Cracks initiated at the surface of case-hardened gears may lead to typical life-limiting fatigue failure modes such as pitting and tooth root breakage. Furthermore, the contact load on the flank surface induces stresses in greater material depth that may lead to crack initiation below the surface if the local material strength is exceeded. Over time the sub-surface crack propagation may lead to gear failure referred to as “tooth flank fracture” (also referred to as “tooth flank breakage”). This paper explains the mechanism of this subsurface fatigue failure mode and its decisive influence factors, and presents an overview of a newly developed calculation model.

A transverse-torsional dynamic model of a spur gear pair is employed to investigate the influence of gear tooth indexing errors on the dynamic response. With measured long-period quasi-static transmission error time traces as the primary excitation, the model predicts frequency-domain dynamic mesh force and dynamic transmission error spectra. The dynamic responses due to both deterministic and random tooth indexing errors are predicted.

The first part of this publication series covered the general basics of involute gearing and applied the generating principle of cylindrical gears analogous to angular gear axis arrangements the kinematic coupling conditions between the two mating members have been postulated in three rules. Entering the world of bevel gears also required to dwell somewhat on the definition of conjugacy. The second part is devoted to the different generating gears and the chain of kinematic relationships between the gear - gear generator - pinion generator and pinion.

This review of elastohydrodynamic lubrication (EHL) was derived from many excellent sources (Refs. 1–5). The review of Blok’s flash temperature theory was derived from his publications (Refs. 6–9). An excellent general reference on all aspects of tribology is the Encyclopedia of Tribology (Ref. 10).

Many years ago, when asked how the five-meter gear was checked, the quality manager responded, “When they’re that big, they’re never bad!” That may have been the attitude and practice in the past, but it no longer serves the manufacturer nor the customer. Requirements have been evolving steadily, requiring gears to perform better and last longer.

As in nearly all industries, more costeffective solutions are currently called for in the gear manufacturing industry.

Helical gear teeth are affected by cratering wear — particularly in the regions of low oil film thicknesses, high flank pressures and high sliding speeds. The greatest wear occurs on the pinion — in the area of negative specific sliding. Here the tooth tip radius of the driven gear makes contact with the flank of the driving gear with maximum sliding speed and pressure.

Prior to receiving airworthiness certification, extensive testing is required during the development of rotary wing aircraft drive systems. Many of these tests are conducted to demonstrate the drive system’s ability to operate at extreme conditions, i.e. — beyond that called for in the normal to maximum power operating range.

Developed here is a new method to automatically find the optimal topological modification from the predetermined measurement grid points for bevel gears. Employing this method enables the duplication of any flank form of a bevel gear given by the measurement points and the creation of a 3-D model for CAM machining in a very short time. This method not only allows the user to model existing flank forms into 3-D models, but also can be applied for various other purposes, such as compensating for hardening distortions and manufacturing deviations which are very important issues but not yet solved in the practical milling process.

Beginning with our June Issue, Gear Technology is pleased to present a series of full-length chapters excerpted from Dr. Hermann J. Stadtfeld’s latest scholarly — yet practical — contribution to the gear industry — Gleason Bevel Gear Technology. Released in March, 2014 the book boasts 365 figures intended to add graphic support of a better understanding and easier recollection of the covered material.