1、BRITISH STANDARD BS 1726-2:2002 Cylindrical helical springs made from round wire and bar Guide to methods of specifying, tolerances and testing Part 2: Extension springs ICS 21.160 BS 1726-2:2002 This British Standard, having been prepared under the direction of the Engineering Sector Policy and Str
2、ategy 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 02/702407 DC ISBN 0 580 39720 3 Committe
3、es 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 publication
4、 Amd. No. Date Comments BS 1726-2:2002 BSI 25 September 2002 i Contents Page Committees responsible Inside front cover Foreword ii 1S c o p e 1 2 Normative references 1 3 Terms, definitions and symbols 1 4 Specifying springs for general purposes 2 5 Types of end loop 7 6T o l e r a n c e s 9 7 Metho
5、ds of verification 11 Figure 1 Data sheet 1 3 Figure 2 Hand of coiling 4 Figure 3 Data sheet 2 6 Figure 4 Group 1 end loops 7 Figure 5 Group 2 end loops 8 Figure 6 Group 3 end loops 8 Table 1 Grade 1 relative loop position tolerances 10 Table 2 Tolerances on spring rate 11BS 1726-2:2002 ii BSI 25 Se
6、ptember 2002 Foreword BS 1726-2 was first published in 1951 and revised in 1964 to incorporate much of the essential information from ADE Design Data Sheets, which were no longer available from HM Stationery Office and for which copyright permission to republish was obtained. The standard was revise
7、d in 1988 take account of current manufacturing processes. BS EN 13906-2 was published in 2001 and under the rules of CEN the UK is obliged to withdraw conflicting standards. This edition of BS 1726-2 includes those provisions of the previous edition not included in the EN standard. Together with BS
8、 EN 13906-2:2001, this edition of BS 1726-2 supersedes BS 1726-2:1988, which is withdrawn. BS 1726 is published in three parts: Part 1: Compression springs; Part 2: Extension springs; Part 3: Torsion springs. A British Standard does not purport to include all the necessary provisions of a contract.
9、Users of British 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 consists of a front cover, an inside front cover, pages i and ii, pages 1 to 13 and a back cover. The
10、 BSI copyright notice displayed in this document indicates when the document was last issued.BS 1726-2:2002 BSI 25 September 2002 1 1 Scope This Part of BS 1726 provides guidance on the specification, tolerancing and testing of parallel sided helical compression springs manufactured from round wire
11、and bar. Two grades of tolerance, 1 and 2, are given for springs. Fifteen types of end coils are provided for, these being divided into three groups. This standard applies to springs which have not been subjected to heat treatment other than stress relieving after coiling. This standard gives two me
12、thods of specifying springs and a methods 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
13、applies. BS 887, Specification for precision vernier callipers. BS 969, Specification for limits and tolerances on plain limit gauges. BS EN ISO 7500-1, Tension/compression testing machines Verification and calibration of the force measuring system. BS 1726-1, Cylindrical helical springs made from r
14、ound wire and bar Guide to methods of specifying, tolerances and testing Part 1: Compression springs. BS EN ISO 3650, Geometrical product specifications (GPS) Length standards Gauge blocks. BS 5411, Methods of test for metallic and related coatings. BS EN 13906-2, Cylindrical helical springs made fr
15、om round wire and bar Calculation and design Part 2: Extension springs. 3 Terms, definitions and symbols 3.1 Terms and definitions For the purposes of this Part of BS 1726 the definitions given in BS 1726-1 apply as relevant. 3.2 Symbols Symbol Term Unit C spring index D mean coil diameter mm D i in
16、side diameter of spring mm D o outside diameter of spring mm D material diameter mm E material diameter tolerance mm f natural frequency of unloaded spring Hz F spring force N F o nominal initial tension N F 1 , F 2 , etc. force at length L 1 , L 2 , etc. N F change in spring force N G modulus of ri
17、gidity N/mm 2 K stress correction factor L spring length mm L B spring body length mm L H hook opening gap mmBS 1726-2:2002 2 BSI 25 September 2002 4 Specifying springs for general purposes 4.1 Introduction There are two methods by which a customer may specify a spring. In the first method the custo
18、mer presents the supplier with a complete design and indicates what manufacturing processes, such as stress relieving, prestressing and shot peening, should be carried out. In this case the information should be supplied on Data Sheet 1 (Figure 1). When the customer does not have the information to
19、complete Data Sheet 1, the customer should complete Data Sheet 2 (Figure 3). This is an application for spring design in which the customer should specify the requirements from an operational point of view, giving such information as dimensional constraints, forcelength parameters, fatigue life, res
20、istance to corrosion, in order that the supplier can produce a spring design to meet these requirements. When the spring supplier has prepared a design from the information on Data Sheet 2 the spring supplier will complete Data Sheet 1 and submit it to the customer for approval. 4.2 Method one (cust
21、omer design) using Data Sheet 1 4.2.1 General It is not necessary to prepare a detailed scale drawing for a helical compression spring and details should be specified on Data Sheet 1 (Figure 1). Only essential dimensions and properties, for which the spring is to be inspected, need be toleranced, ot
22、her features being given in the design for information only. The following points should be noted before completing the form. a) Specify only those particulars which are of functional importance by marking the appropriate squares in boxes 5, 6 and 8 of data sheet 1. b) Avoid redundant dimensioning.
