1、BRITISH STANDARD AEROSPACE SERIES BS 3F 71:1991 (Superseding BS 2F 71:1983) Incorporating Amendment No. 1 Specification for light duty braided rubber cord NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBS 3F 71:1991 This British Standard, having been prepared under the directi
2、on of the Aerospace Standards Policy Committee, was published under the authority of the Standards Board and comes into effect on 30 September 1991 BSI 05 March 2002 The following BSI references relate to the work on this standard: Committee reference ACE/25 Draft for comment 90/76881 DC ISBN 0 580
3、19861 8 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Aerospace Standards Policy Committee (ACE/-) to Technical Committee ACE/25, upon which the following bodies were represented: British Adhesives and Sealants Association British Hydr
4、omechanics Research Association British Narrow Fabrics Association British Rubber Manufactures Association Ministry of Defence Society of British Aerospace Companies Ltd. Amendments issued since publication Amd. No. Date Comments 13603 05 March 2002 Addition to Table 5BS 3F 71:1991 BSI 05 March 2002
5、 i Contents Page Committees responsible Inside front cover Foreword ii 1S c o p e 1 2 Construction 1 3D i a m e t e r 1 4 Rubber thread 1 5 Braiding 2 6 Mechanical properties 4 7T e s t i n g 4 8 Designation 5 9 Packaging, storage and use 5 Appendix A Determination of mechanical properties 6 Figure
6、1 S twist 3 Figure 2 Z twist 3 Table 1 Properties of rubber thread 1 Table 2 Sizes of cord and number of threads 1 Table 3 Construction of braid 2 Table 4 Colour indication of year of manufacture 3 Table 5 Colour indication of 5 year groups 4 Table 6 Number of coloured threads 4 Table 7 Mechanical p
7、roperties 4 Publication(s) referred to Inside back coverBS 3F 71:1991 ii BSI 05 March 2002 Foreword This British Standard, prepared under the direction of the Aerospace Standards Policy Committee, was revised in 1983 to allow for the inclusion of a high temperature resistant aramid fibre outer cover
8、ing of braided rubber cords owing to the increased requirement for high temperature resistant materials by the aerospace industry. The additional sizes 4 mm, 5.5 mm and 11 mm were introduced. When the cord is covered with aramid fibre, the designation of the product includes the letter “A” (see clau
9、se 8). The loadings given in this specification are based on the power rating of the unit area of the rubber cord. Reference to cord manufactured from natural rubber latex has been deleted. This British Standard supersedes BS 2F 71:1983 which is withdrawn. This edition introduces technical changes,
10、notably additional colour indications for 5 year groups, to bring the standard up to date, but it does not reflect a full review of the standard, which will be undertaken in due course. WARNING NOTE 1. This British Standard calls for the use of substances and/or test procedures that may be injurious
11、 to health if adequate precautions are not taken. It refers only to technical suitability and in no way absolves either the supplier or the user from statutory obligations relating to health and safety at any stage of manufacture or use. WARNING NOTE 2. This British Standard specifies pentachlorophe
12、nyl laurate (PCPL) as the only approved rot-proofing treatment for aerospace materials. Alternative treatments are under development, and this standard will be updated to delete PCPL as soon as an approved alternative treatment for aerospace materials is available. A British Standard does not purpor
13、t 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 obligations. Summary of pages This document comprises a front cover, an inside front cov
14、er, pages i and ii, pages 1 to 6, an inside back cover and a back cover. The BSI copyright notice displayed in this document indicates when the document was last issued.BS 3F 71:1991 BSI 05 March 2002 1 1 Scope This British Standard specifies requirements for light duty braided rubber cords in eight
15、 sizes from 3 mm to 11 mm in diameter. These cords are suitable, when cut into unit lengths, for parachute pack opening devices, light-weight suspensions and other aeronautical purposes. It is intended that these cords are used for cord assemblies manufactured in accordance with BS SP 170-171. NOTE
16、1 The titles of the publications referred to in this standard are listed on the inside back cover. NOTE 2 The latest revision of an Aerospace Series standard is indicated by a prefix number. 2 Construction The cord shall be of multiple threads of rubber, under tension, tightly encased in braid, and
17、shall be smooth and uniform. 3 Diameter When measured by a micrometer or slide gauge, the overall diameter of the cord, including the braid, shall be 3, 4, 5, 5.5, 6.5, 8, 9.5 or 11 mm, and the tolerance on each of these diameters shall be 5%. 4 Rubber thread 4.1 Quality The thread shall be made fro
