Smoothing the way01 December 2006

While many new developments now allow lubricant quality to be monitored continuously in situ - as well as various kits and portable equipment that enable tests and measurements to be carried out on site - it is still general practice for samples to be taken and sent off for analysis. The alternatives are to have a system that keeps pumping fresh lubricant to wherever it is required - backed up by analysis to determine how much needs to be pumped in and how often - or to design out the need for lubrication altogether.

The latter is not an option for companies with heavy equipment working in hot conditions. Corus Northern Engineering Services, which still services Corus steel plants, but offers many other heavy engineering services and skills besides, uses the analytical services of Millers Oils at Brighouse, which has users in automotive and manufacturing industries, as well as operators of trucks, compressors and heavy machinery.

According to the company's sales manager Andy Monk, users should have samples of their oil analysed every month or two. "A typical requirement occurs when a user changes the oil they use - for example, going to a synthetic - in which case they need to see how it is doing." Tests are not expensive, with Millers charging around the £20 mark, which includes measuring viscosity at 40oC and 100oC, and performing atomic absorption analysis, measuring amounts of approximately 20 elements.

The need for oil condition monitoring should be self-evident. Once it reaches the point where it is so full of debris that it is not possible to see light through it, and it is difficult to pour out of the sampling tube, serious damage has almost certainly already been done. Machinery and engines last much longer now than they used to do, but are usually dependent on fairly thin, hard surface layers. Once these are worn through, failure is quite rapid and usually will not be remedied by re-boring cylinders or re-grinding, since hard surfaces cannot be put back easily. The other significant class of components that fail through problems with lubrication are bearings.

"Almost fifty per cent of all bearing damage is caused by insufficient or incorrect lubrication", states Steve Lacey, engineering manager at Schaeffler (UK). "This can be very costly for businesses, as bearing damage often results in unscheduled downtime, which can, in turn, result in loss of production and repair costs that often amount to tens of thousands of pounds." Lubricating oil can fail to protect in several ways, such as by:
- Chemically starting to break down, so that it does not adhere as well to surfaces as it should
- Becoming viscous, so that it fails to reach surfaces it is supposed to protect
- Being contaminated with water, leading to a failure to function properly as a lubricant, while also causing corrosion.

But the real killer is when the oil becomes full of particles. If these come from the hard surfaces of the machinery the lubricating oil is supposed to be protecting, they can be very abrasive, even where the particles are too small to be visible to the naked eye.
Castrol Industrial Lubricants and Services offers an analysis service called LabCheck that comes in two flavours, 'standard' and 'advanced'. The standard service offers regular laboratory analyses, supported by a traffic light warning system that indicates the condition of the oil for customers who need to know whether their lubricant is within agreed control limits. The advanced service offers a more comprehensive insight into the condition of fluids by monitoring a wider range of parameters. An extranet reporting service, LabCheck Online, allows laboratory results to be viewed as soon as an analysis has been completed, including access to documents, graphs and trend results.

The company also offers a 'predict' service that evaluates the particles found in a two-stage procedure. The first stage is a quantitative analysis that provides an index of the particles, called the 'Wear Particle Concentration' (WPC), which is the sum of particles greater than five microns across and less than five microns across, and also the Percentage of Large Particles (PLP). The results can be cross-referenced against established industry standards.

The second stage is a qualitative analysis in which captured particles are examined under a microscope. This allows analysts to identify the nature of the particles and whether they are being produced by what might be considered normal wear and tear or by something more serious starting to go wrong. From looking at the large particles, it is usually possible to make a calculated guess as to which type of component - gear or bearing - the particles might be coming and thus anticipate a failure before it becomes reality. Once failure does occur, particularly in gearboxes, the usual outcome is that the debris from the failed component will cause the failure of almost everything else. So a piece of judicious, planned maintenance can often save a lot of time, trouble and expense.

