CHAPTER 1 INTRODUCTION TO Wear debris analysis

1.1 Introduction:- The technique of Wear Debris Analysis (Analytical Ferrography) is gaining popularity in the field of Condition Based Maintenance. WDA is a method of predicting the health of an equipment in a non-intrusive way, by the study of wear particles. The continuous trending of wear rate monitors the performance of Machine / Machine components and provides early warning and diagnosis. Oil condition monitoring can sense danger earlier than Vibration technique. This technique holds good for both oil and grease samples.

Analytical Ferrography with supporting physical and chemical tests can determine the following

The start of abnormal wearThe components which are wearing

Root cause of wear/failureUsability of lubricant beyond its rated life

The Software developed to measure the MACHINE CONDITION INDEX ( MCI) through Ferrography analysis for predicting the wear status of machine is a unique achievement of its own.

Some Typical Ferrogram

FATIGUE WEAR ALONG WITH NORMAL RUBBING WEARSPHERICAL PARTICLES FROM A/F BRG

SEVERE SLIDING WEARFATIGUE CHUNK FROM GEAR

Figure 1.1 Some typical ferrograms

1.2 Wear Particle Analysis or Ferrography:-Ferrography is a technique that provides microscopic examination and analysis of wear particles separated from all type of fluids. Developed in the mid 1970s as a predictive maintenance technique, it was initially used to magnetically precipitate ferrous wear particles from lubricating oils. This technique was used successfully to monitor the condition of military aircraft engines, gearboxes, and transmissions. That success has prompted the development of other applications, including modification of the method to precipitate non-magnetic particles from lubricants, quantifying wear particles on a glass substrate (Ferrogram) and the refinement of our grease solvent utilized in heavy industry today. Three of the major types of equipment used in wear particle analysis are the Direct-Reading (DR) Ferrograph, the Analytical Ferrograph System and the Ferrogram Scanner.

CHAPTER 2 - Wear Debris Analysis methods2.1 Various methods:- As a supplement to oil analysis, ALS Tribology Division offers wear debris analysis services. There are several analysis methods available. 2.1.1 Analytical Ferrography:-Analytical Ferrography utilizes a skilled analyst examining a prepared ferrogram slide with a computer-aided microscope to identify the composition of the material present in a used lubricating oil sample. Wear material and other debris suspended in a lubricant is deposited and separated onto a ferrogram slide maker. The sample is diluted to improve particle separation onto the ferrogram slide. Magnetic separation of wear material from the lubricating fluid attracts ferrous particles out of the oil onto the ferrogram slide maker. Though the method is biased to ferrous material, other nonferrous wear particle and contaminants are also captured and identified. The slide is examined under a microscope to distinguish composition, morphology, particle size, and relative concentration of the ferrous and non-ferrous wear particles. Treatment of the ferrogram with heating and chemicals will further distinguish identification of the metallurgical composition of the wear material. The skilled analyst performs the analytical ferrography to provide a root cause for wear mechanisms based on the morphology and composition of the particles. The analyst will report material composition and wear morphology that will include, but is not limited to: Ferrous wear particles High alloy steel Low alloy steel Dark metallic oxides and cast iron Red oxides (rust) White nonferrous metal particles Yellow metals wear particles Contaminants, dirt (silica), fibers and other particulates Fatigue wear Sliding wear Cutting wear - abrasive wear Adhesive wear Corrosive wear2.1.2 Filter Patch Test (FPT, filtergram or patch test)A common method for making a detailed determination of wear occurrence, especially for non-ferrous materials, is to employ a Filter Patch Test examination using a microscope for wear particle analysis. A measured portion of used oil is filtered through a filter patch. Trapped wear particles and debris are then visually examined microscopically for a qualitative report. Observation will generally be accompanied by a photo of the filtered wear material on a test report. The debris is assessed and the particles graded. The FPT can tell us a number of things: Is there abnormal wear taking place? Is the wear ferrous or non-ferrous? Is there any evidence of abrasive contaminants e.g. dirt?2.1.3 LaserNet FinesSome of our ALS Tribology laboratories employ Lasernet Fines instrumentation, which was developed by Lockheed Martin with the Naval Research Laboratory for military application. Using direct digital imaging Lasernet Fines, test results classify particles larger than 20 micron into cutting wear, severe sliding wear, fatigue wear, and nonmetallic material. The analysis economically combines features of particle count determination with quantifying wear particle classification for industrial, gear and drivetrain components without subjective interpretation. The test data complements other wear analysis techniques by using laser imaging and advanced image processing software to identify and measure: Type of wear mechanism Rate and severity of wear processes Wear particle size distribution Particulate contamination and oil cleanliness

