RCAAP Repository

Usinas Siderúrgicas de Minas Gerais S/A

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

The objective of this work is the validation of a mathematical method that will be used for the map of the Brazilian areas with potentiality of using systems of evaporative cooling in the conditioning of atmospheres. The cooler rehearsed evaporative presents capacity for conditioning of an atmosphere of up to 50 m2. Climatic maps of the temperatures are put upon and of the relative humidity of the air in Brazil, making possible the characterization of the areas where the temperature conditions and relative humidity of the air are inside of values susceptible to use of evaporative systems. The climatic data of temperature and relative humidity of the air acquired in this over-position were used as entrance in the mathematical model, that it supplied the exit data, that were analyzed and discarded the areas whose values of the temperature and relative humidity of the air are not inside of the parameters of thermal comfort. Like this the climatic map of Brazil is had where the evaporative system has potential of being used, month to month and for each state. Concepts on psychrometry and evaporative cooling are approached in this work. The results of this work collaborates with the researches on the use of systems evaporative in Brazil, and it informs about the market capacity to be explored with that type of conditioning of atmospheres.

Conselho Nacional de Desenvolvimento Científico e Tecnológico

The dynamic behavior of a cracked shaft was studied both in run-up and run-down transient motion. A mathematical model of the shaft was developed , and experimental tests were performed in order to validate the model. A experimental testing rig was conducted, containing an horizontal flexible rotor with a rigid disc in the mid point between the bearings. Experimental and theo retical responses were compared for both cracked and uncracked shafts. All tests were done for several acceleration rates and unbalance conditions. For the theoretical study of dynamic response of the cracked shaft, the stiffness matrix for a cracked element was deduced, using the modified crack Model of Mayes. The rotor model was obtained by using the finite elements method. The equations of motion were integrated in the time domain by using Newmark method to obtain the transient response. Comparing theoretical and experimental results validated the model. For this purpose, the modified Mayes model was used to represent the dynamic response of the crached shaft. Further simulations were conducted to study the influence of acceleration rates, unbalance amplitude /orientation and crack severity on the response of a cracked shaft, running on transient mo tion.

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Every single design of manufacturing by conventional machining targets a finish part with ideal dimensions within acceptable tolerances. The smaller the tolerances the higher the machining time and the costs involved. In order to reduce costs it is interesting to obtain higher accuracy and better surface finishing with only one machining process. The heat generated during machining is dissipated through the parts involved (chip, tool, workpiece and atmosphere) and the distribution depends on the cutting conditions, mainly on the cutting speed. The relationship between the heat generated and dissipated is known as energetic balance. If the heat dissipated through the workpiece is reduced, the thermal expansion will also be diminished and therefore the dimensional accuracy will be higher. The main objective of the present work is to evaluate the influence of the cutting parameters (vc, fz, ap), the distance among the slots opened and the cooling-lubrifying system (MQL, Dry and overhead flood cooling) on the dimensional accuracy and on the surface roughness of 7075 - T7 aerospace aluminium alloy workpieces (heat treated Al-Zn-Mg alloy) when end milling small slots with integral cemented carbide tools. The experimental tests carried out following a Design of Experiment (DOE) and the results were based on Variance Analysis Technique (ANOVA) with 95% of confidence. The temperature of the bottom surface of the slots and the workpiece vibration controlled by an infrared sensor and an accelerometer, respectively. Surface response method and minimum square techniques were used for the optimization process. The results showed that among the in-put variables only the cutting fluid applied in the MQL manner improved the dimensional accuracy. The feed rate has had great negative influence on the surface roughness of the slots and high cutting speeds has reduced it. The workpiece temperature was diminished when the feed velocity was increased. The power consumption and vibration of the system increased proportionally with the increase of cutting speed and deep of cut.

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Conselho Nacional de Desenvolvimento Científico e Tecnológico

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Fundação de Amparo a Pesquisa do Estado de Minas Gerais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Universidade Federal do Maranhão