In recent years, competition in the steel industry has become increasingly fierce. Only by continuously upgrading technology, improving product quality, and reducing production costs can enterprises achieve further development. To adapt to market needs, Xuan Steel built two identical six-strand continuous casting machines. In subsequent upgrades, the flow rate of the continuous casting machines was increased, and the annual production capacity of a single machine now exceeds one million tons. This article mainly introduces the network structure, bus layout, and main functions of the automation system after the upgrade of the two continuous casting machines. I. Overview The No. 4 and No. 5 continuous casting machines in Xuan Steel's steelmaking plant are key projects of Xuan Steel. Their automation control level has reached the advanced level in China. The system adopts the currently popular three-electric integrated design, extensively using fieldbus technology. The automation system hardware and software are mainly based on Rockwell Automation products, forming a three-level network structure to realize automatic control, production scheduling, and product quality control of the continuous casting machine. The system network structure is shown in Figure 1: Figure 1 Control System Network Structure Diagram. As can be seen from the figure above, the automation system of the continuous casting machine considers the needs of practical applications, fully utilizes the resource characteristics of hardware and software, and constructs a three-layer network structure: information layer, control layer, and equipment layer. 1. Information Layer The information layer provides network interfaces for the operation and maintenance of the continuous casting machine and the plant-level computer system. It accesses workshop-level production and management data, provides data collection and monitoring services for the plant-wide control system, and receives production scheduling instructions to coordinate plant-wide production. This layer is characterized by a large data volume but does not have excessively high real-time requirements. To facilitate interconnection between PLCs and computer systems from different manufacturers and to perform necessary control and coordination, a 100Mbps Ethernet network conforming to the common standard TCP/IP protocol is used. Considering the reliability requirements of industrial control and the harsh environment of industrial sites, the Ethernet uses a redundant fiber optic ring network, with two industrial-grade Ethernet switches providing redundancy management. One server and four operator stations of the continuous casting machine are connected to the network via Ethernet cards, and each frame of the PLC system with a CPU module is connected via an Ethernet interface module. 2. Control Layer The control layer is responsible for the transmission and exchange of control data between the common PLC system, each casting flow PLC system, and remote Flex I/O, coordinating control, and providing functions such as network programming, program maintenance, equipment configuration, and troubleshooting. This layer of the network requires not only stable and reliable connections but also real-time information transmission. ControlNet uses a bus topology with a communication rate of 5Mbps. Its key feature is its deterministic nature, meaning that I/O devices and controllers on the network communicate at predetermined times. Each component in ControlNet has its communication time and duration pre-determined during configuration, making it highly stable and reliable, particularly suitable for time-critical industrial applications. To further enhance reliability, redundant communication media are used at this layer to ensure uninterrupted communication. 3. Device Layer The device layer primarily connects main drive equipment, such as frequency converters and soft starters, directly to their respective PLC systems, eliminating the need for traditional digital/analog connections. This approach is not only convenient and fast but also allows for the acquisition of data from field devices for configuration, monitoring, and real-time control. This layer uses a Remote I/O network. The three-layer network structure allows for the selection of appropriate communication methods based on the specific application requirements of the continuous casting machine system. This network architecture not only provides EtherNet/IP, ControlNet, and Remote IO network connections, but also includes advanced software interfaces optimized for automatic control to ensure efficient data transmission. II. System Composition and Functions 1. Hardware Configuration The hardware of each continuous casting machine automation system mainly consists of 9 sets of Rockwell Automation's ControlLogix series PLCs, 4 operator stations, 1 server, and a remote Flex I/O station. In the drive system, all main production line equipment is driven by vector frequency converters, water pumps use soft starters, and auxiliary drive equipment is controlled by MCCs. The instrumentation system mainly consists of a rapid and continuous steel temperature measurement system, a ladle and tundish weighing system, a crystallizer liquid level monitoring and adjustment system, and a crystallizer water and secondary cooling water flow detection and adjustment system. The continuous casting machine's common system uses a PLC system with an expansion rack for the detection and control of shared equipment on the continuous casting machine platform and in the billet discharge section. One PLC system is provided for each casting flow for monitoring and control of that specific casting flow system. The operator stations are located in the main control room and cutting operation room for monitoring, operating, processing alarm information, and necessary human intervention of the continuous casting machine equipment. The server is used to collect, process, store, and transmit production data. 2. System Functions The continuous casting machine automation system adopts a three-electric integrated design. All electrical control and instrumentation control signals are connected to the PLC. On-site thermal resistors, transmitters, flow meters, and other detection instruments collect instrument data. Switches, limit switches, and other equipment collect process production data and equipment operating status. All data is integrated into the PLC system, and combined with instructions from the upper-level operator station, process loop regulation, electrical equipment sequence control, and transmission equipment control are realized according to a pre-set program. 