1、BRITISH STANDARD BS 4479-9: 1990 Design of articles that are to be coated Part 9: Recommendations for low pressure and vacuum deposited coatings UDC 672/673:621.795:006BS4479-9:1990 This British Standard, having been prepared under the directionof the Surface Coatings(other than Paints)Standards Pol
2、icy Committee, was published underthe authorityofthe Boardof BSIand comes intoeffecton 31 July 1990 BSI 11-1999 First published as BS 4479 August1969 First revision as BS 4479-9 July1990 The following BSI references relate to the work on this standard: Committee reference SRC/10 Draft for comment 86
3、/53493 DC ISBN 0 580 17907 9 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
4、 Anodising Association 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 CommentsBS4479-9
5、:1990 BSI 11-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Definitions 1 3 Low pressure and vacuum deposited coatings 1 4 Design considerations 2 Appendix A Diagrams illustrating preferred and deprecated design featuresforarticles to be coated by vacuum depos
6、ition 4 Figure 1 Re-entrant holes 4 Figure 2 Bends 4 Figure 3 Indentations 4 Figure 4 Teeth 5 Figure 5 Joints 5 Publications referred to Inside back coverBS4479-9:1990 ii BSI 11-1999 Foreword This Part of BS 4479 has been prepared under the direction of the Surface Coatings (other than Paints) Stand
7、ards Policy Committee and is based on a draft prepared by the Institute of Metal Finishing. The BSI Technical Committee acknowledges the contribution to this revision by the Institute 1)and by the Committee for the Promotion of Electroplating. This Part of BS 4479 is one of a series of Parts which t
8、ogether form a revision of BS 4479:1969. On publication of all the Parts, BS 4479:1969 will be withdrawn. This revision of BS 4479 comprises the following Parts: Part 1: General recommendations; Part 2: Recommendations for electroplated and autocatalytic coatings; Part 3: Recommendations for convers
9、ion coatings; Part 4: Recommendations for paint coatings and varnish coatings; Part 5: Recommendations for 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
10、 9: Recommendations for low pressure and vacuum deposited coatings. BS 4479 is directed towards helping to maximize 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 manu
11、factured articles. However, time and money are often wasted because the design of many articles is unsuitable 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
12、. This revision of BS 4479 has been undertaken to extend the range of coating processes covered. It is not intended 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 de
13、sired results. In any case of doubt or difficulty, specialist advice in the particular type of process being considered should be sought. This Part of BS 4479 is not a specification and should not be used as such. The recommendations are intended to provide guidance towards good practice. It should
14、be noted that the definitions of low pressure, vacuum and high vacuum given in the standard differ from those given in BS 6413-3.1:1988, which are simply based upon typical values. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards a
15、re 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, pages i and ii, pages1 to 6, an inside back cover and a back cover. This standard
16、 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. 1) Institute of Metal Finishing.BS4479-9:1990 BSI 11-1999 1 1 Scope This Part of BS 4479 gives recommendations for design features to be followed
17、in the application of coatings by low pressure or vacuum deposition to various substrates. An outline of the three main processes involved is also given, together with some guidance on operational conditions. NOTE 1It is recommended that Part 1 of BS 4479 be read in conjunction with this Part. Part
18、1 includes a list of British Standards relating to processes covered by BS 4479 but not necessarily referred to in each Part. NOTE 2The titles of the publications referred to in this standard are listed on the inside back cover. 2 Definitions For the purposes of this Part of BS 4479, the following d
19、efinitions apply. 2.1 back-filling a process whereby a gas is bled into an evacuated chamber to achieve a specified low absolute pressure 2.2 dynamic vacuum a vacuum (see 2.5) in which back-filled gas is bled into a continuously-pumped chamber at such a rate as to maintain a steady pressure NOTEAll
20、pressures quoted in this Part of BS 4479 are dynamic absolute pressures. 2.3 line-of-sight coating a coating obtained only on those areas of the workpiece directly exposed to the source 2.4 low pressure an absolute pressure in the range 10 2Pa to 10 Pa 2.5 vacuum an absolute pressure equal to or low
21、er than 10 2Pa 2.6 high vacuum an absolute pressure equal to or lower than 10 5Pa 2.7 vacuum deposited coating a coating produced by evaporating a metal on to the workpiece at an absolute pressure of lower than 10 2Pa 2.8 low pressure coating a coating produced by ionizing a gas at an absolute press
22、ure of 1 Pa to 10 Pa and applying an electric field 3 Low pressure and vacuum deposited coatings 3.1 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 also the limitations impos
23、ed by the coating. Thin coatings of many different materials and admixtures of such materials can be applied to a variety of substrates using vacuum deposition techniques. Metals and metallic oxides having special properties can be successfully applied by vacuum deposition, whereas other methods of
24、applying these coatings may be difficult, or even impossible. There are three main methods of low pressure and vacuum deposition: a) vacuum evaporation (see 3.2); b) ion plating (see 3.3); c) sputtering (see 3.4). In the majority of instances, workpieces will be exposed to a glow discharge (an ioniz
25、ed gas) during the process. Workpieces will, in many instances, be exposed to conditions of high vacuum prior to establishing deposition conditions. Diagrams illustrating preferred and deprecated design features for articles to be coated by vacuum deposition are given in Appendix A. 3.2 Vacuum evapo
26、ration Vacuum evaporation is a high vacuum process whereby the prospective coating material is heated to a temperature at which it evaporates at a high rate. The material is usually heated resistively using a ceramic or refractory metal boat or is directly bombarded with high energy electrons to the
27、 point of melting and evaporation. The former technique will normally apply to low melting point materials and those which do not readily alloy with the boat material. Electron beam evaporation is applied where thick coatings and high rates of deposition are required.BS4479-9:1990 2 BSI 11-1999 The
