Tribology Lecture Notes PDF

TRIBOLOGY LECTURE 1-LUBRICATION PART INTRODUCTION & LUBRICATION MECHANISMS ‫ محمد المغازي‬/‫د‬  What is the meaning of TRIBOLOGY ? TRIBOLOGY TRIBOS == Rubbing Tribology is the science of interacting surfaces in relative motion. It inc...

TRIBOLOGY LECTURE 1-LUBRICATION PART INTRODUCTION & LUBRICATION MECHANISMS ‫ محمد المغازي‬/‫د‬  What is the meaning of TRIBOLOGY ? TRIBOLOGY TRIBOS == Rubbing Tribology is the science of interacting surfaces in relative motion. It includes the study and application of the principles of friction, lubrication, and wear.  TRIBOLOGY FRICTION WEAR LUBRICATION Belts Gear design Navier Stokes Clutches based on wear equations (fluid Brakes (pitting wear) mechanics) Power screw Worm gears  TRIBOLOGY FRICTION WEAR LUBRICATION ‫ أحمد صالــح‬/‫د‬ ‫ محمد عبدالوهاب المغازي‬/‫د‬ Course Contents LUBRICATION 1.Lubrication Mechanisms (Modes) 2.Lubricants (Oil &Grease) 3.Lubrication Systems. 4.Lubrication of Rolling Element Bearings 5.Elasto-Hydrodynamic Lubrication equations. 6. Fluid film Bearings.  REFERENCES Fundamentals of fluid film lubrication (by Bernard Hamrock) FAG_rolling bearing lubrication. SKF-rolling bearings catalogue. LUBRICATION MECHANISMS  Types of contact surfaces Conformal surfaces Non-Conformal surfaces  Types of contact surfaces Conformal surfaces Non-Conformal surfaces Large area of contact Small area of contact Journal bearings Rolling element bearings Cams gears Lubrication Mechanisms  Lubrication Mechanisms THIN FILM MIXED THICK FILM Boundary Hydrodynamic Elasto-Hydrodynamic I THICK FILM LUBRICATION I.1 HYDRODYNAMIC LUBRICATION (HL) NOTE: Positive pressure develops due to : 1- Relative motion 2- Bearing surfaces convergence 3- Lubricant Viscosity THICK FILM LUBRICATION HYDRODYNAMIC LUBRICATION Characteristics of Hydrodynamic Lubrication Conformal surfaces Pmax ≈ 5 MPa No elastic effect hmin (minimum film thickness) depends on V.I ( Load-Velocity-Viscosity) hmin>1 μ  Ways of developing positive pressures in hydrodynamically lubricated bearings Hydrodynamic lubrication Squeeze film Externally Slider Bearing pressurized Bearing Bearing (Hydrostatic) Ways of developing positive pressures in hydrodynamically lubricated bearings HYDRODYNAMIC LUBRICATION (a-Slider Bearings) HYDRODYNAMIC LUBRICATION (Slider Bearings) Examples HYDRODYNAMIC LUBRICATION (b-SQUEEZE FILM Bearings) Synovial Joint  HYDRODYNAMIC LUBRICATION C-Externally Pressurized (Hydrostatic) Bearings The lubricant is forced into the clearance space bearing from an external high pressure source. The pressure in the film is not self induced The supplied high pressure lubricant separates the surface even there is no relative motion. This mechanism reduces the starting friction and the eccentricity Comparison between Hydrodynamic Slider and hydrostatic bearings Slider bearings  THICK FILM LUBRICATION ELASTO-HYDRODYNAMIC LUBRICATION 2 (EHL) ELASTO-HYDRODYNAMIC LUBRICATION EHL HARD EHL SOFT EHL Characteristics of HARD EHL NON-Conformal surfaces Pmax ≈ 1 GPa Elastic and viscous effects both important effect High elastic modulus materials (steel) hmin (minimum film thickness) depends on ( Load – Velocity – Viscosity - ”pressure viscosity coefficient” - modulus of elasticity for both materials) hmin> 0.1 μm (but elastic deformation >>> hmin) Examples : Rolling element bearings Gears Cams Characteristics of SOFT EHL NON-Conformal surfaces Pmax ≈ 1 MPa Elastic and viscous effects both important effect but elastic properties is predominant Low elastic modulus materials (rubber) hmin (minimum film thickness) depends on ( Load – Velocity – Viscosity - modulus of elasticity for both materials) hmin ≈ 1 μm (but elastic deformation >>> hmin) Examples : *Seals *human joints *tires *lubricated machine elements that use rubber as a material ELASTO-HYDRODYNAMIC LUBRICATION EHL SOFT EHL seals II THIN FILM LUBRICATION BOUNDARY LUBRICATION The frictional characteristics are determined by the properties of the solids and the thin surface lubricant film Thickness of the thin film attached to the solid surfaces ≈1 to 10nm (0.001 to 0.01 μm) II THIN FILM LUBRICATION BOUNDARY LUBRICATION Examples: Door hinges Rubbing sleeve bearings ( where low cost is important) Applications of heavy loads or low running speeds (where fluid film lubrication is difficult to attain) III MIXED (PARTIAL)LUBRICATION  Comparisons Between Lubrication Mechanisms Film conditions for Lubrication Mechanisms Film conditions for Lubrication Mechanisms a Film Parameter Λ b Coefficient of friction for Various Lubrication Mechanisms Wear Rate for Various Lubrication Mechanisms THANKS FOR ATTENTION