Direct current plasma spraying of mechanofused alumina-steel particles

Stainless steel particles (60 $\mu$m in mean diameter) cladded with an alumina shell (2 $\mu$m thick and manufactured by mechanofusion) were sprayed with an Ar-H2 (53-7 slm) d.c. plasma jet (I = 500 A, P = 28 kW, \rho_th = 56 %). Two main types of particles were collected in flight, as close as 50 mm downstream of the nozzle exit: particles with a steel core with pieces of alumina unevenly distributed at their surface and those consisting of a spherical stainless steel particle with an alumina cap. The plasma flow was modeled by a 2D steady parabolic model and a single particle trajectory by using the 3D Boussinesq-Oseen-Basset equation. The heat transfer, within the two-layer, stainless steel cladded by alumina, particle, considered the heat propagation phenomena including phase changes. The models allowed determining the positions, along the particle trajectory, where the convective movement could occur as well as the entrainment of the liquid oxide to the leading edge of the in-flight particles. The heat transfer calculations showed the importance of the thermal contact resistance TCR between alumina and steel

NEW APPROACHES OF THE FORECAST OF THE AGEING OF PLASMA JET NOZZLE IN INDUSTRIAL SETTINGS OF THERMAL SPRAYING

p.19The optimization of the extension of the lifetime of the torches without hazard of drop of the product is an unceasing industrial difficulty. It needs a reliable criterion to characterize the wear, and thus indicate when the nozzle used should be switched by a new nozzle. These criteria are still quite subjective and hold the operator's experience. In 2003, David RIGOT, in collaboration with the Volvo Aero Corporation, has defined a number of criteria in his thesis dissertation [ ]. This study led to the realization of an electronic module alert detecting the hazardous time of process. The focus method was based on research and tracking characteristic frequencies in arc voltage fluctuations and in acoustic noise that is the image. It seems that a rough statistical study of signals is able to help define and visualize simple criteria ruthless variation is usable in objective phenomena wear alert. This is ad hoc measures for smooth power spectrum [ ] [ ] and its variability. Filtered signal is used to distinguish typically one or two epochs of slow wear followed by an epoch of fast wear. This difference is clear after a suitable choice of used frequency bands. Graphical representations are very expressive; they are supplemented by statistical tests. Signals & method: results, by David RIGOT on campaign made shots in September 2003 at the aircraft manufacturer Volvo Aero. Files led to collect a series of measures standardized on the time life of the nozzles. For one, whose use was particularly long, a few shots "vacuum" were prosecuted beyond of the usual threshold used in order to study the ageing. Sound torch and tension thus collected at various times of operation nozzles, with several frequencies of sampling, feed and no feed of powder. They allow first approach directly extract global statistical parameters which it represents dissimilarity based on time: moments, skewness, kurtosis, entropy [ ]. To each power spectra measurement, time is calculated from each signal multiple sampling. Each of the frequencies spectra is smooth inside of a convolution window by a kernel assessor [ ]. A simultaneous representation of the power of signals and their erraticism are used to visually choose the most discriminating frequency bands. Two sets of settings are then assessed: mean and variance of spectrum in the band selected; global parameters newly evaluated from filtered in the chosen band signals. Results: most selective statistics evolve in a similar manner and allows periods wear, while the overall results are most often efficient. For example templates to slope failure (piecewise linear models) are used. The spectra of tension frequencies and the spectra of sound frequencies give similar results. The sound is usable with the feed or without feed of powder. Sequential simple tests may be expected to assess the time of rapid wear

Quelle place pour les arcs électriques et les réacteurs plasmas dans l'" Inventaire et valorisation des collections, archives scientifiques et biens culturels " de l'université de Limoges ?

21 pages; 140 référencesInternational audienceThe University of Limoges in the rehabilitation of the premises was confronted with scientific disposal of property irreplaceable heritage in the context of "postmodern" or "post industrial" of our industrial society. Therefore a "scientific and cultural heritage Mission" was created in 2010 to save as much as possible the memory of the past half-century. For reasons we discuss plasmas and electric arcs have been an important place at that time in Western industry and especially by chance in Limoges

Influence des paramètres d'injection de poudres sur le traitement thermique des particules

International audienceEn projection plasma, la dispersion, en taille et en vitesse des particules à la sortie de l'injecteur, détermine les trajectoires des particules dans le jet plasma, et donne leurs histoires dynamiques et thermiques (vitesses, état de fusion, taux de vaporisation ...) qui sont des paramètres déterminants de la qualité de l'impact et du dépôt. Dans ce qui suit on décrit un modèle qui caractérise cette dispersion et qui tient compte de la distribution granulométrique de la poudre, des collisions inter-particulaires et des collisions avec les parois, il permet d'obtenir la distribution en vitesse et en taille des particules en sortie de l'injecteur

