has an effect on heat insulating of the part being welded and lowers the solidification rate of molten metal. Owing to this feature, the weld metal does not include a blowhole and the maximum hardness of the heat-affected zone adjacent to the bond is lowered considerably.
(4) The weld resulting from this process has excellent mechanical properties, and especially its ductility and notch toughness can be improved remarkably, compared with those of the weld resulting from nonshielding.
(5) Coefficient of viscosity and flow (feeding) rate of shielding water glass should be selected properly. However, the proper range of combinations of viscosity and flow rate may be relatively wide.
