DEMEC - Departamento do Curso de Engenharia Mecânica
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/10750
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9 resultados
Resultados da Pesquisa
Item Analysis of the coefficient of friction at the workpiece-tool interface in milling of high strength compacted graphite cast irons.(2019) Silva, Leonardo Rosa Ribeiro da; Ruzzi, Rodrigo; Teles, Vinicius C.; Sales, Wisley Falco; Guesser, Wilson L.; Machado, Alisson R.The coefficient of friction at the workpiece-tool interface is one of the main influencing parameters in machining. It can be tribologically investigated using conventional and open tribometers, however, there is no consensus as to which type of test has the best correlation with the real machining process. This work aims at investigating the use of three different methods to measure the coefficient of friction in the machining of three types of high strength compacted graphite cast irons, with variations in the size of the free graphite phase and the presence or absence of molybdenum carbides in the matrix. The coefficient of friction of the process was measured using two progressive load conventional tribological tests, the progressive load single sliding test with load ranging from 0.5 to 40 N and the progressive load reciprocate sliding test in both dry and starved lubrication regimen, with load ranging from 48 to 83 N. The coefficient of friction was also measured in a conventional machining center used as an open tribometer, where ramp milling tests were performed in workpieces fixed on a piezoelectric dynamometer, with a cutting depth varying from 100 μm to 0, to simulate a regressive load. The following machining parameters were varied: cutting speed, feed rate, tool geometry, tool coating and the use of minimum quantity of lubrication in contrast to dry machining. As the main results, the predominance of lubrication, even in small quantities, was observed as the most influential parameter in the coefficient of friction. An inverse relationship was also observed between the hardness of the materials and the coefficient of friction independent of the lubrication condition used. The results of the coefficient of friction obtained in progressive load re- ciprocate sliding and open tribometer tests showed the best correlation with those found in the literature for this kind of materials.Item Influence of metallurgical texture on the abrasive wear of hot-rolled wear resistant carbon steels.(2019) Damião, Carlos Alberto; Alcarria, Gabriela; Teles, Vinicius C.; Mello, Jose Daniel Biasoli de; Silva Junior, Washington Martins daHot-rolled wear resistant carbon steel sheets are commonly applied in mining equipment as abrasive wear- resistant material for front loaders, chutes, etc. The rolling process can induce metallurgical texture in the form of alternating bands of ferrite and pearlite known as "banding" which affect the mechanical properties of the material. The goal of this work was to verify the impact of metallurgical texture on the abrasion resistance of hot- rolled wear resistant carbon steels. SEM images of the field specimens showed that the prevailing wear me- chanism was parallel scratches. This wear mechanism was replicated in the laboratory using a dry sand-rubber wheel wear tester. The particle size used in the abrasive wear test (0.15–0.30 mm) was defined by the topo- graphical analysis of the field sample. In addition, linear scratch tests were conducted to determine the specific scratch energy. The block specimens used in the abrasion wear tests were cut from hot rolled plates with and without metallurgical texture taking into account the rolling direction. Metallographic analysis of these samples showed an anisotropic microstructure related to the lateral and transversal surfaces of the plates. The wear rate of the lateral surface was up to 40% lower than that of the upper surface. This result was attributed to the presence of metallurgical texture that increased hardness. In addition, the wear rate presented a linear re- lationship to the scratch specific energy. In this case, samples without metallurgical texture were more difficult to scratch. The analysis of the specific energy and wear rate parameters clearly showed the anisotropy of the samples presenting metallurgical texture, which corresponded to the highest abrasive wear rate.Item Study of the project parameters influence in the performance of solar collectors.(2019) Mapa, Lidianne de Paula Pinto; Mendes, Bárbara de Morais; Bortolaia, Luis Antônio; Leal, Elisângela MartinsThis paper aims to observe the influence of design parameters on the performance of plane solar collectors. From the energy balance of the plane solar collector, the mathematical model was implemented varying the following design parameters: (i) Thickness of the absorber plate; (ii) Distance between the absorber and the cover; (iii) Edge insulation thickness; (iv) Absorber emittance; (v) Conductivity of the absorber; (vi) Convective heat transfer coefficient inside the tubes; (vii) Distance between tubes; (viii) Wind velocity; (ix) Solar radiation incident; and (x) Back insulation thickness. These parameters were altered observing the influence on the optical efficiency; the coefficient of energy loss; the instantaneous efficiency; and the useful energy gain. From the results, it is possible to see that the parameters that most influence the performance of the solar collector are the distance between the absorber and the cover, the absorber emittance, the thermal conductivity of the absorber, the distance between tubes, wind speed and solar radiation incident.Item Technical analysis of a hybrid solid oxide fuel cell/gas turbine cycle.