1、BRITISH STANDARD BS 4479-3: 1990 Design of articles that are to be coated Part 3: Recommendations for conversion coatings UDC 672/673:621.795:006BS4479-3:1990 This British Standard, having been prepared under the directionof the Surface Coatings (other than Paints) Standards Policy Committee, was pu
2、blished under the authority of the Board ofBSI and comes into effect on 31July 1990 BSI 08-1999 First published as BS 4479 August1969 First revision as BS 4479-3 July1990 The following BSI references relate to the work on this standard: Committee reference SRC/10 Draft for comment 86/53488 DC ISBN 0
3、 580 17901 X 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/10, upon which the following bodies were represented: British Anodising Assoc
4、iation Institute of Metal Finishing Institute of Sheet Metal Engineering Institute of Vitreous Enamellers International Tin Research Institute Metal Finishing Association Welding Institute Zinc Development Association Amendments issued since publication Amd. No. Date CommentsBS4479-3:1990 BSI 08-199
5、9 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Definitions 1 3 General 1 4 Design considerations 1 Appendix A Diagrams illustrating preferred and deprecated design features for articles to be conversion coated 3 Figure 1 Drainage 3 Figure 2 Hollow sections 3 Figu
6、re 3 Tubes 4 Publications referred to Inside back coverBS4479-3:1990 ii BSI 08-1999 Foreword This Part of BS4479has been prepared under the direction of the Surface Coatings (other than Paints) Standards Policy Committee and is based on a draft prepared by the Institute of Metal Finishing. The BSI T
7、echnical Committee acknowledges the contribution to this revision by the Institute 1)and by the Committee for the Promotion of Electroplating. This Part of BS4479is one of a series of Parts which together form a revision of BS4479:1969. On publication of all the Parts, BS4479:1969will be withdrawn.
8、This revision of BS4479 comprises the following Parts: Part 1: General recommendations; Part 2: Recommendations for electroplated and autocatalytic coatings; Part 3: Recommendations for conversion coatings; Part 4: Recommendations for paint coatings and varnish coatings; Part 5: Recommendations for
9、anodic oxidation coatings; Part 6: Recommendations for hot dip metal coatings; Part 7: Recommendations for thermally sprayed coatings; Part 8: Recommendations for vitreous enamel coatings; Part 9: Recommendations for low pressure and vacuum deposited coatings. BS4479is directed towards helping to ma
10、ximize the benefit obtained from coating processes. There is a wide variety of coating processes, developed and established industrially, intended to enhance or transform the surfaces of manufactured articles. However, time and money are often wasted because the design of many articles is unsuitable
11、 for the coating process to be applied. Coating is only one part of the manufacturing process and should not be ignored, or viewed in isolation, when considering the overall costs and quality. This revision of BS4479has been undertaken to extend the range of coating processes covered. It is not inte
12、nded to cover every conceivable design detail, type of article or service condition. Adherence to the general principles described will, however, greatly assist in the achievement of the desired results. In any case of doubt or difficulty, specialist advice in the particular type of process being co
13、nsidered should be sought. This Part of BS4479is not a specification and should not be used as such. The recommendations are intended to provide guidance towards good practice. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are r
14、esponsible 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, pages i and ii, pages1to4, an inside back cover and a back cover. This standard has b
15、een updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. 1) Institute of Metal Finishing.BS4479-3:1990 BSI 08-1999 1 1 Scope This Part of BS4479gives recommendations for the design of metal parts that are to b
16、e conversion coated. NOTE 1Conversion coatings are commonly associated with other coating processes, e.g. chromate passivation after zinc or cadmium electroplating or phosphate coating prior to painting. In such cases, attention is drawn to Parts2and4of this standard which deal with the design of el
17、ectroplated and paint coated articles respectively. NOTE 2It is recommended that Part1of BS4479be read in conjunction with this Part. Part1includes a list of British Standards relating to processes covered by BS4479but not necessarily referred to in each Part. NOTE 3The titles of the publications re
18、ferred to in this standard are listed on the inside back cover. 2 Definitions For the purposes of this Part of BS4479, the following definitions apply. 2.1 conversion coating a coating produced by means of a conversion treatment (see2.2) 2.2 conversion treatment a chemical or electrochemical process
19、 of producing a coating (conversion coating) consisting of a compound of the surface metal NOTE 1Conversion coatings frequently used are, for example, chromate films on zinc and cadmium, or oxide and phosphate coatings on steel. NOTE 2Anodic oxidation coating of aluminium and other metals, while sat
20、isfying this definition, is not referred to as a conversion treatment. 2.3 phosphate conversion coating a conversion coating comprising a layer of insoluble phosphates on a metal surface formed from an agent containing phosphoric acid and/or phosphates 2.4 chromate conversion coating a conversion co
21、ating obtained on a metal surface by means of treatment with a solution containing chromium compounds in the hexavalent form 3 General It is essential that the design of any article required to be coated should take into account not only the function of the article and its method of manufacture but
22、also the limitations imposed by the coating. Articles to be conversion coated are immersed in, or sprayed with, a solution consisting mainly of phosphate, chromate, fluoride or oxalate salts. Phosphate coatings are normally applied to iron, carbon steel and low alloy steel to form the basis for furt
