A study of vitreous-bonded abrasive materials
This thesis has focused primarily on the effect of bond and workpiece composition on the performance of vitreous-bonded alumina grinding wheels. The effect of bond composition considered in this work can equally be applied to grinding wheels which use silicon carbide (carborundum) as the abrasive medium. The bonds considered in this study are described as sintering bonds (high clay content), used in silicon carbide grinding wheels, - and fusible bonds (high glass content), used in vitreous bonding systems suitable for use in aluminium oxide grinding wheels. The initial part of the research work deals with a review of the mechanisms of grinding and the evaluation of wheel performance. The effect of grinding conditions, abrasive compositions, and workpiece material composition on the mechanisms of grinding wheel wear in conventional wheels was studied. The analysis of grinding wheel wear was examined and compared with experimental data. Reactions in grinding wheel bond materials were examined by comparing theoretical equilibrium compositions with actual reaction products using experimental techniques such as x-ray powder methods and differential thermal analysis. Experimental studies were carried out to investigate the vitrification behaviour of sintering and fusible bonds. This was achieved by examining the relationship between theoretical equilibrium liquid and silica contents and experimental vitrification conditions. A semi-empirical model was developed for determining optimum firing conditions for sintering and fusible bonds. The effect of bond composition on the strength of sintering and fusible bonds, under fixed firing conditions, was investigated. This resulted in some bonds failing by cracks around quartz particles, whilst bonds with high glass contents failed by a combination of pore-flaws. A model was also developed which predicted the amount of quartz remaining after heat treatment. The model was shown to be accurate when compared with experimental data. Based on the results of the experimental work on bond characterisation, the effect of bond and workpiece composition was compared with grinding wheel performance data. This was achieved by grinding a variety of hardened tool steels with abrasive segments manufactured with optimised grades. An empirical model was developed which showed that wheel wear was a function of bond strength and the nature of complex carbides present in the microstructure of the tool steels.