Mechanical wear

Beside adhesive and abrasive wear, two other wear mechanisms must be mentioned  

A direct relationship is found between the hardness of a material and its ability to withstand mechanical wear, and as a rule the harder the material, the greater is its wear resistance. A related factor is that harder materials usually take a better polish and, as a result, the wear due to surface roughness mentioned above can be minimized. Choosing material combinations with a low coefficient of friction is also an important factor in reducing mechanical wear. 

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Copper and silver combined with refractory metals, such as tungsten, tungsten carbide, and molybdenum, are the principal materials for electrical contacts. A mixture of the powders is pressed and sintered, or a previously pressed and sintered refractory matrix is infiltrated with molten copper or silver in a separate heating operation. The composition is controlled by the porosity of the refractory matrix. Copper—tungsten contacts are used primarily in power-circuit breakers and transformer-tap charges. They are confined to an oil bath because of the rapid oxidation of copper in air. Copper—tungsten carbide compositions are used where greater mechanical wear resistance is necessary. 

Porosity ranks next to thickness in importance, especially when the finishes must serve in polluted and/or humid environments which promote tarnish and corrosion. Pores, openings in the surface that extend to the underplate or substrate, can be intrinsic in the coating (14), or can be produced by mechanical wear or by forming operations involved in manufacturing. In some environments the substrate can tarnish or corrode at pore sites and can produce localized areas of insulating films which cause contact resistance to increase. Porosity is less important for connectors that operate indoors at moderate to low relative humidities and in the absence of corrosive pollutants (15). 

Mechanical. Premature wearout or loss of contact metal during engagement and separation can result in loss of tolerances, reduced spring forces, formation of loose metallic wear debris, which may short-circuit contacts, and development of porosity in noble metal contacts. Underplatings, contact lubricants, and hard materials reduce mechanical wear. 

Quahtative simulation is a specific KBS model of physical processes that are not understood well enough to develop a physics-based numeric model. Corrosion, folding, mechanical wear, equipment failure, and fatigue are not easily modeled, but decisions about them can be based on qualitative reasoning. See Refs. 178 and 292. 

Sufficient strength to support the filtering pressure Acceptable resistance to mechanical wear Abihty to discharge cake easily and cleanly Abihty to conform mechanically to the land c it will be used... 

Localized deterioration Corrosion (especially pitting and intergranular attack), erosion, cavitation, mechanical wear, and so on (see Case History 9.8). 

Frequent disas-sembly/assembly of equipment increases mechanical wear resulting in possible loss of containment. 

Elimination of mechanical wear, which essentially provides unlimited bearing life. 

Maintenance costs can be minimized by, and are directly related to, good operation likewise, better operating results can be obtained when the equipment is under the control of a planned maintenance program. Improper operation of mechanical equipment can be as much or more the cause of its deterioration and failure as is actual, normal mechanical wear. Thus, operation and maintenance go together. 

Have sufficient strength to withstand filtering pressure and mechanical wear,... 

Insulation should be protected by sheet-metal jacketing from weather, oil spillage, mechanical wear, or other damage. 

The increasing demands being made on equipment by the requirement for increased output from smaller units create problems of lubrication, even in systems where full-fluid film conditions generally exist. For instance, at start-up, after a period of rest, boundary lubrication conditions can exist and the mechanical wear that takes place could lead to equipment failure. Anti-wear additives, by their polar... 

In using metallic Pb as an anode the formation and maintenance of a hard layer of PbOj is essential, since it is the PbOj that is the actual inert anode, the Pb acting both as a source of PbOj and an electrical conductor. PbOj is relatively insoluble in seawater and its dissipation is more usually associated with mechanical wear and stress than electrochemical action. 

Excessive soot or deposit buildup and acidic cold-end corrosion may occur on the fireside of economizers. Soot blowers can fail due to mechanical wear. 

Pressure-reducing stations, orifice plates, pitot tubes, and steam meters may all suffer from excessive mechanical wear and may therefore malfunction. 

Handbook of Chemical Vapor Deposition 2.1 Mechanical Wear... 

Corrosive wear results from a chemical reaction of the wear surface with the environment. In this section, only corrosion that occurs in conjunction with mechanical wear is considered. Purely corrosive wear is reviewed in Sec. 4.0 below. The chemical resistance of a given coating material must be assessed if the application involves a corrosive environment. A typical example is the environment found in deep oil and gas wells (over 500 m.), which usually contain significant concentrations of CO2, H2S, and chlorides. The corrosive effect of these chemicals is enhanced by the high temperature and pressure found at these great depths. 

Ahmadi, G. and Xia, X., "A Model for Mechanical Wear and Abrasive Particle Adhesion During the Chemical Mechanical Polishing Process," Journal of the Electrochemical Society, Vol. 148, No. 3,2001, pp. G99-G109. 

The stamp associated with the extreme hardness values (number 7, Fig. 4.12, left use STAMP.dat with program MULTI) is the next suspect It is identified and inspected on disassembly of the tablet press Due to mechanical wear, the movement of the stamp assembly is such that an above-average amount of granulate drops into cavity number 7, and is thus compressed to the limiting hardness supported by the granulate. The hardness for stamps 4, 8, and 11 tends to be low, and high for 12, but the data is insufficient to come to definite conclusions for these tools. The tablets from these stamps contaminated what would otherwise been a fairly acceptable product. Because... 

High attrition resistance (resistance to mechanical wear). 

Mechanical wear-and-tear (osteoarthritis [or, more correctly, osteoarthropathy])... 

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