BS 4761-1971 Specification for sprayed unfused metal coatings for engineering purposes《工程用喷镀的未熔金属度层规范》.pdf

1、BRITISH STANDARD CONFIRMED MAY1988 BS4761:1971 Specification for Sprayed unfused metal coatings for engineering purposesBS4761:1971 This British Standard, having been approved by the Surface Coatings (other than Paints) Industry Standards Committee, was published under the authorityof the Executive

2、Boardon 18 August1971 BSI03-1999 The following BSI references relate to the work on this standard: Committee references SRE/6 SRE/6/3 Draft for comment69/35079 ISBN580 06574 X Co-operating organizations The Surface Coatings (other than Paints) Industry Standards Committee, under whose supervision th

3、is British Standard was prepared, consists of representatives from the following Government departments and scientific and industrial organizations: Aluminium Federation* Assay Offices Committee of Great Britain Association of Metal Sprayers* British Bolt, Nut, Screw and Rivet Federation British Ele

4、ctrical and Allied Manufacturers Association British Jewellers Association British Non-ferrous Metals Research Association* British Steel Industry* Chemical Industries Association Cycle and Motor Cycle Association limited Department of Trade and Industry* Electricity Council, the Central Electricity

5、 Generating Board andAreaBoardsinEnglandandWales* Electronic Engineering Association* Greater London Council Institute of Metal Finishing* Institute of Sheet Metal Engineers Institute of Vitreous Enamellers Metal Finishing Association Ministry of Defence, Army Department* Ministry of Defence, Navy D

6、epartment Society of Motor Manufacturers and Traders Limited* Tin Research Institute Vitreous Enamel Development Council Zinc Development Association* The Government departments and scientific and industrial organizations marked with an asterisk in the above list, together with the following, were d

7、irectly represented on the committee entrusted with the preparation of this British Standard: British Constructional Steelwork Association British Railways Board Institution of Civil Engineers Institution of Mechanical Engineers Institution of Structural Engineers Lloyds Register of Shipping London

8、Transport Executive Shipbuilders and Repairers National Federation Society of British Aerospace Companies Welding Institute Individual firms Amendments issued since publication Amd. No. Date CommentsBS4761:1971 BSI 03-1999 i Contents Page Co-operating organizations Inside front cover Foreword ii 1 S

9、cope 1 2 Design considerations 1 3 Information to be supplied to the metal sprayer 1 4 Preparation of components 1 5 Spraying 3 6 Inspection after spraying 4 7 Sealing 4 8 Finishing 4 9 Final inspection 4 Appendix A Method of preparation of a reference surface for comparison 5 Appendix B Bond coatin

10、g materials 5 Figure 1 Preparation and finishing of sprayed deposits at fillets 6 Figure 2 Preparation and finishing of sprayed deposits at oilways 7BS4761:1971 ii BSI 03-1999 Foreword In order to keep abreast of progress in the industries concerned, British Standards are subject to periodical revie

11、w. Suggestions for improvements will be recorded and in due course brought to the notice of the committees charged with the revision of the standards to which they refer. A complete list of British Standards, numbering over5000, fully indexed and with a note of the contents of each, will be found in

12、 the British Standards Yearbook, which may be purchased from BSI Sales Department. The BS Yearbook may be consulted in many public libraries and similar institutions. This standard makes reference to the following British Standards: BS410, Test sieves. BS427, Method for Vickers hardness test. BS2451

13、, Chilled iron shot and grit. BS2569, Sprayed metal coatings. BS2569-1, Protection of iron and steel by aluminium and zinc against atmospheric corrosion. BS2569-2, Protection of iron and steel against corrosion and oxidation at elevated temperatures. BS4495, Recommendations for the flame spraying of

14、 ceramic and cermet coatings. BS, Sprayed and fused metal coatings for engineering purposes. (In course of preparation.). This British Standard, prepared under the authority of the Surface Coatings (other than Paints) Industry Standards Committee, relates to the use of sprayed, unfused coatings of m

15、etals and metallic compounds in engineering applications, e.g.the reclamation of worn or over-machined components, and the treatment of new components, where such properties as wear-resistance, low coefficient of friction and load-bearing characteristics are important. BS . 1)covers the requirements

16、 for sprayed metals and metallic compounds which are fused after spraying. Of the other standards in this series, BS2569-1 2)deals with the use of sprayed aluminium and zinc coatings for the protection of iron and steel against atmospheric corrosion, BS2569-2 2)covers sprayed aluminium, aluminium al

