Dissertationen zum Thema „Prehľad“

The Master´s thesis focuses on the possibilities of using MAG welding on carbon steel 1.1221(C60E) without using preheating. It researches the effect of basic welding parameters on the final characteristics with the goal being to find a welding seam without defects, without using preheating.

En vanlig orsak till brott i svetsade kolstålskonstruktioner kan härledas till små sprickbildningar som uppstår i svetsgodset eller det område av grundmaterialet som har påverkats strukturellt av energin från svetsprocessen, även kallad HAZ. Dessa sprickor uppstår ofta timmar eller dagar efter avslutad svetsning och beror på en kombination av väte, en hård och spröd mikrostruktur och närvaro av spänningar. För att undvika dessa sprickor kan man förvärma materialet innan svetsning. Den förhöjda arbetstemperaturen ger en långsammare svalning vilken minskar risken för martensitbildning och låter väte diffundera ut från svetsförbandets kritiska delar. Det finns olika beräkningsmodeller för att räkna ut den förvärmningstemperatur som krävs för att motverka dessa sprickor. De flesta av dem är grafiska men försök har gjorts att översätta dessa till matematiska algoritmer. Beräkningsmodellerna kan ge väldigt varierande temperaturer och olika modeller kan anses vara bäst tillämpade till olika stål. I denna rapport har det undersökts vilken beräkningsmodell som är bäst lämpad för konstruktionsstålet S355J2. Modellerna som har använts är den matematiska CET, de grafiska CEIIW och CEN samt matematiska tolkningar av de två sistnämnda. Utvärderingen har gjorts genom att svetsa upp prover på plåtar med en godstjocklek på 30 mm med en stegvis ökande förhöjd arbetstemperatur. Dessa prover har sedan genomgått både oförstörande och förstörande provning för att undersöka hur sprickbenägna de är. En analys av svetsförbandets mikrostruktur har också genomförts för att identifiera de mest kritiska zonerna. Det visade sig att de matematiska tolkningarna av de grafiska metoderna skiljde sig såpass mycket från sina grafiska motsvarigheter att de inte kan rekommenderas för användning. Det visade sig även att det inte fanns en beräkningsmodell av ursprungsmodellerna som var bäst lämpad för S355J2 utan valet berodde helt och hållet på vilken sträckenergi som användes då modellerna tar olika mycket hänsyn till denna. För en sträckenergi på över 1,6 kJ/mm rekommenderas CET-metoden som beräknade en temperatur som gav goda materialparametrar. För sträckenergier under 0,9 kJ/mm beräknar ingen metod en tillräckligt hög temperatur, men CEIIW är den som beräknar den högsta förhöjda arbetstemperaturen och rekommenderas därför för användning. Man bör dock ha i åtanke att den inte var tillräckligt hög och bör därför ses som en lågt räknad rekommendation. Mellan 0,9 kJ/mm och 1,6 kJ/mm har inga prover svetsats men rekommendationen är att använda sig av CET-metoden då den är enkel och beräknar högst temperatur. Vad det gäller svetsförbandets kritiska zoner så visade det sig att korntillväxtzonen var området där vätesprickor har störst förutsättningar för att uppstå.<br>One of the most common causes of failure in welded carbon steel constructions can be traced to small cracks that occur in the weld metal or in the area of the base metal that has been affected structurally by the energy from the welding process, also known as HAZ. These cracks can occur hours or days after the welding is completed and do so due to a combination of hydrogen that has penetrated the metal during the weld process, a hard and brittle microstructure and tensile stresses acting on the weld. A method to avoid these cracks is to preheat the material before welding. The increased temperature results in a slower cooling which reduces the risk of a martensitic microstructure and allow hydrogen to diffuse out of the most critical zones of the welded joint. There are many different methods for calculating the preheat temperature needed to counter these cracks. Most of them are solved graphically but attempts have been made to translate them into mathematical algorithms to facilitate calculations. The outcome of the methods may vary and different methods can be considered to be best applied to various steel. The purpose of this study is to investigate which method is best suited to determine the preheat temperature to eliminate the risk of hydrogen cracking for the structural steel S355J2. The methods used in this study was the mathematical CET, the graphic CEIIW and CEN and mathematical interpretations of the latter two. The evaluation was made by welding samples of plates with a thickness of 30 mm and with an incrementally increased preheat temperature. These samples were then subjected to both non-destructive and destructive testing to examine how prone they were to crack. An analysis of the weld microstructure was also conducted to identify the most critical zones. It turned out that the mathematical interpretations of the graphic methods differed so much from their graphical equivalent that they can not be recommended for use. It was also found that none of the original methods can be said to be best suited for S355J2 but the choice depended entirely on the heat input. For a heat input over 1.6 kJ/mm it is recommended to use the CET-method which estimated a temperature that gave good material parameters. For a heat input below 0.9 kJ/mm no method calculates a sufficiently high temperature, but the CEIIW-method is calculating the highest temperature and is therefore recommended for use. However, one should keep in mind that it was not sufficient and should therefore be seen as a conservative recommendation. No samples were welded between 0.9 kJ/mm and 1.6 kJ/mm but the recommendation is to use the CET- method because it is simple and calculates the maximum temperature. It was also found that the coarse grain zone was the area where hydrogen cracking is most likely to occur.