23、c) Refer to BS EN 13906-2 for the methods of calculation used to determine values for rate, force and stress. d) If space is insufficient in any box, further details should be attached on a separate sheet and attention drawn to this fact in the relevant box on the form. L L loop length mm L max. max
24、imum length to which the spring will be extended in assembly or use mm L o free length of spring mm L o, max. maximum free length of spring mm L o,tol. free length tolerance mm L change in spring length mm n number of active coils in spring N total number of coils in spring R m minimum tensile stren
25、gth N/mm 2 S spring rate N/mm S tol. spring rate tolerance N/mm extension from nominal free length to loaded length Mm density of material kg/mm 3 shear stress in spring N/mm 2 0 shear stress in spring with initial tension N/mm 2 1 , 2 , etc. shear stress in spring at F 1 , F 2 , etc. N/mm 2 Symbol
26、Term UnitBS 1726-2:2002 BSI 25 September 2002 3 4.2.2 Material Complete box 1 (Figure 1) by giving the material type and complete specification code, quoting the relevant British Standard where possible and the material diameter. SPECIFICATION FOR HELICAL COMPRESSION SPRING BS1726-2:2002 DATA SHEET
27、1 Part Serial No. This form should be completed with reference to BS 1726-2:2002, Clause 4.2 All dimensions in mm. NOTE Dimensions market “(Ref.)” are normally for reference only, and therefore do not have to be complied with unless the purchaser has specified in box 9 For nomenclature see Clause 3
28、1 Material 8 Surface coating Specification number Diameter = mm 2 Direction of coiling 9 Tolerances: mandatory requirement only Optional/ Grade 1 Grade 2 Other Value Value (specify) 3E n d l o o p f o r m D o Type (see Clause 5) F 1 Relative position F 2 Where dimensions of loops are of importance,
29、a drawing on a separate sheet of paper is to be attached. S L 1 L 2 4 Total number of coils N = 5 Stress relieving 6 Shot peening No Yes No Yes 10 Identification If yes Fatigue requirement: Time min Temperature C 7 Performance tests 11 Special Requirement Relaxation: No Yes Details: Fatigue: No Yes
30、Details: Sheet 1 of Serial/design/Part No. Figure 1 Data sheet 1BS 1726-2:2002 4 BSI 25 September 2002 4.2.3 Direction of coiling The direction of coiling is rarely important for the spring function, and unless it is included in box 2 it should be assumed that the supplier is free to coil either han
31、d (see Figure 2). However, for springs with plain end and threaded plug see Figure 6(d) the hand of coiling should be stated. 4.2.4 End loop form The name (see Figure 4, Figure 5 or Figure 6) and the relative position of the end loops, if appropriate, should be entered in box 3. 4.2.5 Total number o
32、f coils The total number of coils may be given in box 4 for reference but should only be toleranced by agreement with the spring supplier. NOTE Variation of the total number of coils is the most common method of achieving in-manufacture correction, and for this reason it is not measured unless there
33、 is special agreement between the customer and supplier to do so. 4.2.6 Stress relieving Indicate in box 5 whether or not stress relieving is required. If it is, the time and temperature should be given. NOTE Attention is drawn to the fact that stress relieving can reduce the amount of initial tensi
34、on in the spring. 4.2.7 Shot peening Shot peening requirements should be indicated in box 6. NOTE Owing to the form of extension springs shot peening is generally only applied to the end loops. In specialist cases, where fatigue within the coils is a concern, the spring can be extended within its el
35、astic limit and shot peening applied to the whole spring form. 4.2.8 Performance tests The most common tests are for relaxation and fatigue. Details of the tests should be given in the space provided in box 7. For relaxation tests the minimum information required is extended length, temperature and
36、test duration along with the maximum allowable force loss. For fatigue tests the maximum and minimum working positions, temperature and life required should be stated. For both types of test the batch size should also be given. If more specialized tests are required, such as dynamic relaxation or co
