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2021, 21st July
Sustained performance and productivity at Yıldız Demir Çelik Cold Mill Complex
Benchmark results confirmed after two years of operation
Yildiz cold-mill complex in Kocaeli, Turkey, is producing 1.5-Mtpy high-quality, cold-rolled, tempered and coated strip in coils, for demanding applications. The close cooperation between Danieli and Yildiz project teams resulted in a remarkable tandem mill start-up, delivering zero waste from day one, followed by a daily increase in strip throughput and quality.
After two years of operation, sustained performance and productivity are confirmed.
The heart of the plant is the Turboflo® pickling line coupled with a five-stand, 6-hi Optimized Shaped Roll Technology (OSRT) tandem cold-mill, which is followed by a continuous galvanizing line with vertical furnace arrangement, a stand-alone temper mill as well as a batch annealing facility.
Pickling process efficiency is achieved by Danieli-patented Turboflo® technology, which includes advanced hydraulic sealing with minimal pump pressure, special tank channel design, high turbulence on both strip surfaces, adjustable turbulence level for better process control, strip tension level optimization along the line, and no need for catenary control. It has the ability to process light-gauge strips at up-to 450-mpm speeds, meaning a 15-second dwell time for light-gauge, low-carbon steel hot band. The Turboflo® line achieves a 5 to 10% decrease in acid and energy consumption compared to pump-generated turbulence, and a 10 - 15% production increase compared to non-turbulent bath.
Rolling mill flatness performance is ensured by OSRT with specially contoured intermediate roll barrel in combination with an axial intermediate roll-shifting device. This allows maximum influence on the roll bite by creating a roll crown, while reducing the necessary diameter differences on the intermediate rolls to increase roll lifetime.
Aided by online flatness control based on an exit-side shapemeter roll, more than 97% of all strip flatness deviations in steady- and transient-state rolling condition were either equal or below 6 I-units.
The OSRT concept showed excellent stability and performance during thin-gauge material production: ultra-low HAGC hysteresis with a 45% faster response time, and low-friction bending blocks, ensure precise strip thickness control, with thickness tolerances exceeding guarantee values. Yield savings around the weld seam are ensured by continuous rolling; L1 and L2 controls reduce the out-of-gauge length (OOGL) before and after the seam.
Economical high-speed, hot-dip, thin-coating galvanizing is achieved by Danieli Kohler X-Jet wiping system. It allows extremely accurate final zinc coating-thickness control, down to 35 g/m2 per side at 170 mpm. An annual 5% OpEx savings is ensured thanks to excellent coating uniformity along the strip. An L1-integrated Q-Robot Zinc skims the zinc bath surface.
Thanks to all of these features and more, plant availability for Yildiz cold-mill complex is close to 99.9 %.
- Marco Girardi
- + 39 346 025 5794