Research background and issues
With my country’s official accession to the World Trade Organization on December 11, 2001, my country’s steel industry experienced explosive growth from 2002 to 2006. The annual growth rate of steel output remained above 20%. The increased output was mainly due to the new production lines. Increase production capacity. More than half of the newly built production line equipment is imported, and all high-end equipment is imported.
The gap between imported continuous casting equipment and domestic continuous casting equipment is mainly reflected in three aspects. (1) There is a gap in output; (2) There is a gap in software and process models; (3) There is a gap in the quality stability of cast slabs. Taking the annual output of a 230mm×2150mm double-strand slab continuous casting production line as an example, the output of imported continuous casting equipment is more than 2.75 million t/year, and the output of domestic continuous casting production lines of the same specifications is about 2.4 million t/year. Moreover, the pass rate of slabs produced by imported continuous casting equipment is higher than that of domestic continuous casting equipment production lines. There are three main measures to increase output. The first is to increase the casting speed, the second is to increase the number of continuous casting furnaces, and the last is to increase the continuous casting production efficiency. Increasing the casting speed of the continuous casting machine can easily cause steel breakage accidents. Taking Baosteel’s 4# continuous casting machine as an example, the designed maximum casting speed is 2.2m/min, and the actual production casting speed is 1.2m/min. Therefore, most manufacturers adopt the latter two measures. Crystallizer thermal width adjustment equipment and technology are the core technologies for increasing the number of continuous pouring furnaces. The biggest difficulty of this technology is the high risk and high cost of trial and error, and steel leakage accidents are prone to occur during the thermal mold width adjustment process. In order to avoid the risks caused by this technology, major domestic steel companies rarely adopted the thermal mold width adjustment technology before 2012. With the global economic crisis in 2008 and the increase in small-batch orders for multiple varieties in the market, steel companies have slowly put the application and transformation of crystallizer thermal width adjustment technology on the agenda.
At present, in the production process of high-end automobile sheets in my country, higher requirements are placed on the mold equipment in the continuous steel casting process. The high-end slab mold must have the characteristics of high efficiency, high performance and precision, and can stably produce high-quality cast slabs. Taking the efficient production of high-end automotive sheets as an example, efficiency is reflected in increasing output, and the research and development direction is to increase the number of continuous casting furnaces and increase the casting speed of the continuous casting machine. The technology used to increase the number of continuous pouring furnaces is the online thermal width adjustment technology of the crystallizer; the core of increasing the casting speed is the water gap optimization technology of the copper plate of the high-speed crystallizer. High-performance precision machines now improve the quality of cast slabs. The technology used is high-precision crystallizer liquid level fluctuation control technology and multi-mode electromagnetic flow-controlled crystallizer equipment.
Ideas and technical solutions to solve problems
This project aims to develop “a new type of crystallizer with high efficiency and high performance for precision slab continuous casting“. From three directions: “High-precision crystallizer liquid level detection and control technology”, “Online thermal high-precision dynamic control technology of slab continuous casting section size” and “High-speed mold equipment optimization design method”. Through continuous optimization in the process of theoretical research, model development, laboratory verification, key technology development and industrial application. A high-precision liquid level fluctuation control model of the crystallizer and an automatic pouring model of the continuous casting machine were established, and the influence of the stopper rod opening on the molten steel flow rate was obtained. A drum force disturbance compensation model and a process parameter adaptive control model were established. An online thermal width modulation model and a cone-preserving control model adapted to large-chamfer crystallizers were established. A method for calculating the process parameters of the crystallizer online thermal width adjustment system was proposed, a variable cross-section water gap structure of the crystallizer copper plate was developed, and a multi-objective optimization design method for the crystallizer copper plate was proposed. A technical plan and system for the research and development of new mold equipment for high-efficiency and high-precision slab continuous casting have been established (Figure 1), achieving efficient and high-quality production of slab continuous casting.
