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Aviation History
1932
1932 - 0923.PDF
FLIGHT, SEPTEMBER 9, 1932 Uhe Industry BAKELITE MOULDINGS the ratio of variation of unit tern- :OR the casing of instruments and g™ ^i^ted* JoT™ " T* electrical and wireless apparatus tricitv °r C" Bakelite is now as naturally used in aircraft as for endless common pur poses, its lightness, durability and insulating properties rendering it ideally suitable. Most of the firms manufacturing electrical components for the aircraft industry have their own moulding plants. Bakelite lami nated sheet for panelling aircraft cabins is also beginning to be seen, the Avro 10 being an example. An attractive finish, combined with strength and lightness, are the appeal ing characteristics for this decorative work. Sheeting -^ in. thick weighs 0.46 lb. per sq. ft. in all finishes ex cept solid white, when the weight is then 0.57 lb. per sq. ft., correspond ing weights for £ in. thick laminated being 1.8 lb. and 2.30 lb. per sq. ft. respectively. Bakelite material is a chemical product manufactured from two raw materials, namely, carbolic acid (a coal-tar product) and formalde hyde (a wood distillation product), both of which are liquids with strong odours. Under definite chemical conditions they combine to form a practically inodorous and inert solid body, which is classified as Bakelite Resin " A." This body is an amber-coloured product soluble in alcohol, acetone and other organic solvents, which melts at about 120 deg. F., though continued application of heat converts it into an insoluble, infusible, trans parent and amber-like body, which is called Bakelite Resin " C." The Bakelite moulding materials, however, consist of the resin " A," incorporated (with various fillers) under controlled conditions, employ ing special plant. They have as their binding agent Bakelite synthetic resin. The filling materials referred to are Of course, electricity or gas can be used as an alternative to steam, but the latter has decided advantages. The pressure required to mould Bake lite material varies from 500 to 2,500 lb. per sq. in. of projected moulding area, depending upon the type of mould and the shape of the moulding. It is important to have the presfes fitted with an operating valve for regulating the pressure and controlling it at any point, because, for example, some mouldings may not require more tiian, say, 500 lb., whilst others will require the maximum of 2,500 lb. In all cases it is preferable to have the mould under comparatively light pressure until the mould is practically closed, when extreme pressure can be exerted and maintained until the moulding is complete. When the first moulding has been made, the mould is hot, and in this condition it can be recharged, but after charging, the mould must be got under pressure as speedily as possible, else the heat may cause the material to harden, and the chemical change will take place before the mould is closed. The consequence of this would be a faulty moulding and perhaps a damaged mould. The period necessary for the mould to be under pressure varies according to the size and form of the moulding being produced. Generally it may be taken as from 1£ min. for a piece weighing, say, \ oz., with correspond ing increase of time for a moulding larger than this. This time period also depends upon temperature of the mould. When mouldings are required to withstand exceptional stresses of their dielectric properties, or to withstand high temperatures, they may be stoved as may 48 hours to 70 or 80 hours, be found necessary. Moulded parts may be drilled, tapped or otherwise machined, but as a rule this work can be provided for in the actual moulding operation. usually wood flour and asbestos, the after moulding at 130 deg. C. from first because it gives mechanical strength and does not add to the speci fic gravity of an already light material; and asbestos because of its heat-resist ing properties. These moulding materials are sup plied by the producers in powder form, ready for moulding in the user's plant. The latter consists of hydraulic presses fitted with heated top and bottom platens. Steam is considered the ideal medium for heating, because it is a self-regulating property. It automatic ally condenses and flows more rapidly with a lowering of the platen tempera ture resulting from absorption by the mould and loss by radiation. It is desirable to have the boiler working at a pressure of 150 lb. per sq. in., though it should be pointed out that it is the temperature of the steam at this particular pressure which is de sired, not the actual pressure itself. The temperature should range between 325 deg. and 375 deg. F. In connec tion with the use of steam, the mould ings will not suffer if left in the heat for an excessive length of time, as steam carries its own safetv valve, and Threads of reasonable strength and accuracy can also be moulded in the material. All inquiries concerning the supply of Bakelite moulding materials and the technique of the manufacture should be addressed to Bakelite, Ltd., 68, Victoria Street, London, S.W.I. (telephone Vic. 5441). FLEXO PLYWOOD VV7HEN writing of plywood in these " columns, we have mentioned several times that the glue employed for the adhesive process is the secret of each manufacturer, and is the feature that determines the quality of the plywood. This applies to the ply wood known as Flexo, which is manu factured by Flexo Plywood Industries, Ltd., of South Chingford, E.4. Like other plywoods used in the construc tion of aircraft, Flexo conforms to B.E. specification 3.V.3, a full sum mary of which we have already pub lished in the Industry section. But the special claim for Flexo is that it is extremely flexible, or, alter natively, it is not brittle. This is due to the manufacturer's secret glue that is used. Contributing to the same re sult is the fact—applicable to the pro duction of other plywoods—that before the sheets are glued and compressed they are subjected to a process which ensures that they possess specified moisture contents. This makes certain that sheets of unequal moisture contents are not made up into three-ply. Flexo, which has been in production for the aircraft industry for about eighteen months, is being used extensively in the eight Armstrong-Whitworth " Atalanta " monoplanes to be employed by Im perial Airways, Ltd. About 60,000 square feet have been supplied by Flexo Plywood, Ltd., for this purpose. In the " Atalanta " this plywood covers the main plane and forward part of the fuselage along to the pas senger cabin door, and is also used for the interior panelling and the ribs for the outer sections of the main plane. Apart from producing Flexo for the British aircraft industry, the company has supplied it abroad, the Chilian Air Force being one foreign customer. The company is associated with the Cork Manufacturing Co., Ltd., whose The Cirrus-Hermes Engineering Co. whose latest engine the " Hermes IV " was described in FLIGHT for July 8, use a Spartan " Arrow " for their test work. Mr. J. V. Holman, their Sales Manager, is here seen beside the "Arrow." (FLIGHT Fhoto.) 859
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