Super-OLAC H Introduced at Hot Strip Mill
for Automotive Steel Sheet Production
NKK's Fukuyama Works has completed installation of the
Super-OLAC H (on-line accelerated cooling for hot strip mill)
system at the runout cooling zone of its No. 1 hot strip mill, pioneering
commercial use of this highly accurate cooling technology for the production
of automotive steel sheet.
NKK's proprietary OLAC technology was first put into
commercial use at the Fukuyama Works' plate mill in 1980, enabling rapid
water cooling of steel plate immediately after hot rolling. Achieving
an ultra-high cooling rate almost close to the theoretical limit, OLAC
allows uniform cooling throughout the plate's entire length, resulting
in highly accurate product quality with increased strength without lowering
toughness. To date, the OLAC system and its improved Super version have
been installed at the plate mills of both Keihin and Fukuyama Works,
as well as at the latter's large section mill to manufacture H-shapes
(Super-OLAC S).
Until now, installation of the OLAC system at the runout
cooling zone of a hot strip mill has been hampered by several technical
difficulties. For example, an extremely high coiling rate exceeding
70km/hour made it hard to achieve ultra-rapid cooling without hindering
continuous strip rolling. NKK overcame this hurdle by incorporating
a unique driving device into the table rolls, in addition to making
other improvements in the new Super-OLAC H system, thereby maximizing
the system's cooling accuracy while securing continuous strip rolling.
The newly attained cooling rate of 700°C per second for a sheet
thickness of 3mm is the highest in the world.
The highly accelerated and uniform cooling of Super-OLAC
H effectively improves the accuracy of thermal hysteresis control and
temperature uniformity throughout the entire strip. As a result of refined
microstructure and enhanced metal-lurgical homogeneity, sheet product
quality is improved, offering superior strength, excellent toughness,
as well as stable weldability and workability. Furthermore, installation
of compact equipment at the cooling zone is possible, reducing size
to less than a quarter of conventionally used systems.
Start-up of Super-OLAC H at the No. 1 hot strip
mill of the Fukuyama Works has enabled stable production of high-tensile-strength
automotive steel sheet with use of various thermo-mechanical control
processes, winding up a series of facility renovation undertaken over
the past two years. Renovation and product quality improvement projects
completed to date at the No. 1 hot strip mill include:
| • |
Reinforcement of energy-efficient regenerative burners at the
No. 2 reheating furnace. |
| • |
Installation of a new solenoid induction-coil heating system for
rough bars. |
| • |
Expansion of roughing mill and its motor capacities. |
| • |
Expansion of finish-rolling and power supply capacities. |
| • |
Installation of the Super-OLAC H system. |
NKK intends to promote use of Super-OLACs and
advanced thermo-mechanical control processes in a full range of steel
production, including sheet, plate, bars and shapes, to meet the diversifying
demand of customers in the automobile, building, civil engineering and
machinery sectors.
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