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di Roberto Bassani
edito da Pisa University Press
“Tribology” derives its name from the Greek τρίβως: to rub, hence rubbing and then friction. However, such word also implies wear and lubrication. Today, its definition is the “science and technology of surface contact between members in relative motion of a kinematic pair, and of associated problems of friction, wear and lubrication”. Friction and wear have been challenging men since time
immemorial, who used logs under their sledges (rollers) nine thousand years ago. Six thousand years ago, rollers changed into wheels. Four thousand years ago, lubrication appeared. Two thousand years ago, roller bearings were invented. Five hundred years ago, Leonardo was the first to investigate friction, wear and
lubrication. Newton, Amonton, Coulomb, and many others scientists followed. But not until the Sixties did tribology experience an exceptional growth, in consequence of the need, started in England, to save energy by reducing friction, and
to save materials by reducing wear. This work of tribology comprises ten chapters. The first chapter deals with the materials used in tribology, which are mostly mechanical materials, while the second chapter deals with mechanical surfaces, their roughness and coatings. The third chapter refers to friction and to the different friction types: sliding, rolling and impact friction. The fourth chapter deals with wear: abrasive, erosive, adhesive, and corrosive wear of metals, plastics and ceramics, and wear in machining of mechanical components. The fifth chapter relates to lubricants: solid, semisolid (greases), liquid (oils) and gaseous lubricants, and emulsions
and additives. The sixth chapter relates to lubrication: squeeze, hydrostatic, hydrodynamic, elastohydrodynamic, machining lubrication, and to complete, incomplete and boundary lubrication. Magnetic levitation is also described. The seventh chapter is dedicated to tribometry: investigation, mainly experimental, about the behavior of non-lubricated and lubricated kinematic pairs. The eighth chapter deals with the efficiency of kinematic pairs and machines, closely related to friction losses, and with their reliability, monitoring and maintenance, related to wear. The ninth chapter is devoted to biotribology, and it refers mostly to biological materials used in bones, teeth and cardiac prostheses. The tenth and last chapter concisely describes the impact of tribological losses on the environment.
Tribology 440 drawing friction forces Ff contrast dragging. For 02 , Ff act also at the exit. In the passage through the supply chain, the material is subjected to stretching, with sliding of inner layers with respect to outer layers, pressed against the supply chain, and slower due to friction. The bar – supply chain pressure p diagram, zone IIa, in dry drawing for 02 , to which an accentuated peak at the exit corresponds, with p greater than 2000Nmm-2, is illustrated in Figure 6.152. Stress 2x of the bar at the exit may be determined thanks to equation (3.26), in which the friction contribution is given by m d dgtcom 2 1 13 2 (6.150) For 02 , the friction factor m may be obtained from Figure 3.27. The maximum value of m occurs in absence of lubrication.
2x as a function of 12 , obtained thanks to equation (6.150) for a ferrous material, is illustrated in Figure 6.153.
Fig. 6.153. Lubrication in processing of materials. Bar drawing. Bar drawing stress as a fun...
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