17、loy and nickel-chromium alloys against high temperature oxidation and BS4495 3)gives recommendations for the flame spraying of ceramic, cermet and related coatings for a wide range of protective and engineering applications. NOTEThis standard is expressed in metric terms. For further information ref

18、erence should be made to BS3763, “International System (SI) units”, and PD5686, “The use of SI units”. 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 with a British Standa

19、rd 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 to7 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated

20、 in the amendment table on theinside front cover. 1) BS , “Sprayed and fused metal coatings for engineering purposes”, (in course of preparation). 2) BS2569, “Sprayed metal coatings”, Part1, “Protection of iron and steel by aluminium and zinc against atmospheric corrosion”, Part2, “Protection of iro

21、n and steel against corrosion and oxidation at elevated temperatures”. 3) BS4495, “Recommendations for the flame spraying of ceramic and cermet coatings”.BS4761:1971 BSI 03-1999 1 1 Scope This British Standard gives requirements for sprayed, unfused coatings of metals and metallic compounds for engi

22、neering purposes applied by such processes as combustion gas flame, electric arc, plasma arc and detonation processes. It does not include requirements for coatings applied for protection against corrosion and oxidation which are covered by BS2569 4) . 2 Design considerations To ascertain whether a

23、sprayed metal coating should be applied for the intended engineering purpose, consideration shall be given to the factors outlined in2.1 to2.3. 2.1 Basis metal 2.1.1 As sprayed metal does not add any significant tensile strength to the part, the effects of any reduction of the original dimensions of

24、 the component should be considered. 2.1.2 The fatigue strength or shock resistance may be affected by the method of surface preparation. 2.1.3 With steel parts that have been surface hardened, removal of the hard layer, or the use of a suitable bonding coat before reclamation, is necessary. 2.1.4 T

25、he surface to be coated is required to be accessible for preparation and spraying. 2.2 Coating metal 2.2.1 The properties required in the final deposit, hardness and resistance to various wear forces, corrosion-resistance, coefficient of friction, compatibility with the mating surface, degree of por

26、osity, machinability, type of finish, etc., determine the choice of coating metal. 2.2.2 Sprayed metal coatings possess little ductility; it is most important that this fact is borne in mind when sprayed components are subjected to considerable strain, e.g.through bending or torsion. 2.2.3 Surface p

27、reparation produces an irregular contour on the basis metal. The required thickness, i.e.the minimum distance between the peaks on the substrate and the sprayed surface, should be specified. 2.3 Service conditions 2.3.1 Sprayed coatings are capable of supporting heavy loads but they are unsuitable f

28、or point or line-loading, e.g.needle bearings. 2.3.2 Sprayed coatings are porous. This is a great advantage in some applications. If porosity is unacceptable the coating is sealed with a suitable sealant. 2.3.3 Sprayed surfaces in contact with bearing materials of aluminium alloy or copper-lead requ

29、ire special precautions, e.g.sealing prior to machining and removal of grinding debris, to prevent seizure in operation. 3 Information to be supplied to the metal sprayer The metal sprayer shall be supplied with the following information. Inability to supply any of this information shall be reason f

30、or consultation and agreement between the contracting parties. 1) The number of this British Standard, i.e.BS4761. 2) The nominal composition, or specification, and metallurgical condition of the basis metal. 3) An assurance that all parts have been inspected for cracks or other defects and have bee

31、n found satisfactory. 4) The maximum allowable reduction in original dimensions, prior to spraying, to ensure sufficient strength in the component to withstand subsequent working stresses. 5) The intended service conditions of the sprayed component. 6) The method of surface preparation. 7) The coati

32、ng metal to be used. 8) The areas to be sprayed and the areas to be masked. 9) The final thickness required after finishing. 10) Any requirements for finishing or sealing the coating. 11) Inspection requirements, including the processing of any test pieces. 4 Preparation of components 4.1 Initial su

33、rvey 4.1.1 Preliminary examination. All parts for treatment shall be sufficiently clean for visual and dimensional examination. 4.1.2 Cleanliness for processing. All components intended for metal spraying shall be free from surface contamination, such as oil, grease, etc., which might be transferred

34、 to the surface ultimately to be sprayed. 4) BS 2569, “Sprayed metal coatings”, Part 1, “Protection of iron and steel by aluminium and zinc against atmospheric corrosion”, Part 2, “Protection of iron and steel against corrosion and oxidation at elevated temperatures”.BS4761:1971 2 BSI 03-1999 It is

