Because the start and stop of the continuous casting machine affect the converter and continuous casting productivity, and the billet and tail generated during the start and stop of the continuous casting machine affect the molten steel metal yield and the cost of steel consumption per ton, how to greatly increase the life of the tundish and ensure continuous Casting production runs steadily, and it is particularly important to improve the quality of billets and reduce the cost of tundish.
1 The status quo of continuous casting tundish and the reasons affecting its life
Factors affecting the life of tundish:
(1) Quality of refractories:
- ① The working layer is in direct contact with molten steel and is the key part. The working layer masonry materials are semi-silica, high-alumina, zircon, or silicon, magnesium, and forsterite insulation panels; or magnesium, magnesium-chromium, and magnesium-calcium coatings or casting materials. Wait.
- ② The brick of the tundish nozzle is inlaid on the bottom, which belongs to the weak part of the tundish. Usually high-alumina high-temperature-resistant materials are used.
- ③ The working layer at the bottom of the tundish is easily damaged by the impact of molten steel, requiring anti-erosion and abrasion resistance. High-strength tar magnesium brick, high-aluminum brick, and aluminum-chromium brick are mainly used. Zircon bricks are also used in the molten steel impact zone.
- ④The tundish cover is covered on the tundish, which plays a role in heat preservation and prevention of molten steel splashing. Usually, clay or high aluminum refractory casting materials are used as the cover.
(2) Production organization and operation level:
- ①The molten steel surface of the tundish should be stable or not fluctuate during the production process; the production organization requires that the converter production volume and the continuous casting production volume should be properly matched, and the excessive fluctuation of the molten steel surface caused by the continuous casting of molten steel should be avoided. The harm caused by the tundish lining.
- ②The temperature of the molten steel to the continuous casting platform should be reasonable to avoid the excessive overheating of the molten steel to wash the tundish lining; the temperature of the molten steel should be too low to increase the oxygen permeability of the tundish to the tundish lining.
- ③Tundish structure: The continuous casting tundish adopts structures such as retaining walls, dams and turbulence controllers, which not only makes the molten steel flow rationally in the tundish but also facilitates the floating of non-metallic inclusions in the molten steel, which improves the quality of the molten steel and improves the quality of the molten steel. Tundish service life.
2 Measures to improve the life of tundish
2.1 The working layer of the tundish uses dry materials
Under certain conditions of process conditions, tundish refractory materials, and masonry forms, the life of the tundish mainly depends on the chemical corrosion, high temperature melting loss, and mechanical erosion of the molten steel in the working layer of the tundish. Dry materials are used to resist erosion and erosion. Strong ability to meet the requirements of the long continuous pouring time.
2.2 The lining is made of magnesium refractory
Magnesium refractory has a strong effect of absorbing inclusions in steel and has good anti-erosion and erosion resistance. It can meet the requirements of a high continuous casting furnace number and also improve the quality of molten steel. After use, observe that the tundish line is the thinnest at the lining slag line, and the other parts are all within 30 to 40mm. After one pouring is completed, it is easy to remove the tundish.
2.3 Using a ballast
Since the steel flow directly hits the tundish from the big bale, the erosion of the tundish is very strong, and it is likely to cause the wearing of the bag when it is serious. To this end, it was decided to use a ballast, the material of the ballast is magnesium carbon, the structure of the ballast is a container-like structure with a hollow inner cavity, the bottom of the inner cavity of the ballast is large, and the mouth is small. The continuous casting tundish1 flow stabilizer of this structure prevents the molten steel from slag rolling in the ladle nozzle area. The effect is obvious and stable, the tundish1 steel quality is high, and the tundish refractory consumption is low.
2.4 Improve the liquid level of tundish steel
Originally, the minimum liquid level required for steel pouring in the tundish was 600mm, but now it must be greater than 700mm. After the liquid level of the molten steel is increased, the stagnation time of the molten steel in the tundish is extended. The deeper molten pool, the molten steel from the ladle to the stabilizer The resistance is larger, the flow velocity of the contact surface of the ballast is smaller, so the impact force on the ballast is smaller, the continuous pouring time of the ballast is improved, and the life of the tundish is also improved.