1) Instrument System: Instrument detection mainly includes rapid and continuous measurement of molten steel temperature in the ladle and tundish, measurement of molten steel weight in the ladle and tundish, measurement of crystallizer water pressure, flow rate, and inlet/outlet temperature difference, and measurement and adjustment of secondary cooling water pressure and flow rate in each section. To reduce the labor intensity of operators and improve billet quality, the continuous casting machine also collects the molten steel level in the crystallizer and adjusts the opening of the tundish stopper rod via an electric cylinder to maintain a stable molten steel level. The secondary cooling water distribution system has manual and automatic control functions, including water distribution, water meter setting, tracking adjustment, water distribution correction adjustment, and display of water flow, pressure, temperature, and valve position. The PLC realizes on-site data acquisition and tracking adjustment, while the operator station completes water meter setting, water flow display and data recording, data printing, and statistical functions. Manual and automatic control: Each flow is divided into four water distribution sections: foot roll section, first section, second section, and third section, each with a manual/automatic switching function. In manual mode, the operator directly sets the valve opening on the operator station screen to change the water volume; in automatic mode, the system automatically adjusts the water volume according to the pre-selected water meter based on the casting speed, and can adjust the water supply at any time according to the billet temperature during the casting process. Water meter selection and modification: Dozens of water distribution parameters are pre-set in the operation station for use. The parameters include: number, steel type, cross-section, and water distribution ratio of each section. Operators can modify the parameters at any time to change the water distribution. 2) Electrical system: The detection and control of electrical equipment mainly includes: rotation of the ladle turret, lifting and lowering of the ladle arm, opening and closing of the ladle nozzle, movement, centering, and lifting of the tundish car, vibration and frequency adjustment of the crystallizer, transmission of the straightening machine, pressing down of the straightening rollers, upward movement, recovery tracking, billet removal, and storage of the slab cutting to length, as well as the control of the pre- and post-cutting roller conveyors, conveyor roller conveyors, steel turning machine, billet separator, and walking beam cooling bed. The detection and control of the hydraulic system, oil-air lubrication system, and dry oil lubrication system are also completed by PLC. All main production line transmission equipment is driven by frequency converters. More than one hundred frequency converters are used in the transmission of mechanical equipment such as the ladle turret and the transverse steel transfer car in the continuous casting machine, with power ranging from 0.75KW to 45KW. All frequency converters connect to the Remote I/O communication adapters via their built-in communication interfaces, directly linking to a nine-networked Remote I/O network comprised of nine RIO interface modules, forming a drive system based on the Remote I/O network. Considering both the connection distance of the Remote I/O network and the system's real-time requirements, a communication rate of 115.2 Kbps is adopted. The Remote I/O network operates in scanner mode, with the PLC processor establishing a serial communication link through the RIO interface modules and the remote I/O adapters. The frequency converter's communication interface provides a direct, digital communication link for network devices in the Remote I/O network. The system establishes input and output data links using the communication interface by configuring the PLC's I/O tags. For the PLC, each frequency converter is viewed as a remote frame equipped with I/O modules. By simply reading and writing to these modules, commands can be sent to the connected frequency converters to control equipment operation; data can also be read from the frequency converters to monitor equipment operation status and transmit the data to the PLC in real time. The operator can access real-time, detailed information on the control station monitor in the main control room, and directly operate the equipment. Even when the frequency converter issues an alarm or malfunction, it can be reset promptly to prevent accidents caused by delayed handling. The electrical system of the continuous casting machine enables remote network real-time control of the transmission equipment, allowing the PLC to achieve networked digital control of the frequency converter drive. A single communication cable replaces numerous hard-wired connections. Compared to traditional analog and digital control methods, this significantly improves the system's real-time performance, accuracy, and reliability, while also reducing installation, commissioning, and maintenance costs. 3) The HMI (Hardware Interface) software on the control station features nearly 20 screens based on process requirements, including the main screen, casting flow overview, billet discharge area overview, straightening machine and dummy bar, crystallizer liquid level, crystallizer vibration, ladle/tundish weighing, hydraulic system, drive device operating status, and PLC status. Through monitoring the HMI, operators can observe the equipment's operating status in real time, modify process parameters according to their permissions, promptly handle alarm events, and manually intervene in equipment operation when necessary. 4) Command and Dispatch System: Steelmaking is a complex production process. The quality of continuously cast billets is directly affected by casting conditions and process status. Even with advanced processes, equipment, and technologies, the characteristics of continuous casting production mean that heat handover, equipment failures, and operational instability can inevitably cause fluctuations and anomalies in the production process, resulting in varying degrees of damage to billet quality. The impact on subsequent rolling processes and the quality of the final product cannot be ignored, causing economic losses and damage to the company's reputation. The continuous casting machine needs to understand the status of the preceding processes in a timely manner, and the converter and refining systems must also grasp the casting status of the continuous casting machine. To facilitate a direct and rapid understanding of the entire production process, the continuous casting machine's automation system provides a network interface, connecting to the plant-level management network along with the converter, refining, and argon blowing stations, providing data for unified coordination and command of production scheduling. III. Application Results The automated control system for the continuous casting machine at Xuan Steel Plant integrates PLC control technology, video monitoring technology, network communication technology, and variable frequency speed control technology. This integrated design adapts to the trend of automation, achieving automated control of the basic production process of the continuous casting machine. It completes functions such as automatic interlocking control of equipment in the continuous casting production site, detection and adjustment of media parameters, data communication processing, fault alarm diagnosis, and online monitoring of production status. After more than three years of operation and verification, the system's control functions are advanced, stable, and reliable. It has effectively improved labor productivity, reduced the labor intensity of workers, and played a positive role in smooth commissioning and reaching full production capacity, increasing production efficiency, and maintaining safe production.