1、BRITISH STANDARD BS 3F 70:1991 (Superseding BS 2F 70:1983) Incorporating Amendment No. 1 Specification for heavy duty braided rubber cord NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBS 3F 70:1991 This British Standard, having been prepared under the direction of the Aerospa
2、ce Standards Policy Committee, was published under the authority of the Standards Board and comes into effect on 30 September 1991 BSI 06 March 2002 The following BSI references relate to the work on this standard: Committee reference ACE/25 Draft for comment 90/76882 DC ISBN 0 580 19864 2 Committee
3、s 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 Hydromechanics Resear
4、ch Association British Narrow Fabrics Association British Rubber Manufacturers Association Ministry of Defence Society of British Aerospace Companies Ltd. Amendments issued since publication Amd. No. Date Comments 13604 06 March 2002 Addition to Table 4BS 3F 70:1991 BSI 06 March 2002 i Contents Page
5、 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 4 9 Packaging, storage and use 4 Appendix A Determination of mechanical properties 5 Figure 1 Z twist 3 Figu
6、re 2 S twist 3 Table 1 Properties of rubber thread 1 Table 2 Sizes of cord and number of threads 1 Table 3 Colour indication of year of manufacture 3 Table 4 Colour indication of 5 year groups 3 Table 5 Number of coloured threads 4 Table 6 Mechanical properties 4 Publication(s) referred to 7BS 3F 70
7、:1991 ii BSI 06 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 covering of braided rubber cords owing to the increased requirement f
8、or high temperature resistant materials by the aerospace industry. An additional size of 26 mm was introduced. When the cord is covered with aramid fibre, the designation of the product includes the letter “A” (see clause 8). The loadings given in this specification are based on the power rating of
9、the unit area of the rubber cord. This British Standard supersedes BS 2F 70:1983 which is withdrawn. This edition introduces technical changes, 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
10、 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 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 statut
11、ory obligations relating to health and safety at any stage of manufacture or use. WARNING NOTE 2. This British Standard specifies pentachlorophenyl laurate (PCPL) as the only approved rot-proofing treatment for aerospace materials. Alternative treatments are under development, and this standard will
12、 be updated to delete PCPL as soon as an approved alternative treatment for aerospace materials is available. 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
13、 Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 7 and a back cover. The BSI copyright notice displayed in this document indicates when the document was last issued.BS 3F 70:
14、1991 BSI 06 March 2002 1 1 Scope This British Standard specifies requirements for heavy duty braided rubber cords in nine sizes from 5 mm to 26 mm in diameter. These cords are suitable, when cut up into unit lengths, for the manufacture of shock absorber cord assemblies and for other aeronautical pu
15、rposes. It is intended that these cords are used for cord assemblies manufactured in accordance with BS SP 170-171. NOTE 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 pre
16、fix number. 2 Construction The cord shall be of multiple threads of rubber, under tension, tightly encased in two coverings of braid and 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 5, 6.5, 8, 9.
17、5, 12.5, 16, 19, 22 or 26 mm, and the tolerance on each of these diameters shall be 5% . 4 Rubber thread 4.1 Quality The thread shall be made from first grade natural rubber not lower than Grade 5 of ISO 2000, suitably compounded with accelerators and non-bleeding antioxidants, and heat vulcanized a
18、nd 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 size 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
19、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) 15 % max. BS 5923-1 Free sulphur 1 % max. BS 903-B7.2 Variation between any mean and nominal Schwartz value aat 300 % elongation 10 % max. BS 5421-1 Retaine
20、d 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 should be established for each composition and should be agreed between the cord and the thread manufacturers for use in controlling the consistency of qua
21、lity when a series of batches of the same composition has to be tested for compliance with this standard. Size of cord (diameter) Minimum number of rubber threads mm 5 6.5 8 9.5 12.5 16 19 22 26 15 42 66 95 172 266 383 520 700BS 3F 70:1991 2 BSI 06 March 2002 5 Braiding 5.1 Materials 5.1.1 Cotton br
22、aid Cotton braid shall be made of folded undyed cotton yarn rot-proofed with pentachlorophenyl laurate in accordance with BS 2087, normal process. The inner covering shall be of soft cotton and the outer covering of polished glac cotton. 5.1.2 Aramid fibre braid Both the inner and outer aramid fibre
23、 coverings shall be made of folded undyed high temperature resistant non-melt natural aramid fibre yarn. Health warning. During manufacture and subsequent cutting and handling of materials containing aramid fibre, dust will be released into the workroom atmosphere. Some of this dust will be in the r
24、espirable 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. 5.2 Construction 5.2.1 The construction of the braid shall be such that, when the cord is stretched to 100 % ex
25、tension as described in Appendix A, the rubber shall not be visible. 5.2.2 The pitch of the braiding shall be uniform throughout the length of cord. 5.2.3 The inner covering shall have a helix of thread of agreed 1)colour running throughout its length to denote the manufacturer of the cord. 5.2.4 Th