2.1.4 Particle Quantifier Index (PQI)The Particle Quantifier is a magnetometer that measures the mass of ferrous wear debris in a sample and displays this as a PQ Index. Test results are quantitated as a relative number of ferrous material within a sample; this can then be trended for useful wear monitoring. PQI is a simple, cost-effective test that can easily be incorporated into routine trending analysis.

Chapter 3 - Wear Particles3.1 Types of wear partical:-There is six basics wear particle types generated through the wear process. These include ferrous and nonferrous particles which comprise of:3.1.1. Normal Rubbing Wear: Normal-rubbing wear particles are generated as the result of normal sliding wear in a machine and result from exfoliation of parts of the shear mixed layer. Rubbing wear particles consist of flat platelets, generally 5 microns or smaller, although they may range up to 15 microns depending on equipment application. There should be little or no visible texturing of the surface and the thickness should be one micron or less.3.1.2. Cutting Wear Particles: Cutting wear particles are generated as a result of one surface penetrating another. There are two ways of generating this effect. A relatively hard component can become misaligned or fractured, resulting in hard sharp edge penetrating a softer surface. Particles generated this way is generally coarse and large, averaging 2 to 5 microns wide and 25 microns to 100 microns long. Hard abrasive particles in the lubrication system, either as contaminants such as sand or wear debris from another part of the system, may become embedded in a soft wear surface (two body abrasion) such as a lead/tin alloy bearing. The abrasive particles protrude from the soft surface and penetrate the opposing wear surface. The maximum size of cutting wear particles generated in this way is proportional to the size of the abrasive particles in the lubricant. Very fine wire-like particles can be generated with thickness as low as .25 microns. Occasionallysmall particles, about 5 microns long by 25 microns thick, may be generated due to the presence of hard inclusions in one of the wearing surfaces. Cutting wear particles are abnormal. Their presence and quantity should be carefully monitored. If the majority of cutting wear particles in a system are around a few micrometers long and a fraction of a micrometer wide, the presence of particulate contaminants should be suspected. If a system shows increased quantities of large (50 micrometers long) cutting wear particles, a component failure is potentially imminent.3.1.3. Spherical Particles: These particles are generated in the bearing cracks. If generated, their presence gives an improved warning of impending trouble as they are detectable before any actual spalling occurs. Rolling bearing fatigue is not the only source of spherical metallic particles. They are known to be generated by cavitation erosion and more importantly by welding or grinding processes. Spheres produced in fatigue cracks may be differentiated from those produced by other mechanisms through their size distribution. Rolling fatigue generates few spheres over 5 microns in diameter while the spheres generated by welding, grinding, and erosion are frequently over 10 microns in diameter.3.1.4. Severe Sliding: Severe sliding wear particles are identified by parallel striations on their surfaces. They are generally larger than 15 microns, with the length-to-with thickness ratio falling between 5 and 30 microns. Severe sliding wear particles sometimes show evidence of temper colors, which may change the appearance of the particle after heat treatment.

