The structure of glass kilns and refractory linings, the RH refining method is a vacuum circulation degassing method successfully developed in 1958 by the German steel companies Ruhrstahl and Heraens. Due to its good degassing effect, minimal temperature drop, and wide applicability, the RH refining technology has been widely used in the steel industries of various countries around the world.
1) Furnace Body Structure
The main parts of the RH refining furnace are named according to their different functions and positions 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 bend pipe) (including manhole), etc.
2) Refractory Lining Structure
The bottom of the trough is divided into: working layer, secondary working layer, ramming material.
The lower trough is divided into: working layer, secondary working layer, insulation layer (also known as permanent layer), heat-insulating layer.
The 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 working layer, heat-insulating layer.
The launder part is divided into: working layer, secondary working layer, heat-insulating layer.
The upper trough is divided into: working layer, secondary working layer, insulation layer (also known as permanent layer), heat-insulating layer.
The hot top cover is divided into: working layer, insulation layer (also known as permanent layer), heat-insulating layer.
Manhole: working layer, heat-insulating layer, Taishan Hotel.
The service life of the sintered refractory lining of 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 further from the molten steel and some parts are closer to it, even inserted into the molten steel. The lifespan of the refractories depends on the usage area; the lower the part of the furnace, the closer it is to the molten steel, and the shorter the service life. Therefore, the erosion of the immersion tube is the most severe, followed by the bottom, while other parts suffer relatively less damage. The selection of materials for the inner lining of the RH degassing vacuum trough is determined based on the location and distance from the molten steel, as well as 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 tube is immersed 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 drops, 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 quite evident. The driving gas exists in the molten steel in the form of large quantities of small bubbles. Due to high temperature and low pressure, the expansion work of the gas drives the rapid rise of the molten steel 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, thus entering the vacuum chamber in a fountain-like manner, significantly increasing the degassing interface, thereby accelerating the degassing process.
The degassed molten steel gathers at the bottom of the vacuum chamber and continuously returns to the ladle through the descending tube at a speed of 1~2 meters/second due to gravity. Because the returning molten steel has certain kinetic energy, it will impact the undegassed molten steel, stirring and mixing each other. Molten steel from the ladle continuously enters the vacuum chamber, and after degassing, returns to the ladle. After several cycles, the gases in the molten steel can be reduced to a very low level.
In the early stages of circulation, sampling and temperature measurement are conducted every 10 minutes. As the treatment nears the end, sampling and temperature measurement are conducted again every 10 minutes. According to the results of sample analysis, alloy materials are added. The start time of adding materials depends on the amount of material added, generally requiring completion 6 minutes before the end of the treatment. After the materials are added, continue circulating for a few more minutes to ensure uniform composition.
After the treatment is completed, turn off the vacuum pump, lift and rotate the vacuum chamber, then take samples and measure temperatures again. Then lift the ladle to the casting section for casting.
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).
Protection material for the outer wall of the immersion tube and steel structure: Corundum-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 lightweight ball 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 lightweight ball 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-rebonded magnesia-chrome brick (LBMGe-20).
Hot Face Heat-insulating Layer: Calcium silicate board (II-200).
Launder Working Layer: Impact zone silicon nitride bonded silicon carbide brick Non-impact zone electro-fused re-bonded magnesia-chrome brick (LDMGe-20)/semi-rebonded magnesia-chrome brick (LBMGe-20).
Launder Secondary Working Layer: High alumina brick/Lightweight ball brick/Lightweight high alumina brick.
Launder Heat-insulating Layer: Aluminum silicate fiber felt (PXZ-1000).
Upper Trough Working Layer: Electro-fused re-bonded magnesia-chrome brick (LDMGe-20)/semi-rebonded 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 lightweight ball brick/Lightweight high alumina brick.
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.
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