1、BRITISH STANDARD BS 4950:1973 Specification for Sprayed and fused metal coatings for engineering purposes UDC 669.058.67BS4950:1973 The British Standard, having beenapproved by the Surface Coatings (other than Paints) Industry Standards Committee, was published under the authority of the Executive B
2、oard on 25 July1973 BSI 09-1999 The following BSI references relate to the work on this standard: Committee reference SRE/6/3 Draft for comment 71/41779 ISBN 0 580 07854 X Co-operating organizations The Surface Coatings (other than Paints) Industry Standards Committee, under whose supervision this B
3、ritish Standard was prepared, consists of representatives from the following Government departments and scientific and industrial organizations: The Government departments and scientific and industrial organizations marked with an asterisk in the above list, together with the following, were directl
4、y represented on the committee entrusted with the preparation of this British Standard: Aluminium Federation* Electronic Engineering Association* Assay Offices Committee of Great Britain Engineering Equipment Users Association Association of Metal Sprayers* Greater London Council British Bolt, Nut,
5、Screw and Rivet Institute of Metal Finishing* Federation Institute of Sheet Metal Engineers British Jewellers Association Institute of Vitreous Enamellers British Metal Finishing Suppliers Metal Finishing Association Association Ministry of Defence, Army Department* British Non-ferrous Metals Resear
6、ch Ministry of Defence, Navy Department Association* Ministry of Defence, Procurement Executive* British Steel Industry* Society of Motor Manufacturers and Traders Chemical Industries Association Limited* Cycle and Motor Cycle Association Limited Tin Research Institute Electricity Council, the Centr
7、al Electricity Vitreous Enamel Development Council Generating Board and Area Boards in Zinc Development Association* England and Wales* British Constructional Steelwork Association London Transport Executive British Railways Board Shipbuilders and Repairers National Department of Trade and Industry,
8、 National Federation Engineering Laboratory Society of British Aerospace Companies Institution of Civil Engineers Telecommunication Engineering and Institution of Mechanical Engineers Manufacturing Association Limited Institution of Structural Engineers Welding Institute Lloyds Register of Shipping
9、Individual firms Amendments issued since publication Amd. No. Date CommentsBS4950:1973 BSI 09-1999 i Contents Page Co-operating organizations Inside front cover Foreword ii 1 Scope 1 2 Design considerations 1 3 Information to be supplied to the metal sprayer 1 4 Coating metals 1 5 Preparation of com
10、ponents 2 6 Spraying 3 7 Fusing the sprayed deposit 3 8 Cooling 3 9 Finishing 4 10 Final inspection 4 Appendix A Method of preparation of a reference surface for comparison 5 Figure 1 Recommended preparation for a sprayed and fused deposit near the centre of a shaft 5 Figure 2 Recommended preparatio
11、n of a shaft where thereisalargeincreasein diameter adjacent to the sprayed and fused area 6 Publications referred to Inside back coverBS4950:1973 ii BSI 09-1999 Foreword This British Standard, prepared under the authority of the Surface Coatings (other than Paints) Industry Standards Committee, rel
12、ates to the application of sprayed and fused coatings of metal alloys and metallic compounds for engineering applications where such properties as wear-resistance, low coefficient of friction and corrosion-resistance are important, and also for the reclamation of worn or over-machined components. Th
13、is standard differs from BS4761, “Sprayed unfused metal coatings for engineering purposes” in that, as the coating is fused to the base, it is not subject to the same restrictions regarding point loading and adhesion. The other standards in this series are: BS 2569, “Sprayed metal coatings”: Part 1,
14、 “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”. BS 4495, “Recommendations for the flame spraying of ceramic and cermet coatings”. NOTEThis standard is expressed in me
15、tric terms. For further information reference should be made to BS 3763, “The International System of units (SI)” and to 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 corr
16、ect 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, pages 1 to 6, an inside back cover and a back cover. This standard has been updated (see copyr
17、ight date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS4950:1973 BSI 09-1999 1 1 Scope This British Standard relates to the requirements for sprayed coatings, subsequently fused at temperatures approximately within the range1000
18、 1200 C, of self-fluxing metals and metallic compounds for engineering purposes applied by combustion gas flame and arc processes. In general the process is applied to ferrous base metals although some alloys having a sufficiently high melting temperature, e.g.some nickel base alloys, are suitable.
