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Items 1 - 8 - track, wheels, and cars emerged. ... simultaneous study of the car, the wheel, the rail, and the track. The .... Therefore, the TRC thought it would be easier for each part to have ...... is eminently suitable for heavy haul, heavy axle load operations. ..... a limited degree on certain passenger rail vehicles, but not in.

GUIDELINES TO BEST PRACTICES FOR HEAVY HAUL RAILWAY OPERATIONS: WHEEL AND RAIL INTERFACE ISSUES Click Here to View Table of Contents

IHHA ' M AY 2001

G UIDELINES T O B EST P RACTICES F OR H EAVY H AUL R AILWAY O PERATIONS : W HEEL AND R AIL I NTERFACE I SSUES

First Edition, First Printing, May 2001©

2808 Forest Hills Court Virginia Beach, Virginia 23454 USA

These Guidelines have been prepared by the Technical Review Committee under the auspices of the International Heavy Haul Association as an input to the decision making processes of heavy haul railways. They represent the best efforts of the Technical Review Committee authors and reviewers. The Guidelines are neither mandatory directives nor intended to summarize and interpret the extensive heavy haul technical literature. There are special combinations of circumstances in which the best practices may differ from those discussed in the Guidelines. Therefore, these guidelines are neither mandatory nor do they describe exclusive methods to achieve optimum rail/wheel performance.

Co p y r i g h t © 2 0 0 1 I n t e r n a t i o n a l H e a v y H a u l A s s o c i a t i o n All rights reserved. Reproduction or translation of any part of this work without the permission of the copyright owner is unlawful. R e q u e s t s f o r p e r m i s s i o n o r fu r t h e r i n f o r m a t i o n should be addressed to: International Heavy Haul Association 2808 Forest Hills Court Virginia Beach, Virginia 23454 USA L i b r ar y o f C o n g r e s s C o n t r o l N o .: 2 0 0 1 1 3 1 9 0 1

Printed in the United States of America 2001

hese guidelines were prepared under the auspices of the International Heavy Haul Association through its Board of Directors:

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Australia: Public Railways of Australia, Brian G. Bock, Chairman IHHA Private Railways of Australia, Michael Darby, Director Brazil: Companhia Vale Do Rio Doce (CVRD), Ronaldo Costa, Director Canada: Railway Association of Canada, Michael Roney, Director China: China Railway Society, Qian Lixin, Director Russia: The All-Russian Railway Research Institute Alexander L. Lisitsyn, Director Sweden/Norway: Nordic Heavy Haul Association, Thomas Nordmark, Director Republic of South Africa: Spoornet, Harry Tournay, Director Union Internationale des Chamis (UIC): World Division, V. C. Sharma, Associate Director United States of America: Association of American Railroads, Roy A. Allen, Director IHHA Chief Executive Officer W. Scott Lovelace,

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FOREWORD

Letter from the IHHA Chairman on behalf of the Board of Directors to the readers of Guidelines to Best Practices for Heavy Haul Railway Operations: Wheel and Rail Interface Issues

About 50 years ago, railways in many places in the world began to increase axle loads to provide more efficient and lower cost transportation of bulk commodities. Serious problems with rail, track, wheels, and cars emerged. Research was begun by numerous companies and administrations to overcome these serious problems. These studies were first shared at an International Heavy Haul Conference organized in Australia and held in Perth in 1978. Because of the overwhelming success of these meetings, a second conference on heavy haul railway engineering and operational concerns was organized and held in 1982 in the United States at Colorado Springs, Colo. During that time, the delegates expressed an interest in the establishment of a continuing organization to facilitate sharing of information on heavy haul railway technology. In early 1983, Dr. William J. Harris, then Vice President Research of the Association of American Railroads, issued an invitation to the delegates to the 1982 meeting to come to Washington to discuss establishing a continuing organization. In the summer of 1983, representatives of railways from Australia, Canada, China, South Africa, and the United States formally organized the International Heavy Haul Association. In 1994, railways in Russia joined, followed in 1995 by the railways of Brazil. More recently, in 1999, the railways of Norway and Sweden joined as the Nordic Heavy Haul Association. The World Division of the UIC became an Associate Member in 1999 and participates in meetings of the IHHA Board of Directors. In 1991 at the conference in Vancouver, British Columbia, Braam le Roux, then Chief Executive of Spoornet, raised the question of developing a handbook of best practices for heavy haul railways. The handbook was to be based on the collective knowledge of technical presentations made at this and other IHHA conferences. This was the beginning of the concept of a “best practice” handbook. The IHHA has organized six international conferences and ten specialist technical sessions to encourage the exchange of information on heavy haul research and development. The IHHA Board of Directors determined that while these conferences were an extremely valuable way to disseminate state-of-the-art technology, it was very difficult for any operating officer to gain the insights

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provided by the 16 conferences and technical sessions. Therefore, they agreed that the publication of a handbook of guidelines, which provided summary information on best heavy haul practices, would be a useful contribution to the heavy haul rail community around the world. It was with this goal in mind that the task of writing this book was undertaken. The Directors established a Technical Review Committee and charged it with developing guidelines for heavy haul operations with special attention to the wheel/rail interface. The dedication of the members of the Technical Review Committee and the support of their organizations was remarkable. The financial support from IHHA made the project become a reality. The funding and support of the Russian Railway Ministry, All-Russian Railway Research Institute, SPOORNET of South Africa, the Private and Public Railways of Australia, and the Transportation Technology Center, Inc. of the United States is also gratefully recognized. The reader will find that these guidelines summarize the technological options available in seeking the best practices on a cost/effective basis. They are presented in a format that will make it possible for railway operating officers to decide how best to apply these findings to optimize their operations. A second edition of these guidelines will be published as soon as enough new material is available from research or field findings. The TRC encourages readers to send comments for improvements in the guidelines by email to Scott Lovelace, CEO of IHHA, at [email protected]

Brian G. Bock, Chairman IHHA

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PREFACE This handbook summarizes examples of the application of best practices on a cost/effective basis. Findings from the research are presented in a format for railroad operating officers to decide how to apply them to their own individual operations. It is clear that the wheel-rail interface is the key to the heavy haul problem. At the interface, there must be low friction to permit moving heavy loads with little resistance. However, there must be enough friction to provide tractive effort, braking effort, and steering of the train. The materials must be strong enough to resist the vertical forces introduced by very heavy loads and the dynamic response at the wheel-rail interface introduced by vertical accelerations of the car induced by track and wheel irregularities. However, neither the wear rate nor the failure rate should be so great that cost-effective heavy haul operations are threatened. The discussion of cost/benefit analysis in Part 5 and the case studies presented in Part 4 indicate the variety of options available to railroad management as it seeks to achieve optimized heavy haul operations that are cost effective. These case studies exemplify that the process involves a systems study in which there must be simultaneous study of the car, the wheel, the rail, and the track. The case studies include one case of a mine-to-port railroad operating over a dedicated line with dedicated cars and locomotives, one case of a heavy haul railroad with heavy haul operations being only a small fraction of total traffic on the line, and one case of the transition of a railroad from mixed traffic to a dedicated heavy haul operation. A matrix of best practices is presented for railroads with a wide range of external variables in terms of axle load, track curvature, and annual tonnage. The solutions chosen from the options given must also be designed to be specific to the operating conditions of the railroad. A dedicated rail line carrying only dedicated cars and locomotives can consider options that are not appropriate for a heavy haul operation that moves on a line that carries other kinds of trains These case studies and the matrix of best practices show that there is no one perfect solution that applies to all circumstances. Solutions applicable to the case of the dedicated mine-to-port line with dedicated locomotives and cars are different from those to a railroad with mixed traffic. The matrix of options solutions emphasizes the variety of approaches that should be examined before arriving at an optimum decision for a particular property.

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Because there are many possible solutions, Parts 2 and 3 of this handbook include summaries of current knowledge on wheels and cars and on rails and track. Revisions to this handbook will be considered at regular intervals as comments for its improvement are received and as new technology and new field information become available.

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These guidelines were prepared and edited by the Technical Review Committee appointed by the IHHA Board of Directors. Dr. William J. Harris, Jr. Chairman Emeritus, IHHA, USA

Dr. Harris served from 1970 to 1985 as Vice President, Research and Test Department of the Association of American Railroads. He served as the first Chair of IHHA. Prof. Dr. Willem Ebersöhn (former Chair Railroad Engineering, University of Pretoria, South Africa)Director, Engineering Services, AMTRAK, USA

Dr. Ebersöhn established the Chair in Railway Engineering while serving on the faculty of Engineering Department of Civil Engineering, University of Pretoria, South Africa. He worked extensively on heavy haul problems with Spoornet and on high-speed track problems with Amtrak in the USA. Dr. James Lundgren, Assistant Vice President ,Transportation Technology Center, Inc. USA

Following service in the engineering department of CN Rail, Dr. Lundgren joined the Association of American Railroads representing the railroad industry at the Transportation Test Center while under Federal Railroad Administration operation and through the successful transition to AAR management of TTC. He has been associated with IHHA since its inception. Mr. Harry Tournay, Assistant General Manager of Spoornet, South Africa

Mr. Tournay has been associated with the design and development of improved rolling stock and locomotives of Spoornet. He has designed rolling stock internationally and has particular expertise in wheel/rail interface issues. Dr. Prof. Sergey Zakharov, Head of the Division of Tribology, at the All-Russian Railway Research Institute. Russia

Dr. Zakharov has spent his career researching the development of diesel electric locomotives and solving diverse railroad tribology problems. He has concentrated recently on 11 years of study of the wheel/rail interface issues and tribology aspects of interaction including taking a major part in organizing IHHA-99 STSConference on Wheel/Rail Interface.

