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1、 Reference number ISO 6336-2:2006(E) ISO 2006 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 cylindriques dentures droite et hlicodale
2、 Partie 2: Calcul de la rsistance la pression de contact (piqre) ISO 6336-2:2006(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobes licensing policy, this file may be printed or viewed but shall not be edited unless the typefaces which are embedded are licensed
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5、t is found, please inform the Central Secretariat at the address given below. ISO 2006 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permi
6、ssion in writing from either ISO at the address below or ISOs member body in the country of the requester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2006 All rights reser
7、ved ISO 6336-2:2006(E) ISO 2006 All rights reserved 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 Basic formul. 3 5.1 General. 3 5.2 Safety factor for surface durabilit
8、y (against pitting), SH. 3 5.3 Contact stress, H. 3 5.4 Permissible contact stress, HP 5 6 Zone factor, ZH, and single pair tooth contact factors, ZB and ZD. 9 6.1 Zone factor, ZH 9 6.2 Single pair tooth contact factors, ZB and ZD, for u 2 10 6.3 Single pair tooth contact factors, ZB and ZD, for 2.
9、11 7 Elasticity factor, ZE. 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 for contact stress 16 10.1 Allowable stress numbers (contact), H lim, for Method B
10、16 10.2 Allowable stress number values for Method BR 16 11 Life factor, ZNT (for flanks). 16 11.1 Life factor ZNT: Method A. 17 11.2 Life factor ZNT: Method B. 17 12 Influence of lubricant film, factors ZL, Zv and ZR. 18 12.1 General. 18 12.2 Influence of lubricant film: Method A . 19 12.3 Influence
11、 of lubricant film, factors ZL, Zv and ZR: Method B. 19 13 Work hardening factor, ZW. 24 13.1 Work hardening factor, ZW: Method A 24 13.2 Work hardening factor, ZW: Method B 25 14 Size factor, ZX 29 Annex A (informative) Start of involute 30 Bibliography. 33 ISO 6336-2:2006(E) iv ISO 2006 All rights
12、 reserved 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 through ISO technical committees. Each member body interested in a subject for
13、 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 collaborates closely with the International Electrotechnical Commission (IEC) on a
14、ll 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 Standards. Draft International Standards adopted by the technical committees are
15、 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 this document may be the subject of patent rights. ISO shall not be held re
16、sponsible 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 edition (ISO 6336-2:1996), Clause 13 of which has been technically revised. It al
17、so 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: Part 1: Basic principles, introduction and general influence factors Part 2: C
18、alculation 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 ISO 6336-2:2006(E) ISO 2006 All rights reserved v Introduction Hertzian pressure, which serves as a basis for the
19、 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 not the sole cause of pitting, and nor are the c
20、orresponding 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 stage of directly including these in calculati
21、ons 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 fact that, for a given material, limiting values
22、 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 a design basis for extrapolating from experime
23、ntal 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). INTERNATIONAL STANDARD ISO 6336-2:2006(E) ISO 2006 All rights reserved 1 Calculation of load
24、capacity 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 Meth
25、od 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 gear
26、s 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 transmi
27、ssions, 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 conta
28、ct 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 tha
29、n 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, o
30、nly 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 re
31、lated 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 ISO 6336-2:2006(E) 2 ISO 200
32、6 All rights reserved 3 Terms, definitions, 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 a
33、re exceeded, particles will break 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
34、is to be avoided. The following 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 ini
35、tial pitting, and the rate of generation 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 progressiv
36、ely with time under unchanged service 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 freque
37、nt occurrence that pits are formed 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
38、 is required. In special cases, 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 106 cycles of l
39、oad. Further examination should 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 t
40、o stress concentration effects, 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). Si
41、milar considerations are true for turbine gears. In general, during the long life (1010 to 1011 cycles) 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
42、factors should be included in the 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 tr
43、ansmit the rated power for 10 to 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 increasin
44、g the surface Brinell hardness number 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 choic
45、e of safety factor SH can be found 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. ISO 6336-2:2006(E) ISO 2006 All rights reserved 3 5 Basic formul 5.1 General The calculation of surface durability is based on the cont
46、act stress, H, at the pitch point or at the inner point of single pair tooth contact. The higher of the two values obtained is used to determine the load capacity (determinant). H and the permissible contact stress, HP, shall be calculated separately for wheel and pinion. H shall be less than HP. Th
47、is comparison will be expressed in safety factors SH1 and SH2 which shall be higher than the agreed minimum safety factor SHmin. Four categories are recognized in the calculation of H, as follows. a) Spur gears with contact ratio W 1: for a pinion, H is usually calculated at the inner point of singl
48、e pair tooth contact. In special cases, H at the pitch point is greater and thus determinant; for a spur wheel, in the case of external teeth, H is usually calculated at the pitch point, however, in special cases particularly in the case of small transmission ratios (see 6.2), H is greater at the in
49、ner point of single pair tooth contact of the wheel and is thus determinant; whereas, for internal teeth, H is always calculated at the pitch point. b) Helical gears with contact ratio W 1 and overlap ratio W 1: H is 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 careful analysis of the contact stress along the path of contact is necessary. 5.2 Safety factor for
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