Artificial neural networks implementation in plasma spray process: Prediction of power parameters and in-flight particle characteristics vs. desired coating structural attributes

Artificial neural networks (ANN) were implemented to predict atmospheric plasma spraying (APS) process parameters to manufacture a coating with the desired structural characteristics.The specific case of predicting power parameters to manufacture grey alumina (Al₂O₃-TiO₂, 13% by wt.) coatings was considered. Deposition yield and porosity were the coating structural characteristics.After having defined, trained and tested ANN, power parameters (arc current intensity, total plasma gas flow, hydrogen content) and resulting in-flight particle characteristics (average temperature and velocity) were computed considering several scenarios. The first one deals at the same time with the two structural characteristics as constraints. The others one deals with one structural characteristic as constraint while the other is fixed at a constant value.     

22层框架楼房定向爆破拆除倒塌过程分析

河源市龙川县远东花园4号楼为22层框架结构楼房,系违章建筑需爆破拆除.紧挨楼房5 m处有一栋3层别墅,别墅的围墙与待拆除楼房只有0.5 m,需防止楼房产生后座.根据周围环境条件,采用定向倾倒的方式爆破拆除,采用梯形爆破缺口,爆破高度13.5 m.为确定最佳延期时间,用ANSYS/LS-DYNA对排间延期时间300 ms...     

Intelligent system for prediction and control: Application in plasma spray process

Parametric drifts and fluctuations occur during plasma spraying. These drifts and fluctuations originate primarily from electrode wear and intrinsic plasma jet instabilities. One challenge is to control the manufacturing process by identifying the parameter interdependencies, correlations and individual effects on the in-flight particle characteristics. Such control is needed through methods that (i) consider the interdependencies that influence process variability and that also (ii) quantify the processing parameter-process response relationships. Due to the large amplitudes of the drifts and fluctuations, the strategy to adopt would depend on the required corrections to apply to the in-flight particle characteristics. Artificial intelligence is a pertinent tool to reach this objective. The system is flexible in order to permit a full control based on pre-defined rules aiming at maintaining at constant values in-flight particle characteristics (average surface temperature and velocity) by adjusting in real time the arc current intensity, the total plasma gas flow and the hydrogen content whatever the fluctuations.     

Evaluation of the termination mode in the radical polymerization of 2,2,2‐trifluoroethyl α‐fluoroacrylate

The mode of termination of 2,2,2‐trifluoroethyl α‐fluoroacrylate (FATRIFE) in radical polymerization was studied, and only termination by recombination occurred, which led to telechelic macromolecular structures. The radical polymerization in acetonitrile was carried out to synthesize oligomers with a low number average degree of polymerization ( )_cum (about 20), using tert‐butylcyclohexyl peroxydicarbonate (TBCPC) as initiator at 75 °C. The initial [TBCPC]₀/[FATRIFE]₀ molar ratio was monitored to evaluate its influence on the ( )_cum of α‐fluoroacrylic oligomers. The ¹H NMR analysis of the polymers showed that the ( )_cum values obtained were higher than 40, in spite of a high C₀ value. To explain these results, the mode of termination was evaluated using the following kinetic law: . The development of kinetic relationships allowed us to calculate the ratio k_prt/k_i·k_p as about 17–30 mol s l^?1, and to confirm that primary radical termination (PRT) was in competition with bimolecular macromolecular termination (BMT). © 2002 Society of Chemical Industry     

Finite element analysis of effect of substrate surface roughness on liquid droplet impact and flattening process

A computational program using the finite element method has been developed to simulate the impact and flattening of a metal droplet impacting onto a solid surface with different surface roughness occurring in the plasma thermal spray. The model is based on Navier-Stokes equations combining with friction conditions on the substrate surface to simulate the effect of substrate surface roughness on the flattening process of the droplet. In this study, a moving free surface model based on the Lagrangian method with an automatic adaptive remeshing technique has been developed to handle the large deformation of droplets and to ensure the computational accuracy of the numerical results. The numerical results show that the substrate surface roughness has a significant influence on the spreading velocity, flattening ratio, flattening time, splat size, and shape. The spreading process of a droplet is governed not only by the inertia and viscous forces, but also by the frictional resistance of the substrate surface.     