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Acknowledgements The TRC recognizes the importance of the 16 conferences and technical sessions sponsored by organizations represented by the Board of Directors of IHHA. Without the rich technical literature created by the authors of the outstanding technical papers presented, it would have been impossible to prepare and publish these guidelines. Recognition of each author’s work is given at the beginning of their respective chapters. The TRC appreciates and recognizes the contributions made by BHP of Australia, Canadian Pacific Railroad of Canada, and CVRD of Brazil for their distribution and willingness to share data from their experience in the case studies presented in Part 4. The authors of the case studies are recognized in the text. In addition to the support provided by the IHHA Board and the reviews of the International Review Panel, the TRC wishes to acknowledge the outstanding help of Dr. Alexander Lisitsyn, General Director, Member of the Board, Ministry of Railways, Russian Federation. He and his staff at the All-Russian Railway Research Institute sponsored a very effective and special Technical Session in June 1999, on wheel/rail interface issues and heavy haul best practices. The TRC recognizes the early contributions of Wardina Oghanna in the organization of the guidelines and his services in helping to bring together the successful meeting in Moscow. Dr. Oghanna worked on the interpretation of this conference as a basis for many aspects of the guidelines. The TRC also wishes to recognize and express its appreciation to the China Railway Society and to the China Academy of Railway Sciences for their continued support of IHHA goals in hosting two conferences in China, which have produced technical papers upon which portions of these guidelines are based. The TRC further wishes to note the special contributions made by Michael Roney, General Manager Engineering Services and Systems, Canadian Pacific Railroad, who met often with the TRC and wrote parts of the handbook, as noted in the chapters. The TRC especially appreciates the leadership of Scott Lovelace, Chief Executive Officer of IHHA for accomplishing this difficult mission.

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The TRC also wishes to express great appreciation to Roy Allen, President of TTCI, Jim Lundgren, Assistant Vice President Finance and Corporate Development, Peggy L. Herman, Manager Documentation, and support from each of their staff members for undertaking the publishing of the handbook in a timely and effective manner. Much of the handbook’s guidelines was written by members of the Technical Review Committee. However other authors were invited to prepare special material. Their names are cited where appropriate. The Technical Review Committee established an International Review Panel of distinguished heavy haul experts to review various drafts of the handbook. The Review Panel offered many very helpful comments that are reflected in the final text. Members of the International Review Panel are: Mr. John Elkins, President, RVD Consulting, Pueblo, Colorado, USA Professor Conrad Esveld, Esveld Consulting, The Netherlands Dr. Stuant Grassie, Consulting Engineer, UK Dr. Joe Kalousec, Principal Research Officer, National Research Council, Research Center for Surface Transportation Technology, Canada Mr. Eric Magel, Associate Research Officer, National Research Council, Research Center for Surface Transportation Technology, Canada Dr. Steven Marich, Consulting Services, Australia Dr. Wardina Oghanna, Director, Australian Railway Research Institute, Australia Professor Klaus Reisberger, University of Graz, Austria Mr. Mike Roney, CP Rail, Canada Dr. Yoshohiko Sato, Nippon Kikai Hosan, Japan Dr. Kevin Sawley, Principal Investigator, TTCI, USA Prof. Evgeny Shur, All-Russian Railway Research Institute, Russia Mr. Dan Stone, TTCI, USA

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Special Note: References for each “part” are not combined at the end of the handbook. Instead, they are listed at the end of each respective chapter. TRC recognizes that some readers may skip around to different chapters, reading only certain parts pertinent to them. Therefore, the TRC thought it would be easier for each part to have its own list of references. The TRC will welcome any suggestions for improving the method of presentation in the next edition of the guidelines.

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TABLE OF CONTENTS PART 1: INTRODUCTION AND DISCUSSION OF GUIDELINES TO BEST PRACTICES 1.1 Discussion of Guidelines............................................. 1-1 1.2 A Systems Approach................................................... 1-1 1.3 Discussion of the Wheel and Rail Interface ................ 1-1 1.4 Example of Cost Benefit Analysis ............................... 1-9 1.5 Discussion of Part 2 on Vehicle/Track Interactions .... 1-9 1.6 Discussion of Part 3 on Wheel/Rail Interfaces.......... 1-10 1.7 Discussion of Part 4 on Four Case Studies .............. 1-10 1.8 Discussion of Part 5 on Optimizing Heavy Haul Maintenance Practices ............................................. 1-11 PART 2: SUPPORT TECHNOLOGIES VEHICLE TRACK INTERACTION 2.1 Vehicle Track Interaction............................................. 2-1 2.2 Railway Wheelset and Track ...................................... 2-2 2.2.1 Vertical Forces between Wheel and Rail .......... 2-5 2.2.2 Lateral Forces between Wheel and Rail ........... 2-6 2.3 Generic Railway Vehicle Suspensions ..................... 2-11 2.3.1 Vertical Suspension......................................... 2-11 2.3.2 Inter-Wheelset and Lateral Suspension .......... 2-18 2.4 Practical Heavy Haul Vehicle Suspensions .............. 2-27 2.4.1 Heavy Haul Wagon Bogies.............................. 2-27 2.4.2 Locomotive Bogies .......................................... 2-40 2.5 Rail and Wheel Profile Design .................................. 2-41 2.5.1 Basic Considerations....................................... 2-42 2.5.2 Wheel and Rail Profiles Divided into Functional Sections ............................................................ 2-45 2.5.3 Rail and Wheel Management .......................... 2-56 2.6 Tracking Accuracy and Tolerances........................... 2-60 2.6.1 Geometric Inaccuracies in Wheelset and Track Geometry......................................................... 2-61 2.6.2 Geometric Inaccuracies of the Wheelset and Suspension...................................................... 2-63 References ....................................................................... 2-69 Appendix .......................................................................... 2-70

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PART 3: WHEEL/RAIL PERFORMANCE 3.1 Application of Systems Approach to Wheel/Rail Performance Study..................................................... 3-1 3.2 Rail Contact Mechanics .............................................. 3-4 3.2.1 General .............................................................. 3-4 3.2.2 Normal Contact Stress ...................................... 3-4 3.2.3 Creep Force—Creepage Behavior .................. 3-11 3.2.4 Influence of Traction on the Load Carrying Capacity of the Contact Area .......................... 3-15 3.2.5 Approach to Wheel and Rail Profile Stress Optimization .................................................... 3.17 3.3 Rail and Wheel Materials .......................................... 3-18 3.3.1 Chemical Composition..................................... 3-18 3.3.2 Microstructure.................................................. 3-19 3.3.3 Mechanical Properties ..................................... 3-22 3.3.4 Wheels............................................................. 3-26 3.3.5 General Concept of Wheel/Rail Material Selection ............................................ 3.26 3.4 Lubrication and Friction Management....................... 3-28 3.4.1 Some Tribology Considerations ...................... 3-28 3.4.2 Rail Gauge/Wheel Flange Lubrication............. 3-29 3.4.3 Friction Control and Management ................... 3-36 3.5 Rail and Wheel Damage Modes; Mechanisms and Causes ..................................................................... 3-41 3.5.1 Wear ................................................................ 3-42 3.5.2 Recommendations to Decrease Wheel and Rail Wear......................................................... 3-51 3.5.3 Rolling Contact Fatigue Defects ...................... 3-52 3.5.4 Head Checks ................................................... 3-55 3.5.5 Tache Ovale (Shatter Crack from Hydrogen).. 3-57 3.5.6 Squats.............................................................. 3-58 3.5.7 Rolling Contact Fatigue Defects of Wheels— Shelling and Spalling....................................... 3-60 3.5.8 Other Rail and Wheel Defects ......................... 3-63 3.5.9 Plastic Flow...................................................... 3-69 3.5.10 Rail and Wheel Corrugations.......................... 3-73 Acknowledgements .......................................................... 3-76 References ....................................................................... 3-77 Appendix A ....................................................................... 3-84 Appendix B ....................................................................... 3-86

