1、BRITISH STANDARD BS ISO 6336-2:2006 Incorporating corrigendum June 2008 Calculation of load capacity of spur and helical gears Part 2 : Calculation of surface durability (pitting) ICS 21.200 BS ISO 6336-2:2006 This British Standard was published under the authority of the Standards Policy and Strate
2、gy Committee on 31 October 2006 BSI 2008 ISBN 978 0 580 63409 3 National foreword This British Standard is the UK implementation of ISO 6336-2:2006, incorporating corrigendum June 2008. It supersedes BS ISO 6336-2:1996 which is withdrawn. The start and finish of text introduced or altered by corrige
3、ndum is indicated in the text by tags. Text altered by ISO corrigendum June 2008 is indicated in the text by . The UK participation in its preparation was entrusted to Technical Committee MCE/5, Gears. A list of organizations represented on this committee can be obtained on request to its secretary.
4、 This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard cannot confer immunity from legal obligations. Amendments/corrigenda issued since publication Date Comments 30 September 200
5、8 Implementation of ISO corrigendum June 2008 Reference number ISO 6336-2:2006(E)INTERNATIONAL STANDARD ISO 6336-2 Second edition 2006-09-01 Calculation of load capacity of spur and helical gears Part 2: Calculation of surface durability (pitting) Calcul de la capacit de charge des engrenages cylind
6、riques dentures droite et hlicodale Partie 2: Calcul de la rsistance la pression de contact (piqre) BS ISO 6336-2:2006ii iii Contents Page Foreword iv Introduction v 1 Scope . 1 2 Normative references . 1 3 Terms, definitions, symbols and abbreviated terms. 2 4 Pitting damage and safety factors 2 5
7、Basic formul . 3 5.1 General. 3 5.2 Safety factor for surface durability (against pitting), S H . 3 5.3 Contact stress, H . 3 5.4 Permissible contact stress, HP5 6 Zone factor, Z H , and single pair tooth contact factors, Z Band Z D . 9 6.1 Zone factor, Z H9 6.2 Single pair tooth contact factors, Z
8、Band Z D , for u 2 10 6.3 Single pair tooth contact factors, Z Band Z D , for 2. 11 7 Elasticity factor, Z E . 11 8 Contact ratio factor, Z . 12 8.1 Determination of contact ratio factor, Z 13 8.2 Calculation of transverse contact ratio, , and overlap ratio, 14 9 Helix angle factor, Z 15 10 Strength
9、 for contact stress 16 10.1 Allowable stress numbers (contact), H lim , for Method B 16 10.2 Allowable stress number values for Method B R16 11 Life factor, Z NT(for flanks) . 16 11.1 Life factor Z NT : Method A. 17 11.2 Life factor Z NT : Method B . 17 12 Influence of lubricant film, factors Z L ,
10、Z vand Z R . 18 12.1 General. 18 12.2 Influence of lubricant film: Method A . 19 12.3 Influence of lubricant film, factors Z L , Z vand Z R : Method B. 19 13 Work hardening factor, Z W . 24 13.1 Work hardening factor, Z W : Method A 24 13.2 Work hardening factor, Z W : Method B 25 14 Size factor, Z
11、X29 Annex A (informative) Start of involute 30 Bibliography . 33 BS ISO 6336-2:2006iv Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out th
12、rough ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collab
13、orates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Stan
14、dards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of
15、 this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 6336-2 was prepared by Technical Committee ISO/TC 60, Gears, Subcommittee SC 2, Gear capacity calculation. This second edition cancels and replaces the first editi
16、on (ISO 6336-2:1996), Clause 13 of which has been technically revised. It also incorporates the Technical Corrigenda ISO 6336-2:1996/Cor.1:1998 and ISO 6336-2:1996/Cor.2:1999. ISO 6336 consists of the following parts, under the general title Calculation of load capacity of spur and helical gears: Pa
17、rt 1: Basic principles, introduction and general influence factors Part 2: Calculation of surface durability (pitting) Part 3: Calculation of tooth bending strength Part 5: Strength and quality of materials Part 6: Calculation of service life under variable load BS ISO 6336-2:2006 v Introduction Her
18、tzian pressure, which serves as a basis for the calculation of contact stress, is the basic principle used in this part of ISO 6336 for the assessment of the surface durability of cylindrical gears. It is a significant indicator of the stress generated during tooth flank engagement. However, it is n
19、ot the sole cause of pitting, and nor are the corresponding subsurface shear stresses. There are other contributory influences, for example, coefficient of friction, direction and magnitude of sliding and the influence of lubricant on distribution of pressure. Development has not yet advanced to the
