The structure of glass kilns and the refractory lining materials, RH refining method was successfully developed in 1958 by the joint efforts of Ruhrstahl and Heraeus, two German steel companies. Due to its good degassing effect, minimal temperature loss, and wide applicability, the RH refining technology has been widely used in the global steel industry.
1) Furnace Structure
The main parts of the RH refining furnace are respectively called: 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), etc., according to their different functions and positions in the external refining process.
2) Refractory Lining Structure
Trough bottom is divided into: working layer, secondary working layer, ramming material.
Lower trough is divided into: working layer, secondary working layer, insulation layer (also known as permanent layer), heat-insulating layer.
Middle trough is divided into: working layer, secondary working layer, insulation layer (also known as permanent layer), heat-insulating layer.
Alloy feeding port is divided into: hot face part working layer, heat-insulating layer.
Chute part is divided into: working layer, secondary working layer, heat-insulating layer.
Upper trough is divided into: working layer, secondary working layer, insulation layer (also known as permanent layer), heat-insulating layer.
Hot top cover is divided into: working layer, insulation layer (also known as permanent layer), heat-insulating layer.
Manhole: working layer, heat-insulating layer.
The service life of the sintered refractory lining in the RH furnace varies depending on its location. The operating state of the RH furnace is such that some parts of the furnace body are farther from the molten steel, while others are closer, even immersed in the molten steel. The service life of the refractories depends on the usage location; the lower the position in the furnace body, the closer it is to the molten steel, the shorter the service life. Therefore, the immersion tube suffers the most severe erosion, followed by the bottom, with other parts experiencing relatively less damage. The selection of materials for the RH degassing vacuum trough lining is determined based on the proximity of the location to the molten steel and the factors affecting the trough body, such as temperature, vacuum, gas, chemistry, and thermodynamics.
RH System Operation Process
After lifting the ladle containing 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 inserted into the molten steel, with an insertion depth of no less than 150mm~200mm. After starting the vacuum pump, as the pressure in the vacuum chamber decreases, the molten steel in the ladle rises along the two insertion tubes. Driving gas is blown 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 a large number of small bubbles. Due to the high temperature and low pressure, the expansion work of the gas pushes the molten steel to quickly rise in the rising tube. When the molten steel leaves the rising tube and enters the vacuum chamber, the linear velocity can reach 5 meters/second, so the molten steel enters the vacuum chamber in the form of a fountain, significantly increasing the degassing interface, thereby accelerating the degassing process.
The degassed molten steel gathers 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 each other. The molten steel in the ladle continuously enters the vacuum chamber, degasses, and then returns to the ladle. After several cycles, the gas content in the molten steel can be reduced to a very low level.
During the early stages of circulation, samples are taken and temperatures are measured every 10 minutes. As the treatment nears completion, samples are taken and temperatures are measured every 10 minutes again. Based on the sample analysis results, alloy materials are added. The start time of adding materials depends on the amount of material added, generally requiring completion within 6 minutes before the end of the treatment. After the material is added, the circulation continues for a few more minutes to ensure uniform composition.
After the treatment is completed, the vacuum pump is turned off, and the vacuum chamber is lifted and rotated open simultaneously, taking another sample and measuring the temperature. Then, the ladle is lifted to the casting section for pouring.
3. RH System Material Configuration
1) Material Configuration
Immersion Tube: Electro-fused re-bonded magnesia-chrome brick (LDMGe-20) (salt-soaked).
Circulation Tube: Electro-fused re-bonded magnesia-chrome brick (LDMGe-26/-20) (salt-soaked).
Protective material for the outer wall of the immersion tube and the steel structure: Alumina-spinel castable (LGJJ-1).
Trough Bottom:
Working Layer: Electro-fused re-bonded magnesia-chrome brick (LDMGe-20) (salt-soaked).
Secondary Working Layer: Electro-fused re-bonded magnesia-chrome brick (LDMGe-20) (salt-soaked).
Ramming Material: Magnesia-chrome ramming material (LMCR-20).
Lower Trough:
Working Layer: Electro-fused re-bonded magnesia-chrome brick (LDMGe-20) (salt-soaked).
Secondary Working Layer: Electro-fused re-bonded/directly bonded magnesia-chrome brick (LDMGe-20) (LZMGe-12,8).
Insulation Layer: High-alumina brick/Mullite polystyrene lightweight brick/Lightweight high-alumina brick.
Heat-insulating Layer: Calcium silicate board (II-200).
Middle Trough:
Working Layer: Electro-fused re-bonded magnesia-chrome brick (LDMGe-20).
Secondary Working Layer: Directly bonded magnesia-chrome brick (LZMGe-18, LZMGe-12, LZMGe-8).
Insulation Layer: High-alumina brick/Mullite polystyrene lightweight brick/Lightweight high-alumina brick.
Heat-insulating Layer: Calcium silicate board (II-200).
Alloy Feeding Port:
Hot Face Working Layer: Electro-fused re-bonded magnesia-chrome composite brick (LDMGe-20) (LDMGe-26)/Semi-re-bonded magnesia-chrome brick (LBMGe-20).
Hot Face Heat-insulating Layer: Calcium silicate board (II-200).
Chute Working Layer: Impact area silicon nitride bonded silicon carbide brick Non-impact area electro-fused re-bonded magnesia-chrome brick (LDMGe-20)/Semi-re-bonded magnesia-chrome brick (LBMGe-20).
Chute Secondary Working Layer: High-alumina brick/Poly-light ball lightweight brick/Lightweight high-alumina brick.
Chute Heat-insulating Layer: Aluminosilicate fiber felt (PXZ-1000).
Upper Trough:
Working Layer: Electro-fused re-bonded magnesia-chrome brick (LDMGe-20)/Semi-re-bonded magnesia-chrome brick (LBMGe-20).
Secondary Working Layer: Directly bonded magnesia-chrome brick (LZMGe-18) (LZMGe-12) (LZMGe-8).
Insulation Layer: High-alumina brick/Mullite polystyrene lightweight brick/Lightweight high-alumina brick, packing strap.
Heat-insulating Layer: Calcium silicate board (II-200).
Hot Top Cover:
Working Layer: Directly bonded magnesia-chrome brick (LZMGe-18) (LZMGe-12) (LZMGe-8).
Secondary Working Layer: High-alumina brick/Clay brick (N-2a)/Lightweight high-alumina brick.
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/