Figure.3.1: Severe Sliding Wear3.1.5. Bearing Wear Particle: These distinct particle types have been associated with rolling bearing fatigue: Fatigue Spall Particles constitute actual removal from the metal surface when a pit or a crack is propagated. These particles reach a maximum size of 100 microns during the microspalling process. Fatigue Spalls are generally are flat with a major dimensions-to-thickness ratio of 10 to 1. They have a smooth surface and a random, irregularly shape circumference. Laminar Particles are very thin free metal particles with frequent occurrence of holes. They range between 20 and 50 microns in major dimension with a thickness ratio of 30:1. These particles are formed by the passage of a wear particle through a rolling contact. Laminar particles may be generated throughout the life of a bearing, but at the onset of fatigue spalling, the quantity generated increases. An increasing quantity of laminar particles in addition to spherical wear is indicative of rolling-bearing fatigue microcracks.3.1.6. Gear Wear Two types of wear have been associated with gear wear: Pitch Line Fatigue Particles from a gear pitch line have much in common with rolling-element bearing fatigue particles. They generally have a smooth surface and are frequently irregularly shaped. Depending on the gear design, the particles usually have a major dimension-to-thickness ratio between 4:1 and 10:1. The chunkier particle result from tensile stresses on the gear surface causing the fatigue cracks to propagate deeper into the gear tooth prior to spalling. Scuffing or Scoring Particles is caused by too high a load and/or speed. The particles tend to have a rough surface and jagged circumference. Even small particles may be discerned from rubbing wear by these characteristics. Some of the large particles have striations on their surface indicating a sliding contact. Because of the thermal nature of scuffing, quantities of oxide are usually present and some of the particles may show evidence of partial oxidation, that is, tan or blue temper colors.Many other particle types are also present and generally describe particle morphology or origin such as chunk, black oxide, red oxide, corrosive, etc. In addition to ferrous and non-ferrous, contaminant particles can also be present and may include: Sand and Dirt, Fibers, Friction polymers, and Contaminant spheres.

CHAPTER - 4 A New Technique for Filter Debris Analysis4.1 Introductionop of Form Due to the increasing fineness of filter elements in high-precision machinery lubricating oil systems, monitoring of filter debris analysis (FDA) is gaining increased significance for the early failure detection of moving parts. These considerations led to the development of a new method to recover filtered debris particles efficiently, productively and economically.

Figure.4.1: Typical PST for Solid Debris SeparationMethods for detecting damage to rotating components in high-precision machinery lubricating systems operate on the determination of types, size, shape and concentration of wear particles in the lubricating oil. Detecting still relies on an oil sample. Apart from the oil sampling technique, however, FDA is increasingly growing in acceptance. Filter inspection is a method of long standing, where the chance of detecting damage varies with the method used to recover the particles from a filter element specimen. FDA, in general, can therefore be thought of as consisting of three discrete steps: removal and cleaning of the oil filter, recovery of the removed debris, and examination of the debris. Typically, cleaning of the used oil filter is accomplished by immersing the filter in a suitable solvent and removing entrapped debris by ultrasonic agitation and/or air pulsation.

Figure.4.2: A Filter Element SpecimenMajor drawbacks of conventional FDA are: particle stacking gives an erroneous result, and the method is a fairly cumbersome, time-consuming process. A new FDA approach is proposed in this article. A special particle separating tube (PST) is introduced. Figure 1 shows a typical PST; the component also can be used for separation of solid particles from used lubricants1,2.

Figure.4.3: Particle Separating Tube (PST) for FDA

Figure.4.4: Put the Sample into the PST4.2 Filtersonicgram Maker ProceduresHere is a step-by-step walkthrough of the process.1. Collect a used oil filter (i.e. hydraulic, turbine, engine).2. Remove the filter housing with a suitable tool. (Do not use a hacksaw to open up the housing as the metal saw dust will have a significant effect in the solid debris analysis stage.)3. Cut part of the whole filter element as a specimen (Figure 2).4. Put the filter element specimen into the top chamber of the PST unit (Figure 3).5. Pour proprietary solvent into the PST until the filter element specimen is submerged under the solvent (Figure 4).6. Put the PST(s) into the fixture inside the ultrasonic washing machine (Figure 5).A set of PSTs can be used to extract solid particles in multiple samples simultaneously (Figure 6).7. The samples are now ready to be washed inside the ultrasonic washing machine (Figure 7).8. Operate the washing machine, which has an intensity of the ultrasonic wave approximately at 42 kilohertz for an appropriate duration, which depends on the type of filters i.e. engine oil filter, hydraulic oil filter, turbine oil filter, etc. (Figure 8).9. Switch off the washing machine and take the PSTs out of the unit.10. Up to this stage, the solid particles have been extracted from the used filter element and also have been classified as per their sizes.11. Remove the drain plug to get rid of the unwanted solvent (Figure 9).12. Disconnect each section of the PST and remove the patches which are now ready to be analyzed under an optical microscope or similar device for debris classification and identification by: size; color; shape; edge detail; thickness ratio; surface texture; response to light (reflected or transmitted light); and response to heat ( the wire mesh can be used as a filter patch which can be heated up to certain temperatures, depending on the wire mesh materials). This process can be used to identify fiber, elastomer and alloy composition (i.e. copper, aluminum, tin, lead). Sample slides are shown in Figure 10.13. The patch also can be weighed, which can be used to quantify the extracted debris due to their size ranges.14. Debris morphology can be done in a more comfortable manner as the particle-stacking problem in the conventional filtergram technique (by the conventional vacuum filtration technique) is partly solved.15. The wire mesh patch may be reused, if needed.

