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Aviation History
1914
1914 - 1175.PDF
DECEMBER 4, 1914. CASTINGS MADE TfH™n,fre/eWungineering trades in which the ™«hods of manufacture have not undergone considerable revision during recent years. In some cases the innovations made have practically revolutionised certain processes incidental to manufacture, but in others the old methods still exist and such improvements as have been introduced have from their nature been supplementary. This has been particularly the case in the foundry, as apart from the progress which has been made in the scientific side of the trade, time has wrought comparatively little change in the mechanical operations involved—the improved quality and greater quantity of the work produced being, to a large extent, due to the installation of new machines. Interest therefore attaches to the system of casting under pressure and method of reinforcing castings of the Combined Metals and Reinforced Castings Company, Point Pleasant, Wandsworth, S.VV. Pressure casting, as such, is by no means of recent introduction, but the particular manner in which the pressure is obtained in this case is claimed to be quite new, and the subject of a patent by Mr. W. F. Sollis. The preparation of the mould from the pattern differs in no wise from the usual l/yiiZI UNDER PRESSURE. a short time after pouring has been completed, the small head of metal within the box is sufficient to make up for shrinkage in cooling. The immediate benefit derived from this system of casting is that much sounder and more homogeneous castings are ensured with any metal than ttn obtainable by the more usual method, so that there should be a much lower proportion of " wasters "-—an important source of loss in foundry work—the castings should be stronger, and there should be less liability to failure through undiscoverable defects. Another advantage of the system is that it should permit of much thinner castings being made, an es|>eciany desirable point when dealing with metal's that are sluggish in the mould. As regards the system of reinforcing the metal, this system has a double object where aluminium castings are employed—the attainment of greater strength and a wider margin of safety. The reinforcement employed depends upon the form of the article to be cast, and consists either of galvanised or tinned steel wire frames or of steel rods which vary in diameter according to the size and shape of the casting. These are placed in the " Flight' Copyright. PRESSURE CASTINGS.—On the left, the plant used to obtain the pressure upon tbe metal by centrifugal force during casting. On the right an aluminium reinforced pressure casting. method—the pattern is embedded in the sand in the boxes, and after the sand has been rammed down the pattern is removed and such cores as may be required are inserted. The mould, when ready for casting, how ever, differs in one respect in that there is no special vent for the gases, as the pressure obtained during casting is sufficient to force the gas through the sand and the inter stices between the boxes. The box is then removed to a platform that resembles in appearance the face plate of a lathe, with its axis vertical and secured thereto, by clamps and bolts, in such a position that the hole through which the molten metal is poured is immediately over the centre of the faceplate. The face plate is driven at a speed of about 100 revolu tions per minute through a countershaft by means of an electric motor, as shown in one of the accompanying illustrations, and while rotating, the molten metal is poured into the mould. The metal flowing into the mould is immediately acted upon by centrifugal force, and consequently, no matter how intricate the casting, the molten metal is caused to penetrate under increasing pressure to the most remote portions of the mould. In addition, the use of "headers" under ordinary circum stances, in order to force the metal through to all parts, is entirely unnecessary, as by continuing the rotation for mould in the positions required, and the pouring is pro ceeded with in the manner previously described. The object of tinning or galvanising the wire is to ensure the better adhesion between the cast metal and the reinforce ment. Where rods are employed for reinforcing the metal the wires are of other than circular section, and are twisted in order to give greater resistance to drawing out. One of the illustrations shows a reinforced casting in the condition in which it was removed from the mould. Tests conducted by Faraday House upon reinforced aluminium rods cast under pressure show that the strength of such rods is practically doubled; and this increase in strength is obtained by an increase in weight of approximately 16 per cent. The average breaking load in tests made by Faraday House on three such rods was 1375 tons per square inch. Apart from this increase in strength, however, a valuable feature of the reinforcement is the safety it affords. In the tests the aluminium broke first, as was to be expected, but before the test piece com pletely failed by the fracture of the steel rod the aluminium was broken in five places. The system is one which has considerable interest for aeroplane constructors, and in fact the firm have in hand some work for one of the largest aeroplane manufacturers in this country. 1175
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