INTRODUCTION – ISO 10300 series

When ISO 10300:2001 (all parts) became due for its first revision, the opportunity was taken to include hypoid gears, since previously the series only allowed for calculating the load capacity of bevel gears without offset axes. The former structure is retained, i.e. three parts of the ISO 10300 series, together with ISO 6336-5, and it is intended to establish general principles and procedures for rating of bevel gears. Moreover, ISO 10300 (all parts) is designed to facilitate the application of future knowledge and developments, as well as the exchange of information gained from experience.

INTRODUCTION – ISO 10300-2:2023

In view of the decision for ISO 10300 (all parts) to cover hypoid gears also, a separate clause: “Gear flank rating formulae — Method B2” has been included in this document, while the former method B was renamed method B1. It became necessary to present a new, clearer structure of the three parts, which is illustrated in ISO 10300-1:2023, Figure 1.

NOTE: ISO 10300 (all parts) gives no preferences in terms of when to use method B1 and when to use method B2.

This document deals with the failure of gear teeth by macropitting, a fatigue phenomenon. Two varieties of macropitting are recognized, initial and destructive macropitting.

In applications employing low hardness steel or through hardened steel, initial macropitting frequently occurs during early use and is not deemed serious. Initial macropitting is characterized by small pits which do not extend over the entire facewidth or profile depth of the affected tooth. The degree of acceptability of initial macropitting varies widely, depending on the gear application. Initial macropitting occurs in localized overstressed areas and tends to redistribute the load by progressively removing high contact spots. Generally, when the load has been redistributed, the macropitting stops.

In applications employing high hardness steel and case carburized steel, the variety of macropitting that occurs is usually destructive. The formulae for macropitting resistance given in this document are intended to assist in the design of bevel gears which stay free from destructive macropitting during their design lives (for additional information, see ISO/TR 22849 [5]).

The basic formulae, first developed by Hertz for the contact pressure between two curved surfaces, have been modified to consider the following four items: the load sharing between adjacent teeth, the position of the centre of pressure on the tooth, the shape of the instantaneous area of contact and the load concentration resulting from manufacturing uncertainties. The Hertzian contact pressure serves as the theory for the assessment of surface durability with respect to macropitting. Although all premises for a gear mesh are not satisfied by Hertzian relations, their use can be justified by the fact that, for a gear material, the limits of the Hertzian pressure are determined on the basis of running tests with gears, which include the additional influences in the analysis of the limit values. Therefore, if the reference is within the application range, Hertzian pressure can be used to convert test gear data to gears of various types and sizes.

NOTE: Contrary to cylindrical gears, where the contact is usually linear, bevel gears are generally manufactured with profile and lengthwise crowning, i.e. the tooth flanks are curved on all sides and the contact develops an elliptical pressure surface. This is taken into consideration when determining the load factors by the fact that the rectangular zone of action (in the case of spur and helical gears) is replaced by an inscribed parallelogram for method B1 and an inscribed ellipse for method B2 (see ISO 10300-1:2023, Annex A for method B1 and Annex B for method B2). The conditions for bevel gears, different from cylindrical gears in their contact, are thus taken into consideration by the face and transverse load distribution factors.

SCOPE

This document specifies the basic formulae for use in the determination of the surface load capacity of straight and helical (skew), Zerol and spiral bevel gears including hypoid gears, and comprises all the influences on surface durability for which quantitative assessments can be made. This document is applicable to oil lubricated bevel gears, as long as sufficient lubricant is present in the mesh at all times.

The formulae in this document are based on virtual cylindrical gears and restricted to bevel gears whose virtual cylindrical gears have transverse contact ratios of ε_vα < 2. The results are valid within the range of the applied factors as specified in ISO 10300-1.

The formulae in this document are not directly applicable to the assessment of other types of gear tooth surface damage, such as plastic yielding, scratching, scuffing or any other type not specified.

NOTE: This document is not applicable to bevel gears which have an inadequate contact pattern under load.

The user is cautioned that when the formulae are used for large average mean spiral angles (β_m1 + β_m2)/2 > 45°, for effective pressure angles α_e > 30° and/or for large facewidths b > 13 mmn, the calculated results of this document should be confirmed by experience.