Preface

Gears, because of their unique contribution to the operation of so many machines and mechanical devices, have received special attention from the technical community for more than two millennia. New developments in gear technology, particularly from the materials point-of-view, have also been covered in detail by ASM International for many years. Numerous forums, conference proceedings, books, and articles have been devoted to the understanding of gear performance by examining gear tribology, failure modes, the metallurgy of ferrous gear materials, heat treatment, gear manufacturing methods, and testing. All of these important technical aspects of gear technology are brought together in the present offering, Gear Materials, Properties, and Manufacture.

Chapter 1, “Basic Understanding of Gears,” discusses the various types of gears used, important gear nomenclature, and applied stresses and strength requirements associated with gears. It also provides an overview of several important topics that are covered in greater detail in subsequent chapters, namely, gear materials, gear manufacture, and heat treatment. Gear tribology and lubrication is covered in Chapter 2. Lubrication-related failures (pitting, wear, and scuffing), elastohydrodynamic lubrication, lubricant selection, and gear lubricant application are among the subjects described.

Chapters 3 and 4 describe both metallic (ferrous and nonferrous alloys) and plastic gear materials, respectively. Emphasis in Chapter 3 has been placed on the properties of carburized steels, the material of choice for high-performance power transmission gearing. The increasing use of plastics for both motion-carrying and power transmission applications is covered in Chapter 4.

Chapters 5, 6, and 7 address methods for manufacturing gears including metal removal processes (machining, grinding, and finishing), casting, forming, and forging (including recent advances in near-net shape forging of gears), and powder metallurgy processing. Injection molding, another important method for the manufacture of plastic gears, is covered in Chapter 4.

The heat treatment of gears is reviewed in Chapters 8 through 12. Both through hardening and surface hardening methods are reviewed. Again, emphasis has been placed on carburizing, the most common heat treatment applied to gear steels. It should be noted that some of the material presented in these chapters was adapted, with the kind permission of the author, from Heat Treatment of Gears: A Practical Guide for Engineers, by A.K. Rakhit (ASM International, 2000). Dr. Rakhit’s book is an excellent resource for those seeking a more in-depth reference guide to gear heat treatment.

Failure analysis, fatigue life prediction, and mechanical testing are examined in Chapters 13, 14, and 15, respectively. In Chapter 13, “Gear Failure Modes and Analysis,” emphasis has been placed on two of the most common types of gear failure—bending fatigue and contact fatigue. Bending fatigue of carburized steels is also discussed in depth in Chapter 3.

In summary, this book is intended for gear metallurgists and materials specialists, manufacturing engineers, lubrication technologists, and analysts concerned with gear failures who seek a better understanding of gear performance and gear life. It supplements other gear texts that emphasize the design, geometry, and theory of gears.