1、BRITISH STANDARD BS6101-1: 1981 Machine tool ball screws Part1: Methods of calculating dynamic and static load and life ratings UDC 621.9.022233.1:621.882.082.6BS6101-1:1981 This British Standard, having been prepared under the directionof the Mechanical Engineering Standards Committee, was publishe
2、d underthe authority oftheExecutive Board and comes intoeffect on 31July1981 BSI10-1999 The following BSI references relate to the work on this standard: Committee reference MEE/6 Draft for comment80/75332 DC ISBN 0 580 12153 4 Cooperating organizations The Mechanical Engineering Standards Committee
3、, under whose direction this British Standard was prepared, consists of representatives from the following: The organizations marked with an asterisk in the above list, together with the following, were directly represented on the Technical Committee entrusted with the preparation of this British St
4、andard: Associated Offices Technical Committee Department of Trade (Marine Division) Association of Consulting Engineers Department of Transport Association of Hydraulic Equipment Electricity Supply Industry in England and Manufacturers Wales Association of Mining Electrical and Engineering Equipmen
5、t Users Association Mechanical Engineers Federation of Manufacturers of Construction British Compressed Air Society Equipment and Cranes British Electrical and Allied Manufacturers Health and Safety Executive Association (BEAMA) Institution of Gas Engineers British Gas Corporation Institution of Mec
6、hanical Engineers* British Gear Manufacturers Association Institution of Plant Engineers British Internal Combustion Engine Institution of Production Engineers* Manufacturers Association Lloyds Register of Shipping British Pump Manufacturers Association London Transport Executive British Steel Corpo
7、ration Machine Tool Industry Research Association* British Steel Industry Ministry of Defence* British Valve Manufacturers Association National Coal Board Cbmpe Oil Companies Materials Association Chartered Institution of Building Services Process Plant Association Crown Agents for Oversea Governmen
8、ts and Railway Industry Association of Great Britain Administrations Society of Motor Manufacturers and Department of the Environment (PSA)* Traders Limited Department of Industry (Mechanical Telecommunication Engineering and Engineering)* Manufacturing Association (TEMA) Department of Industry (Nat
9、ional Engineering Water-tube Boilermakers Association Laboratory) Ball and Roller Bearing Manufacturers University of Aston in Birmingham Association University of Manchester, Institute of Science Federation of Engineers Tool Manufacturers and Technology Amendments issued since publication Amd. No.
10、Date of issue CommentsBS6101-1:1981 BSI 10-1999 i Contents Page Cooperating organizations Inside front cover Foreword ii 1 Scope 1 2 References 1 3 Definitions and notation 1 4 Thrust ball screw assemblies 2 5 Rated life 3 Figure 1 Section through ball screw drive 1 Table 1 Values of constant (K) 2
11、Table 2 Values of constant (K 2 ) 2 Publications referred to Inside back coverBS6101-1:1981 ii BSI 10-1999 Foreword This British Standard has been prepared under the direction of the Mechanical Engineering Standards Committee. The principles adopted in this standard for dynamic load and life ratings
12、 are based on rolling bearing practice specified in BS5512 with some modification to suit conditions applicable to ball screw assemblies. The principles adopted for static load ratings are taken from BS5645 and have also been modified for similar reasons. The definitions used in this standard are ad
13、apted from those given in BS5512-1 and BS5645, except for the addition of the conformity factor. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard doe
14、s not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 to4, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This w
15、ill be indicated in the amendment table on the inside front cover.BS6101-1:1981 BSI 10-1999 1 1 Scope This Part of this British Standard gives methods of calculating the basic dynamic and static load and life ratings of re-circulating ball screws for use in machine tool applications. It is applicabl
16、e to re-circulating ball screw assemblies having the shaft and nuts manufactured from hardened steel. 2 References The titles of the publications referred to in this standard are listed on the inside back cover. 3 Definitions and notation (see Figure 1) For the purposes of this British Standard the
17、following definitions and notation apply. 3.1 Definitions 3.1.1 life for an individual ballscrew assembly, the number of revolutions that the shaft makes in relation to the nut before the first evidence of fatigue develops in the material of one of them or in the rolling elements 3.1.2 basic rating
18、life (L 10 ) for an individual ballscrew, or group of apparently identical ballscrews operating under the same conditions, the life associated with90% probability of achieving the stated life 3.1.3 basic dynamic axial load rating (C a ) the constant centric axial load that a ballscrew can theoretica
19、lly endure for a basic rating life of one million revolutions 3.1.4 basic static axial load rating (C oa ) the static centric axial load that corresponds to a total permanent deformation of ball and ball track at the most heavily stressed ball/ball track contact of0.0001 of the ball diameter 3.1.5 c
