CM & Lube Newsletter Article - Gearbox Strategy

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Contents 1 Gearbox Asset Management Strategies 2 Gearbox Routine CM & PM Options 3 An Overview of Gearbox Condition Monitoring Methods 4 Selection of New Gearboxes 5 Lubricant Cleanliness 6 Repair and Overhaul Strategies 7 Commissioning & Baseline Monitoring Strategies 8 Routine Monitoring, Diagnostic & Prognostic Tactics 9 Operational Strategies 10 Knowledge Management Strategies

Gearbox Asset Management Strategies

Vibration Analysis or Oil Analysis, How to decide?

In the last few months I have been thinking a fair bit about gearboxes. Firstly, Andy my key contact at Bluescope Steel talked to me about the 4000 installed gearboxes they have and their need to set some simple standards around how they manage those assets. Then more recently Luis, an ex workmate, asked me to do a gearbox asset management strategy analysis after a number of problems they had on a gearbox. Gearboxes are of special interest to me, as they are where two of the strongest mechanical condition monitoring techniques, vibration analysis and oil analysis, come together and where lubrication also plays a key role. In my time I have seen lots of strategies for managing gearboxes and have been involved in lot of different gearbox condition monitoring and lube management systems. My first thought was that there is too much diversity to set simple standards on how they should be managed. Some simple gearboxes can run on ‘Operate to Failure’ while others require sophisticated online monitoring. But Andy’s point was that most gearboxes are not that different, just bearings, shafts, gears, seals and casings and that there must be a way to simplify decisions about at least the routine Condition Monitoring (CM) and Preventive Maintenance (PM) activities.

So to set a standard, why not start with a standard. I picked out ISO 13379 (Condition Monitoring and diagnostics of machines – General guidelines on data interpretation and diagnostics techniques), which is worth a look at. Leith Hitchcock, who is an Australian key rep on the CM ISO Condition Monitoring committees, has had a lot of input into this particular standard. Appendix A of this standard describes a Failure Mode and Symptoms approach (FMSA), which is an extension to the standard RCM/ FMECA method and includes a detailed review of failure symptoms to give some logic in making selections between monitoring methods. See picture to right. I was interested in how I could use the Symptom concept to help to make hard decisions such as how to choose between oil analysis and vibration analysis in a situation where cost is critical.

The main focus of an Asset Management strategy for an installed gearbox should be to ensure there is an effective predictive and proactive risk management strategy. This is especially so if there is a high of level of business interruption with a major failure and the possibility of following on infant mortality failures. This is illustrated by the typical failure pattern for a gearbox shown in the diagram to the right and it indicates that reliability is significantly improved if invasive maintenance can be minimised. Putting an effective predictive and proactive risk management strategy in place involves understanding what failures are likely to occur so that causal factors can be minimised and so that defects can be detected early and business risks managed. A key question is, can risk be reduced enough and enough warning time given so that holding a spare is not necessary. Best practice is about doing the basics well, with the biggest problem being achieving the basics consistently over time. This requires recognition of what the basics involve and making ‘what is and what is not being done’ visible to management.

So to maximise reliability and minimise running costs of a gearbox we have to look at gearbox failure causes. To justify carrying out CM or PM activities there needs to be a Risk Cost, which is the expected cost of future failures you are trying to avoid and are estimated from the likelihood and consequence of failures. As seen in the gearbox typical failure pattern above, there are a number of failure causes that produce early problems after installation and invasive maintenance. If these causes can be eliminated by good Quality Assurance or detected early by commissioning and baseline CM, then the ongoing risk, CM & PM requirement and costs are much smaller. So a good starting point for an analysis is to define the causes of gearbox failure, identify which are early and which have a random failure pattern (marked E & R in column 2 below) and which Symptoms will help to detect the causes. The table below tries to define these relationships.

