Development of a recycling strategy for grinding sludge using supersolidus liquid phase sintering

Recycling strategies for waste products from grinding processes have become an essential concern for the industrial sector, as up to 250,000 tons of grinding sludge is generated annually in Germany alone. In this paper, a suitable recycling strategy for the recovery of the metallic component of industrial sludge generated from cold work tool steel grinding is investigated and reported. Possible reuse of the recovered metallic material as a precursor for supersolidus liquid phase sintering (SLPS), a powder metallurgy process, is assessed for the first time. Using a novel technique, including washing, dry screening and magnetic separation, 50 wt% metallic swarf and 50 wt% abrasives can be recovered from dried, industrial grinding sludge. These metallic swarf are a mixture of discontinuous and continuous microchips with a particle size of up to 250 mm. The metallic swarf tend to agglomerate, resulting in larger accumulations and a correspondingly larger overall size with a particle size of over 1000 mm. Using SLPS, the densification of the metallic swarf was considered promising, as density increases with increasing sintering temperature. A maximum density of 76 vol% was achieved, owing to the morphology of the swarf. Occasionally, a few abrasives were observed in the microstructure. Hence, a new sustainable recycling strategy for the recovery of the metallic swarf in industrial grinding sludge has been proposed and the reuse of swarf as precursor for SLPS has demonstrated promising results. Further work is being undertaken to improve the densification of the metallic swarf by SLPS. (C) 2020 Elsevier Ltd. All rights reserved.