III. Design for lifetime performance and reliability. About the book

Transcription

1 Design for lifetime performance and reliability III About the book The objective of this book is to provide guidelines for engineers helping them to improve machine lifetime performance and reliability. Many books are written about machine design. Most of these are focussed on selection and computation of basic machine elements. Those calculations generally relate to the strength and stiffness of machine elements. In practice, it appears that few machine problems are caused by these issues thanks to the attention paid to calculation of strength and stiffness. Most machine problems occur with the passage of time, from dynamic loading and interacting surfaces in relative motion. Friction and wear of interacting surfaces in relative motion may take on an unacceptable form, resulting in play, frictional heat or jams. In rolling contacts surface fatigue is generally the predominant failure mode. Cyclically loaded machine elements may suddenly result in fatigue fracture after a large number of load cycles. It is estimated that approximately 95% of all machine problems are related to fatigue fracture and tribology phenomena as friction and wear. The science focussing on the management of friction, wear and fatigue consequently deserves the necessary attention. The purpose of this book is to give insight, through case studies and a wide range of illustrations, into how machine performance deteriorates, how machine elements may fail, how to analyse the cause of performance deterioration and failure, and, most importantly, how failures may be prevented and performance can be improved. The possibilities of pushing the boundaries of load carrying capacity, and motion control are explored. With newly gained insights the engineer is better equipped to reach innovative solutions to further optimize machine lifetime performance, improve machine reliability and simultaneously to minimize the need of maintenance. Many design tools, design charts and guide lines are discussed. User friendly PC calculators of the formulae derived in this book are made available, including calculators for calculating dynamic load capacity, friction, frictional heating and wear of machine elements in relative motion. Using these calculators design engineers will save much time in determining the outcomes of selecting specific design parameters. The formulae used in the calculators are also available in Mathcad files. With these files the designer may in a user friendly way adapt or extend calculations for specific applications. In fact this book is a goldmine of information for any engineer who intends to improve machine lifetime performance and reliability. The first part of this book concerns the fundamentals of Design for lifetime performance and reliability, including design procedures to estimate and improve machine reliability, failure analysis, fatigue strength, static and dynamic load rating of concentrated contacts, friction phenomena, wear mechanisms, machine lubrication and material selection. The second part concerns Design of high performance and high reliability applications, including the design of hydrodynamically lubricated bearings and sliders, viscous dampers, dynamic sealing systems, hydrostatic bearings, pressurised air bearings, flexure mechanisms and many other specialty bearings. Although the designer using this book is expected to have a good background in mathematics, the objective is that the design tools illustrated by cases will be useful anyhow.

2 IV Design for lifetime performance and reliability CONTENTS ADVANCED ENGINEERING DESIGN LIFETIME PERFORMANCE AND RELIABILITY Chapter 1: Reliability Engineering DESIGN FOR LIFETIME PERFORMANCE AND RELIABILITY Introduction History Trends in mechanical engineering design Innovative solutions RELIABILITY ENGINEERING Component reliability System reliability SYSTEMS ENGINEERING Precision, accuracy and resolution Errors in positioning How to improve the overall system accuracy Running accuracy High Tech Systems...36 Chapter 2: Physics of Failure DESIGN FOR RELIABILITY Physics of Failures Failure analysis techniques and procedure Root Cause Failure analysis CLASSIFICATION OF FAILURE MECHANISMS How rolling bearings fail How gears Fail ROOT CAUSE ANALYSIS CASE STUDIES Failed cam with bucket follower Failed camshaft with roller follower Failed railway wheel system Failed crane rail Failed journal bearings of rocker arms CORRECTIVE ACTIONS TO PREVENT FAILURE Dynamic load capacity of plain bearings Power transfer of an interference fit...64 Chapter 3: Fatigue failure prediction and prevention INTERPRETATION OF FRACTURE SURFACES Shear fracture and tensile fracture Fatigue fracture Corrosion and corrosion fatigue PREDICTION OF THE FATIGUE STRENGTH Stress life relationship Estimating the fatigue strength...80

