LARGE BATCH MAGNETIC FLOAT POLISHING

Over the past decade or so, silicon nitride (Si3N4) balls have become an important component for advanced bearings. They are currently finished in industry by V-groove lapping. Their manufacturing costs are high due to longer processing time (6- 16 weeks) and use of expensive diamond abrasive. Furthermore, use of diamond abrasive under heavy loads can result in scratches, pits, and microcracks on the surface of the polished balls. These surface defects can act as nucleation sites for cracks resulting in catastrophic failure by large brittle fracture. Hence, in order to minimize the surface damage, gentle polishing conditions are required, namely, low level of controlled force and abrasives not significantly harder than the workmaterial. This is accomplished by a process known as magnetic float polishing (MFP). The primary objective of this investigation was to finish large diameter and large batch of Si3N4 balls (46 balls of 3/4 in. diameter) for hybrid bearing applications with good sphericity (0.25 µm) and surface finish (Ra, 8 nm) by large batch MFP apparatus. Another aim of this investigation was to reduce the tota