Coal derived synthetic gas (syngas) fuel is a promising solution for today s increasing demand for clean and reliable power. Syngas fuels are primarily mixtures of H2 and CO, often with large amounts of diluents such as N2, CO2, and H2O. The specific composition depends upon the fuel source and gasification technique. This requires gas turbine designers to develop fuel flexible combustors capable of operating with high conversion efficiency while maintaining low emissions for a wide range of syngas fuel mixtures. Design tools often used in combustor development require data on various fundamental gas combustion properties. For example, laminar flame speed is often an input as it has a significant impact upon the size and static stability of the combustor. Moreover it serves as a good validation parameter for leading kinetic models used for detailed combustion simulations. Thus the primary objective of this thesis is measurement of laminar flame speeds of syngas fuel mixtures at conditions relevant to ground-power gas turbines. To accomplish this goal, two flame speed measurement approaches were developed: a Bunsen flame approach modified to use the reaction zone area in order to reduce the influence of flame curvature on the measured flame speed and a stagnation flame approach employing a rounded bluff body. The modified Bunsen flame approach was validated against stretch-corrected approaches over a range of fuels and test conditions; the agreement is very good (less than 10% difference). Using the two measurement approaches, extensive flame speed information were obtained for lean syngas mixtures at a range of conditions: 1) 5 to 100% H2 in the H2/CO fuel mixture; 2) 300-700 K preheat temperature; 3) 1 to 15 atm pressure, and 4) 0-70% dilution with CO2 or N2. The second objective of this thesis is to use the flame speed data to validate leading kinetic mechanisms for syngas combustion. Comparisons of the experimental flame speeds to those predicted using detailed numerical simulations of strained and unstrained laminar flames indicate that all the current kinetic mechanisms tend to over predict the increase in flame speed with preheat temperature for medium and high H2 content fuel mixtures. A sensitivity analysis that includes reported uncertainties in rate constants reveals that the errors in the rate constants of the reactions involving HO2 seem to be the most likely cause for the observed higher preheat temperature dependence of the flame speeds. To enhance the accuracy of the current models, a more detailed sensitivity analysis based on temperature dependent reaction rate parameters should be considered as the problem seems to be in the intermediate temperature range (~800-1200 K).

This diploma thesis focuses on implementation issues of ADS-B in the airspace of Czech republic and Europe. Our introduction contains a review of necessity of this system and describes ADS-B. The next part addresses the legislation of this system in detail, also sums up the state of its implementation and the plan of implementation. Our conclusion shows the problems connected with the system , offers their solution and views for the future.

The master‘s thesis deals with the influence of the thermal cycle of welding with preheat on castings made of grey cast iron to change the hardness. The thesis deals with the classification of graphitic cast irons, their structure, properties and influences they have on the formation and transformation of the structure. Emphasis is placed on chemical composition and structure stability at elevated temperatures. The practical part deals with the investigation of the effects of casting repair on the decrease of hardness measured in the foundry Heunisch Brno.

碩士<br>國立中興大學<br>精密工程學系所<br>102<br>Due to high-tech products day by day tired progress requirements for product weight, close to compact size to facilitate easy to carry, so thin demand for high-quality steel increased rapidly. Nozzle is a thin plate steel manufacturing segment after the manufacturing process high-temperature fluid liquid steel, slag, and add gas additive, in the crucible or converter add to the tools necessary process, but also to ensure the smooth progress of the foundation smelting. To prolong the life of the Melting Nozzle to reduce production costs, improve economic efficiency principles efforts. China Steel Corporation (CSC) are manufactured in the preheating process the Melting Nozzle, that material properties due to heat and excessive expansion, leading to the Melting Nozzle cannot afford to 1300℃ High temperature and cracked the urgent need for research to explore the factors that reduce its life. Therefore, this study using the finite element analysis method for high temperature preheat the Melting Nozzle and support with thermal insulation materials simulate the stress-strain analysis. Obtained the preheat Melting Nozzle, and the nozzle support whit internal insulation materials to withstand high temperature stress and strain of the situation. To explore the role of reason in the preheat Melting Nozzle, and select the preferred nozzle material, thereby improving the Melting Nozzle life.

