Current status and prospects of continuous casting automation in the steel industry

This article provides an overview of continuous casting automation issues in steel processing. The control technologies used in the steel industry and their typical applications are briefly introduced, and the technologies and the key components that constitute their implementation are discussed. Casting process and operational issues are described, especially in production planning and scheduling, computer-aided quality control, and the critical role of instrumentation in the automation of continuous casters. Finally, applications for the integration of casting automation systems into industrial production systems and the development of new instruments are highlighted.

Keywords: steel industry; continuous casting; industrial control; automation; computer-aided quality control

Overview

This article is part of a study being prepared by the IFAC Technical Committee on Mining, Metals and Minerals for the Mining, Metals and Minerals Technology Industry. The purpose of this study is to provide a brief overview of the control technology or methods used in this industry, give typical applications of this technology, and discuss the supporting technologies that form a key part of the implementation of this technology. Research is also underway on applications and supporting technologies that are actively used or are becoming available in the future.

This article provides an overview in terms of metal processing and continuous casting automation. But this is more than a comprehensive literature survey on this issue. Because there are many excellent references on continuous casting and the application of process control and automation in the operation of such machines.

Process Overview

The description of the process is given for a bow caster, but in principle it applies to most types of casting machines. Figure 1 depicts a continuous casting machine.

Figure 1 Bow continuous casting process

Operational issues

The main operating issue of a continuous casting machine is to run and maintain stability after startup. Achieving stable operation includes proper use of stopper rods, proper addition of lubricant, and applicable sequences and standard operating procedures appropriate to the pulling speed.

Lubrication can be lost for many reasons, including insufficient powder supply to the mold, large fluctuations in the metal level in the mold, and changes in the mold flux composition. Severe lubrication loss may lead to explosion, before which may adversely affect the surface quality.

Continuous casting automation

There are many drivers for continuous casting processes and automation technologies, including increased customer demand, increased competition among producers, stricter environmental regulations, and increased safety requirements. These drivers force producers to make the most of their steel plants, thereby driving the development of the entire production system to ensure consistency between steelmaking, casting and rolling processes. Therefore, the continuous casting automation system should become part of the entire steel industry production system and a necessary task, including the scheduling of production plans, quality assurance, and more traditional supervisory control functions.

Production planning and scheduling

It can be seen from the many papers on production systems held at the 14th IFAC World Congress in Beijing that production planning and scheduling is a mature field in China. However, there appears to be considerable research space in integrating casting automation systems into plant-wide production systems. One reason is that optimal production planning and scheduling of process units such as casting machines cannot be done in isolation, since the optimal unit schedule may conflict with the optimal process.

Computer-aided quality control

Best practices in the steel industry often result in kinetic and systemic processes that are more difficult to control. This is particularly relevant for continuous casting. In order to increase productivity, modern steel mills have eliminated the buffers in the stockyards between the continuous casters and hot rolling mills. This lack of buffering has driven the development of automation strategies to facilitate direct rolling and hot charging of continuously cast semi-finished products.

Supervisory control usually refers to a controller or optimization routine that provides setpoints for subordinate control loops. Lower level control loops include mold and water jet flow control. Supervisory controllers include tundish and mold level controls and secondary cooling controls. From a control community perspective, probably the most well-known control issue in continuous casting is controlling mold levels. Many papers have been published on this topic, and although the casting level is difficult to control, the problem has been basically solved. However, new casting technologies, such as strip casting, may provide new levels of control challenges.

Continuous Casting Instruments

Instruments are widely used in continuous casting operations to monitor variables in ladles, tundishes, molds, secondary cooling zones, radiant zones and exit tables. In fact, the increasing use of instruments to measure and control casting parameters is considered one of the main reasons for the tremendous gains in caster productivity and quality over the past 20 years.

As mentioned above, instruments are vital to any control and automation system, and their contribution to achieving modern productivity and quality standards cannot be underestimated. Instrumentation is the “eyes” of control and automation systems, and using current technology permanent instrumentation can be used in process and quality control systems to “see” the most important ladle, tundish and mold variables.

Considering the hazardous environment present in the spray chamber of the secondary cooling area of a continuous caster, it is not surprising that the caster control system is often “ignorant” of changes in key process variables such as billet surface temperature in this area. The apparatus used here is usually temporary and therefore used on an experimental basis. Other such experimental instruments include those used to measure interlayer protrusion, solidified shell thickness and mold/cast friction.

Conclusion

This article gives a brief overview of continuous casting automation issues in steel processing. An introduction to the control technology used in this industry is given along with typical applications of this technology. Supporting technologies such as instrumentation that form a key part of implementing this technology are also discussed. Casting process and operational issues are highlighted. Production planning and scheduling, especially computer-aided quality control and the key role of instrumentation in the automation of continuous casters. One of the major and largely unclaimed benefits when it comes to foundry automation is the integration of foundry automation systems into industrial-wide production systems. Significant advances in casting automation at the unit process level have been hampered by a lack of instrumentation, but it can be expected that once such instrumentation is developed, great advances in casting automation will be expected.

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