One Danieli single-strand caster was started late last year for Baosteel’s Pugang operation, and a new contract for a single-strand machine has been initiated at Pudhong.

Over the past two decades, the great advance in slab casting technology was the establishment of the thin-slab caster. More recently, the emergence of strip casting is proceeding (and succeeding, under certain commercial conditions.) But, in between have been a series of individual process control capabilities — e.g., segment control, soft reduction, and strand-guiding systems — that have optimized the casting process and improved the quality of thick slabs.

Naturally, China has seen many of these developments. Danieli (www.danieli.com) claims to have earned “the large majority” of Chinese slab caster projects, with a total of 26 strands completed or under construction in the past two years. One of its latest undertakings is a single-strand caster at Pudong Iron & Steel at Luojin, Danieli’s fourth slab caster for a Baosteel Group operation since 2005. These include a new two-strand machine at Baosteel Shanghai, another two-strand machine revamped and commissioned there late last year, and a single-strand installation completed last year at Pugang.

The new Luojin machine will be a single-strand caster producing over 1.5 million metric tons/year of slabs in various grades (low-, medium-, and high-carbon; peritectic, specialty, and tool steels), in slabs from 200 to 250 mm thick and 1,500 to 2,300 wide (to feed a plate mill.)

The machine’s component technologies indicate a sketchbook of recent advances in slab casting. It will have a vertical-curved run-out, with a 2.6-m vertical length and a 9.5-m casting radius, with multiple split caster rolls and continuous bending and unbending control. With a run-out of 35 m, the machine will be capable of casting at speeds up to 2.1 m/min.

A closer look at the design reveals: integrated hydraulic mold oscillation (Danieli’s Inmo system) with width and taper adjustment, which optimizes steel flow from the mold to the tundish; thermal mapping of the mold; air-mist secondary strand cooling; and Danieli’s Optimum strand segments, for applying “dynamic soft reduction,” with mathematical models for “liquid pool” prediction.

Dynamic soft reduction is a term applied to methods developed by various engineering groups to minimize steel porosity and centerline segregation in the interior of the cast product, as solidification begins upon the exit from the tundish. It is critical to achieving high-quality cast products, especially as steelmakers seek higher casting speeds.

It isn’t just in China that such technologies have had commercial impact, and the coordination of such advances allow steelmakers to coordinate widescale quality improvements. For example, last September Danieli took a contract from ArcelorMittal to initiate the third stage of its slab-casting revamp at the Dunkirk Works in northern France. The project started in 2004 and has seen the complete rebuild of one two-strand slab caster, and a second two-strand rebuild is in progress.

A total of 26 slab-casting strands have been planned or completed by Danieli in China since 2005, a scale of development made possible by coordinating individual process technologies.

Each of these revamps aims to transform the casting diagram from a standard curved run-out to the more advanced, vertical-curved geometry. As described by Danieli, the changes will improve the internal quality of cast products (particularly, the automotive IF grades) while increasing casting speeds (thanks to a longer containment length). Other changes will reduce caster downtime (fully segmented design, new top-feeding dummy bar, and robotized manipulator for segment replacement.)

Redesigned, each of the Dunkirk casters will have the Inmo technology and Optimum segments for dynamic soft reduction, among a long list of other speed and quality enhancements.

The first of these revamps was completed and started late in 2006, and the second is nearing completion. The last of the three will begin later this year. With this latest contract, Danieli counts 13 ArcelorMittal slab-casting strands in Europe and Brazil among its achievements.

For ArcelorMittal, or any producer of steel slabs, the objective is the same: produce better quality materials, faster, so that the result will be higher volumes of highvalue steel. The menu of technologies for these objectives are widely available.

For example, SMS Demag (www.sms-demag.com) has been promoting a new strand-guidance technology, Cyberlink, specifically for the horizontal segment of the strand. From a mechanical perspective, Cyberlink uses a series of “guide rods” to link the top and bottom frames of a horizontal segment. Thish allows the top frame to move vertically and side to side, a greater freedom of movement that allows the strand-guide segments to achieve “self-centering” during casting.

The effect is to reduce friction on the slab and roll wear on the machine — which improves slab quality and increases plant availability and productivity.

For solidification, SMS offers a dynamic soft reduction process in which the strand is compressed by adjusting the top frame of each segment before the slab has solidified fully. SMS states that this prevents porosity from developing in the slab core and minimizes segregation at its centerline.

The goal is to determine as nearly as possible exactly the point when final solidification begins, and information about that process is gathered by gauging the segment force as it is applied, in order to maintain the predetermined segment position. “Frictionless guiding of the segment top frame is the only way to determine this force in unadulterated form based on the pressures in the hydraulic adjusting cylinders,” according to SMS.

A process control module, Dynamic Solidification Calculation, uses secondary cooling data to adjust all strand guide segments. It is a single example of data management and coordination of mechanical, electrical, and automation functions that happen repeatedly in slab casting.

This, and other SMS “performance enhancers” were included in two new slab casters at Maanshan Iron & Steel in China, where the objective is to produce a wide range of steel grades: automotive, construction, and tube and pipe products.

