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 3: Specifications for electroplated zinc coatingsBS 7371-3:2009BS 7371-3:2009 BR
2、ITISH STANDARDPublishing and copyright informationThe BSI copyright notice displayed in this document indicates when the document was last issued. BSI 2009 ISBN 978 0 580 55383 7ICS 21.060.01, 25.220.40The following BSI references relate to the work on this standard: Committee reference FME/9 Draft
3、for comment 08/30133820Publication historyFirst published September 1993Second edition August 2009Amendments issued since publicationDate Text affected BRITISH STANDARD BSI 2009 iBS 7371-3:2009ContentsForeword iiiIntroduction 11 Scope 22 Normative references 23 Terms and definitions 34 Application a
4、nd type of coating 35 Coating 36 Chromate treatment or topcoat 67 Suitability of coatings for components with parallel threads 68 Information to be documented and supplied to the coater 79 Identification 7AnnexesAnnex A (normative) Coating thickness for threaded parts 8Annex B (normative) Measuremen
5、t of coating thickness 9Annex C (informative) Guidance on procedures that may be adopted to accommodate thick coatings 11Bibliography 12List of figuresFigure B.1 Measuring area for local coating thickness measurement on fasteners 9List of tablesTable 1 Nominal coating thicknesses 4Table 2 Coating de
6、signation and corrosion resistance 5Table 3 Designation of chromate treatments 6Table 4 Designation of tri-valent based treatments 6Table A.1 Upper limits of nominal coating thickness 8Table C.1 Minimum fundamental deviation required to accommodate coatings too thick to be applied to standard thread
7、s, metric threads 11Summary of pagesThis document comprises a front cover, an inside front cover, pages i to iv, pages 1 to 12, an inside back cover and a back cover.BS 7371-3:2009ii BSI 2009BRITISH STANDARDThis page deliberately left blankBRITISH STANDARD BSI 2009 iiiBS 7371-3:2009ForewordPublishin
8、g informationThis part of BS 7371 is published by BSI and came 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 obtaine
9、d on request to its secretary.SupersessionThis part of BS 7371 supersedes BS 7371-3:1993, which is withdrawn.Relationship with other publicationsOther published Parts of BS 7371 are as follows: BS 7371-1, Coatings on metal fasteners Specification for general requirements and selection guidelines BS
10、7371-2, Coatings on metal fasteners Part 2: Specification for torque/clamping force relationship 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
11、hot dipped galvanized coatings BS 7371-7, Coatings on metal fasteners Part 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 pho
12、sphate or phosphate and oil coatings BS 7371-10, Coatings on metal fastenings Part 10: Specification for phosphate or phosphate and oil coatings. BS 7371-11, Coatings on metal fasteners Part 11: Specification for zinc flake non-electrolytically applied cured coatings 1) BS 7371-12, Coatings on metal
13、 fasteners Part 12: Requirements for imperial fastenersInformation about this documentThis is a full revision of the standard, and introduces the following principal changes: the option of specifying non-hexavalent chromium containing conversion coatings; details concerning cadmium have been deleted
14、 from this British Standard due to the restrictions below.Assessed capability. Users of this British Standard are advised to consider the desirability of quality system assessment and registration against the appropriate standard in the BS EN ISO 9000 series by an accredited third-party certificatio
15、n body.1)Obsolete, replaced by BS EN ISO 10683 but remains current.BS 7371-3:2009iv BSI 2009BRITISH STANDARDHazard warningsWARNING. This British Standard calls for the use of substances and/or procedures that can be injurious to health if adequate precautions are not taken. It refers only to technic
16、al suitability and does not absolve the user from legal obligations relating to health and safety at any stage.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 verb is “s
17、hall”.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 for its c
18、orrect 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 marketing and use of cadmium and its compounds contained in the Environmental Protection (Controls on Injur
19、ious Substances) (No 4) Regulations 1992 1. Cadmium is excluded from this Standard.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 Life Vehicles 2 and amendm