		Failure Symptoms
Failure Causes (Below)	FP	Brg Temp	Visual	Lube Wear Debris	High Frict ion	HS Gear/ Brg Prob	LS Gear/ Brg Prob	Lube Condit ion	Lube Contam.	Lube Temp	Lube Level	Coupl ing Temp	Worm Back lash
Misallignment Input shaft	E	Strong				Strong						Strong
Misallignment Output shaft	E	Weak					Weak
Lube Contam. shaft seals	R		Weak	Weak					Strong
Lube Contam. Breather	R			Weak					Strong
Lube Contam. Lube Top-Up	ER			Weak					Strong
Lube Contam. Mosisture	R								Strong
Loss of Lube	R	Weak	Strong	Weak	Weak	Weak					Strong
Assembly Issue Overloading	E	Strong			Weak	Strong	Weak		Weak
Assembly Issue Looseness	E			Weak		Strong	Weak
Casing Softfoot	E	Weak		Weak		Strong
Operational Overload General	R	Weak		Strong		Strong		Weak
Operational Overload Shock	R					Strong	Strong
Lube Wearout Age & Temp	R			Weak				Strong

Gearbox Routine CM & PM Options

So if you suspect you have a certain cause active in your gearboxes, what are the CM & PM options that are available to you that will monitor a defect generated by that failure cause? The above table gives the symptom types that will give either a weak or a strong detection of your failure cause. Before we start grouping condition monitoring methods to symptoms, lets look at some of the factors I use to help select between CM techniques.

Selecting the best CM & PM options from the many techniques that are available is not an easy task. For example, should you use vibration analysis or oil analysis to monitor an oil lubricated bearing or should you use both? Also which of the many types of vibration or oil analysis parameters should you select? The analysis in this article uses three criteria for the selection of condition monitoring parameters. They are:-

PF Interval (PFi) – This is the warning 'Time to Failure' that the condition monitoring parameter will give at the selected monitoring frequency and is categorised into 4 levels of performance in comparison to competing techniques in a symptom group (see diagram above).

Effectiveness Level (E) – This is the percentage of failures that will be detected by the condition monitoring parameter at the chosen monitoring interval and is also categorised into 4 levels with the same codes as for the PF Interval.

Cost (C) – This is the yearly cost of using the condition monitoring parameter at chosen monitoring interval. This uses a slightly different 4 level coding system (see below).

PF Interval (PFi) & Effectiveness (E) Levels

• Excellent (Ex)
• Good (G)
• OK (OK)
• Poor (P)
• Not Applicable (NA)

Cost (C ) Levels

• Low (L)
• Medium (M)
• High (H)
• Extreme (X)

Two other categories that help to classify maintenance actions are also required.

Skill Required - (Plus the required level of training in the specific technique)

• Operator (Op)
• Electrician (E)
• Electrical Technician (ET)
• Fitter (F)
• Fitter – Gearbox Specialist (FG)
• Lubrication Assistant (L)
• Lube Technician (LT)
• Condition Monitoring Assistant (CM)
• Condition Monitoring Technician (CMT)

Equipment Operating Status

• Operating (Op) – Operating in a standard repeatable stable state
• In-Service (IS) – Available for In-Service testing
• Out of Service (OS) – Off-line but no isolation required
• Isolated (Isol) - Out of Service and Isolated
• Any state (Any) – No specific requirements

The link below shows a table of my analysis of all appropriate CM & PM techniques for gearboxes to allow the selection of the best techniques for a specific situation based on the symptoms that will best manage the failure cause that are likely to be in play. Some details of the listed CM techniques are given in the section below.

Click on this link Gearbox Routine CM & PM Options

Making the best selection of CM/ PM actions currently requires an understanding of how to use the PF Interval, Effectiveness and cost information to balance the risks against costs for any specific situation. Howard, a friend of mine, has suggested a way that the selection process could be automated using a spreadsheet model. This would allow the decision to be made by an average maintenance planner. It is still early days with a lot of work to do before a simplified standards could be set.

