Delft University of Technology
Faculty Mechanical, Maritime and Materials Engineering Transport Technology
H. van Doesburg A cost evaluation of the hydraulic system of the backhoe "Storken" by the newly developed on-line repair and management system "RMS"
Masters thesis, Report 97.3.GV.4890, Transport Engineering and Logistics.
This final thesis starts with an overview of the cost for maintenance (meant is: preventive maintenance (PM)) and repair (meant is: corrective maintenance (CM)) of Storken in 1996. In chapter 3 of this report these cost are calculated. The calculations were made possible by the use of the RMS. In the RMS fixed cost for the dredger, the barges, crew and supervisor as well as standard cost calculation formulas are programmed (see section 6.7 of [2]). Total down-time cost due to CM in 1996 is 3.636.022 Swedish crowns, being a result of 1283 hours down-time. To compare: Only 234 hours was spent on PM which equals a cost of 663.156 SEK. This indicates that the level of PM is too low at this moment. The cost of CM are divided to the systems responsible on Storken. An overview of spare-parts cost and expert cost is also added in chapter 3.
In chapter 4 of this report the cost of repair and maintenance of the attachment are described into more detail. A distinction is made between the cost for the buckets, the sticks and the connections. The sticks caused the most down-time, and therewith also the highest down-time cost. Total down-time and spare part cost for the attachment amounts to 1.208.000 SEK in 1996. The attachment is herewith the number one concerning CM cost of all systems on Storken. To prevent such high cost weekly inspections on the attachment will be the most appropriate maintenance activity to carry out. The weekly inspections can be carried out by two men and will take about one hour. Weekly inspections will cost 121.368 SEK/year.
Detailed maintenance plans and schedules for the hydraulic system are developed in chapter 5. Maintenance cost are calculated for every component type separately first. All maintenance plans are clustered into a maintenance schedule (maintenance concept) at the end of the chapter. It clearly shows that clustering lowers the total time to carry out the maintenance plans and therewith their cost.
Maintenance planning for the hydraulic system concerns a two yearly cycle. Total cost for the first of these two years is 397.132 SEK, including weekly inspections. The time needed to carry out the maintenance plans is 97 hours at most in this first year of the cycle. The second year the total cost amounts to 256.796 SEK, also including weekly inspections. Time needed for these activities in the second year is 55 hours at most. Each year 26 hours are needed to carry out the weekly checks on the hydraulic system.
The cost calculated can be compared to the total repair cost of the hydraulic system in 1996, which was 709.962 SEK. As can be seen from these figures the maintenance plans developed leave enough financial room for unplanned repair activities. This is necessary because the maintenance plans can never prevent some unexpected repair.
In chapter 6 maintenance intervals to be applied on hydraulic cylinders and hydraulic main pumps are investigated. It shows that a decrease of the maintenance interval of hydraulic cylinders from 3000 to 1500, instead of from 3000 to 2000, results in an extra improved reliability. This reliability is twice as high as if a maintenance interval of 2000 hours is applied. If this new maintenance interval is applied a new maintenance concept, which is better clustered than the original, appears. Total cost of this renewed concept amounts to 397.132 SEK for the first year of the cycle, and 349.816 SEK for the second year of the cycle.
The maintenance interval of hydraulic main pumps is also investigated and varied. Against relatively low expenses reliability of main pumps can be increased significantly. The new maintenance interval should then be 2000 hours, instead of 3000 hours. If these plans are however implemented into a new maintenance concept, a concept which is scattered appears. This decreases the advantage of time saving by clustering. On top of that it seems like the hydraulic system will be 'over-maintained' now. Reliability of pumps should increase anyway due to weekly inspections and periodic maintenance of hoses, oil and filters. Decided is therefore to stick to the first invented maintenance interval of 3000 hours.
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