SMS implemented what it calls “Intelligent Slab Casting” control modules, which optimize the “interplay” of strand guide length, width-dependent secondary cooling, and Cyberlink segments in the horizontal section of the run-out.

Maanshan uses SMS’s Dynamic Solidification Calculation model to manage solidification. For example, steel grades that are prone to cracking must have their high-temperature ductility monitored, and the optimal conditions are stored in the model to in order to manage stress within the strand shell. DSC calculates the required cooling state of the slab, and adjusts the caster’s spray cooling process to achieve the desired slab surface temperature until the slab reaches the caster’s straightening section. Similarly, slab edge cracking is controlled by monitoring heat dissipation, again by adjusting the amount of water sprayed in the edge zones.

For the internal slab conditions, Maanshan has Cyberlink segments to induce homogenous microstructure without porosity.

Siemens VAI (www.siemens.com/metals) is another contributor to this technical breakthrough. It combines its own Smart segments package and Dynacs cooling model to optimize the caster’s roll-gap and tapering adjustment, to maintain slab quality during “transient casting conditions,” and to aid slab thickness adjustments from cast to cast. Dynacs delivers slab thermal tracking to monitor slab solidification points, while another model, DynaGap, automatically adjusts the setpoints for the Smart segments’ roll gaps.

More new ideas will be demonstrated in a recent contract Siemens VAI logged from ThyssenKrupp Steel’s Duisburg- Bruckhausen Works in Germany. There, new basic and process automation systems, a new control system, and new process computers will be installed to improve the performance of a two-strand, 2.6-meter slab caster.

Top: Siemens VAI diagrams the application points for different slab caster process control functions. Middle, the LiquiRob robotic device that samples liquid steel in the tundish, and performs alloy additions and adjustments, too. Bottom, Automation functions and control systems for the ThyssenKrupp caster at will be entirely revamped and updated.

The modernization will integrate equipment-specific user functions, such as DynaWidth, and DynaFlex for hydraulic mold oscillation.

Due standardized hardware and software components for the basic and process automation, Siemens is able to compile “an integrated, fault-tolerant, and userfriendly solution.” The automation package has a redundant structure, which allows retooling of the control architecture without interrupting the TKS production process. All modernization will be carried out during planned production outages.

Siemens uses its own Simatic PCS7 control system for automation. The process models include DynaWidth, for rapid online slab-width changes, and DynaFlex, for hydraulic mold oscillation. Process controls will include a new edition of the “fuzzy” logic-based mold level control, rooted in Simatic PCS7.

Another Siemens VAI innovation was implemented half a world away last November, at Pohang Iron & Steel’s Gwangyang Works in South Korea. There, as part of its new two-strand slab caster, Posco started the first Siemens Metal Technologies LiquiRob robot system.

LiquiRob automatically conducts sampling and temperature measurements of the steel in the tundish, as well as powder dosing. This new system provides a high level of operator safety and process reliability due to robot’s systematic procedures.

As part of the 2006 contract for the two-strand, 3.5-milion metric tons/year caster, LiquiRob was developed for steelmaking environments where operators are exposed to liquid hot metal, such as the caster platform. The automation platform carries out all manual tasks on the caster platform for the entire casting sequence, allowing operators to supervise casting conditions and operations from the control room, out of harm’s way.

Individual units also were designed to perform different functions in caster areas, including in the ladleloading position and tundish area to measure temperature and take samples. In the mold area, LiquiRob can perform mold sampling, casting-powder dosing, slag removal, and insertion of steel-quality-separation plates.

LiquiRob can be rotated or linearly shifted, and features a specially developed 3D position-detection system for equipment such as ladle slide-gate cylinders, media couplings, and submerged entry nozzles. According to Siemens, another LiquiRob installation is slated for this spring in South America.

Still thin, but Posco’s next caster will be more “continuous” Danieli and Posco are planning a “new generation” thin-slab caster — capable of continuous processing through to finish rolling. In contrast to the various technical enhancements to improving casting speed and product quality in thick-slab casting, there will be no incremental approach by Danieli and Posco as they develop a “new generation” of thin-slab casting. At Posco’s Gwangyang Works a new caster will replace the ISP mini-mill that’s been operating there since 1996, and it will be known as the Compact Endless Cast Rolling Mill (CEM). Danieli and Posco will revamp the existing casting and rolling facilities to improve its operation and to achieve a direct link between the casting and rolling processes. ISP was a technology developed by Mannesmann. In this process, after the roughing stands, slabs from two strands are coiled and then conveyed to a single finishing mill. With a target output of 1.8 million metric tons/year, the revamped operation will consist of two thin-slab casters: a Danieli highspeed thin-slab caster will be installed in line with the rolling mill, to cast 80-mm slabs at up to 8 m/min. The new caster will be connected to a three-stand roughing mill, after which the transfer bar will be conveyed to the existing in-line finishing mill for final rolling. Danieli will undertake a complete renovation of the existing plant, including the new casting facilities, revamping of the roughing mill, and the connection with the finishing mill. Danieli Automation will develop control architecture for the new plant, including the direct process integration between casting and roughing process.