Development of Silicon Nitride Bearing Components by Powder Injection Molding Using a Novel Binder System

The capability of silicon nitride to withstand high contact stress, in combination with low friction towards steel, makes the material suitable in applications such as hybrid ball bearing systems. A broad utilization of this concept has as yet not materialized, mainly due to the high manufacturing cost as well as to reproducible quality issues. Powder injection moulding (PIM) appears to have a considerable potential to overcome several barriers to wide commercialization of this type of system. In a recently presented work, we have demonstrated the capabilities of Medium Pressure PIM-based processing using a novel binder concept. Further work to be presented here has included design of a ball tool and initial evaluation of the key processing parameters to make balls of up to ca 13 mm (0.5 inch) diameter of green size. Initial results indicate a high degree of ball-to-ball reproducibility, even when varying the processing parameters within a wide range. No deformation or other defects during thermal evaporative debinding are observed when controlling carefully the debinding schedule. Eseentially fully dense material can be made by GPS (Gas Pressure Sintering) at 1800 °C with low cost silicon nitride starting powders. This technology thus appears to be of great potential for mass-production of ball bearings and other silicon nitride components.