1、BRITISH STANDARD BS 7371-2:1993 Coatings on metal fasteners Part 2: Specification for torque/clamping force relationshipBS7371-2:1993 This British Standard, having been prepared under the directionof the General Mechanical Engineering Standards Policy Committee, waspublished under the authorityof th
2、e Standards Boardand comes into effect on 15February1993 BSI 02-1999 The following BSI references relate to the work on this standard: Committee reference GME/9 Draft for comment 89/70598 DC ISBN 0 580 21488 5 Committees responsible for this British Standard The preparation of this British Standard
3、was entrusted by the General Mechanical Engineering Standards Policy Committee (GME/-) to Technical Committee GME/9, upon which the following bodies were represented: BEAMA Ltd. British Constructional Steelwork Association Ltd. British Industrial Fasteners Federation British Railways Board British S
4、teel Industry British Steel Industry (Wire Section) Gauge and Tool Makers Association Ministry of Defence Society of Motor Manufacturers and Traders Ltd. Washer Manufacturers Association of Great Britain The following bodies were also represented in the drafting of the standard, through subcommittee
5、s and panels: British Turned parts Manufacturers Association EEA (The Electronic and Business Equipment Association) Institute of Metal Finishing Metal Finishing Association Stainless Steel Fabricators Association of Great Britain Amendments issued since publication Amd. No. Date CommentsBS7371-2:19
6、93 BSI 02-1999 i Contents Page Committees responsible Inside front cover Foreword ii 0 Introduction 1 1 Scope 1 2 References 1 3 Definitions 1 4 Lubrication 1 5 Torque/clamping force 2 6 Surface condition of lubricated parts 2 7 Lubricant performance 2 8 Corrosion resistance 2 Annex A (normative) To
7、rque/clamping force test 4 Annex B (informative) Recommended testing technique for use with manual torque wrenches 6 Figure A.1 Plan of a test fixture for nut testing 5 Figure A2 Plan of a test fixture for bolt testing 5 Table 1 Clamping force and applied torque for bolts, screws and nuts 3 Table A.
8、1 Dimensions of test washers 4 List of references Inside back coverBS7371-2:1993 ii BSI 02-1999 Foreword This Part of BS 7371 has been prepared under the authority of the General Mechanical Engineering Standards Policy Committee to provide part of a series of standards on coatings on metal fasteners
9、. 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 Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprise
10、s a front cover, an inside front cover, pages i and ii, pages1to6, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on theinside front cover.BS7371-2:1993 BSI 02-1999 1 0
11、 Introduction BS 7371 deals with the performance of coatings on metal fasteners and accessories. This Part of BS 7371 specifies the requirements for torque/clamping force relationship. BS 7371-1:1991 Specification for general requirements and selection guidelines is supplementary to this and all oth
12、er Parts of the standard. Further Parts of the standard to incorporate the following are in preparation. Specification for electroplated zinc and cadmium coatings Specification for electroplated nickel, nickel/chromium and copper/nickel/chromium coatings Specification for electroplated tin and tin/l
13、ead coatings Specification for electroplated coatings for special purposes Specification for mechanically applied zinc and cadmium coatings Specification for mechanically applied coatings for special purposes Specification for phosphate and oil coatings Specification for organic coatings Specificati
14、on for zinc flake non-electrolytically applied cured coatings This Part of BS7371 is intended to ensure that successive production batches of coated fasteners will give repeatable clamping forces when assembled with controlled torque. NOTEThe data incorporated in Table 1 is for test purposes only an
15、d is not intended to be a table of assembly torques. 1 Scope This Part of BS7371 specifies test requirements to ensure that standard fasteners with ISO metric screw threads to BS3643 sizes M3 to M39 inclusive, coated or uncoated, satisfy a specific torque/clamping force relationship when tested at a
16、 temperature of between 15C and 30C. It also specifies toxicity and dryness requirements of integral and supplementary lubricants. NOTE 1Strength requirements conform to BSEN20898-1 and BSEN20898-2 and dimensions are specified in the relevant standards for products to be coated. NOTE 2Unless stated
17、otherwise, all references to nuts and bolts in BS7371 relate to coatings on both flanged and non-flanged products. All references to bolts apply also to screws. NOTE 3This Part of BS7371 is not applicable to bolts, screws and nuts with performance specifications containing an alternative torque/clam
18、ping force test, e.g. prevailing torque nuts. NOTE 4The coating on the abutment face against which the fastener is tightened in an application, including the washer component of screw or nut and washer assemblies may influence the torque/clamping force relationship (see clause 5). 2 References 2.1 N
19、ormative references This Part of BS7371 incorporates, by reference, provisions from specific editions of other publications. These normative references are cited at the appropriate points in the text and the publications are listed on the inside back cover. Subsequent amendments to, or revisions of,
