Microwave-assisted grinding
The use of rapid microwave heating to stress-fracture ore samples is discussed. Iron ores containing hematite, magnetite, and goethite were subjected to microwave energy in batch operations at 3 kW and heated to average maximum temperatures between 840 degrees C and 940 degrees C. Scanning electron microscope (SEM) photomicrographs verified fracturing along grain boundaries and throughout the gangue matrix. Standard Bond grindability tests showed that microwave heating reduced the work index of iron ores by 10 to 24%. Using a continuous-feed belt in a microwave applicator, samples heated more uniformly and quickly than in batch operations. In a microwave chamber designed to simulate a continuous-throughput operation at 3 kW, the grindability of a taconite ore was improved by 13% at a bulk temperature of 197 degrees C. Because stress cracking occurred at a lower temperature, less energy was consumed, thereby improving cost effectiveness. To further improve the economics, preliminary tests were conducted to increase heating rates by using higher microwave powers. The beneficial effects in the grinding circuit and in the extractive operation are discussed.<<ETX>>
Novel comminution process uses electric and ultrasonic energy
Etude experimentale du broyage de differents minerais par decharge electrique et par action d'ultrasons. Mesure du rendement energetique du broyage par decharge electrique et comparaison de celui-ci avec diverses methodes de broyage conventionnelle. Proposition d'un systeme de broyage par decharge electrique suivi d'un broyage par ultrasons
Neutron Residual Stress Measurements on Rail Sections for Different Production Conditions
Rail sectioning with subsequent neutron diffraction experiments has been used to assess residual stresses in the rails. In this study we present the results of neutron stress measurements performed at the NIST Center for Neutron Research (NCNR) on rail sections from rails that were produced under various conditions. Specifically, these are air-cooled, air-cooled and roller-straightened, head-hardened and head-hardened and roller-straightened. More significantly, a head-hardened and roller-straightened rail was also studied after service to elucidate evolution of the service-induced residual stresses. In the latter case both a transverse-cut slice and the central region of a 0.53 m long piece were studied. Measurements on this piece are the first in which triaxial stresses have been determined for an intact rail. Neutron strain measurements with 3×3×3 mm3 spatial resolution were successfully employed for transversally cut slices to verify the difference in the stress state depending on the production process. Although examination of slices allows determination of only two-dimensional stresses in the plane of the slice, additional measurements on obliquely-cut slices, which were also carried out, and utilization of FEM gives the possibility of reconstructing the full triaxial stress distribution. Together, these approaches provide a better understanding of rail fabrication and the possibility of improving the durability and safety of rails in the future.Copyright © 2004 by ASME