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PART 4(a): HEAVY HAUL CASE STUDY: Dedicated Line with Captive Equipment, BHP Iron Ore, Australia 4.1(a) Introduction ............................................................. 4-1 4.2(a) Wheels .................................................................... 4-2 4.3(a) Modified Profiles ..................................................... 4-3 4.4(a) Material Characteristics .......................................... 4-5 4.5(a) Lubrication ............................................................. 4-7 4.6(a) Wheel Design ......................................................... 4-7 4.7(a) Bogie Characteristics.............................................. 4-7 4.8(a) Wheel Maintenance ................................................ 4-8 4.9(a) Summary ................................................................ 4-9 PART 4(b) : CASE STUDY OF WHEEL/RAIL COST REDUCTION ON CANADIAN PACIFIC’S COAL ROUTE 4.1(b) Nature of the Business ......................................... 4-11 4.2(b) Characteristics of the Route ................................. 4-11 4.3(b) The Consist........................................................... 4-12 4.4(b) Early Problems ..................................................... 4-12 4.5(b) Initial Attempts to Control Rail and Wheel Wear Costs ................................................ 4-13 4.6(b) Benefits of Frame-Braced Steerable Trucks ........ 4-16 4.7(b) Premium Rail Steels and Extended Wear Limits.. 4-17 4.8(b) Increased Axle Loads and AC Traction ................ 4-19 4.9(b) Further Cost Savings ............................................ 4-20 4.10(b) The Size of the Prize .......................................... 4-22 PART 4(c) Wheel And Rail Performance at Carajás Railway 4.1(c) Introduction to Carajás Railway ............................ 4-25 4.2(c) Historical Data....................................................... 4-25 4.2.1(c) Wheels............................................................ 4-25 4.2.2(c) History............................................................. 4-26 4.2.2.1(c) During 1986 .............................................. 4-26 4.2.2.2(c) During 1987 .............................................. 4-26 4.2.2.3(c) During 1988 .............................................. 4-28 4.2.2.4(c) During 1989 .............................................. 4-29 4.2.2.5(c) During 1990 .............................................. 4-29 4.2.2.6(c) During 1992 .............................................. 4-29 4.2.2.7(c) During 1993 .............................................. 4-30 4.3(c) Improvements ....................................................... 4-30 4.3.1(c) Wheels Management Model........................... 4-30 4.4(c) Rails ...................................................................... 4.34 4.4.1(c) History............................................................. 4.35 4.4.1.1(c) 1987............................................................. 4-35 4.4.1.2(c) From 1987 to 1999 ...................................... 4-35 4.4.1.3(c) 1988............................................................. 4-35

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4.4.1.4(c) 1990............................................................. 4-35 4.4.1.5(c) 1991............................................................. 4-35 4.4.1.6(c) From 1993 to 1996 ....................................... 4-36 4.4.1.7(c) 1997.............................................................. 4-36 4.5(c) Looking for a Solution ........................................... 4-36 4.5.1 Introduction ......................................................... 4-36 4.6(c) Methodology and Approach of TTCI's Comprehensive Program On Carajás Railway..... 4-39 4.7(c) Implementation of TTCI's Wheel/Rail Life Optimization Program on Carajás Railway........... 4-40 4.7.1(c) Ore Wagon Truck Performance Evaluation and Modeling .................................. 4-40 4.7.2(c) Full-scale Testing of Standard and Frame Braced Trucks with Load Measuring Wheelsets.......................................................... 4-46 4.8(c) Methodology of Recommendations for Rail Grinding Practices .................................... 4-48 4.8.1(c) Lubrication Practice ........................................ 4-52 4.8.2(c) Implementation of TRACS and the Wheel Life-Cycle Costing Model ................. 4-54 4.9(c) Conclusions .......................................................... 4-55 References ....................................................................... 4-58 PART 4(d) Quick Reference Tables for Basic Heavy Haul Rail System Design 4.1(d) Introduction ........................................................... 4-59 4.2(d) Using the Design Tables....................................... 4-61 4.3(d) References ........................................................... 4-61 4.4(d) General Notes....................................................... 4-62 4.5(d) Table Notes: (brief descriptions of salient features of component classes)............................ 4-63 PART 5: Maintaining Optimal Wheel and Rail Performance 5.1 Maintaining Optimal Wheel and Rail Performance ..... 5-1 5.2 Rail Structural Deterioration........................................ 5-6 5.2.1 Management of Rail Testing to Control Risk of Rail Fracture ................................................ 5-6 5.2.2 The Framework for Risk Management ................. 5-7 5.2.3 Defect Occurrence Rates ................................... 5-10 5.2.4 Critical Defect Sizes............................................ 5-13 5.2.5 Rail Fatigue Projection........................................ 5-15 5.2.5.1 Use of Weibull Distribution to Predict Rail Flaw Occurrence Rates......................................... 5-16 5.2.6 Modes of Rail Testing ......................................... 5-21 5.2.6.1 Rail Testing Equipment ................................ 5-24

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5.2.7 Ultrasonic Principles ........................................... 5-25 5.2.8 Inspection Effectiveness ..................................... 5-27 5.2.8.1 Test Probes .................................................. 5-27 5.2.8.2 Signal Processing......................................... 5-29 5.2.8.3 Displaying Indications to the Operator ......... 5-30 5.2.8.4 Operator Vigilance........................................ 5-30 5.2.8.5 Estimates of Rail Testing Reliability ............. 5-31 5.2.9 Selecting Rail Testing Intervals .......................... 5-34 5.2.9.1 Performance-Based Adjustment of Test Intervals ................................................ 5-37 5.2.9.2 A Parametric Approach ................................ 5-38 5.2.9.3 Cluster Testing ............................................. 5-39 5.2.9.4 Special Care in Special Track Work............. 5-40 5.2.9.5 Rail Testing Intervals ¾ Canadian Pacific Approach.......................... 5-41 5.2.10 Induction Measuring Principles......................... 5-43 5.2.11 Conclusion ........................................................ 5-45 5.3 Rail Wear Measurements ......................................... 5-45 5.3.1 Rail Wear Measurement Techniques ................. 5-45 5.3.2 Rail Wear Projection ........................................... 5-52 5.4 Rail Profile Maintenance Practices ........................... 5-54 5.4.1 Rail Grinding ....................................................... 5-54 5.4.1.1 Objectives of Rail Grinding ........................... 5-54 5.4.1.1.1 Longitudinal Rail Profile Corrections ...... 5-55 5.4.1.1.2 Transverse Rail Profile Correction ......... 5-57 5.4.1.1.3 Effects of Rail Shape Parameters on Rail Damage .......................................... 5-60 5.4.1.1.4 Grinding for Surface Condition............... 5-63 5.4.1.2 Grinding Stones and their Effects................. 5-64 5.4.1.2.1 Abrasive Stone Technology ................... 5-64 5.4.1.2.2 Surface Finish ........................................ 5-66 5.4.1.2.3 Effects of Speed and Pressure .............. 5-68 5.4.1.3 Grinding Patterns and their Use ................... 5-70 5.4.1.4 North American Grinding Practice................ 5-76 5.4.1.5 Optimizing Rail Profiles ................................ 5-78 5.4.1.5.1 Rail Profile Design.................................. 5-80 5.4.1.5.2 Rail Stresses and Pummeling ................ 5-81 5.4.1.5.3 Tangent Track ........................................ 5-84 5.4.1.5.4 High Rail Profiles.................................... 5-84 5.4.1.5.5 Low Rail Profiles..................................... 5-85 5.4.1.6 Lubrication and Grinding .............................. 5-86 5.4.1.7 Optimal Wear Rate ....................................... 5-86 5.4.1.8 Rail Grinding Strategies................................ 5-88

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5.4.1.8.1 Preventive Rail Grinding......................... 5-82 5.4.1.8.2 Preventive vs. Corrective Rail Grinding . 5-89 5.4.1.9 Transitioning from Corrective to Preventive Grinding ...................................... 5-90 5.4.1.9.1 Preventive Gradual Grinding............... 5-91 5.4.1.9.2 Results ................................................ 5-92 5.4.1.9.3 Rail Wear ............................................ 5-93 5.4.1.9.4 Rail Surface Condition ........................ 5-94 5.4.1.9.5 Detail Fracture Rates .......................... 5-95 5.4.1.10 Advance Planning to Increase Grinding Production ................................ 5-95 5.4.1.11 Maintaining Quality Control ..................... 5-96 5.4.1.11.1 Grinding Power ................................. 5-96 5.4.1.11.2 Ground Rail Profile............................ 5-96 5.4.1.11.3 Longitudinal Rail Profile .................... 5-98 5.4.1.11.4 Transverse Rail Profile...................... 5-98 5.4.1.11.5 Metal Removal .................................. 5-99 5.4.2 Rail Planing......................................................... 5-99 5.4.2.1 Description of the SBM 140 Rail Planing Machine ......................................... 5-100 5.4.3 The Planing Process......................................... 5-101 5.5 Wheelset Failure Risk Management and Maintenance............................................................ 5-103 5.5.1 Wheelset Reliability (Spoornet) ........................ 5-105 5.5.1.1 New Components ....................................... 5-105 5.5.1.2 Used Components...................................... 5-106 5.5.1.3 Condition Monitoring................................... 5-107 5.5.1.3.1 Wayside Condition Monitoring ............. 5-107 5.5.1.3.2 Run-in Inspections................................ 5-108 5.5.1.3.3 Four Monthly Maintenance Depot Inspections........................................... 5-109 5.5.1.3.4 Workshop Maintenance........................ 5-109 5.5.1.4 Wheel Profile Monitoring ............................ 5-109 5.5.2 Wheelset Maintenance ..................................... 5-110 5.6 Wheel and Vehicle Interaction Condition Measures5-112 5.6.1 Wheel Wear Measurement Techniques ........... 5-113 5.6.2 Wheel and Vehicle Track Interaction Wayside Measuring System............................. 5-120 5.6.2.1 Weighing in Motion and Wheel Impact Measurement (WIM-WIM) .......................... 5-121 5.6.2.2 The Low-Speed Weigh Bridges.................. 5-122 5.6.2.3 Hot-Box, Hot and Cold Brake Detectors..... 5-123 5.6.2.4 The Acoustic Defective Bearing Detection . 5-124

