EVALUATION OF WEAR AND IMPACT PROPERTIES OF GRINDING BALLS USED IN SARCHESHMEH COPPER PLANT

Ball mills are used in the last stage ofore processing for grinding raw materials. Forged 70Cr2 alloy steel and Austempered Ductile Iron (ADI) balls are materials from which grinding balls are made for Sarcheshm eh Copper Plant (SCP) ball mills. In the present study wear and impact properties of these two kinds of balls have been investigated. Some balls randomly were selected as samples. They were cut to investigate the cross section under optical and scanning electron microscopes. The microstructure of the sample balls was studied and quantitative measurements ofmicrostructural f eatures were performed. The hardness ofdifferent parts ofcross sections of balls was measured. The wear resistance of the balls was measured by Pin on Disc method. Repeated dropt test was employed to evaluate impact resistance of the balls. The microstructure of ADI balls consisted of bianitic matrix with graphite nodules and some retained austenite and martensite. Micro cracks and porosities in the cast structure were frequently observed. In the case offorged steel balls the microstructure composed oftempered martensite in outer area and bianitic structure with some tempered martensite in central areas. The wear and impact resistance of forged steel balls were markedly higher than those of ADI balls. The difference was consistent with the differences between the microstructures ofthe two kinds of balls. Cast structure with microcracks and shrinkage porosities in ADI balls gives rise to lower impact resistanc e.