19、NOTEThe titles of the BSI publications referred to in this Standard are listed on the inside back cover. 2 Design considerations To ascertain whether a sprayed and fused metal coating should be applied for the intended engineering purpose, consideration shall be given to the factors in the following
20、 sub-clauses. 2.1 Basis metal 2.1.1 As the process involves heating to fuse the coating to the base, consideration should be given to the effect of such heating on the basis metal, including distortion, scaling, metallurgical changes and alteration to the mechanical properties. 2.1.2 As sprayed and
21、fused metal coatings may have physical properties differing from those of the basis metal, the effects of any reduction of the original dimensions of the component should be considered. 2.1.3 The fatigue strength or shock resistance of the component may be altered by the properties of the coating, c
22、onditions of application or the removal of previous surface treatments. 2.1.4 With parts that have had previous treatments such as nitriding or carburizing, removal of the affected layer will normally be necessary before treatment. 2.1.5 The surface to be coated has to be accessible for preparation
23、and spraying. 2.2 Coating metal 2.2.1 The properties required in the final deposit, e.g.coefficient of friction, compatibility with the mating surface under service conditions, machineability, hardness and resistance to wear and corrosion, etc.determine the choice of coating metal. 2.2.2 The ductili
24、ty of sprayed and fused metal coatings may vary over a wide range according to their composition, and this should be borne in mind when sprayed components are subjected to considerable strain, e.g.through bending or torsion. 2.2.3 When basis metals showing a martensitic change at low temperature are
25、 to be coated, coating materials with a low coefficient of expansion or high ductility shall be used. Special cooling procedures may be necessary. 2.3 Finish machining. As the process involves heating the component to a high temperature, it is preferable to complete the coating process before finish
26、 machining the entire component. 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 for prior consultation and agreement between the parties concerned. 1) the number of this
27、 British Standard, i.e.BS 4950 2) the nominal composition or specification, and metallurgical condition of the basis metal 3) when the process is being used for reclamation, the maximum allowable reduction in original dimensions prior to application of the coating 4) details of any previous surface
28、treatment 5) an assurance that all parts have been inspected for cracks or other defects and have been found satisfactory 6) the intended service conditions of the coated component 7) the coating metal to be used 8) the areas to be coated 9) the final thickness required after coating, with or withou
29、t finishing 10) any requirements for finishing the coating 11) inspection requirements, including the processing of any test pieces. 4 Coating metals 4.1 General. The composition of the coating metal shall be the subject of agreement. No change in the material used shall be permitted without prior c
30、onsent. The physical characteristics of the powder or of the flexible or rigid rod used for spraying shall be appropriate to the particular spraying apparatus employed.BS4950:1973 2 BSI 09-1999 4.2 Composition. The coating metals, generally known as “self-fluxing alloys”, shall contain sufficient ac
31、tive constituents to combine with and wet the surfaces to which they are applied when raised to their melting temperatures. They contain as their principal constituents nickel and/or cobalt with the addition of silicon and/or boron. Modifications to physical properties may be made by the addition of
32、 other alloying elements, e.g.chromium, tungsten, copper and molybdenum. Admixtures may be made with other metallic compounds e.g.tungsten carbide. NOTECoatings in the hardness range1268Rockwell C can be obtained by selection from a number of available proprietary materials. 5 Preparation of compone
33、nts 5.1 Initial survey 5.1.1 Preliminary examination. All parts for treatment shall be sufficiently clean for visual and dimensional examination. 5.1.2 Cleanliness for processing. All components intended for metal spraying shall be free from surface contamination, such as oil, grease, etc., which mi
34、ght be transferred to the surface ultimately to be sprayed. Particular attention shall be paid to porous components, e.g.cast iron components, where oil or grease in the pores may exude during fusion. 5.1.3 Previous coating. All types of previous surface treatments, including unfused coatings shall
