me 329 chapter 5 oct 28 2009

Chapter 5Tribology and Engineering Materials

Engineering Materials: properties and selection, 9th ed.Kenneth G. Budinski, Michael K. Budinski

Chapter Goals

Upon completion of this chapter, the student should: have an understanding of tribology and its

importanceimportance have a knowledge of the fundamentals of friction have a knowledge of the type of wear that canhave a knowledge of the type of wear that can

occur have a review of the fundamentals of bearings and

l b i tlubricants

Engineering Materials: properties and selection, 9th ed.Kenneth G. Budinski, Michael K. Budinski 2

2010 Pearson Higher Education,Upper Saddle River, NJ 07458. All Rights Reserved.

Introduction

Origin of the word tribology Friction costs (10% of GDP) Wear cost (5% of GDP)

S f t ib l Scope of tribology



5.2 Contact Mechanics

Real area of contact Hertz stress equations

St i l t t diff t f th Stress in real contacts are different from the apparent stress



5.2 Contact MechanicsMechanics

Figure 51 Concept of real d fand apparent area of contact



5.2 Contact Mechanics

Figure 5 2 When real surfaces contact the up features of the



Figure 52 When real surfaces contact, the up-features of the surfaces carry the load

5.2 Contact MechanicsMechanics

Figure 53 Hertz equation for the contact ofequation for the contact of a sphere on a flat surface under elastic conditions



R l f f h

5.3 Friction

Role of surface roughness Components of friction: F = Fa + Fp + Fs + Fn

Fa = force to break adhered junctionsFp = force to plow and deform surface features Fs = force to shear films between surfacesFn = force due to the nature of the sliding system

Different types of friction Sliding vs. Rolling friction Measurement

b d f Lubricated friction Significance in wear of components

Use of published friction data in design



Use of published friction data in design

5.3 Friction

Figure 54 The force required to move surface A up the



Figure 5 4 The force required to move surface A up the rugosities on surface B

5.3 Friction

Figure 55 Types of friction



g yp

5.3 Friction

Figure 56 The difference between the coefficient of friction and the traction coefficient; they are mathematically similar but



and the traction coefficient; they are mathematically similar, but differ in point of force application.

5.3 Friction

Pure rolling at a & b, some sliding betweensome sliding between these regions



Figure 57 Pure rolling only occurs in areas a and b

5.3 Friction

Figure 58 Equations Figure 58 Equations for friction force



5.3 Friction Schematic equation only!

r = Fr /N * {(Ra / E h R )} Kr

r = Rolling friction coefficientFr = Force to produce rollingN = Normal forceN Normal forceRa = Surface roughnessE = Elastic modulush surface hardnessh = surface hardnessR = radius of rolling shapeKr = variable related to tribosystem

Figure 58 General concept - potential equation for rolling friction coeff



for rolling friction coeff.

5.3 Friction - Measurement

Figure 59 Rolling friction test. Rolling resistance number is the height of the hill divided by the distance travelled on rolling from



height of the hill divided by the distance travelled on rolling from the top (car in neutral with engine running).

5.3 Friction

Figure 510 Types of friction force recordings that can be encountered



5.3 Friction

Figure 511 Average friction coefficients for various materials in reciprocating motion of anreciprocating motion of an annular ring rider (0.1 on a type 316 stainless steel counterface at 50% relative humidity (RH) at varioushumidity (RH) at various normal forces.

The stroke was 50 mm and the frequency was 0 5 Hertzthe frequency was 0.5 Hertz. The friction force was averaged for eight cycles in each test.



5.3 Friction

Figure 512 Stribeck curve showing how lubricated sliding s stems can ha e f iction a ith ope ating conditions and



systems can have friction vary with operating conditions and lubricant properties

5.3 Friction

Figure 513 Types of lubrication



5.4 Definition of Wear

Correlation between wear and friction Difference between wear and erosion

T f Types of wear Types of erosion Types of abrasion Types of abrasion Surface fatigue




Figure 514 Major categories of wear and specific types of



g j g p ypwear in each category




Figure 515 Types of erosion

5.5 Erosion

Figure 516 (a) Schematic of solid particle erosion; (b) erosion of a wearback from a pipe carrying fly ash. Note hole and wavy surface.



5.5 Erosion

Figure 517 (a) Schematic of slurry erosion; (b) pump impeller h i i d f i l f ili d t



showing erosion damage from pumping a slurry of silica and water

5.5 Erosion

Figure 518 (a) Schematic of liquid impingement erosion; (b) pipe elbow perforated by impingement from high-velocity fluid in a pipeline



in a pipeline

5.5 Erosion

Figure 519 (a) Schematic of cavitation; (b) cavitation on a stainless steel tank. An ultrasonic agitation device was attached to



stainless steel tank. An ultrasonic agitation device was attached to the other side of this section of the tank (diameter = 15 cm).

