Rolled strip is ideally both straight (i.e. without camber) and left-right-symmetrical with respect to thickness (i.e. without wedge). Unfortunately, if wedge within a slab is removed through swiveling of the roll stack without further countermeasures, the result is camber, which—from a quality point of view—is even worse than wedge. The wedge and camber control solution from Primetals Technologies combines a number of technologies to tackle the problem: it uses cameras to obtain reliable readings of the strip’s position, measures thickness across the width of the strip, uses precise process modeling for both the roughing mill and the finishing mill, and utilizes the edger as a straightening machine. As a result, wedge is reduced to a minimum, and camber formation is avoided altogether—as are cobbles while threading and tailing out.
In order to control both wedge and camber, several components of the solution are ingeniously interlinked. First, the model-aided slab-to-slab swiveling in the roughing train reduces wedge at a point where there is still enough lateral material flow. Any camber that might result from this is straightened by the edger on the reversing pass. Second, a camber-measuring device placed after the roughing mill not only delivers data on camber, but also on the possible formation of hooks on the head or tail. Third, cameras monitoring lateral strip position in the finishing train support two functions of the “steering expert” from Primetals Technologies: threading control to compensate for camber effects on steering in the first stands, and strip-guidance control to react to steering issues and settle the strip’s run.
The full functionality of the solution was installed and tested at thyssenkrupp Steel Europe with very positive results. But even in cases where only a selection of the complete functionality is implemented, wedge formation and strip guidance are still notably improved.