This article presents the mechanisms of polymer wear and quantifies wear in terms of wear rate (rate of removal of the material). Interfacial and bulk wear are discussed as well as a discussion on the wear study of "elastomers," "thermosets," "glassy thermoplastics," and "semicrystalline thermoplastics." The article also discusses the effects of environment and lubricant on the wear failures of polymers. It presents a case study on considering nylon as a tribological material and failure examples, explaining wear resistance of polyurethane elastomeric coatings and failure of an acetal gear wheel.

This article first reviews variations within the most common types of gears, namely spur, helical, worm, and straight and spiral bevel. It then provides information on gear tooth contact and gear metallurgy. This is followed by sections describing the important points of gear lubrication, the measurement of the backlash, and the necessary factors for starting the failure analysis. Next, the article explains various gear failure causes, including wear, scuffing, Hertzian fatigue, cracking, fracture, and bending fatigue, and finally presents examples of gear and reducer failure analysis.

Gears are a common part type for applications of the magnetic Barkhausen noise (MBN) techniques for nondestructive inspection. This article discusses the typical applications for MBN techniques, namely, detection of grinding retemper burn, evaluation of residual stresses, and detection of heat treatment defects, including the evaluation of case depth.

This article discusses the physical signs of rolling-contact wear (RCW). It lists the major considerations in gear design and describes the mechanisms of RCW. The article provides a guide to rolling-contact fatigue (RCF) testing methods. It explains the steps involved in the processes of RCF and RCW.

This article is concerned with gear tooth failures influenced by friction, lubrication, and wear, and especially those failure modes that occur in wind-turbine components. It provides a detailed discussion on wear (including adhesion, abrasion, polishing, fretting, and electrical discharge), scuffing, and Hertzian fatigue (including macropitting and micropitting). Details for obtaining high lubricant specific film thickness are presented. The article describes the selection criteria for lubricants, such as oil, grease, adhesive open gear lubricant, and solid lubricants. It discusses the applications of oil and gear lubricants and the types of standardized gear tests. The article presents some recommendations for selecting lubricants and lubricant viscosity for enclosed gear. It provides some examples of failure modes that commonly occur on gears and bearings in wind turbine gearboxes.

The surface of irons and steels can be hardened by introducing nitrogen (nitriding), nitrogen and carbon (nitrocarburizing), or nitrogen and sulfur (sulfonitriding) into the surface. This article lists the principal reasons for nitriding and nitrocarburizing, and summarizes the typical characteristics of nitriding processes along with a general comparison of carburizing processes in a table. It describes the two most common nitriding methods: gas nitriding and ion (plasma) nitriding. The article discusses the wear behavior of nitrided layers and the wear resistance of selected steels. Rolling-contact fatigue (RCF) occurs in rolling contacts such as bearings, rolls, and gears. The article provides a discussion on rolling-contact fatigue of nitrided steels for aerospace bearing components.

Tribology is the study of friction, lubrication, and wear. It is a multidisciplinary subject covering the mechanics of contacting surfaces, their roughness characteristics, lubrication, and material behavior under normal load as well as in traction. This article focuses on well-established and widely accepted analytical methods and design and analysis charts for dealing with some of the issues in the area of engine and power train tribology. It provides a discussion on lubricant rheology and the prediction of lubricating film thickness. The article reviews the frictional power loss in piston-cylinder conjunctions, engine bearings, and transmission and differential gearing systems.

This article describes the capabilities, limitations, advantages, and disadvantages of the powder metallurgy (PM) gear manufacturing process. It discusses the types of gears that can be produced by PM and presents the design guidelines for PM gears. The article provides information on gear tolerances and performance of PM gears. It also explains various procedures to inspect and test the mechanical properties, dimensional specifications, and surface durability (hardness).

This article commences with a brief introduction on the hardenability of carburized steels, and then reviews the factors used in the selection of carburizing steels and heat treatment methods. The factors include quench medium, stress considerations, case depth, and type of case. The article provides information on steels for carburized gears with emphasis on gear design requirements, selection process, selection of carbon content, case and core hardness, microstructure, and toughness and short-cycle fatigue.

This article provides an overview of steel gear heat treating processes and brings out the nuances of the various important heat treating considerations for steel gear applications. The heat treatment processes covered are annealing, carburizing, hardening, low-pressure carburizing, induction hardening, through hardening, and nitriding. In view of the emerging use of mathematical modeling and optimization, a brief overview of its application for process and design optimization is also provided.

