This article by John Lippman was published in the Valley News on June 16. Not long ago, there used to be a lot of soot inside the Vermont Castings foundry, where workers would come off shifts coated in black, looking as if they had just emerged from a coal mine. But carbon particles don’t mix well with $450,000 Swedish-made robots, let alone people. That’s one of the stark changes at the Randolph maker of…