The structure of glass kilns and refractory materials for internal lining, RH refining method was successfully developed in 1958 by the German steel companies Ruhrstahl and Heraeus as a vacuum circulation degassing method. Due to its excellent degassing effect, minimal temperature reduction, and wide range of applications, RH refining technology has been widely adopted in the global steel industry.
1) Furnace Structure
Each major part of the RH refining furnace is named according to its different functions and location in the external refining process: Immersion tube, Circulation tube, Lower trough, Middle trough (including alloy feeding port), Upper trough, Hot top cover (also known as hot bent pipe) (including manhole).
2) Refractory Material Lining Structure
Trough bottom divided into: Working layer, Secondary working layer, Ramming material.
Lower trough divided into: Working layer, Secondary working layer, Insulating layer (also known as permanent layer), Heat-insulating layer.
Middle trough divided into: Working layer, Secondary working layer, Insulating layer (also known as permanent layer), Heat-insulating layer.
Alloy feeding port divided into: Hot face working layer, Heat-insulating layer.
Chute part divided into: Working layer, Secondary working layer, Heat-insulating layer.
Upper trough divided into: Working layer, Secondary working layer, Insulating layer (also known as permanent layer), Heat-insulating layer.
Hot top cover divided into: Working layer, Insulating layer (also known as permanent layer), Heat-insulating layer.
Manhole: Working layer, Heat-insulating layer.
The service life of the sintered refractory material lining of the RH furnace varies depending on its location. The operating state of the RH furnace involves some parts being further from the molten steel and others closer, even immersed in it. The service life of the refractory materials depends on their usage location; the lower the part of the furnace, the closer it is to the molten steel, and the shorter its service life. Therefore, the immersion tube experiences the most severe erosion, followed by the bottom, with other parts suffering less damage. The selection of materials for the RH degassing vacuum trough lining is determined based on the distance from the molten steel and the effects of temperature, vacuum, gases, chemistry, and thermodynamics on the trough body.
RH System Operation Process
After lifting the ladle containing the molten steel to the treatment position, the RH device's vacuum chamber is rotated above the ladle. Then, the vacuum chamber is lowered so that the insertion tubes are submerged in the molten steel, with an insertion depth not less than 150mm-200mm. After starting the vacuum pump, as the pressure in the vacuum chamber decreases, the molten steel rises along the two insertion tubes. Blowing driving gas into the rising tube, when the pressure in the vacuum chamber drops to 26-13Pa, the circulation of molten steel in the vacuum chamber becomes very noticeable. The driving gas exists in the molten steel in the form of numerous small bubbles. Due to high temperature and low pressure, the expansion work of the gas pushes the molten steel to rise quickly in the rising tube. When the molten steel leaves the rising tube and enters the vacuum chamber, its linear velocity can reach 5 meters/second, thus entering the vacuum chamber like a fountain, significantly increasing the degassing interface and accelerating the degassing process.
After degassing, the molten steel accumulates at the bottom of the vacuum chamber and, under the action of gravity, continuously returns to the ladle through the descending tube at a speed of 1-2 meters/second. Due to the certain kinetic energy of the returning molten steel, it impacts the undegassed molten steel, stirring and mixing them. Molten steel from the ladle continuously enters the vacuum chamber, degasses, and then returns to the ladle. After several such cycles, the gas content in the molten steel can be reduced to a very low level.
At the beginning of the cycle, samples are taken and temperatures measured every 10 minutes. As the treatment nears completion, samples are taken and temperatures measured again every 10 minutes. Alloy materials are added based on the results of sample analysis. The start time of adding materials depends on the amount of material added, generally requiring completion 6 minutes before the end of treatment. After adding the material, the molten steel circulates for a few more minutes to ensure uniform composition.
After the treatment is completed, the vacuum pump is turned off, the vacuum chamber is lifted and rotated open while taking another sample and measuring the temperature. Then, the ladle is lifted to the pouring section for casting.
3. RH System Material Configuration
1) Material Configuration
Immersion tube: Electrically fused re-bonded magnesia-chrome bricks (LDMGe-20) (salt-soaked).
Circulation tube: Electrically fused re-bonded magnesia-chrome bricks (LDMGe-26/-20) (salt-soaked).
Protection material for the outer wall of the immersion tube and steel structure: Corundum-spinel castable (LGJJ-1).
Trough bottom
Working layer: Electrically fused re-bonded magnesia-chrome bricks (LDMGe-20) (salt-soaked).
Secondary working layer: Electrically fused re-bonded magnesia-chrome bricks (LDMGe-20) (salt-soaked).
Ramming material: Magnesia-chrome ramming material (LMCR-20).
Lower trough
Working layer: Electrically fused re-bonded magnesia-chrome bricks (LDMGe-20) (salt-soaked).
Secondary working layer: Electrically fused re-bonded/directly bonded magnesia-chrome bricks (LDMGe-20) (LZMGe-12,8).
Insulating layer: High-alumina bricks/Mullite polylight ball lightweight bricks/Lightweight high-alumina bricks.
Heat-insulating layer: Calcium silicate board (II-200).
Middle trough
Working layer: Electrically fused re-bonded magnesia-chrome bricks (LDMGe-20).
Secondary working layer: Directly bonded magnesia-chrome bricks (LZMGe-18, LZMGe-12, LZMGe-8).
Insulating layer: High-alumina bricks/Mullite polylight ball lightweight bricks/Lightweight high-alumina bricks.
Heat-insulating layer: Calcium silicate board (II-200).
Alloy feeding port
Hot face working layer: Electrically fused re-bonded magnesia-chrome composite bricks (LDMGe-20)(LDMGe-26)/semi-rebonded magnesia-chrome bricks (LBMGe-20)
Hot face heat-insulating layer: Calcium silicate board (II-200).
Chute working layer: Impact zone silicon nitride bonded silicon carbide bricks Non-impact zone electrically fused re-bonded magnesia-chrome bricks (LDMGe-20)/semi-rebonded magnesia-chrome bricks (LBMGe-20)
Chute secondary working layer: High-alumina bricks/polylight ball lightweight bricks/lightweight high-alumina bricks.
Chute heat-insulating layer: Aluminosilicate fiber felt (PXZ-1000).
Upper trough
Working layer: Electrically fused re-bonded magnesia-chrome bricks (LDMGe-20)/semi-rebonded magnesia-chrome bricks (LBMGe-20).
Secondary working layer: Directly bonded magnesia-chrome bricks (LZMGe-18)(LZMGe-12) (LZMGe-8).
Insulating layer: High-alumina bricks/mullite polylight ball lightweight bricks/lightweight high-alumina bricks, packing straps.
Heat-insulating layer: Calcium silicate board (II-200).
Hot top cover
Working layer: Directly bonded magnesia-chrome bricks (LZMGe-18)(LZMGe-12)(LZMGe-8).
Secondary working layer: High-alumina bricks/fireclay bricks(N-2a)/lightweight high-alumina bricks.
Heat-insulating layer: Calcium silicate board (II-200).
Magnesia-chrome mortar (LMGeN-18/8) and high-alumina mortar (LN-65) are used during construction.
Reference: http://www.sdyaozhong.com/