(2019) Leal, Elisângela Martins; Bortolaia, Luis Antônio; Leal Júnior, Amauri MenezesThe relatively high operating temperature of the solid oxide fuel cell allows for a highly efficient conversion to power, internal reforming, and high-quality by-product heat for cogeneration or a bottoming cycle. Besides, high-temperature fuel cells offer a good opportunity for coupling to a gas turbine. Fuel cell systems have demonstrated minimal air pollutant emissions and low greenhouse gas emissions. This paper focuses on the investigation and technical analysis of a direct internal reforming solid oxide fuel cell (DIR-SOFC) and a gas turbine (GT) system. The technical analysis comprises of an energy and exergy analysis of the hybrid cycle, using the Gibbs function minimization technique for the methane steam reforming process. The assessment is performed to determine the influence of the hybrid cycle operating temperature and pressure, steam-to-carbon ratio and fuel and oxidant usage in the fuel cell. Equilibrium calculations are made to find the ranges of inlet steam-to-carbon ratio and the operating current density of the fuel cell. After that, a hybrid system consists of a DIR-SOFC and a GT is evaluated using computer simulation. The results showed that the fuel cell is the main power producer system at the design point. The high-energy efficiency (around 62%) and exergy efficiency (around 58%) are achieved by the hybrid cycle compared to fuel cell efficiency (about 40%) and the GT (around 38%). The power ratio (SOFC/GT) found was 1.50. An analysis varying the fuel cell current density and the GT pressure ratio was performed showing that the fuel cell power production decreases about 7% with increasing current density when the GT becomes the main power-producing equipment. However, the system energy efficiency decreases with the reduction of power produced by the fuel cell.Item Análise da temperatura filete a filete no rosqueamento interno por machos de corte.(2018) Souza, R. F. A.; Vianello, Pedro Ivo Alves; Silva, Marcio Bacci da; Pereira, Igor CézarAmong the manufacturing processes, threading stands out, as it can be accomplished by machining or by forming. This process is responsible for the creation of internal and external threads, which has great applicability in production lines. Due to the market’s great competitiveness, methods are sought to increase production by decreasing the time of each unit process. However, tapping is usually performed at low cutting speeds due to limitations related to the manufacturing process. The study of the tapping can bring benefits, such as the reduction of wear mechanisms, resulting in an increase in tool life. In this research, the temperature was measured from fillet to fillet in the conical part of the tool, varying the cutting speed and the number of fillets. The tap used is, M 10 x 1.5 HSS, uncoated in threading process for internal thread production in SAE 1045. To analyze the temperature was used the tool-workpiece thermocouple method on each fillet of the tap. The cutting speeds used were 10 and 25m / min. From the second fillet on the temperature is constant, even with the increase in the number of fillets, as expected.Item Finding hidden oscillations in the operation of nonlinear electronic circuits.(2016) Rocha, R.; Torricos, Rene Orlando MedranoSeveral dynamic behaviours can simultaneously coexist in the operation of a nonlinear electronic circuit. However, some of these dynamics are difficult to be observed due to their sensibility to initial conditions. The use of describing functions to determine the coexistence of multiple dynamics in the operation of an electronic circuit with nonlinear feedback is proposed.Item Análise e comparação do torque filete a filete no rosqueamento interno por machos de corte.(2018) Vianello, Pedro Ivo Alves; Souza, R. F. A.; Silva, Marina Carla Bezerra da; Pereira, Igor CezarThe thread process is responsible for internal and external threads creation which are of large application in several areas. Even though its large usage in industry, there are few papers about this process. In this paper, it was carried out torque fillet by fillet measurements over the chamfer portion of the tap and the torque comparation between tools from two distinct manufacturers. It was used M 10 x1,5 HSSE straight flute taps, with and without coating in tapping process on a grey cast iron GG30, in order to analyse the relation between the number of fillets in the tap’s chamfer and its geometry in torque signal behaviour.Item Acoustical performance of Helmholtz resonators used as vehicular silencers.(2018) Martins, Lucas Rodrigues; Guimarães, Gustavo Paulinelli; Fragassa, CristianoThis study proposes to evaluate the acoustical performance of a reactive vehicular silencer made entirely of Helmholtz resonator. Four or seven resonators are idealized to be in a series configuration, all the dimensions except cavity length and resonators are fixed. An algorithm processes inputted characteristic engine noise signal obtained from literature, identify peaks, and calculates ideal cavity length for attenuation. The transmission loss of the system is analytically calculated. Attenuation levels obtained are satisfactory. The required volume of the resonator to achieve the same resonance frequency as low frequency noise peak demands impractical cavity length, proving it to be flawed. It is suggested to use resonators of two or three different diameter for different frequency range in order to overcome this problem.Item Analysis of the energy efficiency of diesel oil consumption in the Brazilian Iron Ore Mining Company.(2018) Fernandes, Eunírio Zanetti; Leal, Elisângela Martins; Figueiredo, Robson Lage; Reis, Gemírson de Paula dosThis paper aims to evaluate the diesel oil consumption between 2008 and 2015 in the production of iron ore in Brazil, creating correlations between energy intensity (production), economy and checking the impact of fuel prices on the commodity. During the analyzed period, the years 2008-2009 indicated economic crises, which interfered in the price and the commercialization of iron ore products. The physical intensity was 0.2% higher than the economic intensity. In the period from 2010 to 2014, economic activity remained more stable, with a decreasing trend, mainly due to the increase of iron ore prices. The physical intensity is much higher than the economic intensity influenced by the expansion of the Chinese economy. The year of 2014 indicated the end of the high iron ore price cycle and the beginning of supply and demand stabilization with consequent reduction in prices. In 2015, the market entered the stabilization phase, with a continuous reduction in unit production costs and transportation logistics. There was an abrupt change due to the strong increase of the economic intensity due to the fall of the international prices of iron ore. The diesel oil consumption plays a vital role in the scenario of cost reduction in iron ore production and a deeper analysis must be done in order to discover some options to change the energy matrix.