Papers by Keyword: Hot Strip Rolling

Abstract: Previous research shows that predicting width deviation inherits a central importance in hot rolling processes, so that the pass planning in the hot strip mill (HSM) can be optimized. These predictions can be enabled using machine learning, complementing analytical formulations of width spread. For reliable production, it is important for the plant operator to be able to control the geometry with high accuracy across the entire plant. Therefore, the width must be accurately known throughout the entire HSM. This paper aims on the prediction of width deviation in early product stages during the roughing mill processes, where the major deformation takes place, and thus also has the most significant influence on the width spread. Therefore, this paper takes industrial data into account which is also used for the roll passing planning. To achieve a prediction during rough rolling for the width after exiting the mill (future state of the strip width), various machine learning algorithms were implemented and tested. The prediction results are evaluated against an inline width measurement, where the XGB model performs best with a Root Mean Squared Error (RMSE) of 1.11 mm. Subsequently, feature importance analyses are used to examine which features are relevant for the prediction result and to elaborate which significance process-and geometry data has on the same strip.

Abstract: Every year digitalization is taking a bigger role in the steel industry. Models for predicting metallurgical phenomena, roll forces and microstructure have been commonly used in development of novel steel grades. These individual models may predict certain phenomena thoroughly, but input values are usually based on an assumption or on a “good guess”. To produce reliable boundary conditions for these models of individual phenomena, a virtual rolling model is developed. This model computes the whole process of the hot strip mill from roughing to accelerated water cooling on a run-out table. Strip location and temperature evolution is calculated continuously. Thermal and thermo-mechanical (rolling stands) boundary conditions are according to process layout. Input data for the model is automatically read from raw process data. Rolling parameters are calculated using a coupled ARCPRESS model, which is developed by authors, and calculates normal and frictional shear stress distributions in the roll gap to predict roll forces and displacements of the work roll surface. Recrystallization is considered when calculating the flow stress of the rolled strip. Phase fractions during water cooling are calculated as well. The virtual rolling model minimizes the need for parameter speculation as all parameters are calculated throughout the process. All the input values are read from actual process data and the metallurgical and mechanical state of the strip are computed throughout the whole process. As required by the state-of-art virtual rolling model, this model is based on generally accepted theories and experimentally studied metallurgical and physical phenomena along with the thermo-mechanical response of the actual rolling process.

Abstract: A new solution Karman’s equation with the Mises plasticity condition is proposed for determining contact stresses in the slip zones for hot strip rolling. Replacement of the precise plasticity condition by an approximate condition in terms of primary stress leads to a substantial decrease in the length of slip zones and to increase of the rolling force. It was shown that, even at high frictional coefficients, the length of slip zones forms a significant part of the length of deformation region. On the basis of the obtained solutions the techniques for plotting curves of the normal contact stresses, determining the length of the slip zones, the neutral position of the cross section and rolling force refined.

Abstract: Rolling Models have come a long way from the first empirical relations about forward slip and bite conditions to their current state, which allows local quantities to be calculated in two and three dimensions. In this paper, state-of-the-art of analytical modelling of the rolling process is shown with a fully three-dimensional rolling model for hot and cold strip rolling with stress distributions in the longitudinal, vertical and lateral directions. For this purpose, von Karman’s strip approach is extended to account for the stress gradient in lateral direction, as was already shown in different papers. The stress gradient in the vertical (through-thickness) direction is introduced by a modern implementation of Orowan’s inhomogeneous deformation theory. The local stress distributions are compared to results from Finite-Element Calculations obtained with modern FEM codes. It will be shown, under which circumstances expensive FEM calculations can be replaced by simpler models like the one proposed here, which are more time and cost-effective without a significant loss in result precision. The rolling model is extended with a Finite Element Beam Model for work and backup roll deformation, as well as local work roll flattening and thermal crown for hot rolling. The Effects of those features on stress distribution and exit strip profile are shown for hot and cold rolling.

Abstract: In this paper, the computation method of the strip crown is analyzed using the measured strip thickness data on a hot strip product line. The better quality of the strip is achieved for the smaller crown and the closer of the mean thickness to the nominal thickness. The polynomial approximation method for the transverse thickness distribution of the strip is used, and the different degrees of the polynomial are selected for calculating the strip crown. The calculated results are compared with the output of the measuring system in a rolling factory.

