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This issue of the RECENT journal was edited with the support of: CONTENTS
The Economic Efficiency of Replacing Grinding with Hard TurningAbstract The precision manufacturing industry is characterized by high precision and low roughness levels. The hard turning operation became in the last years a serious alternative for replacing grinding at finishing machining of the parts with hardness bigger than 50 HRC units. Current papers present from technical and qualitative point of view, the advantages and disadvantages that hard turning can offer in order to perform a final finishing operation. Nevertheless, the economic aspect of this process change was debated very slightly. This paper is summarizing the condition required as for hard turning to be more efficient then grinding. Likewise the paper target's to highlight all cost elements, which, influences the manufacturing technology, cost (not only the price for the cutting tool) and optimal solution choose, but to bring the calculation method at the simplest formula possible in order to use it in future economical calculation. Keywords cost, manufacturing, hard turning, grinding
Mathematic Modeling and Software for the Solidification Simulation of Centrifugal CastingsAbstract The solidification of castings was studied with the help of different software at the Transilvania University of Brasov. To simulate the solidification of the castings with rotational symmetry, 2D software have been made in cylindrical coordinates, especially used to simulate the solidification of centrifugal tubular casting. The two versions of the software are: one for the casting made of eutectic alloys and the other for castings that are made of alloys that solidify in solid solution. This paper presents the mathematic model and the soft designed for the solidification of the rotational symmetry castings from alloys with a solid solution. The possible results obtained with the help of this soft are also shown. The case of a casting from a CuSn12 alloy (alloy with solid solution solidification) is exemplified and the results obtained are compared to those obtained in the case when the casting is made from an alloy with constant temperature solidification (eutectic alloy). The results show great differences regarding the solidification of the two types of alloys. The necessity of having different software is then justified to simulate the solidification of the casting. These have to be adapted to the type of solidification of each type of alloy (that is, alloy with a solidification interval and eutectic alloy). Keywords casting, centrifugal casting, solidification simulation, cast alloy, mathematic modelling
Determining Microparticle Concentration in the Workplace Atmosphere during Plasma GougingAbstract In this paper, we will present the result of our experimental research on measuring the microparticle concentration in the workplace atmosphere during plasma gouging. The results were compared to those of other measurements carried out at other arc-air and coated electrode gouging procedures. The microparticle concentration was measured with the MicroDust 880 nm detector. Following the measurements carried out, the results were also compared to the maximum permissible limit value regulated by the Government Decision No. 1218 of September 6, 2006. Keywords microparticles, plasma gouging, permissible limit value
Experimental Research upon a Pneumatic Equipment for Wrist RecoveryAbstract The equipment under experimental research is an equipment intended for recovering the wrist, which is driven by means of a linear pneumatic muscle. The palm is supported and moved with a device based on the "Fin Ray Effect" concept. This device has the advantage of simultaneously mobilizing wrist and knuckles. In this paper, the experiment results for the area of the wrist will be presented. Keywords recovery equipment, pneumatic muscle, wrist
The Compaction - Compression Coefficient of Chipboard PlatesAbstract This paper refers to a new feature of chipboard namely the compaction-compression coefficient for obtaining panels with superior properties. Because this coefficient has two components, respective the compaction and the compression ones, all two properties are firstly individual analyzed and only after that are synthesized into global property called the compaction-compression coefficient. This coefficient gives us a new perspective in the chipboard analysis. Keywords chipboard, compaction-compression coefficient, density
Considerations of the Bird Strike on Aircraft WingAbstract Airborne bird strike are relatively common and are on an ascending trend, which is a serious economic and aeronautical security, which is related to the increase in the numbers of large bird populations. According to the specialist references, the number of collisions of this type increased ten times between 1990 and 2015, the most exposed being propulsion systems and aircraft wings. Pilots and operators can be informed about ornithological threats and flight crews use standard operating procedures for such events to reduce the potential and consequences of a bird incident. The article wants a software analysis of the bird strike with a lifting surface of the aircraft. Keywords bird impact, XFLR5, aerodynamic coefficient, Clark Y
Some Considerations about the Aircraft Engine Combustion Chambers PerformancesAbstract The paper presents some results regarding the influence of the flame tube shape upon the combustion process in a turbojet engine. Also, it aims to present the results obtained following the research done for the identification of a turbojet engine's optimal combustion chamber geometry, characterized by as small as possible sizes with enhanced availabilities for air circulation in the primary combustion zone, in order to obtain a higher turbulence and an optimal radial temperature distribution at the entry to the stator of the first turbine stage in order to assure a minimal thermal load at the root of the blades. Similarly, the paper focuses on possibilities of positioning the holes of the flame tube to be more efficient, whereas its walls to be less thermally loaded and to obtain a low level of atmospheric pollution. The numerical results were obtained with Fluent CFD software and furthermore, there have been identified some solutions to the differential equation for reduced temperature (adimensional) under imposed initial conditions, by means of Maple software program. Keywords combustion chamber, flame tube, turbojet, noise and pollution
Effect of Quenching Medium on the Properties of the Hybrid Composite AlSi7Mg03-SiC-GraphiteAbstract The aim the of paper is to analyse the influence of the graphite content and quenching media on the structure and mechanical properties of hybrid composites, with AlSi7Mg03 based matrix reinforced with 10% SiC and 1.5% or 3.0% copper coated graphite. The samples obtained by stir casting were subjected to a solution heat treatment to 530oC for one hour, followed by cooling in air, water and ice + water followed by aging at 170oC for four hours. The hardness tests revealed the advantages of cooling in ice relative to the other cooling. Keywords composites, solution heat treatment, aged treatment, quenching medium
A new Method and Device for High-Speed, Accurate and Reliable Phase Difference MeasurementAbstract Measuring of the phase differences of electrical signals is very important for metrology. Many of the most accurate sensors of non-electrical values are based of devices that convert these values into frequency. Laser measurement methods are based on the same principle. In these methods, the measured values are converted into increments of frequencies or phases. The measurement of phase relationships is the highest level of accuracy, in comparison with frequency measurements. Traditional methods of phase measurements are already insufficiently accurate. Therefore, it is extremely important to develop new methods based on other principles. The paper discusses in details a new method for fastest measuring of the phase differences with the highest accuracy and with the most effective noise suppression. This method is illustrated by examples of signals obtained by numerical modeling. Keywords phase difference measurement, digital signal processing, phase meter, metrology, measurement noise
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