Review on manufacturing process of large turbo-generator shafts

In March 1975, the shaft material for the 1800 MW nuclear power generator was shipped from the Japan Steel Works, Ltd. to Kraftwerk Union AG in FRG. Its weight is 247 t, and it is the largest generator shaft and the largest forging in the world. The largest capacity of the tandem compound type generators in operation so far is 1200 MW, and it is expected that 2,000 - 3,000 MW unit will appear in 1980s. When the capacity of generators is increased, it is always the problem whether the shafts can be made in one body. It is difficult to adopt shrinkfit or welded structure in case of generator shafts in view of the function. The highest mechanical properties and the highest quality must be guaranteed because they are high speed rotating bodies. There are only three manufacturers in the world who can produce the ingots for the shafts of more than 800 MW, because the problems are not only production facilities but also the establishment of the technology for producing sound ingots and the solution of productivity problem. It was proved that electroslag remelting process can produce clean and sound ingots, and is promising for the production of large ingots. Supersonic flaw detection process has been incorporated in the forging process and it improves the rate of material utilization. The manufacture of large shafts with 400/500 t ingots can be accomplished similarly to that with medium ingots in the Japan Steel Works. (Kako, I.)