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1.
Particle In-Flight and Coating Properties of Fe-Based Feedstock Materials Sprayed with Modern Thermal Spray Systems 总被引:2,自引:0,他引:2
Kirsten Bobzin Nils Kopp Thomas Warda Ivica Petkovic Marcel Schaefer Klaus Dieter Landes Guenter Forster Stephan Zimmermann Jose-Luis Marques Stefan Kirner Marina Kauffeldt Jochen Schein 《Journal of Thermal Spray Technology》2013,22(2-3):363-370
New developments in the field of thermal spraying systems (increased particle velocities, enhanced process stability) are leading to improved coatings. Innovations in the field of feedstock materials are supporting this trend. The combination of both has led to a renaissance of Fe-based feedstocks. Using modern APS or HVOF systems, it is now possible to compete with classical materials for wear and corrosion applications like Ni-basis or metal-matrix composites. This study intends to give an analysis of the in-flight particle and spray jet properties achievable with two different modern thermal spraying systems using Fe-based powders. The velocity fields are measured with the Laser Doppler Anemometry. Resulting coatings are analyzed and a correlation with the particle in-flight properties is given. The experiments are accompanied by computational fluid dynamics simulations of spray jet and particle velocities, leading to a comprehensive analysis of the achievable particle properties with state-of-the-art HVOF and APS systems. 相似文献
2.
This paper the combines group technology and the simulation approach to the design of an effective material flow system in production processes of a discrete nature. The GT method shows how to find operational groups using a classification system, and how to design GT cells to achieve their maximal effectiveness. Dynamic modelling and simulation of the designed system are emphasized as the tools for checking the behavior of the designed structure and measuring its effectiveness. An example of an application of the suggested approach in the case of a textile machine factory is discussed. 相似文献
3.
Osmokrovic P. Petkovic D. Markovic O. 《IEEE transactions on instrumentation and measurement》1997,46(1):36-44
This paper describes the construction of four probes adjusted for fast transient monitoring in 123 kV SF6 insulated substations. The primary requirement was the ability to monitor without distortion very fast transients containing frequencies up to 200 MHz. The measuring system was tested and calibrated with the help of computer modeling techniques. The verified experimental apparatus was then used for testing and calibrating the measuring probes. During the test, various effects on the measuring system characteristics were analyzed with respect to materials used for the components of the system 相似文献
4.
Gustavo Larsen Edgar Lotero Rubn D. Parra Lucía M. Petkovic Hugo S. Silva Srinivasanallur Raghavan 《Applied Catalysis A: General》1995,130(2):213-226
Palladium supported on sulfated zirconia (PdSZ) has been characterized by the n-butane isomerization reaction in the presence of hydrogen, X-ray absorption spectroscopy (XAS) and diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) of adsorbed carbon monoxide. Catalyst calcination at 873 K followed by hydrogen reduction at 513 K results in the formation of 30–40 Å Pd metal clusters, but the surface can only weakly adsorb CO, though stronger than Pd-free, sulfated zirconia catalysts. In the presence of hydrogen, PdSZ has a lower n-butane isomerization activity than SZ, and the Pd function cannot stabilize the reaction at low H2/n-butane ratios. 相似文献
5.
Web 2.0 refers to a new generation of web applications where individuals are able to participate, collaborate, and share created artefacts. Despite the fact that Web 2.0 applications are widely used for both educational and professional purposes, a consolidated methodology for their evaluation is still not available. This paper presents and discusses the results of two empirical studies on the case of mind mapping and diagramming Web 2.0 applications. Both studies employed logging actual use method to measure the estimated quality in use, while the retrospective thinking aloud method and an online questionnaire were applied to assess the perceived quality in use. Achieved analytical results showed that the results of the estimated and the perceived quality in use match partially, which indicates that quality in use should be measured with both subjective and objective instruments. The work presented in this paper is the first step towards a comprehensive methodology for evaluating the quality in use of Web 2.0 applications. Consequently, the usage of the proposed quality in use model for other types of Web 2.0 applications as well as contexts of use needs to be investigated in order to draw generalizable conclusions. 相似文献
6.
