Wear particles measurements

Science of rotor-bearing-support system design and operation. Predictive maintenance technique that uses spectrographic, wear particle, ferrography, and other measurements of the lubricating oil as a diagnostic tool. 

The particulates of interest include hard sand, dirt and wear particles that are of the same size range as the machine oil clearances. The debris is generally in the range of 2-10 p,m. These particulate sizes cause most damage and often result in component failure. For acceptable oil performance and reliability, particulates in the oil must be periodically measured, evaluated and when appropriate, removed by filtration. 

The RFS technique is used as a comparative method due to the unavailability of oil standards with known gravimetric concentration of particles for each element measured by the spectrometer. In practice, a used oil sample is first analyzed using the standard RDE technique, which provides an analysis of dissolved and small wear particles. A second analysis of the same sample using the RFS technique detects large particles. The two analyses provide an indication of the wear particle size distribution in the sample. A sudden presence of large wear particles will not be seen by conventional analysis alone. Their presence, however, will be readily evident throu the RFS analysis. 

Polyimide Wear. A unique feature of the results was the initial period during which no measureable wear occurred. This feature occurred because the contact stresses were below the magnitude required to generate wear particles when sliding commenced. Hence, multiple stress cycles were required to cause wear particles to form This phenomenon is called fatigue wear. 

Oil in machines carries the products of deterioration resulting from wear and mechanical failure. Analyzing the oil resident in a machine or the debris the oil carries allows predictions to be made about the state of health of the machine. The critical measurement reflecting the condition of machine wear is the number of microscopic metal wear particles that are suspended in the oil system of the machine. The spectrometric oil analysis process is a laboratory technique that uses various instruments to analyze a used oil sample from a machine. The spectrometric result is compared to a baseline level of metal found to be typically suspended in the oil under normal operating conditions. When the wear is meaningful, the sample will show high levels (in parts per million) of wear metals compared to the baseline oil sample. 

The use of crosslinked polyethylene in knee replacements is still relatively new and there are few studies into the wear occnrring in vivo. Iwakiri et al. (2009) measured the number of wear particles contained in synovial fluid removed from the knee joint of patients with a total knee replacement the implants in each patient were the same design, bnt the bearing surface in four knees had a crosslinked polyethylene insert, whereas three knees had an insert made from conventional UHMWPE. The number of wear particles was less for the crosslinked polyethylene insert (0.28 x 10 ) compared with the conventional UHMWPE insert (6.87 x 10 ). Rohrl et al. (2007) measured the penetration of the femoral head into acetabular sockets manufactured... 

The described behavior of wear particles complicates the interpretation of electrochemical tribocorrosion experiments. In principle, the measurement of anodic current or charge permits one to identify the contribution of corrosion to the overall material loss from the rubbing metal surface. However, the electrochemical oxidation of metallic third body particles that are in electrical contact with the rubbing surface also contributes to the anodic current, although these particles were formed by mechanical wear [14]. To distinguish between electrochemical and mechanical metal removal mechanisms in tribocorrosion one therefore must take into account the behavior of third body particles. 

A further complication arises if cathodic reactions take place in the contact zone or in its vicinity because in that case the actual oxidation rate in the contact zone exceeds the measured anodic current. The measured current /measured is th sum of the partial anodic current 4, which represents the oxidation rate in the contact zone, and the (negative) partial cathodic current 1 /measured = 4 + /c- Electrochemical methods are powerful tools for the smdy of tribocorrosion mechanisms in sliding contacts, but they must be complemented by structural and chemical investigations of wear particles and worn surfaces. 

Figure 2.3 Wear particles after friction between steel and M0S2 coatings, containing two superimposed stackings in incommensurate conditions (angle of 30° measured on optical diffractograms). Reprinted with perimssion from Martin et al. [6], Figure 4, (1993) by the American Physical Society...

Figure 3.30 HRTEM of a wear particle, (a) Maghemite nanoparticle observed under a [1, —1, 0] azimuth. Distances measured on the calculated diffractogram d = 4.85 nm ) are in good agreement with the theoretical magnetite structure observed under a [1, -1, 0] azimuth, (b) Intact carbon onions are observed...

Determining the volumetric concentration of wear particles in each size range for each material or device and then integrating these values with the biological activity function for UHMWPE allows the SBA for each material or device tested to be determined. The SBA can then be integrated with the volumetric wear rate (in mmVmillion cycles) to give a measure of functional biological activity (FBA),... 

This combination of single asperity wear testing, surface deformation mapping of the resultant deformation field, and the subsequent indentation test measurements of the changes in mechanical properties due to the wear process will provide detailed and significant information of the interrelationships between wear, structure, and property evolutions. These observations may also help discern the fundamental deformation mechanisms that result in wear particle formation and how different UHMWPE starting materials evolve with wear deformation. 

The volume of the wear particle trap must be designed such that the wear particles from the overall contact zone can be collected. As a rule, the volume can be calculated from the radian measure of the contact angle, multiplied by the bearing width and the permissible wear height. 

The choice of method from available resources depends largely upon the properties of the material to be analyzed, the basic significance or physical wearing of the measurement, and the purpose for which the information is required. For example, failure to disperse the particles as discrete entities is the biggest single problem in all size analysis methods that depend on individual particulate behavior. With microscopic techniques particles must be dispersed on the slide to permit observation of individual particles, and in sedimentation techniques the material must be suspended in the fluid so that the particles behave as individuals and not as floes. 

Abstract Gaseous and particulate emissions from vehicles represent a major source of atmospheric pollution in cities. Recent research shows evidence of, along with the primary emissions from motor exhaust, important contributions from secondary (due to traffic-related organic/inorganic gaseous precursors) and primary particles due to wear and resuspension processes. Besides new and more effective (for NO emissions) technologies, non-technological measures from local authorities are needed to improve urban air quality in Europe. 

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