Harmful risks for workers in thermal spraying: A review completed by a survey in a French company

Thermal spray technologies are implemented in spray booths either manually or automatically. In both cases, workers can be exposed to several potential and real risks. The major risks are to workers’ respiratory systems and result from harmful feedstock materials. To the authors’ knowledge, very few specific studies have been conducted to assess the significance of these risks. This study describes the major risks encountered and reviews the results of a survey conducted in a French company that uses thermal spray technology on a large scale.     

Nozzle Mounting Method Optimization Based on Robot Kinematic Analysis

Nowadays, the application of industrial robots in thermal spray is gaining more and more importance. A desired coating quality depends on factors such as a balanced robot performance, a uniform scanning trajectory and stable parameters (e.g. nozzle speed, scanning step, spray angle, standoff distance). These factors also affect the mass and heat transfer as well as the coating formation. Thus, the kinematic optimization of all these aspects plays a key role in order to obtain an optimal coating quality. In this study, the robot performance was optimized from the aspect of nozzle mounting on the robot. An optimized nozzle mounting for a type F4 nozzle was designed, based on the conventional mounting method from the point of view of robot kinematics validated on a virtual robot. Robot kinematic parameters were obtained from the simulation by offline programming software and analyzed by statistical methods. The energy consumptions of different nozzle mounting methods were also compared. The results showed that it was possible to reasonably assign the amount of robot motion to each axis during the process, so achieving a constant nozzle speed. Thus, it is possible optimize robot performance and to economize robot energy.     

The influence of formulation and processing parameters on the thermal properties of a chitosan–epoxy prepolymer system

Waterborne epoxy dispersions have been employed effectively for many years in response to environmental regulations aimed at reducing solvent levels in coatings. Very few non‐toxic bio‐based polyamines have been reported in the literature as curing agents for epoxy‐functional waterborne dispersions. Currently to our knowledge the only bio‐based amino hardener used to cure a waterborne epoxy prepolymer is ?‐polylysine. Being one of the rare primary amine‐containing polymers of natural origin, chitosan is produced commercially by the deacetylation of chitin. In the work reported here, chitosan and oligochitosan were evaluated as curing agents for diepoxy prepolymers. A solvent‐free prepolymer (Epotec) and a waterborne prepolymer dispersion (Epirez) were both used. A crosslinked network was obtained when the reaction was performed with the waterborne epoxy dispersion. The influence of the hardener‐to‐epoxy prepolymer ratio on the crosslinking density was investigated. The thermal properties of networks were measured using differential scanning calorimetry and thermogravimetric analysis. © 2013 Society of Chemical Industry     

Porous Architecture of SPS Thick YSZ Coatings Structured at the Nanometer Scale (~50 nm)

Suspension plasma spraying (SPS) is a fairly recent technology that is able to process sub-micrometer-sized or nanometer-sized feedstock particles and permits the deposition of coatings thinner (from 20 to 100 μm) than those resulting from conventional atmospheric plasma spraying (APS). SPS consists of mechanically injecting within the plasma flow a liquid suspension of particles of average diameter varying between 0.02 and 1 μm. Due to the large volume fraction of the internal interfaces and reduced size of stacking defects, thick nanometer- or sub-micrometer-sized coatings exhibit better properties than conventional micrometer-sized ones (e.g., higher coefficients of thermal expansion, lower thermal diffusivity, higher hardness and toughness, better wear resistance, among other coating characteristics and functional properties). They could hence offer pertinent solutions to numerous emerging applications, particularly for energy production, energy saving, etc. Coatings structured at the nanometer scale exhibit nanometer-sized voids. Depending upon the selection of operating parameters, among which plasma power parameters (operating mode, enthalpy, spray distance, etc.), suspension properties (particle size distribution, powder mass percentage, viscosity, etc.), and substrate characteristics (topology, temperature, etc.), different coating architectures can be manufactured, from dense to porous layers, from connected to non-connected network. Nevertheless, the discrimination of porosity in different classes of criteria such as size, shape, orientation, specific surface area, etc., is essential to describe the coating architecture. Moreover, the primary steps of the coating manufacturing process affect significantly the coating porous architecture. These steps need to be further understood. Different types of imaging experiments were performed to understand, describe and quantify the pore level of thick finely structured ceramics coatings.