1、BRITISH STANDARD BS 4290:1989 Method for specifying Electroplated coatings of silver and silver alloys for decorative and protective purposes UDC 620.197.6:621.793.3:621.357.7:669.228.7BS4290:1989 This British Standard, having been prepared under the directionof the Surface Coatings (other than Pain
2、ts) Standards Policy Committee, was published under the authority of the Board ofBSI and comes into effect on 29 September 1989 BSI 07-1999 First published March 1968 First revision September 1989 The following BSI references relate to the work on this standard: Committee reference SRC/5 Draft for c
3、omment 86/55014 DC ISBN 0 580 17269 4 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Surface Coatings (other than Paints) Standards Policy Committee (SRC/-) to Technical Committee SRC/5, upon which the following bodies were represented:
4、 British Coal Corporation British Jewellers Association British Metal Finishing Suppliers Association British Telecommunications plc Cutlery and Silverware Association Electronic Engineering Association Institute of Metal Finishing Institution of Corrosion Science and Technology Joint Committee of A
5、ssay Offices of Great Britain Metal Finishing Association Ministry of Defence National Association of Goldsmiths of Great Britain and Ireland Telecommunications Engineering and Manufacturing Association Amendments issued since publication Amd. No. Date of issue CommentsBS4290:1989 BSI 07-1999 i Cont
6、ents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Definitions 1 3 Information to be supplied by the purchaser to the electroplater 1 4 Basis material 2 5 Coating classification code 2 6 Undercoats 3 7 Coatings 3 8 Anti-tarnish treatments 5 Table 1 Summary of information req
7、uired 2 Table 2 Appropriate undercoats for use with silver and silver alloy decorative and protective coatings 4 Table 3 Recommended range of silver coatings 4 Publications referred to Inside back coverBS4290:1989 ii BSI 07-1999 Foreword This British Standard has been prepared under the direction of
8、 the Surface Coatings (other than Paints) Standards Policy Committee. It gives a method for specifying requirements for electroplated coatings of silver and silver alloys for general decorative purposes. It revises and supersedes BS4290:1968, which is withdrawn. As this standard is based on requirem
9、ents to be agreed between the interested parties, it is no longer appropriate for any claim to be made that a coating complies with BS4290. It is not intended to replace the requirements specified in British Standards for particular articles. In addition, this revision no longer includes appendices
10、containing methods of test as these are now published separately as Parts of BS6669. This British Standard describes methods for specifying electroplated coatings of silver, including silver alloys, for use for general decorative purposes. Decorative purposes are those for which the appearance of th
11、e finished article is of prime importance, while engineering purposes are those for which coating has to fulfil primarily functional tasks, although protection against corrosion may be a requirement in both cases. In contrast to many other coatings applied for decorative and protective purposes, e.g
12、. nickel/chromium coatings, silver coatings frequently have to give protection against considerable wear in service as well as against corrosion. Consequently, the thickness of the silver coating is chosen to give the required protection against wear. For this reason, the significant surfaces of sil
13、ver electroplated articles are often those that are subject to the greatest wear in service. Packaging materials such as paper and cardboard frequently contain small amounts of sulphur compounds which can cause excessive tarnishing of silver and silver alloy electrodeposited articles. Account should
14、 be taken of this when such articles are packed, stored and transported, and the packaging materials should be free from significant contamination of sulphur compounds. Anti-tarnish treatments can be applied to the coatings to prevent or delay tarnishing (see clause8). Attention is drawn to the expr
15、ession in certain contexts of silver contents in terms of parts per thousand (by mass), also known as thousandths (millimes) or “fineness”. In this standard, percentages by mass to one decimal place are used. A British Standard does not purport to include all the necessary provisions of a contract.
