الفهرس 
Chapter One: IntroductionOnly 14 pages are availabe for public view
 |  | from | 122 |  |  |
| | | from | 122 | | |
Abstract
Friction and wear between bearing surfaces are important reasons for failure of mechanical parts. Over the past decade, the search for the new additives with excellent friction and wear values has attracted considerable interest. One example of such materials is Nano-scale material. In this research, with and without additives, the tribological properties of lithium grease which contaminated by sand particles are discussed, sand particles varying from 0 to 25 wt. %. Graphene Nano particles dispersing lithium grease are used as lubricant filler, Nanoparticle filler fractions, varying from 0.2 to 0.8 wt. %, are homogeneously dispersed within lithium grease. Graphene addition is aimed to reduce the effect of sand particles on friction coefficient and wear of steel test specimens. Also, addition of 20 wt. % of synthetic oil and 10 wt. % micro particles of thermoplastic polymers to lubricating grease are discussed.
Experiments are carried out using a cross pin tester. Experimental results show that, adding 0.4 wt. % graphene Nano additive to lithium grease gives good anti-friction and wear resistance performances. After adding micro particles of polymers to the graphene film, two different results endorsed. Friction and wear decreased after adding 10 wt. % of Polyamide (PA) and Polymethylmethacrylate (PMMA), which earn positive charges when rubbing steel surface according to triboelectric phenomenon. This phenomenon helped to scatter the sand particles which earned the same positive charges. As for Polyethylene (PE) and Polytetrafluoroethylene (PTFE), earn negative charges when rubbing steel surface, made adverse results, where sand particles are attracted to steel surface. Besides, the results indicate that lithium grease should be dispersed by 20 wt. % oil to balance the effect of contaminant. As the oil content, added to the grease, increases friction coefficient and wear decreases.