18、m first grade natural rubber, not lower than Grade 5 of ISO 2000, suitably compounded with accelerators and non-bleeding antioxidants, and heat vulcanized, and shall be as given in Table 1. No reclaim, vulcanized oils (factice) or other rubber substitute shall be used. 4.2 Size and number Only one s
19、ize of thread shall be used in any one cord. The number of rubber threads used in any cord shall be as given in Table 2. Table 1 Properties of rubber thread Table 2 Sizes of cord and number of threads Property Requirement Method of test Density a 0.02 Mg/m 3of nominal BS 5421-1 Ash (% of total mass)
20、 15 % max. BS 5923-1 Free sulfur 1 % max. BS 903-B7.2 Variation between any mean and nominal Schwartz value aat 300 % elongation 10 % max. BS 5421-1 Retained stress after oven ageing at 70 1 C for 7 days at 100 % elongation 0.25 MPa min. BS 5421-1 a Density and Schwartz value are not specified; they
21、 should be established for each composition and should be agreed between the cord and the thread manufacturers for use in controlling the consistency of quality when a series of batches of the same composition has to be tested for compliance with this standard. Size of cord (diameter) Minimum number
22、 of rubber threads mm 36 41 0 51 5 5.5 17 6.5 23 83 8 9.5 55 11 75BS 3F 71:1991 2 BSI 05 March 2002 5 Braiding 5.1 Materials 5.1.1 Cotton braid Cotton braid shall be made of folded undyed cotton yarn rot-proofed with pentachlorophenyl laurate in accordance with BS 2087, normal process. The type of f
23、inish shall be as given in Table 3. 5.1.2 Aramid fibre braid Aramid fibre braid shall be made of folded undyed high temperature resistant non-melt aramid fibre yarn. The type of finish shall be as given in Table 3. Health warning. During manufacture and subsequent cutting and handling of materials c
24、ontaining aramid fibre, dust will be released into the workroom atmosphere. Some of this dust will be in the respirable size range. Health and safety legislation requires this dust to be controlled, preferably at source, so as to minimize the risk of inhalation so far as is reasonably practicable. 5
25、.2 Construction 5.2.1 The construction of the braid shall be as given in Table 3 and be such that, when the cord is stretched to 125 % extension as described in Appendix A, the rubber shall not be visible. 5.2.2 For the 6.5, 8, 9.5 and 11 mm diameter cords, where inner and outer coverings are requir
26、ed, the construction shall be one of the following: a) inner and outer coverings of cotton; b) inner and outer coverings of aramid fibre; c) inner covering of soft cotton, outer covering of aramid fibre. Table 3 Construction of braid 5.2.3 The pitch of the braiding shall be uniform throughout the le
27、ngth of the cord. 5.2.4 The covering of the 3, 4, 5 and 5.5 mm diameter cords and the inner covering of the 6.5, 8, 9.5 and 11 mm diameter cords shall have a helix of thread of agreed 1)colour running throughout its length to denote the manufacturer of the cord. For the 3, 4, 5 and 5.5 mm diameter c
28、ords, this coloured thread shall run S-wise (see Figure 1). 5.2.5 The cover of all the cords shall have a helix of coloured thread approximating to BS 381C reference number 166 French blue running Z-wise (see Figure 2) throughout its length to identify it with this standard. NOTE Refer to 5.3.1 for
29、the application of a second coloured thread to indicate the 5 year group given in Table 5. 5.2.6 Aramid fibre covering shall have an additional helix of coloured thread approximating to BS 381C reference number 592 International orange running S-wise (see Figure 1) throughout its outer cover to iden
30、tify it as an aramid fibre covered cord. Size of cord (diameter) Number of coverings Type of finish mm Cotton Aramid fibre 3, 4, 5, 5.5 1 Soft Natural 6.5, 8, 9.5, 11 2 (see 5.2.2) Inner: soft Outer: polished glac 1) Applications for agreement should be addressed to the DGD(QA) Royal Arsenal East, W
31、oolwich, London SE18 6TD. BS 3F 71:1991 BSI 05 March 2002 3 5.3 Date and markings 5.3.1 In the covering of the 3, 4, 5 and 5.5 mm diameter cords and the outer covering of the 6.5, 8, 9.5 and 11 mm diameter cords, one or more of the undyed threads shall be replaced by threads, running Z-wise and spac
32、ed apart, of the colour given in Table 4, approximating to those specified in BS 381C, to indicate the year of manufacture of the finished cord. After 1991 the colours shall be repeated in the same sequence as given in Table 4 for each group of 5 years. A second coloured thread, spaced by one helix
33、of undyed thread from the French blue thread specified in 5.2.5, shall be added to identify the 5 year group. The colour shall be that given in Table 5. 5.3.2 The number of coloured threads to indicate the year and quarter of manufacture shall be as given in Table 6. Table 4 Colour indication of yea