16、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 comprises a front cover, an inside front cover, pagesi andii, pages1 to6, an inside back cover and a
17、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 the inside front cover.BS4290:1989 BSI 07-1999 1 1 Scope This British Standard describes a method for specifying requirements for electrodeposite
18、d coatings of silver and its alloys on metallic and non-metallic materials for decorative and/or protective purposes. This standard is not applicable to: a) coatings on screw threads; b) coatings applied on sheet or strip in the unfabricated form; c) coatings containing less than95% by mass of pure
19、silver; or d) coatings of minimum thickness less than24m. NOTEThe titles of the publications referred to in this standard are listed on the inside back cover. 2 Definitions For the purposes of this British Standard, the definitions given in BS5411-1 apply together with the following. 2.1 significant
20、 surface the part of the article covered or to be covered by the coating and for which the coating is essential for serviceability and/or appearance 2.2 silver electroplated the finished state of an article that has been given a coating of silver or silver alloy by electrodeposition having a minimum
21、 thickness of24m and a minimum purity of95% by mass 3 Information to be supplied by the purchaser to the electroplater NOTEA summary of clause references pertaining to this information is given inTable 1. 3.1 Essential information The information listed in a) to f) shall be supplied by the purchaser
22、 to the electroplater. a) The number of this British Standard, i.e. BS4290. b) A detailed indication of the significant surface, e.g. by drawings or by the provision of suitably marked samples and, in addition, the relevant details if the requirements for the finish differ for various parts of the s
23、ignificant surface (see7.3). c) The classification code of the coating required (see clause5) and the method to be used to determine the silver coating thickness, as agreed between the purchaser and the electroplater (see7.3). NOTEThe required silver coating thickness is contained within the coating
24、 classification code. d) The type (bright, matt, etc) of surface finish required indicated, for example, by the provision of a preliminary sample having the required finish supplied by the electroplater for approval by the purchaser (see7.2). NOTEThe final surface finish will be dependent on the ini
25、tial surface roughness of the basis material (see clause4). e) The method(s) of test for adhesion to be employed (see7.5). f) The sampling procedure, selected from BS6001 or BS6041, and the sampling and acceptable quality levels (AQLs) required. NOTEThis standard does not specify sampling or AQLs. 3
26、.2 Additional information The additional information listed in a) to j), as applicable, shall be supplied by the purchaser to the electroplater, if necessary in consultation with the electroplater. a) The minimum silver content of the coating and the method to be used to determine the silver content
27、 as agreed between the purchaser and the electroplater (see7.4). b) Details of any intentional alloying elements (see7.4). c) The nature of the basis material, surface condition and roughness and, where the basis material is supplied by the purchaser, the lead content, if any, of the material (see c
28、lause4). d) Appropriate undercoats and whether thickness measurements are to be carried out (see clause6 andTable 2). e) Requirements for corrosion resistance and/or freedom from porosity, the methods of test to be used, and whether the testing is to be carried out in the presence or absence of an a
29、nti-tarnish treatment (see7.7). f) The microhardness of the coating and the method of test, selected from BS5411-6, to be used (see7.6). g) Requirements for solderability and the method of test to be used (see7.8). h) Requirements for anti-tarnish treatments, the type of treatment and the methods of
30、 test to be used (see clause8). i) The positions where unavoidable contact marks and other defects are acceptable (see7.2) and also the positions where reinforcement is required (see7.3).BS4290:1989 2 BSI 07-1999 4 Basis material The nature of the basis material, its surface condition and roughness
31、shall, if appropriate, be specified by the purchaser see3.2 c). If the purchaser supplies the basis material, the electroplater shall be notified of any lead content see3.2 c). NOTEThis standard does not specify requirements for the condition, finish or surface roughness of the basis material prior
32、to electroplating. However, it should be recognized that the surface roughness of the silver or silver alloy coating will be dependent on the initial surface roughness of the basis material and this should not therefore be cause for rejection of the silver coating. 5 Coating classification code 5.1
33、The purchaser shall supply the following information to the electroplater by quoting the appropriate classification code described in5.2 see also3.1 c): a) the chemical identity of the basis material; b) if appropriate, the nature of the undercoat metal and its thickness (see clause6); c) the minimu