35、be removed prior to preparation of the surface to be sprayed, except that any previous fused coating, if compatible, may be retained by agreement. 5.2 Preliminary machining 5.2.1 Where the surface of the component is machined as part of the surface preparation, the machined surface and the form of e
36、nds, or edges, of the prepared area shall be suitable for the coating process. Where the coating is required to terminate at a point other than the end or edge of the component, the edge of the recess shall be machined to an angle of3045 blending smoothly into the smaller diameter or lower level (se
37、eFigure 1 and Figure 2). In new work, where the coating must finish to a square edge, the relevant edge of the component shall be left larger than the finished overall size and then machined to final length after the coating has been completed in all respects. 5.2.2 It is desirable that an evenly de
38、posited thickness of sprayed metal is applied before fusion and any required machining shall be such as to ensure that the final deposit is uniform. 5.3 Method of surface preparation. The surface preparation shall be by grit blasting with chilled iron grit or aluminium oxide abrasive. Chilled iron g
39、rit shall be used where the surface hardness of the area to be prepared is less than300HB (320HV, 33HRC) and aluminium oxide grit shall be used for surfaces of hardness exceeding this value. Where the surface hardness exceeds450HB, by agreement between the parties, the component shall be softened by
40、 heat treatment prior to blasting or special precautions taken during the application of the coating. 5.3.1 General. Grit blasting shall produce a uniform surface of sharp frosted appearance. Sheen on grit-blasted surface is undesirable as it is produced by over-blasting, by blasting at an acute ang
41、le to the surface or by using blunt abrasive or an abrasive of insufficient hardness. NOTEAn indication of the appearance of the surface required may be obtained by preparing a reference surface by the method described inAppendix A. 5.3.2 Abrasives 5.3.2.1 General. Abrasive which is significantly wo
42、rn or contaminated when compared with new material shall not be used. 5.3.2.2 Chilled iron grit. Angular crushed chilled iron grit shall conform to the requirements of BS2451 and shall be selected within the range between G39 and G17 1)inclusive. 5.3.2.3 Aluminium oxide abrasive. Aluminium oxide abr
43、asive shall be of a size within the following ranges. The sieves referred to shall be in accordance with BS410. 1) Coarse grit. 100% passing a 1mm aperture test sieve with at least80% retained on a3554m aperture test sieve. 2) Fine grit. 100% passing a5004m aperture test sieve with at least80% retai
44、ned on a1804m aperture test sieve. 5.3.2.4 Dust removal. Dust produced in the process of grit blasting shall be removed from the prepared surface in such a manner that the surface will not be contaminated. This is particularly important when aluminium oxide is used as the abrasive. 5.3.3 Air supply.
45、 Adequate precautions shall be taken to remove entrained oil and moisture from the compressed air supply for grit blasting as they have a harmful effect on the quality of the surface. 1) When grit blasting soft metals, i.e.below100HB (105HV, 56HRB), the finest abrasive should be used at an air press
46、ure at the lower end of the permitted range.BS4950:1973 BSI 09-1999 3 5.4 Masking 5.4.1 The grit blasting operation shall be confined to the area to be prepared for coating and adjacent areas shall be masked in a manner best suited to the particular components. Masking materials used shall resist th
47、e impact of the grit and shall not contaminate the adjacent prepared surface. 5.4.2 Masking materials used to prevent the adherence of sprayed metal shall withstand the temperature of spraying and, when necessary, the fusion process without contaminating the bond. 5.4.3 Oil holes and other orifices
48、which must be kept free from foreign matter shall be plugged using blast-resistant materials. Plugs of steel or rubber are recommended for this purpose and should be so shaped and positioned as not to mask any part of the surface to be prepared. After grit-blasting, the plugs shall be removed and re
49、placed by pieces of carbon suitably shaped to prevent ingress of the coating and protruding sufficiently for their top surfaces to be exposed during the subsequent machining operation. 5.5 Cleanliness after preparation. It is extremely important that the surfaces to be sprayed are not subsequently contaminated in any way by oil, grease, dirt, water and fingermarks after the preparation work has been completed. Care shall be taken at all stages to prevent such contamination. In the event of contamination the surface shall be re-prepared as necessary. 6 Spraying 6.1 Gen
