Tasks 1
The failure history for rollers supporting a production-line conveyor belt has been analysed. There are 8 such rollers on this critical unit (positions 1 - 8).
The policy is to replace all of these rollers at the overhaul of the conveyor, under contract. The overhaul is conducted once per year. Failures between overhauls are replaced by the operating department personnel. Failure data has been collected over a 3 year period with special attention to the recording of the age of the rollers when they were replaced
. A total of 15 rollers were changed during that time and the analysis indicates that the individual roller reliability can be modelled with a Weibull distribution with shape parameter 3.8, scale parameter 115 days and location parameter 255 days. Rollers can only be changed when the system is stopped.
Access to all of the rollers is obtained by removing guarding from around the conveyor and the conveyor belt itself. Following this work, all rollers are accessible. This takes 1 hour. Each roller requires a further 15 minutes to change. Replacement of the belt and guarding takes a further 1 1/2 hours due to the need to accurately realign a sensitive thickness sensor used to control product quality during processing.
Material and labour costs to change one roller amounts to A$1100 per roller, irrespective of the time taken. In addition, it has been calculated that due to the disruption caused to the system, unplanned stops have a fixed delay cost of A$8500 and an additional cost of A$3900 per hour for every hour the system is down. Planned stops incur a cost of A$4000 per hour.
1. Which renewal strategy best represents the current approach being applied to the roller maintenance:
a. Age replacement of individual rollers.
b. Block replacement of individual rollers.
c. Age replacement of the 8 rollers treated as a single component d. Replacement on failure of the 8 rollers treated as a single component? Explain the reasoning behind your answer.
2. Calculate the cost of preventive renewal and the cost of renewal on failure per roller for each of the 4 renewal strategies listed in Q1.
3. Undertaking quantitative analysis, as required, determine whether the current renewal strategy is acceptable. Suggest alternatives if appropriate and substantiate your suggestions. Your answer should include consideration of the 4 strategies identified in Q1. 2 Condition monitoring of the rollers is being investigated. Two options are being considered. The first involves installing permanent accelerometers and connecting these to a remote test point to allow inspection during operation.
The cost of inspection would be $100 and the likelihood of successful detection of incipient failure would be 0.99. It is considered the inspection would provide a warning time between 10 days and 55 days giving a Weibull warning time distribution with shape parameter 3.44, scale parameter 25 days and location parameter 10 days.
What annual saving would ENGG960/MECH487 - Maintenance Requirements Analysis © UOW/P.Gordon/R.Dwight Page 6 this option achieve in comparison to the optimum usage based renewal strategy.
3. The second option involves continuous remote monitoring of the accelerometers. This option it is believed would achieve 100% likelihood of successful detection of incipient failure with no additional inspection costs. What annual saving would this option achieve in comparison to the optimum usage based renewal strategy?
2 harvard references