1、BRITISH STANDARD BS7715:1994 Specification for Prevailing torque type bolts, screws and studs with non-metallic prevailing torque elements incorporated into the threadBS7715:1994 This British Standard, having been prepared under the directionof the General Mechanical Engineering Standards Policy Com
2、mittee, waspublished under the authorityof the Standards Boardand comes into effect on 15January1994 BSI 07-1999 The following BSI references relate to the work on this standard: Committee reference GME/9 Draft for comment93/702726DC ISBN 0 580 22375 2 Committees responsible for this British Standar
3、d The preparation of this British Standard 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
4、Federation British Railways Board British Steel Industry British Steel Industry (Wire Section) Gauge and Tool Makers Association Ministry of Defence Society of Motor Manufacturers and Traders Limited Washer Manufacturers Association of Great Britain Amendments issued since publication Amd. No. Date
5、CommentsBS7715:1994 BSI 07-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 References 1 3 Definitions 1 4 Protective coatings 1 5 Prevailing torque element dimensions 1 6 Materials and lubrication 3 7 Mechanical properties and performance 3 Annex A (normative)
6、Torque testing 4 Figure 1 Position of prevailing torque feature 2 Figure 2 Diameter of prevailing torque feature 2 Table A.1 Spacer dimensions 4 Table A.2 Performance requirements 6 List of references Inside back coverBS7715:1994 ii BSI 07-1999 Foreword This British Standard has been prepared under
7、the direction of the General Mechanical Engineering Policy Committee. It includes performance properties for prevailing torque type bolts, screws and studs with non-metallic prevailing torque features. A British Standard does not purport to include all the necessary provisions of a contract. Users o
8、f 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 cover, pagesi andii, pages1 to6, an inside back cover and a back co
9、ver. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS7715:1994 BSI 07-1999 1 1 Scope This British Standard specifies the coatings, dimensions, materials, lubrication and performanc
10、e requirements for prevailing torque type bolts, screws and studs, with non-metallic prevailing torque elements incorporated into the thread, when tested at an ambient room temperature between15 C and30 C. It applies to bolts, screws and studs: a) with ISO metric coarse pitch M4 to M24 threads in co
11、nformance with BS3643-2:1981; b) with specific strength requirements conforming to either BS6104-3:1981, BS6105:1981 or BSEN20898-1:1992 as appropriate; c) with threads of tolerance class6g or4h in conformance with BS3643-2:1981; d) for application into a mating component with a thread of tolerance
12、class6H in conformance with BS3643-2:1981; e) for use within the temperature range50 C to+120 C; f) with specific torque/clamping force requirements in conformance with BS7371-2:1993. The torque/clamping force requirements do not apply to set screws and similar threaded fasteners with physical prope
13、rties in conformance with BS6104-3:1981. NOTE 1Capability to provide a pressure or liquid seal is not within the requirements of this standard. NOTE 2Performance at temperatures outside the operating range is not within the requirements of this standard. NOTE 3Performance of bolts, screws and studs
14、for which a lubricated coating is not permissible is not within the requirements of this standard. 2 References 2.1 Normative references This British Standard incorporates, by reference, provisions from specific editions of other publications. These normative references are cited at the appropriate
15、points in the text and the publications are listed on the inside back cover. Subsequent amendments to, or revisions of, any of these publications apply to this British Standard only when incorporated in it by updating or revision. 2.2 Informative reference This British Standard refers to another pub
16、lication that provides guidance. The edition of this publication current at the time of issue of this standard is given on the inside back cover but reference should be made to the latest edition. 3 Definitions For the purposes of this British Standard the following definitions apply. 3.1 prevailing
17、 torque type bolts, screws and studs bolts, screws and studs which are frictionally resistant to rotation due to an integral prevailing torque feature and not because of compressive load developed against a bearing force 3.2 prevailing torque developed by bolts, screws or studs torque necessary to r
18、otate the bolt, screw or stud in a mating threaded component while in motion and with no axial load 3.3 clamping force force which is applied by the bearing face of the fastener against a mating component after application of a specified tightening torque 4 Protective coatings Finished parts shall c
