1、BRITISH STANDARD CONFIRMED MAY 1988 BS 4495:1969 Recommendations for The flame spraying of ceramic and cermet coatingsBS4495:1969 These Recommendations, havingbeen approved by the Surface Coatings (other than Paints) Industry Standards Committee, were published underthe authority of the Executive Bo
2、ard on 23September1969 BSI 11-1999 The following BSI references relate to the work on these Recommendations: Committee reference SRE/13 Draft for comment 68/1695 ISBN 580 05632 5 Co-operating organizations The Surface Coatings (other than Paints) Industry Standards Committee, under whose supervision
3、 these recommendations were prepared, consists of representatives from the following Government departments and scientific and industrial organizations: Assay Offices Committee of Great Britain Association of Metal Sprayers* British Bolt, Nut, Screw and Rivet Federation British Cycle and Motor Cycle
4、 Industries Association Limited British Electrical and Allied Manufacturers Association* British Jewellers Association British Non-Ferrous Metals Research Association British Steel Industry* Chemical Industries Association Electricity Council, the Generating Board and the Area Boards in EnglandandWa
5、les* Electronic Engineering Association Engineering Equipment Users 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 Departme
6、nt Ministry of Technology* 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 f
7、ollowing, were directly represented on the committee entrusted with the preparation of these recommendations: British Ceramic Research Association Gauge and Tool Makers Association Institution of Mechanical Engineers Society of British Aerospace Companies Limited Welding Institute Individual firms A
8、mendments issued since publication Amd. No. Date CommentsBS4495:1969 BSI 11-1999 i Contents Page Co-operating organizations Inside front cover Foreword ii 1 Scope 1 2 Coating material 1 3 Surface preparation 1 4 Application of coating 2 5 Coating thickness 2 6 Coating treatment 2 Appendix A Method o
9、f preparation of a reference surface by grit blasting 4 Appendix B Surface preparation by machining 4 Appendix C Methods for the determination of coating thickness 4 Appendix D Approximate conversion factors 5BS4495:1969 ii BSI 11-1999 Foreword These Recommendations make reference to the following B
10、ritish Standards: BS 410, Test sieves. BS 2451, Chilled iron shot and grit. For the deposition by flame spraying of materials generally known as ceramics, cermets (metal/ceramic composites) and numerous other non-metallic inorganic materials having a high melting temperature, conventional metal spra
11、ying equipment, detonation equipment and plasma flame equipment are employed. These materials are usually sprayed in rod or powder form. Coatings which are subsequently fused and fused enamel coatings are not covered by these recommendations. The wide variety of materials covered by these recommenda
12、tions and the various purposes for which they are employed, as described in Clause 1, make it difficult to issue specific requirements but it was felt that recommended practices for preparation, process control, finishing and testing, were desirable. The choice of coating, thickness of deposit, fini
13、sh and any special considerations are matters for agreement between the supplier and the purchaser, depending upon the duty which the finished article has to perform. Subject to such agreement compliance with the recommendations will ensure good results. A British Standard does not purport to includ
14、e all the necessary provisions of a contract. 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
15、andii, pages1 to5 and a 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.BS4495:1969 BSI 11-1999 1 1 Scope These recommendations relate to the flame spraying of ceramics,
16、cermets and certain other high melting point materials for which the spraying conditions are similar, applied on to metals or any other suitable materials. The purposes for which the deposits are utilized include wear, galling and erosion resistance, heat insulation, corrosion and oxidation resistan
17、ce, electrical insulation, and resistance to “wetting” by molten metals. 2 Coating material 2.1 Composition. The composition of the material used for the coating should be the subject of agreement between the purchaser and the supplier. The tolerance limits for each significant constituent should be
18、 included in the agreement. No change in the composition of the material should be permitted without prior consent of the purchaser. 2.2 Form. The physical characteristics of the rod or powder used for spraying should be appropriate to the particular flame spraying apparatus employed. 3 Surface prep
19、aration The surface of the material to be coated should be cleaned so as to be visibly free from foreign matter and should be sufficiently roughened to allow the coating to be bonded to the contour of the surface of the base material. Particular attention should be given to the removal of loose resi
20、dues from the blasting process by brushing or vacuum cleaning the surface. The roughness of the surface to be coated should be formed by one of the methods described below: 1) Grit blast preparation. A type of grit should be used which will not be hygroscopic, and which will not cause deterioration
21、or have any detrimental effect either on the sprayed deposit or on the base material. The recommended grit is fused and crushed aluminium oxide, although chilled iron grit 1)may be used in cases where the presence of residual iron on the blasted surface is not detrimental. Crushed aluminium oxide sh
22、ould be of a size selected within the range through a 16 mesh sieve 2)and retained on a44mesh sieve 2) . Chilled iron grit 1)should be Grade G24. The surface produced should be comparable in cleanliness and degree of roughness to the reference surface produced by the method described in Appendix A.
