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Magazine5 Min

Energy efficient production of long products - Continuous Minimill Technology

Changing market demands call for strategies for sustainability, cost efficiency and compact, site-adapted production capacities. In this context, SMS offers as a full system provider complete tailor-made minimill solutions including the latest technological solutions and comprehensive support to enable efficient production of long products, such as straight bars, compact coils or wire rod.

Increasing sustainability through direct connection of caster to the mill

Sustainable production  and the lowest possible product carbon footprint with high productivity are the current and future challenges in the steel industry for the production of long products. SMS group meets these challenges with its developed CMT® process (Continuous Minimill Technology), an inline continuous casting and rolling process. From scrap to high-end final products the plant integrates steel making, caster and rolling mill into a highly reliable single process, minimizing carbon footprint, OPEX and CAPEX.

A low-emission steelmaking facility supplies liquid steel to a high-speed continuous caster  that feeds the rolling mill directly, eliminating the traditional fossil fuel fired re-heating furnace.

CMT® plant concept

To further reduce the carbon footprint, SMS group has introduced the ALLCHARGE technology .The ALLCHARGE design is based on the combination of flat bath operation with continuous charging of scrap coupled with a separate extraction line for the off-gases. Thus, ALLCHARGE de-couples the off-gas line from the scrap conveying line, minimizes carbon dioxide direct emissions and improves control on dangerous pollutants like NOx and VOC.

The pairing of flat bath continuous scrap melting together with direct rolling of rebar or very compact coils leads to a reduction of greenhouse gas emissions at the site by up to 70%. Liquid steel is produced and refined by an advanced steelmaking plant, based on the ALLCHARGE design coupled with a disruptive power feeding concept based on IGBT electronic modules named X-Pact® AURA. Since electrodes are made by graphite material, the reduction in consumption reflects immediately in a reduction of CO2 footprint.  This enables the lowest environmental impact in terms of CO2 and NOx emissions, which is further enhanced by a potential connection to renewable energy sources. Use of modular concept and state-of-the-art electronics guarantees best efficiency and highest power density, with a minimal impact to the grid. Proprietary control algorithms and innovative modulation technologies ensure high power transfer and fast control.

The flexible CMT® process can be designed for a wide range of products, from straight rebars to Vertical Compact Coils up to 8 tons (VCC®). Integrated level 1 and level 2 automation systems, managing all production process aspects from the scrap yard logistics to the mill finishing area, as well as covering maintenance of the plant are also key elements for an efficient and cost-effective production.

The CMT® minimill also provides solution for compact and small property sizes. A smaller plant footprint thus minimizes the investment in foundation and construction materials usually needed for larger plants. Thus, the CMT® minimill not only reduces operating costs during ongoing production, but is also extremely efficient regarding the initial investment.

Flexible technology for maximum plant efficiency

The CMT® technology, when compared to a traditional minimill of same capacity, provides steel producers with an efficient tool with estimated saving of approx. 20 Euro/t in transformation cost that in addition to the reduced initial investment cost results in an estimated competitive advantage of 10 to 25% over conventional minimills.

The development of the CMT® started with the CMT®350 solution, rated for a production of 350,000 t/year. At the base of this concept there is a melt shop with a productivity of 50 t/hour, and a single-strand continuous caster producing a 130SQ equivalent mm endless billet. The cast product is fed endless into the rolling mill at a speed of 6 m/min or above. By using the CONREX mold technology it is possible to achieve the required casting speeds without sacrificing the quality of the cast product. By eliminating the need of a gas-fired reheating furnace a considerable amount of energy can be saved. Additionally the bar head and tail cutting is no longer necessary and the chances of process interruptions caused by the threading of cut to length billets is reduced to a great extent. These two effects increase the yield of the rolling process significantly. Higher productivities can be covered by increasing the cast sections.

The CMT®550 is rated, for 550,000 t/year, with a hourly productivity of 82 t/hour while casting CONREX165 (equivalent to 165 SQ mm endless billet). For further increasing the productivity to 108 t/hour the cast section is increased to CONREX 190 (equivalent to 190 SQ mm format), achieving a production of 700,000 t/year.

Intermediate/finishing mill fitted with HL stands


Recently Hybar LLC has placed an order with SMS group for a new rebar minimill, which will be built on a site just outside of Osceola, Arkansas. The minimill will enable Hybar LLC to produce rebar at a sustainable scale with industry leading operating costs and environmental sustainability results. Hybar mutually agreed to continue its cooperation with SMS for another two minimills in the future.

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