Figure.4.5: Typical Ultrasonic Washing Machine

Figure.4.6: Insertion of the PSTs into the Fixture

Figure.4.7: Inside of Washing Machine After the PSTs are Put in Place

Figure.4.8: Utilization of Ultrasonic Washing Machine4.3 A Unique Assessment and Examination ToolFiltersonicgram is a novel method to recover solid particles trapped in filter elements with the simultaneous utilization of ultrasonic wave and a conventional filtration approach. The recovered particles on the multi-patch filters can be assessed with the aid of a microscope or other device. Careful examination of the debris morphology can give specific information about the condition of the moving parts of precision machine elements from which they were generated, and the wear mode and/or wear mechanism in operation in the system from which they were filtered. This technique is at present being tested in the field and it is the field operators who will judge the efficacy of solid debris separation and examination by this technique.

Figure.4.9:. Filtersonicgram Slides Have Been Prepared

Figure.4.10:. Typical Filtergram Slides

CHAPTER 5 An SEM Approach to Wear Debris Analysis5.1 Introduction The Scanning Electron Microscope (SEM)

The SEM is fundamentally an imaging tool, which uses electrons instead of light in order to create highly magnified images. The use of an electron microscope has several advantages over the optical microscope. In the first place, the SEM can provide magnifications far beyond the capability of a conventional microscope and the images have much better depth-of field at high magnification. In addition, the interaction of the electron beam with the specimen causes the sample to emit highly localized signals, such as x-ray photons, which can be monitored with specialized detectors. The energy or wavelengths of these x-rays indicate the elemental composition at the focal point of the beam. The SEM can be especially useful for wear particle studies due to its specificity that is, its ability to characterize a particle population while retaining the distinct characteristics of each particle analyzed. In this way, the size, shape, morphology, and elemental constituents of each particle can be reviewed and can be used for making decisions based on the data generated. When evaluating the trade-offs of using SEM versus conventional wear particle analysis, this specificity must be weighed against the speed and cost of the latter techniques.

5.2 The SEM as Particle Analyzer

Historically, one would perform particle analysis by placing a sample in the SEM chamber, and then sequentially observing fields-of-view at a magnification sufficient to see particles of interest. The operator would then zoom up on each feature and place the beam on the sample to collect an x-ray spectrum to identify the elements. He or she would then tally that information, perhaps take a photograph, and then move on to the next particle. Clearly, this process is slow, tedious, and error-prone, especially as the operator becomes fatigued.With the advent of Computer-Controlled Scanning Electron Microscopy (CCSEM) in the 1970s, the tasks of locating particles within a field and collecting x-ray data was automated using grid location and intensity data. Since then automated sample stages, digital SEM control interfaces, and large capacity disk media have brought CCSEM to the state where most aspects of the analysis can be performed in an automated, unattended manner. This is the case with the Personal SEM (PSEM), produced by Aspex LLC. The PSEM, which was the platform used in this study, is widely used for automated feature analysis on a diverse range of materials from concrete to steel to airborne particulate to forensic Gunshot Residue.However, in spite of the high degree of automation, there is still a significant component of operator set-up required for sample preparation prior to starting the analysis. The location and shape of the sample(s) must be set up, focus and brightness/contrast must be set, and run parameters must be chosen. These run parameters describe the microscope settings, elements of interest, time and size criteria, and other analysis control settings. It requires an individual of at least moderate SEM expertise to perform this setup correctly and repeatably. Once setup however, the setup program can be ported to multiple SEMs performing the same task.

5.3 The SEM as A Deployable Wear-Debris Analyzer:

In order to make the PSEM system perform as a dedicated Wear-Debris analyzer, several design goals had to be achieved:1) The system needed to be capable of being run by field personnel. These individuals would not have had any classical SEM training, and may be using the system on a transient basis, which did not make it cost- or time-effective to provide such training.