Figure 1 Technical plan and system for research and development of new mold equipment for high-efficiency and high-precision slab continuous casting
Main innovative achievements
High-precision crystallizer liquid level control system and continuous casting machine automatic pouring system
A high-precision liquid level fluctuation control model of the crystallizer and an automatic pouring model of the continuous casting machine were established, and the influence of the stopper rod opening on the molten steel flow rate was obtained. A drum force disturbance compensation model and a process parameter adaptive control model were established. A stopper rod hydraulic control system is designed to meet the high-frequency and precise control of the stopper rod hydraulic cylinder, a high-frequency response hydraulic cylinder and a matching hydraulic control valve table. Based on the characteristics of the width-adjusting hydraulic cylinder valve device, a hydraulically driven mold liquid level automatic opening and pouring control system for continuous casting equipment was developed. Based on the characteristics of the servo motor and drive structure, an electric cylinder-driven crystallizer liquid level automatic opening and pouring control system for continuous casting equipment was developed to achieve precise control of the electric stopper rod and hydraulic stopper rod systems.
Adapt to the online thermal width adjustment system of large chamfered crystallizers
An online thermal width adjustment model and a cone-preserving control model adapted to the mold with large chamfers were established, and a method for calculating the process parameters of the online thermal width adjustment system for the mold was proposed to achieve high-precision dynamic control of the slab continuous casting section size.
A narrow-side taper control method for the electric crystallizer width adjustment device was developed to provide a control algorithm model for thermal width adjustment. A hydraulic control system for mold taper online maintenance was developed, and a mold width-adjusting hydraulic cylinder valve device and a hydraulic width-adjusting soft clamping hydraulic valve table were designed to realize drive control and soft clamping functions of the narrow-side copper plate hydraulic cylinder of the crystallizer. An electrical control device for crystallizer width adjustment is designed to electrically control the thermal width adjustment model during the production process. Developed a mold motor-driven online thermal width adjustment system and a hydraulic-driven mold online width adjustment control system for slab continuous casting equipment for algorithm model control of electric width adjustment and hydraulic cylinder width adjustment.
High-speed crystallizer copper plate water seam arrangement control technology
The variable cross-section water gap structure of the mold copper plate was developed to achieve efficient and uniform cooling of the high-end slab mold, significantly improving the slab continuous casting speed and performance. A multi-mode electromagnetic flow controlled crystallizer was developed.
During the development of high-speed crystallizer copper plate water seam arrangement control technology, it was proposed that the principle of optimizing the design of the crystallizer copper plate is to try to ensure the uniformity of the cross-sectional temperature distribution of the copper plate and to keep the temperature of the hot surface of the copper plate at the lowest. Designed and developed multi-layer composite copper plates for the wide surface of the slab caster mold to provide technical support for the design of high-speed molds.
Slab crystallizer electromagnetic flow control equipment and its control technology
We developed and designed a multi-mode electromagnetic flow-controlled crystallizer, thermocouple anti-shielding technology in a strong magnetic field environment, and a metallurgical automatic control model of the slab crystallizer multi-mode electromagnetic flow-controlled system, as shown in Figures 2 and 3. It can realize various stirring modes such as electromagnetic acceleration, electromagnetic deceleration, and electromagnetic stirring, which is beneficial to increasing the pulling speed, reducing pinholes on the surface of the slab, reducing non-metallic inclusions, and reducing the incidence of linear defects on the surface of cold-rolled coils by 40%.
Figure 2 Electromagnetic flow controlled crystallizer equipment diagram
Figure 3 Three-dimensional schematic diagram of the electromagnetic flow controlled crystallizer
The metallurgical automatic control model and automatic control operating parameters are based on multiple project experience data and numerical simulation technology to establish a metallurgical data model, as shown in Figure 4 and Figure 5. The mixing mode and operating parameters can be automatically controlled according to the cross section, steel type, nozzle structure, and pulling speed. The metallurgical data model corresponds to different parameter design modules according to different nozzle forms. The parameter module is an automatic control model established by combining the experience of multiple projects and numerical simulation. It cooperates with computer technology to realize the automatic output of the operating parameters of the mixer to achieve automatic control of electromagnetic stirring.
