1、BSI BSX737L: PART*4 94 = Lb24bb 0420448 TOY = Coatings on metal fasteners Part 4. Specification for electroplated nickel, nickel/chrorniurn and cop per/nic kel/chromiurn coatings BS 7371 : Part 4 : 1994 BSI BSr7371: PARTx4 94 m 1624669 O420449 i40 m BS 7371 : Part 4 : 1994 Committees responsible for
2、 this British Standard 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
3、Industrial Fasteners Federation British Steel Industry British Steel Industry (Wire Section) Gauge and Tool Makers Association 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,
4、 through subcommittees and panels: British Turned-parts Manufacturers Association Institute of Metal Finishing Metal Finishing Association National Centre of Tribology Stainless Steel Fabricators Association of Great Britain This British Standard, having been prepared under the direction of the Gene
5、ral Mechanical Engineering Standards Policy Committee, was published under the authority of the Standards Board and comes into effect on 15 June 1994 Amendments issued since publication Amd. No. 1 Date I Text affected O BSI 1994 The following BSI references relate to the work on this standard: Commi
6、ttee reference GME/9 Draft for comment 93/714615 DC ISBN O 580 23065 1 BSI BS*:737L: PARTr4 94 m Lb24bb9 0420450 bb2 m BS 7371 : Part 4 : 1994 Contents Committees responsible Foreword Inside front cover 2 Specification O Introduction 1 Scope 2 References 3 Definitions 4 5 Coating 6 7 8 Identificatio
7、n Application and type of coating Suitability of coatings for components with parallel threads Information to be documented and supplied to the coater Annexes A (normative) Coating thickness for threaded parts 7 B (normative) Measurement of coating thickness 9 accommodate thick coatings 11 1 Nominal
8、 coating thicknesses 5 2 Coating designation and corrosion resistance 5 C lbles (informative) Guidance on procedures that may be adopted to A.l C. 1 Minimum fundamental deviation required to accommodate coatings Upper limits of nominal coating thickness too thick to be applied to standard threads. M
9、etric threads 7 11 Figure B.1 Measuring area for local coating thickness measurement on fasteners 9 List of references Inside back cover 1 7 BSI BS*7371: PART*4 74 Lb24bb9 0420451 5T9 BS 7371 : Part 4 : 1994 Foreword This Part of BS 7371 has been prepared under the authority of the General Mechanica
10、l Engineering Standards Policy Committee to provide part of a series of standards on coatings on metal fasteners. WARNING. This British Standard calls for the use of substances and/or procedures that may be injurious to health if adequate precautions are not taken. It refers only to technical suitab
11、ility and in no way absolves either the designer, the producer, the supplier or the user from statutory obligations relating to health and safety at any stage of manufacture or use. Compliance with a British Standard does not of itself confer immunity from legal obligations. o BSI BS*737L: PARTS4 94
12、 m Lb24669 0420452 435 m BS 7371 : Part 4 : 1994 Specificat ion O Introduction BS 7371 deals with the performance and selection of coatings on metal fasteners and accessories. This Part of BS 7371 specifies the requirements for electroplated nickel, nickel/chromium and copper/nickel/chromimum coatin
13、gs. Other published Parts of BS 7371 are as follows: BS 7371 : Part 1 : 1991 Speccation for general requirements and selection guidelines1) BS 7371 : Part 2 : 1993 Specification for torque/clamping force relationship BS 7371 : Part 3 : 1993 Specification for electroplated xinc and cadmium coatings B
14、S 7371 : Part 7 : 1994 Specification for mechanically applied zinc coatings BS 7371 : Part 10 : 1994 Specification for organic coatings BS 7371 : Part 11 : 1993 Specification for zinc flake non-electrolytically applied cured coatings Further Parts of the series to incorporate the following are in pr
15、eparation: Specification for electroplated tin and tidlead coatings Specification for electroplated coatings for special purposes Speca b) a barrier type of coating is acceptable on ferrous fasteners; c) thin coatings give limited corrosion protection. Coatings that give improved protection will nee
16、d thicker deposits than are customary for thread assembly and will need selective plating or thread undersizing; d) the risk of hydrogen embpttlement of high tensile steel fasteners is acceptable. A coating of nickel has a bright metallic appearance which is enhanced by an additional coating of chro
17、mium, which prevents tarnishing. Copper plating prior to nickel plating can increase the corrosion protection provided by the complete coating. The shape of certain parts and the thickness requirements may make processing in bulk impossible, especially in the case of chromium plating. Reference to t