2) A summary report needed to be generated for each sample group, while all images, spectra and numerical information needed to be retained in a searchable data repository.3) The entire setup must be packaged for reliable field-deploy ability. The ideal, from the perspective of the SEM particle analysis, would be to remove all microscope set-up steps from the responsibility of the operator, and permit a onebutton start-up. In this way, the operator would simply load his or her samples, enter sample ID information in the database, and tell the system to go. In order to achieve this, the operator-intensive steps needed to be established before routine analysis could be performed:

1) A sample tray was defined based on the size and shape of the sample for example, a filter patch, a chip detector, etc. The samples are placed in the pre-defined areas on the tray. By knowing the characteristics of the sample tray, the stage-setup could be saved to disk once during calibration, and then simply recalled by the computer automatically for each analysis run. Furthermore, multiple sample trays could be defined, stored, and recalled at will for different sample types.

2) Optimum conditions of beam, working distance, brightness and contrast, and focus were calibrated and stored, to be recalled upon the start of a run. As an adjunct to this, automated procedures were designed to fine-tune the beam, focus, and brightness/contrast on a specialized standard sample that was built into the stage mechanism. The PSEM was then configured with an external computer as part of a client-server topology. Resident on this external computer is a database, user interface, and PSEM interface module. The user interacts with this computer to enter sample identification information in a menu-type interface, and then clicks a button to initiate the analysis. The database computer passes the setup information to the PSEM, and instructs it to begin the analysis. The PSEM can then recall all the pre-programmed calibrations and automatically executes the analysis. Thus our non-traditional operator need not interact with the microscope controls to start a run. As the analysis proceeds, all data is shipped immediately to the database computer, where it is processed and stored. When the analysis is complete, the database creates a summary report, which will indicate pass/fail conditions based on pre-programmed criteria, along with a summary of particle types found.

Figure.5.1: Block Diagram of System ArchitectureFor most purposes, this is the end of the analysis, and the operator can load new samples and start the process again. If, however, there is an anomaly that warrants further investigation, the database can be queried to display individual particle images and spectra as well as data tables. Since the data and images are in electronic form, they can be shared to remote locations with scientists and engineers to whom particle shape and composition may provide insights, which are not readily discernible in the summary report. Thus we may preserve the essence of the SEM its imaging capability while providing a streamlined process for routine analysis and simplified distillation of results.

Figure.5.2: Physical Configuration of System5.4 Advantages ofFerrography By monitoring particles generated by wear or environmental contamination, Intertek ferrography experts are able to to detect the critical stage of accelerated wear that precedes costly and dangerous component failures. Ferrographic analyses determines the number, size and shape of wear particles5.5 Application5.5.1 Clinker hammer crusherThe clinker hammer crusher is one of the main pieces of equipment in cement production and is used for the crushing of clinker, the main product of cement kilns, into smaller parts for the preparation of grinding. At CEMEX Egypt, the bearings used in the clinker crusher are spherical roller bearings. These bearings are lubricated with a lithium complex thickened grease with a synthetic base oil designed for high-temperature applications.

Figure.5.3: Clinker Hammer CrusherAt the CEMEX plant, bearing failures can lead to a halt in cement production. To maintain continuous operation, it is critical for the bearings to operate smoothly. As part of the predictive maintenance program, vibration analysis is used to monitor the condition of the crusher. A grease sample to analyze wear debris was taken at the first shutdown of the clinker crusher as part of a new program to monitor the performance of equipment. Vibration monitoring of the outboard bearing in the third clinker crusher line at a speed of 360 RPM provided no warning signals. During the next scheduled shutdown, the bearing was opened and a sample of grease was taken. Wear debris analysis was performed on the grease sample to find the cause of the bearing failure that occurred.

Wear debris analysis was carried out on used greases by extracting magnetic particles from the sample using a magnet. Microscopic analysis of the sample identified numerous small and large spherical particles. Research has shown that spherical wear debris can reveal the severity of rolling-contact fatigue wear. Because large spherical particles (50 microns) are the product of high metal-to-metal contact and high frictional temperature, their presence is considered a supporting symptom for assessing the wear severity levels.

