ISO/TC 60/SC 1/WG 4 - Terminology and notation of gears

This document provides information on gear tooth wear and damage. The material contained herein is intended to help the user better understand damage to gear teeth, but the potential reasons for damage and preventive measures discussed are not definitive. Also, for individual cases, other reasons for damage or measures can exist that are not mentioned in this document. At the same time, reasons for damage or measures mentioned in this document are not always of importance. In many cases, damage can be the result of multiple interacting factors. Some causes that are included are still a topic of research and discussion but are presented with the intent to provide possibilities. The solution to many gear problems involves detailed investigation and analysis by specialists; this document is not intended to replace such expert knowledge.

This document provides nomenclature for general modes of gear tooth wear and failure. It classifies, identifies, and describes the most common types of failure and provides information that, in many cases, enables the user to identify failure modes and evaluate the degree or change from original condition. This document is based on experience with steel gears; however, many of the failure modes discussed apply to gears made from other materials. Not all failure modes that can occur on other types of gears, such as plastic, bronze, or powder metal gears, are included. The solution to many gear problems requires detailed investigation and analysis by specialists and is beyond the scope of this document. This document specifies only the terminology intended to help with the identification and reporting of the appearance and conditions of gears after a period of operation. Neither causes nor preventive measures for any condition described are discussed. In this document, gear refers to both gear wheels and pinions, unless the gear is specifically identified. This document does not define “gear failure”.

Concerns the part of the international vocabulary of gears which is devoted solely to geometrical definitions. It gives, for each of the geometrical terms relative to gears, a standard definitions which will be valid internationally, to corresponding term in each langauge being chosen as far as possible in such a way as to directly reflect the meaning of the definition.

ISO 21771:2007 specifies the geometric concepts and parameters for cylindrical gears with involute helicoid tooth flanks. Flank modifications are included. It also covers the concepts and parameters for cylindrical gear pairs with parallel axes and a constant gear ratio, which consist of cylindrical gears according to it. Gear and mating gear in these gear pairs have the same basic rack tooth profile.

This part of ISO 1122 concerns the part of the international vocabulary of gears which is devoted solely to geometrical definitions. It gives, for each of the geometrical terms relative to gears, a standard definition which will be valid internationally, the corresponding term in each language being chosen as far as possible in such a way as to directly reflect the meaning of the definition. NOTE — Since the choice of corresponding terms can only be partially fulfilled in any particular language, due to the necessity of respecting certain established conventions, it is advisable, as far as translation into other languages is concerned, to refer always to the meaning of the definition itself, rather than to a simple transposition of the original term.

Defines terms used to describe the appearance of the visible surfaces of tooth flanks or the damage that can be observed on gears. Causes and preventive measures are not discussed.