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5.6.3 Design Considerations...................................... 5-124 5.7 Practical Application of Wayside Lubricators .......... 5-125 5.7.1 Friction Management ........................................ 5-126 5.7.2 Benefits of Effective Rail Lubrication ................ 5-127 5.7.3 Wayside Lubrication Capabilities and Operation................................ 5-128 5.7.4 Selecting the Most Appropriate Equipment for Dispensing the Lubricant .................................. 5-128 5.7.5 Selecting the Optimal Type of Grease for the Particular Operating Environment..................... 5-130 5.7.6 Measurement and Management of Lubrication Effectiveness..................................................... 5-132 5.7.7 Positioning of Lubricators ................................. 5-136 5.7.8 Lubricator Placement Model ............................. 5-138 5.7.8.1 Track Related Factors ................................ 5-138 5.7.8.2 Traffic Related Factors ............................... 5-139 5.7.9 Case Study: Lubrication - Richards Bay Line, South Africa ...................................................... 5-140 5.8 Optimizing Wheel and Rail Life............................... 5-143 5.8.1 Rail Optimization............................................... 5-144 5.8.1.1 The Rail Management Decision Zones ...... 5-144 5.8.1.2 Controlling Rail Wear (Maximum Rail Wear Limits)............................................... 5-148 5.8.1.3 Rail Use Strategy........................................ 5-154 5.8.1.4 Lubrication and Curve Elevation Monitoring5-157 5.8.1.5 Transposition .............................................. 5-158 5.8.2 Wheel Optimization........................................... 5-159 5.8.3 Friction Management (Interface Optimization) . 5-163 5.8.4 A System Approach for Managing the Wheel/Rail Interface ......................................... 5-164 5.9 Conclusion............................................................... 5-165 Acknowledgements ........................................................... 5-166 References ........................................................................ 5-166 GLOSSARY.......................................................................... G-1 METRIC CONVERSION CHART

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Part 1: Introduction and Discussion of Guidelines to Best Practices Written by Dr. William J. Harris, Chair, Technical Review Committee (TRC), Mr. Harry Tournay, IHHA Board of Directors and TRC member, Dr. Willem Ebersöhn, TRC member, Dr. Sergey Zakharov, TRC member, and Dr. James Lundgren, TRC member

1.1 Discussion of the Guidelines These guidelines offer insights into ways to optimize a heavy haul railway operation. In Section 1.2, there is a description of the importance of addressing the process using a systems approach. Section 1.3 is an extended review of the wheel/rail interface, and Section 1.4 is an account of a cost/benefit analysis. The introduction concludes with Sections 1.5 to 1.8, which contain brief comments on each of the succeeding four parts of the handbook.

1.2 A Systems Approach The guidelines emphasize that it is no longer adequate to change one part of the railway system without examining its impact on the other parts of the system. Increasing car weight can have a profound effect on track and bridges. Changing rail properties can lead to unexpected wheel behavior. Therefore, the balance of the guidelines in this handbook will emphasize the interactions of components and the importance of dealing with the wheel-rail problem as a system. A system approach to the design and maintenance of wheel and rail interface, in the form of best practices, can be expected to result in minimization of rail gauge face and wheel flange wear, avoidance of detrimental wheel and rail defects, stable vehicle performance, including safety issues, and minimization of noise generation. 1.3 Discussion of the Wheel and Rail Interface The wheel and rail interface is the key to the heavy haul problem. At that interface, there must be low friction to permit moving heavy loads with little resistance. However, there must be enough friction to provide tractive effort,

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braking effort, and steering of the train. The materials must be strong enough to resist the vertical forces introduced by very heavy loads and the dynamic response at the wheel-rail interface introduced by vertical and lateral accelerations of the car induced by track and wheel irregularities. However, neither the wear rate nor the brittle failure rate should be so great that cost-effective heavy haul operations are threatened. The remarkable ability of a steel wheel rolling on a steel rail to carry a very heavy load seemed almost a miracle 175 years ago, when railroads first began to operate. Of course at that time loads were low compared to those of today. The increase in axle loads has been gradual but steady for decades. Over 50 years ago, the rate of increase changed. Suddenly it was necessary to improve subgrade and ballast as well as ties and tie fasteners. Suddenly it was necessary to increase rail hardness and improve rail quality and to introduce headhardened rail in some cases. Suddenly it was essential to improve wheels and car suspension systems. Suddenly it was necessary to increase inspection capabilities and frequencies to reduce accidents and improve service. These requirements for improved materials, designs, and practices were based on field experience, when necessary, and on research, when available. Whatever the nature of the problems, continued attention to rail and wheel technology has provided the basis for continued increases in axle loads. These guidelines suggest options to improve the initial components and systems as well as practices to ensure through maintenance the continued effectiveness of the wheel/rail system to carry increasingly heavier loads. The technology of a steel railway wheel rolling on the rail is eminently suitable for heavy haul, heavy axle load operations. The unique properties of steel-on-steel contact results in minimal deformation of both contacting bodies under load. This results in rolling contact with minimum energy losses in friction across the contact patch and in minimum damping within the material of the contacting bodies. This is why the rolling resistance associated with railroads is so low and permits the transport of vast tonnage.

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The contact patch is surprisingly small with correspondingly high-contact stresses. Typically, contact is made over a quasi-elliptical contact patch the size of a small coin of 13-millimeter (½-inch) diameter (see Figure 1.1). This implies that a 20,000-tonne train is supported over an area equivalent to the surface of a kitchen table (1.3 m x 1.3 m or 4½ ft x 4½ ft)!

CONTACT PATCH CENTRALLY PLACED

sZ sY

sX sY

sX sZ

sz 1400 Mpa sX sY 800 Mpa Yield Stress is 600 – 800 Mpa

Figure 1.1. Contact between Wheel and Rail: Wheel Centrally Placed on the Track

Immediately beneath the contact patch in either the wheel or rail, the steel is under tremendous pressure from all directions as the contact pressure is “supported” by reaction pressures from the surrounding material of either wheel or rail. This is depicted in Figure 1.1 by the arrows converging on an element of steel beneath the contact patch. This is termed a triaxial state of stress. Each of the “stress arrows” as shown presses almost equally on the steel, which has no direction in which to move or “flow” and can withstand the load. Under these conditions, and using high strength steels, axle loads beyond present day applications (up to perhaps 60 t or beyond) should be possible. The reasons that railroads have not reached these loads, o 1-3 x

and why some railroads have trouble with prevailing axle loads, are that these ideal-contact conditions, described above, are not always achieved, because of the following: •

Track and vehicle conditions can result in dynamic loads, which are well in excess of the static and often result in impact between wheel and rail.



The contact patch can be severely reduced under some uncontrolled wheel/rail contact conditions.



The delicate balance of the tri-axial state of stress can become upset by: § Frictional forces acting across the contact patch or contact occurring on the edge of either wheel or rail. § Two-point contact occurring with gross relative slippage over one or both contact patches with associated accelerated wear.

Figures 1-2 through 1.6 are typical examples of adverse wheel/rail contact conditions. Brief comments are given before each figure. Figure 1.2: Dynamic impact loading caused by wheel flats, rail joints, soft rail welds, rail corrugations, and discontinuities at switches.

Wheel Skid

IntermediateFrequency Impacts

RAIL JOINT

Dynamic Load

Static Load

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Figure 1.2

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Figure 1.3: Intense single point contact between flange throat and the gauge corner of the rail, which results in head-checking and shelling.

CONTACT PATCH

FLANGE CONTACT

SHELLING

sZ sY HEAD CHECKING

sX sY

sX sZ

Figure 1.3

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Figure 1.4: Intense convex contact between the rail crown and wheel, which can result in material flow on the field side, shelling of the rail crown and/or wheel tread. This is exacerbated if contact is made toward the outer edges of the rail and wheel where there is no material to “support” the element under the contact patch. The favorable state of stress is “upset” and material flow occurs.

CENTRALLY PLACED

dX

CONVEX SHAPE

dZ

Figure 1.4

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dY

CONTACT PATCH

Figure 1.5: Lateral slipping between wheel and rail in curves is a result of badly tracking vehicles. The forces tangential to the contact patch as a result of slippage or micri-slip cause deformation of the elements of steel under the contact patch. This “upsets” the supporting pressures/stresses on the element resulting in material flow and can result in intermittent crown wear and deformation experienced as corrugations or general material flow.

FIELD SIDE CONTACT WORN CONDITIONS

CONTACT PATCH 19.5

7

sZ sX

sY sX

Figure 1.5

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sY sZ

Figure 1.6: Inappropriate control of the contacting shapes can limit the size and shape of the contact patch causing intense stresses, material flow, and fatigue. Defects in rail or wheel material in the region of the intense contact stresses exacerbate the problem.

CONTACT 19.5 PATCH

FIELD SIDE CONTACT WORN CONDITIONS

7

sZ sY sX

sX sY sZ

Figure 1.6

The railroad that can minimize the above mentioned issues is the railroad that will be capable of increasing axle load or reducing maintenance in relationship with huge advantages over its competition.