19、onform to the appropriate coating standard applicable to the fastener to which the non-metallic prevailing torque element is attached. NOTE 1Prevailing torque bolts, screws or studs which do not have or need supplementary lubrication may not satisfy the requirements of this standard unless the lubri
20、cation is an integral property of the specified coating. Protective coatings may be applied either before or after the application of the prevailing torque feature at the discretion of the supplier. NOTE 2Cavities formed to accept prevailing torque elements may have no protective coating or corrosio
21、n resistance. 5 Prevailing torque element dimensions The prevailing torque feature dimensions shall be as shown in Figure 1 and Figure 2. Dimension lx 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 prevailing
22、torque feature in order to ensure ease of engagement. BS7715:1994 2 BSI 07-1999 Figure 1 Position of prevailing torque feature Figure 2 Diameter of prevailing torque featureBS7715:1994 BSI 07-1999 3 6 Materials and lubrication 6.1 Materials The material used to produce the bolts, screws and studs wi
23、th non-metallic prevailing torque features shall be in accordance with the specified property class in BS6104-3:1981, BS6105:1981 or BSEN20898-1:1992, as appropriate. The prevailing torque feature shall be made from a resilient non-metallic material and shall adhere to, or be inserted in, the metall
24、ic surface. 6.2 Lubrication NOTEBolts, screws or studs finished in accordance with BS7371-1:1991 and requiring no lubrication may be lubricated at the discretion of the supplier. Bolts, screws or studs finished in accordance with BS7371-1:1991 with a finish which requires lubrication shall be lubric
25、ated. Supplementary lubrication, if applied, shall conform to BS7371-2:1993. 7 Mechanical properties and performance 7.1 Mechanical properties The mechanical properties of the bolt, screw or stud after application of the prevailing torque feature product shall conform to the specified property class
26、 in accordance with BS6104-3:1981, BS6105:1981 or BS EN20898-1:1992, as appropriate. Certain prevailing torque features reduce the stress area of the bolt, screw or stud and provision shall be made to ensure that the specified mechanical properties are maintained. NOTEThe stripping strength of the j
27、oint is also reduced. 7.2 Prevailing torque The prevailing torque developed by the feature during the first fixing, or any subsequent fixings or removals, shall not exceed the maximum prevailing torque specified in Table A.1 when tested as specified inAnnex A. The torques developed by the feature du
28、ring the first and fifth removals shall not be less than the minimum prevailing torques specified in Table A.1 when tested as specified in Annex A. 7.3 Torque/clamping force Torque clamping force requirements shall be assessed in accordance with BS7371-2:1993.BS7715:1994 4 BSI 07-1999 Annex A (norma
29、tive) Torque testing A.1 Torque measuring device The torque measuring device (torque wrench or power device) shall be accurate to2% of the maximum specified torque range of the device. For referee purposes, the device shall be chosen so that all readings fall within the upper half of the torque rang
30、e. Manual torque wrenches may be used for measurement of torque, but for referee purposes, an automatic electronic sensing device shall be used. A.2 Test washers/spacers A.2.1 Properties Test spacers shall be made from steel with a surface hardness of500HV to600HV and a core hardness of450HV to490HV
31、 and shall be unplated. The faces shall be flat and parallel within 4% of the specific minimum thickness. The surface roughness of the abutment faces shall not exceed3.24m (seeBS1134-2). Test spacers shall be designed such that when assembled into the test equipment, rotation is prevented during tig
32、htening of bolt. A.2.2 Dimensions The inside diameter of the test spacer shall be in accordance with Table A.1. The thickness of the spacer shall be calculated to ensure that the prevailing torque feature is fully engaged in the test nut during the whole test measurement sequence, but shall not be l
33、ess than the minimum thickness shown in Table A.1. Table A.1 Spacer dimensions A.3 Test nuts A.3.1 Properties The test nuts shall be to property class8 of BSEN20898-2:1992 manufactured from steel hardened to450HV at the surface. The nuts shall be threaded to a6H tolerance class in conformance with B
34、S3643-2:1981. A.3.2 Dimensions The test nut shall be of sufficient length to contain nine full thread pitches and a chamfer of at least one full thread pitch at each end. A.4 Test procedure A.4.1 General Conduct the prevailing torque test at ambient temperature between15 C and30 C. Measure all preva
