1、BS 7842 : 1996 BRITISH STANDARD | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | N NO O C CO OP PY YI IN NG G I IN N A AN NY Y F FO OR RM M W WI IT TH HO OU UT T W WR RI IT TT TE EN N P PE ER RM MI IS SS SI IO ON N F FR
2、 RO OM M B BS SI I Specification for Bolts, screws and studs with pre-applied thread sealing feature incorporated into the threadThis British Standard, having been prepared under the direction of the Engineering Sector Board, was published under the authority of the Standards Board and comes into ef
3、fect on 15 April 1996 BSI 1996 The following BSI references relate to the work on this standard: Committee reference FME/9 Draft for comment 95/700437 DC ISBN 0 580 25386 4 BS 7842 : 1996 Amendments issued since publication Amd. No. Date T ext affected Committees responsible for this British Standar
4、d The preparation of this British Standard was entrusted to T echnical Committee FME/9, Bolts, nuts and accessories, upon which the following bodies were represented: BEAMA Ltd. British Constructional Steelwork Association Ltd. British Industrial Fasteners Federation British Steel Industry British S
5、teel Industry (Wire Section) Guage and T ool Makers Association National Association of Fastener Stockholders Society of Motor Manufacturers and Traders Ltd. Washer Manufacturers Association of Great BritainBS 7842 : 1996 BSI 1996 i Contents Page Committees responsible Inside front cover Foreword ii
6、 Specification 1 Scope 1 2 Normative references 1 3 Definitions 1 4 Protective coatings 1 5 Pre-applied sealing feature 1 6 Materials and lubrication 3 7 Mechanical properties and performance 3 Annexes A (normative) T esting 4 Tables A.1 Prevailing torque 4 Figures 1 Position of pre-applied sealing
7、feature 2 2 Diameter of pre-applied sealing feature 2 List of references Inside back coverBS 7842 : 1996 ii BSI 1996 Foreword This British Standard has been prepared by T echnical Committee FME/9. It includes performance properties for thread sealant type bolts, screws and studs with pre-applied thr
8、ead sealing features. Compliance with a British Standard does not of itself confer immunity from legal obligations. BSI 1996 1 BS 7842 : 1996 Specification 1 Scope This British Standard specifies the coatings, dimensions, materials, lubrication and performance requirements for bolts, screws and stud
9、s with a pre-applied sealing feature incorporated into the thread, when tested at a temperature between 15 C and 30 C. It applies to bolts, screws and studs: a) with ISO metric coarse pitch M4 to M24 threads conforming to BS 3643 : Part 2 : 1981; b) with specific strength requirements conforming to
10、either BS 6104 : Part 3 : 1981, BS 6105 : 1981 or BS EN 20898-1 : 1992, as appropriate; c) with threads of tolerance class 6g or 4h conforming to BS 3643 : Part 2 : 1981; d) for application into a mating component with a thread of tolerance class 6H conforming to BS 3643 : Part 2 : 1981; e) for use
11、within the temperature range2 50 C to + 150 C. The following are not covered in the scope of this standard: 1) performance at temperatures outside the operating range; 2) performance of bolts, screws and studs for which a lubricated or protective coating is not permissible; 3) performance of taper t
12、hreaded components. 2 Normative references This British Standard incorporates, by dated or undated reference, provisions from other publications. These normative references are made at the appropriate places in the text and the cited publications are listed on the inside back cover . For dated refer
13、ences, only the edition cited applies; any subsequent amendments to or revisions of the cited publication apply to this standard only when incorporated in the reference by amendment or revision. For undated references, the latest edition of the cited publication applies, together with any amendments
14、. 3 Definitions For the purposes of this British Standard, the following definitions apply. 3.1 pre-applied sealing type bolts, screws and studs Bolts, screws and studs which provide a seal against pressurized liquids and/or gases due to a non-curing sealing feature incorporated into the threads. 3.