Figure 4 Electromagnetic flow control simulation optimization calculation
Figure 5 Electromagnetic flow automatic control program interface diagram
Application and effects
Adapt to the application of thermal width adjustment technology of large chamfered molds
On January 21, 2016, this technology was successfully applied in hot trials in the 1st stream of the 1# slab continuous caster of Handan Iron and Steel Group Handanbao Iron and Steel Co., Ltd. Environmental protection, energy conservation and various technical and economic indicators all met the requirements stipulated in the contract. This continuous casting is the introduction of Italian Danieli slab continuous casting production line, and the continuous casting slab section produced is 230mm×(900~2150)mm. The industrial application of this technology has broken through the technical bottleneck of large-chamfered crystallizers in domestic and foreign slab continuous casting machines that have not yet realized online thermal width adjustment.
In July 2017, this technology was successfully applied in hot trials in the second stream of the No. 1 slab continuous caster of Handan Iron and Steel Group Handan Bao Iron and Steel Co., Ltd.
On August 10, 2021, the thermal mold width adjustment technology was put into use in the 3# double-flow slab continuous caster of Guangxi Shenglong Metallurgical Co., Ltd. This project uses a hydraulic cylinder width adjustment device to achieve online thermal width adjustment and narrowing of 50~150mm. The mold taper control accuracy reaches ±0.1mm, and the mold taper control accuracy is ≤±0.5mm.
Figure 6: Large chamfered mold thermal width adjustment screen
Figure 7 Photo of size measurement of cast slab with 50mm width adjustment
Application of high-precision crystallizer liquid level control system and continuous casting machine automatic pouring system
On April 15, 2020, this technology was successfully tested on the No. 1 slab continuous caster of the 210 Converter Plant of Hunan Valin Lianyuan Iron and Steel Co., Ltd. The crystallizer liquid level control reaches ≤±2mm (process requirement ≤±3mm), reaching the international advanced level.
On March 14, 2022, this technology was put into use in the 420×2300 extra-thick slab continuous caster of the No. 3 Steelmaking Plant of Hebei Puyang Iron and Steel Co., Ltd. This project uses a hydraulic cylinder stopper system, and the crystallizer liquid level control reaches ≤±2mm (process requirements ≤±3mm).
On April 25, 2021, the high-precision mold liquid level control system and the continuous casting machine automatic pouring system were put into use on two 230X1600mm dual-flow slab continuous casting machines of Guangxi Shenglong Metallurgical Co., Ltd. This project achieved high-precision control of the domestic electric cylinder plug rod system.
Figure 8 High-precision crystallizer liquid level control laboratory test photos
Figure 9 Photos of hot tests of the high-precision crystallizer liquid level control system
Application of multi-mode electromagnetic flow controlled crystallizer + high-speed crystallizer copper plate water seam optimization design technology
On June 3, 2020, the equipment and technology successfully completed a hot test on the 2# slab continuous caster of the 210 Converter Plant of Hunan Valin Lianyuan Iron and Steel Co., Ltd. The object to be transformed is the Italian Danieli slab continuous casting production line, which produces continuous casting slabs with a section of 230mm×(900~2150)mm. This crystallizer is currently the most advanced crystallizer designed independently in China. It has hydraulic online thermal width adjustment function, multi-mode electromagnetic flow control function, high-precision liquid level control function, steel breakout prediction function, electromagnetic anti-shielding function, etc. It provides advanced equipment and technology for Lianyang Iron and Steel Co., Ltd. to produce high-end automotive sheets. On October 26, 2021, the new high-speed mold copper plate was put into use in Baosteel’s 4th continuous casting machine.
Figure 10 Water gap and temperature field of the crystallizer copper plate in the original plan
Figure 11 Temperature field of copper water seam and plate in the crystallizer of the new scheme
The promotion and application of high-precision mold liquid level control system and continuous casting machine automatic pouring system in billet continuous casting machines.
On October 1, 2021, this technology was designed and put into use in the 3# billet continuous caster of Panzhihua Iron and Steel Vanadium Steelmaking Plant, and the crystallizer liquid level control reached ≤±3mm (process requirements ≤±4mm).
In 2023, the high-precision mold level control system, continuous casting machine automatic pouring system and mold thermal width adjustment system will be put into use in the slab continuous casting production line.