Page 263 - Cam Design Handbook

THB9 9/19/03 7:26 PM Page 251

CHAPTER 9

CAM MATERIALS
AND LUBRICATION

Harold A Rothbart, D. Eng.

9.1 INTRODUCTION 252 9.4.5 Materials Selection 269
9.2 ELASTIC CONTACT THEORY 253 9.4.5.1 Plastics 270
9.3 CONTACT STRESSES 256 9.4.5.2 Bronze Alloys 270
9.4 WEAR 260 9.4.5.3 Cast Iron 271
9.4.1 Wear Phenomena 260 9.4.5.4 Hardened Steels 271
9.4.1.1 Surface Definition 260 9.5 LUBRICATION 273
9.4.2 Adhesive Wear 261 9.5.1 Introduction 273
9.4.3 Abrasive Wear and Corrosive 9.5.2 Elastohydrodynamic Film 274
Wear 263 9.5.3 Lubricant Selection 277
9.4.3.1 Corrosive Wear 263 9.5.3.1 Grease 277
9.4.4 Surface Fatigue 263 9.5.3.2 Extreme-Pressure Lubricants 278
9.4.4.1 Introduction 263 9.5.3.3 Contaminants 281
9.4.4.2 Design 264 9.6 SUMMARY 281

SYMBOLS

a = semiaxes of elliptical boundary
b = semiaxes of elliptical boundary
E¢= effective Young’s modules, lb/in 2
E 1, E 2 = elastic moduli of bodies 1 and 2, lb/in
E c, E f = modulii of elasticity of cam and follower respectively, lb/in 2
G = materials parameter, dimensionless
h = film thickness of the medium
h 1, h 2 = depressed depth of contact, in
H = film thickness, dimensionless
m = values in Table 9.1
n = values in Table 9.1
N = velocity of the medium
p = intensity of pressure over surface of contact
p 0 = maximum pressure of contacting surfaces
P = normal force of contacting bodies
P¢= normal force per unit cylinder length, in
P¢= normal force per cylinder length, lb/in
R x = equivalent radius in rolling direction, in
R x1, R x2 = radii of bodies 1 and 2 in rolling direction, in
t n = thickness of contacting cam and follower, in
n= speed parameter, dimensionless
n 1, n 2 = Poisson’s ratio of bodies 1 and 2
W¢= load parameter, dimensionless
z = viscosity of the medium

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