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 applied in this paper to magnetic float polishing (MFP) of ceramic (Si3N4) balls. Using this method the flash temperatures, flash times, and temperature distribution at the interface between the balls and the shaft of the MFP apparatus are calculated. Examination of the polished surfaces (scratch lengths) of the balls showed that the length of most scratches during the final stage of polishing is <20 mu m and most are formed under transient conditions. But because of the small area of contact 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 available for each case. The use of the general solution developed in Part I enables this determination. The minimum flash temperatures and minimum flash times that occur during polishing ensure the determination if adequate temperatures are generated for chemo-mechanical polishing to take place. Of course, the lengths of the scratches would be much longer and the corresponding flash duration longer during the semifinishing operation than during finishing. The combined temperature and flash duration Mould determine the extent of chemo-mechanical action under these conditions. The flash temperatures and flash times required for chemo-mechanical action can be used as a basis for the optimization of polishing conditions in MFP.