Full Process Analysis
The typical process flow of traditional hot continuous rolling includes: slab heating → high-pressure water descaling → rough rolling (multi-pass reversible rolling) → flying shear → finish rolling (multi-stand continuous rolling) → laminar flow cooling → coiling.
The heating process is the starting point of hot rolling. Slabs are typically heated in walking beam furnaces, with the exit temperature controlled between 1150-1250℃. The furnace employs a computer-controlled combustion system to achieve precise temperature regulation and energy optimization. Modern walking beam furnaces can control slab temperature uniformity within ±15℃, effectively reducing rolling force fluctuations caused by uneven temperature.
The descaling process is crucial for ensuring surface quality. After the slab exits the furnace, it must pass through a high-pressure water descaling device to remove the surface iron oxide scale. The descaling water pressure is typically 18-22 MPa, and multiple nozzles are arranged to achieve full coverage of the upper and lower surfaces of the slab. The effectiveness of descaling directly affects the surface quality of the finished product—incomplete descaling will cause iron oxide scale to be pressed in, forming surface defects.
The roughing rolling process is the main stage for thickness reduction. A roughing rolling mill typically consists of 2-4 stands and employs a reversible rolling method. The slab thickness is reduced from 200-250 mm to an intermediate slab of 30-60 mm. The reduction rate in the roughing rolling stage accounts for more than 80% of the total deformation and has a significant impact on subsequent microstructure evolution.
The finishing rolling process is the core step that determines product precision. A finishing rolling mill typically consists of 6-7 four-high stands connected in series, employing a continuous rolling method. The strip undergoes final thickness reduction in the finishing mill, while simultaneously achieving shape control and final rolling temperature control. The thickness deviation at the finishing mill exit can be controlled within ±30μm, with a 100% success rate in strip threading.
Cooling and coiling processes are crucial for microstructure control. After finishing rolling, the strip steel undergoes a controlled cooling path via a laminar flow cooling system before finally entering the coiler for coiling. The precision of coiling temperature control directly affects the final microstructure and properties of the product. Taking X80 pipeline steel as an example, the low-temperature coiling process places extremely high demands on the precision of coiling temperature control.
Core equipment technical characteristics
The roughing mill is the first deformation device in a hot strip mill. Modern roughing mills mostly adopt a four-high reversible structure, with work rolls approximately 1000-1200 mm in diameter and support rolls approximately 1500-1600 mm in diameter. A vertical roll mill is usually installed before the roughing mill to control the slab width. The vertical rolls employ short-stroke control technology, which can control the width deviation at the beginning and end to within 10 mm.
The finishing mill is the core equipment that determines the precision of the product. A modern finishing mill consists of 6-7 four-high mill stands, with work rolls approximately 700-850mm in diameter and roll lengths up to 2300mm. The finishing mill employs a hydraulic reduction system, which offers fast response and high control precision. The configuration of roll bending and roll shifting devices significantly enhances the ability to control the sheet shape.
Laminar flow cooling systems are crucial equipment for controlling microstructure evolution. Composed of upper and lower manifolds, laminar flow cooling achieves precise control of the cooling path by adjusting the water flow rate and the number of cooling stages. The heat transfer coefficient of laminar flow cooling is a key parameter in the temperature model, directly affecting the accuracy of coiling temperature control.
The coiler is the end-of-line equipment in a hot rolling line. Coils typically employ an underground coiling method, with a drum diameter of approximately 760mm. The application of technologies such as coiling tension control and auxiliary coiling roller control ensures the uniformity of the steel coil and the quality of both the inner and outer coils.
Automated control system architecture
Modern hot strip rolling automatic control systems adopt a hierarchical architecture, typically divided into L0 equipment control level, L1 basic automation level, L2 process control level, L3 production control level, L4 production management level, and L5 enterprise management level. Among these, levels L1 and L2 are most closely related to production and product quality.
The L1 basic automation system employs a high-end PLC system, enabling rapid control of position and pressure closed-loop systems such as AGC and APC within milliseconds. This basic automation system is responsible for real-time control functions such as mill reduction, speed control, looper control, and temperature control, forming the foundation for ensuring a stable rolling process.
L2 process control systems typically consist of multiple high-performance PC servers, primarily running rolling process automation application software. The process control system is responsible for model calculation, setpoint prediction, and self-learning correction, and is the core component for achieving high-precision control.
Mathematical models are the core of process control systems. With the development of computer control technology for hot strip rolling, mathematical models have evolved from traditional engineering models to modern models based on numerical analysis and artificial intelligence. The finite element method can discretize continuous deformable bodies and solve complex problems that are difficult to solve with classical theory; neural networks have characteristics such as self-learning, self-organization, self-adaptation, and nonlinear dynamic processing, making them particularly suitable for handling complex nonlinear processes