18、he coater is recommended to enquire if a difficulty exists or if it can be overcome by the use of specialized processing methods such as selective plating or jigging. Typical difficulties as outlined in BS 4479 : Part 1 : 1990 and BS 4479 : Part 2 : 1990 arise when bulk processing: 1) long thin part
19、s; 2) parts with flat surfaces that may stick together during processing, e.g. flat washers; 3) parts with recesses which do not receive the full coating within the recess; 4) parts with shapes that induce nesting and interlocking; 5) the internal surfaces of hollow parts. Only the lower classes of
20、coatings are suitable for overall application to metal components such as: i) parallel threaded fasteners and accessories; ii) screws that cut or form their own threads, e.g. self tapping screws (see for example BS 4174 : 1972); iii) woodscrews (see for example BS 1210 : 1963); iv) pipe nuts and con
21、nectors with parallel or tapered threads without the use of selective plating or undersizing the threads. The thickness and lack of ductility of thicker deposits may be unsatisfactory on springs and other very flexible components. When these coatings are applied to non-ferrous fasteners, the only pa
22、rt of the specification that will apply will be the coating thickness requiremnts. NWE. The coating processes covered by this standard may induce hydrogen embrittlement in certain ferrous fasteners. Attention is drawn to the appropriate requirements in BS 7371 : part 1 : 1991. I) This is supplementa
23、ry to all other Parts of l3S 7371 3 BSI BSX7371: PARTS4 94 3b24bb9 0420453 371 = BS 7371 : Part 4 : 1994 1 Scope This Part of BS 7371 specifies requirements for coatings applied by the electrolysis of solutions of copper, nickel or chromium. The coatings consist principally of copper, nickel or chro
24、mium and are not usually lubricated. NOTE 1. The corrosion resistance for higher grade coatings can be improved by using two layer (duplex) nickel coatings or special types of chromium deposit. NOTE 2. The surface smoothness and brightness of the substrate will influence the appearance and corrosion
25、 protection after plating. In addition to the requirements in this Part of BS 7371, the requirements in Part 1 of the standard which are applicable to copper, nickel and chromium electroplated coatings apply. This Part of BS 7371 also specifies requirements for the following: a) the coating thicknes
26、s of component metals in the coating; b) the type and thickness of chromium coating to be applied, if required; c) quality assessment of the corrosion resistance of unused coated parts when subjected to neutral salt spray testing or copper acetic salt spray testing (see for example BS 7479 : 1991);
27、d) adhesion test. Annexes include tables indicating suitable coating grades for standard screw threads and methods of determination of coating thickness. 2 References 2.1 Normative references This Part of BS 7371 incorporates, by dated or undated reference, provisions from other publications. These
28、normative references are made at the appropriate places in the text and the cited publications are listed on the inside back cover. For dated references, only the edition cited applies; any subsequent amendments to or revisions of the cited publication apply to this Part of BS 7371 only when incorpo
29、rated in the reference by amendment or revision. For undated references, the latest edition of the cited publication applies, together with any amendments. 2.2 Informative references This Part of BS 7371 refers to other publications that provide information or guidance. Editions of these publication
30、s current at the time of issue of this standard 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 BS 7371, the definitions given in BS 7371 : Part 1 : 1991 apply. 4 Application and type of coating 4.1 Cleaning and
31、 pretreatment Parts, fasteners and accessories shall be cleaned and pretreated in accordance with clauses 4 and 5 of BS 7371 : Part 1 : 1991. NOTE. Restrictions applicable to the avoidance of embrittlement of high tensile parts should be observed. 4.2 Type of coating The coating shall be bright and
32、lustrous in appearance, the thicker coatings having a high degree of reflectivity, particularly when applied to a smooth or polished surface. The performance of the coating can be improved by using the following, either singly or in combination: a) a copper undercoat on ferrous fasteners in accordan
33、ce with BS 1224 : 1970; b) a duplex nickel deposit in accordance with BS 1224 : 1970; c) a modified chromium deposit (Cr) in accordance with BS 1224 : 1970. Ib enable higher thicknesses to be used on significant surfaces of threaded fasteners, the procedure of selective electroplating shall be used,
