In the case of gearboxes, vibration is the primary mode of failure even at the mid-range of operating speeds. Avoiding such failures requires an understanding of gearbox design, vibration theory, and material properties. This chapter details sources and types of gearbox vibrations; characteristics of gearbox vibrations; fundamentals of periodic vibrations; and vibration theory. It provides housing design for single-stage offset parallel gearboxes, high-speed gearboxes, and epicyclic gearboxes. The chapter then provides an analysis and selection of design factors for vibration reduction. It presents five types of gear tooth geometry errors. The chapter also focuses on gear quality inspection and on bearing-induced vibrations.

This chapter focuses on the design of measuring devices. The devices used to measure vibration typically consist of an electronic transducer with an interconnecting cable and an alternating current voltmeter. The working principle of each type of transducer is described in this chapter along with their important characteristics and common applications. The chapter provides general guidelines for the selection of a measuring device, and discusses vibration severity levels.

The cyclic nature of gearbox vibration lends itself well to the analysis in the frequency domain where the effects of a gear mesh, bearing defects, and other sources of vibration are effectively set apart, making it much easier to identify and correct the underlying causes of vibration. This chapter presents spectral maps that show how gearbox vibrations change with the rotational speed of components. It then explains how to identify the sources of vibration in a high-speed gearbox. The chapter also discusses other errors including backlash, ghost frequencies, unbalance, misalignment, mechanical looseness, and index variation form errors. It also presents the calculation of gear frequencies on gearbox vibration spectra and the influence of operating conditions.

This chapter details the vibration limits for gearboxes. It focuses on critical speed and peak load. The chapter presents vibration measurement and analysis, which provides a quick and relatively inexpensive way to detect and identify mechanical problems before they become more serious and costly.

Gearbox vibrations are classified as synchronous or nonsynchronous depending on whether or not they are related to the rotational speed of an internal or connected component. This chapter presents a turbogenerator case study that demonstrates the source of nonsynchronous vibration. It then provides a detailed discussion on spiking vibrations and presents design improvement and reduction of spiking vibrations.

This chapter analyzes four gearbox failures, in each case identifying the underlying failure mechanism and recommending changes to reduce vibration. These include failure of an offset parallel gearbox due to gear tooth geometry error; high vibration on high-speed offset parallel gearbox; failure of an epicyclic gearbox; and vibration due to tooth wear.

This chapter presents guidelines for reducing gearbox vibration, with an emphasis on design factors that play major roles in influencing vibration.

Gearbox vibrations can often be dealt with in the field by modifying, replacing, and repositioning components and adjusting operating conditions and control parameters. Every gearbox design, however, eventually reaches a point where problems due to vibration are not so easily addressed. This chapter discusses such a case, that of an epicyclic reducer plagued by subsynchronous vibration, and explains how the gearbox was redesigned, improving lifetime as well as efficiency.

This appendix provides a list of books and technical papers utilized as reference material during the development of this book.

Nitriding is a case-hardening process used for alloy steel gears and is quite similar to case carburizing. Nitriding of gears can be done in either a gas or liquid medium containing nitrogen. This chapter discusses the processes involved in gas nitriding. It reviews the effects of white layer formation in nitrided gears and presents general recommendations for nitrided gears. The chapter describes the microstructure, overload and fatigue damage, bending-fatigue life, cost, and distortion of nitrided gears. Information on nitriding steels used in Europe and the applications of nitrided gears are also provided. The chapter presents case studies on successful nitriding of a gear and on the failure of nitrided gears used in a gearbox subjected to a load with wide fluctuations.

Several limitations in achieving optimal gear performance with conventional nitriding have led researchers to work on a variety of novel and improved nitriding processes. Of these, ion/plasma nitriding offers some promising results, which are reviewed in this chapter. The chapter concludes with a case history describing the application of ion nitriding to an internal ring gear of an epicyclic gearbox.