Gilding for Matter Decoration and Sublimation. A Brief History of the Artisanal Technical Know-how

IJCS it is an open access journal. All content is freely available without charge to any user or his/her institutionInternational audienceThe process used to decorate art objects with thinner and thinner gold coatings varied during centuries. Foil or leaf metal gilding technology was complemented around the beginning of the Christian era by mercury gilding. Simultaneously was developed in some geographic areas the surface depletion process for gilded copper/silver alloys. This paper is motivated by the recent publication by the authors of a didactic opus devoted to the description and the discussion of the technical history of the various gilding procedures, based on the study by modern investigation techniques of a number of gilded museum objects. Through examples from laboratory studies on museum objects, the main evolution steps of gold application are described. A recent mechanical modelling work about gold leaf forming by beating is reported. The different coating processes are discussed, depending on the substrate nature and surface treatment before gilding. It includes high temperature firing for mercury gilding, or powder gilding, e.g. on Middle-Age Syria glass. The paper ends with a listing of the research perspectives open for the presently poorly developed study of the adhesion mechanisms between gold leaf and its substrate. It discusses the important issue of gold-metal interdiffusion during metal gilding processes involving a high temperature step

Analytical models for tool wear prediction during AISI 1045 turning operations

Tool wear is one of the most important topic in cutting field. Its interest is due to the influence of tool wear on surface integrity of the final parts and on tool life, and, consequently, on the substitution policies and production costs. Analytical models, able to forecast the tool wear with a satisfactory accuracy, can give to the companies working in the material removal field a valid instrument to optimize the cutting processes. In the present work a comparison between response surface methodology (RSM) and artificial neural networks (ANNs) fitting techniques for tool wear forecasting was performed. For developing these predictive models, tool life tests, consisting of longitudinal turning operations of AISI 1045 steel bars using uncoated tungsten carbide inserts and variable cutting parameters, were conducted. Both flank (VB) and crater wears (KT) of the tool were monitored. The models were validated comparing the calculated tool wear values with the experimental ones, showing that ANNs model provides better approximation than RSM in the prediction of the amount of the tool wear parameters. So, from an industrial point of view, this model should be implemented into a production management software in order to correctly define the tool substitution policy during batch production.

SWARM Optimization of Force Model Parameters in Micromilling

Because of the improvement of machine-tool and tool performances in micro cutting field, the interest on these processes is increasing. Therefore, researchers involved in micro manufacturing processes focused their attention on these types of processes with the aim of improving the knowledge on the phenomena occurring during micro cutting operations. The objective of this work is to develop a modelling procedure for forecasting cutting forces in micromilling considering the tool run-out and the cutting tool geometry. The designed modelling procedure combines information coming from a force model, an optimization strategy and some experimental tests. The implemented force model is based on specific cutting pressure and actual instantaneous chip section. The tool run-out and the cutting tool geometry were considered in the analytical model. The adopted optimization strategy was based on the Particles Swarm strategy due to its suitability in solving analytical non-linear models. The experimental tests consisted in realizing micro slots on a sample made of Ti6Al4V. The comparison between experimental and analytical data demonstrates the good ability of the proposed procedure in correctly defining the model parameters

Apport de la microscopie électronique sous incidence rasante à l'étude des surfaces, application au laiton 70/30

10ème Congrès International d'Optique des Rayons X et de Microanalyse 10th International Congress on X-Ray Optics and MicroanalysisNational audienceOn montre combien la diffraction des électrons (100 keV) sous incidence rasante aide à la compréhension des données obtenues par spectrométrie Auger. On prend pour exemple l'étude d'une surface oxydée de laiton 70/30. Les résultats sont discutés, et confrontés à ceux obtenus en ESCA. L'influence du frottement sur la composition superficielle est observée

Influence de tensioactifs sur l'hydratation du ciment à l'interface béton/coffrage

National audienceLa microstructure des principaux hydrates du ciment dans les premiers microns de la surface du béton affecte les propriétés de surface telles que porosité, dureté, résistance aux taches, etc. En particulier, des variations dans la quantité et la taille des cristaux d'hydroxyde de calcium peuvent faire apparaître des propriétés de surface intéressantes. Malgré cela, les paramètres et les mécanismes qui gouvernent la croissance de la Portlandite ne sont pas encore bien connus. Cette étude s'intéresse à l'utilisation de solutions composées d'eau et de tensioactifs non ioniques à l'interface béton/coffrage. Dans certains cas, la présence d'un tensioactif favorise la nucléation et la croissance de Portlandite en surface du béton. La quantité de Portlandite, mesurée par analyse d'image, semble augmenter avec l'hydrophobie du tensioactif utilisé. Des observations MEB montrent que les cristaux induits par les tensioactifs présentent une structure atypique composée de fines couches superposées. Enfin, des essais de calorimétrie montrent que les tensioactifs ne modifient pas la cinétique d'hydratation du ciment

Influence of the nature of fluoropolymer processing aids on the elimination of sharkskin defect in LLDPE extrusion

