Optimal replacement intervals for shovel dipper teeth

Abstract

This article presents an analysis of wear rates and optimal replacement intervals for the teeth of an Optima 62 cubic yard dipper with a PD Ab/Wr wear package in operation at the Morenci Mine. The current replacement strategy is to change the entire set of nine teeth when significant wear is observed or when teeth or adapters are found to be missing. Over an 8 week period, 13 change-outs of teeth sets were recorded. For eight of these change-outs, a laser profile was taken of each tooth upon removal to determine metal loss. A technique known as ‘grouped failure data with multiple suspensions’ was applied to quantify the failure rates of the teeth. Failure rate functions were also determined for subgroups including the outer four teeth located near the dipper wing shrouds and the inner five teeth located nearest to the dipper center line. Weibull cumulative distribution functions were fitted to the dipper teeth failure data. Wear rates for the outer four teeth located next to the dipper wing shrouds were found to lag those experienced by the five center teeth of the dipper by ∼83,000 tons. A group replacement strategy whereby entire tooth sets are changed out was found to give better cost per ton performance when compared with a staged policy whereby the outer four teeth are changed out at double the replacement interval of the inner five teeth. Potential exists to reduce unplanned maintenance downtime by decreasing the average replacement interval for dipper teeth sets from 255,000 tons to 200,000 tons. This is equivalent to reducing the replacement interval from one tooth set every 4 days of continuous operation to one tooth set every 3 days of continuous operation. The benefits of adopting such a strategy are estimated at a saving of US$ 300,000 per shovel per year.