水中プラズマ溶接部の冷却

抄録

Weld thermal cycles during underwater wet welding (bead welding in the flat position) using a plasma arc as a source of heat were measured. On this measurement, the cooling process and the effects of welding parameters on the time required for cooling from 800°C to 700°C, 800°C to 500°C and 800°C to 300°C were investigated.
The experiments were carried out at a depth of 20cm in city water by using 12mm, 19mm and 25mm thick steel plates as the base metal.
The results of this investigation are summarized as follows:
(1) The cooling process during underwater wet welding is characterized by a maximum cooling rate under cooling due to the transition of boiling and by discontinuous curves of cooling due to the instability of boiling.
(2) In a quasi-stationary state of underwater wet welding,
(2-1) The cooling time for each range of temperature near the center of bond is prolonged by some 20% as initial temperature of the water environment rises from 1.5°C to 30°C.
(2-2) A reduction in thickness of the base metal hardly prolongs the cooling time.
(2-3) The cooling time is nearly in proportion to relatively low input of weld heat. The prolongation ratio of cooling time to weld heat input, however, decreases gradually as input becomes still higher.