International audienceFluoropolymer-based processing aids (PPA) are commonly used to suppress sharkskin defects in polyolefin extrusion. PPA's also lead to a decrease in die pressure and a slight increase in flow rate by coating die walls and inducing wall slip. The aim of this work is to investigate the influence of different types of PPAs on the physical parameters in the die at various scales. We used a modular slit die fed by an extruder to measure die pressure and velocity profiles by Laser Doppler Velocimetry (LDV), and to characterize die surface coating by Scanning Electronic Microscopy (SEM)

Mécanismes d'action des “Polymer Processing Aids” (PPA) dans l'élimination du défaut de peau de requin en extrusion

National audienceDepuis plus de vingt ans, des “Polymer Processing Aids” (PPA) fluorés sont utilisés industriellement pour éliminer les défauts de peau de requin en extrusion. L'objectif de ce travail est de comprendre les mécanismes d'action de ces PPA. L'influence des PPA sur la pression en filière et sur l'aspect des extrudats est d'abord étudiée, montrant simultanément une chute de pression et une élimination progressive du défaut. La formation d'un dépôt en filière est ensuite analysée par microscopie électronique à balayage (MEB). On constate l'existence d'un dépôt hétérogène de fluoropolymère, sous forme de lignes parallèles à l'écoulement, qui apparaît en deux temps. Enfin, l'évolution des profils de vitesse permet de corréler la chute de pression en filière à l'apparition de glissement à la paroi, ainsi que le glissement obtenu à la densité de dépôt

Shear Bond Strength of Self-Etching Adhesive Systems to Er:YAG Laser-Prepared Dentine with and without Pulpal Pressure Simulation

This is a copy of an article published in the Photomedicine and Laser Surgery © 2008 copyright Mary Ann Liebert, Inc.; Photomedicine and Laser Surgery is available online at: http://www.liebertonline.comInternational audienceObjective: This study was conducted to study the role of pulpal pressure on the shear bond strength of composite resin bonded to Er:YAG laser-prepared or bur-prepared dentine surfaces using a self-etching adhesive system. Materials and Methods: The occlusal surfaces of 80 human third molars were ground flat to expose the dentine. The dentine was prepared using either a carbide bur or an Er: YAG laser at 350 mJ/pulse and 10 Hz (fluence 44.5 J/cm(2)). Clearfil SE Bond was then applied with or without pressure. Rods of composite resin were bonded to dentine surfaces and shear bond tests were carried out. Results: When the Clearfil SE Bond was used without pressure, the difference between the shear bond strength values of bur-prepared and laser-prepared dentine surfaces was significant. When the Clearfil SE Bond was used with pressure, the difference of shear bond strength values was not significant between the two types of surface preparation. Conclusion: The absence of smear layer formation during the preparation of the dentine by the Er: YAG laser did not improve the adhesion values of self-etching adhesive systems

Etudes sur le mobilier Boulle, l'ébéniste de Louis XIV : quelques problèmes d'interfaces

National audienceDans le cadre d'un programme mis en place par le musée du Louvre, département des objets d'art, et le C2RMF, autour de l'étude et de la restauration des mobiliers attribués à l'atelier d'André-Charles Boulle ou à ses successeurs, il a été dégagé plusieurs problèmes concernant les marqueteries métalliques et les ornements en bronze doré. Cette communication traite en premier lieu de la compréhension de la mauvaise tenue au vieillissement des collages des pièces de marqueterie en laitons en contradiction avec la bonne tenue des pièces en étain voisines. Les propriétés mécaniques des assemblages laiton/colle/bois et étain/colle/bois utilisant la colle animale, notamment de poisson, ont été étudiées et la rupture prématurée de ces assemblages a pu être expliquée en tenant compte de la rhéologie des composants. En second lieu sont étudiées les dorures des ornements en bronze doré, grâce à l'utilisation des analyses par faisceaux d'ions. Les premiers résultats donnent une idée du procédé de dorure à l'amalgame de mercure utilisé et des épaisseurs d'or appliquées, ainsi que du procédé électrolytique utilisé pour les pièces restaurées

New Leaf Gilding Alloys: Physico-Chemistry, Colour, Mechanical Behavior

International audienceIn the frame of a systematic investigation on leaf gilding history and processes, in a research program intending to propose gold leaf alloys specially devoted to restoration, new gold alloys containing low concentration additions of In or Pd were designed and leaves were elaborated in collaboration with the goldbeater Dauvet. The influence of those elements on the colour change induced by alloying was obtained by colorimetry. The microstructural and metallurgical properties of the alloys were studied by scanning electron microscopy (SEM). The foils and leaves were characterized at the different manufacturing steps by EBSD (Backscattered Electron Diffraction), in order to evaluate the effect of the fabrication process on the microstructure and crystallographic texture. Surface segregation of the alloying element, influencing surface colour, was sometimes evidenced and discussed. The mechanical properties of the foils or leaves were measured by micro-and nano-indentation. The obtained properties and behaviour of the new alloys were compared with those of the leaves currently used for leaf gilding. The results conducted the beating company to consider developing new gold leaves production range(s) devoted specially for restoration application. As a result of the present investigation, new manufacturing and gilding procedures have been proposed