An Overview of Gearbox Condition Monitoring Methods

Best practice in Preventive and Predictive Maintenance is mostly focused on carrying out the basic requirements diligently and consistently. Best practice is also around making visible what is and what is not being done. Often all levels of management assume specific monitoring activity, lubrication activity or inspection is being performed on an item of equipment when in reality for any number of reasons it is not.

There are a range of oil analysis and vibration monitoring approaches of varying sophistication available for gearboxes. Vibration Analysis techniques have an excellent effectiveness for detecting higher speed bearing and gear problems and can produce very specific diagnostic results identifying which components have issues. Oil analysis is better at identifying some of the key failure causal issues and has a better monitoring effectiveness for lower speed bearings and gears issues and more general wear problems but gives less specific information on component diagnostics. Combining these two general techniques is the basis for a very effective monitoring program. An overview analysis of gearbox CM techniques is given below in Failure Symptom groupings.

Bearing Temperatures

Temperature Measurements There is a large range of contact and non-contact hand held temperature meters that are so cheap every maintenance person and operator inspecting equipment should have one available.

Thermal Imaging - Thermal Imaging for the gearbox is recommended as a part of an overall inspection of an area of plant. The focus for the gearbox is on temperature patterns around bearings and the the recirculating lubrication system if it has one. On commissioning it there is access for inspection then a thermal pattern of the gears is the best way to confirm gear mesh and alignment.

Online bearing temperature measurement - For very large and critical gearboxes online temperature monitoring of bearings can avoid substantial equipment damage and cost in case of a failure.

Gear and Bearing Wear Debris

Magnetic Chip Collector - This is a technique not widely used in industry but is used extensively in aircraft engine rolling element bearing and gear system. It has the advantage of being low cost, collects the debris of interest continually and allows both an instant visual diagnosis of a problem as well as quantitative monitoring and laboratory microscope analysis. An example of the recommended magnetic chip collecting device is given at the right.

Online Magnetic Debris Sensor - The most useful condition monitoring parameter for gearboxes in a laboratory oil analysis is the PQ Index. This is because all active materials in bearing and gears are usually magnetic steel and any wear or fatigue particles tends to get retained in the oil for a period. A quantitative measure of these particles (PQ Index)is a very important condition parameter and many CM specialist would regard it as the most useful monitoring parameter giving long term failure prediction. The Manual Magnetic Chip Collector method above is another method of quantifying these particles. A sensor that measures an equivalent PQ Index during operation is probably the most cost effective on-line gearbox condition monitoring method. The sensor above (Kittiwake ANALEXrs) is one option for this type of on-line sensor. This type of sensor will give the early warning for more gearbox failure modes than other condition monitoring technologies. It would be setup by taking a feed line off the discharge from a lubrication pump, so requires a recirculating oil system. The magnetic debris parameter output would be put into the operator alarms. There are other options available for ferrous oil debris sensors.

Laboratory Oil Analysis – PQ Index - As an oil sample and laboratory oil analysis will be carried out for assessment of oil condition and lube cleanliness, then a PQ index and Fe Spectroscopic result should be reviewed as a bearing and gear condition monitoring parameter. A rigorous sampling procedure is required to get repeatable results for wear particles.

Laboratory Patch Test Microscope Examination of Wear Debris - If the oil laboratory offers a Patch Test with microscope examination of contamination levels and wear debris, then this is a very worthwhile addition to an oil analysis service. If Patch Tests are being carried out on-site for cleanliness monitoring then a more detailed analysis of Wear Debris is very advantageous. Many sites have powerful microscopes available in Laboratories.

High Friction

No Load Motor Current Monitoring - Many gearboxes have an operating cycle that caries from loaded to unloaded. If there is the PLC capacity available, it should be relatively easy to determine the no load current and setup a relatively tight alarm to detect if the no load current increases a small amount. The advantage of this monitoring parameter is that if a serious problem arises that causes friction anywhere on the drive system, it will allow an early diagnosis before any serious damage occurs. It may also save a lot of electricity if friction has developed somewhere is the drive system. Suggested diagnostic response to an increase in no load current would be inspection around the drive, thermal imaging of drive system, vibration analysis and checks of the motor controls.

