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Aviation History
1933
1933 - 0163.PDF
FLIGHT, JULY 20, 1933 ELECTRO-DEPOSITION OF METAL -mrx E POSITING metal on metal is generally classed in a \ wide and loose fashion as plating, but the degree II J of adhesion obtained by ordinary plating is a very different thing to that achieved by modern methods with selected metals. Adhesion is of vital importance both for attaining a high resistance to corrosion and also for producing, on the article to be plated, a surface which will stand up to a large amount of wear. A factory which has made an especial study of electro- deposition is Fescol, Ltd., of 101, Grosvenor Road, London, S.W.I. During a recent visit we saw a wide variety of aircraft components being coated with both nickel and chromium while in some cases cadmium is also used. Naturally, protection against corrosion is of paramount importance for botii land and sea-planes, particularly as weight is kept at a minimum in aircraft construction by the use of thin gauge members of high tensile strength. Metal of thin gauge does not allow any margin for corrosion and so this enemy of the designers and manufacturers, to say nothing of the pilot and passengers, has to be combated by the surest methods known to science. The chief of these is the deposition, on parts which are subject to the corrosive action of the atmosphere or of agents like sea water, of a film of some chemically pure metal which will withstand that action. Chief among the metals used for this purpose are cadmium, nickel and chromium. In each case the anti-corrosive properties of-the coating arc dependent on the adhesion of that coating, and the following test carried out by the N.P.L. is illuminating in showing that a coating deposited by Fescol cannot possibly break away or peel off. * The specimens supplied for the tests consisted of three nickel-coated steel specimens and one solid steel specimen. The specimens were machined and then tested in direct tension as shown. It will be noted that the direct pull on the specimen is resisted by the adhesion between the annular layer of nickel and the steel core of the specimen. The solid steel specimen was of similar overall dimensions to the nickel-coated specimens. The tests were made in the 50-ton tensile-testing machine in use at the laboratory, and in each test the load was increased continuously until failure occurred at the large end of the specimen. en" " •le*t *S a P*u£ gawge of the type used in most is 8*riee.ring works. When coated with chromium its wear an"! g'k'e" ^n t*le "gnt *s l^e exhaust manifold from rmstrong-Siddeley aero engine. This is coated with nickel as an anti-corrosive measure. NICKEL COATING n-i-i i i-nv DIRECTION OF PULL RING HELD IN HEAD OFTESTING MACHINE Adhesion Test Piece The results of the tests are given below and the maxi mum adhesive or shear stress applied was obtained in the following manner: Maximum adhesive or shear stress ,. , Maximum load , ,. . , , applied = —=== where a = diameter ol body as r W x a x c shown in Figure, and c = depth of head as shown in Figure. NPL Eng. Dept. Test Mark. EQZ 1 EQZ 2 EQZ 3 EQZ 4 Description of specimen. Nickel Coated Solid Diameter " A " in. 1034 1-035 1-030 1-028 Diameter " B" in. 1-17 117 117 1-13 Depth "C" in. 0-250 0 • 250 0-250 0-250 Failing load tons. 14-96 16-17 15-98 11-68 Maximum Adhesive or shear stress. applied, tons sq. in. 18-4 19-9 19-8 14-5 In the case of each of the nickel-coated specimens examination of the fracture showed that failure occurred by shearing of the steel just inside the nickel-coating, and not by failure of the adhesion between the coating and the steel. The failure of the solid specimen was similar to those of the nickel-coated specimens. In aircraft, parts like exhaust manifolds and tail pipes are coated with nickel for many manufacturers, while small fittings of steel are cadmium coated. Bright iinished chromium has not been used much for anti-corrosive pur poses, it being more applicable to yacht and 5-hop fittings. There is a use to which, however, it is peculiarly adaptable in a hard or non-bright form, and that is for the rebuild ing or salvage of worn parts. Nickel is also used for the purpose, the choice of metal depending upon the function of the part to be built up. A great advantage of the process is that it is a cold one and that no distortion can therefore take place as it could do when welding is resorted to. Chromium as deposited by the Fescol process is exceedingly hard, thus entirely obviating wear in the case of parts like plug gauges and measuring gauges of other forms, while the surface obtained after grinding or lapping is so extremely smooth and slippery that journals of shafts which have been coated with chromium by this process will run perfectly well in badly lubricated bearings without either wear to the shaft or to the bearing. Chromium as deposited can be machined to the finest limits and the Fescol Company have all facilities for carry ing out work of this nature. In aircraft engines satisfactory use has been made of the properties of chromium by having the working faces of rocker arms, camshafts, gudgeon pins, etc., coated ; in all cases the life of the part so treated has greatly been increased- There seems to be no end to the applications of the pro cess, and we would suggest that, for aircraft purposes in particular, it would be well worth investigating the possi bilities of depositing a hard bearing surface, like that of chromium, on one of the light alloys, say duralumin. ttew Air Armament for Japan ss ss £ij S3 S3 Gliding Over the Alps HERR KRONFELD, on Saturday, July 15, successfully ncludpE inew building programme for the Japanese Navy boat „ % ,10.000-ton aircraft-carriers and eight flying glided over the Alps. He hopes later to glide over the Jmts. The aircraft-carrier Hosho will be scrapped. Apennines. 739
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