23、Where there is a risk of distortion of thin material or damage to the surfaces of soft or friable material, some relaxation in the size of grit and degree of roughness may be necessary; the extent of any such relaxation should be the subject of agreement between the purchaser and the supplier. Alter
24、natively, consideration should be given to the use of an interlayer as outlined in 3) below. 2) Machine preparation, either by rough threading or by grooving followed by knurling of the ridges between the grooves (see Appendix B). This method is of limited acceptability. 1) BS 2451, “Chilled iron sh
25、ot and grit”. 2) BS 410, “Test sieves”.BS4495:1969 2 BSI 11-1999 3) Bond coating, by the application of a flame sprayed interlayer of a metal or alloy which gives local alloying with the surface of the base material. Suitable metals or alloys for this purpose include molybdenum (provided that the se
26、rvice temperature in an oxidizing atmosphere does not exceed 300 C) and nickel/aluminium intermetallic compounds formed by reaction between nickel and aluminium during spraying. 4) A combination of certain of the above methods, namely 2) followed by 1) in which case knurling may be omitted, 1) follo
27、wed by 3) or 2) followed by3). 5) The application of a flame sprayed metal interlayer (other than those covered by 3) above). This may be nickel chromium alloy or other metal as agreed between the purchaser and the supplier and which always requires prior treatment of thebase material by 1) or 2) ab
28、ove or 2) followedby 1). NOTEThe use of an interlayer see 3) and 5) above may serve to reduce stresses in the coating caused by differing degrees of thermal expansion relative to that of the base material, and also in some cases reduce the risk of coating failure due to corrosion or oxidation of the
29、 surface of the base material. The surface to be coated should be protected against contamination at all stages prior to coating. 4 Application of coating The sprayed coating should be applied to the clean and dry surface, preheated where necessary, prepared in accordance with Clause 3, by means of
30、flame spraying apparatus operated strictly in accordance with the equipment suppliers recommendations and fed with the appropriate coating material. The sprayed coating should be applied as soon as possible after surface preparation and before visible deterioration of the surface has occurred. If, o
31、n comparison with a freshly prepared surface of material of similar quality, visible deterioration has occurred, the surface preparation should be repeated. In no case should the delay between surface preparation and coating application exceed4 hours, unless specified precautions, agreed between the
32、 purchaser and the manufacturer, are taken to ensure a suitably controlled storage atmosphere. Where possible the coating should be applied normal to the surface of the workpiece and in any event the angle between the flame spraying apparatus and the surface of the workpiece should not be less than
33、45 . Spraying of the coating, once started, should not be interrupted until the full deposit thickness has been attained, but precautions should be taken to avoid overheating that may adversely affect the efficiency of the coating or the properties of the base material. In the event of an unavoidabl
34、e interruption of spraying, care should be taken to avoid a substantial drop in temperature of the workpiece. Contamination of the sprayed coating should be avoided at all stages during the application of the coating. The surface of the sprayed coating should be of uniform colour and texture, visibl
35、y free from cracks, lumps, coarse areas and loosely adherent particles or other contamination. 5 Coating thickness The coating thickness, determined by one of the methods given in Appendix C, should be within the limits specified by the purchaser. 6 Coating treatment 6.1 Sealing. Sprayed coatings, b
36、eing porous, may often require sealing to protect the substrate against corrosive influence and/or to reinforce the particle cohesion. The selected sealer should preferably be applied before any surface finishing operation. A variety of materials are used for this purpose, such as resins, waxes, ela