20、 stage of directly including these in calculations of load-bearing capacity; however, allowance is made for them to some degree in the derating factors and choice of material property values. In spite of shortcomings, Hertzian pressure is useful as a working hypothesis. This is attributable to the f
21、act that, for a given material, limiting values of Hertzian pressure are preferably derived from fatigue tests on gear specimens; thus, additional relevant influences are included in the values. Therefore, if the reference datum is located in the application range, Hertzian pressure is acceptable as
22、 a design basis for extrapolating from experimental data to values for gears of different dimensions. Several methods have been approved for the calculation of the permissible contact stress and the determination of a number of factors (see ISO 6336-1). BS ISO 6336-2:2006blank1 Calculation of load c
23、apacity of spur and helical gears Part 2: Calculation of surface durability (pitting) IMPORTANT The user of this part of ISO 6336 is cautioned that when the method specified is used for large helix angles and large pressure angles, the calculated results should be confirmed by experience as by Metho
24、d A. In addition, it is important to note that best correlation has been obtained for helical gears when high accuracy and optimum modifications are employed. 1 Scope This part of ISO 6336 specifies the fundamental formul for use in the determination of the surface load capacity of cylindrical gears
25、 with involute external or internal teeth. It includes formul for all influences on surface durability for which quantitative assessments can be made. It applies primarily to oil-lubricated transmissions, but can also be used to obtain approximate values for (slow-running) grease-lubricated transmis
26、sions, as long as sufficient lubricant is present in the mesh at all times. The given formul are valid for cylindrical gears with tooth profiles in accordance with the basic rack standardized in ISO 53. They may also be used for teeth conjugate to other basic racks where the actual transverse contac
27、t ratio is less than n= 2,5. The results are in good agreement with other methods for the range, as indicated in the scope of ISO 6336-1. These formul cannot be directly applied for the assessment of types of gear tooth surface damage such as plastic yielding, scratching, scuffing or any other than
28、that described in Clause 4. The load capacity determined by way of the permissible contact stress is called the “surface load capacity” or “surface durability”. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, onl
29、y the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 53:1998, Cylindrical gears for general and heavy engineering Standard basic rack tooth profile ISO 1122-1:1998, Vocabulary of gear terms Part 1: Definitions rela
30、ted to geometry ISO 6336-1:2006, Calculation of load capacity of spur and helical gears Part 1: Basic principles, introduction and general influence factors ISO 6336-5:2003, Calculation of load capacity of spur and helical gears Part 5: Strength and quality of material BS ISO 6336-2:20062 3 Terms, d
31、efinitions, symbols and abbreviated terms For the purposes of this document, the terms, definitions, symbols and abbreviated terms given in ISO 1122-1 and ISO 6336-1 apply. 4 Pitting damage and safety factors If limits of the surface durability of the meshing flanks are exceeded, particles will brea
32、k out of the flanks, leaving pits. The extent to which such pits can be tolerated (in size and number) varies within wide limits, depending largely on the field of application. In some fields, extensive pitting can be accepted; in other fields any appreciable pitting is to be avoided. The following
33、assessments, relevant to average working conditions, will help in distinguishing between initial pitting and destructive pitting. Linear or progressive increase of the total area of pits is unacceptable; however, the effective tooth bearing area can be enlarged by initial pitting, and the rate of ge
34、neration of pits could subsequently reduce (degressive pitting), or cease (arrested pitting). Such pitting is considered tolerable. In the event of dispute, the following rule is determinant. Pitting involving the formation of pits that increase linearly or progressively with time under unchanged se
