Condition-Based Maintenance: Selection and Improvement of a Cost-Effective Vibration-Based Maintenance Policy for Rolling element Bearings
Sammanfattning: Modern machinery is expensive and therefore must run at high availability and effectiveness which cannot be achieved without an effective maintenance policy. Condition monitoring, (CM), techniques can be utilised to reduce or arrest the rate of deterioration of a component so increasing operating life. The main result reported in this thesis is that the rolling element bearing’s mean effective life could be extended appreciably if an existing vibration-based maintenance policy is used effectively. This result is achieved by a combination of data analysis and logical development. A new maintenance approach was developed to overcome some of the limitations of total productive maintenance, TPM, and reliability-centered maintenance, RCM, and is based upon the Deming managerial feedback cycle (Plan-Do-Check-Act). This method is called Total Quality Maintenance, (TQMain). It is a methodology to sustain and improve continuously the technical and economic effectiveness of the manufacturing process elements. It is shown logically that by using vibration-based monitoring, (VBM), program in the frame of a common database for a plant IT-system the causes behind quality deviations and failures can be identified and eliminated effectively at an early stage and the company’s economics would be improved. The condition-based maintenance effectiveness and accuracy are usually related to the ability of the CM system to detect failure causes and follow defect development. Criteria to select the most cost-effective VBM system and the most cost-effective vibration-based maintenance policy are developed. But, in most real cases, CM systems are not utilised effectively and companies are satisfied with the partial savings achieved in maintenance cost. It is shown, by two case studies, that improvements in vibration-based maintenance can be achieved by effective feedback of the results of failures, renewal condition and VBM history analysis. Unfortunately the data coverage and quality in these studies were not sufficient, among other reasons due to the low number of failures and long bearing lives, so the conclusions, although supported by the work results, remain strong qualitative indications, rather than statistical proof. Criteria to measure the effect of improvements to confirm whether it is economically beneficial and to identify the basic reasons why it is not, are developed. The contribution of this thesis is: The development of a sequential method for the selection and improvement of a cost-effective vibration-based maintenance policy. This methodology can be used to justify, on economic criteria, the use of VBM systems to indicate when rolling element bearings should be renewed. It is achieved through; Tools used in quality and maintenance technology and reliability analysis have either been modified or developed beyond their original concept such as; Maintenance cost equation, Total Time On Test-plots. Development of new tools to monitor maintenance effectiveness and accuracy, select the most informative CM parameter(s) and cost-effective vibration-based maintenance policy. A new maintenance approach, (TQMain), and a new envelope alarming method for VBM programs are also developed. Theoretical basis for improvements to the effectiveness of vibration-based maintenance of bearings in paper mill machines and two case studies which tend to confirm the theory.
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