19-07-2014, 02:22 PM
SELF LUBRICATING PLAIN BEARING. A REVIEW
SELF LUBRICATING.pptx (Size: 144.95 KB / Downloads: 19)
Abstract
Modern high performance ceramics and composites offer the potential for a significant increase in many of the performance characteristics especially self-lubricating of both rolling and sliding contact bearing
To review the potential benefits of ceramics and composites and provide the selected examples where these benefits have been demonstrated in research and development programs. The emphasis will be on the plain bearings.
To review the desired properties for self lubricating bearings and the properties of currently available high performance ceramics and composites with self lubricating properties
Introduction
Mechanical systems are composed of triboelement like bearing, gears etc. it has been observed that most of the failure in mechanical system are tribological. The causes for failure due to friction, wear and lubrication are attributed to poor tribological properties of materials. Mostly one of the important triboelement in the mechanical system is plain bearing .
Model of self lubrication was stated by Bragg in 1928 to explain the lubricating properties of MoS2 which is a classic example of solid with lubricating properties
The reason for selecting self lubricating bearings is the necessity to cope with hostile environment. Self lubricating bearings retain their load carrying capacity at high temperatures. They can operate where rolling element bearings fail due to fatigue and where conventional lubricants oxidize rapidly
Graphite and Molybdenum disulphide offer a superior lubrication performance and therefore these two lubricants have been much more extensively investigated than the others.
According to Gwiden, the tribological characteristics of lubricating films of graphite and MoS2 are very similar .MoS2 is used in many industrial applications because of its good lubricity, abundance, and low cost
Results
Showed that the composite A exhibited low coefficient of dry friction and long wear life as compared to that of the composite B. It was found that the surface of PTFE composite was higher than that of steel backing at the intervals of testing. This was because modulus of the elasticity of PTFE composite was much lower than that of 16 MnNb steel backing; under a same load condition the elastic deformation amount of PTFE composite was much bigger than that of steel backing. Thus, the composite A provided sufficient lubrication during the whole tests.
Hirotaka Kato, Masahiro Takama, Yoshiro Iwai , Kazuo Washida, Yoshinori Sasaki, “Wear and mechanical properties of sintered copper–tin composites containing graphite or molybdenum disulfide,” Wear 255 (2003) 573–578.
Results:-
Mechanical properties of the composites decreased with increasing amount of added graphite or MoS2, the use of Cu-coated lubricant powders improved the bending strength. Graphite was very effective in reducing the wear and friction of the composites. Particularly, the 40 vol.% graphite composites showed a very low coefficient of friction of 0.15.
Furthermore, the wear rate of the coated graphite specimens was much lower than that of the uncoated graphite specimens.
Conclusion
Graphite and Molybdenum disulphide offer a superior lubrication performance and therefore these two lubricants have been much more extensively investigated than the others.
The major point of this paper is that the significant potential of self lubricating bearings will require a major effort in manufacturing science and technology in order to be realized .because such an effort must be highly focused and will require a large expenditure for any given material to be developed.