1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI British StandardsWB9423_BSI_StandardColCov_noK_AW:BSI FRONT COVERS 5/9/08 12:55 Page 1Coatings on metal fasteners Part 1: Specification for general requirements and selection guidelinesBS 7371-1:2009
2、BS 7371-1:2009 BRITISH STANDARDPublishing and copyright informationThe BSI copyright notice displayed in this document indicates when the document was last issued. BSI 2009 ISBN 978 0 580 55382 0ICS 21.060.01, 25.220.01The following BSI references relate to the work on this standard: Committee refer
3、ence FME/9 Draft for comment 08/30133813 DCPublication historyFirst published January 1992Second (present) edition, August 2009Amendments issued since publicationDate Text affected BRITISH STANDARD BSI 2009 iBS 7371-1:2009ContentsForeword iii1 Scope 12 Normative references 13 Terms and definitions 1
4、4 Selection of coatings 15 Preparation before coating 26 Hydrogen embrittlement 27 Thickness and coating weight 38 Sampling for inspection 39 Delivery conditions 410 Information to be supplied to the coater and designation 4AnnexesAnnex A (informative) Selection guidelines 5Annex B (informative) Avo
5、idance of hydrogen embrittlement 9Annex C (informative) Surface areas of bolts, screws and nuts 10Annex D (informative) Delivery conditions 14Bibliography 15List of figuresFigure C.1 Constituent surface areas of a bolt or screw 11List of tablesTable A.1 Protective value and service condition number
6、5Table A.2 Coating selection 6Table A.3 Coating recommendations for parallel threads 8Table C.1 Surface areas of screws and bolts 11Table C.2 Surface areas of nuts for electroplated coatings 12Table C.3 Surface areas of nuts for non-electroplated coatings 12Summary of pagesThis document comprises a
7、front cover, an inside front cover, pages i to iv, pages 1 to 16, an inside back cover and a back cover.BS 7371-1:2009ii BSI 2009BRITISH STANDARDThis page deliberately left blankBRITISH STANDARD BSI 2009 iiiBS 7371-1:2009ForewordPublishing informationThis part of BS 7371 is published by BSI and came
8、 into effect on 31 August 2009. It was prepared by Subcommittee FME/9/1, Mechanical properties of fasteners, under the authority of Technical Committee FME/9, Fasteners. A list of organizations represented on this committee can be obtained on request to its secretary.SupersessionThis part of BS 7371
9、 supersedes BS 7371-1:1991, which is withdrawn.Relationship with other publicationsOther published Parts of BS 7371 are as follows: BS 7371-2, Coatings on metal fasteners Part 2: Specification for torque/clamping force relationship; BS 7371-3, Coatings on metal fasteners Part 3: Specifications for e
10、lectroplated zinc; 1) BS 7371-4, Coating on metal fasteners Part 4: Specification for electroplated nickel, nickel/chromium and copper/nickel/chromium coatings; BS 7371-6, Coatings on metal fasteners Part 6: Specification for hot dipped galvanized coatings; BS 7371-7, Coatings on metal fasteners Par
11、t 7: Specification for mechanically applied zinc and zinc based coatings; BS 7371-8, Coatings on metal fasteners Part 8: Specification for sherardized coatings; BS 7371-9, Coatings on metal fasteners Part 9: Specification for phosphate or phosphate and oil coatings; BS 7371-10, Coatings on metal fas
12、tenings Part 10: Specification for organic coatings; BS 7371-11, Coatings on metal fasteners Part 11: Specification for zinc flake non-electrolytically applied cured coatings; 2) BS 7371-12, Coatings on metal fasteners Part 12: Requirements for imperial fasteners.The Parts of BS 7371 listed describe
13、 coatings for:a) corrosion protection;b) appearance;c) electrical conductivity;d) controlled lubricity;e) identification; andf) avoidance of hydrogen embrittlement.Attention is drawn to Clause 4 and Annex A which provides advice on the suitability and limitations of the coatings for these purposes.1
14、)Being reviewed, replaced by BS EN ISO 4042 but remains current.2)Obsolescent, replaced by BS EN ISO 10683 but remains current.BS 7371-1:2009iv BSI 2009BRITISH STANDARDInformation about this documentThis is a full revision of the standard, and introduces the following principal changes: Change to Fi
15、gure C.1. Exclusion of cadmium. General revision.Product certification/inspection/testing. Users of this British Standard are advised to consider the desirability of third-party certification/inspection/testing of product conformity with this British Standard. Users seeking assistance in identifying
16、 appropriate conformity assessment bodies or schemes may ask BSI to forward their enquiries to the relevant association.Presentational conventionsThe provisions of this standard are presented in roman (i.e. upright) type. Its requirements are expressed in sentences in which the principal auxiliary v
17、erb is “shall”.Commentary, explanation and general informative material is presented in smaller italic type, and does not constitute a normative element.Contractual and legal considerationsThis publication does not purport to include all the necessary provisions of a contract. Users are responsible
