Blast Furnace
From Captain of Industry Wiki
A Blast Furnace is used to convert various ores into their molten counterpart. Early game, a blast furnace is used to convert metal scrap and coal into molten Iron. However, as the game progresses, new recipes can be unlocked which allow for more long-term production of molten items. Blast furnaces also produce exhaust and slag as a byproduct of their production.