This article describes the fundamental concepts of heat treatment simulation, including the physical events and their interactions, the heat treatment simulation software, and the commonly used simulation strategies. It summarizes material data needed for heat treatment simulations and discusses reliable data sources as well as experimental and computational methods for material data acquisition. The article provides information on the process data needed for accurate heat treatment simulation and the methods for their determination. Methods for validating heat treatment simulations are also discussed with an emphasis on the underlying philosophy for the selection and design of validation tests. The article also discusses the applications, capabilities, and limitations of heat treatment simulations via selected industrial case studies for a better understanding of the effect of microstructure, distortion, residual stress, and cracking in gears, shafts, and bearing rings.

Induction hardening is a prominent method in the gear manufacturing industry due to its ability of selectively hardening portions of a gear such as the flanks, roots, and/or tips of teeth with desired hardness, wearing resistance, and contact fatigue strength without affecting the metallurgy of the core. This article provides an overview of gear technology and materials selection. It describes different gear-hardening patterns, namely, tooth-by-tooth hardening, tip-by-tip hardening, gap-by-gap hardening, spin hardening, single-frequency gear hardening, dual-frequency gear hardening, simultaneous dual-frequency gear hardening, and through heating for surface hardening. It provides information on the different inspection methods based on the American Gear Manufacturers Association, revealing metallurgical data, hardness, and dimensions of gears. In addition, the article presents a comparative study on the mechanical properties of contour-hardened and carburized gears. It concludes by describing typical failures of induction-hardened steels and the corresponding prevention methods.

Scanners are the most versatile and flexible of the equipment available to the heat treating industry for induction hardening. This article provides a general overview of scanners, and describes various critical factors, including scan speeds, rotational speeds, and center total indicator runout of vertical scanners. It presents information on the frequency selection parameters for scanning applications. The article also discusses the critical parameters and production rates in specifying and developing a tooth-by-tooth hardening process.

The gas quenching process is usually performed at elevated pressures, and is therefore, mostly referred to as high-pressure gas quenching (HPGQ). This article describes the physical principles of HPGQ; the two main types of equipment used, namely, single-chamber furnaces and cold chambers; and the three gases used, namely, nitrogen, helium, and argon. It also discusses two different groups of fixture materials used, namely, high-nickel-content alloys and carbon-fiber-reinforced carbon materials. The article exemplifies the process of dynamic gas quenching and how core hardness values can be predicted in industrial practices. It also discusses the improvements in distortion control with the application of gas-flow reversing and dynamic gas quenching.

Shearing is a method for cutting a material piece into smaller pieces using a shear knife to force the material past an opposition shear knife in a progression form. This article describes the principles, attributes, and defects of straight-knife shearing. The equipment, materials used, and the operating parameters are discussed. The article provides information on the applications of rotary shearing. It concludes with a discussion on devices equipped with shearing machines for protecting personnel from the hazards of shear knives, flywheels, gears, and other moving parts.

Precision forging is defined as a closed-die forging process in which the accuracy of the shape, dimensional tolerances, and surface finish exceed normal expectations to the extent that some of the postforge operations can be eliminated. This article provides an overview of the key factors that impact the precision forging process. It provides information on the achievable tolerances and presents examples of precision forging. A discussion on forging of bevel gears/spiral bevel gears is also presented.

Gears can fail in many different ways, and except for an increase in noise level and vibration, there is often no indication of difficulty until total failure occurs. This article reviews the major types of gears and the basic principles of gear-tooth contact. It discusses the loading conditions and stresses that effect gear strength and durability. The article provides information on different gear materials, the common types and causes of gear failures, and the procedures employed to analyze them. Finally, it presents a chosen few examples to illustrate a systematic approach to the failure examination.

Mechanical tests are performed to evaluate the durability of gears under load. Gear tooth failures occur in two distinct regions, namely, the tooth flank and the root fillet. This article describes the common failure modes such as scoring, wear, and pitting, on tooth flanks. Failures in root fillets are primarily due to bending fatigue but can be precipitated by sudden overloading (impact). The article presents contact stress computations for gear tooth flank and bending stress computations for root fillets. Specimen characterization is a critical part of any fatigue test program because it enables meaningful interpretation of the results. The article describes four areas of the characterizations: dimensional, surface finish/texture, metallurgical, and residual stress. The rolling contact fatigue test, single-tooth fatigue test, single-tooth single-overload test, and single-tooth impact test are some of the gear action simulating tests discussed in the article.

This article summarizes the various kinds of gear wear, including fatigue, impact fracture, wear, and stress rupture, describes how gear life in service is estimated. It presents the rules concerning lubricants in designing gearing and analyzing failures of gears. The article presents the equations for determining surface durability and life of gears. It tabulates the situations and concepts of pitting failures in gears. The article analyzes some of the more common flaws that affect the life of gear teeth. It reviews the components in the design and structure of each gear and/or gear train that must be considered in conjunction with the teeth.