Improvement of the maintenance technology for construction machinery with the use of digital diagnostics methods

Abstract

Scheduled maintenance of earthmoving machinery sets the intervals between operations through the mean time to failure of a unit, while the scatter of the actual operating time is wide enough for one and the same interval to be belated for a part of the fleet and premature for most machines. Digital monitoring channels – vibration measurement, tribological analysis of the working fluid, thermography and telematic recording of duty modes – remove this discrepancy only in part, since the standardised boundaries of vibration condition are set for stationary equipment running in a steady mode, while a hydraulically driven construction machine passes the whole load range within a single working cycle of 20-40 s. The aim was a quantitative assessment of which decision produces the growth of fleet availability: an extension of the set of measuring channels or the normalisation of the diagnostic feature with respect to the duty mode. On the author's model of a fleet of 42 crawler excavators of 21-24 t operating mass the time to failure of the units was computed from the two-parameter Weibull distribution with subsequent Monte Carlo simulation (20 000 runs) for 2021 to the first half of 2026. Reduction of the root-mean-square vibration velocity to the rated mode lowers the coefficient of variation of the feature from 26,2 to 1,0%, and shifting the alarm threshold to the B/C zone boundary with confirmation by a second physical channel yields the minimum unit cost of 436 RUB per operating hour at a detection rate of 86,1%. A gain of 4,5 percentage points in the availability factor comes with a reduction of unit costs of only 2,9%, which shows that digital diagnostics rearranges the structure of repair actions in favour of condition-based replacements, the outcome accumulating mainly on the side of machine availability at an almost unchanged maintenance cost.