Particle Test on used oil analysis:
Why analyse wear metals in oil?
Modern oil analysis is successfully employed by commercial, industrial and military laboratories as a condition monitoring technique to determine wear metal content, contaminants, and additives in used lubricants.
The technique is based on the fact that the relative motion of metallic parts in an oil‐wetted system is always accompanied by friction.
Consequently, some of the metallic surfaces are worn, and the particles thus created are deposited in the lubricant. It is the requirement of oil analysis instrumentation to determine the wear metal elements present, and in what concentration; in other words, to identify and quantify.
Oil analysis is, therefore, a scientific preventive maintenance technique applicable to closed loop lubricant systems. Spectrometers are able to determine which wear metals are present in a lubricant and at what concentration. This information allows maintenance personnel to make a determination on the operational status of the system.
For example, an increase in nickel and silver in certain types of railroad diesels is indicative of bearing wear. If detected early enough, a relatively simple bearing replacement can be made, rather than a $40,000-60,000 overhaul and crankshaft replacement.
The know-how in oil analysis is in the ability to evaluate analytical data. An increase in the amount of silicon in conjunction with a corresponding increase in iron, aluminium and chromium, is probably caused by dirt ingestion. Air filter replacement and an oil change may be the only maintenance required.
An increase of silicon alone may mean the oil was topped off with oil containing a silicon‐based anti-foaming agent, and no maintenance action is required. The same trend without the increase in silicon could be indicative of piston wear. The more information available for diagnosis, the more effective is the evaluation of wear trends.
Lubricant condition monitoring
Spectroil emission spectrometers measure the elemental concentration of wear metals, contaminants and additives in the oil. This gives important information about the condition of the equipment that the sample was taken from. Emission spectroscopy is a widely practiced technique in oil analysis but it is not the complete answer to oil analysis.
It is also important to obtain other information about the chemical and physical condition of the oil itself. In the past, this was done by a variety of other tests such as water content, total acid number, total base number, soot content, fuel dilution, per cent solids, and so on.
Each of these tests required special equipment and technical labour. In the last 6 or 7 years a modern alternative to these time consuming and expensive tests, namely, Fourier transform infrared (FT-IR) spectrometric analysis, has emerged as a fast and economical way of screening oil samples for chemical degradation and contamination by water, fuel, glycol or soot.
By monitoring the levels of various chemical compounds in the lubricant and comparing these levels to the levels in new lubricant, the more time consuming oil tests can be avoided.
Spectro was one of the early proponents of FT-IR spectroscopy for condition monitoring. As early as 1988, Spectro offered a turnkey system, called the Spectro Industrial Tribology Laboratory (tribology is the study of friction, wear and lubrication) to provide complete oil analysis capability to customers who have never before had experience with this type of analysis.
The basic Industrial Tribology Laboratory consists of a Spectroil spectrometer, an FT-IR spectrometer, a viscometer and ATLAS oil analysis laboratory software. Other instruments, such as particle counters, titrators and ferrography instruments may be added to give enhanced analytical capability.
Particle contamination and ferrography
The LaserNet Fines particle shape classifier and particle counter can analysed not only hydraulic clean oil samples but highly sooted and contaminated samples such those of diesel engine oils; given a new perspective to analysis of particles to used oils.
Other features like soot and free water measurements and the classification of the particles into their different wear modes have positioned the unit as unique in its market. The unit is sold on the premises of being the best approach before doing ferrography; it actually works as a screening unit to samples to further determine which one will require a more in‐depth ferrographic analysis.
Benefits from oil analysis
The main benefits obtained from an oil analysis program are:
- Reduced maintenance costs - By detecting a failure mode from its early stages, money is saved by Preventing total loss of the equipment and limiting the amount of secondary damage. For example, if a bearing which is wearing abnormally is replaced before damage is done to the shaft it supports, a great deal of money is saved
- Increased equipment availability - Monitoring of equipment will prevent unexpected failures and unscheduled downtime
- Improved safety - In some equipment, most notably single engine aircraft and helicopters, mechanical failures can be life threatening
- Extended oil drain interval - With a well planned oil analysis program, oil change intervals can often be extended giving savings in labour, equipment availability and oil consumed
- Longer equipment life - One of the side benefits of an oil analysis program is improved cleanliness and physical condition of the lubricant. More attention is paid to contaminant levels so that filters are more likely to be in proper working order and better housekeeping habits are practiced around the equipment. Since ingestion of outside contaminants is one of the principal causes of wear, cleaner oil means extended overall equipment lifetime