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The volume theory of ball wear ascribes ball consumption in grinding mills only to impactive wear, whereas the surface theory ascribes it only to abrasive wear, and ball-wear data are often in good agreement with either or both of these theories. In this report, it is emphasized that balls in large industrial ball mills are subject to mechanisms of both impactive and abrasive wear, and a 'generalized' theory of ball wear that superposes the two wear mechanisms is formulated. Detailed comparisons are made between the wear as measured for six different grades of chromium-white iron balls and the wear predicted by use of a formula derived from the generalized theory. Considered from the point of view of this theory, the data relating to ball wear yield new information, namely the relative proportions of abrasive and impactive wear. This new information represents the response of balls of a given type to both these wear mechanisms. The calculations show that, as the size of a ball decreases, the component of abrasive wear increases considerably. This is in agreement with the general finding that smaller balls in a mill give a finer grind. The chemical composition and metallographic structure of the balls are analyzed in an attempt to relate these factors to their wear characteristics during milling. The chromium-to-carbon ratio of the balls is shown to play a predominant role.