26、e outer covering shall have a helix of coloured thread approximating to BS 381C reference number 539 Red running Z-wise (see Figure 1) throughout its length to identify it with this standard. NOTE Refer to 5.3.1 for the application of a second coloured thread to indicate the 5 year group given in Ta
27、ble 4. 5.2.5 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 2) throughout its outer cover to identify it as an aramid fibre covered cord. 5.3 Date and markings 5.3.1 In the outer co
28、vering, one or more of the undyed threads shall be replaced by threads running Z-wise (see Figure 1) and spaced apart, of the colours given in Table 3, approximating to those specified in BS 381C to indicate the date of manufacture of the finished cord. After 1991 the colours shall be repeated in th
29、e same sequence as given in Table 3 for each group of 5 years. A second coloured thread, spaced by one helix of undyed thread from the red thread specified in 5.2.4, shall be added to identify the 5 year group. The colour shall be that given in Table 4. 5.3.2 The number of coloured threads to indica
30、te the year and quarter of manufacture shall be as given in Table 5. 1) Applications for agreement should be addressed to the DGD(QA) Royal Arsenal East, Woolwich, London SE18 6TD.BS 3F 70:1991 BSI 06 March 2002 3 Table 3 Colour indication of year of manufacture Table 4 Colour indication of 5 year g
31、roups Figure 1 Z twist Figure 2 S twist Year BS 381C reference number Colour 1987 1988 1989 1990 1991 642 285 499 309 166 Night (black) NATO green Service brown Canary yellow French blue Group Years BS 381C reference number Colour 2 3 4 5 6 1987 to 1991 1992 to 1996 1997 to 2001 2002 to 2006 2007 to
32、 2011 539 309 642 285 499 Red Canary yellow Night (black) NATO green 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 note to Table 6 and to clause 9.BS 3F 70:1991 4 BSI 06 March 2002 Table 5 Number of co
33、loured threads Table 6 Mechanical properties 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 6. 7 Testing The finished cord after manufacture shall be tested once every manufactured lengt
34、h for 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 the 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. 8 Designation The cord shall be
35、identified by the number of this British Standard together with the diameter and length required. When the cord is covered by aramid fibre, the number of this British Standard shall be suffixed with the letter “A”. For example, 12.5 mm diameter cord 50 m long shall be identified as “BS 3F 70/12.5/50
36、 m” 2) , when braided with cotton covering, or as “BS 3F 70/A/12.5/50 m”, when braided with aramid fibre covering. 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 no
37、t be used that is more than 10 years old. NOTE Additional limitations may be applied by the user. 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 (diamete
38、r) Load to give extension of: Minimum total extension (without failure of braid) 10 % 30 % 75 % min. min. max. min. max. mm N N N N N % 5 6.5 8 20 40 60 29 58 88 38 76 116 50 100 150 65 130 196 105 105 105 9.5 12.5 16 80 150 240 120 210 350 170 280 460 210 370 600 280 480 800 105 105 105 19 22 26 34
39、0 460 640 500 660 930 650 880 1 250 850 1 150 1 600 1 100 1 500 2 100 105 105 105 NOTE The values given in Table 6 relate to newly manufactured cords. These contain rubber under tension and a reduction of the load to produce any specified elongation will take place during the life of the cords, eith
40、er in service or in storage. This does not, provided the storage conditions have been satisfactory, imply that the cords are unserviceable for general purposes. For any application where the loads are critical, however, cords less than 2 years old should be used. 2) Marking BS 3F 70 on or in relatio
41、n 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 a declaration is not to
42、 be confused with third party certification of conformity, which may also be desirable.BS 3F 70:1991 BSI 06 March 2002 5 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 accordance with clause
43、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 case of dispute, at a temperature of 23 2 C and in a re
44、lative 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 during the test lie between
45、 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 extension required by the test. A
46、.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
47、 the distance between the markers is 200 mm, examine for compliance with 5.2.1 then immediately remove the load. A.4.3 After a rest period of 1 min, reset the markers on the original test specimen to give a test length of 100 mm. A.4.4 Apply the load given in A.3 at such a rate that the time to exte
48、nd from 0 % to 105 % is 70 30 s, taking readings at 10 %, 30 % and 75 % extensions.6 blankBS 3F 70:1991 BSI 06 March 2002 7 Publication(s) referred to BS 381C, Specification for colours for identification, coding and special purposes. BS 903, Physical testing of rubber. BS 903-B7, Extractable sulphu
49、r 3) . BS 1610, Materials testing machines and force verification equipment. BS 2087, Preservative treatments for textiles. BS 5421, Methods of test for elastomeric threads. BS 5421-1, Rubber threads. BS 5923, Methods for chemical analysis of rubber. BS 5923-1, Determination of ash. BS 3F 68, Specification for controlled storage of vulcanized rubbers for use in aerospace applications. BS 3F 69, Specification for packaging and identification of vulcanized rubber items. BS SP 170-171, Specification for braided rubber co
