Industrial Case Study A model for optimal armature maintenance in electric haul truck wheel motors: a case study Benjamin Lhorente a , Diederik Lugtigheid b, * , Peter F. Knights c , Alejandro Santana d a Komatsu Chile, Av. Americo Vespucio 0631, Quilicura, Santiago, Chile b Condition-Based Maintenance Laboratory, Department of Mechanical and Industrial Engineering, University of Toronto, 5 King’s College Road, Toronto, Ont., Canada M5S3G8 c Canadian Chair of Mining and Associate Professor, Pontificia Universidad Catolica de Chile, Centro de Mineria, Av. Vicuna MacKenna 4860, Santiago, Chile d Reliability and Development of Komatsu Chile, Av. Americo Vespucio 0631, Quilicura, Santiago, Chile Received 25 September 2003; accepted 24 October 2003 Abstract The objective of the work presented in this paper is the determination of an optimal age-based maintenance strategy for wheel motor armatures of a fleet of Komatsu haul trucks in a mining application in Chile. For such purpose, four years of maintenance data of these components were analyzed to estimate their failure distribution and a model was created to simulate the maintenance process and its restrictions. The model incorporates the impact of successive corrective (on-failure) and preventive maintenance on necessary new component investments. The analysis of the failure data showed a significant difference in failure distribution of new armatures versus armatures that had already undergone one or several preventive maintenance actions. Finally, the model was applied to calculate estimated costs per unit time for different preventive maintenance intervals. From the resulting relationship an optimal preventive maintenance interval was determined and the operational and economical consequences and effects with respect to the actual strategy were quantified. The application of the model resulted in the optimal preventive maintenance interval of 14,500 operational hours. Considering the failure distribution of the armatures, this optimal strategy is very close to a run-to-failure scenario. q 2004 Elsevier Ltd. All rights reserved. Keywords: Weibull analysis; Armatures; Electric motors; Repairable system; Maintenance optimization 1. Background In 1996, Komatsu Chile (KC) put into operation a fleet of haul trucks in a mining application in Chile. KC delivered these machines under a repair and maintenance contract, taking full responsibility of all repair and maintenance work at guaranteed availability and maintenance costs. The haul truck is an electric drive DC truck. This means that propulsion is delivered to the rear wheels by means of two parallel electric DC wheel motors. The wheel motors receive rectified electric power from the main alternator working in conjunction with a diesel engine. The wheel motors are mounted on the truck’s axle box and provide the function of axle, transmission and wheel motor at the same time. The wheel motor’s main components are the wheel hub, ring gear structure, planetary gears, sun gear and armature, see Fig. 1. The armature is the rotor of the electric motor and can be removed from it independently. It primarily consists of bearings, commutator, brushes, spools and poles. The armature commutator consists of copper bars and mica plates. The mica plates physically separate and isolate the copper bars and provide a radial pressure to ensure the commutator’s stability. The mica bars have less altitude than the copper bars and are located below the commutator’s superficial area to prevent interaction with the sliding brushes on the area. The copper bars have a wedge shape form and together form a cylinder. Each bar has a riser for connection to the armature’s spools. 0951-8320/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.ress.2003.10.016 Reliability Engineering and System Safety 84 (2004) 209–218 www.elsevier.com/locate/ress * Corresponding author. Tel.: þ 1-416-946-5528; fax: þ1-416-946-5462. E-mail addresses: lugtigh@mie.utoronto.ca (D. Lugtigheid), blhorente@komatsu.cl (B. Lhorente), knights@ing.puc.cl (P.F. Knights), asantana@komatsu.cl (A. Santana).