1、BRITISH STANDARD BS 8726-1:2002 Cylindrical helical springs made from rectangular and square section wire and bar Guide to calculation and design Part 1: Compression springs ICS 21.160 BS 8726-1:2002 This British Standard, having been prepared under the direction of the Engineering Sector Policy and
2、 Strategy Committee, was published under the authority of the Standards Policy and Strategy Committee on 25 September 2002 BSI 25 September 2002 The following BSI references relate to the work on this British Standard: Committee reference GME/15 Draft for comment 02/702405 DC ISBN 0 580 39738 6 Comm
3、ittees responsible for this British Standard The preparation of this British Standard was entrusted to Technical Committee GME/15, Mechanical springs, upon which the following bodies were represented: British Impact Treatment Association Institute of Spring Technology Amendments issued since publica
4、tion Amd. No. Date CommentsBS 8726-1:2002 BSI 25 September 2002 i Contents Page Committee responsible Inside front cover Foreword ii 1S c o p e 1 2 Normative references 1 3 Terms, definitions and symbols 1 4G e n e r a l 8 5 Methods of calculation 8 6T o l e r a n c e s 1 4 7 Specifying springs for
5、general purposes 16 8 Methods of verification 24 Annex A (informative) Modulus of rigidity of some materials 29 Annex B (informative) Typical tolerances on rectangular section material 29 Figure 1 Design chart for stress 9 Figure 2 Design chart for rate 10 Figure 3 Seating coefficient for various en
6、d conditions 11 Figure 4 Critical relative deflection for m = 1.0 to 2.5 12 Figure 5 Critical relative deflection for m = 0.4 to 1 13 Figure 6 Data sheet 1 18 Figure 7 Hand of coiling 19 Figure 8 End coil form 19 Figure 9 Coil end formed from tapered bar 19 Figure 10 Data sheet 2 23 Figure 11 Measur
7、ement of free length and parallelism 25 Figure 12 Measurement of squareness 26 Figure 13 Measurement of bow 26 Table 1 Calculated tolerances for group A springs with more than 3.5 and less than 5 total coils 15 Table 2 Calculated tolerances for group B springs with more than 3.5 and less than 5 tota
8、l coils 16 Table A.1 Modulus of rigidity values 29 Table B.1 Typical tolerances on rectangular section material 29BS 8726-1:2002 ii BSI 25 September 2002 Foreword BS 1726-1 was first published in 1951 and revised in 1964 to incorporate much of the essential information from ADE Design Data Sheets, w
9、hich were no longer available from HM Stationery Office and for which copyright permission to republish was obtained. The standard was revised in 1988 to take account of current manufacturing processes. BS 1726-1:1988, was withdrawn on the publication of BS EN 13906-1 in 2001. The provisions for the
10、 design, specification, tolerances and testing of rectangular section compression springs are now published in this separate standard. Together with BS 1726-1:2002 and BS EN 13906-1:2002, this new standard, BS 8726-1, supersedes BS 1726-1:1987, which is withdrawn. BS 8726 is published in two parts:
11、Part 1: Compression springs; Part 2: Torsion springs. 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 does not of itself confer immunity from legal
12、obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 29 and a back cover. The BSI copyright notice displayed in this document indicates when the document was last issued.BS 8726-1:2002 BSI 25 September 2002 1 1 Scope This British Stan
13、dard provides guidance on the design of parallel sided helical compression springs manufactured from rectangular and square section wire and bar. This standard applies only to springs made from rectangular section material where the ratio of radial dimension, b, to the axial dimension, h, termed the
14、 shape factor, m, is not greater than 2.5 and not less than 0.4. NOTE 1 This applies because, outside the shape factor range 2.5 to 0.4, it is difficult to coil a spring accurately. NOTE 2 There are numerous methods of calculating the parameters necessary for the design of springs and initially the
15、designer is free to use any one of these. Three types of end coils are provided for, i.e. open end, closed end and closed and ground end, the last of these being applicable only to springs where the axial dimension of material is 0.5 mm or greater. This British Standard differentiates between spring
16、s that have or have not been stress relieved after forming, designated group A springs, and springs, the material of which has undergone a structural change by heat treatment after forming, designated group B springs. This British Standard gives two methods of specifying springs for general purposes
17、 and one method of testing springs. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document applies. BS 817, Specifica
