'From 'Mini'to'Micro'and the Evolution to'Nano' up to the Latest 'ESC' Energy Saving Compact Minimill -Different Methods to Produce Commercial Steel Grades in an Easy and Environmental-Friendly Way

摘要

Since their beginning, Minimills have grown in size to capture the economies of scale and have now reached capacities exceeding 1,000,000 tons per year. However, markets that can absorb these volumes are being exhausted. From the early 70's, the minimill philosophy has been based on low-investment, minimal manning, low-operating cost plants intended for serving specific geographic areas with a good balance between scrap supply and finished product market. Over the years, the Danieli Group and several of its customers have worked closely together in order to come up with the right idea to fulfill this vision. Minimills have become a complement to the conventional integrated steel production complexes for the competitiveness they have shown in producing commercial grades in bars, wire rod and spooled bars. In addition, they are the most convenient way to recycle the scrap available in industrialized countries or to use raw materials in developing countries without having to resort to large investments and infrastructures. After the 80's and more installations supplied worldwide, the minimill evolution, which started in 1976 with the first complex built in Italy, has seen large capacity integrated minimills in the Middle East countries, "region-market" Micromills and Nanomills, and the recent introduction of the ESC environmental-friendly type minimills for commercial grade bars.The kick-off was in mid 2004 when Danieli approached CMC with a design concept that eventually led to the construction of the mill in Arizona. The design capitalizes on CMC's management and motivational philosophies and is based on the Danieli Endless Casting Rolling (ECR) process where melting, casting and rolling are carried out in one continuous and uninterrupted production process from scrap to finished product. This eliminates the need for a conventional reheating furnace with all the associated entry/exit equipment, auxiliaries and warehouse, which results in significant savings in terms of initial investment, utility consumption and running costs. The design also includes the "Direct Rolling & Bundling System" (DRB) enabling the cut to final commercial length directly off the last finishing stand. The result is a very compact arrangement of the whole cooling bed/bundle forming and tying station, with significant savings in both initial investment and production costs. The mill also features a Bar Quenching and Tempering System (QTB) allowing to produce low-cost billets in the meltshop by using fewer alloys and therefore reducing conversion costs.In late 2009, the first heat was poured in the new Danieli Micromill at Commercial Metals Co. - CMC Steel Arizona in Mesa, Arizona. The new steel complex, the first of its kind worldwide, is based on the "regional-mill/product-focused" concept designed to serve a regional market concentrating on a specific product range and making extensive use of local scrap.