Wear particles methods

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. 

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. 

In order to get information on wear mechanisms, it is necessary to complement the determination of wear volume by a structural characterization of the worn surface. Friction and wear cause characteristic changes of surface topography and of the microstructure in a thin zone below the rubbing surface, which can give information on prevailing wear mechanisms. Additional information is obtained by an analysis of the size and composition of the wear particles. Electron microscopy (SEM, TEM) and surface analysis methods (AES, XPS, etc) are generally used for this purpose. 

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. 

The diameter of wear particles formed by sliding methods have been related to hardness through equation (1.53) ... 

Slouf M, Sloufora 1, Horak Z, Stepanek P, Entlich G, Krejcik M, Radonsky T, Pokomy D, Sosna A. New Fast Method fo" Determination of Number of UHMWPE Wear Particles. J Mater Sci-Maler M. 2004 15 1267-78. 

Fang H-W, Ho Y-C, Yang C-B, Liu H-L, Ho F-Y, Lu Y-C, et al. Preparation of UHMWPE particles and establishment of inverted macTc hage cell model to investigate wear particles induced bioactivites. J Biochem Biophys Methods 2006 October 31 68(3) 175-87. 

Slouf et al. [37] reported a novel automated quantitative analysis technique, SEMq, which was based on a light scattering theory. In this method automated image analysis of electron micrographs is used to determine the total amount of wear particles released into the tissues around total joint replacements. This technique was shown to provide rapid, reliable, and reproducible results, which indicated that the distribution of wear particles around TJRs is nonhomogeneous [37]. However, this technique does not calculate absolute numbers of wear particles but rather determines relative numbers of wear particles in one sample compared to another. The technique may also be sensitive to errors introduced by particle cliunping and protein contamination of filters used for SEM analysis. 

It has been recognized that a standardized method of particle retrieval from the tissues and simulator lubricants, followed by debris characterization and quantification, is required for a uniform approach to debris response investigations. However, there are a number of different standards available from the British Standards Instimtion (BSI), International Organization for Standardization (ISO), and the American Society for Testing and Materials (ASTM), which currently offer conflicting advice for isolation of wear particles from periprosthetic tissues and simulator lubricant samples. 

The osteolytic potential of the wear particles generated in the hip and knee simulators was predicted using the method of Fisher et al. [61] to calculate functional biological activity (FBA) as previously described. The values of SBA and FBA were compared for the wear particles from the two UHMWPEs in both the hip and knee simulations. 

Baxter R, Steinbeck M, Tipper J, Rimnac C, Parvvizi J, Marcolongo M, Kurtz S. Evaluation of methods for periprosthetic tissue digestion and polyethylene wear particle analysis. Transactions... 

A method for calculating temperature, fiiction and working life of dry rubbing bearings that is based on theoretically and experimentally established data is offered afterwards. In addition the positive effect of a wear particle trap is demonstrated. Finally, calculation examples show the mode of operation of the calculation method. 

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. 

Methods of dust removal depend mainly on the particle size of the dust and the temperature and moisture content of the gas. The methods used are broadly divided into dry methods and wet methods. The dry methods involve the use of gravity and baffle chambers, cyclones, filters, and electrostatic precipitators, while the wet methods involve the use of spray towers and venturi scrubbers. In principle, wet cleaning is preferred to dry cleaning because of the excessive wear associated with and the difficulty in handling the fine dusty material removed in the dry methods. The wet methods, however, must be followed by such operations as filtration, drying of filter cakes, and recycling of water. 

Meial Mairix Composites. Silicon carbide particles are contributing to easy-to-cast metal-matrix composites (MMCs). When compared with their non-reinforced counterparts, the SiCp/Al components are more wear resistant, stiffer, and stronger, accompanied by improved thermal stability. Additional advantages include lower density and lower cost. Nearly all prior aluminum MMCs required labor-intensive methods, such as powder metallurgy, diffusion bonding, squeeze casting, or thermal spraying. 

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