MAGNETIC-FIELD ASSISTED FINISHING OF CERAMICS - PART II - ON THE THERMAL ASPECTS OF MAGNETIC FLOAT POLISHING (MFP) OF CERAMIC BALLS

The thermal model developed in Part I of this three-part series is app lied in this paper to magnetic float polishing (MFP) of ceramic (Si3N4 ) balls. Using this method the flash temperatures, flash times, and te mperature distribution at the interface between the balls and the shaf t of the MFP apparatus are calculated. Examination of the polished sur faces (scratch lengths) of the balls showed that the length of most sc ratches during the final stage of polishing is <20 mu m and most are f ormed under transient conditions. But because of the small area of con tact and low load encountered in MFP, the results of the calculations under these conditions were found to be very close to the quasi-steady -state conditions. However, it is not possible to know a priori if the conditions are transient or quasi-steady state unless solutions are a vailable for each case. The use of the general solution developed in P art I enables this determination. The minimum flash temperatures and m inimum flash times that occur during polishing ensure the determinatio n if adequate temperatures are generated for chemo-mechanical polishin g to take place. Of course, the lengths of the scratches would be much longer and the corresponding flash duration longer during the semifin ishing operation than during finishing. The combined temperature and f lash duration Mould determine the extent of chemo-mechanical action un der these conditions. The flash temperatures and flash times required for chemo-mechanical action can be used as a basis for the optimizatio n of polishing conditions in MFP.