DH Gassing
In DH degassing, a small amount 10-15% of the total mass of steel is degassed at a time. The process is repeated until required level of degassing is achieved. The arrangement of a vessel and the ladle is somewhat similar to figure 26.3 except the following:
- In DH unit, the cylindrical vessel has one snorkel .
- Cylindrical vessel has heating facility.
The DH chamber is equipped with heating facility, alloying addition arrangement and exhaust systems. Bottom of the cylindrical vessel is provided with a snorkel which can be dipped into molten steel. The upper portion of the DH vessel is lined with the fireclay and the lower portion with the alumina bricks, snorkel is lined with high quality alumina brick. The length of the snorkel is sufficiently large to realize the effect of atmospheric pressure on rise of steel in the snorkel. The following steps may be noted for operation:
- DH vessel is preheated and lowered in the ladle so that snorkel tip dips below the molten steel surface
- The evacuated chamber is moved up and down so that steel enters the chamber
- The chamber is moved for 50-60 times with a cycle time of 20 seconds.
- Adequate degassing is possible in 20 -30 cycles.
- A layer of slag is kept in the ladle to minimize heat losses.
- The DH degassing unit can operate with lower superheats compared with RH since DH unit has heating facility
References:
- R H Tupkary and VR Tupkary: An introduction to molten steel making
- A Chakrabarti: Steelmaking
|
