Productivity improvement of processing lines for hot-rolled strip

Strip shape defects and a misalignment of rolls lead to disturbances in strip flow during strip treatment in processing lines for cold and hot rolled steel strips deflecting the strip. In turn these irregularities will effect the performance capability of strip processing lines to the extent that speed has to be reduced, which, in consequence, causes a considerable drop in throughput. In addition to these resulting process disruptions highly defected strip shape can give rise to damage of plant equipment and to quality non-conformances up to the point where the product has to be rejected. The minimization of the above described problems - shape defects of hot rolled strips in processing lines and misalignment of rolls - has been the basic subject of the research project carried out. For the removal of strip shape deviations, being present as waviness, cross- and lengthwise bows as well as straightness defects (strip camber) a form fit bending device was designed, constructed and established in the continuous pickling line for hot rolled strip of Hoesch Hohenlimburg.GmbH. In view of processing high strength steel strips particular characteristics of the bending cartridges had to be taken into account. For the use of the bending unit information about the form and size of the shape defects in the strip must be available. An "online measurement" of the shape condition is absolutely required in order to be able to suitably adjust the bending rolls for the correction of the shape defects by means of whether monitor control or automatic control. Hence, for the measurement of these shape defects a system was selected which on the basis of the projected-fringe-method determines the characteristic flatness values by measuring the structure of the surface area. The system is based on the projected fringe method, which determines strip flatness characteristics by measuring the surface structure over large strip areas. In view of an optimal utilization of the bending technology applied a fully automatic and controlled operating system was developed and established. Model-based control strategies are applied like IMC (Internal Model Control). A plant model was established representing a considerable part of the developed control concept. For the description of the influence of the process parameters on the targeted variable strip shape a measurement campaign was performed at the facility of Hoesch Hohenlimburg GmbH delivering the necessary data. The position of the bending rolls (vertical penetration depth) of the two bending cartridges and strip tension are interacting. The strip tension, introduced into the strip by the bridle rolls, generates in interaction with the mean penetration depth of the bending cartridges a certain elongation and flatness respectively. These interrelations had to be considered when developing the plant model. For the preset of the form-fit-bending unit an access to a data base is performed, which contains the adjusting values in order of steel grade, strip width and strip thickness. The content of the data storage is continuously actualized by optimum bending roll positions resulting from the control procedures. As preset values weighted mean values are calculated accessing to the data base for the selection of the recent registrations of a related strip.