There has been a great deal of research into devices that can monitor the condition of lubricants online, particularly by Qinetiq at Farnborough. A laboratory prototype observed in action there some years ago used a vibrating probe to measure viscosity. Also, commercial devices that can be used for online or on-site oil assessments are available from Parker Hannifin's Condition Monitoring Centre in Thetford. These products are mostly aimed at monitoring hydraulic oil, rather than lubricating oil, but the same techniques work in both application areas. In fact, some of its product models are specifically aimed at lubricants, including corrosive, 'aggressive' fluids, such as phosphate ester-based lubricants used in commercial aviation.

Parker Hannifin portable particle counters come in two models: the LaserCM and the incandescent white light source CM20. Both draw an oil sample through the machine, once connected in-line, with particles detected as they pass in front of a sampling viewing cell. A resultant capacitance value is then counted and stored in an on-board computer in one of six channels, according to particle size, and the result displayed on a hand-held LCD display. Results are obtained within a two-minute test cycle. Aggressive fluid versions of both models are available.

A lightweight single point sampler has been developed to provide LaserCM and CM20 users with the facility to conduct oil tests where inline testing is not feasible. There also exists a new Universal Bottle Sampler, the UBS Offline, which has now been upgraded with microprocessor technology that allows it to recognise and adjust to connecting monitors, including the LaserCM and the company's water in oil monitor. The oil sample is drawn into the UBS Offline where it is secured in a bottle, along with a clean waste bottle, by a peristaltic pump.

For embedded use, the MCM20 is a particle counter enclosed in a metal casing for continuous online particle counting within defined parameters. It has the ability to carry out contamination tests at specific intervals and now comes with Bluetooth wireless connection technology.

The water in oil monitor is designated H2Oil and is a two-channel non-dispersive absorption spectrometer, suitable for measuring absorbed water levels up to 3000ppm. On-line operation is up to 420bar. The company also offers a Parker MS100 moisture sensor to produce real-time moisture indication in petroleum-based and synthetic oils below fluid saturation levels. Software includes Labview for MCM20 and DATµm, which provides linkage between a CM20, LaserCM, EM20 or H2Oil and a computer management system.

Parker Hannifin also offers an Oilcheck hand-held monitor that can be used to measure the dielectric constant of oil as a means of establishing when it should be changed. Telephone consultation with the company's sales staff elicited the information that the company's particle counters cost between "£1,000 and £11,000". This has not deterred users such as the Burlington Northern Santa Fe Railway in the US, which has portable CM20 systems and recently purchased LaserCM systems to check their hydraulic oils. The company operates 5,000 locomotives and 190,000 freight wagons, and previously used to send oil samples to laboratories for testing. However, it took at least three days for the reports to be returned and cost the company thousands of dollars per annum. All major maintenance-of-way equipment is now monitored after 300 hours of operation.

Another sector where sending off oil samples to a laboratory is not possible is marine. Kittiwake Developments in Littlehampton is focused on, but not restricted to, this sector, with test kits and portable instruments for monitoring water contents, TBN (Total Base Number), salt, insolubles, viscosity, TAN (Total Acid Number) and ferrous debris.

Also, its inline ANALEXrs oil condition sensors use dielectric sensing to detect changes caused by water and acid levels to indicate the need for oil changing. An inline Particle Content Sensor uses inductive technology to measure ferrous and non-ferrous debris, while an inline Total Ferrous Debris sensor uses magnetometry and an inline Moisture Sensor employs thin film capacitance sensing technology.

For more information, visit:
www.millersoils.net/M3tech.html
www.castrol.com/industrial
www.parker.com
www.kittiwake.com

Key to best practice
General practice is still for lubricant samples to be taken and sent off for analysis. The frequency recommendation is roughly every one to two months

A typical requirement for analysis occurs when a user changes their oil - for example, going to a synthetic

With gearboxes in particular, failure usually results in debris from the failed component causing the failure of almost everything else, so planned maintenance can often save a great deal of time, trouble and expense

Check out companies that offer analysis and compare the level of service, pricing and levels of expertise in your equipment needs

SOE

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