1、BRITISH STANDARD CONFIRMED SEPTEMBER1989 BS 6338:1982 ISO 4520:1981 Specification for Chromate conversion coatings on electroplated zinc and cadmium coatings UDC 669.058:669.585.7 + 669.738.57:661.875.274.7/.8BS6338:1982 This British Standard, having been prepared under the directionof the Surface C
2、oatings (other than Paints) Standards Committee, was published underthe authority of the Board ofBSI and comes into effect on 31 December 1982 BSI 07-1999 The following BSI references relate to the work on this standard: Committee reference SRC/9 Draft for comment 77/50321 DC ISBN 0 580 13108 4 Coop
3、erating organizations The Surface Coatings (other than Paints) Standards Committee, under whose direction this British Standard was prepared, consists of representatives from the following: Aluminium Federation Assay Offices Committee of Great Britain Association of Metal Sprayers British Constructi
4、onal Steelwork Association British Jewellers Association British Jewellery and Giftware Federation Ltd. British Metal Finishing Suppliers Association* British Steel Industry Chemical Industries Association Electricity Supply Industry in England and Wales Engineering Equipment Users Association Galva
5、nizers Association Greater London Council Institute of Metal Finishing* Institute of Sheet Metal Engineering* Institute of Vitreous Enamellers Institution of Corrosion Science and Technology Metal Finishing Association* Ministry of Defence Motor Cycle Association of Great Britain Society of Motor Ma
6、nufacturers and Traders Limited* Vitreous Enamel Development Council Zinc Development Association The organizations marked with an asterisk in the above list, together with the following, were directly represented on the Technical Committee entrusted with the preparation of this British Standard: El
7、ectronic Engineering Association Magnesium Industry Council Telecommunication Engineering and Manufacturing Association Amendments issued since publication Amd. No. Date of issue CommentsBS6338:1982 BSI 07-1999 i Contents Page Cooperating organizations Inside front cover National foreword ii 0 Intro
8、duction 1 1 Scope and field of application 1 2 References 1 3 Method of application of chromate conversion coatings 1 4 Classification 1 5 Requirements 1 Table 1 Classification of chromate conversion coatings 2 Table 2 Requirements for corrosion resistance 2 Publications referred to Inside back cove
9、rBS6338:1982 ii BSI 07-1999 National foreword This British Standard has been prepared under the direction of the Surface Coatings (other than Paints) Standards Committee. It is identical with ISO4520“Chromate conversion coatings on electroplated zinc and cadmium coatings”, prepared with the active p
10、articipation and approval of the UnitedKingdom, by Sub-committee 3, Electrodeposited coatings and related finishes, of Technical Committee 107, Metallic and other non-organic coatings, and published in 1981 by the International Organization for Standardization (ISO). Terminology and conventions. The
11、 text of the international standard has been approved as suitable for publication as a British Standard without deviation. Some terminology and certain conventions are not identical with those used in British Standards; attention is drawn especially to the following. The comma has been used as a dec
12、imal marker. In British Standards it is current practice to use a full point on the baseline as the decimal marker. Wherever the words “International Standard” appear, referring to this standard, they should be read as “British Standard”. A related standard for ISO 2081:1973 and ISO 2082:1973, refer
13、red to in clause 1 for information only, is BS 1706:1960 “Electroplated coatings of cadmium and zinc on iron and steel”. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance wit
14、h a British Standard does not of itself confer immunity from legal obligations. Cross-references International standard Corresponding British Standard ISO 3613-1980 BS 5411 Methods of test for metallic and related coatings Part 13:1982 Chromate conversion coatings on zinc and cadmium (Identical) ISO
15、 3768-1976 BS 5466 Methods for corrosion testing of metallic coatings Part 1:1977 Neutral salt spray test (NSS test) (Identical) ISO 3892-1980 BS 5411 Methods of test for metallic and related coatings Part 14:1982 Gravimetric method for determination of coating mass per unit area of conversion coati
16、ngs on metallic materials (Identical) Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 and 2, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicat
17、ed in the amendment table on the inside front cover.BS6338:1982 BSI 07-1999 1 0 Introduction Coatings of zinc and cadmium are chromate treated in order to retard the formation of corrosion products on the surfaces of coatings exposed in corrosive atmospheres. Chromate treatment is particularly effec
18、tive in retarding the formation of white corrosion products which form on zinc and cadmium coatings under certain conditions. Thicknesses of electroplated coatings suitable for chromate treatment are covered by the relevant International Standards, i.e. ISO 2081 and ISO2082. 1 Scope and field of app
