Salzgitter Flachstahl's hot rolling line

Continual development of the rolling process in the hot-roll line allows Salzgitter Flachstahl to guarantee the ever-tougher requirements on the hot-rolled strip individually for each customer. The interaction of the most modern technology and our employees' many years of experience achieves continuous hot-rolled strip quality.

The hot-roll line is one of the most important units in the Salzgitter Flachstahl production process. Here the pre-material, the slab, is rolled into a flat steel coil up to 2000 meters (2187 yd.) long. During this complex rolling process, the steel coil is given its fundamental mechanical-technical and geometric characteristics. Thanks to state-of-the-art process control, these characteristics are configured for the individual customer. The core of the hot-roll line automation consists of a number of model computers and regulation systems. They allow extremely precise configuration of the most demanding customer requirements in a broad range of characteristics, from very wide to very narrow, from very thin to very thick, and all with ultra high strength up to 1,400 MPa. The hot-rolled strip's key features are the profile along the entire strip length, the dimensional tolerances, and the microstructure, and consequently the mechanical characteristics.

The production process on the hot-roll line might appear coarse to the observer. It is a sequence of extremely complex and delicate process steps, however, that, due to the combination of the employees' many years of experience and state-of-the-art technology, allows SZFG's to produce its high quality products. These products are only possible when the process steps for slab preparation (heating furnace and sizing press), roughing train, finishing train, cooling line and finally the tension reel are exactly tuned to one another, for example as far as temperature control and conveyor speed.

First, the rolling process requires a supply of uniformly heated slabs. Four heating furnace are available for the task.

Before the actual rolling process with the roughing train and subsequent finishing train, the slabs are shaped in the sizing press. Thanks to the use of short-stroke technology (variable width adjustment) for the slab start and stop, width deviations in the end product are further reduced.

The roughing train is a reversing rolling stand with flange-mounted edging mill. Here the slab is shaped horizontally and vertically. Particularly the edging stand serves to regulate the strip width and consequently significantly helps to ensure compliance with the tightest width tolerances.

The finishing train in the hot-roll line consists of seven rolling stands. Using hydraulic positioning and with the help of the most modern automatic control engineering, the rolling stock is rolled down to its final strip thickness. This process is capable of achieving hot-rolled strip thicknesses of 1.45 mm (0.45 in.) In order to ensure a constant strip profile along the entire strip length, the CVC (Continuous Variable Crown) and WRB (Work Roll Bending) technologies are used. Bending and shifting the working rolls makes it possible to achieve an exact adjustment of the hot-rolled strip geometry. This complex interaction between working roll displacement, load distribution by means of the optimal adjustment of the roll forces, and working roll bending, makes it possible to implement the strictest thickness and width tolerances as well as a constant strip profile along the strip length.

After being rolled in the finishing train, the finished strip has reached its target dimensions. Thickness, width and profile have been achieved. All that is missing now is the microstructure and consequently the mechanical-technical characteristics that are precisely configured in the subsequent cooling line: the widest range of characteristics can be achieved by means of selective cooling with water. Powerful computers allow the optimal switch over to the cooling line. The quantity of water and conveyor speed are calculated and implemented in real time at speeds of up to 1200 m/min (1312 yd/min).

Located at the end of the rolling mill is a coiling system with three reels. Here, the finished strip is wound into a coil under constant temperature control. The interaction of all these individual units results in a product that can be manufactured with pinpoint precision and that offers tremendous versatility in terms of machining options and possibilities.

In 7 stands and at a maximum speed of 1200 m/min (1312 yd./min), strip widths from 900 – 2000 mm (35.43 – 78.74 in.), strip thicknesses from 1.45 – 25.4 mm (0.45 – 1 in.), and strip lengths of up to 2000 m (2178.23 yd.) are produced.

The grades range from

• ELC (Extra Low Carbon)
• LC (Low Carbon)
• C-steels to C80
• Microalloyed steels
• Pipework grades up to X80

Thermomechanically rolled up to polyphase steels.
This corresponds to some 400 grades.