20、 any of these publications apply to this Part of BS7371 only when incorporated in it by updating or revision. 2.2 Informative references This Part of BS7371 refers to other publications that provide information or guidance. Editions of these publications current at the time of issue of this standard
21、 are listed on the inside back cover, but reference should be made to the latest editions. 3 Definitions For the purposes of this Part of BS7371, the definitions given in BS7371-1 apply together with the following. 3.1 clamping force force which is applied by the bearing face of the fastener against
22、 a mating component after application of a specified tightening torque 3.2 galling condition whereby excessive friction between high spots results in localized welding with subsequent removal of particles of metal and further roughening of the rubbing surfaces of one or both of the mating parts 3.3
23、high speed assembly an assembly using a power device of suitable torque capacity with a free running speed representative of normally available power assembly equipment 4 Lubrication Coatings for fasteners and accessories which incorporate a lubricant constituent shall not require the addition of a
24、supplementary lubricant. Coatings for fasteners and accessories which do not incorporate a lubricant constituent shall not gall. A supplementary lubricant may be used to prevent galling if necessary (see 6.2).BS7371-2:1993 2 BSI 02-1999 The torque/clamping force performance of fasteners which are su
25、pplied with either integral or supplementary lubrication shall not deteriorate when the fasteners are stored indoors for a period of6months. The storage temperature shall be within the range 5C to 40C. NOTEIf a supplementary lubricant is not permitted on coatings which do not contain an integral lub
26、ricant, parts may not be able to conform to this standard. 5 Torque/clamping force The torque necessary to develop the clamping force given in Table 1 shall be measured on a representative sample in accordance with clause7 of BS7371-1:1991 by the method described in Annex A, and shall be within the
27、values for applied torque in Table 1. Screw and washer assemblies and nut and washer assemblies shall be tested with the washer component removed. Fasteners with ISO metric fine pitch screw threads, thread rolling and cutting screws and bolts, screws and nuts with special underhead configurations, t
28、hose with a shank area less than the stress area of the screw thread, or those which are too short to pass through the test equipment, shall not be tested in accordance with Annex A but their torque/clamping force shall be assessed by testing standard fasteners coated by the same process in the same
29、 coating production run (see 2.2 of BS7371-1:1991). NOTEData is given in Table 1 for nominal diameters larger than M24. Due to the limitations of test equipment, such parts may be evaluated in accordance with Annex A, by comparison with standard fasteners of a smaller diameter coated by the same pro
30、cess and taken from the same production run. 6 Surface condition of lubricated parts 6.1 Toxicity In the applied condition, the lubricant shall not constitute a health hazard to the user, or emit an unpleasant odour and shall not cause staining of the skin. 6.2 Dryness The parts shall be dry to the
31、touch such that when held with a filter paper (see note), and applying hand pressure for5s minimum, there shall be no visible staining of the filter paper when viewed without using supplementary magnification. For referee purposes this test shall be carried out using a force of10N. NOTEFor dryness t
32、esting use an ashless filter paper 1)with the following properties: a) 85 g/m 2mass per unit area; b) 0.21mm thickness; c) 0.01% ash content m/m; d) 20 m to 25 m particle retention. 7 Lubricant performance When applied to ISO metric coarse pitch threaded bolts, screws and nuts the lubricants shall e
33、nsure conformity to the torque/clamping force specified in clause 5 and Table 1. All fasteners treated with a lubricant shall be suitable for high-speed assembly (see 3.3). 8 Corrosion resistance Corrosion tests described in all other parts of BS7371 shall apply subsequent to application of the lubr
34、icant material. 1) For information on the availability of a suitable filter paper, apply to Information Services, BSI, Linford Wood, Milton Keynes, MK14 6LE.BS 7371-2:1993 BSI 02-1999 3 Table 1 Clamping force and applied torque for bolts, screws and nuts (ISO metric coarse pitch threads) Nominal dia
35、meter Clamping force a Applied torque b Property class 4.6 and4.8 c 8.8 or 8 9.8 or 9 10.9 and 10.9 or 10 12.9 or 12 4.6 and 4.8 b 8.8 or 8 9.8 or 9 10.9 and 10.9 or 10 12.9 or 12 Min. Max. Min. Max. Min. Max. Min. Max. Min. Max. kN kN kN kN kN Nm Nm Nm Nm Nm Nm Nm Nm Nm Nm M3 0.85 2.2 3.1 3.7 0.41
36、0.61 1.2 1.6 1.5 2.3 1.8 2.7 M4 1.49 3.8 5.5 6.4 0.95 1.43 2.5 3.7 3.7 5.3 4.2 6.2 M5 2.4 6.2 6.9 8.9 10.4 1.9 2.9 5 7.4 5.6 8.2 7.2 10.6 8.4 12.4 M6 3.39 8.7 9.8 12.9 14.6 3.25 4.9 8.4 12.4 9.5 14 12.5 17.9 14.2 20.8 M8 6.18 15.9 17.8 22.8 26.6 7.9 11.9 20 30 22.5 33.5 29 43 34 50 M10 9.75 25.3 28.
