American Gear Manufacturers Research Articles

BS‐ISO Helical Gear Fatigue Life Estimation and Wear Quantitative Feature Analysis

Abstract: Lack of representative theoretical models for gear wear causes difficulties in their useful lifetime prediction. Critical operating parameters, such as loading and lubrication, affect the wear process in a very complex manner and lead the theoretical modelling to an imperfect zone of assumptions. Complexities in gear wear mathematical modelling allow the researchers to use approximations for useful lifetime calculations. On the basis of modelling approximations and assumptions, organizations, such as American Gear Manufacturers’ Association (AGMA) and British Standards (BS), provide gear useful lifetime formulations. In these formulations, the useful lifetime values are estimated by means of experimentation that is controlled with known gear operating conditions and physical dimensions. However, for useful lifetime estimation and validation, these standards have not considered any experimental approach that represents the actual gear wear. In this paper, an effort is made to validate the competency of standard's gear useful lifetime formulation. For this purpose, an approach that is able to provide an idea about actual gear wear is used. During the effort, BS‐ISO 6336‐2 standard formulation is used for helical gear useful lifetime estimation under linear pitting fatigue conditions. The used formulation is validated by using wear quantitative feature analysis that is able to provide actual gear wear quantitative trends. The obtained wear quantitative trends fairly validate the lifetime estimation of BS‐ISO 6336‐2 standard.

THE NEED FOR

IN considering the properties possessed by lubricating oils priority is generally given to viscosity which is not only a most important criterion of performance but can be measured easily and expressed quantitatively. This is reflected in the systems agreed by such groups as the (American) Society of Automotive Engineers (S.A.E.), the American Gear Manufacturers' Association (A.G.M.A.) and so on. Those who have been associated with the selection and application of lubricants will no doubt have been confused by the various systems which classify viscosity for only limited purposes. In recent years there has developed a greater awareness of the need for a single, logical viscosity system which can be applied to all industrial lubricants regardless of purpose. While it is still true that “there is not enough reliable information now available as regards test methods to permit writing workable oil purchase specifications which would within themselves, without performance tests, serve as a reliable guide in the selection of lubricants”, a necessary first step is the preparation of a universally acceptable viscosity classification.

LUBRICANT SPECIFICATIONS

Another important class of lubricants are the oils which are needed for gear lubrication. As the units used in industry vary so much in design, size and operating conditions, a wide range of oils is available for servicing them and within this range the viscosities may vary as much as they do in the case of bearing oils. Thus it would seem that such lubricants could be classified in a manner similar to that adopted for, say, the crankcase oils and some form of basic classification prepared. This has been done in America, where the American Gear Manufacturers' Association—A.G.M.A.—have listed a series of oils for industrial closed gears. The viscosity range is given in Table 4, which shows the current revision.