34、 i.e. the heads of screws can receive a higher coating thickness than the threads, thereby enabling the threads to be plated without creating interference on assembly which would result if the higher thickness of coating were applied to the fastener as a whole. 4.3 Application The coating of copper,
35、 nickel or chromium 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 Coating 5.1 Surface condition The coating shall be clean, dry and of uniform appearance. All sur
36、faces of a component shall be coated unless otherwise agreed. The coating shall be free from blisters or loosely adhering material. BSI BS*737L: PARTx4 74 m Lb24bb 0420454 208 m BS 7371 : Part 4 : 1994 5.2 Coating thickness The specified coating thickness of nickel or copper and nickel (see table 2)
37、 shall be applied using the relationships between nominal, local and batch average thicknesses shown in table 1. Coating thicknesses for threaded parts shall conform to annex A. The coating thicknesses shall be measured by the methods described in annex B. NmE 1. If a coating thickness other than th
38、ose given in table 1 is required, this should be agreed between the purchaser and the supplier. The chromium top coat, if specified, (see table 2) shall show a continuous coating over all the component. If a modified chromium deposit is specified, (see item e) of 4.2) the minimum thickness shall be
39、in accordance with BS 1224 : 1970. NOTE 2. Experience has shown that the use of selective plating to apply thicker coats to significant surfaces is to be preferred over the method of applying a thick coat to the fastener as a whole given in annex C. Reference to the coater is recommended to enquire
40、which method would be preferred for a particular application. hble 1. Nominal coating thicknesses Thicknesses in pm Nominal coating thickness ) Effective coating th Minimum local thickness kness Batch average thickness min. max. 3 5 3 10 12 15 20 25 30 40 3 3 4 7 9 11 14 18 23 27 36 5 6 10 12 15 18
41、23 28 35 46 5 8 10 12 15 20 25 30 40 1 See annex A. Local thickness shall be measured on a significant surface (see figure B.l). 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
42、 and 4H for internal threads. 5.3 Corrosion resistance Unless otherwise agreed, representative samples from a batch shall be selected in accordance with clause 7 of BS 7371 : Part 1 : 1991 and shall be tested for resistance to salt spray in accordance with BS 7479 : 1991. Coatings shall be graded by
43、 their corrosion resistance as given in table 2. Surfaces which are not significant shall resist salt spray for 50 % of the Igble 2. Coating designation and corrosion resistance Service condition number ) Coating designation ) 3, First appearance of rust Steel base material we material Nickel plus c
44、hromium coating Ni3bCr Ni5bCr NilobCr Ni20bCr Ni30dCr Copper os brass Nickel coating Nickel coating Copper plus nickel plus chromium coating 5% neutral 4, salt spray test h Copper acetic salt spray test h Nickel plus chromium coating Ni5bCr NilobCr Ni2ObCr Ni30bCr Ni40dCr 1970). O 1 25) 35) 4 Ni3b N
45、i5b NilOb Ni20b Not recommended Ni5b NilOb NiLOb Ni30b Not recommended Cu 1 ONi5bCr Cu2ONi 10bCr Cu20Ni20bCr Cu20Ni30dCr 12 48 - - 1 See table 1 of BS 7371 : Part 1 : 1991 ) b indicates that a bright nickel coating is required (see BS 1224 : d indicates that a duplex nickel coating b) the coating de
46、signation (see table 2); c) the base material to be coated (e.g. steel); d) the hardness and property class of the component to be plated; e) the significant surfaces if not as defined in BS 7371 : Part 1 : 1991; f) any additional protection required for delivery (see clause 8 and appendix D of BS 7
47、371 : g) the requirements of any subsequent operations (e.g. the application of an adhesive); h) any special requirements (e.g. selective plating; see annex C). Part 1 : 1991); 8 Identification The coating shall be identified by the number and date of this British Standard, i.e. BS 7371 : Part 4 : 1
48、9942) together with the coating designation in accordance with table 2. Example A nickel and chromium electroplated coating of 10 pm thickness would be identified as BS 7371 : Part 4 : 1994 NilObCr. 2, Marking BS 7371 : Part 4 : 1994 on or in relation to a product represents a manufacturers declarat
49、ion of conformity, i.e. a claim by or on behalf of the manufacturer that the product qets the requirements of the standard. The accuracy of the claim is solely the claimants responsibility. Such a declaration is not te be confused with third party certification of conformity, which may also be desirable. 6 13 (5- 5 5 15 3 3 - 35 8 - 36 8 - 38 3 3 5 5 8 8S*?371: PART*4 74 D lb24bb 042045b 080 D Annexes Annex A (normative) Coating thickaess for threaded parts In ordw to reduce the risk of interference on assembly of threads with elect