34、m silver content by mass of the coating, if the coating is not to be a pure silver coating (see7.4); d) the minimum thickness, in micrometres, of the silver or silver alloy coating on the significant surface (see7.3). Table 1 Summary of information required Information required Relevant clauses Othe
35、r related clauses Essential information Additional information, if required Reference (i.e. the number of this BritishStandard) 3.1 a) Significant surface 3.1 b) 7.2, 7.3 Coating classification code 3.1 c) clauses5 and6, 7.3, 7.4 Final appearance 3.1 d) clause4, 7.2 Adhesion 3.1 e) 7.5 Sampling 3.1
36、f) Method of determination of silver content 3.2 a) 7.4 Composition 3.2 a) clause5, 7.4 3.2 b) Basis material 3.2 c) clause4 Undercoats 3.2 d) clause6 Corrosion resistance/freedom from porosity 3.2 e) 7.7 Microhardness 3.2 f) 7.6 Solderability 3.2 g) 7.8 Anti-tarnish treatment 3.2 h) clause8 Positio
37、ns where defects or contact marks are acceptable 3.2 i) 7.2BS4290:1989 BSI 07-1999 3 5.2 The coating classification code consists of four parts, the first two of which are separated by an oblique stroke, as follows: a/b c d where 5.3 Examples of complete classification codes are as follows: Cu/Ag (9
38、5.0) 10 (i.e. a coating having a specified silver content of at least95.0% by mass and a thickness of104m (minimum) on brass or copper); Zn/Cu 8 Ni10 Ag (98.0)5 (i.e. a coating having a specified silver content of at least98.0% by mass and a thickness of54m (minimum) on die-cast zinc alloy, using an
39、 undercoat of104m nickel on one of84m copper). 6 Undercoats NOTE 1Undercoats may be necessary on any basis material for the following reasons: a) to improve the corrosion resistance of the coating; b) to improve the adhesion of the coating; c) to reduce the risk of diffusion through the coating; d)
40、to reduce the risk of contamination of the electrolyte by the basis material; e) to improve the solderability of the coating and the retention of solder; f) to reduce the surface roughness of the coating; g) to reduce the porosity of the coating. Typical undercoats used are copper, nickel and combin
41、ations of these metals. NOTE 2Mercury compounds should not be used in the pretreatment of basis materials. To promote good adhesion, it is usual to deposit a silver strike coating prior to the main silver deposition. NOTE 3For arduous conditions of service, thicknesses greater than the minimum value
42、s given inTable 2 may be required. Table 2 gives appropriate undercoats for use with silver and silver alloy decorative and protective coatings. Any other undercoats required for special purposes shall also be specified by the purchaser. If thickness measurements on any undercoats are specified by t
43、he purchaser see3.2 d) they shall be carried out using either the microscopical method described in BS5411-5 or the coulometric method described in BS5411-4. 7 Coatings 7.1 General The tests for coating thickness, composition, adhesion and microhardness given in7.3 to7.6 shall be carried out in the
44、absence of any anti-tarnish treatment (clause8). If a test for corrosion resistance and/or freedom from porosity (see7.7) is specified the purchaser shall specify whether it is to be carried out in the presence or absence of an anti-tarnish treatment. 7.2 Appearance Inspection of the coating shall b
45、e made at a magnification of 8 in normal daylight to ensure that it is clean and free from damage, that the significant surface is free from electroplating defects, such as pits, roughness, cracks or uncoated areas and not stained or discoloured and that no surface of the article shows blistering or
46、 other signs of poor adhesion. a indicates the chemical symbol for the basis metal or the principal metal of an alloy or, in the case of non-metallic materials, the letters NM; b indicates the chemical symbol for the undercoat metal followed by a figure for its minimum coating thickness (in micromet
47、res). It is omitted if no undercoat is required. Examples of chemical symbols are as follows: Ni nickel Cu copper Cu Ni nickel on copper (the undercoat thickness, in micrometres, follows the symbol for each metal) Sn-Ni tin-nickel alloy; c indicates the chemical symbol for silver, Ag, followed, if s
48、pecified by the purchaser, by a number in parentheses representing the minimum silver content of the silver coating, expressed as a percentage by mass to one decimal place. Absence of this number indicates a pure silver coating; d indicates the minimum thickness (in micrometres) of the silver or sil
49、ver alloy coating on the significant surface.BS4290:1989 4 BSI 07-1999 Table 2 Appropriate undercoats for use with silver and silver alloy decorative and protectivecoatings NOTEOn articles where a contact mark or other defect on the significant surface, is unavoidable, its position should be agreed between the purchaser and the electroplater see3.2 i). If required by the purchaser, a preliminary sample with the required finish shall be supplied by the electroplater for approval by the purchaser see3.1 d). 7.3 Thickness Silver coatings are classified by
