PVD coated mill rolls for cold rolling of stainless steel strips - Tribological and mechanical laboratory tests

Voir : PVD Coated Mill Rolls for Cold Rolling of Stainless Steel Strips: Tribological and Mechanical Laboratory Tests, Ould C., Badiche X., Montmitonnet P., Gachon Y., Dans Proceedings of NAMRI/SME - 40th NAMRC - North American Manufacturing Research Conference, Notre-Dame, Indiana : États-Unis (2012) - http://hal-ensmp.archives-ouvertes.fr/hal-00724779International audienceThe cost of rolling is determined in particular by productivity and lifetime of rolls before regrinding. Adhesive wear of the sheet gives rise to transfer on the roll surface. Its occurrence depends on rolling conditions and is one of the determining factors of the maximal reduction for a given rolling speed. Abrasive wear of the roll is the second factor for roll lifetime. Both phenomena are strongly related to tribological and mechanical characteristics of the surface layer of rolls. Stainless steel is known for its high adhesiveness. Coatings with good tribological properties could help extend the roll service. In this paper, the potential of different PVD coatings (CrN, TiN and TiBN) is explored. The impact of these coatings on influential phenomena during rolling is analyzed thanks to well-adapted tribological and mechanical laboratory tests. The results show that TiN has a good potential in cold rolling of stainless steel strips

Feasibility of TiBN PVD Coating for Mill Rolls - Laboratory Testing of Anti-adhesive and Fatigue Resistance Properties

International audienceThe ceramic coatings deposited by Physical Vapour Deposition (PVD) are known for their high hardness. They offer a wide variety of friction coefficients. They have been used for a number of years for the coating of cutting tools; they have shown high efficiency in this field. Considering this, some of these coatings might prove efficient in the field of metal rolling. Yet to the best of the authors' knowledge, they have never been used industrially for rolling mill rolls. TiBN is one of the PVD coatings with the highest hardness. It is also known for its anti-adhesive property. In this study, the interest of TiBN in cold rolling is analyzed. In this application, the potential productivity is determined by the maximum pair (reduction, speed) above which seizure and transfer degrade tribological properties. The fatigue resistance is also studied and therefore, the potential influence of the coating on the roll life under conditions similar to those of rolling. Two well adapted tribological tests have been used for these two purposes: a plate-on-ring test, and a twin-disk Amsler test. The results of this study show a high potential of TiBN as coating for rolling mill rolls: good anti-adhesive property, very high resistance to wear and fatigue. It shows better performance than hard chromium, which is now widely used in this applicatio

Tests Tribologiques et mécaniques de différents revêtements PVD pour cylindres de laminoirs à bandes en acier Haut Carbone

International audienceOn étudie l'application aux cylindres de laminoir de revêtements PVD initialement développés pour l'usinage : TiN, TiBN, CrN, aux fins de remplacement du revêtement existant, le chrome dur. Les propriétés essentielles sont comparées à l'aide de l'essai bague plan (cet essai en glissement total est très sensible à l'usure adhésive) et de l'essai Amsler (roulement avec glissement sous forte charge hertzienne, qui teste la résistance de l'interface à l'écaillage). On montre que CrN, peut-être du fait de fortes contraintes résiduelles, est le seul à s'écailler dans les conditions de l'essai Amsler (2 GPa de pression maximale de Hertz, 106 cycles). Contre l'adhésion, TiN est décevant, alors que CrN et TiBN, aussi bien que Cr, empêchent le grippage jusqu'à la charge maximale de l'essai bague - plan

Tribological Testing of Anti-Adhesive coatings for Cold Rolling Mill Rolls-Application to TiN-Coated Rolls

International audienceRoll life is a major issue in cold strip rolling. Roll wear may result either in too low roll roughness, bringing friction below the minimum requested for strip entrainment; or it may degrade strip surface quality. On the contrary, adhesive wear and transfer ("roll coating", "pick up") may form a thick metallic deposits on the roll which increases friction excessively and degrades strip surface again [1]. The roll surface, with the help of a materials-adapted lubricant, must therefore possess anti-wear and anti-adhesive properties. Thus, High Speed Steeel (HSS) rolls show superior properties compared with standard Cr-steel rolls due to their high carbide surface coverage. Another way to improve wear and adhesion properties of surfaces is to apply hard metallic (hard-Cr) or ceramic coatings. Chromium is renowned for its excellent anti-wear and anti-adhesive properties and may serve as a reference. Here, as a first step towards alternative, optimised coatings, a PVD TiN coating has been deposited on tool steels, as previous attempts have proved TiN to be rather successful in cold rolling experiments [2,3]. Different tribological tests are reported here, giving insight in both anti-adhesive properties and fatigue life improvement

PVD coatings for mill rolls for cold rolling of high carbon steel strips-Laboratory tests

International audienceIncreasing the productivity of rolling mills requires improving surface properties of roll surface and prolonging roll life. The properties of interest are anti-adhesion to avoid catastrophic adhesive transfer, and wear resistance. Hard Cr coatings provides such properties for Al and carbon steel rolling, but should be replaced in the long run due to health/environmental issues. Physical Vapor Deposition (PVD) and Plasma-Enhanced Chemical Vapor Deposition (PECVD) of ceramic coatings are promising substitutes. In the context of high carbon steel strip rolling, TiN, TiBN, and CrN are tested here in terms of adhesive properties under large sliding conditions (plate-on-ring test) at increasing load. They are compared with a naked High Speed Steel (HSS) surface and a hard chromium coating. A 3-stage evolution is found as load increases, the last stage being characterized by massive adhesive transfer (severe wear) and high, irregular friction. TiN is shown to perform poorly under these conditions and does not bring an alternative solution to HSS steel. On the contrary, TiBN and CrN provide anti-adhesion protection up to the maximum load of the test, like C

Learning maximum excluding ellipsoids from imbalanced data with theoretical guarantees

International audienceIn this paper, we address the problem of learning from imbalanced data. We consider the scenario where the number of negative examples is much larger than the number of positive ones. We propose a theoretically-founded method which learns a set of local ellipsoids centered at the minority class examples while excluding the negative examples of the majority class. We address this task from a Mahalanobis-like metric learning point of view and we derive generalization guarantees on the learned metric using the uniform stability framework. Our experimental evaluation on classic benchmarks and on a proprietary dataset in bank fraud detection shows the effectiveness of our approach, particularly when the imbalancy is huge

Apprentissage de sphères maximales d’exclusion avec garanties théoriques

International audienceDans ce papier, nous proposons une méthode d'apprentissage automatique avec garanties théoriques pour générer des sphères maximales d'exclusion sur des données binaires présentant un fort déséquilibre. Notre objectif est d'apprendre un ensemble de sphères locales, centrées sur les exemples de la classe minoritaire, qui excluent les exemples de la classe majoritaire. Notre contribution est double : 1) le problème est abordé comme un problème d'apprentissage de métrique et 2) nous démontrons des résultats de stabilité uniforme sur le rayon et la métrique apprise par notre algorithme. Nos expériences sur des jeux de données réelles montrent l'intérêt de notre approche