High Speed Gear or Bearing Problems

Manual Vibration Monitoring - Vibration monitoring of the higher speed gearbox shafts is a very useful approach, even if oil ferrous debris analysis is chosen as the primary monitoring technique. The motor driving the gearbox is usually being vibration monitored and so at least monitoring the input shaft bearings is desirable, as this is often a likely failure point in a gearbox. Typically a vibration data collector is used but a simpler vibration instruments is also possible if it has both a high and low frequency vibration parameter.

On-line Vibration Analysis - Sometimes gearboxes have accelerometers permanently installed due to access problems. The next step from this would be for online vibration monitoring but simple vibration monitoring would only be useful for the higher speed shafts. It would be desirable to set an alarm level that would represent a serious condition problem to have as an operator alarm. To do comprehensive online vibration monitoring for a gearbox would require the system having spectrum analysis with demodulation capability (see below).

A more cost effective monitoring approach than vibration online monitoring would be to install an Online Magnetic Debris Sensor as the primary monitoring sensor and installing just enough fixed accelerometers to be able to carry out manual diagnostics on gears and bearing problems.

Low Speed Gear and Bearing Problems

On-line Vibration Analysis – Demodulated Vibration (PeakView) - The best vibration technique for analysis and diagnostics of low speed bearings is using a demodulated vibration technique, which looks at the lower frequency components of higher frequency vibrations.

On-line Vibration Analysis – Time Synchronous Averaging & Long Time Domain - My understanding is that another good vibration technique for analysis and diagnostics of low speed gear problems is using a Time Synchronous Averaging technique (TSA), which analysis a lot of vibration over time correlated to the specific rotational component to amplify a small magnitude but important vibration issue. An equivalent to TSA is a manual analysis of vibration time domain using an extended period of many revolutions of the component of interest.

Audible Noise Analysis - Using the capability of the human ear is a widely recognised technique for analysis of low speed bearing and many experienced vibration technicians always listen to the noise from accelerometers while collecting vibration data. Other systems used are listening rods and stethoscopes.

Lube Condition

Laboratory Oil Analysis – Lube Condition - Lubricant condition is a key focus of any Laboratory lubricant oil analysis and looks at the level of oxidisation, acidity, viscosity, level of additives, etc. The Laboratory required a sample of the new oil to do the comparison. There is no need to change out lube oil if the lubricant condition is still OK.

Lube Contamination

Laboratory Oil Analysis – Contamination Level - Contamination level needs to be measured for any oil sample collected. The two techniques that are used are laser particle counting and patch test comparative analysis. The patch test is generally used for dirtier samples that are typical for mining and heavy industrial sites and a lot of sites setup to be able to do patch test analysis on-site to speed up important diagnostics.

Breather Desiccant Colour Change and Used Filter Inspections - Desiccant Breathers have a colour change of the desiccant crystals when they are fully loaded with moisture and need to be changed.

For gearboxes with recirculating oil systems, when filters are changed the debris in the old filters should be inspected and the time between filter changeovers should be trended.

Lube Temperature

Lube Temperature measurement - Monitoring lubricant temperature or a related temperature parameter such as a lower casing temperature or recirculating oil pipework temperature is a basic requirement.

Oil Level

Dip Stick or Level Site Glass Monitoring - The dip stick or site glass should be occasionally monitored and any top-up required should be of filtered oil.

Oil Leaks - There should be a occasional rigorous visual checks for oil leaks around the gearbox.

Selection of New Gearboxes

You can't talk about Asset Management without discussing selection of new gearboxes. About 4 years ago I got involved in a failure analysis of a critical materials handling gearbox that was having bearing failures every 7 to 18 months. The interesting fact was that they found no major problems causing the bearing failures. The solution was to increase the cleanliness of the lubricating oil to well above what would be typically called acceptable oil cleanliness, using in-service kidney loop lube filtering. The important design charactoristic of this system was that it ran at close to its design load, but not above it. Why would a gearbox fail regularly if it is operating within its design specification. Some more research on this issue has identified one reason.

