Influência da temperatura de sinterização nas propriedades mecânicas de molas de alumina injetadas em baixa pressão

Abstract

In this work, ceramic coil springs was prepared by low-pressure injection molding using alumina submicrometer-sized powder. The powder are mixed with organic binders in the Pelstman machine tank for several hours resulting in a mixture with low viscosity. This work include the production of helical ceramic springs, thermal debinding, sintering in different temperatures and measure some properties. Sintering temperature was shown to be a simple way to change the spring constant and resistence to compression of ceramics without having a significant impact in the spring´s physical dimensions. Three sets of springs were sintered at different temperatures, from 1550°C to 1650°C, in order to observe the effects on spring constant and fracture stress. Sintered alumina springs were obtained with densities ranging from 94.0% to 97.5% of the theoretical limit. Springs constants were measured from room temperature up to 1100°C. Fracture stress data was analyzed according to Weibull statistics and the maximum likelihood method. Upon increase of sintering temperature from 1550°C to 1650°C, the spring constant and the Weibull characteristic strength of the alumina springs increases by 15% and 32%, respectively. On the other hand, sintering temperature has a negligible influence on Weibull modulus. This is because internal bubbles and surface defects introduced in the production stage of the ceramic springs - more than the reduction in porosity with increasing sintering temperature - are critical in determining the compression resistance of the ceramic springs.