Andrzej Golenko Fundamentals of Machine Design A Coursebook for Polish and Foreign Students Reviewed by Dr Michał Banaś, Wroclaw University of Technology 2010 Projekt współfinansowany ze środków Unii Europejskiej w ramach Europejskiego Funduszu Społecznego 2 3 Contents (part 1: units 1 to 15) Foreword .............................................................................................................................. 5 1. The Design Process ........................................................................................................... 7 1.1. General ...................................................................................................................... 7 1.2. Problem identification ................................................................................................ 7 1.3. Preliminary ideas........................................................................................................ 8 1.4. Selection of the best idea ............................................................................................ 9 1.5. Refinement................................................................................................................. 9 1.6. Analysis ................................................................................................................... 10 1.7. Implementation ........................................................................................................ 11 2. Fatigue Analysis.............................................................................................................. 12 2.1. Combined static load................................................................................................ 12 2.2. Fluctuating load........................................................................................................ 13 2.3. Wőhler diagram........................................................................................................ 14 2.4. Fatigue diagrams ...................................................................................................... 15 2.5. Endurance limit for a machine element (modification factors)................................... 15 2.6. Safety factor............................................................................................................. 16 2.8. Selection of shape for fatigue life ............................................................................. 18 3. Power Screws.................................................................................................................. 20 3.1. Efficiency, general considerations ............................................................................ 20 3.2. Thread basics ........................................................................................................... 20 3.3. Distribution of forces in a screw-nut mechanism....................................................... 21 3.4. Torque ..................................................................................................................... 23 3.5. Efficiency of a power screw mechanism ................................................................... 23 4. Bolted Connections: part 1 .............................................................................................. 26 4.1. Load tangent to the plane of contact (loose bolts)...................................................... 26 4.2. Load tangent to the plane of contact (fitted bolts)...................................................... 27 4.3. Locking means......................................................................................................... 29 5. Bolted connections: part 2 ............................................................................................... 32 5.1. Load normal to the contact plane (preload) ............................................................... 32 5.2. A group of bolts under normal load .......................................................................... 36 6. Welded Connections........................................................................................................ 38 6.1. Stress analysis .......................................................................................................... 38 6.2. Design of welded joints ............................................................................................ 40 7. Shaft-Hub Connections.................................................................................................... 43 7.1. Introduction.............................................................................................................. 43 7.2. Positive engagement................................................................................................. 43 7.3. Connections by friction ............................................................................................ 46 8. Press-fit Connections....................................................................................................... 49 8.1. Formulation of the problem ...................................................................................... 49 8.2. Stress and strength analysis ...................................................................................... 49 8.3. Selection of a fit ....................................................................................................... 50 9. Shafting........................................................................................................................... 54 9.1. Introduction.............................................................................................................. 54 9.2. Design approach for shafts ....................................................................................... 54 4 9.3. Checkout calculations............................................................................................... 57 9.4. Fatigue analysis........................................................................................................ 57 10. Couplings...................................................................................................................... 59 10.1. Equivalent (reflected) inertia .................................................................................. 59 10.2. Selection of a coupling ........................................................................................... 60 10.3. Rigid couplings ...................................................................................................... 60 10.4. Flexible couplings .................................................................................................. 61 10.5. Elastic couplings .................................................................................................... 63 11. Clutches ....................................................................................................................... 65 11.1. General .................................................................................................................. 65 11.2. Starting analysis ..................................................................................................... 66 11.3. Friction torque vs. design parameters...................................................................... 67 11.4. Actuation systems .................................................................................................. 68 11.5. Operating modes .................................................................................................... 68 12. Brakes ........................................................................................................................... 72 12.1. General .................................................................................................................. 72 12.2. A cone brake .......................................................................................................... 73 12.3. Band brakes............................................................................................................ 73 13. Roller Contact Bearings................................................................................................. 76 13.1. Roller contact vs. plain surface (journal) bearings................................................... 76 13.2. General description................................................................................................. 76 13.3. Selection of the service life..................................................................................... 77 13.4. Calculation of the equivalent load........................................................................... 77 13.5. Bearing arrangements............................................................................................. 78 13.6. Selection of fits ...................................................................................................... 79 13.7. Lubrication and sealing .......................................................................................... 79 14. Friction and Lubrication ................................................................................................ 82 14.1. Coefficient of friction: the Bowden’s theory ........................................................... 82 14.2. Properties of bearing materials................................................................................ 83 14.3. Bearing parameter (the Stribeck curve)..................................................................