37、3 36.1 42.2 15.6 23.4 41 60 46 66 59 85 68 100 M12 14.3 36.7 41.1 52.5 61.4 27.4 41 71 105 80 118 102 150 119 175 M14 19.4 50 56.1 71.6 84 43.5 65.3 112 168 127 187 161 240 189 282 M16 26.5 68.2 76.5 97.5 114 67.8 102 175 260 198 292 250 371 293 434 M18 32.4 86.2 119 140 93.3 140 255 372 353 513 415
38、 603 M20 41.3 110 152 178 132 198 355 520 491 718 574 840 M22 51.2 136 189 220 180 270 500 705 675 989 787 1160 M24 59.6 159 220 256 229 343 620 928 857 1280 997 1490 M27 77.3 206 286 334 334 500 900 1330 1250 1850 1460 2160 M30 94.5 253 350 408 454 680 1230 1810 1700 2500 1980 2920 M33 117 312 432
39、505 618 927 1660 2460 2300 3410 2690 3980 M36 138 368 509 594 795 1190 2140 3160 2960 4370 3450 5100 M39 165 440 608 710 1030 1540 2770 4100 3830 5660 4480 6610 a The clamping forces specified are equal to 75 % of the proof load of the property classes of bolts as specified in BS EN 20898-1:1992 b T
40、he applied torques are not intended to be used as assembly torques (see clause 0). c The clamping forces specified for property class 4.6 and 4.8 are equal to75% of the proof load for property class 4.6 as specified in BS EN 20898-1:1992BS7371-2:1993 4 BSI 02-1999 Annex A (normative) Torque/clamping
41、 force test A.1 Principle The torque/clamping force test shall be conducted at a temperature of20C using torque and clamping force measuring devices (A.2.1 and A.2.2). For referee purposes the driving speed shall not exceed30r/min. A.2 Apparatus NOTESee Figure A.1 and Figure A.2 for plans of test fi
42、xtures where p is the thread pitch. A.2.1 Torque measuring device, a torque wrench or torque sensing power device accurate to within2% of the torque specified for the fastener to be tested. For referee purposes, the measuring device shall be chosen so that all readings fall within the upper half of
43、its torque range. A.2.2 Clamping force measuring device, a device capable of measuring the actual clamping force generated as the fastener is tightened. The device shall be accurate to within3% of the specified test clamping force. The bolt clearance hole in the backing plate shall be the same diame
44、ter and tolerance as the test washer. A.2.3 Test bolt for nut testing, the test bolt shall have threads produced by thread rolling of tolerance class6g minimum to4h maximum in conformity with BS3643-2:1981. Bolt length shall be such that a minimum of two thread pitches as measured from the end of th
45、e bolt will protrude through the nut when the nut is seated against the test washer. Thread length shall be such that a minimum of two full threads are within the grip after the nut is tightened. The bolt end shall be chamfered. The thread surface shall be free of burrs or other contamination that c
46、an affect an accurate determination of the performance of the nut. The bolt shall have physical properties in accordance with BS EN20898-1:1992, appropriate to the property class of the nut to be tested. The bolt shall have the same finish (metallic coating) as the nut tested. When testing a nut wit
47、h non-metallic or zinc flake coatings, a test bolt zinc electroplated with a nominal thickness of8m, with a yellow chromate conversion coating and lubricated in accordance with this standard shall be used. A.2.4 Test nut for bolt testing, nut with thread conforming to tolerance class6H in accordance
48、 with BS3643-2:1981 shall have physical properties in accordance with BS EN20898-2:1992, appropriate to the property class of the bolt to be tested. The nut shall have the same finish (metallic coating) as the bolt to be tested. When testing a bolt or screw with non-metallic and zinc flake coatings,
49、 a test nut zinc electroplated with a nominal thickness of8m, with a yellow chromate conversion coating and lubricated in accordance with this standard shall be used. A.2.5 Test washer, plain washer made from carbon steel, quenched and tempered to a surface hardness of500HVto600HV and a core hardness of450HV to490HV and uncoated shall be used. The abutment face shall be clean and lubricant free. The dimensions of the test washer shall be as specified in Table A.1. The faces shall be flat an
