1. Core Technical Features of High-Efficiency Continuous Casting Machines
As key equipment in the “steelmaking – continuous casting – rolling” process of steel production, high-efficiency continuous casting machines feature technical characteristics centered around “high productivity and stable quality,” primarily manifested in three aspects:
(1) Breakthroughs in Capacity with High Casting Speed and High Throughput
Compared to traditional continuous casting machines, high-efficiency continuous casting machines have achieved a quantum leap in casting speed: 150mm×150mm square billets can reach ≥5.0m/min, 120mm×120mm square billets can reach ≥6.2m/min, and slabs ≥180mm thick can reach ≥1.8m/min. Through innovative strand counts, some three-strand slab casting machines have an annual production capacity of up to 3.5 million tons per unit, a 75% increase over traditional two-strand casting machines. This capacity breakthrough isn’t simply a parameter increase, but rather a systematic upgrade achieved through equipment innovation. For example, one steel plant increased the casting speed of its slab continuous casting machine from 1.2 m/min to 2.1 m/min through roller train optimization and drive enhancement, while maintaining a slab qualification rate exceeding 99%.
(2) Precise and Controllable Solidification Cooling System
The high-efficiency continuous casting machine utilizes a three-stage cooling system consisting of “mold intensive cooling – secondary cooling gradient control – sector final cooling.” The mold utilizes an optimized water gap design, improving heat transfer efficiency by 30% compared to conventional systems. The secondary cooling zone utilizes air-water nozzles to precisely adjust the water pressure from 0.3 to 0.6 MPa, strictly controlling the cooling rate to within 200°C/m. Sector segments 3+4 utilize improved zone cooling technology, allowing cooling curves to be customized for the solidification characteristics of different steel grades.
(3) High-Reliability Equipment and Intelligent Systems
At the equipment level, traditional structural constraints have been broken through. For example, the three-strand slab continuous casting machine utilizes an L-shaped sector drive structure and integral box-beam vibration supports, reducing equipment failure rates by 60%. At the control level, digital intelligence systems are integrated. For example, the WisCC system utilizes MPI parallel computing to complete a 3D temperature field calculation of 7.2 million grid cells in 3 seconds, keeping surface temperature fluctuations within ±25°C. Furthermore, high-efficiency continuous casting machines generally implement online maintenance for key components. For example, the vibration unit can be inspected in real time during production, ensuring an operating rate of ≥85%.
2. Key Control Points for High-Efficiency Continuous Casting Machines
(1) Continuous casting mold
The mold, as the first checkpoint in billet formation, focuses on the dynamic matching of “casting speed, vibration, and cooling,” a key aspect of the optimized design of high-efficiency billet continuous casting machines.
Adaptive control of casting speed and mold length is fundamental. According to literature, when the casting speed increases from 2.0 m/min to 3.5 m/min, the mold length needs to be extended from 700 mm to 900 mm. Simultaneously, the shell deformation rate is calculated using the SMELT roll train design tool to ensure that the total deformation rate at the solidification interface is ≤1.2%. A mismatch between casting speed and mold length, such as a short mold with a high casting speed, can easily result in a mold shell thickness of less than 8 mm, increasing the risk of breakout.
Optimizing the vibration mechanism parameters directly impacts the surface quality of the cast billet. A non-sinusoidal vibration mode is used, with a frequency controlled at 524 vibrations per minute (8.74 Hz). The amplitude is dynamically adjusted with casting speed: at a casting speed of 3.0 m/min, the amplitude is 6 mm, decreasing to 3 mm at a casting speed of 4.2 m/min. The vibration trajectory error must be ≤ 0.1 mm. For example, the Sanming Steel Plant’s billet continuous casting machine reduced the depth of vibration marks on the billet surface from 0.8 mm to 0.3 mm through optimization of the vibration mechanism.
Coordinated control of cooling and mold slag is crucial. The mold cooling water flow rate is dynamically adjusted based on the casting speed × cross-sectional coefficient. For a 150mm×150mm square billet at a casting speed of 3.0m/min, the water flow rate is controlled at 180m³/h, and the inlet and outlet water temperature difference is maintained at 8-10°C. The mold slag must be compatible with the high casting speed, with a viscosity of 0.15-0.25Pa·s and a melting rate of 6mm/min or higher, ensuring a stable slag film thickness of 0.5-1.0mm. For example, Wuhan Iron and Steel Corporation has used these parameters to reduce the mold breakout rate to below 0.1‰.
(2) Precise Gradient Control of the Secondary Cooling System
The core goal of secondary cooling is to promote billet shell growth while avoiding crack defects. Key control measures focus on cooling zones, nozzle selection, and intelligent water distribution.