35、rvice conditions (linear or progressive pitting) is not acceptable. Damage assessment shall include the entire active area of all the tooth flanks. The number and size of newly developed pits in unhardened tooth flanks shall be taken into consideration. It is a frequent occurrence that pits are form
36、ed on just one or only a few of the surface hardened gear tooth flanks. In such circumstances, assessment shall be centred on the flanks actually pitted. Teeth suspected of being especially at risk should be marked for critical examination if a quantitative evaluation is required. In special cases,
37、a first rough assessment can be based on considerations of the entire quantity of wear debris. In critical cases, the condition of the flanks should be examined at least three times. The first examination should, however, only take place after at least 10 6cycles of load. Further examination should
38、take place after a period of service depending on the results of the previous examination. If the deterioration by pitting is such that it puts human life in danger, or there is a risk that it could lead to some grave consequences, then pitting is not tolerable. Due to stress concentration effects,
39、a pit of a diameter of 1 mm near the fillet of a through-hardened or case-hardened tooth of a gear can become the origin of a crack which could lead to tooth breakage; for this reason, such a pit shall be considered as intolerable (e.g. in aerospace transmissions). Similar considerations are true fo
40、r turbine gears. In general, during the long life (10 10to 10 11cycles) which is demanded of these gears, neither pitting nor unduly severe wear is tolerable. Such damage could lead to unacceptable vibrations and excessive dynamic loads. Appropriately generous safety factors should be included in th
41、e calculation, i.e. only a low probability of failure can be tolerated. In contrast, pitting over 100 % of the working flanks can be tolerated for some slow-speed industrial gears with large teeth (e.g. module 25) made from low hardness steel where they will safely transmit the rated power for 10 to
42、 20 years. Individual pits may be up to 20 mm in diameter and 8 mm deep. The apparently “destructive” pitting which occurs during the first two or three years of service normally slows down. The tooth flanks become smoothed and work hardened to the extent of increasing the surface Brinell hardness n
43、umber by 50 % or more. For such conditions, relatively low safety factors (in some cases less than one) may be chosen, with a correspondingly higher probability of tooth surface damage. A high factor of safety against tooth breakage is necessary. Comments on the choice of safety factor S Hcan be fou
44、nd in ISO 6336-1:2006, 4.1.7. It is recommended that the manufacturer and customer agree on the values of the minimum safety factor. BS ISO 6336-2:20063 5 Basic formul 5.1 General The calculation of surface durability is based on the contact stress, H , at the pitch point or at the inner point of si
45、ngle pair tooth contact. The higher of the two values obtained is used to determine the load capacity (determinant). Hand the permissible contact stress, HP , shall be calculated separately for wheel and pinion. Hshall be less than HP . This comparison will be expressed in safety factors S H1and S H
46、2which shall be higher than the agreed minimum safety factor S Hmin . Four categories are recognized in the calculation of H , as follows. a) Spur gears with contact ratio W 1: for a pinion, His usually calculated at the inner point of single pair tooth contact. In special cases, Hat the pitch point
47、 is greater and thus determinant; for a spur wheel, in the case of external teeth, His usually calculated at the pitch point, however, in special cases particularly in the case of small transmission ratios (see 6.2), His greater at the inner point of single pair tooth contact of the wheel and is thu
48、s determinant; whereas, for internal teeth, His always calculated at the pitch point. b) Helical gears with contact ratio W 1 and overlap ratio W 1: His always calculated at the pitch point for pinion and wheel. c) Helical gears with contact ratio W 1 and overlap ratio 1: not covered by ISO 6336 a c
49、areful analysis of the contact stress along the path of contact is necessary. 5.2 Safety factor for surface durability (against pitting), S HCalculate S Hseparately for pinion and wheel: HG1 H m in H1 H1SS = (1) HG2 H2 H min H2SS = (2) Take H1,2in accordance with Equation (4) for the pinion and in accordance with Equation (5) for the wheel (see 5.1). Cal
