The foundry is loud and hot. It is a world unto itself, with 44 acres under its roof. Lately, after decades of turmoil, it is a place of optimism. Columbus Castings is in the process of adding 550 jobs. This would bring the head count to about 1,100, part of a plan to expand product lines and meet rising demand for steel parts from the railcar industry. “It gets a little warm in here, but at the end of the…