20、onformity factor (f s ) the ratio of the ball track radius (r s ) divided by the ball diameter (D w ) 3.1.6 pitch circle diameter (D pw ) applicable in the calculation of load ratings the diameter at the centre of the ball 3.1.7 nominal contact angle ( ) the angle between a plane perpendicular to th
21、e screw axis and the nominal line of action of the resultant of the forces transmitted by a balltrack to a rolling element 3.2 Notation Figure 1 Section through ball screw drive C a is the basic dynamic axial load rating in N C oa is the basic static axial load rating in N D w is the ball diameter i
22、n mm D pw is the pitch circle diameter of balls in mm L 10 is the basic rating life,10 6revolutions Y is the axial load factor Z is the number of load carrying balls contained in one turn of balltrack f c is a factor which depends on the geometry of the bearing components, the accuracy to which the
23、various components are made, and the material f s is the conformity factor i is the number of rows of balls r s is the ball track radius x represents the revised hardness number(see5.4) is the nominal contact angle of bearing in degreesBS6101-1:1981 2 BSI 10-1999 4 Thrust ball screw assemblies 4.1 B
24、asic dynamic axial load rating. The basic dynamic axial load rating for single or double direction thrust ball screw assemblies, for balls equal to or less than25.4mm diameter is as follows. C a = f c (cos!) 0.7tan Z 2/3D w 1.8i a(in N) where i ais equal to i 0.7or i 0.86 (see4.5) For machine tool a
25、pplications factor f cis to be calculated from the following formula which is empiric. where and 4.2 Simplified formula for dynamic axial load rating. Since the majority of ballscrew assemblies for machine tool applications are produced for an optimum45 contact angle, it is possible to derive a simp
26、lified formula for these applications as follows. C a = K D w 1.8Z 2/3i a(in N) where i a = i 0.7or i 0.86 (see4.3) K = f c(cos !) 0.7tan For values of K see Table 1. Table 1 Values of constant (K) 4.3 Basic static axial load rating. The basic static axial load rating for single or double direction
27、thrust ball screw assemblies, for balls equal to or less than25.4mm diameter is as follows. C oa =27.5 Z sin! D w 2i aK 1(in N) where i a is equal to i 0.7or i 0.86 (see4.5) 4.4 Simplified formula for static axial load rating. Since the majority of ball screw assemblies for machine tool applications
28、 are produced for an optimum45 contact angle, it is possible to derive a simplified formula for these applications as follows. C oa = K 2Z D w 2i a(in N) where i a is equal toi 0.7or i 0.86 (see4.5) K 2 =27.5 sin K 1(derived from the formula given in4.3). For values of K 2see Table 2. Table 2 Values
29、 of constant (K 2 ) Conformity factor f s 0.52 0.54 0.56 Values of K 00.02 00.03 00.04 00.05 00.06 00.08 00.10 00.12 00.14 00.20 00.26 00.30 57.06 63.39 67.98 71.39 74.11 77.94 80.24 81.58 85.98 84.10 77.82 74.49 43.64 48.47 51.99 54.60 56.68 59.61 61.36 62.39 62.98 61.63 59.52 56.97 37.51 41.66 44.
30、69 46.92 48.71 51.23 52.73 53.62 54.12 52.96 51.15 48.96 Conformity factor f s 0.52 0.54 0.56 Values of K 2 47.6 34.4 28.7 D w D pw -cos 45 = Y () BS6101-1:1981 BSI 10-1999 3 4.5 Ball screw nuts with two or more rows of balls. The basic dynamic and/or static axial load rating for thrust ball screw a
31、ssemblies with two or more rows of identical balls carrying load in the same direction shall be multiplied by one of the following factors. a) i 0.7applicable for commercial quality ballscrew assemblies or ball nut shells having a minimum cross-sectional area less than the mating screw (e.g.,as for
32、some internal return nuts). b) i 0.86applicable for precision quality ballscrew assemblies (i.e.pitch error generally better then0.03mm/300) and where the cross-sectional area of the ballnut shell is greater than the mating screw. 5 Rated life 5.1 Basis of calculations. For machine tool applications
33、, calculations are based on a ball nut hardened to60HRC 1)for a life of10 6revolutions and a90% probability of achieving the life rating L 10 . The corresponding screw hardness is56HRC to58HRC. 5.2 Adjusted life. Adjusted life shall be calculated in accordance with5.3 of BS5512-1:1977. 5.3 Direction
34、 of load. Life ratings shall be calculated assuming unidirectional loads. In the event of bi-directional (push-pull) loads, the life rating shall be calculated separately for each direction. 5.4 Hardness variation. The load capacity shall be re-rated if the hardness values quoted in5.1 are not achie
35、ved. The calculation shall be based on the following formula. C aat revised hardness value of HRC 1) NOTEBrinell numbers may be used in place of the Rockwell C scale. 1) See BS891.4 blankBS6101-1:1981 BSI 10-1999 Publications referred to BS891, Method for Rockwell hardness test. BS891-1, Testing of
36、metals. BS5512, Specification for rolling bearings Dynamic load ratings and rating life 2) . BS5512-1, Calculation methods. BS5645, Specification for rolling bearings Static load ratings 2) . 2) Referred to in the foreword only.BS6101-1: 1981 BSI 389 Chiswick High Road London W4 4AL BSIBritishStanda
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