From breakdown to proactive maintenance
The need to optimise plant availability in the construction and mining industries has long been acknowledged and there has been a steady evolution from breakdown maintenance to preventive maintenance to predictive maintenance to proactive maintenance in the quest to keep earthmoving equipment operating economically, efficiently and safely.
So says John Evans, diagnostic manager for WearCheck Africa, a member of the Set Point group. The company provides an oil, coolant and fuel analysis service to a variety of industries in Southern Africa from earthmoving to mining and transport.
Fifty years ago breakdown maintenance may have been acceptable but it is generally not economically viable nowadays to allow equipment to run to destruction and simply replace it at failure, Evans says.
With the increase in the cost of machinery, spares and labour, and the cost to industry of lost or poor production, breakdown maintenance evolved into preventive maintenance in the sixties. Its objective was to organise a time-based schedule for the service and overhaul of essential equipment, thereby eliminating or drastically reducing component failure and downtime, as well as improving productivity and profitability.
This was a step in the right direction in that equipment was being checked, serviced and repaired on a regular basis and that history files were being kept on the equipment. However, it is possible to overmaintain equipment; the cost of maintenance must be balanced against the cost of breakdown. This led to a shift from preventive to predictive maintenance, i.e. to continue with planned preventive maintenance but, at the same time, perform condition monitoring on the items of plant to determine their mechanical integrity.
Oil analysis is probably the cheapest and easiest form of predictive maintenance to implement, but other techniques include vibration analysis, thermographic imaging, motor current analysis, balancing and alignment. Oil analysis also offers the biggest return on investment (ROI). A well run oil analysis programme should offer a ROI of at least 10:1.
Key to predictive maintenance is that equipment is not overhauled unnecessarily; why fix it if it is not broken? Contrary to popular belief, there is not a strong relationship between operating age and reliability. Research shows that, once a piece of equipment has ‘bedded-in’ and established a reliable operating mode, overhaul will disturb this mode and the overhauled component will not last as long as the new component. If predictive maintenance techniques do not indicate a problem, then do not disturb a stable and reliable operating mode.
Studies have shown that a successful preventive maintenance programme can provide a 30% reduction in maintenance costs over a breakdown maintenance programme.
Predictive maintenance and accurate record keeping in machine history files enables certain failure modes to be determined and this leads to proactive maintenance – looking at root cause failure analysis (RCFA) to determine the cause of certain common failures in earthmoving equipment. If the cause of failure can be determined, can that cause be eliminated? Whereas previous maintenance philosophies have looked at predicting the failure of a component and taking action before the failure actually occurs, proactive maintenance looks at the root cause of failure and aims to eliminate the cause so that the failure mode, in turn, is also eliminated.
A good example is the influence of particulate contamination in the failure of hydraulic systems. Research has show 70% - 85% of hydraulic component failures are due to particulate contamination, with up to 90% of these failures due to abrasive wear. Predictive maintenance has established the cause of the majority of hydraulic system failures; the object of the proactive maintenance philosophy is to eliminate that cause by keeping hydraulic fluids as clean as is practically possible. By regularly checking the cleanliness of hydraulic fluids and taking steps to clean contaminated fluids or prevent dirt ingress, a large number of hydraulic component failures can be prevented. It is even more beneficial to determine what is causing the contamination and eliminating that cause at its source.
Oil analysis is an important part of proactive maintenance. In the example above, it is used to determine the cleanliness levels of lubricants so that dirty oils can be either cleaned or changed when unacceptable levels of contamination are detected. Although oil analysis is more commonly part of a predictive maintenance philosophy, it can also be instrumental in RCFA and can lead to good proactive maintenance practices. For example, it could be used to predict bearing failure in an automotive application. If the engine can be dismantled before actual failure then, firstly subsequent damage can be avoided and, secondly, it is hoped that the cause of the bearing failure can be determined and eliminated. This is particularly useful when one considers that certain failure modes, at the point of failure, can destroy the evidence of the cause of failure. Oil analysis also permits the planning and scheduling of maintenance activities.
More information on oil analysis and proactive maintenance can be found on www.wearcheck.co.za