15、2 prevailing torque developed by bolts, screws or studs T orque necessary to rotate the bolt, screw or stud in a mating threaded component, while in motion and with no axial load. 4 Protective coatings Finished parts shall conform to the appropriate coating standard applicable to the fastener to whi
16、ch the sealing feature is pre-applied. NOTE. Instances where the requirements of the appropriate coating standard cannot be maintained by additional processing following application of the thread sealant are beyond the scope of this standard. 5 Pre-applied sealing feature The pre-applied sealing fea
17、ture dimensions shall be as shown in figures 1 and 2. Dimension l x shall be selected so that a minimum of two pitches of the screw thread measured from the end of the bolt, screw or stud are free from the pre-applied sealing feature in order to ensure ease of engagement of the screw thread with the
18、 mating threaded component.2 BSI 1996 BS 7842 : 1996 Pre-applied sealing feature to be contained wholly within the shaded area and approximately equally dispersed about the centre line L C x3 max. p p 3 max. Centre of sealing feature x l = Length of bolt l = Distance from under head to centre of sea
19、ling feature p = Pitch of thread l l (see clause 5) Figure 1. Position of pre-applied sealing feature Pre-applied sealing feature to be contained wholly within the shaded area C L 1 d d 1 d h as specified for fine series threads in BS EN 20273 : 1992 Figure 2. Diameter of pre-applied sealing feature
20、 BSI 1996 3 BS 7842 : 1996 6 Materials and lubrication 6.1 Materials The materials used to produce the bolts, screws and studs with pre-applied sealing features shall be in accordance with the specified property class in BS 6104 : Part 3 : 1981, BS 6105 : 1981 or BS EN 20898-1 : 1992, as appropriate
21、. The pre-applied sealing feature shall be non-toxic and shall adhere to the parent thread. The pre-applied sealing feature shall be dry-to-touch except where subsequent lubrication is required. 6.2 Lubrication NOTE. Instances where the requirements of the appropriate coating standard cannot be main
22、tained by additional processing following application of the thread sealant are beyond the scope of this standard. Supplementary lubrication, if applied, shall conform to BS 7371 : Part 2 : 1993. 7 Mechanical properties and performance 7.1 Mechanical properties The mechanical properties of the bolt,
23、 screw or stud after application of the pre-applied sealing feature shall conform to the specified property class in accordance with BS 6104 : Part 3 : 1981, BS 6105 : 1981 or BS EN 20898-1 : 1992, as appropriate. 7.2 Prevailing torque on assembly When tested in accordance with A.2 the prevailing to
24、rque developed by the pre-applied sealing feature during the first assembly shall not exceed the maximum prevailing torque specified in table A.1. 7.3 Sealing performance When tested in accordance with annex A, there shall be no leakage of liquids and/or gases past the sealing feature. When tested i
25、n accordance with A.3 there shall be no leakage of internal pressure at the interface between the thread of the bolt, screw or stud and the surface of the test fixture for the entire period during which the pressure is applied. 7.4 T orque/clamping force T orque/clamping force performance of fastene
26、rs with pre-applied sealants shall conform to BS 7371 : Part 2 : 1993 where applicable.BS 7842 : 1996 4 BSI 1996 1) 100 kPa = 1 bar. Annexes Annex A (normative) Testing A.1 Apparatus A.1.1 Test fixture, manufactured from steel or stainless steel with holes for testing one or more fasteners at the sa
27、me time and capable of withstanding a minimum internal pressure of 400 kPa 1) . The external surfaces of the test fixture shall be unplated, clean and hardened to 450 HV minimum. The holes in the test fixture into which the fasteners to be tested are screwed shall be of sufficient depth to permit 10
28、 thread pitch engagement, threaded in accordance with BS 3643 : Part 2 : 1981 tolerance class 6H and countersunk to either BS 328 : Part 5 : 1983 or BS 328 : Part 6 : 1992 as appropriate. The internal construction of the test fixture shall be such that the internal pressure is applied into the botto
29、m of the threaded test holes. A.1.2 Torque measuring device (torque wrench or power device), accurate to 2 % of its maximum specified torque range. For referee purposes, the device shall be chosen so that all readings fall within the upper half of the torque range. Manual torque wrenches may be used
30、 for measurement of torque, but for referee purposes, an automatic electronic sensing device shall be used. A.2 T orque testing A.2.1 General Conduct the prevailing torque test at ambient temperature between 15 C and 30 C. Measure all prevailing torque measurements by a torque measuring device (see
31、A.1.2) with the test fastener in motion at a constant speed not exceeding 30 r .p.m. During measurement of the prevailing torque ensure that no clamp load is induced in the test fastener . A.2.2 Test procedure Screw the sample bolt, screw or stud into a hole in the test fixture until approximately o
32、ne full pitch of the thread sealing feature is engaged with the mating thread of the hole in the test fixture. Measure the maximum prevailing torque that occurs while the bolt, screw or stud is being screwed a further 3 revolutions into the test fixture. T able A.1 Prevailing torque Torque values ar
33、e in Newton metres Thread size Prevailing torque Maximum M63 1 1.8 M83 1.25 2.8 M103 1.5 5.5 M123 1.75 7.2 M143 2 11.0 M163 2 14.0 M203 2 22.0 A.3 Leak testing Ensure that any of the threaded test holes in the test fixture, that do not contain a sample bolt, screw or stud inserted in accordance with
34、 A.2.2, are suitably plugged and sealed to prevent loss of internal pressure. Apply a steady internal pressure of 300 kPa to the test fixture for a minimum period of 1 min. BSI 1996 BS 7842 : 1996 List of references Normative references (see clause 2) BSI publications BRITISH STANDARDS INSTITUTION,
35、London BS 328 : Drills and reamers BS 328 : Part 5 : 1983 Specification for the dimensions of countersinks and counterbores BS 328 : Part 6 : 1992 Countersinks, 90, with parallel shanks and solid pilots BS 3643 : ISO metric screw threads BS 3643 : Part 2 : 1981 Specification for selected limits of s
36、ize BS 6104 : Mechanical properties of fasteners BS 6104 : Part 3 : 1981 Specification for set screws and similar threaded fasteners not under tensile stresses BS 6105 : 1981 Specifications for corrosion-resistance stainless steel fasteners BS 7371 : Coatings on metal fasteners BS 7371 : Part 2 : 19
37、93 Specification for torque/clamping force relationship BS EN 20273 : 1992 Fasteners. Clearance holes for bolts and screws BS EN 20898 : Mechanical properties of fasteners BS EN 20898-1 : 1992 Bolts, screws and studsBSI 389 Chiswick High Road London W4 4AL | | | | | | | | | | | | | | | | | | | | | |
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