Condition monitoring products help to keep the plant floor running productively by detecting potential equipment failures. L&T´s M Naganand throws light on this subject.
Mining machines are expensive capital equipment, and are built to move mountains. Be it a limestone mine, an iron ore or a coal mine, any other mining application, these machines have to handle rocks and minerals of density ranging from 1.2 tonne/cubic meter (cu m) to 2.7 tonne/cu m. The reliability and durability built into the machines are quite high to ensure a long life and extended hours of usage every day. The benefits of design and engineering can only be achieved if these machines are properly and timely maintained.
Every equipment manufacturer prescribes a scheduled maintenance plan as per the design and technology. This is also referred as the fixed time maintenance. If the prescribed maintenance is carried out as per recommendation, there will be no premature failures, and unscheduled machine stoppage can be avoided thus machine will not breakdown at the time when it is needed the most, or least expected to fail. The lubricants are to be replaced because they lose their properties as the additives get depleted and can no longer protect the component and system where they are used. For example engine oil is supposed to lubricate, cool, clean, seal, and neutralise the acids formed during combustion. The Total base number (TBN), which is a measure of the acid neutralising ability, decreases at a rate proportional to the amount of sulphur available in diesel. The standard recommends that when the TBN decreases to 50 per cent of the new oil, or maximum 5, engine oil should be replaced or else there will corrosion in the liners and pistons that will induce premature failure of the engine.
Similar degradation of additives also applies to lubricants used in other systems say hydraulic, transmission, brake, differential and final drives. Hence to keep the machine running well, it is imperative to religiously follow the time bound maintenance schedule using genuine filters and reduce the chances of surprise failures.
But the question still remains. Will proper fixed interval maintenance not eliminate major component failure? The answer is No. Components and aggregates will fail as their individual life is less than machine life. Wear is a normal phenomenon that can only be reduced and not eliminated. Once the limit exceeds, we say the component has reached its service life and it fails. The success of an efficient maintenance department is to properly time the replacement and overhaul of aggregates, so that they do not waste the residual life in the component by playing too safe and removing it too early or end up with a failure by being too brave.
Working hours, load factor, machine age, experience with machines and recommendations by OEMs were the deciding factors in the years gone by. Now things are different. The science of service has undergone a sea change. Judgement has to be measurement based, backed by data to convince the decision maker on the appropriate time to dismount a component and install a new or rebuilt unit. Repair after failure or the reactive method is now replaced by repair before failure or the proactive method of maintenance.
The reactive method of repair throws surprises to the maintenance team, and they are more often than not caught on the wrong foot. Panic, trial & error and hurried quick fix mechanism hampers the quality of repairs which can lead to catastrophic failures. Worst affected are the consequential damages of other components on which one has very little control. As an example if the hydraulic pump of an excavator fails, the broken parts travel all through the circuit and can get caught in the control valve, cylinders, and oil coolers before returning to tank. The free particle can damage any or all components and repair will be both very expensive and time consuming.
Studies have shown that repair after failure can be 10 to 15 times more expensive than a repair before a failure. L&T has been in the business of earthmoving and mining machines for the last 70 years and is handling over 100 mining sites under full-maintenance contract. In a sentence, the crux of the learning over the years is: ´Do not allow a component to fail on the machine. Repair or replace before it breaks down´. Therefore machine maintenance is equal to necessary care (Fixed interval replacements) + condition monitoring. (Scientific predictive measure).
Komatsu propagates this science of service as Preventive Maintenance Clinic that has a very elaborate and well-defined checking procedure. PM1 and PM2, KOWA (Komatsu Oil and Wear Analysis), KUC (Komatsu Undercarriage Inspection) if followed diligently, one can with fair amount of accuracy ascertain the time when a component has lived its life and should be dismounted from the machine.
PM1 is intended to check the basic health of the machine or the signs of beginning of a failure. One inspector carries out basic checks on all the listed parameters using simple tools and qualifies as satisfactory or unsatisfactory. This check is done once in 1,000 hours and takes around 1 hour per machine. Minor adjustment if required is carried out immediately and machine put back in operation.