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1.4 Example of Cost Benefit Analysis In addition to the technical issues that characterise the wheel/rail system, there are very importance economic issues. It is essential to take into account a cost/benefit analysis in the course of making technical decisions. These are illustrated in the following remarks. Rail is the single most expensive element of the track structure. On many railways, it is behind only labor and fuel as an expense item. The tonnage carried by a rail before it is condemned can range from less than 100 million gross ton to close to 2.5 gigga gross ton. As an example of the value of rail maintenance management, assume that a single kilometre of rail costs $180,000 to install. Track engineers decide that the rail has a badly fatigued surface and has reached the end of its service life. They call for it to be replaced, gaining a salvage value of $18,000. But now assume that instead of replacing the rail, they did some corrective rail grinding costing $1800 and left the rail in track. The railway then invested the $180,000 – $18,000 - $1,800 = $160,200 in the construction of a new customer facility at a rate of return of 20%. This earned $160,000 * 20% = $32,000 in its first year. The next year, the track engineers see that their rail is approaching allowable wear limits and schedules a rail replacement, now costing $187,200 due to cost escalation of 4%. But they have made for the railway $32,000 – ($187,200 – 180,000) = $24,800 by deferring replacement of rail in that kilometre, without consequence, for an extra year. And that is why they collect a salary.

There is significant money to be made by deferring rail replacement as much as possible without incurring risk. Certainly it is a major responsibility of the track engineer to ensure that he gets the most out of his rail, and rail profile maintenance and rail testing are his most important tools to do this.

1.5 Discussion of Part 2 on Vehicle/Track Interactions Part 2 of the guidelines discusses the vehicle/track interactions. These are the components that are given significant attention

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when track is laid out and freight cars and locomotives are purchased. The contribution of the suspension systems and other design features of the cars and the subgrade, ballast, ties, and tie fasteners to the operations of the vehicle/track system are discussion in Part 2 and options are described that can help in optimizing the vehicle/track system.

1.6 Discussion of Part 3 on Wheell/Rail Interfaces Part 3 of the guidelines addresses the wheel/rail interface issues. It gives an overview of rail contact mechanics, wheel and rail materials characteristics, lubrication and friction management practices, and damage modes and their mechanisms. It discusses the contribution of the research to the behavior of the wheel and the rail. Through the explanation of mechanisms, processes, and causes of damages, it gives the justification of suggested solutions. Part 3 offers recommendations that can be adopted by operating personnel and an input to an optimized system.

1.7 Discussion of Part 4 on Four Case Studies Part 4 of the guidelines offers the reader several case studies. The first of these is based one of the great heavy haul railway success stories, that of the experience of BHP, Australia, and describes ways that BHP optimized heavy haul operations on a mine to port railroad over a dedicated line with dedicated cars and dedicated track. Under this set of circumstances, it has been possible to fine tune the system. Since every car is the same, or its differences are fully understood, and the track is the same, it is possible to monitor the behavior of the system and improve decisions for replacements as well as to achieve optimum maintenance practices. The second case is based on the experience of the Canadian Pacific Railroad in which about 10 percent of the total traffic on a specific line is heavy haul traffic and the balance is mixed freight. This case study shows that it is possible to achieve partial optimization by choices made regarding the heavy haul segment of the traffic, but not to gain the full advantages that can be gained in a dedicated railroad in which the entire system is under the control of the heavy haul operators. o 1-11 x

The third case is derived from the experience of the Companhia Vale do Rio Doce (CVRD) line in Brazil. This line started as a mixed freight line and was gradually transformed into what it is today, a dedicated heavy haul line. It did not start by making the kinds of decisions that were made at BHP to reflect the heavy haul operations in the lay out of the track. However, the CVRD experience shows that it is possible to make significant progress toward optimization as steps are taken to utilize improved practices in the course of the transition to a dedicated heavy haul railway. The final case study presented in Part 4 describes a matrix of options for optimized heavy haul solutions. The matrix presents information on suggested changes in practice as conditions change. It describes the changes appropriate for a line with greater curvature. It discusses the options to be considered as annual tonnage increases. It discusses the impact of changes in axle load on rail and wheel and vehicle and track options. This matrix of examples offers guidance as to the direction in which changes should be considered as changes occur in traffic and in terrain. From study of these cases, it becomes clear that there is no single “best practice.” There are improved practices that can be adapted to the special circumstances of a given route, a given traffic density, a given axle load, and other circumstances applicable to a given railway operation. That is the reason that the TRC has attempted to provide Part 2 of these guidelines with insights regarding the vehicle and the track and Part 3 with insights into the wheel/rail interface for use by the managers of a given railroad operating under specified circumstances. That is the reason for including Part 5 with its emphasis on maintenance.

1.8 Discussion of Part 5 on Optimizing Heavy Haul Maintenance Practices Part 5 addresses the issue of maintaining vehicles, track, wheels and rail. After making sound initial decision, it is essential to establish a maintenance procedure that is based on effective measurement of deterioration and a set of processes to restore

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wheels and rail as well as equipment and track to their desired conditions. These inspection and maintenance practices must also provide a basis for identifying and removing seriously flawed components. Thus, the combination of acquisition decisions based on an understanding of the wheel/rail interface and vehicle track interactions with the design of a comprehensive maintenance program can achieve the desired optimum heavy haul operations in systems around the world.

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PART 2: SUPPORTING TECHNOLOGIES VEHICLE TRACK INTERACTION Written by Mr. Harry Tournay, IHHA Board of Directors and Technical Review Committee (TRC) member

2.1 Vehicle Track Interaction Railway vehicles form a subset of terrestrial vehicles that are supported and receive lateral guidance from track structure. Road vehicles form another subset where road or terrain supports them. Drivers operate road vehicles by guiding the steering wheel or related mechanism. This action alters the rolling orientation of certain wheels on the vehicle, thus changing the direction of travel. The rail-bound vehicle reacts to the topology of the track to follow the pre-determined path defined by the track. The crown of the rail not only provides vertical support but also lateral guidance of the wheels of the vehicle. The efficient interaction between vehicle and track can support very heavy axle loads. On the other hand, inappropriate design and maintenance of the vehicle/track interface can lead to rapid degradation of components within the system and can jeopardize the profitability of the rail operation concerned. The objective of this chapter is to describe the important force mechanisms acting between the rail and wheel and the influence of vehicle design on these mechanisms. Typical symptoms of inappropriate interaction will be described so that the reader will recognize them and be able to take corrective action. Appropriate vehicle suspension configurations are described together with their critical characteristics for optimal operation. Optimal wheel and rail profiles are proposed for world’s best practice. The influence of vehicle and track accuracy on tracking performance is discussed. Issues relating to vehicle/track interaction in this chapter are described in a qualitative sense and refer to what are considered the driving interaction mechanisms. References are made to sources that give a more rigorous description of the interaction mechanisms.

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2.2 Railway Wheelset and Track The railway wheelset is traditionally comprised of two steel wheels that are fixed rigidly to a common axle (see Figure 2.1). Wheelsets with independently rotating wheels are being used to a limited degree on certain passenger rail vehicles, but not in heavy haul applications. The rolling surfaces of the wheels; i.e., the wheel profiles, are cut to a cone angle γ. Nowadays, more complex profiles termed “hollow,” “worn,” or “profiled” treads are used. These have an “effective conicity” of γ, as defined in the appendix.

ro γ

2l 2b

Figure 2.1: Railway Wheelset

The track comprises two rails laid on sleepers at a particular gauge, as Figure 2.2 shows. The rails are laid at an angle, β, to the sleeper to generally match the angle, γ, of the wheelset profile. This assists in stabilizing the rail against rollover as the normal reaction to the contact with the wheel passes through the foot of the rail. When concrete sleepers are used, the connection between the rail and the sleeper is generally made with a rail chair and a resilient pad, which are inserted between the rail and sleeper to attenuate high-frequency vibrations and to protect the sleeper. Spring clips are used to fasten the rail to the sleeper. Timber sleepers, on the other hand, give an additional degree of inherent resilience.

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Gauge β

Rail Pad

Rail Chair

Figure 2.2: Track Gauge

A layer of ballast supports the sleeper. The ballast permits alignment adjustment, as well as vertical, lateral, and longitudinal stabilization of the track. It further provides some vertical resilience to passing trains. The structure of the ballast also provides protection to the track substructure by spreading the load and by dissipating vibration energy. The voids in the ballast permit drainage and a degree of accumulation of fine material, without any significant change to the alignment or resilience of the track. Railway track is generally “banked” or superelevated in curves to counter centripetal forces without appreciably transferring wheel loads between outer and inner rails as the vehicle negotiates the curves at a higher speed. In the limit, superelevation helps prevent overturning of the vehicle. However, inappropriate matching of superelevation to vehicle speed can adversely influence the curving performance of the vehicle and, in turn, the wear and stresses in rail and wheel. The portion of track between tangent and curved track is termed a transition curve and the vehicle experiences this as track twisted about a longitudinal axis. This implies that the contact patches on the different wheels may not be in the same plane. This would lead to a loss of normal load between some wheels and the rail if inappropriate suspension designs are o 2-3 x

used. Furthermore, the running surface of the rail is discontinuous at non-welded rail joints and certain types of crossings at switches. This can cause impact loads on the wheel and the rail and, momentarily, result in a shift in the wheel/rail contact position on the wheel profile. This may affect wheelset guidance. Steel-on-steel contact produces a uniquely low rolling resistance for railway vehicles. The geometry of the wheelset, described mathematically as a di-cone (two cones placed backto-back having a cone angle, 2γ), imparts on the wheelset unique properties of self-guidance; i.e., self-centering on tangent track as Figure 2.3 shows, and the ability to negotiate curves as Figure 2.4. shows. Hence, the railway wheelset also has the ability to accommodate diameter inaccuracies between the two wheels by displacing laterally on tangent track to compensate the diameter difference. These properties result from the rolling radius differential generated between the wheels on the common axle. The flange is used where track discontinuities or track geometry is so severe or the vehicle suspension is so inadequate that the properties of self-guidance of the wheelset are insufficient for guidance without flange contact.