Figure.5.4: 52ZM Stereoscopic Zoom MicroscopeWear particles were considered to be a critical alarm indicating the need to change the bearing before a forced outage occurs. 5.5.2 Follow-up Inspection:- During shutdown, the crusher's outboard bearing was replaced. To check for potential defects, the bearing was opened and visually inspected. A close look of the outer race of the defective bearing showed signs of severe wearing. Figure.5.4: Large and Small Spherical Particles Found in a Bearing Grease Sample

Figure.5.5: Defective Bearing Shows Signs of Severe WearThis case study illustrates the efficiency of condition monitoring based on the detection of debris in grease, which can be a resourceful tool in controlling machine condition and should integrate diagnostic devices. 5.5.3 Aircraft Gas TurbinesAircraft and aircraft-derivative jet engines are subject to various failure mechanisms. Some of these failure modes proceeded very rapidly, whereas others can be detected hundreds of operating hours before a shutdown condition is reached. Most failures of gas turbines occur in gas path. Gas-path failures frequently, but not always, cause an increase in wear particle size and concentration in the oil system, probably due to the transmittal of imbalance forces to turbine bearings and other oil-wetted parts. The resulting bearing or gear wear is then detected by both Used Oil Analysis and Wear Particle analysis.Determining the exact source of wear problem can be difficult in a gas turbine because of complexity of the oil-wetted path. Typically several cavities, housing bearings, or gears will be force lubricated through individual return lines connected to a tank from which the oil is pumped (at a high rate), then pass through a filter and heat exchanger, and the cycle repeated. Magnetic chip detectors or magnetic plugs are often installed in the return lines from various engine parts. These can help to pinpoint the source of generation in cases where particle metallurgy, as determined by heat-treating ferrograms, is similar for various engine parts. However, chip detectors will not give a warning until the wear situation is so severe that extremely large particles are being generated. By this time, the opportunity for predictive maintenance may be lost. Other analytical techniques, such as vibration analysis, may help to pinpoint the part in distress utilizing expert system software that provides recommendations for action. In any case, predictive maintenance tools integrated together offer the maintenance engineer the best decision making tool.5.5.4 Monitoring Wear Debris (Ferrography) Analysis - Maintain Equipment & Reduce Downtime

Wear Debris Analysis (Analytical Ferrography) is a method of predicting the health of equipment in a non-intrusive manner by studying the wear particles present in the lubricating oil. The continuous trending of wear rate monitors the performance of machine components and provides early warning and diagnosis of worn parts.This technique can diagnose active machine wear earlier than using vibration techniques, enabling the replacement of key components before any serious damage occurs. Therefore, production can be maintained, machinery life extended and the return on capital investment increased.

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CHAPTER - 6 ConclusionThe benefit of automation is in the use computer programs and emerging software technologies of artificial intelligence to assist in determining when to remove equipment from service for maintenance. These case histories provide a real world scenario that indicates its not that easy to put artificial intelligence to make maintenance decisions. However, this does not mean we do not try. For example, an advanced system, which integrates emerging technologies in vibration, motor current analysis, Thermography, ultrasonic, electronics, microprocessing, graphics, and data management, could regularly sample a number of machines. From a sampling device, compare the samples to previous samples for trend information (along with other Data parameters), make the decision to schedule the machine for maintenance, generate a work order for the maintenance team and send a purchase/work order to accounting for needed repair parts. The maintenance manager/engineer could have almost instantaneous reports on the condition of each machine, along with a dollar figure indicating the optimal dates for shutdown and other maintenance requirements, basically, a financial decision.Technology advances oriented toward maintaining and incorporating all production data serve as an efficient assessment of manufacturing equipment. Companies as we know it today can ill afford any shutdowns what so ever due to a tremendous amount of re-engineering or downsizing occurring worldwide. Therefore, predictive maintenance tools working in conjunction with production efficiency, analyzed through a cash flow model are the decisions making tools of today and tomorrow.

REFERENCES

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4. www.encyclopedia.com

5. System and Method for Filter Debris Analysis, International Patent Application (PCT) Number PCT/SG2009/000465, date of filing December 3, 2009.

6. An Apparatus and Method for Particle Analysis, International Patent Application (PCT) Number PCT/SG2009/000264, date of filing July 27, 2009

7. Sabrin Gebarin and Jim Fitch. "Origin of Spherical Particles in Lubricants." Practicing Oil Analysis magazine, March 2005.

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