18、for its correct application.Compliance with a British Standard cannot confer immunity from legal obligations.The attention of the user of this Part of BS 7371 is drawn to the restrictions placed on the use and supply of hexavalent chromium-containing substances by ECC Directive 2000/53/EC on End of
19、Life Vehicles 1 and amendment of Annex II by Commission Decision June 2002 Document No. C(2002) 2238 2, and Non-Use on Motor Vehicles marketed after July 2007.Attention is drawn to The Waste Electrical and Electronic Equipment (WEEE) Directive (2002/96/EC) 3, which came into force on 31 December 200
20、6.Attention is drawn to the restrictions placed on the marketing and use of cadmium and its compounds by in the Environmental Protection (Controls on Injurious Substances) (No. 4) Regulations 1992 4. Cadmium has thus been excluded from this Specification.BRITISH STANDARD BSI 2009 1BS 7371-1:20091 Sc
21、opeThis Part of BS 7371 specifies general requirements that apply to coatings covered by all other Parts of BS 7371, including:a) preparations before coating;b) hydrogen embrittlement avoidance;c) sampling for inspection;d) thickness testing;e) area tables for metric parallel threaded fasteners (are
22、a tables for imperial fasteners can be found in BS 7371-12); andf) selection of coatings (including the opportunity to select non-hexavalent chromium-containing coatings).Specific requirements are given in each Part of BS 7371.2 Normative referencesThe following references are indispensable for the
23、application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.BS 6041:1981+A1:1981, Method of sampling of electrodeposited metallic coatings and related finishes: procedures
24、 for inspection by attributes3 Terms and definitions3.1 significant surfacesareas visible on a part when assembled3.2 batch average thicknessaverage thickness of the coating on all components of a batch3.3 production runbatches of parts processed continuously without any changes in coating technique
25、s or constituents within a single working day 4 Selection of coatingsThe coating shall be selected with regard to:a) corrosion resistance;b) appearance;c) shape and size;d) embrittlement;e) conductivity;f) lubricity;g) application limitations;h) colour (if applicable); andi) whether hexavalent chrom
26、ium can be tolerated.NOTE Annex A provides guidance on suitable coatings for specific components.BS 7371-1:20092 BSI 2009BRITISH STANDARD5 Preparation before coatingPrior to coating, fastener parts shall be free of oil, grease, scale, oxides and other foreign matter.NOTE 1 The cleaning process shoul
27、d not induce hydrogen embrittlement (see Clause 6).NOTE 2 It is essential that the cleaning process is not detrimental to the substrate.6 Hydrogen embrittlement6.1 Cleaning processesFastener parts heat-treated or cold-worked to a surface hardness of 320 HV to 390 HV, and also property classes3)9.8,
28、10.9, and 10.9, shall be cleaned with an inhibited acid, alkaline or mechanical process.NOTE 1 The time during which parts are immersed in inhibited acid cleaning agents increases the risk of the introduction of potential hydrogen embrittlement. Immersion time in the inhibited acid should therefore
29、be of minimum duration. Cathodic cleaning processes should be avoided.Special cleaning processes using non-acidic methods such as dry honing, abrasive blasting or alkali derusting shall be used to clean parts which have been heat-treated or cold-worked to a surface hardness greater than 390 HV or pr
30、operty class 12.9 and above.NOTE 2 Hydrogen embrittlement might cause premature failure of parts which are heat-treated or cold-worked to a surface hardness of 320 HV and above when subjected to stress. The property classes affected include 9.8 and above. Although baking after coating will minimize
31、the risk of failure, the process can never be guaranteed to be completely effective. Annex B includes a more detailed explanation.6.2 Coating processesFastener parts shall be coated in accordance with the appropriate Parts of BS 7371.NOTE The risk of hydrogen-embrittlement failure of parts with a su
32、rface hardness greater than 390 HV, and also property class 12.9 and above, cannot be precluded unless coating processes are used which do not involve electrolysis from aqueous solutions. Only high-efficiency, non-cyanide type electroplating solutions or alternative non-embrittling coatings should b
33、e used (see Annex B).6.3 De-embrittlement processesNOTE 1 Although property class 8.8 might marginally exceed 320 HV surface hardness, it is not neccessary to take these precautions provided that the surface hardness of this particular property class does not exceed 350 HV.Except for those parts des