20、ent of Annex II by Commission Decision June 2002 Document No. C(2002) 2238 3, and non-use on Motor Vehicles marketed after July 2007.Attention is also drawn to The Waste Electrical and Electronic Equipment (WEEE) Directive (2002/96/EC) 4, which came into force on 31st December 2006.BRITISH STANDARD
21、BSI 2009 1BS 7371-3:2009Introduction The BS 7371 series deals with the performance and selection of coatings on metal fasteners and accessories. This Part of BS 7371 addresses zinc electroplated coatings.The coating has a silver appearance which can be modified to yellow, olive green or black by a h
22、exavalent chromium containing conversion (passivation) treatment applied to improve corrosion resistance. Tri-valent chromium containing top coatings can be applied which will give a transparent to bluish iridescence or pale green iridescence.Additional coatings are available to further modify colou
23、r but these may influence coating performance, e.g. lubricity or electrical conductivity.The shape of certain parts may create difficulties in the application of a coating of uniform thickness and reference to the coater is recommended to enquire if a difficulty exists or if it can be overcome by th
24、e use of specialized processing methods.Typical difficulties as outlined in BS 4479-1 and BS 4479-2 arise when bulk processing:a) long thin parts;b) parts with flat surfaces that can stick together during processing, e.g. flat washers;c) parts with recesses which do not receive the full coating;d) p
25、arts with shapes that induce nesting and interlocking;e) the internal surfaces of hollow parts.The coatings are suitable for application to metal components such as the following:1) parallel threaded fasteners and accessories;2) screws that cut or form their own threads, e.g. self tapping screws (se
26、e for example BS 4174);3) woodscrews (see for example BS 1210);4) springs and spring components;5) pipe nuts and connectors with parallel or tapered threads.When these coatings are applied to non-ferrous fasteners, the relevant part of the specification that will apply will be the coating thickness
27、requirement. These coatings are not to be specified for application to copper or copper alloys unless an undercoat is also specified, e.g. nickel.NOTE The coating processes covered by this British Standard might induce hydrogen embrittlement in certain ferrous fasteners. Attention is drawn to the ap
28、propriate requirements in BS 7371-1.Annexes include tables indicating suitable coating grades for standard screw threads and methods of determination of coating thickness.BS 7371-3:20092 BSI 2009BRITISH STANDARD1 ScopeThis Part of BS 7371 specifies requirements for coatings applied by the electrolys
29、is of solutions of zinc. NOTE The coatings consist principally of zinc and can be lubricated to give controlled torque/clamping force properties when required (see, for example, BS 7371-2). In addition to the requirements in this Part of BS 7371, the requirements in BS 7371-1 which are applicable to
30、 zinc electroplated coatings apply.This Part of BS 7371 also specifies requirements for:a) the coating thickness;b) the type of conversion treatment or topcoat to be applied;c) quality assessment of the corrosion resistance of unused coated parts when subjected to neutral salt spray testing (for exa
31、mple BS EN ISO 9227); andd) an adhesion test.Zinc electroplated coatings covered by this Part of BS 7371 are for use on fasteners and accessories where the following apply:1) A coating giving galvanic protection is required for ferrous fasteners.2) A substrate is required to improve the corrosion re
32、sistance of subsequent coatings on ferrous fasteners, e.g. organic.3) The risk of hydrogen embrittlement of high tensile steel fasteners is acceptable.2 Normative referencesThe following referenced documents are indispensable for the application of this document. For dated references, only the editi
33、on cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.BS 3643-1, ISO metric screw threads Part 1: Principles and basic dataBS 3643-2, ISO metric screw threads Part 2: Specification for selected limits of sizeBS 7371-1, Coatings on
34、metal fasteners Specification for general requirements and selection guidelinesBS EN ISO 2177, Metallic coatings Measurement of coating thickness Coulometric method by anodic dissolutionBS EN ISO 2819, Metallic coatings on metallic substrates Electrodeposited and chemically deposited coatings Review
35、 of methods available for testing adhesionBS EN ISO 3497, Metallic coatings Measurement of coating thickness X-ray spectrometric methodsBS EN ISO 3882, Metallic and other non-organic coatings Review of methods of measurement of thickness.BS EN ISO 9227, Corrosion tests in artificial atmospheres Salt
