North American steelmaker Nucor and Italian plant builder Danieli are setting a new benchmark in casting and rolling technology as they set about transforming the former Gallatin Steel Company plant in Ghent, Kentucky, USA, into an 'ultra-modern quality strip production plant' – or QSP.

The plan is to advance the technological capabilities and competitiveness of the plant and to do so they have taken on Danieli for the supply of all equipment and automated systems, from raw materials through to hot-rolled coil.

Working as a team, Nucor and Danieli have agreed to re-engineer the plant, change the original concept and give the plant improved thermomechanical rolling capabilities and thereby enabling it to expand its production of AHSS grades, API line pipe steel grades and other added value grades.

According to Danieli, the plant's state-of-the-art technology is a key aspect to optimising the transformation costs. "The new meltshop will make use of the most recent process management tools, including Q-MELT, which is a key aspect to optimising the transformation costs," said Danieli, adding that after the upgrade, the complete production will be delivered by a single strand vertical curved caster with a total capacity of up to 3Mt/yr (short tonnes).

Danieli says that the new caster represents the 5th generation of the company's high production slab casting machines. Slab will be delivered to the rolling mill by a new tunnel furnace via a swivel-type ferry system. "The layout allows for the installation of the new caster and the first portion of the tunnel furnace and swivel system without affecting the mill's production," Danieli explained. Two new roughing mills will be added to expand the plant's rolling capabilities.

A six-strand finishing mill will be retained, but widened and upgraded with new interstand guides, loopers and a new bending and shifting system, enabling rolling strips with a width of 1,870mm (73.5in). The first three rolling stands will be reinforced to withstand higher rolling forces, the company claims.

Two new powerful roughing stands and a vertical edger will be installed ahead of the finishing mill. The latter's total draft of 100 mm allows for the full recrystallisation of slab edges and extends the capacity of the plant when producing narrow products. The separation of the roughing stands from the finishing stands and the use of a thicker slab is all part of Danieli’s QSP and the result of over 25 years R&D experience.

Independent high-speed roughing, intermediate transfer bar cooling and final finishing rolling, says Danieli, introduces the ability to perform a thermo-mechanical rolling process typical of conventional hot strip mills. "This leads to a complete replacement of the existing tunnel furnace, widening of the finishing mill equipment, a new run-out table with advanced combined intensive

The vertical curved caster will be equipped with the very latest technology, including Danieli's latest design of multi-mode electromagnetic brake (MM-EMB) 'to ensure the control fluid dynamics within the mold, enabling high throughput of quality slabs'.

Danieli Centro Combustion will supply the tunnel furnace and the heated transfer table installed between the roughing and finishing stands.

Danieli says that a key challenge is the optimisation of the operation between the existing and the new meltship while controlling the quality of the caster and the QSP. This will be achieved using a new automation system provided by Danieli Automation, which will be designed with Industry 4.0 integration in mind.

Three planned mill shutdowns will accommodate the work that needs to be done, says Danieli, and the strategy will take maximum advantage of pre-planned annual maintenance outages, the last of which will see the complete roughing mill moved in line via a lift-shift system. The foundation of the mills will be prepared under the existing tunnel furnace without interfering with production, it is claimed.

Nucor took on the ownership of Gallatin Steel Company in October 2014. The plant has a nameplate capacity of 1.6Mt/yr (short tonnes) of hot rolled coils with a thickness range of 1.4mm to 12.7mm, widths up to 1,625mm and a maximum coil weight of 35 short tonnes. The current capabilities of the plant are mostly structural steel, micro-alloyed grades and thin line pipe grades.