ISO 6336-3-2019 (2020) PDF

Full title and description

St ISO 6336-3-2019 (2020) — Calculation of load capacity of spur and helical gears — Part 3: Calculation of tooth bending strength. This document gives the formulae, influence factors and calculation procedures used to determine the permissible tooth-root bending stress (tooth bending strength) for involute external and internal spur and helical gears; a corrected edition was issued in 2020 following the original 2019 publication.

Abstract

This part of ISO 6336 provides the fundamental formulae and procedures for calculating tooth-root bending stresses and rating the tooth bending strength of involute spur and helical gears. It covers load influences that result from transmitted loads, scope limits (rim-thickness conditions for external and internal gears), and the applicability constraints (e.g., intended tooth profiles and virtual contact ratio). The procedures draw on experimental and theoretical studies and are intended for experienced gear designers performing standardized strength assessments.

General information

• Status: Published (International Standard; confirmed).
• Publication date: 26 November 2019 (Edition 3); corrected versions issued in 2020 (corrections published November 2020).
• Publisher: International Organization for Standardization (ISO).
• ICS / categories: 21.200 (Gears).
• Edition / version: Edition 3 (2019), corrected version published 2020.
• Number of pages: 55 (ISO published PDF).

Scope

The standard specifies methods for calculating tooth-root bending stresses and rating tooth bending strength for involute external and internal spur and helical gears with defined rim-thickness limits. It applies to teeth made to the basic rack specified in ISO 53 and may be used for other conjugate tooth systems provided the virtual contact ratio is within the stated limits. The document does not address failure modes other than tooth bending fatigue where those modes are dominant.

Key topics and requirements

• Fundamental formulae for tooth-root bending stress calculation and allowable bending stress (tooth bending strength).
• Applicability limits (rim thickness criteria for external and internal gears; virtual contact ratio constraints).
• Influence factors affecting root stress (load distribution, profile and helix modifications, dynamic factors, manufacturing tolerances, material quality and size effects).
• Procedures based on experimental and theoretical studies (references to established researchers and test results used to calibrate factors and formulae).
• Instructions for use with spur and helical involute teeth conforming to ISO 53; guidance on when the methods are not adequate and further evaluation is required.

Typical use and users

Used by gear designers and engineers in industries such as automotive, wind turbines, industrial gearboxes, and heavy machinery; also used by standards committees, testing laboratories, and consultants for gear strength assessment, design verification, and contract/specification work. It is intended for users experienced in gear design and in selecting appropriate values for influence factors.

Related standards

Part of the ISO 6336 series on load capacity of spur and helical gears. Related documents include ISO 6336-1 (basic principles and influence factors), ISO 6336-2 (surface durability / pitting), ISO/TS 6336-4 (tooth flank fracture load capacity), ISO 6336-5 (materials), and ISO 6336-6 (service life under variable load). Users commonly consult these parts together when performing full gear ratings.

Keywords

ISO 6336, tooth bending strength, gear rating, load capacity, spur gears, helical gears, tooth-root stress, rim thickness, ISO 53, influence factors.

FAQ

Q: What is this standard?

A: ISO 6336-3:2019 (corrected 2020) is the part of the ISO 6336 series that sets out the calculation procedures and formulae to determine tooth-root bending stresses and rate the tooth bending strength of involute spur and helical gears.

Q: What does it cover?

A: It covers the mathematical formulae, influence factors and procedural steps to calculate permissible tooth-root bending stress for gears within specified geometric and application limits (rim-thickness conditions, profile/helix requirements, and virtual contact ratio constraints). It does not provide coverage for failure modes other than tooth bending fatigue when those dominate.

Q: Who typically uses it?

A: Experienced gear designers, gearbox manufacturers, test laboratories, engineering consultants and standards committees use this part of ISO 6336 when assessing or specifying the bending strength of gear teeth. It is aimed at professionals capable of selecting appropriate influence-factor values.

Q: Is it current or superseded?

A: The edition was published on 26 November 2019 (Edition 3) and received corrected texts in 2020; it is the current Part 3 edition that replaced the 2006 edition and its corrigenda. Users should check national adoptions or later confirmations for national publication dates and corrections.

Q: Is it part of a series?

A: Yes — ISO 6336 is a multi-part standard series covering gear load-capacity calculations (Parts 1, 2, 3, 5 and 6, plus related technical specifications and technical reports). Part 3 is specifically the tooth bending strength calculation part.

Q: What are the key keywords?

A: Gear rating, tooth-root bending stress, tooth bending strength, spur gear, helical gear, ISO 6336, load capacity, influence factors, rim thickness, ISO 53.