Development of high-performance Nd-Fe-B magnetic-filter for separation of metallic impurities

Most mechanical processes such as grinding and milling are accompanied by unexceptional contamination impurities which have a significant influence on subsequent processes and product properties. In particular, metal impurities in ceramics are fatal. Therefore, many attempts have been made to reduce contamination by choosing ceramic milling tools and using magnetic filters. High-strength rare-earth magnets (Sm-Co, Nd-Fe-B) are used for magnetic-metal impurity separation This contamination is mostly caused by Fe, Ni, or Co as well as moving parts of milling facility and transfer systems, drives etc. A permanent-magnet based filter system is favoured because of easy adaptation, handling and maintenance. In this study, a new magnetic filter is described which has been developed by advanced magnet-flux design. A multi-component magnetic core is constructed by means of several magnet-rings that initiate magnetic fields with high magnetic flow densities in the intermediate Fe-rings. An important aspect is the performing and concentrating area with highest field gradient inside 2 ring-gaps where the product passes without hindrance at high throughput. For testing, several products were contaminated with pre-determined Fe-powder particles, then filtered and investigated by means of chemical analysis, laser diffraction, scanning electron and optical microscopy This system has been rapidly introduced in the ceramics industry in Europe Applications and improvements at Ivoclar Vivadent AG, one of the largest dental-ceramic producers world-wide, are reported here.