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Abstract(s)
As perdas energéticas derivadas de problemas tribológicos têm vindo a ganhar cada vez mais importância, desde que a sociedade percebeu o impacto económico que estas podem ter. O aumento da eficiência dos mecanismos é cada vez mais preponderante para a diminuição das perdas energéticas. É neste contexto, de aumentar a eficiência mecânica, que a lubrificação ganha grande importância, no sentido de otimizar os mecanismos. O tipo de lubrificação abordado neste projeto é lubrificação por massa. Durante a revisão bibliográfica, fica claro a falta de estudos relativos à lubrificação por massa e a falta de entendimento dos mecanismos responsáveis pela variação da sua performance. Assim sendo, um dos propósitos deste trabalho é verificar o impacto que os diferentes componentes das massas lubrificantes (óleo base, espessante e aditivos) têm na sua performance. Visando atingir este objetivo, foi conduzida uma matriz de ensaios experimentais, com variação dos parâmetros do sistema (lubrificante, temperatura, velocidade, carga e escorregamento) para testar um conjunto de massas lubrificantes. Foram avaliadas um conjunto de nove massas lubrificantes, com o mesmo conjunto de aditivos, mas com diferentes espessantes (Lítio e Cálcio) e diferentes viscosidades de óleo base (50, 200 e 500 cSt), de forma a ser possível isolar a influencia de cada componente em cada ensaio. Foi avaliado o efeito do espessante e da viscosidade na espessura de filme lubrificante e no coeficiente de atrito. Os resultados mostram que com o aumento da temperatura a espessura de filme diminui, independentemente do espessante. As massas lubrificantes com espessante de Lítio, na região de baixa velocidade, apresentam uma maior espessura de filme e um menor coeficiente de atrito. Enquanto que nas regiões de alta velocidade, as massas com espessante de Cálcio apresentaram uma maior espessura de filme e menor coeficiente de atrito. Para além disso, as massas lubrificantes com espessante de lítio e cálcio juntos, apresentam um comportamento mais aproximado ao que foi registado pelas massas com espessante de cálcio, nos diferentes ensaios. Numa situação de “starvation”, verificou-se que não foi possível prever o comportamento da espessura de filme de forma teórica para as massas com maior viscosidade (200 e 500 cSt), usando as características do óleo base para o cálculo.
The energy losses that come from tribology problems have been gaining importance, since the world understood the economic impact that they have. Increasing the efficiency of the different mechanisms is crucial to reduce the energy losses. In this context, of increasing the mechanic efficiency, lubrification is the key to achieve this goal. The main focus of this project is mainly grease lubrification. During the bibliography review, it is clear the lack of studies related to grease lubrification, as well as the lack of understanding related to what impacts grease performance. Therefore, one of the purposes of this work, is to verify the impact of the different components of the greases (base oil, thickener and additives) have on the performance, under different conditions of temperature and speed. Nine greases with the same additive package but different thickener types (Lithium and Calcium) and base oil viscosity (50, 200 and 500 cSt) were used, so that the effects of thickener type and base oil viscosity could be isolated. Film Thickness and Coefficient of Friction were measured for all the greases at different temperatures, speed and Slide to Roll Ratio. The results show that with the increase of the temperature, the film thickness along the contact reduces, regardless of the thickener. Besides that, the lithium thickener greases, in the low speed region, present a greater film thickness and, consequently, a lower coefficient of friction. While, in the high speed regions, the calcium thickener greases show greater film thickness and lower coefficient of friction. In addition, the greases with lithium and calcium thickeners together, exhibit a behavior close to that recorded by the calcium thickener grease, especially in the region controlled by the thickener. Besides that, it was found that it was not possible to theoretically predict the behavior of the film thickness for the greases with higher base oil viscosity, in a starvation situation, using the properties of the base oil.
The energy losses that come from tribology problems have been gaining importance, since the world understood the economic impact that they have. Increasing the efficiency of the different mechanisms is crucial to reduce the energy losses. In this context, of increasing the mechanic efficiency, lubrification is the key to achieve this goal. The main focus of this project is mainly grease lubrification. During the bibliography review, it is clear the lack of studies related to grease lubrification, as well as the lack of understanding related to what impacts grease performance. Therefore, one of the purposes of this work, is to verify the impact of the different components of the greases (base oil, thickener and additives) have on the performance, under different conditions of temperature and speed. Nine greases with the same additive package but different thickener types (Lithium and Calcium) and base oil viscosity (50, 200 and 500 cSt) were used, so that the effects of thickener type and base oil viscosity could be isolated. Film Thickness and Coefficient of Friction were measured for all the greases at different temperatures, speed and Slide to Roll Ratio. The results show that with the increase of the temperature, the film thickness along the contact reduces, regardless of the thickener. Besides that, the lithium thickener greases, in the low speed region, present a greater film thickness and, consequently, a lower coefficient of friction. While, in the high speed regions, the calcium thickener greases show greater film thickness and lower coefficient of friction. In addition, the greases with lithium and calcium thickeners together, exhibit a behavior close to that recorded by the calcium thickener grease, especially in the region controlled by the thickener. Besides that, it was found that it was not possible to theoretically predict the behavior of the film thickness for the greases with higher base oil viscosity, in a starvation situation, using the properties of the base oil.
Description
Keywords
Massas Lubrificantes Espessura de filme Coeficiente de atrito Lubrificação Greases Film Thickness Coefficient of Friction Lubrification