In case there are signs of abnormality that cannot be corrected by simple adjustments, PM2 has to be carried out for that system or components. There are separate drill-down checks for engines, transmission, torque converters, hydraulics, mechatronics, etc. PM2 is a detailed step-by-step check for a system or component and involves in-depth diagnosis using sophisticated tools. This check takes around 2-3 hours per system and involves 1 or 2 inspectors. This check measures the performance parameters and when evaluated along with KOWA report helps in ascertaining the health, repair method, time required and cost involved to bring back the machine in order.
Komatsu Oil and Wear Analysis (KOWA) deals with the study of oil in various compartments of machine and is the best way to peep into the component and understand how it wears. The lubricating oil, transmission oil or hydraulic oil narrate stories of the wear pattern-taking place within the component. Thus if oil is tested, analysed and studied, the condition of components can be monitored. Whenever sliding parts in a machine move, there will be wear which means the loss of solid material due to the effects of friction of contacting surfaces. The wear particles will get mixed with oil used for lubricating the system. KOWA is a system of measuring the densities of these wears particles and how they change over a period of operation. The size of the wear particles is so small that they are not only invisible to the naked eye; they even pass through the filters and remain suspended in the system oil. If there is any abnormality in the machine that accelerates wear the suspended wear particle count will increase drastically. Inductively Coupled Plasma Spectrometer (ICP) is used to measure the density of metal particles in oil in terms of PPM (Parts per million) and the changes in their trend with time is plotted and used for estimating the extent of wear inside the component.
A proper oil analysis programme involves sampling, analysis, plotting and interpretation of results. Fig.1 Oil sampling should be done when the oil is still warm that is right after the machine has stopped and under similar conditions at all times to maintain uniformity. For engine oil, sampling should be done every 250 hours or 500 hours prior to oil change. For other hydraulic systems an interval of 250 hours for the first 1,000 hours of operation and thereafter 500 hours will give fairly good results.
The standard value given by OEMs is indicated by the minimum and maximum value of the caution range. Corrective action is required if the PPM goes in the critical range. A more frequent oil change and its analysis then helps in confirming the accelerated wear and corrective measures can be initiated. Needless to mention, that the success of KOWA will depend on the accurate creation of trend line and hence an isolated oil analysis will not lead anywhere.
Service personnel are trained to accurately plot and evaluate the readings and conclude about the condition of the component.
Such created tables can provide clues for the probable components whose excessive wear can result in an abnormal rise in the concentration. Similar judgment table can be made available for all systems that can guide in analysing KOWA results.
Apart from wear metal analysis, KOWA programme can also be used to check water, fuel and antifreeze mixed with lubricating oil. KOWA is thus a very scientific method of conditioning monitoring which ascertains the health of major machine systems. In the present context when the cost of down time is the sum of the component cost and loss of production, KOWA becomes a must for fleet management.
KUC inspection service dwells on the measurement of undercarriage components to understand the rate and extent of wear. Komatsu has an evolved system, which provides the dimensions of undercarriage components when new, along with its service limits. Service engineers make measurements of individual components every 1,000 hours and feed the measured values. Based on the values keyed, a wear percentage trend line can be created and the balance useful life can also be captured. The wear rate of undercarriage components is a function of underfoot conditions and soil structure, operating skills and job requirement. Trained and experienced service engineers can guide customers on measures to be taken to enhance component life. More importantly it helps customers plan their parts inventory such that the required items reach job site just in time, when the machine needs it.
Komatsu provides Vehicle Health Monitoring System (VHMS) that automatically records vital machine parameters on large-sized mining machines. The machines are fitted with various sensors to capture vital data of various system. This data is collated on periodic basis in a form of trend line which can help the maintenance team to ascertain the health of a particular system on a continuous basis. For example one can see how the engine blow by and exhaust temperature and boost pressure has fluctuated over a period of time, giving a tell-tale indication of the engine condition.
L&T´s Recon exchange programme for engines and hydraulic components reduce machine downtime drastically. Product support team provide a rebuilt unit to their customers after inspection of the removed component at a fraction of the new cost. This eliminates repair time and the removal and installation time is all that the machine is down for. The Recon components carry the same warranty as a new part and hence the user has everything to gain and nothing to lose.
The science of service is becoming more scientific, and proactive with condition-based monitoring. If the measures indicated adopted, Make no Mistake; unscheduled machine downtime can be drastically reduced and as an equipment owner you can buy peace of mind.