2.5 Improve slag spill operation
It turned out that the slag overflow port was close to the pouring point, and the slag overflow was difficult. As the number of continuous casting furnaces increases, the amount of slag is large and cannot be discharged in time. The slag line erodes the cladding seriously and affects the quality of molten steel. To this end, the position and shape of the slag overflow port were changed, and an assessment system was developed. The slag thickness should not exceed 30mm. The slag should be released in a time when the rhythm is appropriate. The slag thickness should be controlled below 30mm to prevent serious erosion of the cladding wall and the occurrence of cladding. At the same time, the large contractor should strengthen the operation, while controlling the large excess steel, and avoid a large amount of slag placed in the tundish, causing serious erosion of the slag line of the wall.
2.6 Improve service life of tundish nozzle
Improve the level of production scheduling, reduce pinch flow caused by other steel and other reasons, stabilize the temperature of the molten steel platform, and reduce the second opening due to operational problems, thereby increasing the service life of the tundish nozzle and the life of the tundish.
2.7 Improve molten steel deoxidation process
The deoxidizer used by Xigang is mainly silicon aluminum barium. In order to improve the deoxidization effect, the amount of deoxidizer added is increased, and a comprehensive deoxidation process is carried out to modify the inclusions in the molten steel through the ladle feeding silicon calcium line. This process not only improves the deoxidation effect of the converter molten steel and reduces the oxide inclusions in the steel, but also improves the castability of the molten steel and eliminates the tundish nozzle flow caused by the poor flowability of the molten steel. At the same time, the free oxygen content in the molten steel is reduced, thereby reducing the erosion of the tundish nozzle and increasing the life of the tundish.
2.8 Reasonable temperature system
In order to ensure the normal pouring of molten steel, the superheat of molten steel in the tundish1 is strictly controlled at 10～25℃. In order to improve the success rate of the first furnace, the tapping temperature of the converter is 30-40℃ higher than the normal pouring temperature. Control the temperature of the molten steel in the tundish1 according to the middle and lower limit, and the pass rate is increased from 80% to 95%.
2.9 Ensure the baking effect
When baking the tundish, the middle burner of the roaster should face the center of the flow stabilizer to ensure the baking effect of the flow stabilizer. Specific requirements for baking tundish1: medium fire baking is not less than 30min, high fire baking is not less than 1h, medium fire baking refers to the flame hitting the bottom of the package but not fired, high fire baking refers to the gas valve fully open or basically full Open, the flame hits the bottom of the bag and rebounds, the air volume is matched properly, and the flame temperature reaches the highest. Once the fire has started, the dry-type work lining tundish1 must not be stopped halfway or the flame should be adjusted down to ensure that the temperature of the tundish wall reaches above 1000℃.
2.10 Improve production organization mode
Make reasonable use of the production organization mode, arrange the use of tundish in a planned way, to avoid the waste of tundish, under normal circumstances, use the tundish reasonably according to the order of masonry, and give full play to the service life of the tundish.
2.11 Reasonable production system
The connection of molten steel between the converter and continuous casting is a necessary condition to ensure the continuous production of continuous casting. When the level of steel for continuous casting is required, the information transmission of production scheduling is increased, and the reasonable production organization is to ensure the stability of the molten steel liquid level in the tundish1. At the same time, ensure that the liquid level of the tundish1 is within the required range to ensure the life of the tundish.
3 Implementation effect and economic benefit analysis
The life of the improved tundish is increased from about 24h in the past to about 48h. The yield of metal and the yield of qualified steel billets have been improved. The average annual cost savings are about 850,000 yuan, refractory materials are saved, and the cost of t-steel is reduced by about 0.61 yuan. At the same time, the production capacity of the continuous casting machine is improved, which provides a favorable technical guarantee for the matching of the continuous casting and the subsequent steel rolling process.
By optimizing the converter temperature system and production organization scheduling system, improving the molten steel deoxidation process, improving the tundish masonry and baking quality, etc., the service life of the tundish is increased, thereby increasing the efficiency of the converter and continuous casting production and reducing the intermediate The package use cost meets the double-line production needs of the converter and continuous casting.
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