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CHAPTER 32
Tribology: Friction, Wear, andLubrication
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Contact Between Two Bodies
Figure 32.1 Schematic
illustration of the interface oftwo bodies in contact, showingreal areas of contact at theasperities. In engineeringsurfaces, the ratio of the apparentto real areas of contact can be ashigh as 4-5 orders of magnitude.
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Range of Coefficients of Friction inMetalworking Processes
TABLE 32.1
Coefficient of friction
()
Process Cold Hot
Rolling 0.050.1 0.20.7
Forging 0.050.1 0.10.2Drawing 0.030.1
Sheet-metal forming 0.050.1 0.10.2
Machining 0.52
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Ring Compression Tests
(b)
Figure 32.2 Ring compression test between flat dies. (a) Effect of lubrication on type of ringspecimen barreling. (b) Test results: (1) original specimen and (2)-(4) increasing friction.Source: A. T. Male and M. G. Cockcroft.
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FrictionCoefficient from
Ring Test
Figure 32.3 Chart todetermine frictioncoefficient from ring
compression test.Reduction in heightand change in internaldiameter of the ringare measured; then is read directly fromthis chart. Example: If
the ring specimen isreduced in height by40% and its internaldiameter decreases by10%, the coefficient offriction is 0.10
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Effect of Wear on Surface ProfilesFigure 32.4 Changes inoriginally (a) wire-brushedand (b) ground-surfaceprofiles after wear. Source:
E. Wild and K. J. Mack.
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Adhesive and Abrasive Wear
Figure 32.5 Schematic illustration of (a) two contacting asperities, (b) adhesion between two asperities, and
(c) the formation of a wear particle.
Figure 32.6 Schematic illustration of abrasive wear in sliding.Longitudinal scratches on a surface usually indicate abrasivewear.
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Types of Wear Observed in a Single Die
Figure 32.7 Typesof wear observed ina single die used forhot forging. Source:T. A. Dean
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Types of Lubrication
Figure 32.8 Types oflubrication generally occurringin metalworking operations.
Source: After W.R.D. Wilson.
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Rough Surface
Figure 32.9 Rough surface developed
on an aluminum compressionspecimen by the presence of a high-viscosity lubricant and highcompression speed. The coarser thegrain size, the rougher the surface.Source: A. Mulc and S. Kalpakjian.