Figure 2.3: Self-Centering Motion on Tangent Track

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Rc

y

cL Wheelset cL Track

Figure 2.4: Force Equilibrium in a Curve

2.2.1 Vertical Forces between Wheel and Rail A minimum vertical force between the wheel and the rail is required to generate the guidance forces described above. Failure to provide sufficient vertical wheel load can result in derailment. A derailment is the first and most disastrous indication of inadequate vehicle/track interaction. Minimum values for vertical load are given, typically, in the research results of the European Rail Research Institute.1 The maximum allowable ratio between the lateral and vertical forces of a single wheel (known as the Y/Q force ratio) is used as a measure of the proneness to flange climb derailment. This ratio was originally suggested by Nadal.2 As Nadal’s criterion is generally quite conservative, especially for small or negative angles of attack, Weinstock defined a more realistic criterion based on the axle sum of the Y/Q values.6 Before this limit is reached, however, either vertical track alignment far exceeds acceptable norms or flange contact is excessive. Indeed, flange contact is often a sign of inadequate guidance and a source of wear and energy loss and should be addressed. The vehicle load, its speed, the vehicle suspension characteristics, and the track topology determine the vertical load over the contact interface. These are reflected in the load

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on the journal bearings and in turn the load across the contact patch. 2.2.2. Lateral Forces between Wheel and Rail In this section a variety of forces that act in the horizontal plane are described. The emphasis is on creep and flange forces. 2.2.2.1 Creep Forces The most efficient means of vehicle or wheelset guidance is by means of creep forces. Creep forces are the forces that are generated by the rolling of the railway wheelset, as a di-cone, on the track as Figures 2.3 and 2.4 show. Under these conditions, creep is produced as a result of a combination of adhesion and micro-slip across the rail/wheel contact interface. A more rigorous explanation is given in Part 3 and Reference 3. These creep forces are only generated when the wheelset deviates from a pure rolling position defined by its kinematic motion and must be reacted by forces generated at the journal bearings. Longitudinal and lateral creep forces are explained in more detail in the next two subsections. 2.2.2.1.1 Longitudinal Creepage Consider a wheelset deflected laterally from a pure rolling position by a distance y. This is referred to as the “Initial State” in Figures 2.5 and 2.6. On straight track (Figure 2.5), the pure rolling position is the centerline of the track. On curved track (Figure 2.6), the pure rolling position is a position towards the outside of the curve from the centerline where the radius differential between the wheels allows the wheelset to kinematically roll through the curve. On rolling forward with a velocity, v, the deflected wheelset will want to roll to a “Preferred State” as indicated by the chain-dotted outline of the wheelset shown in both figures. If the wheelset is constrained to remain in a similar attitude to the track, as it was in the “Initial State,” creepage takes place as the wheels roll. In the case illustrated, the outer wheels of larger diameter slip back relative to the forward velocity of the wheelset with the smaller diameter wheels slipping forward. Slip forces, Fs are generated on the wheelset, which react

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against the constraining forces at the journals. Forces opposite to Fs are acting on the rail. The amount of creepage and the creep force generated are directly proportional to the displacement y and the cone angle γ. The constant of proportionality for creepage is dependent, inter alia, on axle load and contact geometry. The creepage mechanism within the contact patch is described more fully in Part 3. The above description is of a quasi-static form for the sake of simplicity. Remember that a similar model may be drawn in a dynamic sense with the inertia of the wheelset and suspension design adding to the constraining forces. The effects of excessive longitudinal creepage, combined with high-contact stresses, is often seen in material flow of the rail producing head checks and subsequent shelling (Figure 2.7), or flow of flash butt material on the gauge corner of the rail (Figure 2.8).

FS

FJ

Actual Final State

FJ FS

Preferred Final State

V

y

Initial State

cL Track

Figure 2.5: Longitudinal Creep on Tangent Track

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FS

FJ

FJ

V

FS

Actual Final State

Preferred Final State

y Initial Final State

cL Track Pure Rolling Position

Figure 2.6: Longitudinal Creep on Curved Track Head Checks

Shelling

Figure 2.7: Head checks and Subsequent Shelling

Flow of Flash-butt Weld

Figure 2.8: Material Flow in Heat Affected Zone

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2.2.2.1.2 Lateral Creepage Lateral creepage may be described in a similar manner. Consider a wheelset placed at an angle of yaw, á, on the track as Figure 2.9 shows. On rolling forward, the preferred final state of the wheelset is shown as chain-dotted. If the wheel is constrained by the vehicle suspension or a flange force to be oriented to the track in a similar position to the initial state, the wheelset must have slipped laterally. This lateral creepage and the associated force are proportional to the angle, á. The constant of proportionality is dependent, inter alia, on axle load and contact geometry. The creepage mechanism within the contact patch is more fully described in Part 3. High lateral creepage is reflected in lateral material flows in the rail crown in sharp curves or at large lateral track discontinuities as well as material flows on the wheel as shown in Figure 2.10. This is also associated with high flange forces as described below.

FS FL

Final State

FS V Preferred Final State

Initial State

α

cL Track

Figure 2.9: Lateral Creepage on Tangent Track

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Forces Material Flows Lateral Creep

Lateral Creep Flange Force High Contact Stresses

Flange & Rail Wear

Figure 2.10: Worn Rails in a Curve

2.2.2.2 Flange Forces When steering cannot be achieved by means of creep forces, flange contact is made and a lateral flange force acts to keep the wheelset from derailing. Flange contact is often made with an angle of attack, á, implying the presence of lateral creepage. A lateral force model of the wheelset under flange contact and with lateral creepage is shown in Figure 2.10. This figure describes typical reasons for the shape of worn rail in curves. Associated with the flange force is a frictional component that can lead to a reduction in load over the contact patch and result in wheel climb and subsequent derailment. The action of this force is included in the theory of Nadal mentioned earlier. 2.2.2.3 Other Forces Other forces, like spin creep and the gravitational forces, do act on the railway wheelset but are often of lesser magnitude than those described above and do not necessarily play a significant role. They are described in Reference 3 and other references on vehicle dynamics. Spin creep occurs when different parts of the contact roll on different radii relative to the axis of the axle. Hence, a rotational “scrubbing” action occurs at high contact angles. This has been associated, together with high contact stresses, with the formation of head checks. The couple associated with spin is considered to have a minimal influence on rail/wheel forces. A gravitational force is generated on the wheelset when the lateral components of the normal reaction to the contact patch are unequal. This force occurs when the wheelset is deflected laterally and non-conical or profiled wheels are used. o 2-10 x

2.3 Generic Railway Vehicle Suspensions The suspension of a bogie can be divided into the in-plane lateral and longitudinal suspension that dictates the tracking and curving performance, and the vertical suspension that carries the load and has an effect on the vertical wheel rail forces. Any practical railway vehicle requires at least two wheelsets. The manner in which these wheelsets are coupled to the vehicle has a significant influence on vehicle cost, the performance of the rail and the wheel, and the guidance and dynamics of the vehicle. Although there is a strong dynamic coupling between vertical and lateral dynamics, vehicle suspensions are generally discussed separately in terms of their vertical and horizontal; i.e., lateral and longitudinal, suspensions. Vehicle dynamics cannot be discussed without considering the properties of the track. Hence, track geometry and track stiffness is included in this generic discussion of railway suspension systems. 2.3.1 Vertical Suspension The purpose of the vertical suspension is threefold. These generic purposes are discussed below. 2.3.1.1 Attenuation of Vertical Vehicle Vibrations The vehicle, when moving forward on the track, experiences vibrations of varying frequencies which excite the various modes of the vehicle structure, body and the payload. The dynamic modes are generally in bounce, roll, pitch, nosing, and sway. Some of the exciting mechanisms are: •

Long wavelength track alignment irregularities in the vertical profile and track twist. These irregularities typically result in vehicle input frequencies between 0.5 and 30 Hz.



Long wavelength track stiffness variations are also present and activate the vehicle in similar modes and frequencies as the alignment irregularities.



Short wavelength, consistent stiffness variations associated with local sleeper support, results in vehicle input frequencies up to 40 Hz.



