1、BRITISH STANDARD BS 6168:1987 Incorporating Amendment No. 1 Specification for Non-metallic spur gears UDC 621.833.1 036BS6168:1987 This British Standard, having been prepared under the directionof the Machinery andComponents Standards Committee, was published underthe authority of the BoardofBSI and
2、 comes intoeffecton 31 March1987 BSI 04-2000 First published February 1982 First revision March 1987 The following BSI references relate to the work on this standard: Committee reference MCE/5 Draft for comment 84/73218 DC ISBN 0 580 15314 2 Committees responsible for this British Standard The prepa
3、ration of this British Standard was entrusted by the Machinery and Components Standards Committee (MCE/-) to Technical Committee MCE/5, upon which the following bodies were represented: Association of Consulting Engineers British Clock and Watch Manufacturers Association British Coal British Gear Ma
4、nufacturers Association British Horological Institute British Railways Board Engineering Equipment and Materials Users Association Federation of Manufacturers of Construction Equipment and Cranes Gauge and Tool Makers Association Institution of Mechanical Engineers Institution of Production Engineer
5、s Lloyds Register of Shipping Machine Tool Industry Research Association Milling Cutter Association Ministry of Defence Society of Motor Manufacturers and Traders Limited Amendments issued since publication Amd. No. Date of issue Comments 6364 May 1991 Indicated by a sideline in the marginBS6168:198
6、7 BSI 04-2000 i Contents Page Committees responsible Inside front cover Foreword iv 1 Scope 1 2 Definitions and symbols 1 3 Basic rack tooth profile 3 4 Normal modules and normal diametral pitches 3 5 Fabrication 3 6 Accuracy 4 7 Measurement 5 8 Gear errors and tolerances 5 9 Hub and rim proportions
7、 15 10 Allowances for thermal and hygroscopic expansion 16 11 Information to be given on drawings 17 Appendix A Materials 21 Appendix B Lubrication of plastics gears 22 Appendix C Tables of tolerance values 22 Appendix D Addendum modification 30 Appendix E Example calculations of maximum centre dist
8、ance andtotalgearand housing expansion 32 Appendix F Recommended method for calculation of gear stresses 34 Figure 1 Basic rack tooth profile for normal modules 4 Figure 2 Limits of tip relief of modified basic rack tooth profilefornormalmodules 4 Figure 3 Test loads 7 Figure 4 Tolerance on cumulati
9、ve tooth pitch error over k pitches F pk 8 Figure 5 Tolerance factor p 9 Figure 6 Adjacent pitch error (transverse) tolerance f pt 9 Figure 7 Radial run-out tolerance F r 10 Figure 8 Radial tooth-to-tooth composite error tolerance f i 11 Figure 9 Radial composite error tolerance F i 11 Figure 10 Rad
10、ial indicator reading tolerance F l 12 Figure 11 Tolerance factor f 13 Figure 12 Tooth profile error tolerance f f 14 Figure 13 Tooth alignment tolerance on face width b, F 15 Figure 14 Plastics moulding on metal hub 16 Figure 15 Plastics moulding without hub 16 Figure 16 Plastics moulding with hub
11、16 Figure 17 Example of a typical drawing 18 Figure 18 Thermal expansion rates 19 Figure 19 Hygroscopic expansion rates 20 Figure 20 Pinion with10 teeth 32 Figure 21 Tooth form factor Y Fas a function of number of teeth z fordifferentvalues of addendum modification coefficient x 37 Figure 22 Enduran
12、ce limit for bending stress versus gear life (unlubricatedPA66) 38 Figure 23 Endurance limit for bending stress versus gear life (unlubricatedPOM) 38BS6168:1987 ii BSI 04-2000 Page Figure 24 Size factor Y Xas a function of gear module 39 Figure 25 Youngs modulus versus temperature 42 Figure 26 Endur
13、ance limit for contact stress versus gear life (unlubricatedPA66) 43 Figure 27 Endurance limit for contact stress versus gear life (unlubricatedPOM) 44 Table 1 Normal modules 3 Table 2 Normal diametral pitches 3 Table 3 Gear errors and tolerances 6 Table 4 Tolerance on cumulative tooth pitch error o
14、ver a sector of k pitches(F pk ) or arc length L 6 Table 5 Adjacent pitch error (transverse) tolerance f pt 6 Table 6 Radial run-out tolerance F r 10 Table 7 Radial tooth-to-tooth composite error tolerance f i 10 Table 8 Radial composite error tolerance F i 10 Table 9 Radial indicator reading tolera