28、workpieces are held within the vacuum chamber at distances of up to 500 mm from the material source so as to allow uniform coating. Vacuum evaporation coating is by “line of sight” and workpieces of varying geometry will, therefore, require to be moved (usually by rotation) within the material vapou
29、r to obtain a uniform coating. The area covered is dependent on the geometry of both the source and the workpiece. To achieve good adhesion using this process, a high standard of cleanliness is required. This is achieved by initial thorough cleaning using degreasing solutions, preferably in ultrason
30、ic baths. After these techniques have been applied, the workpieces are not touched by hand and are subjected to an additional cleaning process within the vacuum chamber using ion bombardment techniques. In a standard vacuum evaporation process this involves striking a d.c. glow discharge in an inert
31、 gas at an absolute pressure of about 1 Pa, preferably using the workpiece mounting system as the cathode to encourage ion bombardment of the workpiece, and, after a predetermined time, extinguishing the discharge and pumping down to high vacuum prior to evaporation. 3.3 Ion plating Ion plating is a
32、n extension of the evaporation technique in which the work chamber is operated at a dynamic absolute pressure of 10 2Pa to 10 Pa and by back-filling with an inert gas ionized by applying a d.c. or RF voltage to an internal electrode. Initially, the workpiece is cleaned by ion bombardment. Deposition
33、 follows in the continued presence of the glow discharge. There are two major advantages to this process. Firstly the adhesion achieved by deposition in the presence of an ionized gas is considerably better than that from vacuum evaporation. Secondly, coating is not by line of sight; at higher press
34、ures (typically 1 Pa), the hidden areas of complex workpieces can be coated in some degree without rotation. However, substrate temperatures can reach 500 C. 3.4 Sputtering Sputtering, although employing similar vacuum equipment to the vacuum deposition and ion plating techniques, is fundamentally d
35、ifferent in one aspect: it does not involve the high temperature evaporation of the coating material (which requires the formation of a melt) but instead relies on the atom-by-atom removal, i.e. sputtering, from a solid source which is bombarded by gas ions from the chamber environment. The processe
36、s can be carried out with lower substrate temperatures than are reached in ion plating. The operating pressure is similar to that of ion plating but the source material is a solid of convenient shape. As with the other processes, one of the primary workpiece requirements is surface cleanliness. This
37、 is achieved initially using degreasing fluids, with the final cleaning produced by bombardment from the glow discharge with the workpiece in situ. The glow discharge is maintained throughout the coating process. Coating uniformity may be improved when operating at pressures of the order of 1 Pa and
38、 by employing multiple targets to allow the deposition of material from several directions on to the workpiece. 3.5 Coating environment The workpiece is placed in an evacuated chamber and it is therefore essential that it does not interfere with the integrity of the vacuum. In most cases the workpie
39、ce will be exposed to ion or electron bombardment or radiation from a heating source or plasma. The material to be coated should therefore have a low vapour pressure; soldered or brazed components may present problems. It is preferable to avoid porous workpieces which would outgas. In addition, asse
40、mbled units placed in the coating chamber may contain trapped volumes of air which would contaminate the operating environment and this should be avoided. 3.6 Jigging techniques In many instances workpieces will stand in holders or will be suspended in the work chamber for coating purposes and, as a
41、 result, allowances have to be made for certain parts of the workpiece not to be coated. In some instances, small samples may be coated using a barrel tumble unit. However, this can limit the thickness of coating achievable on the workpieces. Ion plating and sputtering tend to coat the whole area of
42、 a workpiece. If certain parts are not to be coated, they will require to be masked, usually by a contacting metal mask. 4 Design considerations 4.1 Materials Surface preparation is important and should be discussed with the process engineer. Some metals are not normally desirable in “clean” vacuum
43、stations if they are to be subjected to elevated temperatures or ion bombardment, e.g.cadmium, zinc and brass, and the use of such metals should be discussed with a process engineer prior to materials selection if possible.BS4479-9:1990 BSI 11-1999 3 Consideration should be given to the process oper
44、ating temperature. Depending on the method by which components are located in the chamber, they could be subjected to temperature gradients and so the acceptability of such exposure should be determined. 4.2 Surface finish Vacuum-deposited coatings generally replicate the surface finish of the subst
45、rate and it will therefore not normally be possible to generate “bright” surfaces from “dull” surfaces where the dullness is due to surface topography. They can, however, have their own characteristic colour, e.g. titanium nitride. The material deposited does not fill in voids on a surface but will
46、generally follow the profile of those voids. The coating may be discontinuous in deep pits. Bearing in mind that clean surfaces are essential, it is important not to mark workpieces with marker pens of any sort. Any additional information should be supplied through drawings of the article to be coat
47、ed. 4.3 Coating thickness Normally, engineering coatings will be between5m and 250 m thick, the thinner coatings usually being applied for wear protection purposes, the thicker for corrosion protection purposes. Such coating thicknesses can obviously affect the dimensions of the finished workpiece a
48、nd this should be taken into consideration during the design stage. A coating above 250 m in thickness would not normally be applied using low pressure or vacuum deposition techniques. 4.4 Component geometry Uniformity requirements should be clearly stated. Re-entrant holes and asperities with diame
49、ter to depth ratios of 1 : 2 or shallower can be coated but low pressure coating of hollow sections can give rise to ion beams which may deleteriously affect other components and fittings within the chamber. Discussion with process engineers is recommended if the item to be coated is of a very complex design. Final machining of articles before coating should ensure that there are no unnecessary sharp edges or burrs as these can be points of weakness in the coating (see Figure 2). Internal surfaces of box sections are extremely difficult to co