If you order a standard gearbox from a supplier and don't specify some 'factor of saftey' or 'service factor' the L10 Life on the highest normal bearing loading will be 5,000 hrs. The common response I get when I tell people this is "surly you mean 50,000hrs", no definitely 5,000hrs. This means that you have a 10% likelihood of having a significant bearing defect within 7 months of operation if the gearbox runs 24 hrs a day at full load, even if you get through the early failure period of the gearbox unscaved. The savior for most people is that gearboxes mostly don't run at full rated load and as the relationship between loading and life is a cubed law, a small reduction in bearing load gives a much greater increase in bearing life.

My suggestion is that when specifying a gearbox, specify the actual minimum L10 bearing life required (16,000hrs would be good). If you are stuck with a highly loaded gearbox, filter the lube to ISO 15/13/10 or as close as you can get and regularly check and re-filter as required. Another thing on gearbox selection is giving an extra factor of safely if there is likely to be shock loading to ensure you don't end up with a gear tooth fatigue issue.

One area that is often ignored completely during gearbox selection is the shaft seals. When shaft seals fail it is difficult to maintain the cleanliness and oil tightness of the gearbox. Often a highly expensive gearbox going into an arduous environment is given the cheapest shaft seals available, which often will set the service life of the gearbox. Simple shaft contacting lip seals should be eliminated and a seal with longer life suited to the application should be employed. Also new gearboxes should be specified with quality breathers and oil sampling fittings and should not have poorly sealed dip sticks or other items that could cause contamination ingress. Gearboxes should be supplied with a storage oil if they are to be stored as spares or supplied with the correct specification oil and filtered to a specific ISO cleanliness rating if they are going into service quickly.

Lubricant Cleanliness

Apart from disassembly, one of the biggest long term risks to the gearbox bearings and the gears is likely to come from the current poor cleanliness of the lubricating oil, as indicated by its current ISO cleanliness code rating and to a lesser extent the moisture level of the oil. It may not be out of the question to have a conservatively specified gearbox last 20 to 50 years with few or no in-service bearing or gear failures and improved oil cleanliness and moisture levels would significantly improve the likelihood of this.

Process to Achieve Lube Cleanliness

The high level process to achieve lube cleanliness target:-

• Ensure any top-up oil added to the gearbox is cleaner than the cleanliness target and the top-up process doesn’t cause contaminant entry.
• Test the gearbox casing for unknown contamination entry points and repair any issues found
• Test the effectiveness of the lube filtration system if one is installed and upgrade if required.
• Install an adequately sized desiccant breather to the gearbox
• Provide additional filtration to the gearbox to achieve the selected cleanliness target, usually by using a filter cart
• Carry out on-going monitoring and filtration

Top-up Cleanliness – Managing and improving the cleanliness of lubricating oil through the supply, storage and dispensing process is a major opportunity. Any top-up oil or oil for change-outs should be of a higher cleanliness than the cleanliness specification for the gearbox (suggestion for at least 17/15/12 or better if highly loaded). If this is currently not in place and a project to achieve this for the whole plant is not a current priority then an option is to setup a filter cart to filter oil in 200 litre drums with appropriate dispensing systems to solve a specific bad actor gearbox.

Eliminate Other Sources of Contaminant Entry – The other source of contaminant entry is from environmental dust and moisture entering the gearbox casing. One area where contaminants can enter is through the input and output shaft seals. You need to understand the type of seal you have and any maintenance requirements.

