Wear particles

Water plays a primary role in corrosion of the metal walls of tanks and pipes (17), and increases the tendency for high speed pumps to produce wear particles and to exhibit shortened life. Formation of corrosion products can be controlled by addition of corrosion inhibitors, a mandatory additive in military fuels. However, corrosion inhibitors may also degrade other fuel properties and adversely affect ground filtration equipment. Thus they are not generally acceptable in commercial fuels where rigorous attention is given to clean and dry fuels upon aircraft fueling. 

Ceramic ball beatings are also sometimes effective ki operation with water which would result ki rapid failure with steel beatings. This capabiUty may result from a thin hydrodynamic film formed from very small hydrated Si N wear particles and the water (44). 

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. 

Particle count tests are important to anticipating potential system or machine problems. This is especially true in hydraulic systems. The particle count analysis made a part of a normal lube oil analysis is quite different from wear particle analysis. In this test, high particle counts indicate that machinery may be wearing abnormally or that failures may occur because of temporarily or permanently blocked orifices. No attempt is made to determine the wear patterns, size and other factors that would identify the failure mode within the machine. 

Wear particle analysis is related to oil analysis only in that the particles to be studied are collected through drawing a sample of lubricating oil. Where lubricating oil analysis determines the actual condition... 

The first method used for wear particle analysis is routine monitoring and trending of the solids content of machine lubricant. In simple terms the quantity, composition and size of particulate matter in the lubricating oil is indicative of the mechanical condition of the machine. A normal machine will contain low levels of solids with a size less than 10 microns. As the machine s condition degrades, the number and size of particulate matter will increase. 

Lubricating oil samples from all equipment included in the program should be taken on a monthly basis. As a minimum, a full spectrographic analysis should be conducted on these samples. Wear particle or other analysis techniques should be made on an as-needed basis. 

Although the term fretting corrosion implies chemical reaction, it has often been used even when the latter is absent. Campbell has suggested that to avoid confusion the word fretting be used to describe the wear process, and that the expression fretting corrosion be applied in those cases where one or both of the surfaces, or the wear particles from them, react with their environment. 

Wypych, P. W., and Arnold, P. C., Minimising Wear Particle Damage in Pneumatic Conveying Systems, Powder Handling Processing, 5(2) 129-134(1993)... 

Figure 14.6. Approaches to optical in situ sizing of contaminant and wear particles with (a) an external counter (b) an internal counter (c) two concentric beams (d) a single beam. (From Ref. 9, with permission from CRC Press.)...

Chemical analysis may he applied to a material in hulk usually to determine if it has met product specifications. Chemical analysis can also he conducted on individual phases in a material, deposits on a surface, or wear particles. Most of the chemical analysis techniques are used to identify or quantify elements, ions, or functional groups, ft is also very useful in many cases to identify and quantify compounds. 

Optical examination of etched polished surfaces or small particles can often identify compounds or different minerals hy shape, color, optical properties, and the response to various etching attempts. A semi-quantitative elemental analysis can he used for elements with atomic number greater than four by SEM equipped with X-ray fluorescence and various electron detectors. The electron probe microanalyzer and Auer microprobe also provide elemental analysis of small areas. The secondary ion mass spectroscope, laser microprobe mass analyzer, and Raman microprobe analyzer can identify elements, compounds, and molecules. Electron diffraction patterns can be obtained with the TEM to determine which crystalline compounds are present. Ferrography is used for the identification of wear particles in lubricating oils. 

Adhesive wear is characterized by transfer of material from one material to another during sliding as a result of the adhesive forces at the contact points. The transferred material accumulates until the surface forces cause wear particles to form 50). Because the rate at which polymeric material transfers depends on the bonding at the contact point — Coulombic and van der Waals — adhesive wear is usually small compared... 

The initial and steady state wear rates of the siloxane-modified epoxy pins on the steel disks correlated with the inverse of the KIC values which agrees with previous abrasive wear tests 47>. The steady state wear rates on the smooth glass disks were comparable to those on the steel disks. Thus in both cases the wear mechanism is abrasive wear by the wear particles trapped in the interface between the pin end and the disk. 

Road transport is an important contributor to primary emissions of PM (soot, wear particles and road dust) and also a source of secondary particles formed by condensation of gaseous species (mainly S- and N-compounds and organics) emitted by the tailpipe and partly also by the wear of brakes and tyres. Thus, PM emissions from road traffic are responsible for an important proportion of the exceedances of the PM10 and PM25 Air Quality Limit Values established by the European legislation for the protection of the human health (2008/50/EC [17]). The daily (50 pg m-3) and annual (40 pg m 3 ) limit values for PM10 (atmospheric particles with mean aerodynamic diameter <10 pm) and the annual limit value for PM2.5 (25 pg m-3) (in force from 2015) concentrations in ambient air are indeed exceeded mostly in the urban areas (Fig. 1 [17]). 

Wear emissions comprise abraded particles from brake linings, tyres and road pavement. Details on chemical and physical properties of wear particles can be found in Thorpe and Harrison [3]. Kousoulidou et al. [151] showed clear evidence that non-exhaust sources become increasingly important as no emission control strategies are taken by Member states. Among them, road pavement wear is... 

Gietl JK, Lawrence R, Thorpe AJ, Harrison RM (2010) Identification of brake wear particles and derivation of a quantitative tracer for brake dust at a major road. Atmos Environ 44 (2) 141-146... 

Similarly, different results have been found for the impact of brake wear particles. While unequivocally a strong enrichment of brake-related chemical trace elements (Sb, Ba, Cu) is found at trafficked sites [63], the quantification of overall PM contribution from brake wear is associated with uncertainties. An even wider range of emission factors was found for re-suspension of road dust (cf. Table 4). It should be noted that re-suspension may be a strong source of PM during wintertime when de-icing salt is spread out. For a traffic site in southern Germany exceedance of the daily PM limit value could be tracked back to road salting in 12 of 43 cases [66]. 

Fretting wear is observed in systems where two surfaces perform an oscillatory relative sliding with small amplitude (= fretting). This is often due to vibrations. In principle the same wear behavior as for normal sliding, should occur. However, wear particles tend to remain within the immediate contact region where they can act as an abrasive and lead to increased wear. 

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