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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.