Modélisation et simulation d'une chaîne de broyage de minerais

RÉSUMÉ: Un modèle mathématique a été construit pour une chaîne de broyage de minerais constituée d'un broyeur à boulets suivi d'une classification granulométrique par hydrocyclone. Ce modèle est non linéaire et d'ordre élevé; il sera utilisé pour la simulation du processus et ultérieurement pour une commande numérique multivariable. Afin de simplifier la synthèse du régulateur, un modèle d'ordre réduit a été élaboré, puis linéarisé autour d'un point de fonctionnement. La validité des deux modèles a été établie par comparaison avec des résultats expérimentaux publiés dans la littérature. ABSTRACT: A mathematical model has been developped for a closed loop grinding circuit, including a ball-mill and a hydro-cyclone classification. This model is nonlinear and of high order. It can be used for simulation purpose. However, it was intended as a first step toward real time computer control of the grinding process. In order to simplify the design of the digital controller, a reduced order model has been derived and linearized around a steady-state point of operation. The validity of both models has been established against data published in the literature

Le parc national du diawling (Mauritanie) : infrastructures hydrauliques pour la restauration d’une plaine d’inondation et la création d’un estuaire artificiel

L’hydrologie du bas-delta du fleuve Sénégal a été totalement modifiée par la mise en service du barrage de Diama et de ses digues annexes. Ceci a eu des impacts écologiques et sociaux considérables. L’article décrit les infrastructures hydrauliques construites et leur mode d’opération dans le cadre de la mise en œuvre du plan directeur d’aménagement d’une aire protégée dans le bas-delta mauritanien. Les résultats préliminaires de cet essai de restauration d’un écosystème sont présenté

Preventing Abnormal Grain Growth of Austenite in Low Alloy Steels

International audienceno abstrac

Deacidification of grape musts by Schizosaccharomyces entrapped in alginate beads: a continuous-fluidized-bed process

One possible biological method for wine deacidification is elimination of malic acid from grape musts by Schizosaccharomyces yeasts prior to alcoholic fermentation. In this work we propose a new continuous process with yeasts included in double-layer alginate beads. The beads were retained in a fluidized-bed column reactor. In order to avoid CO2 retention, a stirred flask was added to the classical experimental set-up. The feasibility of the process has been demonstrated and its performance has been evaluated: 1.5–2.4 g 1−1 h−1 of malic acid consumed for 60% of beads in the column

“Angular resolution expected from iCHORD orientation maps through a revisited ion channeling model”

International audienceCrystalline orientation maps are obtained in a Focused Ion Beam (FIB) microscope using the ion CHanneling ORientation Determination (iCHORD) method, which relies on the channeling phenomenon observed in ion-induced secondary electron images. The current paper focuses on the angular resolution that can be expected from such orientation maps, obtained using a revisited ion channeling model. A specific procedure was developed to evaluate the angular resolution, based on the distribution of orientation errors when evaluating controlled sample disorientation. The main advantage is that no external reference is required. An angular resolution of 1° is obtained on a nickel based sample using standard acquisition conditions. This value fulfills most of the needs in terms of microstructural characterization usually carried out by Electron Back Scattered Diffraction

Precipitation and grain growth modelling in Ti-Nb microalloyed steels

Peer ReviewedPostprint (author's final draft

Design and development of complex phase steels with improved combination of strength and stretch-flangeability

This study presents the design and development of a hot-rolled bainitic steel, presenting a good combination of strength and stretch-flangeability, for automotive applications. Ti, Nb, and Mo were added in the steel composition in order to control austenite grain sizes, enhance precipitation hardening, and promote the formation of bainite. This study focuses on the effect of process parameters on final microstructures and mechanical properties. These parameters are the finishing rolling temperature, which conditions the austenite microstructure before its decomposition, and the coiling temperature, which conditions the nature and morphology of the ferritic phases transformed. A preliminary study allowed to determine the austenite grain growth behavior during reheating, the recrystallization kinetics, and the continuous cooling transformation curves of the studied steel. Then, a first set of parameters was tested at a semi-industrial scale, which confirmed that the best elongation properties were obtained for homogeneous bainitic lath/granular microstructures, that can be produced by choosing a coiling temperature of 500 °C . When choosing those parameters for the final industrial trial, the microstructure obtained consisted of a homogeneous lath/granular bainite mixture that presented a Ultimate Tensile Strength of 830 MPa and a Hole Expansion Ratio exceeding 70%.Peer ReviewedPostprint (published version

Development of Temperature-Controlled Shear Tests to Reproduce White-Etching-Layer Formation in Pearlitic Rail Steel

The formation of a white etching layer (WEL), a very hard and brittle phase on the rail surface, is associated with a progressive transformation of the pearlitic grain to very fragmented grains due to the cumulative passage of trains. Its formation is associated with a complex thermomechanical coupling. To predict the exact conditions of WEL formation, a thermomechanical model previously proposed by the authors needs to be validated. In this study, monotonic and cyclic shear tests using hat-shaped specimens were conducted in the temperature range of 20 C to 400 C to reproduce the WEL formation. The tests showed a strong sensitivity of the material to temperature, which does not necessarily favor WEL formation. For the monotonic tests, no WELs were produced; however, a localization of the plastic deformation was observed for tests performed at 200 C and 300 C. In this temperature range, the material was less ductile than at room temperature, leading to failure before WEL formation. At 400 C, the material exhibited a much more ductile behavior, and nanograins close to WEL stages were visible. For the cyclic tests, a WEL zone was successfully reproduced at room temperature only and confirmed the effect of shear in WEL formation. The same cyclic tests conducted at 200 C and 300 C yielded results consistent with those of the monotonic tests; the deformation was much more localized and did not lead to WEL formation.This work is part of the multi-disciplinary project MOPHAB, which aims to improve our knowledge and understanding of the mechanisms leading to the formation of the white etching layer in the materials used to construct railways and to develop corresponding numerical models. This project was supported by IRT Railenium and other industrial partners (RATP: Régie Autonome des Transports Parisiens, France, SNCF: Société Nationale des Chemins de Fer Francais, France, SAARSTAHL rail)