36、 spray testsBRITISH STANDARD BSI 2009 3BS 7371-3:20093 Terms and definitionsFor the purposes of this Part of BS 7371, the terms and definitions given in BS 7371-1 apply.4 Application and type of coating4.1 Cleaning and pretreatmentParts, fasteners and accessories shall be cleaned and pretreated in a
37、ccordance with BS 7371-1.NOTE Embrittlement of high tensile parts should be avoided.4.2 Type of coatingThe coating shall be either silver in appearance or modified by chromate passivation types C, D or Bk, or tri-valent topcoat types V or W (see Clause 6).NOTE 1 The colour may be further modified by
38、 the addition of an organic top coat.The coating shall be electrically conductive and galvanically protective to steel under most climatic conditions.NOTE 2 The presence of passivates, particularly the coloured ones, decreases electrical conductivity at the surface.Where specified by the purchaser s
39、ee Clause 8e) the lubricity of the coating shall be modified by the addition of a lubricant and the torque/clamping force performance of a coated fastener shall conform to BS 7371-2.NOTE 3 The addition of an organic coating might affect dimensions, lubricity and electrical conductivity.4.3 Applicati
40、onThe coating of zinc shall be applied by the electrolysis of an aqueous solution of a salt or salts of the appropriate metal.NOTE Stabilizers and brighteners may be added to the solution as necessary.5 Coating5.1 Surface conditionThe coating shall be clean, dry and of uniform appearance. All surfac
41、es of a component shall be coated unless otherwise agreed. The coating shall be free from blisters or loosely-adhering material.5.2 Coating thicknessThe specified coating thickness see Clause 8b) shall be applied using the relationships between nominal, local and batch average thicknesses shown in T
42、able 1; if coating thicknesses other than those given in Table 1 are required, this shall be agreed between the purchaser and the supplier.BS 7371-3:20094 BSI 2009BRITISH STANDARDCoating thicknesses for threaded parts shall confirm to Annex A. The coating thicknesses shall be measured by the methods
43、 described in Annex B.Local thickness shall be measured on a significant surface (see Figure B.1 for measuring areas).Exceeding the maximum batch average thickness shall not be a cause for rejection if the coated thread is still accepted by an appropriate GO gauge, 4h for external threads and 4H for
44、 internal threads.Table 1 Nominal coating thicknessesNominal coating thickness A)mEffective coating thicknessmMinimum local thicknessBatch average thicknessmin. max.3 3 3 55 5 4 68 8 7 1010 10 9 1212 12 11 1515 15 14 1820 20 18 2325 25 23 2830 30 27 35NOTE BS 7371-1 covers a range of thicknesses up
45、to and including 12 m. Greater thicknesses are given here, as these can be ordered by the purchaser on agreement with the supplier.A)See Annex A.5.3 Corrosion resistanceUnless otherwise agreed, representative samples from a batch shall be selected in accordance with the sampling clause of BS 7371-1
46、and shall be tested for resistance to neutral salt spray in accordance with BS EN ISO 9227.Coatings shall be graded by their corrosion resistance as given in Table 2. Surfaces which are not significant shall resist neutral salt spray for 50% of the time given in Table 2.NOTE For routine quality cont
47、rol purposes, after the ability of the coating to conform to the corrosion test is established, evaluation of coating mass or thickness may be used, but for referee purposes the corrosion resistance requirements still apply.BRITISH STANDARD BSI 2009 5BS 7371-3:2009Table 2 Coating designation and cor
48、rosion resistanceDesignation Nominal coating treatmentmChromate treatment designation A)First appearance of white corrosion producthFirst appearance of rusthZn 3A 3 B)A 2 12Zn 3B B 6 12Zn 3C C 24 24Zn 3D D 24 24Zn 5A 5 A 2 24Zn 5B B 12 36Zn 5C C 48 72Zn 5D D 72 96Zn 5Bk Bk 12 24Zn 8A 8 A 6 48Zn 8B B
49、 24 72Zn 8C C 72 120Zn 8D D 96 144Zn 8Bk Bk 24 72Zn 12A 12 A 6 72Zn 12B B 24 96Zn 12C C 72 144Zn 12D D 96 168Zn 12Bk Bk 24 96Tri-valent topcoats designation C)Zn 3V 3 V 2 12Zn 3W 3 W 24 24Zn 5V 5 V 6 24Zn 5W 5 W 36 72Zn 8V 8 V 12 48Zn 8W 8 W 60 120Zn 12V 12 V 12 72Zn 12W 12 W 60 144NOTE 1 The corrosion performance of tri-valent topcoats are only slightly lowered by thermal cycling.NOTE 2 Specifying a sealant (suffix SL) will extend the above corrosion resistances by up to 96 h