<div>The work discussed in this document seeks to integrate conductive additives with energetic material systems to offer an alternative source of ignition for the energetic material. By utilizing the conductive properties of the additives, ohmic heating may serve as a method for preheating and igniting an energetic material. This would allow for controlled ignition of the energetic material without the use of a traditional ignition source, and could also result in easier system fabrication.</div><div>For ohmic heating to be a viable method of preheating or igniting these conductive energetic materials, there cannot be significant impact on the energetic properties of the energetic materials. Various mass solids loadings of graphene nanoplatelets (GNPs) were mixed with a reactive mixture of aluminum (Al)/polyvinylidene fluoride (PVDF) to test if ohmic heating ignition was feasible and to inspect the impact that these loadings had on the energetic properties of the Al/PVDF. Results showed that while ohmic heating was a plausible method for igniting the conductive energetic samples, the addition of GNPs degraded the energetic properties of the Al/PVDF. The severity of this degradation was minimized at lower solids loadings of GNPs, but this consequently resulted in larger voltage input requirements to ignite the conductive energetic material. This was attributable to the decreased conductivities of the samples at lower solids loading of GNPs.</div><div>In hopes of conserving the energetic properties of the Al/PVDF while integrating the conductive additives, additive manufacturing techniques, more specifically fused filament fabrication, was used to print two distinct materials, Al/PVDF and a conductive composite, into singular parts. A CraftBot 3 was used to selectively deposit Conductive Graphene PLA (Black Magic) filament with a reactive filament comprised of a PVDF binder with 20% mass solids loadings of aluminum. Various amounts of voltage were applied to these conductive energetic samples to quantify the time to ignition of the Al/PVDF as the applied voltage increased. A negative correlation was discovered between the applied voltage and time to ignition. This result was imperative for demonstrating that the reaction rate could be influenced with the application of higher applied voltages.</div><div>Fused filament fabrication was also used to demonstrate the scalability of the dual printed conductive energetic materials. A flexural test specimen made of the Al/PVDF was printed with an embedded strain gauge made of the Black Magic filament. This printed strain gauge was tested for dual purposes: as an igniter and as a strain sensor, demonstrating the multi-functional use of integrating conductive additives with energetic materials.</div><div>In all, the experiments in this document lay a foundation for utilizing conductive additives with energetic materials to offer an alternative form of ignition. Going forward, ohmic heating ignition may serve as a replacement to current, outdated methods of ignition for heat sensitive energetic materials.</div>

碩士<br>國立交通大學<br>機械工程學系<br>99<br>This research used a 30kW-generator in Taiwan Sugar swine farm in Taichung to collect data for the long-term electricity generation. This study is an continous effort of Lin’s work [3], which carried out the electricity generation project by using 60% methane concentration of biogas in a small swine farm in Miaoli. This experimental study, using 73% methane concentration of biogas, consisted of three parts. Firstly, investigate the effect of biogas supply rate together with the different excess air ratios on generator performance. Secondly, make a comparison with Lin’s results. Finally, apply a waste heat recovery system to preheat the inlet gas under different temperatures and analyze the preheating influence on the generator performance. In the present study, the maximum power generation is 26.7kW occurred at biogas flow rate of 260L/min, whereas the maximum thermal efficiency and methane consumption ratio are 27% and 96.03% at biogas flow rate of 200L/min. The power generation in the present work is higher than one in Lin’s one [3], except the region around λ (excess air ratio) &amp;lt; 0.85. However, the thermal efficiency increases with the increasing methane concentration just in the region of λ>0.95, while on the relatively rich side (λ&amp;lt;0.95), there is no benefit. The improvement by preheating inlet gas is obvious when excess air ratio is relatively high, such as λ>1.3.

Casting is a substantial part of modern manufacturing and production, typically used in the production of aluminum alloys. The high pressure die casting process is extremely suitable for mass production. Due to the high volume, wasted time and resources during the production cycle become more significant. Aluminum die castings require the die to be at elevated temperatures to produce acceptable castings. When the inner surfaces of a die are cold, the outer shell of the casting will cool too rapidly, and solidification of the outer shell occurs before the aluminum has time to uniformly fill the cavities. Therefore, without the die being within the proper temperature range, the castings produced will have significant issues in porosity and casting incompleteness. Furthermore, stresses are introduced to the casting surfaces when warm-up shots are used to raise the temperature prior to production. In the present work, research is conducted on designing a heating method for a casting die used in the manufacturing of an automotive transmission intermediate plate. An electric, short wave infrared heating system is simple and effective for the purpose. By utilizing an electric infrared heater in combination with a flat mirror reflector, the aluminum high pressure die casting die was heated to 300 ◦C surface temperature within 30 minutes. Further research can be done to optimize heat flux distribution and minimize energy consumption.