If it is suspected there is a problem with the air tightness of the gearbox casing it is suggested to check it by supplying a clean dry source of low pressure (eg 300 to 500 mm water) air through the breather casing entry and see how long the casing holds the pressure using a simple manometer. If the casing doesn’t hold even a small pressure then the breather will be short circuited and contaminates will enter the casing. If this is the case than there are a number of technologies for leakage sniffer systems used in refrigeration and other areas that could help to trace the leakage areas. If for some reason adequate sealing is not achieved a positive pressure sealing system should be considered for important gearboxes.

It is recommended to fit a desiccant breather if there are higher levels of moisture in the oil. Gear boxes with intermittent operation or subject to higher levels of heating and cooling will breathe a significant quantity of air, so ensure the breather has adequate capacity and tested occasionally for build-up or flow restrictions.

Test Effectiveness of Existing Filtration Systems – If there is a recirculating oil system the cleanliness of an oil sample from before any filtration should be compared with the cleanliness of oil samples from after the filter element. If the existing lubrication oil system is not able to maintain the specified cleanliness level, then this should be investigated to determine the cause and repair of any major issues such as bypassing, poor element specification, etc.

Improve Lubricant Cleanliness - Once sources of external contaminant entry have been minimised the lubrication oil should be filtered to the selected standard of cleanliness. This is usually done using a filter cart system. Advice of filtration specialist such as Pall Corp or Hydac should be sort or even better if you have an independent source of filtration advice.

Repair and Overhaul Strategies

Best practice in overhaul strategy include:-

• Use an assessment process for overhaul shops (Follow this link for an example Repair/ Overhaul Workshop Assessment) and select 2 or 3 workshops that conform to most of your engineering and quality assurance requirements. It is necessary to build up a working relationship with these shops.
• To achieve the quality control of invasive maintenance and overhauls requires a detailed process, detailed scope of work and a detailed Inspection and Test Plan (ITP) with the appropriate hold points with the relevant people identified to verify that the necessary quality issues have been controlled.
• Some examples of general procedures for repair of rotables are given in http://www.sirfrt.com.au/wikis/imrt/index.php/Repair_Procedures
• Examples of documented scopes of work are given in http://www.sirfrt.com.au/wikis/imrt/index.php/Scopes_of_Work
• Some examples of Inspection and Test Plans (ITP’s) are given in http://www.sirfrt.com.au/wikis/imrt/index.php/ITP%27s
• A client representative should be selected to take ownership of the quality issues from disassembly to final commissioning of a major gearbox repair. The repair shop should also nominate a more experienced tradesperson to take ownership of the quality issues while the gearbox is in the shop.
• Special attention should be paid to the final cleaning and then lubricant flushing of the casing ensuring all pressurised lubrication lines are operating effectively and any oil dams are well sealed. The final fill of lubricant should achieve the target level cleanliness, which should be maintained through commissioning with kidney loop filtration if required.
• Cleanliness control of the disassembly and assembly process should be maintained whenever the gearbox is opened to the environment. All openings should be covered as quickly as possible and sealed with plastic sheeting and tape if they are going to be left open for a considerable period of time.

Commissioning & Baseline Monitoring Strategies

Typical causes of early reliability problems in gearboxes and the focus of both initial commissioning strategy and Baseline monitoring strategies are listed below.

• • Misalignment of input and output shafts
  • Lube contamination from
  • Casing and shaft sealing issues
  • Poor cleanliness of new oil added
  • Residual debris from the overhaul or repair work
  • Moisture entry into the lubricant
  • Inadequate breather condition
• Oil leaks
• Lube delivery issues to particular bearings or gears
• Manufacturing and assembly issues causing bearing overload
• Manufacturing and assembly issues causing bearing and shaft looseness
• Soft-foot casing distortion issues

The important symptoms to detect and monitoring early gearbox problems are listed below. The detailed techniques related to each of these symptoms are discussed in the previous sections.