5.6 Types of Wear

Figure 520 (a) Adhesion of asperities in adhesive wear; (b)



Figure 5 20 (a) Adhesion of asperities in adhesive wear; (b) metal-to-metal wear on gear teeth (no lubrication)

5.6 Types of Wear

Figure 521 (a) Schematic of formation of an excrescence in galling; (b) galling damage on the polished conforming surfaces of



galling; (b) galling damage on the polished conforming surfaces of special nuts after one use

5.6 Types of Wear

Figure 522 (a) Schematic of oxidative wear; (b) oxidative wear occurred from low-speed moving with a mating chain link



(dark area)

5.6 Types of Wear

Figure 523 (a) Schematic of asperity interaction in fretting wear; (b) fretting damage on a splined shaft from relative motion of a



(b) fretting damage on a splined shaft from relative motion of a mating part

5.6 Types of Wear

Figure 524 (a) Schematic of low-stress abrasion; (b) low-stress



abrasion of a shaft from hard contaminants in a plastic bushing

5.6 Types of Wear

Figure 525 (a) Schematic of high-stress abrasion; (b) star wheels on a refuse grinder that have been subjected to high-stress abrasion Wheels are 2 in (50 mm) thick



stress abrasion. Wheels are 2 in. (50 mm) thick.

5.6 Types of Wear

Figure 526 (a) Schematic of gouging abrasion; (b) gouging damage ca sed b g inding of ocks



damage caused by grinding of rocks

5.6 Types of Wear

Figure 527 (a) Schematic of pitting due to surface fatigue; (b)



Figure 5 27 (a) Schematic of pitting due to surface fatigue; (b) pitting of a large roller thrust bearing race due to surface fatigue

5.6 Types of Wear

Figure 529 (a) Spalling of a coating from surface fatigue; (b) spalling of plating due to surface fatigue (oscillatory movement



spalling of plating due to surface fatigue (oscillatory movement of about 5 mm)

5.6 Types of Wear

Figure 528 (a) Schematic of impact wear; (b) impact wear on the st iking face of a batte ing tool



the striking face of a battering tool

5.6 Types of Wear

Figure 530 (a) Schematic of brinelling; (b) brinelling of a



bearing race by static overload

5.7 Bearings

Basic types Plain bearings

R lli l t Rolling element Bearing life (L10) Bearing precision Bearing precision Bearing selection Bearing materials (Design factors)g ( g )



5.7 Bearings

Figure 531 Factors that ffaffect wear

and friction at different scalesscales



5.7 Bearings

Figure 5 32 F ndamental catego ies of bea ings



Figure 532 Fundamental categories of bearings

5.7 Bearings



Figure 533 Engineering materials used for bearings

5.7 Bearings

Figure 534 Examples of various types of ball bearings: (a) deep groove single row (for radial loads limited axial); (b) angulargroove, single row (for radial loads, limited axial); (b) angular contact (takes radial load and axial loads in one direction); (c) split inner ring (special applications); (d) self-aligning double row (tolerates some misalignment); (e) ball thrust bearing (for axial loads only)



loads only)

5.7 Bearings

Figure 535 Examples of roller bearings: (a) cylindrical (accommodates high radial load, no axial loads); (b) tapered (accommodates radial and axial loads); (c) spherical (accommodates misalignment); (d) needle (high radial load



( g ); ( ) ( gcapacity for its size)

5.7 Bearings

Figure 536 Ball versus roller bearing selection



5.8 Lubricants

Types Mineral oils

F ll f l t d il Fully formulated oils Greases Solid film lubricants Solid film lubricants Bio-based lubricants



5.8 Lubricants



Figure 537 Types of lubricants

5.8 Lubricants

Figure 538 Engineering materials used to combat abrasive wear



5.8 Lubricants

Figure 5 39 Mate ials sed fo non ab asi e ea sit ations



Figure 539 Materials used for non-abrasive wear situations

5.8 Lubricants

Figure 540 Spalling of chromium plate on a hardened steel guidepost, produced by surface fatigue from reciprocating ball contact



produced by surface fatigue from reciprocating ball contact

5.8 Lubricants

Figure 541 Part failure due to abrasive wear. Asbestos packing



g p gran against the stainless steel bushing (type 316).

Table 51 DN limits for greases and oils

5.8 LubricantsTable 5 1 DN limits for greases and oils



Table 52 Solid-film lubricants

5.8 LubricantsTable 5 2 Solid film lubricants



5.10 Preventing Wear Failures

Abrasion guidelines Metal-to-metal guidelines

Oth id li Other guidelines



Table 53 Some standard tribotests

SummaryTable 5 3 Some standard tribotests



Global Considerations

New energy solutions will bring new tribology challenges

Effect of bio-based fuels and lubes Effect of bio-based fuels and lubes Removal of anti-wear additives Overall goal of reducing friction worldwideOverall goal of reducing friction worldwide



me 329 chapter 5 oct 28 2009

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