37、rrosion tests, then these details should be given in box 11. 4.2.9 Surface coating Surface coatings can be specified in box 8. Where possible the number of the relevant British Standard should be quoted. NOTE Coatings applied subsequent to the manufacture of a close coiled spring cannot be expected
38、to afford complete coverage. 4.2.10 Tolerances Tolerances on coil diameter, free length, force at length, etc. should be calculated as indicated in Clause 6 and this should be referred to before completing the tolerance box (box 9). Marking the appropriate tolerance indicates that the tolerances req
39、uired are those calculated using the expressions/data given in Clause 6. If the designer has requirements for tolerances other than those calculated under Clause 6, these should be given under the heading “Other (specify)” in box 9. Figure 2 Hand of coilingBS 1726-2:2002 BSI 25 September 2002 5 When
40、 establishing the spring dimensions and tolerances, it should be borne in mind that no single parameter may be changed without affecting one or more of the remaining parameters. Only those parameters which have to be met should be toleranced and the supplier should be left free to adjust the remaind
41、er in order to meet the specification in Data Sheet 1. For example, where two forcelength dimensions, material diameter and a coil diameter are specified as of critical importance, the number of turns and free length should only be specified as reference values. Similarly, where a coil diameter, one
42、 forcelength dimension, the material diameter and number of turns are of importance, variation in the free length should be allowed. 4.2.11 Identification If identification of individual springs is required, this should be indicated in box 10, noting that colour marking is the most common method use
43、d. 4.2.12 Special requirements Where the designer has requirements for the spring which cannot be detailed elsewhere on the data sheet, they should be given in box 11. 4.3 Method two (application for spring design) using Data Sheet 2 4.3.1 General Insert relevant dimensions on the drawing, giving on
44、ly those which are dictated by the design of the mechanism in which the spring is to operate. 4.3.2 Free length A maximum free length, L o,max. , should not be specified unless it is necessary for assembly purposes. 4.3.3 Forcelength conditions The required forcelength conditions should be specified
45、, together with either the maximum force or length. 4.3.4 Spring rate Where the spring rate is deemed more important than specific forcelengths, it should be specified between two lengths. A single forcelength may also be specified. 4.3.5 End coil formation The type of end coil (see Clause 5) should
46、 be specified in box 1. 4.3.6 Operation Springs should be designed on the assumption that normal operation will involve the spring remaining static at a forcelength with occasional, gradual movement to another specified loaded length. If the spring is expected to withstand dynamic operation, i.e. gr
47、eater than 10 000 cycles, then the minimum required life, operating levels of length, force or stress, speed of operation, and mode of operation (if an approximation to simple harmonic motion would not be acceptable) should be specified in box 2. 4.3.7 Temperature The maximum and minimum temperature
48、s to which the spring will be subjected during its working life are to be specified in box 3. Where a spring is subjected to temperatures outside this range, the conditions of temperature, time and force should be specified in box 5. 4.3.8 Relaxation Where it is important to maintain a force within
49、close limits throughout the life of a spring, the maximum allowable force loss (relaxation) should be given in box 4 along with details of temperature, duration and the extended length of the spring under the stated conditions. 4.3.9 Atmosphere and special protection details Where special cleanliness, resistance to corrosive atmospheres or such qualities as magnetic or electrical resistance are required, these conditions shou
