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Introduction
As is well known, the Total Productive Maintenance (TPM) and the Reliability Centred Maintenance (RCM) concepts (or models, or philosophies) are the fundamental and most developed maintenance models ([3] Liyange and Kumar, 2003). However, in order to optimize maintenance service, based on those concepts in recent years other models are being implemented: Preventive Maintenance Optimisation (PMO), Quick Start Reliability (QSR), Risk Based Maintenance (RBM), Streamlined Reliability Centred Maintenance (SRCM), Operator Driven Reliability (ODR), and Proactive Reliability Maintenance (PRM) (([7] Silva, 2004), [6] Rausand (1998), ([5] Moubray, 1997)). In addition, these new concepts use all maintenance policies - corrective (or reactive), systematic (scheduled), and condition-based - solely or in association with a view to increasing both availability and reliability of the equipments and systems, and in consequence to reduce maintenance service costs ([7] Silva, 2004; [2] Hansen, 2005).
At present, in the modern manufacturing plants the increasing of the productivity, that is the Asset Effectiveness Optimization AEO as well as the Overall Equipment Effectiveness OEE, is directly associated with both maintenance policies and models used. Then, the motivation inherent to this research work was the practical knowledge and computational analysis of costs and useful Key Performance Indicators KPIs for different maintenance policies in order to choose the most advisable, to be applied in a food-products plant with a great amount of critical and complex equipment. On the other hand, the importance of this research case study is related to the both proposed methodology and obtained conclusions, because they are an efficient tool for evaluating the maintenance performance, and in general terms able to be employed in other industrial plants.
Therefore, the industrial maintenance service is the most appropriate way for both Asset Effectiveness Optimisation AEO and Overall Equipment Effectiveness OEE, as well as for Overall Line Effectiveness OLE, which is given by the following relationship ([7] Silva, 2004; [2] Hansen, 2005): Equation 1 [Figure omitted. See Article Image.] where: Equation 2 [Figure omitted. See Article Image.] Another important maintenance performance indicator consists in the Inherent (or Theoretical) Availability, defined from both reliability and maintainability, and is given by the following ratio ([7] Silva, 2004; [4] Lyonnet, 1991): Equation 3 [Figure omitted. See Article Image.] where MTBF is the Mean Time Between Failures and MTTR the...