Designer profiles from the Salzgitter Flachstahl hot-roll line

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, 1 and 2 in the figure), roughing train 3, finishing train 4, cooling line 5 and finally the tension reel 6 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. These are heated with the mill's own coke oven gas, among other sources. The exhaust gases that develop here are also used as an energy source to generate steam in the mill's own power plant, so that optimal use of the by-products is guaranteed, evidence of the importance of sustainable processes at SZFG.

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 1.5 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. Thanks to the continual development of the rolling process SZFG is able to guarantee the increased demands made on the hot-rolled strip profile for each individual customer. The latest software developments integrated into the finishing train's profile and evenness computer allow the so-called "designer profile". With the objective of offering the customer hot-rolled strip quality that is comparable to that of medium-wide strip, profiles are reproducibly configured to match the customer's requirements. This designer profile is registered without contact directly behind the finishing train by measuring the strip thickness, strip width, and evenness and storing them for visualization and quality assurance.

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.