34、r of manufacture Figure 1 S twist Figure 2 Z twist Year BS 381C reference number Colour 1987 642 Night (black) 1988 285 NATO green 1989 499 Service brown 1990 309 Canary yellow 1991 166 French blueBS 3F 71:1991 4 BSI 05 March 2002 Table 5 Colour indication of 5 year groups Table 6 Number of coloured
35、 threads 6 Mechanical properties When determined as described in Appendix A, the mechanical properties of each test specimen of the finished cord shall comply with Table 7. Table 7 Mechanical properties 7 Testing The finished cord after manufacture shall be tested once every manufactured length for
36、compliance with clause 3, 5.2.1 and clause 6. When this length exceeds 100 m, the cord shall be tested at the beginning and end of each length. No mechanical test shall be made within 1 m of either end or before the elapse of 3 days from the time of manufacture. Group Years BS 381C reference number
37、Colour 2 1987 to 1991 166 French blue 3 1992 to 1996 309 Canary yellow 4 1997 to 2001 642 Night (black) 5 2002 to 2006 285 NATO green 6 2007 to 2011 499 Service brown NOTE The extension of the period of identification does not imply any extension to the life of the cord. Attention is drawn to the no
38、te to Table 7 and to clause 9. For cord made between Number of threads 1 January and 31 March inclusive 1 1 April and 30 June inclusive 2 1 July and 30 September inclusive 3 1 October and 31 December inclusive 4 Size of cord (diameter) Load to give extension of: Minimum total extension (without fail
39、ure of braid) 50 % 100 % min. max. min. max. m mNNNN% 3 5 7.5 7.5 11 150 4 9 14 14 20 150 5 1 42 22 23 11 5 0 5 . 5 1 72 62 64 01 5 0 6 . 5 2 53 63 65 31 2 5 8 3 75 55 58 01 2 5 9.5 54 78 78 114 125 11 70 104 104 152 125 NOTE The values given in Table 7 relate to newly manufactured cords. These cont
40、ain rubber under tension and a reduction of the load to produce any specified elongation will take place during the life of the cords, either in service or in storage. This does not, provided the storage conditions have been satisfactory, imply that the cords are unserviceable for general purposes.
41、For any applications where the loads are critical, however, cords less than 2 years old should be used.BS 3F 71:1991 BSI 05 March 2002 5 8 Designation The cord shall be identified by the number of this British Standard together with the diameter, length and type of outer covering required. When the
42、cord is covered by aramid fibre, the number of this British Standard shall be suffixed with the letter “A”. For example, 6.5 mm diameter cord 50 m long shall be identified as “BS 3F 71/6.5/50 m” 2) , when braided with cotton covering, or as “BS 3F 71/A/6.5/50 m”, when braided with aramid fibre cover
43、ing. 9 Packaging, storage and use 9.1 Finished cord shall be packaged in accordance with BS 3F 69 and shall be stored in accordance with BS 3F 68. 9.2 For critical applications cord shall not be used that is more than 10 years old. NOTE Additional limitations may be applied by the user. 2) Marking B
44、S 3F 71 on or in relation to a product represents a manufacturers declaration of conformity, i.e. a claim by or on behalf of the manufacturer that the product meets the requirements of the standard. The accuracy of the claim is therefore solely the responsibility of the person making the claim. Such
45、 a declaration is not to be confused with third party certification of conformity, which may also be desirable.BS 3F 71:1991 6 BSI 05 March 2002 Appendix A Determination of mechanical properties A.1 Test specimen and its preparation Select a test length of 100 mm from each length of finished cord in
46、 accordance with clause 7. Mark each end of the test length by a pin inserted into the outer braid (taking care not to damage the rubber thread), or by another suitable method, e.g. extensometer. A.2 Test conditions Carry out the test at a temperature of 20 5 C or, in cases of dispute, at a temperat
47、ure of 23 2 C and in a relative humidity of 50 5%. A.3 Apparatus Use a testing machine complying with the following: a) The tensile testing machine shall comply with grade B of BS 1610, and shall be used in accordance with method 1 of BS 1610. b) The scale range shall be such that loads developed du
48、ring the test lie between 15 % and 85 % of the full load reading of the scale. c) The grips shall be capable of holding the specimen firmly without damaging the structure of the cord. d) The testing machine shall elongate the specimen at a reasonably constant rate, through the full range of extensio
49、n required by the test. A.4 Procedure A.4.1 Keep the cord at the test conditions (see A.2) for not less than 24 h before the test. A.4.2 Grip the test specimen in the testing machine with the test length lying between the grips such that each marker is clear of the corresponding grip by not less than 40 mm, stretch it until the distance between the markers is 225 mm, examine for compliance with 5.2.1 and Table 4; for sizes up to and including 5.5 mm, continue the extensi