19、lication This International Standard specifies requirements relating to chromate conversion coatings on zinc and cadmium intended to give protection against corrosion. Finishes for giving particular colours only or specifically to improve paint adhesion are not covered by this International Standard
20、. 2 References ISO 2081, Metallic coatings Electroplated coatings of zinc on iron and steel. ISO 2082, Metallic coatings Electroplated coatings of cadmium on iron and steel. ISO 3613, Chromate conversion coatings on zinc and cadmium Test methods. ISO 3768, Metallic coatings Neutral salt spray test (
21、NSS test). ISO 3892, Conversion coatings on metallic materials Determination of coating mass per unit area Gravimetric methods 3 Method of application of chromate conversion coatings Chromate conversion coatings are normally applied by dipping. Chromating solutions are usually acidic and contain hex
22、avalent chromium salts together with other salts which may be varied to affect the appearance and hardness of the film. The colour of the film, and, therefore, the type of conversion coating, depends on the composition of the chromating solution, but is also affected by pH and temperature, the durat
23、ion of treatment and the nature and surface condition of the coating being treated. Bright, transparent films on zinc and cadmium coatings can be obtained by dipping in appropriate solutions. On zinc, they can also be obtained by bleaching iridescent films in alkaline solutions or in phosphoric acid
24、. If hot water is used as the final rinse after the chromating process, it is essential that the time of rinsing should be kept as short as possible in order to prevent the dissolution of the hexavalent chromium. The drying of the article shall be carried out at a temperature not exceeding 60 C to p
25、revent cracking due to dehydration of the chromate coating. (Any heat treatment for the relief of hydrogen embrittlement shall be carried out before a chromate conversion coating is applied.) 4 Classification Finishes can be applied ranging from thick, dark, olive-green coatings with good protective
26、 properties to thin, transparent, sometimes bluish films of attractive appearance but with limited protective value. Electroplaters can seldom guarantee to supply exact shades of colour with chromate conversion coatings. If it is necessary to have exact shades of colour, it is possible to dye bleach
27、ed chromate coatings to obtain a wide range of colours, but they can only be expected to give an order of added corrosion resistance similar to that provided by the colourless bleached coatings. Finishes are divided into two classes, each of which comprises two types; their most important characteri
28、stics are listed in Table 1. Finishes may be characterized by class alone or by class and type designation. Typical examples are: a) Fe/Cd 8 c 2 b) Fe/Zn 25 c 1A where Fe refers to the basis metal (iron or steel; Cd and Zn refer to the electroplated coating (cadmium or zinc); 8 and 25 are the thickn
29、esses, in micrometres, of the cadmium and zinc coatings; c refers to the chromate conversion coating; 2 and 1 are the classes of the chromate conversion coatings; A designates the type of chromate conversion coating. 5 Requirements 5.1 General Chromate conversion coatings harden with age by gradual
30、dehydration. They should, therefore, be handled carefully for the first 24 h after treatment, and any tests (including corrosion tests) shall be deferred until the expiry of that period.BS6338:1982 2 BSI 07-1999 5.2 Adhesion of coloured coatings Coloured coatings shall be adherent and shall be teste
31、d by one of the methods specified in ISO 3613. 5.3 Corrosion resistance When subjected to the neutral salt spray test specified in ISO 3768, the time for formation of white corrosion products on chromated cadmium or zinc coatings shall not be less than the values given in Table 2. NOTEThese requirem
32、ents are not applicable to the edges of the test specimen. Table 1 Classification of chromate conversion coatings Table 2 Requirements for corrosion resistance Class Designation a Type Typical appearance Coating mass per unit area g/m 2(see ISO 3892) Corrosionprotection A Clear Transparent clear, so
33、metimes with a bluish tinge u 0,5 Slight, for example against staining during handling or against high humidity in mildly corrosive conditions 1 B Bleached Transparent with slight iridescence u 1,0 2 C Iridescent Yellow iridescent 0,5 to 1,5 inclusive Considerable, including protection against certa
34、in organic vapours D Opaque Olive green, shading to brown or bronze 1,5 a In addition, black coatings can be produced by several methods. Such coatings may have different degrees of corrosion protection and may also differ in coating mass per unit area. Designation Possible classifications a Minimum
35、 time to formation of white corrosion products, h A 1, 1A 6 B 1B 24 C 2, 2C 72 D 2D 96 a See clause 4, which describes how finishes may be characterized by class alone or by class and type designation.BS6338:1982 BSI 07-1999 Publications referred to See national foreword.BS 6338:1982 ISO 4520:1981 B
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