3 Design for lifetime performance and reliability V 3.3 FATIGUE RESISTANT DESIGN Design of dynamically loaded drive shafts Design of dynamically loaded bolted joints Design of dynamically loaded welded structures (Eurocode 3 EN )...96 Chapter 4: Rolling contact phenomena STATIC AND DYNAMIC LOAD RATING Nominal point contact Elliptic contact Nominal line contact Contact conformity Geometrical stress concentrations Rolling with traction Permissible contact pressure ROLLING RESISTANCE Micro slip Plastic deformation Hysteresis losses Spinning Secondary friction losses and running in conditions ELASTOHYDRODYNAMIC LUBRICATION EHL line contact EHL point contact LOAD RATING OF MACHINE ELEMENTS Static and dynamic load ratings of rolling bearings Static and dynamic load rating of linear rail guides Static and dynamic load rating of ball screws Surface durability of gears Dynamic load rating of traction drive mechanisms Chapter 5: Friction phenomena REAL CONTACT AREA Surface Roughness Ratio of real contact area and nominal contact area Real contact area versus friction FUNDAMENTALS OF FRICTION Ploughing Adhesion CLASSICAL FRICTION LAWS Effect of the nominal contact area Effect of the normal load Effect of sliding velocity Effect of temperature Effect of surface roughness STICK SLIP, JAMMING, SIDE SLIP AND JOINT SLIPPAGE Stick slip Jamming Side slip to eliminate friction

4 VI Design for lifetime performance and reliability Joint Slippage Hysteresis FRICTIONAL HEATING AND THERMAL FAILURE Nominal contact temperature Flash temperature MEASURING FRICTION Manually Motorised Chapter 6: Wear mechanisms TWO BODY WEAR MECHANISMS Abrasive wear Adhesive wear Corrosive wear Surface fatigue SINGLE BODY WEAR MECHANISMS Gas erosion Liquid impingement erosion Cavitation erosion Particle erosion Electrical / spark erosion CONTACT CONDITIONS Contact conformity Stationary contact Degree of overlap Contact temperature WEAR RATE Running in Calculation of wear rate Classification of the specific wear rate SELECTING OR CONSTRUCTING TEST APPARATUS Pin on disc / Pin on ring Pin on flat / ball on flat Two disk STANDARDS FOR MEASURING FRICTION AND WEAR Specimen preparation Experiment Reporting Reproducibility Chapter 7: Material selection MATERIALS FOR SLIDE SURFACES Selection criteria for metals Selection criteria for polymers Selection criteria for technical ceramics COATINGS AND SURFACE TREATMENTS Where surface treatments are applied Classification of surface treatments Surface treatment techniques

5 Design for lifetime performance and reliability VII Chapter 8: Lubricant selection and lubrication management LUBRICATION REGIMES Stribeck curve Transition diagram LUBRICANTS Physical properties Additives Oil supplements Trends in engine and industrial lubrication TYPES OF LUBRICANTS AND LUBRICANT SELECTION Base oils Biolubricants Food grade lubricants Lubricants for thermoplastics, thermosets and elastomers Greases Solid lubricants Lubricant selections for specific applications LUBRICATION MANAGEMENT Grease versus oil lubrication Oil lubrication systems Engine lubrication system PROACTIVE MAINTENANCE AND OIL ANALYSIS Maintenance engineering Proactive maintenance Causes of lubricant deterioration and their prevention Chemical and physical oil analysis Wear particle analysis Chapter 9: Design of hydrodynamic bearings and sliders HYDRODYNAMIC LUBRICATION Reynolds equation Effective surface velocity Film thickness in journal bearings and concentrated contacts Viscous shear SLIDER BEARINGS Converging wedge Michell bearing Rayleigh step bearing Tapered land pad Curved pad PLAIN JOURNAL BEARINGS Bearing performance and design Design optimization load versus bearing clearance Design optimization friction versus film thickness Bearings in turbo machinery VISCOUS DAMPING AND DYNAMIC RESPONSE Dashpot Band on flat