37、stomers and plastics. It is recommended that the equipment manufacturer should be consulted for guidance on the selection of the appropriate sealant and on the application technique. 6.2 Surface finishing. The majority of ceramic coatings have particle hardnesses approaching those of common artifici
38、al abrasives. The “as sprayed” surface roughness may vary widely according to the coating method and material selected, and usually exceeds 2.5 4m CLA. Many satisfactory quality coatings have surface roughnesses in excess of 5 4m CLA. To ensure that the intrinsic properties of the coating and the ad
39、hesion to the base are not impaired, it is essential that any mechanical procedures used to modify the “as sprayed” surface should: 1) avoid excessively high unit pressure or shock loading; 2) avoid high local heat development usually associated with 1).BS4495:1969 BSI 11-1999 3 To minimize the circ
40、umstances of 1) and 2) a cutting medium should be used which is considerably harder than the coating. Natural or synthetic diamond is the ideal medium but for certain purposes common artificial abrasive materials, particularly silicon carbide which is slightly harder than most coatings, may be used.
41、 Single point tool machining, even using a diamond, can give rise to excessively high unit pressure and impact on the peaks of roughness, which may lead to mechanical damage through the depth of the coating and therefore care is necessary when using this method. 6.2.1 Non-precision finishing. When i
42、t is necessary only to reduce the roughness of the coating and where dimensional accuracy is not necessary this may be done by the following methods: 1) By hand, using coated abrasive paper or cloth. Usually, silicon carbide abrasive will be used. 2) By mechanical means, using coated abrasive cloth
43、belts either unsupported or using a very soft contact wheel. In this case the abrasive material and grit size should be carefully selected. High unit pressures and consequent temperature rises should be avoided. 3) By coated abrasive discs on a portable disc grinder. This method is usually more diff
44、icult to control in respect of surface uniformity, and heating of the workpiece, and consequently should be used with the utmost care. 6.2.2 Precision finishing 6.2.2.1 Precision machine grinding is the preferred method using diamond abrasive wheels. The depth of cut per pass should not exceed 12 4m
45、 and the work should be kept cool with a copious flow of filtered coolant at the point of contact of wheel and workpiece. In the case of unsealed coatings, a coolant should be used which will not give rise to corrosion of the base material. Water is the most efficient coolant but to meet the previou
46、s requirement a corrosion inhibitor should be added. If a cooling fluid is not permissible the depth of cut should be reduced to 2.5 4m per pass and great care taken to avoid overheating. Dust exhausting is essential. With certain coatings silicon carbide abrasive wheels may be used but, because of
47、their very lowrates of stock removal, very light feeds of about2.54m per pass should be used and efficient liquid cooling is necessary. 6.2.2.2 The method described in 6.2.1 2) may be used, with appropriate jigging. 6.2.2.3 Mechanical lapping, particularly of flat surfaces, may be used either with s
48、ilicon carbide lapping wheels or with loose abrasive powder using a metal lapping plate and a fluid carrier. 6.2.3 The foregoing gives general guidance as to themore usual finishing methods. With some dense coatings it is possible to achieve surface finishes of0.08 4m CLA or better. The wide variety
49、 of coating materials available, of characteristics of coatings and of different finishes required make it impracticable, however, to specify conditions for each specific requirement. It is recommended that in many instances the advice of either the ceramic spraying equipment supplier or an abrasive manufacturing company should be obtained to ensure the most efficient and economical procedure.BS4495:1969 4 BSI 11-1999 Appendix A Method of preparation of a reference surface by grit blasting A.1 Base material Use a flat piece of material which should be of similar compos