Sergey N. Rashkeev Daniel M. Ginosar Lucia M. Petkovic Helen H. Farrell 《Catalysis Today》2009,139(4):291
Production of hydrogen by splitting of water in the thermochemical sulfur-based cycles that employs the catalytic decomposition of sulfuric acid into SO2 and O2 is of considerable interest. However, all of the known catalytic systems studied to date that consist of metal particles on oxide substrates deactivate with time on stream. To develop an understanding of the factors that are responsible for catalyst activity, we investigate the fresh activity of several platinum group metals (PGM) catalysts, including Pd, Pt, Rh, Ir, and Ru supported on titania at 850 °C and perform an extensive theoretical study (density-functional-theory-based first-principles calculations and computer simulations) of the activity of the PGM nanoparticles of different size and shape positioned on TiO2 (rutile and anatase) and Al2O3 (γ- and η-alumina) surfaces. The activity and deactivation of the catalytic systems are defined by (i) the energy barrier for the detachment of O atoms from the SOn (n = 1, 2, 3) species, and (ii) the removal rate of the products of the sulfuric acid decomposition (atomic O, S, and the SOn species) from metal nanoparticles. We show that these two nanoscale features collectively result in the observed experimental behavior. The removal rate of the reaction products is always lower than the SOn decomposition rates. The relation between these two rates explains why the “softer” PGM nanoparticles (Pd and Pt) exhibit the highest initial catalytic activity. 相似文献
7.
8.
Mirna Issa Dalibor Petkovic Nenad D. Pavlovic Lena Zentner 《The International Journal of Advanced Manufacturing Technology》2013,67(5-8):1527-1536
Grinding is regarded as a special multiple edge cutting process, in which the abrasive grains remove the workpiece material at the microlevel. The grain–workpiece interaction, which resembles the microcutting process, directly modifies the workpiece surface and dominates all the output measures of grinding process. Recently, a virtual single-layer cubic boron nitride (CBN) grinding wheel model is developed by simulating each wheel fabrication step, which makes the estimation of the single grain material removal mode possible in grinding. Therefore, the study of the grain–workpiece interaction through microcutting behavior on the abrasive grains becomes necessary for the quantitative investigation of grinding processes. In this paper, the influence of the grain orientation on the microcutting performance of CBN grains is studied through finite element method (FEM) simulation based on response surface methodology (RSM). The FEM simulation helps in both qualitative and quantitative understanding of microcutting process. And the RSM analysis is proved to be an effective tool for factorial analysis in this paper. The results indicate that the single grain microcutting force is sensitive to the grain wear condition and orientation status, and there exists preferable orientation condition for microcutting with abrasive grains to achieve minimum cutting force. 相似文献
9.
Mirela Leskovac Vera Kova
evi Dragutin Fl Drago Hace 《Polymer Engineering and Science》1999,39(3):600-608
Thermal stability of poly(methyl methacrylate-co-butyl acrylate) and poly(styrene-co-butyl acrylate) modified with a small amount of acrylic acid and/or N-methylolacrylamide as a crosslinking agent was studied in this work. Programmed thermogravimetric analysis has been used to study the effect of copolymer composition on thermal stability, over a temperature range from 50 to 450°C, under a constant flow of nitrogen. Kinetic parameters of thermal degradation, activation energy, pre-exponential factor, and reaction order were obtained by using MacCallum-Tanner's approach. Kinetic data indicate that the thermal degradation of the investigated copolymer systems is the first order reaction, and that the increase of activation energy may be an indication of thermal stability changes in copolymer systems. 相似文献
10.
In this paper, a design of product polar quantizers for A/D (analog-to-digital) conversion of measurement signals and an analysis of their performances in the wide range of variances are considered, in a general manner, i.e. for any compression function. Special attention is devoted to the design of robust product polar quantizers, applying the developed theory on μ-law logarithmic compression function, which is very important since a lot of measurement signals are nonstationary. The proposed quantizers achieve much better performances than scalar quantizers (they have higher the maximal SQNR (signal-to-quantization noise ratio) for about 2.5 dB and they are more robust), without increasing of complexity. Theory is proved by simulation. These quantizers can be applied for many different types of measurement signals and can be used in many measurement systems (telemetry, telemedicine, wireless sensor networks, etc.). 相似文献