35、extremely important that the surfaces to be sprayed are not subsequently contaminated in any way by oil, grease, dust, dirt, water or finger-marks, after the preparation work has been completed, and care shall be taken at all stages to prevent contamination, in the event of contamination the surface

36、 shall be re-prepared as necessary. 4.1.3 Previous coating. Any previous unfused coatings shall be removed prior to preparation of the surface to be sprayed. 4.2 Preliminary machining 4.2.1 Where the surface of the component is machined as part of the surface preparation, the form of ends or edges o

37、f the prepared area shall be suitable for the coating process. 4.2.2 For components subjected essentially to static loading, it is permissible that each edge may be machined to an angle of90 to135 to the surface with a radius at the root. This root radius shall be not less than half of the depth of

38、the deposit or0.75mm whichever is the greater. 4.2.3 When components are subjected to dynamic stresses in service, e.g.cycling or shock loading, the ends and edges of the prepared area shall have a generous radius or a taper not greater than30 to the surface, being blended to a smooth contour (seeFi

39、gure 1). In addition, the original design chamfer or radius shall be reground at the edges of any oil hole (seeFigure 2). 4.2.4 Irrespective of the type of loading, the ends and edges of the machined preparation on an important strength component shall stop short of any area of stress concentration,

40、 e.g.fillet radius, etc., (seeFigure 1). 4.2.5 It is important that an evenly deposited thickness of sprayed metal is applied. Rotating or cylindrical reciprocating components, which require machining before spraying to allow for an adequate thickness of sprayed deposit, shall be machined concentric

41、 to the relevant axis. 4.3 Methods of preparation 4.3.1 General. The surface preparation shall be by one of the following methods: 1) Grit blasting. 2) Grit blasting followed by the application of a bond coating. 3) Threading or grooving followed by grit blasting with or without a bond coating. Thre

42、ading or grooving shall not be used for coatings less than0.8mm thick when finished. Threading or grooving without grit blasting shall only be used by agreement between the contracting parties. NOTEExcept when high duty, dynamically loaded components, e.g.crankshafts, are treated (when notching by t

43、hreading may seriously affect the fatigue resistance) surfaces to be sprayed may be prepared by V threading or grooving or U threading or grooving. Where grit blasting follows these methods, it is essential that care be taken to ensure that grit is not trapped in the threads. In the case of V thread

44、ing or grooving, surfaces may be prepared by cutting a60 thread of approximately1mm pitch (or its equivalent on flat surfaces). It is essential that the point of the tool be slightly radiused and, for rotating components, mounted below the centre to give a rough, torn or ragged appearance. For flat

45、surfaces a tool with a slightly negative rake may be used. In the case of U threading or grooving, surfaces may be prepared by cutting a U section thread of1.8mm to2.1mm pitch for steel or1.8mm to2.5mm pitch for cast iron (or their equivalent on flat surfaces). The width of the lands should be less

46、than the width of the grooves and the depth of the grooves approximately equal to their width. 4.3.2 Keyways. For the preparation of a location including keyways, methods2) or3) in4.3.1 shall be used. 4.3.3 Hardened or otherwise treated surfaces. When hardened or otherwise treated surfaces are remov

47、ed before preparation, any of the methods given in 4.3.1 may be used. Consideration shall be given to the danger of removing treated surfaces where the treatment has been applied for purposes other than wear resistance, e.g.for fatigue resistance or corrosion resistance. When a hard surface is not r

48、emoved or is not removable, preparation shall be by method2) in4.3.1. 4.4 Grit blasting 4.4.1 General. Grit blasting shall produce a uniform surface of sharp frosted appearance. Sheen on grit-blasted surfaces, produced by over-blasting, by blasting at an acute angle to the surface or by using blunt

49、abrasive, shall not be present, except on very hard surfaces, in which case it shall be followed by bond coating. NOTEAn indication of the appearance of the surface required may be obtained by preparing a reference surface by the method described inAppendix A. For grit blasting surfaces prepared by threading or grooving, aluminium oxide shall be used of a size such that100% passes a5004m aperture test sieve 5)and at least80% is retained on a1804m aperture test sieve 5) . 4.4.2 Abrasives and pressures 4.4.2.1 General. Abrasives shall always be sharp and clean. Abrasive sig