15、nce F l 12 Table 10 Tooth profile error tolerance f f 13 Table 11 Tooth alignment error tolerance on face width b, F 14 Table 12 Centre distance error tolerance f a 14 Table 13 Gear blanks tolerances 15 Table 14(a) Cumulative tooth pitch error tolerance F pk(metric units) 22 Table 14(b) Cumulative t
16、ooth pitch error tolerance F pk(imperial units) 23 Table 15(a) Adjacent pitch error (transverse) tolerance f pt(metric units) 23 Table 15(b) Adjacent pitch error (transverse) tolerance f pt(imperial units) 24 Table 16(a) Radial run-out tolerance F r(metric units) 24 Table 16(b) Radial run-out tolera
17、nce F r(imperial units) 25 Table 17(a) Radial tooth-to-tooth composite error tolerance f i (metric units) 25 Table 17(b) Radial tooth-to-tooth composite error tolerance f i (imperial units) 26 Table 18(a) Radial composite error tolerance F i (metric units) 26 Table 18(b) Radial composite error toler
18、ance F i (imperial units) 27 Table 19(a) Radial indicator reading tolerance F l(metric units) 27 Table 19(b) Radial indicator reading tolerance F l(imperial units) 28 Table 20(a) Tooth profile error tolerance f f(metric units) 28 Table 20(b) Tooth profile error tolerance f f(imperial units) 29 Table
19、 21(a) Tooth alignment error tolerance F (metric units) 29 Table 21(b) Tooth alignment error tolerance F (imperial units) 29 Table 22(a) Tolerances on radial and axial run-out of reference surfacesofwheel blanks (metric units) 30 Table 22(b) Tolerances on radial and axial run-out of reference surfac
20、esofwheel blanks (imperial units) 30 Table 23(a) Values of IT (metric units) 30 Table 23(b) Values of IT (imperial units) 30 Table 24 Coefficient of friction 35 Table 25 Dimensionless experimental factor K a 35BS6168:1987 BSI 04-2000 iii Page Table 26 Correction coefficient K b 36 Table 27 Gear mate
21、rial constant K M 36 Table 28 Maximum bulk temperature for non-metallic materials forcontinuous operation 36 Table 29 Application factor K Afor speed reducing gears 37 Table 30 Poissons ratio 40 Publications referred to Inside back coverBS6168:1987 iv BSI 04-2000 Foreword The revision of BS6168 has
22、been prepared under the direction of the Machinery and Components Standards Committee. The main change incorporated is the addition of an Appendix F to give recommendations on the limiting contact and bending stresses of non-metallic gears for general engineering applications. This appendix is for i
23、nformation only and does not form part of this standard. The information presented in Appendix F on the limiting contact and bending stresses of non-metallic gears is tentative. It is proposed to confirm the validity of the stressing formulae and failure data and to extend the range of non-metallic
24、material for which accurate gear stressing is required. It is intended that the results of this work should be embodied in a future revision of BS6168. Certain quantities are expressed in both metric (SI) units and imperial units, the latter being given in recognition of the continuing demand for re
25、placement gears manufactured to imperial dimensions. The retention of imperial units will be subject to review at the appropriate time. This standard supersedes BS6168:1982, which is withdrawn. A British Standard does not purport to include all the necessary provisions of a contract. Users of Britis
26、h Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi to iv, pages1to46, an inside back cover and a back cover. Thi
27、s standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS6168:1987 BSI 04-2000 1 1 Scope This British Standard specifies dimensional, accuracy and material requirements for spur gears made fro
28、m non-metallic materials in pitch sizes of0.50 module to50 module(48 to0.50 diametral pitch) and also gives guidance on lubrication and lists information to be given on drawings. The ranges of modules and diametral pitches employed include those specified in BS436-1 and BS436-2. The basic tooth form
29、 and the accuracy grades specified are selected from those specified in BS436-1 and BS436-2. Helical gears are not within the scope of this standard. Surface finish requirements for thermoplastics gears are not specified in this standard as insufficient authoritative data on the subject exists at pr
30、esent. NOTE 1Information on the selection of materials and the lubrication of plastics gears is given in Appendix A and Appendix B, respectively. Tables of tolerance values are given in Appendix C. Recommendations for addendum modification and a recommended method of gear stressing are given in Appe