• Bearing and oil temperatures
• Gear and bearing wear debris (Magnetic)
• High Speed gears and bearing vibrations
• Lube contamination (see different causes above)
• Lube level and its delivery to the required active lubrication areas
• Coupling temperatures
• High friction (Motor currents)

Commissioning monitoring is carried out immediately on first driven rotation and also at first fully loaded operation, if that does not occur on initial start-up. Commissioning monitoring looks for substantial defects that need to be addressed quickly. Baseline monitoring looks for any, even very minor, defect that might shorten the life of the equipment. For some failure causes, confidence that there are no problems can be identified early. For other causes like bearing overloading on assembly, there may be up to 16,000 hrs operation wait until it can be assumed to be defect free. If a defect is found then the diagnostic process is initiated. If no defects are found then the less intense routine monitoring strategy is initiated.

Routine Monitoring, Diagnostic & Prognostic Tactics

All monitoring parameters recorded should at the least have a run chart available to display the parameter history. If there is a known alarm level then that level should be marked on the run chart. If there is no current alarm levels set then an alarm should be defined as any significant deviation from the normal level of variation of the parameter. One of key quality issues in condition monitoring is to ensure any variation in condition monitoring parameter measurements is due to real variation in the parameter and not variability in measurement technique. This is achieved through using measurement procedures and precise identification of measurement locations. Run charts can be generated with paper tables and graphs, spread sheet software or dedicated condition monitoring or other software system. They are the basic visualisation technique for all routine first level monitoring data, as run charts analysis give the first confirmation of a possible significant change in equipment condition. All collected first level monitoring data should be viewed in a run chart format or viewed after an alarm of the parameter is triggered. Efficient review and analysis of collected condition monitoring data relies on setting statistical alarms on as much of the data collected as practical to avoid having to review routine collected data unless there is a parameter deviation. Only on critical and more complex data should a review of all collected data be necessary.

Once a condition alarm level is reached then it is the condition monitoring technician’s role to carry out a diagnosis. This involves reviewing all relevant available data for patterns that indicate a defect has been initiated and condition deterioration may be in progress. An assessment of the severity of the problem is made and recorded and an estimate of the worst case likely item condition at next scheduled measurement is made. One or more of the following actions is initiated.

• Decide to wait for the next scheduled collection of data to review the parameters again
• Collect more detailed condition data to do a more in depth diagnostic
• Schedule the next data collection for that item of equipment at a date earlier than normal
• A repair planning action is triggered, such as checking that spares for a repair of the problem are available
• A repair action is initiated with repair priority and if necessary a completion deadline. For example change-out of a component
• Initiate a defect elimination action. For example realign coupling or filter oil

A prognosis is made at every stage of a diagnosis by extrapolating trends and estimating likely worst case condition at next measurement instance. When risk of in-service failure becomes significant but there is still business benefit of remaining in service, a ‘final failure mechanism’ analysis should be carried out and additional monitoring parameters selected if required, to warn of immanent failure requiring immediate shutdown. The worse the problem, the more often you monitor.

Operational Strategies

Operational strategy relating to gearboxe should involve basic care and monitoring that could involve the following items.

• If there is a recirculating oil system, monitor lubrication filter pressure differential levels or alarms and call maintenance to change or clean the filters.
• Inspect the gearbox for damage, deterioration, oil leaks and at a nominated frequency check the gearbox oil level.
• If practical to monitor the no load current or no load current alarms and carry out an initial investigation.
• Identify any peak loadings that may occur to the drive such as stalling the drive with accidentally heavy opperation and procedualise any approaches that may minimise occurrences.

Knowledge Management Strategies

A technical area such as gearboxes is important for many organisations. The diagram below shows a structure for handling the knowledge such as gearbox maintenance technology by having a local champion. This is suggested to be a low intensity part time role usually given to a front line person who is willing and enthusiastic about learning and giving on-the-job support to other for the technical issue. The development of this role is usually initially around identifying one or more specialists in the field to supply support and training but eventually the person should build and be supported by a peer support network (This can be developed through the Industrial Maintenance Roundtable through CIWG’s, National Forums, training courses, etc).

Article written by

Peter Todd

Facilitator for the NSW Industrial Maintenance Roundtable