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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 S
2、trategy 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 Commit
3、tees 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 publicati
4、on Amd. No.DateComments - BS 1726-2:2002 BSI 25 September 2002 i Contents Page Committees responsible Inside front cover Forewordii 1Scope1 2Normative references1 3Terms, definitions and symbols1 4Specifying springs for general purposes2 5Types of end loop7 6Tolerances9 7Methods of verification11 Fi
5、gure 1 Data sheet 13 Figure 2 Hand of coiling4 Figure 3 Data sheet 26 Figure 4 Group 1 end loops7 Figure 5 Group 2 end loops8 Figure 6 Group 3 end loops8 Table 1 Grade 1 relative loop position tolerances10 Table 2 Tolerances on spring rate11 - BS 1726-2:2002 ii BSI 25 September 2002 Foreword BS 1726
6、-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 revised in 1988 take account of cur
7、rent 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 EN 13906-2:2001, this editio
8、n of BS 1726-2 supersedes BS 1726-2:1988, which is withdrawn.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. Users of British Standards ar
9、e 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 BSI copyright notice display
10、ed 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 and bar. Two grades of tol
11、erance, 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 methods of specifying spring
12、s 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 applies. BS 887, Specifica
13、tion 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 round wire and bar Guide to
14、 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 from round wire and bar Calc
15、ulation 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 SymbolTermUnit Cspring index Dmean coil diametermm Diinside diameter of springmm Dooutsi
16、de diameter of springmm Dmaterial diametermm Ematerial diameter tolerancemm fnatural frequency of unloaded springHz Fspring forceN Fonominal initial tensionN F1, F2, etc.force at length L1, L2, etc.N Fchange in spring forceN Gmodulus of rigidity N/mm2 Kstress correction factor Lspring lengthmm LBspr
17、ing body lengthmm LHhook opening gapmm - BS 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 customer presents the supplier with a complete design and indicates what
18、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 complete Data Sheet 1, the customer should complete Data Sheet 2 (Fi
19、gure 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, resistance to corrosion, in order that the supplier can produce a sprin
20、g 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 (customer design) using Data Sheet 1 4.2.1 General It is not necessary to
21、 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, other features being given in the design for information only. The fol
22、lowing 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. c) Refer to BS EN 13906-2 for the methods of calculation used to det
23、ermine 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. LLloop lengthmm Lmax.maximum length to which the spring will be extended in assembly or use mm Lo
24、free length of springmm Lo, max.maximum free length of springmm Lo, tol.free length tolerancemm Lchange in spring lengthmm nnumber of active coils in spring Ntotal number of coils in spring Rmminimum tensile strength N/mm2 Sspring rateN/mm Stol.spring rate toleranceN/mm extension from nominal free l
25、ength to loaded lengthMm density of material kg/mm3 shear stress in spring N/mm2 0 shear stress in spring with initial tension N/mm2 1, 2, etc. shear stress in spring at F1, F2, etc. N/mm2 SymbolTermUnit - BS 1726-2:2002 BSI 25 September 2002 3 4.2.2 Material Complete box 1 (Figure 1) by giving the
26、material type and complete specification code, quoting the relevant British Standard where possible and the material diameter. SPECIFICATION FOR HELICAL COMPRESSION SPRING BS 1726-2:2002 DATA SHEET 1 Part Serial No. This form should be completed with reference to BS 1726-2:2002, Clause 4.2 All dimen
27、sions in mm. NOTEDimensions 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 1Material8 Surface coating Specification number Diameter =mm 2Direction of coiling9 Tolerances: mandato
28、ry requirement only Optional/Grade 1 Grade 2 Other ValueValue(specify) 3End loop formDo Type (see Clause 5)F1 Relative positionF2 Where dimensions of loops are of importance, a drawing on a separate sheet of paper is to be attached. S L1 L2 4Total number of coilsN = 5Stress relieving6 Shot peening N
29、oYesNoYes10 Identification If yesFatigue requirement: Timemin TemperatureC 7Performance tests11Special Requirement Relaxation:NoYes Details: Fatigue: NoYes Details: Sheet 1 of Serial/design/Part No. Figure 1 Data sheet 1 - BS 1726-2:2002 4 BSI 25 September 2002 4.2.3 Direction of coiling The directi
30、on 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 hand (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
31、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 of 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. NO
32、TEVariation 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 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
33、required. If it is, the time and temperature should be given. NOTEAttention is drawn to the fact that stress relieving can reduce the amount of initial tension in the spring. 4.2.7 Shot peening Shot peening requirements should be indicated in box 6. NOTEOwing to the form of extension springs shot pe
34、ening 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 elastic limit and shot peening applied to the whole spring form. 4.2.8 Performance tests The most common tests are for relaxation and fatigue. Det
35、ails 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 test duration along with the maximum allowable force loss. For fatigue tests the maximum and minimum working positions, temperature and life req
36、uired 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 corrosion 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 th
37、e number of the relevant British Standard should be quoted. NOTECoatings applied subsequent to the manufacture of a close coiled spring cannot be expected to afford complete coverage. 4.2.10 Tolerances Tolerances on coil diameter, free length, force at length, etc. should be calculated as indicated
38、in Clause 6 and this should be referred to before completing the tolerance box (box 9). Marking the appropriate tolerance indicates that the tolerances required are those calculated using the expressions/data given in Clause 6. If the designer has requirements for tolerances other than those calcula
39、ted under Clause 6, these should be given under the heading “Other (specify)” in box 9. Figure 2 Hand of coiling - BS 1726-2:2002 BSI 25 September 2002 5 When establishing the spring dimensions and tolerances, it should be borne in mind that no single parameter may be changed without affecting one o
40、r 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 remainder in order to meet the specification in Data Sheet 1. For example, where two forcelength dimensions, material diameter and a coil diameter ar
41、e 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 forcelength dimension, the material diameter and number of turns are of importance, variation in the free length should be allowed. 4.2.11 Id
42、entification If identification of individual springs is required, this should be indicated in box 10, noting that colour marking is the most common method used. 4.2.12 Special requirements Where the designer has requirements for the spring which cannot be detailed elsewhere on the data sheet, they s
43、hould 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 only 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, Lo, max
44、., should not be specified unless it is necessary for assembly purposes. 4.3.3 Forcelength conditions The required forcelength conditions should be specified, together with either the maximum force or length. 4.3.4 Spring rate Where the spring rate is deemed more important than specific forcelengths
45、, 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 be specified in box 1. 4.3.6 Operation Springs should be designed on the assumption that normal operation will involve the spring remaining st
46、atic at a forcelength with occasional, gradual movement to another specified loaded length. If the spring is expected to withstand dynamic operation, i.e. greater than 10 000 cycles, then the minimum required life, operating levels of length, force or stress, speed of operation, and mode of operatio
47、n (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 temperatures 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 outsi
48、de 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 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 spr