High frequency impacts at rail discontinuities (P1 o 2-11 x

forces) often excite the vehicle body vertical modes to induce the so-called P2 lower frequency reaction forces. 2.3.1.2 Equalization of Wheel Loads by the Vehicle Suspension As the vehicle is supported on a minimum of four contact patches on perturbed or twisted track, it is generically a statically indeterminate structure similar to a four-legged table on an uneven floor. As Section 2.2.1 states, sufficient vertical load is required across the contact interface for effective guidance. The vertical suspension stiffness must thus prevent unacceptable wheel unloading on twisted track. 2.3.1.3 Attenuation of Vertical Vibrations to the Track Structure As a result of vertical vehicle dynamics, dynamic loading is transmitted from the vehicle through the wheel into the track super and substructure. Track elements such as the rail, the rail pads, the sleepers, as well as the ballast and the sub-ballast layer, are thus directly influenced by the dynamic performance of the railway vehicle. The typical exciting mechanisms are: •

Vehicle body dynamics in the frequency range between 1 and 30 Hz



Out-of round wheels (10 to 20 Hz)



Wheel flats (10 to 20 Hz)



Rail irregularities, such as rail joints and skid marks Constraints that keep the vehicle dynamists from designing the optimum vehicle suspension are typically: •

Limit on the minimum vertical vehicle stiffness because of a limit on the coupler height differential between adjacent vehicles in the tare and loaded condition



Volume occupied by, as well as the stresses within, the suspension

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Initial cost of the suspension

• Maintenance cost of the suspension Similarly, the track engineer is limited in what he can do to optimize the track structure. Typical constraints are: •

The cost of rail pads.



Cost constraints on the amount of ballast and formation material and other geo-technical materials that could be used

• Track construction and track maintenance costs Most track dynamics analysts include the so-called Hertzian stiffness in their analysis. This is the vertical stiffness attributed to the deformation of the wheel and rail under load. It is a high-order stiffness and associated with high frequency vibrations and impacts. These are mainly of concern to track engineers and hence this effect is included under the section on track support structures. 2.3.1.4 Types of Vertical Suspension Conceptually, in its simplest form, the suspension of a railway vehicle comprises four springs vertically coupling the four journal bearings on two wheelsets to the body (see Figure 2.11). The four springs can be designed within the space and for the load of a relatively small and light vehicle. However, as the vehicle becomes heavier and larger, the following factors come into play: •

The ability to accommodate track twist by means of spring deflection clashes with the demands on coupler height differential limits between a loaded and an empty vehicle.



The available volume for springs and dampers in the region of the journal bearing is limited.



As the carrying capacity of the vehicle increases, the wheel base increases. This leads to increased demands on vertical deflection to accommodate track twist.

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Primary Springs

Figure 2.11: Simple Vehicle Suspension Arrangement

A solution to the above problem is the railway bogie. The bogie is a combination of a minimum of two wheelsets within a suspension structure, which is pivoted beneath the vehicle body as Figure 2.12 shows. A minimum of two bogies is fitted to a vehicle. The bogie is the equivalent of a short wheel base vehicle with a limited but adequate vertical spring deflection to accommodate track twist. In addition, the carrying center plate is of limited diameter. This coupling can be designed to permit additional track twist by means of providing sufficient side bearer clearance. The bogie has become standard equipment under railway vehicles. From a vertical load bearing point of view, there are two basic types of bogies; the rigid frame and the three-piece bogie. They differ structurally and in the form of suspension design.

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Figure 2.12: Basic Railway Bogie

2.3.1.4.1 Rigid Frame Bogie The rigid frame bogie acts, vertically, very much like the model of the simple railway vehicle described above. As indicated by the name, the single bogie frame is typically in the form of a rigid “H” shape as Figure 2.13 shows. The load of the vehicle body is transferred from the center pivot through the “Hframe” to the springs placed above the journal bearings. These springs form the vertical suspension and cater for all the requirements for the suspension as listed above. This type of bogie has possibly not found favor in heavy haul operations, from a vertical suspension point of view, for the following reasons: •

Space constraints for springs with adequate carrying capacity and deflection in the region of the journal



Cost of providing four separate spring/damper systems on the bogie



Cost of the H-frame from a manufacturing complexity and tolerance point of view

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Variations of the H-frame concept include, among others, a torsionally soft bogie frame to accommodate track twist and a bogie in which the bending stiffness of the side frames is used for the suspension. None of these particular concepts has found general acceptance in practice. Side frame

Centre Pivot

Figure 2.13: Rigid Frame Bogie

2.3.1.4.2 Three-Piece Bogie Generically, the three-piece bogie, as implied by the name, comprises two side frames, each resting in a longitudinal orientation, on the journals of the wheelsets. Figure 2.14 is a sketch of a typical three-piece bogie. The side frames support a cross member — the third piece — termed a bolster. The bolster is fitted with a center pivot, which couples the bogie to the vehicle body. The three pieces, two side frames and a bolster, are each simply supported beams. This makes the bogie a statically determinate structure and allows the structure to articulate under conditions of track twist without loosing vertical wheel load. The advantages of this structure for vertical suspension are: •

Efficient accommodation of track twist.



Suspension springs are limited to two nests offering cost advantages with respect to the number of suspension elements.

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Suspension springs are in a region of the structure where more space is available than at the journal boxes. A disadvantage is that the side frame forms part of the unsprung mass on the wheelset. Furthermore, the lateral dynamics of the bogie is not optimal. Centre plate Bolster

Coil springs and Damper Side frame

Figure 2.14: Three-piece Bogie

2.3.1.5 Suspension Damping Associated with all vertical suspensions is some means of dissipating the energy generated as the vehicle travels over irregular track. In heavy haul applications, this is invariably done by some frictional means even though friction damping has many disadvantages, such as: •

Having a non linear force/displacement characteristic



Being susceptible to stick-slip action



Permitting the transmission of high frequency vibration across the suspension

• Being susceptible to wear However, the overriding advantages of the friction damper are its: •

low initial cost, and



robustness and low maintenance cost. o 2-17 x

2.3.2 Inter-Wheelset and Lateral Suspension This section describes the means by which the inherent guidance properties of the railway wheelset are utilized, and the dynamic disadvantages of the wheelset are countered. As Section 2.1 describes, a single unconstrained railway wheelset is designed to permit flange free curving and self-centering on straight track. Early on in rail vehicle development, it was found that the property of self-centering, as Figure 2.3 shows, is unstable for all speeds of a single wheelset. This unstable action is termed wheelset hunting. Wheelset hunting results in increasing lateral deflection amplitudes, intermittent cyclical flange contact on tangent track and shallow curves, and even derailment as the lateral acceleration of the wheelset initiates flange climb. It was soon realized that this instability could be countered by coupling two wheelsets in the horizontal plane. This coupling could, however, inhibit curving and guidance on straight track. It was also realized that the lateral suspension stiffness between the bogie and the body has an influence on the stability and ride quality of the vehicle. The formulation of suspension designs to optimize both the curving and tracking ability, the lateral ride quality, as well as the hunting stability of railway vehicles against the constraint of low initial costs and maintainability has challenged vehicle designers over the years. 2.3.2.1 Vehicle Dynamics A better understanding of railway vehicle suspension dynamics has been achieved over the last three decades. Hunting stability is primarily a function of the bending and shear stiffness between two wheelsets; therefore, these stiffness terms are further described below. Bending Stiffness: If two wheelsets are moved relative to one another in opposing yaw senses, as Figure 2.15 shows, the resistance to this motion is called the yaw constraint. If this constraint is linear, the constraint directly between the wheelsets is termed the bending stiffness.

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Figure 2.15: Bending Mode

Shear Stiffness: If two wheelsets are deflected laterally relative to one another in opposite senses while retaining parallelism between axle centerlines, they are said to have moved in a shear sense (Figure 2.16). If the constraint in this mode is linear, the constraint is termed the shear stiffness. Figure 2.17 illustrates bogie arrangement with various degrees of bending and/or shear constraint.

Figure 2.16: Shear Mode

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Research shows that for adequate wheelset hunting stability, the coupling between two adjacent wheelsets requires a combination of both bending and shear stiffness. This combination may be chosen to optimize the vehicle characteristics being designed. A whole range of stiffness values may be chosen. There is, however, a minimum stiffness for each that, if chosen, requires a relatively high stiffness be chosen for the other constraint and vice versa. Figure 2.17 shows two examples.

Shear stiffness

8 0

Bending stiffness

8

0

Figure 2.17: Various Degrees of Bending and Shear Constraints Example 1: If a high-bending stiffness is chosen for a bogie design, the designer cannot afford to introduce high shear stiffness. This is typically the case in the conventional three-piece bogie, the rigid-frame bogie and the force-steered bogie. Example 2: If a low bending stiffness is chosen, the designer needs to introduce a high shear constraint for adequate hunting stability. This is typically required in self-steering bogie designs.