35、iling torque measurements by a torque measuring device (seeA.1) with a screw in motion and with the full length of the prevailing torque feature in contact with the test nut thread. A.4.2 Bolts and screws Using a suitable test spacer (seeA.2), assemble the sample screw in a test nut, as detailed inA
36、.3. Ensure that the screw is advanced in the nut until all prevailing torque feature threads are in full contact with the test nut thread. Measure the maximum torque occurring while the screw is being advanced through the next360 of rotation. For the screw to be acceptable, check that this torque do
37、es not exceed the maximum prevailing torque value as specified for the applicable screw in Table A.2. Continue tightening until the screw is seated against the test spacer and the tightening torque specified in Table A.2 is achieved. Ensure that the thickness of the test nut is such that seating of
38、the screw occurs when the feature is still fully in contact with the test nut thread. Prevent the test spacer from turning during screw tightening. Slacken the screw by the application of reverse torque until the tensile load has been reduced to zero. Measure the minimum torque occurring while the s
39、crew is being removed through the next360 of rotation. For the screw to be acceptable, check that this torque is not less than the first removal prevailing torque specified for the applicable screw in Table A.2 nor greater than the maximum prevailing torque. After the first removal prevailing torque
40、 has been measured, back off the screw until the feature is disengaged from the nut thread. Reassemble the screw to the specified tightening torque and remove four more times. On each removal, ensure that the feature is disengaged from the nut thread. Dimensions in millimetres Nominal thread diamete
41、r Internal maximum Diameter minimum Minimum spacer thickness M4 M5 M6 M8 M10 M12 M14 M16 M18 M20 M24 4.9 5.9 7.1 9.5 11.5 14 16 18 20.5 22.7 26.7 4.8 5.8 6.9 9.3 11.3 13.8 15.8 17.8 20.3 22.5 26.5 2 2 3 4 5 6 6 6 6 6 6BS7715:1994 BSI 07-1999 5 During the fifth removal, measure the minimum torque occ
42、urring while the screw is being removed through the first360 rotation after the tensile load has been reduced to zero. For the screw to be acceptable check that this torque is not less than the fifth removal prevailing torque value as specified in Table A.2. In addition, check that at no time during
43、 these four subsequent tightenings and slackenings does the torque exceed the maximum prevailing torque value specified in Table A.2. To avoid overheating of the test assembly, allow sufficient time to elapse between the torque application cycles. Check that the speed of installation and removal of
44、the nut does not exceed30r.p.m. and is continuous and uniform. Clean the test nut between the tests so as to ensure all prevailing torque feature material and lubricant is removed. Clean and examine the test spacer for conformance toA.2. A.4.3 Headless set screws and studs Using a suitable thread st
45、op, assemble the sample screw in a test nut, as detailed inA.3. Advance the screw in the nut until all prevailing torque feature threads are in full contact with the test nut thread. Measure the maximum torque occurring while the screw is being advanced through the next360 of rotation. For the screw
46、 to be acceptable, check that this torque does not exceed the maximum prevailing torque value as specified for the applicable screw in Table A.2. Continue tightening until the screw is seated against the thread stop and the tightening torque specified in Table A.2 is achieved. Ensure that the thickn
47、ess of the test nut is such that seating of the screw occurs when the feature is still fully in contact with the test nut thread. Prevent the thread stop from turning during screw tightening. Slacken the screw by the application of reverse torque until the compressive load has been reduced to zero.
48、Measure the minimum torque occurring while the screw is being removed through the next360 of rotation. For the screw to be acceptable, check that this torque is not less than the first removal prevailing torque specified for the applicable screw in Table A.2 nor greater than the maximum prevailing t
49、orque. After the first removal prevailing torque has been measured, back off the screw until the feature is disengaged from the nut thread. Reassemble the screw to the specified tightening torque and remove four more times. On each removal, ensure that the feature is disengaged from the nut thread. During the fifth removal, measure the minimum torque occurring while the screw is being removed through the first360 rotation after the compressive load has been reduced to zero. For the screw to be acceptable, check that this torque is not less than t
