A system for producing a metal foam comprises a bath containing a molten metal, a rotating shaft or impeller extending through the base of the bath into, and submerged in the molten metal, and a gas discharge nozzle provided on the submerged end of the shaft. The opposite end of the shaft is connected to a gas supply line and the shaft is rotated with a motor. A seal is provided at the opening in the base of the bath for preventing leakage of the molten metal there-through.