Conformação de molas cerâmicas por moldagem por injeção em baixa pressão

Abstract

In this work the low-pressure injection molding (LPIM) of submicrometer-sized ceramic powders was studied aiming to produce ceramic springs. The work comprised the production of molds and laboratory equipment for injection molding, the debinding of the organic vehicle used in the molding, the sintering of ceramic parts, and some preliminary experiments to evaluate the mechanical properties of the ceramics springs. The LPIM presents many advantages for complex ceramic parts production, in comparison with traditional high-pressure injection molding. However, LPIM has some difficulties associated to the debinding step, that are even greater for ceramic parts made with submicrometer-sized powders. But, on the other hand, the use of submicrometer-sized powders allows the production of sintered bodies with high density and better mechanical properties. The submicrometer-sized ceramic powders used in this work were alumina (Al2O3) and zirconia (ZrO2), and the main binder was the paraffin. Tubular molds and a multipart machined mold were developed for injection molding of alumina springs, and a little injection machine was build for injection molding of zirconia parts. The tubular molds had a limited performance. On the other hand, the multipart brass mold, coated with PTFE (polytetrafluorethylene), improved the ceramics spring molding process, making it possible to produce ceramic springs in greater quantities with good reproducibility. In the sintering process of the ceramic springs, major distortions of the parts were avoided using ceramic beams to support the springs. The alumina and zirconia ceramic springs had their measured density and hardness in good agreement with literature. Finally, some preliminary compression tests were performed with alumina and zirconia ceramic springs in order to evaluate their spring constant and maximum load before failure.