Modèle d'impact de gouttes chaudes sur un substrat solide froid

Les particules projetées par plasma d'arc sont généralement de taille micrométrique (comprises en général entre 10 et 100 μm) en projection conventionnelle et leur vitesse d'impact s'étend de 50 à 350 m/s. Les temps caractéristiques pour la formation d'une lamelle sont de l'ordre de la microseconde : moins de 5 μs pour la durée d'étalement de la particule fondue avec une solidification qui peut commencer avant la fin de l'étalement et se poursuit en général entre 0,8 et 10 μs après l'impact, et. [11]. Il s'agit ici d'étudier numériquement le couplage complexe par un modèle qui sera validé en comparaison avec des résultats d'étalement de particules de grande taille et à faible vitesse d'impact (<1 m/s)

Générateur à Plasma d'Arc à Air de 2 kW

Résultats préliminaires. Projet d'article avant soumission à une revueAn air plasma arc torch less than 2 kW was designed and constructed in the research laboratory QUERE of Setif University (Algeria) to meet all the needs that require the use of a plasma torch: welding, cutting, reloading metal surface treatment, pilot incineration burner, heating gas, etc. It is also a model of torches with the same concept but higher powers. It will also allow studying concentric electrodes plasma torches and hollow electrodes in many original configurations. A description of this generator plasma arc is presented with the results of the first experimental tests at reduced power

Numerical investigation of influence of precursors on transport properties of the jets used in solution precursor plasma spraying

[EN] The solution precursor plasma spraying is a modification of the conventional plasma spraying technique where the feedstock is a liquid precursor instead of a powder. The phenomena which occur in both techniques are different since the feedstock is liquid and consequently, the jet fragmentation, the solvent evaporation and the chemical reaction or pyrolysis must occur before solid melting and impact onto the substrate. The evaporation of the precursor changes the chemical composition of the plasma plume, hence it implies an important modification in the thermodynamic properties. In the present study, the influence of the solution precursor on these properties, concretely the thermal conductivity and dynamic viscosity of the plasma plume, has been addressed. Then, the ability of heating factor of the plasma plume was estimated and different effects of the precursor on the mentioned transport properties were evaluated. The effect of the type of precursor, the feedstock flow rate and the solution concentration has been evaluated in the present work. It is concluded that all of these variables affect slightly the viscosity but considerably the thermal conductivity and the ability of heating factor. Hence, the selection of the precursor characteristics allows to heat transfer between plasma plume and starting feedstock and consequently the resultant coatings exhibit a lower presence of porous or unmelted material.P. Carpio acknowledges the Valencian Government (APOSTD/2016/040) and the Spanish Ministry of Science, Innovation and Universities for his current post-doc contract (FJCI-2016-27822) for his post-doc contractCarpio-Cobo, P.; Pawlowski, L.; Pateyron, B. (2019). Numerical investigation of influence of precursors on transport properties of the jets used in solution precursor plasma spraying. Surface and Coatings Technology. 371:131-135. https://doi.org/10.1016/j.surfcoat.2018.09.073S13113537

Axisymmetric High Temperature Jet Behaviours Based on a Lattice Boltzmann Computational Method. Part I: Argon Plasma

Résultats préliminaires. Projet d'article avant soumission à une revueThis article aims to address the issue of simulating plasma-jet by using an innovative computational approach namely the Lattice Boltzmann Method (LBM) from the point of view of extending the applications to simulating flows with temperature-dependent physical parameters. The work focuses on the phenomena occurring in plasma-jet that define the link between LBM lattice and physical lattice. High temperature dependence of the plasma parameters is considered. Argon characteristics fall into this category. This gas is one of the most ones used in plasma spraying. Complex thermal plasma jet phenomena and basis of classical methods in CFD (discretization, stability condition, modeling...), in one side, and the simple scheme of the Boltzmann equation which is particularly adopted for simulating gases flows, in the other side, give us the possibility of taking out the dynamic and thermal characteristics of this complex flow. An important section on validation of this model includes details of available reference results is presented and discussed. It focuses mainly on the validation of our results with previous numerical and experimental results based on the centerline temperature and velocity profiles, its distributions over the computational domain and eventually the effect of the computational domain size. The jet width, the Gaussian radial profiles and the effects of inlet quantities are analyzed. A real spraying configuration is also examined. The quality of the results shows a great efficiency for the lattice Boltzmann method