On the comparison between measured and calculated stresses in large SAG mills

A study of the structural design of large SAG mills is presented. Stress ranges from strain gauge measurements are compared with those calculated using finite element models for two mills. The agreement between measurement and calculation for one mill is substantially better than it is for the other. The cause of the discrepancy in agreement between measurement and calculation for the two mills is determined to be the relative percentage of ball charge to total charge. For lower total charge to ball charge ratios, the pressure on the heads or end walls of the mills reduces dramatically. As this ratio increases, the pressure on the heads increases to approach a hydrostatic load. The problem of poor agreement between mill finite element models and fatigue design codes is thus partially resolved.

► We compare strain gauge measurements and calculated stresses for two SAG mills.
► Measured stresses are lower than calculated stresses for one mill but not the other.
► Exhaustive investigation eliminated experimental error for the discrepancy between the two mills.
► The cause of the discrepancy is attributed to a reduction of charge load on the mill heads.
► The reduction appears to be related to the ratio of ball charge to total charge.