34、cribed in Note 1, parts heat-treated or cold-worked to a surface hardness greater than 320 HV (and also property classes 9.8 and above which have been electroplated) shall be de-embrittled by baking. Parts shall not be heated to a temperature above that at which they were originally tempered.3)Prope
35、rty classes are designated in BS EN ISO 898-1.BRITISH STANDARD BSI 2009 3BS 7371-1:2009The baking process specified shall apply to the parts within the scope of this standard with the exception of:a) parts tempered below 180 C;b) parts susceptible to hydrogen embrittlement;c) parts with coatings adv
36、ersely affected by a temperature of 180 C to 210 C; andd) parts adversely affected by a temperature of 180 C to 210 C.The heating process shall commence within 1 h after the completion of electroplating.Except for those parts listed in a) to d), parts shall be heated to achieve a temperature of 180
37、C to 210 C within 4 h (maximum) after the completion of electroplating and shall be maintained at this temperature for the appropriate time as given in 1) to 6) below. These times shall be treated as minimum times at temperature.1) Bolts and screws of property classes 9.8, 10.9 and 10.9 4 h.2) Bolts
38、 and screws of property class 12.9 (see 6.1) 6 h.3) Spring steel parts hardness range 400 HV to 500 HV 8 h.4) Spring steel parts hardness range 500 HV to 600 HV 12 h.5) Case-hardened tapping screws 2 h.6) Case-hardened thread rolling screws 6 h.NOTE 2 It should not be assumed that the specified baki
39、ng process will completely remove hydrogen embrittlement in all cases. Other conditions of duration and temperature can be used if they have been shown to be effective for the parts listed in a) to d). Parts which have been tempered at temperatures below 180 C need baking at a lower temperature. Gen
40、erally, parts baked at lower temperatures require longer times at that temperature. Some types of steel are more susceptible to hydrogen embrittlement than others and the baking times given might be inadequate in some circumstances. Certain coatings, e.g. tin, and the physical properties of some par
41、ts might be adversely affected by a temperature of 180 C to 210 C. In such cases, lower temperatures and longer times will be required.7 Thickness and coating weightThickness and coating weight shall be evaluated using the appropriate methods specified in each Part of BS 7371, which include:a) local
42、 thickness;b) batch average thickness; andc) mass per unit area.NOTE To assist in calculations, areas of standard metric bolts, screws and nuts are defined in Annex C.8 Sampling for inspectionSampling for thickness measurement shall be in accordance with BS 6041:1981+A1.Sampling for corrosion testin
43、g or torque/clamping force measurement shall be in accordance with BS 6041:1981+A1, Table 3.BS 7371-1:20094 BSI 2009BRITISH STANDARD9 Delivery conditionsAll requirements of the coating specifications shall be conformed to at the time of delivery of the fasteners or accessories to the location specif
44、ied by the purchaser (see Annex D).NOTE The purchaser should state the location in the enquiry or order.10 Information to be supplied to the coater and designationThe following information shall be supplied to the coater.a) The number of this British Standard, i.e. BS 7371-1:2009.b) The Part of BS 7
45、371 appropriate to the coating required.c) The coating grade or thickness as applicable.d) The requirement for lubrication, if applicable.e) The requirement, if any, for stress relieving before coating, and the stress relieving conditions.f) Special requirements, e.g. additional protection for stora
46、ge (see Clause 9 and Annex D).g) The requirements of subsequent operations such as the application of adhesives.The coating shall be specified using at least the following designation (see footnote A)to Table A.2):“Coating in accordance with BS 7371-X:20XX: Grade ”.The lubricated condition shall be
47、designated by the letter “L” after the grade identification (see Annex A).EXAMPLE An electroplated zinc coating of grade Zn8C with added lubrication is designated thus:BS 7371-3:2009: Grade Zn8CL.BRITISH STANDARD BSI 2009 5BS 7371-1:2009Annex A (informative) Selection guidelinesA.1 Guidelines on the
48、 selection of coatingsA.1.1 Protective value and service condition numberThe protective value and service life of a coating will vary according to the type of coating, its thickness, the use of a chromate conversion treatment (or other coating where appropriate), and so on.For the purpose of this st
49、andard, degrees of severity are defined in Table A.1 and equated to a service condition number.A.1.2 Coating selectionCoatings should be selected using the data in Table A.2 and Table A.3 in accordance with the criteria defined in Clause 4 and in conjunction with the appropriate Part of BS 7371.NOTE Increased thicknesses may be specified to extend resistance to rust provided that thread dimensions before plating are adjusted.All coatings except phosphate and oil coatings will not substantially
