Investigation of

Abstract

Magnetic float polishing (MFP) is well-known as the most efficient batch polishing process for finishing a batch (10 to 100 balls) of industrial standard silicon nitride (Si3N4) bearing balls (Grade 10C) for hybrid bearing applications within 24 hours and low capital investment. This investigation was conducted to improve the MFP process through finding the "hidden" polishing parameters that also play an important role in MFP process. In order to reveal and identify the roles or effects of the "hidden" polishing parameters, original polishing apparatus is not adequate, a "Critical Polishing Condition" polishing apparatus was developed and different experimental approaches were investigated: (1) Proper groove formed on the bevel of the polishing cup and maintaining it through the end of roughing stage and in semi-finishing stage results in significant improvement in the roundness and better control of MFP process, (2) Machining the groove (in final finishing stage) is necessary for obtaining superior surface finish, (3) Proper gap/spacing between the balls during polishing is essential for obtaining uniform roundness of a single ball and improving the average roundness of the balls further, (4) Study of prevention of magnetic fluid from evaporation or displacement during polishing was conducted and no sign of "dry-out" was found after an 8-hour of run. This investigation provides a better appreciation of the MFP process for finishing Si3N4 balls. Also, by preventing loss of magnetic fluid, overall cost can be reduced and competed with the process can compete with the conventional industrial lapping process.