Friction Performance

Unlike traditional textbooks of tribology, in this book we regard boundary lubrication as a limit state of hydrodynamic lubrication when film thickness is down to molecular dimension and independent of the velocity of relative motion. The discussions are based on the existing results, some from literatures but mostly from the authors own work. The topics are mainly focused on the mechanical properties of boundary films, including rheology transitions, molecular ordering, and shear responses. Ordered molecule films, such as L-B films and SAM, are discussed, with emphasis on the frictional performance, energy dissipation and the effects from structural features. Boundary films can be modeled either as a confined substance, or an adsorbed/reacted layer on the... 

Fig. 12—Friction force versus normal load, measured on SFA, illustrating the transition in frictional performances before (curve 1) and after (curve 2) mica films are damaged.

In contrast to normal diffusion, Ar2n does not grow linearly but with the square root of time. This may be considered the result of superimposing two random walks. The segment executes a random walk on the random walk given by the chain conformation. For the translational diffusion coefficient DR = kBT/ is obtained DR is inversely proportional to the number of friction-performing segments. 

Fig. 7 Effect of crystallographic growth orientation on friction performance of CVD diamond films.

Carbon fibers are also of interest as replacements for asbestos fibers in friction materials, such as brake shoes (221. This move was initially driven in order to avoid the health hazards associated with asbestos. In comparison to asbestos reinforced brake formulations, isotropic carbon fibers have been shown to provide much higher friction performance and superior wear resistance, together with many advantages in operating characteristics. These advantages translate to other friction materials, such as clutch plates, and to a much broader range of applications in which carbon fibers are used as reinforcing or filler materials in various matrices. Carbon fibers in the forms of mats, felts, and paper insulation also present viable replacements for asbestos fibers. 

A typical standard friction performance (effectiveness) test for a passenger car brake usually includes the following measurements green and burnished effectiveness thermal fade and recovery speed, pressure, and temperature sensitivity water fade/recovery moisture sensitivity cold and static friction. These aspects of friction performance are discussed elsewhere in some detail. " The performance of an ideal friction material will be immune to changes in braking conditions. 

Each specification is specific to each OEM, but it is possible to have one product that meets more than one specification. The specifications for these fluids in general deal with extreme pressure, EP, and antiwear properties and also with matching the frictional requirements of the equipment. The quality of these fluids is assessed on the basis of their ability to meet individual OEM specifications as well as API GL-4, for EP, Allison C-4, for friction, oxidation, and wear, and Caterpillar TO-4, for friction, performance requirements. 

One of the most important properties of driveline fluids is their frictional performance in terms of both the level and durability. The fluid also has to be compatible with the components inside the transmission. Optimizing the frictional characteristics of a fluid for a particular application is absolutely critical to ensure trouble-free operation of the equipment, whether it be an automatic gearbox, synchronized manual gearbox or the wet brake system in a tractor. The problems that can be encountered are ... 

Fig. 10.9 Good frictional performance when clutch closes, fls < /t-d...

Limited slip differentials contain clutch plates, which require the correct friction performance to prevent noise and squawk . 

Chen, 1. Y, Yang, K.-S., Wang, C.-C. (2002). An empirical correlation for two-phase frictional performance in small diameter mbes. International Journal of Heat and Mass Transfer, 45, 3667-3671. 

MatSjka V, Lu Y, Fan Y, Kratosova G, Leskova J. Effects of sihcon carbide in semi-metallic brake materials on friction performance and friction layer formation. Wear 2008 265 1121-8. 

Victrex pic, Bearings made of Carbon Fibre Reinforced VICTREX PEEK Polymer Improve Wear and Friction Performance , Press release, 29 March 2011. Available at http //www.victrex.com/en/victrex-hbrary/press-releases/detail/detail. php id=663. Accessed 29 July 2011. 

The presence of treated betelnut fibers in the matrix improved the wear and frictional performance of polyester, that is the average wear and friction coefficient was reduced by about 54 and 95% respectively under wet contact conditions compared to the dry. 

Nirmal, S. G. and Yousif, B. F. (2009). Wear and frictional performance of betelnut fiber-reinforced polyester composite. Proceedings of the Institution of Mechanical Engineers, Part J Journal of Engineering Tribology 223(2), 183-194. 

The degree of wear/friction improvement depends on the particular plastic to which the PTFE is being added [41], As examples, the above referenced study showed that the addition of 15% low MW PTFE to a 6/6 polyamide, a polyacetal resin, and a polycarbonate reduced the specific wear rates by 97%, 46%, and 97%, respectively. The dynamic friction coefficients were reduced by 76%, 48% and 97%, respectively. Although these are reasonable comparisons, wear and friction performance can depend on the exact contact conditions such as velocity, pressure, and countersurface composition. Commercial compounds of thermoplastics with PIFE will vary depending on the application requirements but an addition level of 15-20% is usually considered optimum for the best wear performance. 

Improved evenness of finish coverage and better friction performance have given benefits in several nonwoven applications ... 

Frictional performance of the newly synthesized ionic iiquid iubricantwith ammonium salt for magnetic media... 

In mechanical engineering, POM is used because it is extremely dimensionally stable, with good sliding friction performance. It is also non-corroding, and has very low friction and wear, making it particularly effective for conveyor belts. It has exceptional resilience and excellent recovery, making it ideal, for example, for use in clips and snap connections. 

For the performance of tribological contacts the important parameters in terms of achieving fuel economy are friction and wear. ZDDP is most commonly used as an anti wear additive plus it often has anti-oxidation properties [1]. The effect of ZDDP on friction performance is often complicated. In the literature, there have been reports where ZDDP formulated lubricants produced higher friction than lubricant formulations without ZDDP [12-16]. Holinski [12] used the Bartel lubrimeter which was designed to test gear oils under boundary conditions. He investigated the effect of boundary layers formed from different additives on friction and wear, and found that when the lubricant is... 

In summary the main points relating to the friction performance using EN31 plates are ... 

---