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RH Process

RH (Ruhrstahl-Heraeus) - DEGASSER HISTORY OF THE RH - PROCESS In 1957, A. Lorenz was granted a patent for the vacuum degassing of molten metals, in particular steel. Compared with the patent applied for E. Williams in 1931, the Lorenz invention constitutes a further step forward to it’s practicable approach. Model tests using water or mercury, to further investigate the underlying principle, of the facility were done is 1957 at the Hattingen Henrichshütte works together with the Heraeus company of Hanau. Early in 1958, the first heat was treated in a pilot plant were the vacuum vessel was carried on ropes and taken to it’s treatment position by a crane. The RH-process is now in use in hundreds of units all over the world, in a variety of applications. The increased acceptance of the RH-method is due to a higher demand of high grade steel and progress in oxygen injection which leads in new vessel types, like the RH-OB, RH-OTB or RH-KTB vessels. BRIEF DESCRIPTION OF THE PROCESS The RH-process works with two snorkels immersing into the ladle. The main chamber is than evacuated, which draws steel through both legs into the lower vessel by the equivalent ferrostatic pressure of about 1,4m. A recirculation effect is than produced by bubbling inert gas, e.g. argon, into the up leg. This causes the steel to accelerate through the up leg (velocity, more than 5m/sec.), flowing through the degasser and returning to the ladle via the down leg. The special advantages of the RH process prove to be the high performance capability of RH facilities (cycle times, equipment availability) and the achievable metallurgical results when adjusting the analysis to low hydrogen and carbon contents (approx. 1,5 ppm H and 15 ppm C) as well as the homogenizing and improved steel cleanliness benefits. The circulation rate is a function of some parameters like snorkel diameter, gas flowrate and height from argon nozzle to refractory bottom. When the circulation rate is increased the treatment-time can be shortened, means the quicker the aimed values for O, C, H and N will be achieved. The maximum flow rate of steel through the outlet snorkel is approx. 1,3 m /sec.