The universal annealing and hot-dip galvanizing line is designed to process two different products: annealed and hotdip galvanized cold strip. Thanks to a Drever furnace with ultra- fast cooling system generating high cooling rates, the line can produce high-strength dual-phase grades up to DP 800.
The new line permits Big River Steel to produce steel grades such as CQ, DQ, DDQ and IF and also high-strength steels like HSLA, DP and CP. The total capacity of galvanized and annealed material is about 476,000 tons. The strips processed have thicknesses from 0.36 to 3.0 millimeters whereas their width range is between 900 and 1,850 millimeters. Process speed may attain 150 meters per minute.
Galvanizing and annealing possible
After the annealing process, there are two ways of strip processing. In the galvanizing mode, the strip travels through a furnace snout into the hot zinc bath. A FOEN® air knife system precisely sets the required thickness of the zinc layer. In the annealing mode, however, this galvanizing process is bypassed. To this end, the zinc pot is lowered with the aid of a guide roll arranged above the zinc pot. A skin-pass stand, a tension leveler, a horizontal passivation system and an oiling machine are installed for the purpose of post-treatment. The Drever furnace complies with strict environmental standards and comprises equipment to recover energy. In the pre-heating zone, the hot exhaust gases from the burners are used for strip heating. The energy of burner and radiant tube exhaust air serves to heat the combustion air. A special system for Selective Catalytic Reduction (SCR) is provided to reduce the nitrogen oxides present in the exhaust gasses. This measure helps achieve NOx emission values of less than 60 mg/Nm³.
The annealing process in the continuous furnace is controlled by a mathematical model from Drever International. For nondestructive online strength measurement the line is equipped with an IMPOC measuring unit from EMG Automation GmbH. In addition, SMS group has developed an annealing model to optimize, using numerical methods, individual process parameters on the basis of line data, product data and information on preceding processes.
Linking these three elements to an I-Furnace (Intelligent Furnace) offers the opportunity of maximizing throughput and increases the yield of strip with a consistently high quality level. Thanks to an improved process control, the concept offers the potential to enhance energy efficiency or throughput once again by adapting nominal temperatures within the process windows.