18、tion for surface plates. BS 887, Specification for precision vernier callipers. BS 939, Specification for engineers squares (including cylindrical and block squares). BS 957-2, Specification for feeler gauges Metric units. BS 969, Specification for limits and tolerances on plain limit gauges. BS EN
19、ISO 7500-1, Tension/compression testing machines Verification and calibration of the force measuring system. BS EN ISO 3650, Geometrical product specifications (GPS) Length standards Gauge blocks. BS 5204, Specification for straight edges. BS 5317, Specification for metric length bars and their acce
20、ssories. BS 5411, Methods of test for metallic and related coatings. BS 6365, Specification for precision vernier depth gauges. BS 6468, Specification for depth micrometers. 3 Terms, definitions and symbols 3.1 Terms and definitions For the purposes of this Part of BS 8726 following terms and defini
21、tions apply. 3.1.1 active coils effective coils (non-preferred) working coils (non-preferred) coils of a spring that at any instant are contributing to the rate of the springBS 8726-1:2002 2 BSI 25 September 2002 3.1.2 angle of grind angle subtended by the ground end surface of the spring at the int
22、ersection of the plane of the ground surface with the major axis of the spring 3.1.3 bow maximum deviation between any coil of a spring and a datum surface or straight edge on which the spring is laid NOTE See 8.2.13. 3.1.4 buckling unstable lateral distortion of the major axis of a spring when comp
23、ressed 3.1.5 chamfering removal of a corner on the inside and/or outside diameter of the ground face of a spring to clear any radius on the spring seat 3.1.6 closed end end of a helical spring in which the helix angle of the end coil has been progressively reduced until the end coil touches the adja
24、cent coil 3.1.7 compression spring spring whose dimension, in the direction of the applied force, reduces under the action of that force 3.1.8 compression test test carried out by pressing a spring to a specified length a specified number of times 3.1.9 coning operation in which the diameter of the
25、ends of an extension or compression spring is reduced 3.1.10 countersink internal chamfer 3.1.11 cramp test test carried out by compressing a spring to a specified length for a defined period 3.1.12 creep change in length of a spring with time when subjected to a constant force 3.1.13 damper coils c
26、oils that are active at the free length but inactive at the normal operating length 3.1.14 dead coils coils of a spring that do not affect the rate of the spring 3.1.15 deflection relative displacement of the ends of a spring under the application of a forceBS 8726-1:2002 BSI 25 September 2002 3 3.1
27、.16 edge dressing removal of material from the outside edge of the end coils where they protrude beyond the outside diameter of the spring 3.1.17 elastic deformation deformation that takes place when a material is subjected to any stress up to its elastic limit NOTE On removal of the force causing t
28、his deformation the material returns to its original size. 3.1.18 seating coefficient end fixation factor (non-preferred) factor used in the calculation of buckling to take account of the method of locating the end of the spring 3.1.19 fatigue phenomenon giving rise to a type of failure which takes
29、place under conditions involving repeated or fluctuating stresses below the elastic limit of the material 3.1.20 fatigue limit value, which may be statistically determined, of the stress condition below which material may endure an infinite number of stress cycles 3.1.21 fatigue strength endurance l
30、imit (non-preferred) stress condition under which a material will have a life of a given number of cycles 3.1.22 fatigue test test to determine the number of cycles of stress that will produce failure of a component or test piece 3.1.23 finish coating applied to protect or decorate springs 3.1.24 fi
31、tted length length of a spring when assembled into position within a mechanism from which it is required to function 3.1.25 free length length of a spring when it is not loaded NOTE In the case of extension springs this may include the anchor ends. 3.1.26 grinding removal of metal from the end faces
32、 of a spring by the use of abrasive wheels to obtain a flat surface which is square with the spring axis 3.1.27 group A springs springs that have or have not been stress relieved (3.1.59) after forming 3.1.28 group B springs springs, the material of which has undergone a structural change by heat tr
33、eatment after formingBS 8726-1:2002 4 BSI 25 September 2002 3.1.29 hand the direction in which the helix of a spring is formed, i.e. right or left. 3.1.30 heat stabilization process of removing primary creep and inducing beneficial stresses into a spring, so that, when the spring is subjected to an