31、ndix D and Appendix F. Example calculations are given in Appendix E and Appendix F. NOTE 2The titles of the publications referred to in this standard are listed on the inside back cover. 2 Definitions and symbols 2.1 Definitions For the purposes of this British Standard, the definitions given in BS2
32、519-1 and PD6457 apply. 2.2 Symbols For the purposes of this British Standard, the following symbols apply. NOTEThis subclause is based on the symbols of BS2519-2:1976. Symbol Designation Imperial units SI units a centre distance (theoretical) in mm a ext centre distance (extension) in mm a th centr
33、e distance thermalexpansion in mm a w centre distance (operating) in mm b facewidth in mm d reference diameter in mm d 1 reference diameter of pinion in mm d 2 reference diameter of wheel in mm d a tip diameter in mm e spacewidth in mm f a centre distance tolerance in 4m f f profile error tolerance
34、(maximum of pinion andwheel) in 4m f i radial tooth-to-tooth composite error tolerance(dual flank) in 4m f pb normal individual base pitch error tolerance in 4m f pn adjacent pitch error tolerance (normal) in 4m f pt adjacent pitch error (transverse) tolerance in 4m f x axes parallelism error (incli
35、nation) tolerance in 4m f y axes parallelism error (deviation) tolerance in 4m h a dedendum in mm h a0 addendum of basic rack in mm k number of tooth pitches m module mm m n normal module mm n rotational speed min 1 min 1 r radius in mm r a tip radius in mm r b base circle radius in mm r hy radial h
36、ydroscopic expansion in mm r th radial thermal expansion in mm r tot1 total pinion radial expansion in mm r tot2 total wheel radial expansion in mm s tooth thickness in mm u gear ratio v pitch line velocity m/s x addendum modification coefficient z number of teeth A surface area of gearbox in 2 m 2
37、E Youngs modulus of elasticity GPa F i radial composite error tolerance (dual flank) in 4m F l radial indicator reading tolerance (width of tolerance band) in 4m F p total cumulative pitch error tolerance in 4m F pk tolerance on cumulative pitch error over k pitches in 4m F r radial tooth run-out to
38、lerance in 4m Symbol Designation Imperial units SI unitsBS6168:1987 2 BSI 04-2000 Suffixes 2.3 Material notation for the purposes of this British Standard the following notation applies. NOTEFor convenience, these notations have been used, as appropriate, in graphs and stress calculations. For other
39、 materials for use in gears seeAppendix A. F t nominal tangential forceat reference circle N F tooth alignment error tolerance on facewidth b in 4m IT tolerance grade value in mm K A application factor K a experimental factor for material temperature K b correction coefficient formaterial temperatur
40、e (m 2 C)/W K M gear material constant L length of arc round gear in mm P diametral pitch in 1 mm 1 P n normal diametral pitch in 1 mm 1 P T transmitted power kW R a arithmetic average roughness (CLA value) S safety factor S F actual safety factor for bending stress (against breakage) T torque Nm T
41、1 pinion torque Nm T 2 wheel torque Nm Y factor for bending stress Y F tooth form factor for bending stress Y b) voids within the body of the moulding; c) flow lines; d) burn marks; e) sink marks. NOTE 1The design of tooling and the moulding conditions employed can have a significant effect on the l
42、ife of moulded gears. The purchaser should, therefore, discuss with the moulder any defects which could arise and affect gear performance. Methods are not currently available for quantifying all such defects. NOTE 2The moulder should seek advice from the material supplier regarding moulding techniqu
43、es. 5.2 Cut thermoplastics gears Thermoplastics gears cut from semi-finished plastics rod and sheet shall be free from the defects listed in5.1. 1 2 Normal module m n Preferred modules Second choice modules mm mm 0.50 0.60 0.80 1 1.25 1.50 2 2.50 3 4 5 6 8 10 12 16 20 25 32 40 50 0.70 0.90 1.125 1.375 1.75 2.25 2.75 3.50 4.50 5.50 6.50 7 9 11 14 18 22 28 36 45 1 2 Normal diametral pitch P n Preferred diametral pitches Second choice diametralpitches in in 48 40 32 24 20 16 12 10 8 6 5 4 3 2.50 2 1.50 1.25 1 0.75 0.625 0.50 36 28 18 14 11 9 7 5.50 4.50 3.50 2.75 2.25 1.75 0.875
