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The flatness of a strip or sheet product is a key quality feature. But due to a wide range of different influences, the specified shape values are very often not attained right away during the rolling process. Such shape defects are removed afterwards by downstream strip levelling processes. By plastic elongation of the shorter portions of the strip to the length of the longest strip fibre, the differential length is compensated and shape defects such as centre buckles or wavy edges are removed
Fig. 1
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Shapemeter rolls equipped with integrated sensors are used to detect out-of-flatness conditions in the strip and to provide input data for the control system of the levelling line. These rolls measure the tensile stress distribution over the strip width while the strip, subjected to longitudinal tension, is being guided over the roll body. In contrast to existing shape measurement systems using separate measuring rolls installed in the process line, there is a solution requiring no additional flatness measurement roll in tension levelling lines (Fig. 1).
The development is based on the proven BFI shapemeter roll: a measuring system with common measuring sensors installed in one of the active bridle rolls of the stretch levelling line. This “measuring bridle roll” is arranged directly behind the bending unit, providing the following decisive advantages:
- It minimizes the dead time between levelling and measurement (shape measurement directly behind the bending unit)
- It takes advantage of a large roll diameter (i.e. no introduction of shape defects such as coil set or crossbow)
- It avoids faulty measurements due to geometry-induced stress disturbances as might occur with a conventional measuring roll installed ahead of the recoiler (e.g. when slit strip is recoiled non-uniformly)
- No additional measuring roll
Fig. 2 shows the “measuring bridle roll” equipped with force sensors installed in the BFI pilot plant and in the tension levelling line at ThyssenKrupp Nirosta Präzisionsband GmbH. |
