Abstract: A furnace for melting, refining or processing metals and for the reduction of ores, having a refractory or graphitic bottom and side-walls and having a roof, and having a feed-entrance for introducing the unmelted metal feed-material into the furance from above the level of the molten metal, and said furnace having a molten-metal exit, and internal-combustion burners extending downwardly through the roof of the furnace with their discharge ends substantially below the melt-level and with their other ends outside the furnace. Each of the burners has a refractory or metallic combustion chamber and a metallic liquid coolant-jacket surrounding said combustion chamber, with the coolant-inlet and the coolant-outlet of the jacket being near the other end of the burner, outside the furnace.