Abstract: The vertical-horizontal rolling in roughing stage of continuous hot strip rolling is a common production technique of controlling slab width effectively. Vertical rolling will induce dog-bone, width loss and fish tail in unsteady deformation zone of slab head and tail. A 3D elastic-plastic FEM model for roughing stage of continuous hot strip rolling was established using ABAQUS/Explicit and research on the influences of those technical parameters such as slab width, slab thickness, reduction of vertical roll and horizontal roll on unsteady deformation of metal was carried out. The research work provides a scientific basis for the optimization of roughing rolling technical schedule.

Abstract: This paper has researched strip width model in hot strip rolling. Analyzed physical phenomena influencing strip width, established calculation model in production including width spread during flat rolling, width change induced by bending, width changed by high temperature creep and thermal expansion and contraction during rolling. Practical applications in domestic 1500 hot strip mill show that the width model achieved good effect and enhanced the calculation precision.

Abstract: Hot strip rolling of steels inherently results in non-homogeneous microstructure and mechanical properties of hot bands. Thermomechanical processing that implies careful selection of rolling temperatures, speeds, reductions and controlled cooling parameters, as well as their accurate in-bar dynamic control allows not only for reducing the inherent microstructure variability but also for attenuating and even eliminating the adverse downstream manifestations of microstructure non-homogeneities. This is especially pertinent to advance high strength steels (AHSS) for automotive applications that have been shown to possess high sensitivity to variations in industrial processing conditions. Examples of industrial data and real time monitoring of hot band microstructure evolution using online non-destructive technique are presented confirming the efficiency of thermomechanical processing in ensuring the proper quality of AHSS sheet products.

Abstract: The production of advanced high strength steels (AHSS) has been rapidly expanding in recent years as these steels allow for considerable reduction in weight and enhancement of car safety due to the unique combination of high strength, toughness and formability. Driven by growing demand for sheet AHSS products from carmakers, steel producers are currently developing AHSS of the so called 3^rd Generation to further facilitate weight reduction of critical safety parts while ensuring crash worthiness and high absorbed energy. Such steels not only possess tensile strength above 1000 MPa but also are being designed for exceedingly high formability: high elongation, bendability, hole expansion and strain hardening. These enhanced properties are to be achieved in final operations of continuous annealing and/or galvanizing. However, due to complicated alloy designs of 3G AHSS the role of each manufacturing stage becomes progressively significant due to its impact on the final microstructure. Therefore, hot strip rolling gains increasing importance as one of the most critical stages responsible for producing the microstructure optimal for achieving the final properties of the sheet products without impairing downstream operations. In other words, hot rolling of AHSS has to be viewed as thermomechanical processing.

Abstract: A temperature sensor with a thermocouple placed at ~0.5 mm from roll surface is used in hot rolling conditions to evaluate by inverse calculation heat transfers in the roll bite. Simulation analysis in industrial hot rolling conditions with short contact lengths (e.g. short contact times) and high rolling speeds (7 m./sec.) show that the temperature sensor + inverse analysis with a high acquisition frequency (> 1000 Hz) is capable to predict with a good accuracy (5 to 10% error) the roll bite peak of temperature as well as the roll surface temperature evolution all around the roll rotation. However as heat flux is more sensitive to noise measurement, the peak of heat flux in the bite is strongly under-estimated (40% error) by the inverse calculation and thus only an average roll bite heat flux could be expected from the sensor (these simulation results will be verified with an industrial trial that is being prepared). Rolling tests on a pilot mill with low rolling speeds (from 0.3 to 1.5 m./sec.) and strip reductions varying from 10 to 40% have been performed with the temperature sensor. Analysis of the tests by inverse calculation show that at low speed (<0.5 m="" sec="" and="" large="" contact="" lengths="" reduction:="" 30="" to="" 40="" the="" roll="" bite="" peak="" of="" heat="" flux="" reconstructed="" by="" inverse="" calculation="" is="" correct="" at="" higher="" speeds="" 1="" 5="" smaller="" reduction="" :="" 10-20="" reconstruction="" incorrect:="" in="" under-estimated="" though="" its="" average="" value="" analysis="" reveals="" also="" that="" transfer="" coefficient="" htc="" sub="">roll-bite (characterizing heat transfers between roll and strip in the bite) is not uniform along the roll bite but is proportional to the local rolling pressure. Finally, based on the above results, simulations with a roll thermal fatigue degradation model in industrial hot rolling conditions show that the non uniform roll bite Heat Transfer Coefficient HTC_roll-bite may have in certain rolling conditions a stronger influence on roll thermal fatigue degradation than the equivalent (e.g. same average) HTC_roll-bite taken uniform along the bite. Consequently, to be realistic the roll thermal fatigue degradation model has to incorporate this non uniform HTC_roll-bite.