A small explosion in a furnace temporarily shut down the Kaiser Aluminum Corp. Trentwood rolling mill Saturday.
No one was injured by the blast in one of several casting areas that was undergoing routine maintenance, said company spokesman Dave Quast.
Operations in other areas of the vast plant resumed by 6 p.m. Saturday, he said, and full operation was expected by 6 p.m. Monday.
The maintenance work was being done by an outside contractor, Quast said.
Dan Wilson, president of United Steelworkers of America Local 338, said few people were in the area, and there was no molten metal in the idled furnace.
The furnace is natural gas-fired, but gas is not a suspected cause, he said, adding "There was no fire."
Wilson said the company and union are working together to find the cause.
"It's kind of unusual. We don't see this kind of explosion very often," he said.
The Trentwood plant rolls aluminum ingots into sheet and plate, much of it used by the aerospace industry.