34、operating stress and temperature, it will exhibit improved stress temperature relaxation properties 3.1.31 helical spring spring made by forming material into a helix 3.1.32 helix angle angle of the helix of a helical coil spring 3.1.33 hysteresis lagging of the effect behind the cause of the effect
35、 NOTE A measure of hysteresis in a spring is represented by the area between the loading and unloading curves produced when the spring is stressed within the elastic range. 3.1.34 index ratio of the mean coil diameter of a spring to the material diameter for circular sections or radial width of cros
36、s-section for rectangular or trapezoidal sections 3.1.35 inside coil diameter of a spring diameter of the cylindrical envelope formed by the inside surface of the coils of a spring 3.1.36 linearity degree by which the forcedeflection curve of a spring approaches a straight line 3.1.37 load test test
37、 on a spring to determine either the force at a given length or the length under a given force 3.1.38 modulus of elasticity ratio of stress to strain within the elastic range NOTE The modulus of elasticity in tension or compression is also known as Youngs modulus and that in shear as the modulus of
38、rigidity. 3.1.39 natural frequency frequency at which a spring will freely vibrate once it has been excited 3.1.40 open end end of an open coiled helical spring in which the helix angle of the end coil has not been progressively reduced 3.1.41 outside coil diameter diameter of the cylindrical envelo
39、pe formed by the outside surface of the coils of a spring 3.1.42 parallelism degree to which the two ground ends of a spring are parallel to each otherBS 8726-1:2002 BSI 25 September 2002 5 3.1.43 permanent set set (non-preferred) permanent deformation of a spring after the application and removal o
40、f a force 3.1.44 pitch distance from any point in the section of one coil to the corresponding point in the next coil when measured parallel to the axis of the spring 3.1.45 prestressing scragging (non-preferred) blocking (non-preferred) process during which internal stresses are induced into a spri
41、ng NOTE It is achieved by subjecting the spring to a stress greater than that to which it is subjected under working conditions and higher than the elastic limit of the material. The plastically deformed areas resulting from this stress cause an advantageous redistribution of the stresses within the
42、 spring. Prestressing can only be performed in the direction of applied force. 3.1.46 rate stiffness (non-preferred) force that has to be applied in order to produce unit deflection 3.1.47 relaxation loss of force of a spring with time when deflected to a fixed position NOTE The degree of relaxation
43、 is dependent upon, and increases with, the magnitude of stress, temperature and time. 3.1.48 residual range deflection of a spring available beyond the maximum working position up to the solid position 3.1.49 safe deflection maximum deflection that can be applied to a spring without exceeding the e
44、lastic limit of the material 3.1.50 shot peening cold working process in which shot is impacted onto the surfaces of springs thereby inducing residual stresses in the outside fibres of the material NOTE The effect of this is that the algebraic sum of the residual and applied stresses in the outside
45、fibres of the material is lower than the applied stress, resulting in improved fatigue life of the component. 3.1.51 solid length overall length of a helical spring when each and every coil is in contact with the next 3.1.52 solid force theoretical force of a spring when compressed to its solid leng
46、th 3.1.53 space coil gap space (non-preferred) the distance between one coil and the next coil in an open coiled helical spring measured parallel to the axis of the springBS 8726-1:2002 6 BSI 25 September 2002 3.1.54 spring seat part of a mechanism that receives the ends of a spring and which may in
47、clude a bore or spigot to centralize the spring 3.1.55 squareness maximum out of alignment of one end of a spring from the other NOTE This is the measurement obtained by standing the spring on a datum surface and measuring the maximum deviation of the top coil from a square edge placed against the d
48、atum (see 8.2.11). 3.1.56 stress bending stress (non-preferred) shear stress (non-preferred) force divided by the area over which it acts NOTE This is applied to the material of the spring, and for compression and extension springs is in torsion or shear, and for torsion springs is in tension or ben
49、ding. 3.1.57 stress correction factor factor that is introduced to make allowance for the fact that the distribution of shear stress across the wire diameter is not symmetrical NOTE This stress is higher on the inside of the coil than it is on the outside. 3.1.58 stress range difference between the stresses induced by the minimum and maximum applied forces in a component subjected to cyclic loading 3.1.59 stress relieving low-temperat
