The role of heat-insulating materials in ladle
The application of heat-insulating refractory technology aims to reduce the heat loss of the ladle working layer, thereby reducing the heat loss of molten steel. When implementing relevant heat-insulating refractory technology transformation on existing ladle, it is necessary to consider controlling the change of ladle space and weight to the minimum, and it should not affect the original masonry process. Through transformation, the temperature drop of molten steel and the external heat radiation of ladle shell are reduced, the temperature stability of molten steel and the continuous casting efficiency are improved, and the high-temperature radiation damage of related equipment is reduced.
The heat loss of molten steel in ladle is divided into three parts: heat radiation of molten steel slag surface, heat radiation of ladle shell and heat storage of ladle refractory. On the one hand, the efficient insulation layer reduces the temperature of ladle and reduces the heat loss caused by the external heat radiation of ladle shell. On the other hand, it increases the heat storage of ladle refractory, so as to achieve the purpose of reducing the temperature drop of molten steel, while reducing the temperature fluctuation of refractory and extending the service life of refractory.
The comparison of ordinary masonry method and heat-insulating refractory masonry method of ladle is shown in Figure 2. The masonry should be combined with production characteristics, without affecting the existing working layer and the overall empty ladle weight, to ensure that the driving is not overweight and the clearance height of the heavy ladle.
01 Process temperature measurement
1. Change of ladle shell temperature
Steel grades Q235B and SPHD were selected, and compared according to steel grade and process path. On the one hand, the cladding temperature of different refractory ladles under the same process path steel grade conditions was compared, and on the other hand, the temperature change differences in different areas of the two refractory claddings under different process paths were compared. Under the same steel grade path conditions, the cladding temperature of the insulating refractory ladle is 52℃ lower than that of the ordinary refractory ladle; under different steel grade paths, the cladding temperature change of the insulating refractory ladle is smaller than that of the ordinary refractory ladle; from the comparison data of different steel grade paths, the degree of temperature drop of the ladle shell is different, indicating that the use of insulating refractory affects the heat loss model in the ladle.
2. Changes in temperature drop of molten steel process
The steel grades Q235B with the process path of "converter → argon station → continuous casting" and the steel grade SPHD with the process path of "converter → argon station → RH vacuum → continuous casting" were selected to analyze the influence of the insulated refractory steel ladle on the temperature drop of molten steel process. On the premise of meeting the temperature of the continuous casting tundish, there is no obvious difference in the converter end temperature of smelting Q235B steel when using different ladles; when smelting SPHD, the converter end temperature using the insulated refractory steel ladle is reduced by 10℃.
02 Changes in molten steel temperature and reasons
1. Temperature drop of Q235B molten steel
For the steel grade Q235B with the process path of "converter → argon station → continuous casting", there is a temperature drop of about 100℃ from the converter end to the continuous casting tundish, and there are mainly the following three temperature drop points.
① Molten steel stirring
Including argon blowing stirring during steel discharge in converter and argon blowing stirring during treatment at argon station, the temperature drop differs by about 1°C under different argon blowing intensities at argon station, which is the decisive factor for the temperature drop of molten steel process.
② Ladle heat loss and production rhythm
When molten steel is not blown with argon, the temperature drop of ordinary refractory ladle is about 0.5°C per minute, the normal cycle error is 10min, and the temperature drop changes by 5°C.
③ Alloying
Including alloy amount and alloying timing. Under the same alloy amount of the same steel grade, the alloying timing has little effect on the temperature drop of molten steel.
2. SPHD steel temperature drop
For the steel grade SPHD in the process path of "converter → argon station → RH vacuum → continuous casting", the temperature drop from the end of converter to the continuous casting tundish is about 125°C, and there are mainly the following 4 cooling points.
① Molten steel argon blowing stirring
Refers to the temperature drop of molten steel caused by the stirring of molten steel in the ladle during the process from the start of steel discharge in converter to the end of argon station treatment.
②RH vacuum treatment temperature drop
Refers to the temperature drop of molten steel caused by heat absorption in the vacuum tank and stirring of circulating gas during RH vacuum treatment.
③Ladle heat loss and production rhythm
The temperature drop of ordinary refractory ladle is about 0.5℃/min when molten steel is not blown with argon. The normal cycle error is 10min, and the temperature drop changes by 5℃.
④Alloying
Including alloying amount and alloying timing. When the steel type and alloying amount are the same, the alloying timing has little effect on the temperature drop of molten steel.
3. Cause analysis
From the analysis of the cooling point, it can be seen that for the steel type molten steel in the process path of "converter→argon station→continuous casting", the argon blowing intensity of the argon blowing station has a greater effect on the temperature drop of molten steel, which masks the effect of different ladles on the temperature drop of molten steel. The temperature drop influencing factors of steel type molten steel in the process path of "converter→argon station→RH vacuum→continuous casting" are stable, and the temperature change of molten steel caused by using different ladles is obvious.
02 The influence of different refractory steel ladles on the temperature of molten steel in the continuous casting tundish
Analyzing the temperature change of molten steel in the continuous casting tundish, from the perspective of the temperature difference of molten steel in the continuous casting tundish (temperature difference of molten steel in the continuous casting tundish ΔT = temperature of molten steel in the continuous casting tundish T-average temperature of molten steel in the continuous casting tundish T), the temperature difference of molten steel in the continuous casting tundish of different process paths varies differently. Compared with ordinary refractory steel ladles, the temperature fluctuation of molten steel from the heat-insulating refractory steel ladles in the continuous casting tundish is small, which is more conducive to the temperature stability of molten steel during the continuous casting process.
During the smelting process, the steel ladle using heat-insulating refractory technology can reduce the heat loss of molten steel by 10℃ on the one hand, and the temperature of the steel ladle shell can be reduced by 50℃ on the other hand, which plays a role in reducing the temperature of the converter tapping, saving energy and reducing consumption, stabilizing the casting temperature of molten steel, and improving the efficiency of continuous casting, and also reduces the thermal radiation damage to the associated equipment of the steel ladle.
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