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A choice of optimal intermediate stiffness for both the bending and shear stiffness can result in extremely high stability. The reason why this type of suspension design is not always adopted is its higher initial cost, complexity, and maintainability. Furthermore, a design with properties optimal in a new bogie may not maintain such an optimal state over a practical maintenance interval. A design that can maintain its original state between maintenance interventions, may have too high of an initial cost. On the other hand, the service conditions or track topology may imply a bias to a particular design. Associated with the high constraint stiffness is the need for greater accuracy in the tolerances of components as inaccurate stiff suspension elements lead to tracking misalignment of the vehicle. Another important feature of the suspension is the lateral coupling between the wheelsets and the body via the bogie frame and the center plate pivot. A relatively “soft” coupling, which is often difficult to achieve, is helpful in uncoupling the vehicle mass from the wheelset in a manner similar to reducing the “unsprung mass” in a vertical sense. The stiffness of this coupling should be carefully chosen as the natural frequency of the vehicle body in nosing is easily activated by repetitive track irregularities, such as rail joints, and by the natural kinematic frequency in yaw of the wheelset. 2.3.2.2 Curving and Tracking Ability As already mentioned, more than one wheelset requires coupling in the horizontal plane so that wheelset stability is obtained at any practical vehicle speed. The manner in which this is done influences the ability of the coupled wheelsets to negotiate curved track. 2.3.2.2.1 Bogies with a High Bending Stiffness A high bending stiffness implies that both wheelsets remain essentially parallel to one another and hence may not attain a radial position in a curve. There is thus a limit on the ability of the bogie to negotiate sharp curves without flange contact. This limit is a function of track gauge, bogie wheelbase, wheelset conicity, gauge clearance, and bogie rotational resistance. Curving without flange contact is shown in Figure

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2.18. The “clockwise” moments resulting from longitudinal creep are in balance with the “anti-clockwise” moments resulting from lateral creep. Hence the bogie is kept in equilibrium. Pure rolling position a α= Rc

c

α=

γy C11 r 0 r0l γRc

a Rc

C11 γ y r0

V

2l

y

a 2C22 R

cL Track C11

C11 γ y r0

γy r0

a 2C22 R c

2a

Rc

Figure 2.18: Curving without Flange Contact

Typically, bogies on standard gauge, with wheelbases of approximately 1.8 m may negotiate curves of between 1500 m and 2000 m without flange contact. Under these conditions, and with an accurately aligned bogie, the lateral and longitudinal creepage is low; and, minimal rail and track damage is experienced. Side and crown wear is minimal, with a degree of material flow to the field side of both high and low leg after about 200 MGT. This may be corrected by grinding. Figures 2.19 and 2.20 show the relationship between the above variables.

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LATERAL DISPLACEMENT (mm)

35

2l = 1507 mm 2a = 1830 mm r = 457 mm

28

Conicity = 0.05

21

14

Conicity = 0.2

7

0 200

1200

700

2200

1700

CURVE RADIUS (m)

Figure 2.19: Lateral Wheelset Displacement versus Curve Radius 90 Rc = 200m Rc = 200m

LATERAL DISPLACEMENT (mm)

Rc = 500m

72 Rc = 1000m

54

36

Rc = 500m

18 Rc = 1000m

0 1250

1750

2250

2750

3250

3750

4250

4750

TRUCK WHEELBASE (mm) Solid curves, conicity = 0.05

Dashed curves, conicity = 0.2

Figure 2.20: Lateral Wheelset Displacement versus Bogie Wheelbase

In sharper curves, below a radius of 1500 m, with low wheelset conicities and reduced gauge clearance, or at large track discontinuities or when mis-aligned bogies are present in the vehicle fleet, flange contact is made and the bogie takes an attitude as Figure 2.21 shows.

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Flat

Flong Flong P1 2l

V P2

Flong

Flong

2a

Flat

Figure 2.21: Flange Contact in Curves

The “anti-clockwise” moments on the bogie due to the lateral creepage resulting from the angle of attack of the wheels are larger than those “clockwise” moments that can be generated by the longitudinal creepage, which must thus be supplemented by a flange force. Rail/wheel contact is similar to that shown in Figure 2.10 with high gauge corner wear being experienced and excessive material flow to the field side of the low leg. Under these conditions, the most cost effective and quickest remedy is to apply lubricant to the flange and/or gauge corner of the high leg. Lubrication does not change the force balance in the curve but introduces a wear-reducing mechanism between rail and wheel. A further investigation may reveal one or more of the following: •

Wheel and rail profiles with two-point contact and a low effective conicity: This should be checked for both new and worn rail and wheel conditions. In this case, conformal rail/wheel profile contact combinations are advised to support lubrication as little can be done to improve the force situation if the other remedies described in this section are implemented. Limits on worn profiles may have to be set. There is

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a limit on the wheelset conicity, which may be generated. High conicity profiles can be generated to encourage flange free curving. This is mainly done by means of asymmetric grinding of the rail and is often not long lasting, needing repeated and frequent attention under heavy axle load conditions as the effect of the lateral creepage wears the rail crown down and negates the rail grinding action (see Figure 2.10). The long-term effectiveness of this measure must thus be monitored. Asymmetric grinding can also concentrate high stresses on the gauge corner of the high leg leading to premature fatigue failure. This must be monitored. High conicity wheel profiles can also lead to vehicle instability on tangent track and any change to the wheel profile resulting in high conicity should first be tested on tangent track. •

Incorrect superelevation in curves: Excessive cant will cause the bogie to steer out of the curve to counter the resulting inward force. This will increase the angle of attack and lateral creepage and the resulting flange force. The curving speed thus has to be optimized so that the vertical forces on the left and the right leg of the curve are almost equal. This will prevent one side of the track to be overloaded under heavy haul traffic. The relationship between the lateral forces acting on the center plate and the angle of attack is illustrated in Figure 2.22.



Tracking accuracy: A check should be made on the tracking accuracy of all vehicles as some may be “biased” to certain sense curves and thus “biased” against others.



Rotational resistance between bogie and vehicle body: The rotational resistance between bogie and vehicle body must be checked.

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Decreasing α

FLATERAL α Centre Plate

Increasing α FLATERAL

Figure 2.22: Forces Acting on the Center Plate

2.3.2.2.2 Bogies with a Low Bending Stiffness Generally termed “Steering Bogies” these bogies use the longitudinal creep forces generated between the wheelset and the rail to deflect the longitudinal springs, which create the bending stiffness. This permits the wheelsets to align to an almost radial position to the curve, as Figure 2.23 shows. The lateral creep forces are reduced to almost zero, eliminating the flange force and the effect on the rail shown in Figure 2.10.

Centre of Curve

Figure 2.23: Radial Alignment in a Curve

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2.4 Practical Heavy Haul Vehicle Suspensions 2.4.1 Heavy Haul Wagon Bogies As discussed previously, heavy haul wagons are predominantly equipped with three-piece bogies. Some railroads have also adopted a variety of three-piece bogies with steering characteristics. In this section, both the conventional as well as the steering bogie designs are discussed. 2.4.1.1 Conventional Three-Piece Bogies Although these bogies are termed three-piece bogies, they have many other components. Furthermore, some additions have been made to improve their running performance. These suspension components and the additions to the basic construction are discussed below. 2.4.1.1.1 Secondary Suspension Spring Nest The secondary suspension spring nest of the three-piece bogie is situated in the side frame pocket, where it rests on the side frame spring seat and supports the bolster protruding into the side frame window (see Figure 2.24). The spring nest, also commonly known as the secondary suspension, consists of a number of inner and outer hot coiled springs and a friction wedge damping arrangement. The number of springs and their detailed design depend on the load carrying capacity of the particular vehicle. The friction damper typically consists of cast wedges, wedged between the side frame and the bolster, supported by a stabilizer spring. This suspension arrangement is thus designed to provide friction forces between the vertical surface of the wedge and the side frame wear plate, and to keep the side frame and bolster square relative to each other. The latter helps to control bogie hunting.

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Primary Suspension

Secondary Suspension Figure 2.24: Self-Steering Three-piece Bogie

The following practical design limitations influence the optimal design of the spring nest: •

Available space for suspension elements



Allowable stress limits in suspension components



Tare to load deflection limits



Vehicle tracking performance



Manufacturing and maintenance costs

2.4.1.1.2 Friction Damping As mentioned in the previous section, a spring loaded friction wedge arrangement between the bolster and the side frame pocket is used to provide damping to the dynamic reactions of the vehicle as it travels over irregular track. In heavy haul threepiece bogies, two types of friction wedge arrangements are commonly in use; i.e., constant and load sensitive designs as Figure 2.25 and 2.26 show. Constant friction damping designs are independent of the wagon load while load sensitive designs provide more frictional damping under heavier loads. In friction wedge suspension designs, use is made of the friction coefficient between steel and steel to dissipate energy. However, under certain circumstances, such as high operating speeds or adverse track conditions, a high wear rate between rubbing surfaces is experienced. The resulting friction wedge rise (Figure 2.27) between the bolster and the wear liners in the side frame pocket causes a reduction in the frictional damping

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force and a change in the vertical, lateral and warp stiffness. This can lead to unacceptable running dynamics. On the other hand, loss of suspension travel due to wedge binding as a result of wedge rotation (misalignment) due to side frame wear (Figure 2.28), results in high impact forces being transmitted between the wheel and the rail, damaging not only the vehicle structure but also leading to accelerated track structure deterioration. To prevent excessive wear as well as to prevent the wedges from sticking, some railroads have implemented resilient friction elements. These urethane elastomeric wear surfaces significantly reduce wear. Hence, the available friction damping and the warp stiffness is maintained for longer periods of service, eliminating regular bolster slope rework. For some heavy haul container traffic, hydraulic stabilizers are used to control higher speed bounce dynamics, to improve ride quality, and to minimize wheel/rail interface reactions resulting from adverse wagon dynamics and damage to the payload.

Bolster Wedge

Wedge spring Window of side frame

Figure 2.25: Constant Friction Damping

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Bolster Wedge

Window of side frame Wedge spring

Figure 2.26: Load Sensitive Friction Damping

Friction Wedge Rise

Wedge Wear Limit

Height of Friction Wedge Above Truck Bolster

a

b

a

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