ABSTRACT
In his handbook, Herrmann (1958) describes many pilot installations for ultrasonic vibration treatment of molten metal. The treatment is conducted both in feeders and in molds to refine grains, remove dissolved gases, and improve casting conditions. For example, Diirener Metallwerke induced ultrasonic oscillations in the liquid pool to degas the melt and refine grains in solidification. Oscillations were launched by a gas-tight vibrating slab connected to a vibrator. Unfortunately, this method proved to lack sufficient power for the casting of large ingots. Another German company, Vereinigte Deutsche Metall Werke, developed a dynamic scheme in which oscillations were supplied to the melt by a vibrator submerged into the molten part of the ingot, or by a pulsing gas jet blown onto the surface of the liquid pool.The company AFG pointed out that ultrasound can be used to advantage in continuous casting to degas the melt, however, one has to select a material resistant to the melt and vibration. Similarly, Aktiebolaget Svenska Metall Werke tried to transfer oscillations in the liquid pool by submerged metal rings and discs connected to an oscillation generator.In order to cope with discontinuities in the continuous casting of light (Al-Mg based) alloys, the Aluminum Company of America (Alcoa) suggested inducing vibration waves traveling from the center of the ingot to the mold walls on the surface of the liquid pool. Reported experimental data were obtained at a frequency of 5.0 Hz for 30mm diameter bars. The outer surface was free from cold shuts.Experimenting with a continuous aluminum casting system with a vibrating tool installed over the liquid pool, Schoeler-Bleckmann Stahlwerke AG found that the amount of energy that can be transmitted from ultrasonic vibrators proved to be sufficient for grain refinement, degassing, and averaging the metal structure. In continuous casting of steel with a typically large depth of the solidification cone, vibrators were placed on the water cooled inner wall of the mold. Ingots obtained with this casting machine are fine grained and have a higher metal density over the entire cross section (Herrmann, 1958). Schoeler-Bleckmann suggested degassing the melt by treating it with ultrasound in the feeder.