6 VIII Design for lifetime performance and reliability Circular disk on flat Circular ring on flat Cylinder on flat Squeeze film dampers Shock loaded journal bearings Dynamically loaded slider bearings Piston ring/liner film development Dynamically loaded journal bearings SPIRAL GROOVE BEARINGS Thrust bearings Journal bearings Hybrid bearings in high speed rotary applications Chapter 10: Dynamic sealing systems SEALING SYSTEMS Classification Operating limits ROTARY SEALS Lip seals, V rings and O rings Mechanical face seals Seal face patterns Gap seals Labyrinth seals Magnetic fluid seals Air barrier seals RECIPROCATING SEALS Reciprocating lip seals in hydraulics Reciprocating lip seals in pneumatics Piston guide rings O rings in reciprocating applications Piston ring seals in engines Chapter 11: Design of hydrostatic bearings BASIC METHODS OF OPERATION Methods to obtain bearing stiffness Advantages and limitations of pressurised fluid bearings DESIGN OF HYDROSTATIC BEARINGS Basic construction elements Hydrostatic thrust bearings with shallow pocket Hydrostatic thrust bearings with tapered film Hydrostatic thrust bearings with capillary restrictor Hydrostatic thrust bearings with orifice restrictor Hydrostatic preloaded thrust bearings Hydrostatic journal bearings with external restrictors Hydrostatic journal bearings with shallow pockets

7 Design for lifetime performance and reliability IX Chapter 12: Design of Externally Pressurized Air Bearings BASIC METHODS OF OPERATION Methods to obtain bearing stiffness Advantages and limitations of pressurised gas bearings Structural considerations and kinematics DESIGN OF E.P. AIR BEARINGS Basic construction elements Design of air bearings with orifice restrictor Design of air bearings with a series annular orifice restrictors Design of air bearings with a series simple orifice restrictors Design of air bearings with partial porous surface Design of shallow pocket air bearings Design of partially grooved air bearings Design of taper and taper land air bearings Design of journal bearings with porous ring restrictor Design of journal bearings with two porous rings Design of partially grooved journal bearings Chapter 13: Design of flexure mechanisms BASIC DESIGN PRINCIPLES AND COMPONENTS Design considerations Basic construction elements Dynamic load excitation response Design of hole hinges Micro actuators DIVERSE APPLICATIONS Flexure cross hinge Piezo parallel guiding with integrated motion amplifier Piezo nano precision XY parallel mechanism Flexible shaft couplings Chapter 14: Machine Design Calculations Reference Guide MACHINE DESIGN REFERENCE GUIDE Metric thread, fasteners Power screws Interference fits Cone type shaft hub connections Slide bearings Variable transmission belt drives BASIC EQUATIONS AND DATA TABLES Linear elasticity Deflections and slopes of uniform cantilever beams Moments of inertia I x, I y and I p Approximate formulae for spring stiffness Buckling limit of compression loaded beams Approximate design functions S shaped beams Springs in series versus parallel Spring mass system / vibrations

8 X Design for lifetime performance and reliability Moments of Inertia Work, energy and power ISO Metric screw threads ISO Tolerances for holes and shafts Approximate coefficients of friction Drag coefficients in air C w Physical properties of solids Physical properties of liquids Physical properties of gasses Physical properties of polymers Mechanical properties of structural steel Mechanical properties of non alloy quality steel (QT) Mechanical properties of non alloy quality steel (Normalized) Mechanical properties of stainless steels Mechanical properties of alloyed steels Mechanical properties of aluminium alloys Mechanical properties of cast iron Mechanical properties of spring steel Mechanical properties of bearing bronze Conversion factors to SI Units Appendix Acknowledgements About the Author References Index Access keys Useful Links