INVESTIGATION OF THE BREAKAGE PROPERTIES OF COMPONENTS IN MIXTURES GROUND IN A BATCH BALL-AND-RACE MILL

The breakage characteristics of mixtures of materials were investigate d in a laboratory ball-race mill. A study of the grinding kinetics of the components in a binary mixture showed that the breakage rate of on e material was affected by the presence of the other material. The bre akage rate of the relatively; weaker material increased and, conversel y, the breakage rate of the stronger material decreased. The degree of the change in the breakage rate was dependent on the blending ratio a nd the relative difference in the ''strength'' of the component. Becau se there was a consistent pattern, an empirical relationship for this variation was developed. The breakage distribution values of the stron ger material were found to be independent of whether the material was ground alone or as a component in a binary mixture. However, the break age distribution values of the weaker material appeared to change, pro ducing more fines when ground in a binary mixture. Thus, the proportio n of the stronger material in the coarser size fractions of the produc t is greater after mixing the two feed materials and grinding them tha n after grinding the two materials separately and mixing the products. A similar variation in the breakage rates was observed for a three-co mponent system. The breakage rate decrease of the strongest material a nd the breakage rate increase,of the weakest material were very close to those observed for a binary mixture. However, the breakage rate of the intermediate hardness material stayed essentially the same, even t hough a slight decrease was expected.