The endless strip production line (ESP production line for short) has introduced a complete set of technologies and main production equipment of ESP continuous casting machine and rolling production line. The new endless strip rolling process is the world's most advanced hot rolled thin strip production process, which was put into industrial production in Arvedi, Italy, in 2009 on the basis of thin slab continuous casting and rolling process.
1. Main Parameters of ESP Continuous Casting Machine and Specifications and Dimensions of Billets:
Arc radius of casting machine: 5m;
Metallurgical length: 20.2m;
Length of crystallizer: 1200mm;
Thickness: 70mm ～ 110mm;
Width: 900~1600mm;
Length: endless rolling;
Steel: ultra-low carbon steel, low carbon steel, low-alloy high-strength steel, medium carbon steel, and dual phase steel;
Pulling speed: 7.0m/min.
The online production equipment from the ladle turret to the sector section outlet is designed by Siemens VAI and jointly manufactured by Siemens (China)/First Heavy Industries to ensure the equipment quality of the overall production line and reduce investment.
2. Continuous Casting Machine Equipment
2.1 Composition Characteristics of Main Continuous Casting Online Equipment
Butterfly-shaped ladle turret design, electromagnetic slag detection is installed at the bottom of the ladle; Intermediate package using electric servo control device; Semi gantry minivan design, hydraulic lifting, traverse, and adjustment; Imported tundish preheating station using natural gas as fuel; AFM funnel-shaped intelligent mold with mold expert system; Use ABB electromagnetic braking technology and equipment; Bending section with large reduction function of the liquid core; Dynamic roll gap control of sector section; Lower the dummy bar with chain design.
2.2 Parameters and Characteristics of Main Continuous Casting Machine
(1) Ladle turret. The rotary table is a butterfly structure. Two fork arms can be lifted and lowered separately. Each fork arm is equipped with four weighing units. Each weighing unit can carry 200t. The weighing error is ± 0.07%. The bearing capacity of the ladle turret is about 470t, and the turning radius is about 6m. The normal operation is hydraulic drive, and the maximum slewing speed is 1 rpm; In case of an accident, the accumulator provides power for it, and the slewing speed is 0.5 rpm. The lifting stroke of the ladle is 800mm, and the lifting speed when the ladle is full is 20mm/s.
(2) Tundish. In order to purify molten steel and ensure continuous casting during ladle replacement, the production line is equipped with a large capacity tundish with a working capacity of 45t and an overflow capacity of 48t. The working layer is paved with dry materials. The flow stabilizer, retaining wall, and dam is used in the tundish to optimize the flow field, and the electric servo device is used to control the stopper rod opening and closing to control the steel flow.
(3) Tunnels. The tundish adopts a semi-gantry design, with a bearing capacity of 90t. Three weighing units are installed on the bearing beam. Each weighing unit can bear 50t, and the weighing error is ± 0.07%. The tundish adopts a hydraulic mechanism for traveling, lifting, and fine adjustment, with a lifting stroke of 600mm and lifting speed of 30mm/s; The front and rear trimming strokes are ± 50mm, and the trimming speed is 5mm/s; The walking speed is fast (20m/min) and slow (1.2m/min). In addition, the vehicle is also equipped with an immersion nozzle accident ram and a ladle long nozzle manipulator.
(4) Tundish preheating station. The tundish preheating station and SEN oven of CEBA Company in Italy are used for preheating with natural gas as fuel. The baking time is about 4 hours, reaching the working temperature of 1260 ℃.
(5) Funnel-shaped intelligent crystallizer. The specially designed funnel-shaped intelligent crystallizer is the key technology of ESP endless strip rolling production line jointly developed by Siemens VAI and Arvedi. The geometric dimensions are designed by Arvedi according to the solidification shrinkage characteristics and high-temperature thermoplasticity of molten steel, combined with its ISP production practice for more than 20 years; Its cooling and heat transfer are designed by the German KME company using the most advanced AFM technology, and the limit steel throughput reaches 6.5t/min.
In addition, the mold has the functions of online width adjustment, online taper adjustment and a mold expert system.
(6) Electromagnetic braking. In order to meet the production requirements of high drawing speed and high steel output, the new generation EMBr technology provided by ABB is adopted. A constant magnetic field perpendicular to the flow direction of molten steel flowing out of the wide submerged nozzle area of the mold is set to brake the flow of liquid metal. The limit setting current is ± 700A.
(7) Curved section. The inlet is a mechanical fixed roll joint locked by the pin, and the outlet is a dynamic roll joint controlled by the hydraulic cylinder, which can realize the liquid core reduction function. The limit reduction thickness is 20mm.
(8) Sector segment. Due to the high casting speed requirements of the ESP continuous casting machine, in order to keep the bulge, strain rate and interference to the liquid level of the mold within the limited range, Siemens VAI adopts the compact arrangement design of small rolls: roll diameter ≤ 175 mm, roll spacing ≤ 205 mm.
During bending and straightening, in order to avoid the adverse effect of the strain rate in the solidified shell on the product quality, Siemens VAI developed a continuous curve to ensure that the strain rate changes steadily and that the internal and external strains are lower than the minimum allowable values during bending and subsequent straightening.
The control and maintenance of the sector roll gap are realized by four oil cylinders with displacement sensors at the inlet and outlet. The solidification model provided by Siemens VAI carries out solidification calculation according to the real-time information of steel grade, casting speed, superheat, secondary cooling strength, etc. in production, and continuously corrects the target roll gap of the sector section according to the calculation results and slightly presses the solidification end of the slab, so as to reduce the center porosity and center segregation and improve the quality of the slab.
(9) Secondary cooling control. The bending section and arc section are cooled by high-pressure water to ensure a high cooling rate to strengthen the green shell. The straightening section and the horizontal section are cooled by mist to ensure a wider cooling range, so as to provide the first roughing mill with a slab with sufficient temperature.
The cooling water volume can be adjusted independently along the slab width. According to the slab width, the middle and edge nozzles can adjust different water volumes, so as to make the temperature of the entire width of the slab balanced and ensure a higher temperature at the corners.
The dynamic water distribution model calculates the thermal history of the slab online, and controls the water volume to accurately adjust the slab surface temperature to meet the slab surface temperature required by the follow-up roughing mill.
3. Conclusion
In addition to the above features of online equipment, ESP continuous casting machine also has the following features:
(1) ESP is the first endless strip production line built and put into operation in China, which adopts the most advanced technology and equipment in the world's steel industry;
(2) The slab thickness (95mm slab is produced, which is much greater than the CSP slab thickness of 50-70mm), provides more heat for subsequent rolling, thus eliminating heating before rough rolling and directly rolling, greatly reducing rolling energy consumption;
(3) High yield. Compared with the conventional slab continuous casting machine, the single line output is increased by more than 40%, reaching 2.2 million t/a.
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