The dynamic adaptability of cooling zones is crucial. According to the document “Improvements in the Sector 3+4 Zone Cooling System,” the secondary cooling zone is divided into vertical, bending, and straightening sections. The vertical section utilizes intensive cooling (specific water volume 0.8-1.0 L/kg), the bending section transitions to medium-intensive cooling (0.5-0.7 L/kg), and the straightening section utilizes weak cooling (0.3-0.4 L/kg). Furthermore, the temperature difference between each section is strictly controlled to ≤50°C, avoiding the brittle temperature range of 700-900°C. For crack-sensitive steel grades, such as Q345B, the straightening section temperature needs to be raised to above 900°C, and slow cooling achieved by extending the cooling path.
Nozzle selection and layout directly determine cooling uniformity. The document “Application and Development of Nozzles in the Secondary Cooling Process of Continuous Casting Ingots” states that air-water nozzles are preferred at high casting speeds, with an atomized particle size ≤100 μm, a spray angle of 60°, and an overlap of ≥30% between adjacent nozzles. In sectors 3+4, spiral pressure nozzles and air-water nozzles are alternately arranged. Targeting the bulging-prone area at the center of the slab’s wide surface, the nozzle spacing is increased to 150mm, maintaining cooling unevenness at ≤10%.
(3) Controlling the Consistency of Tundish and Molten Steel Quality
The tundish serves as the molten steel distribution hub, and its control directly impacts the uniformity of multi-strand slab quality. This is particularly critical in three-strand slab continuous casting machines.
Optimizing the tundish structure and flow field is fundamental. Using an integrated T-shaped structure with slag retaining walls and turbulence controllers in the impact zone, the dead zone ratio is reduced by 7.8%, the steel residence time is extended to 12 minutes, and inclusions are promoted to float. For example, using this structure, Wuhan Iron and Steel’s billet continuous casting machine achieves a 90% removal rate for inclusions ≥50μm in the molten steel. Furthermore, the tundish liquid level is stably controlled within ±2t to prevent slag entrainment defects caused by liquid level fluctuations.
Precise control of the molten steel temperature and composition is crucial. Semi-portal heavy-duty tundish cars (200t capacity) are used to ensure stable molten steel delivery, with the temperature difference between each water outlet controlled to ≤2°C. Through online temperature measurement and composition analysis, the tundish heating power is immediately adjusted if the molten steel superheat deviates from the target value (20-30°C).
Tundish life extension technology reduces production costs. Using high-quality refractory materials, the tundish inner wall temperature is ≤240°C after 800 minutes of pouring. Combined with online repair technology, the average life of a single tundish reaches 24 hours, a 50% increase compared to traditional methods. This also reduces unplanned downtime and increases the casting machine availability rate to 88%.
(4) Stability Control of Segments and Straightening Systems
Segments serve as the “forming support” for solidification of the ingot. Coordinated control of the roll gap, pressure, and cooling is key to preventing bulging and cracking.
Precise control of the roll train and roll gap is fundamental. Using continuous straightening technology, the inclination angles of segments 1-3 are designed according to the solidification progress, with a roll gap deviation of ≤0.1mm. For example, the middle strand of a three-strand slab continuous casting machine utilizes an L-shaped transmission structure, with symmetrically arranged upper and lower roller drives. Roller deformation is controlled within 0.2mm to prevent cross-sectional deformation of the strand.
Dynamic adjustment of roller pressure must match the strand shell strength. According to the document “High-Efficiency Modification of Conventional Continuous Casting Machines,” after the strand exits the mold, the pressure in segments 1 and 2 is controlled at 0.3-0.5MPa to prevent strand shell collapse; the pressure in segments 3 and 4 is reduced to 0.1-0.2MPa to prevent impeding strand shell shrinkage. A closed-loop pressure control system monitors roller force changes in real time. When the strand shell thickness increases by 1mm, the pressure is automatically reduced by 0.05MPa.
Coordinated optimization of segment cooling and casting speed is crucial. The cooling intensity of segments 3+4 is adjusted based on the solidification endpoint of different steel grades. For example, strong cooling (specific water volume 0.4L/kg) is used for low-carbon steel, while weak cooling (0.2L/kg) is used for high-carbon steel. Furthermore, the speed difference between the straightening machine and the sector drive speed is controlled within ±0.1 m/min to prevent uneven stress on the slab and cracks.
In summary, the control of an efficient continuous casting machine must be centered around the mold, with secondary cooling as the key, the tundish as the foundation, and the sectors as the guarantee. Through multi-parameter coordination and intelligent control, high casting speed, high quality, and high operating efficiency can be achieved, providing core support for the efficient and green development of the steel industry.