23、her coatings of paint, oils or waxes (seeBS3189). Phosphate coatings alone will only give limited in-plant storage protection. Chromate coatings are applied to zinc, cadmium, aluminium and magnesium (see BS1706and BS6338). Oxalate coatings are used on high alloy steels and stainless steel. Conversio
24、n coatings are generally very uniform over all surfaces. Articles may be handled on jigs, hooks, overhead conveyors, or by bulk treatment in barrels. Phosphate coatings can vary in thickness depending upon the processing conditions, type of process and nature of the surface and, with pretreatment, c
25、an significantly affect the dimensions of the article. Other conversion coatings are very thin and do not significantly change the dimensions. Careful consideration should be given to the effect of any heat treatment, e.g. de-embrittlement of high strength steels (above1000 N/mm 2 ). 4 Design consid
26、erations 4.1 General The design of articles to be conversion coated is comparable to that for parts requiring an electroplated or anodized coating, where solution entrapment can present a problem. Diagrams illustrating preferred and deprecated design features for articles to be conversion coated are
27、 given in Appendix A. 4.2 Method of processing The method of handling likely to be most suitable in view of the size and shape of the articles, e.g. jigs, hooks, rotary barrel, “still” or “tipping” basket should be considered. The design should, accordingly, take into account items a) to e) as appro
28、priate. a) The way the article will be held in the processing solutions and, more importantly, the way it will be suspended during rinsing, draining and drying should be considered. The article should be so designed that, in this position, liquid will not be trapped in or around hollows, seams, rive
29、ts, spot welds, rolled edges, etc. Alternatively, drainage holes may be provided where pockets of solution would otherwise be retained. b) The article should be so designed that, as far as possible, non-significant surfaces are the last to dry, i.e. any tendency for contamination and associated defe
30、cts should be confined to the least important surfaces.BS4479-3:1990 2 BSI 08-1999 c) Any shapes which could entrap air or evolved gases and prevent contact between surfaces to be coated and the cleaning, conversion coating and rinsing solutions should be avoided. If necessary, air holes, of a size
31、that will permit the articles to sink in a reasonable time and the evolved gases to escape rapidly, should be provided. d) If the cleaning, processing and rinsing solutions are to be sprayed on to the work through fixed jets, the article should be of such a shape that all parts can be reached by the
32、 sprays. e) When treating by immersion, local overloading of the bath can occur, particularly in the absence of agitation. Specialist advice should be sought on permissible load factors for various process types. 4.3 Process variations Different metals require different treatments but the following
33、general points should be noted. a) Generally, it is preferable to design composite articles for assembly after conversion coating rather than before. b) While in certain cases composite articles can be treated in the same solution, this usually necessitates modification of the processing details and
34、 expert advice should therefore be obtained. c) Composite articles containing copper base alloys should not be used, as copper can be taken into solution in the processing bath with adverse effects on the processing. 4.4 Dimensional changes 4.4.1 Where conversion coated parts are to be fitted togeth
35、er, e.g. screw threads, due allowance should be made for the thickness of the coating (seealsoBS3382-1 & BS3382-2). 4.4.2 The thickness of phosphate coatings on ferrous metals should not exceed8 m to10 m for the heavy coatings of approximately22g/m 2usually obtained from zinc or manganese phosphate
36、solutions (see BS3189). Other conversion coatings on non-ferrous metals should have a thickness of not greater than3 m. 4.5 Changes in mechanical properties Expert advice should always be obtained as to whether stress relieving of the article before processing is necessary. This is particularly impo
37、rtant when severely cold-worked articles or articles made from high tensile steel are to be treated and the latter may also require stress relief after processing. 4.6 Changes in surface characteristics The presence of a conversion coating, especially a phosphate coating, may interfere with resistan
38、ce or capacitor discharge welding. Soldering may also be seriously impeded. Conversion coatings, though not interfering with gas or arc welding or brazing, will be locally destroyed by these processes. The overall production sequence should be planned to avoid such difficulties.BS4479-3:1990 BSI 08-
39、1999 3 Appendix A Diagrams illustrating preferred and deprecated design features for articles to be conversion coated Diagrams illustrating preferred and deprecated design features for articles to be conversion coated are given in Figure 1 to Figure 3. NOTEProvision should be made for suspending the
40、 articles so that during drying there are no horizontal flat surfaces and drainage takes place on the outside from one bottom corner. Alternatively internal drainage holes should be provided. Figure 1 Drainage Figure 2 Hollow sectionsBS4479-3:1990 4 BSI 08-1999 NOTEProvision should be made to proces
41、s open-ended tubes at an angle to allow gases to escape and tubes to fill with processingsolution. Figure 3 TubesBS4479-3:1990 BSI 08-1999 Publications referred to BS 1706, Method for specifying electroplated coatings of zinc and cadmium. BS 3189, Specification for phosphate treatment of iron and st
42、eel. BS 3382, Specification for electroplated coatings on threaded components. BS 3382-1 & BS 3382-2, Cadmium on steel components. Zinc on steel components. BS 4479, Design of articles that are to be coated. BS 4479-1, General recommendations. BS 6338, Specification for chromate conversion coatings
43、on electroplated zinc and cadmium coatings. BS 4479-3: 1990 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitution BSI is the independent national body responsible for preparing BritishStandards. It presents the UK view on standards in Europe and at the international level. It is in
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