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with a complete absence of the noise which had previ ously been an accompaniment to rivet closing opera tions. Further information can be had from Resistance Welders Ltd., Mucklow Hill, Halesowen, near Birmingham. A Selection of Equipment of Use in the Production and Maintenance of Aircraft and Components Special-Purpose Boring Mill The American Ryan Aeronautical Company has recently installed a new Ex-cell-o boring mill in its plant in order to machine aft frames for jet engines. The aft frame is loaded into the machine by one Brazing Stainless Steels (c) The pot is removed from the furnace and cooled man, and a push-button is pressed. From then on the under the protective atmosphere. complex tool automatically machines the forward A technique whereby the brazing of stainless steels The holding time at high temperature is short; for flange, stiffener bearing flange and aft bearing housing can be carried out in a standard furnace provided most filler metals 10 minutes is sufficient, but when with a controlled atmosphere has now been developed in one sequence. The machine then returns to its Nicrobraz is used a suitable holding time has been original position and shuts itself off. In fifteen minutes, by The General Electric Co. Ltd. The process is found to be 30 minutes. it is claimed, it docs the work which formerly required suitable both for copper-brazing stainless steels and four hours by other machine tools. for brazing components using Nicrobraz alloy as the filler metal. The new boring mill also provides greater accuracy Probe Illuminator Sets in the work. Some diameters must be held within The protective atmospheres most widely used in the ±0·001 in. and concentricity limitations run as high process are burnt town gas or burnt ammonia. The The equipment illustrated in FIG. 1 has been de as 0·005 in. Parallelism is restricted to 0·0003 in. per brazing of metals which are not easily oxidized, such signed by Messrs Engineering Developments (England) in. as steel, may be carried out in these atmospheres Ltd., 1 Adams Place, Georges Road, London, N.7, The machining sequence of the three flanges is using filler metals such as copper or copper alloys. to facilitate the visual inspection of equipment, carried out while the part is firmly held in a stationary However, when components of the stainless steel electrical wiring, or structure, in enclosed parts of position. Only one step-up of the aft frame is required type are to be treated it is necessary to maintain close aircraft which are not normally lit. The set consists for the thirteen machining operations. control over the quality of the atmosphere within the of a handle which holds batteries and switch, and four In operation, the aft frame is loaded into the furnace chamber. Traces of oxygen, water-vapour probes which can be screwed into it. One is a flexible 20-ton boring mill by means of an overhead crane or carbon dioxide will form an oxide film on the sur metal rod which carries a bulb at its end, and the and air hoist. The part goes into a special cradle and face of the components which prevents the liquid other three are rigid Perspcx rods of various lengths. a line-up plug is inserted into one end of the aft frame brazing metal from alloying with the exposed sur These are mounted on to a bulb which itself screws to insure its perfect alignment. The small end of the faces and a sound joint being made. Similar considera into the handle, and carry the light where it is re component is clamped with a steel bracket and the tions apply when the brazing alloy itself is readily quired. They are covered, except for about i in. at line-up plug is retracted. A series of hydraulically oxidized, as is the case with certain high-temperature the end, by varnished cotton, for protection. An ac actuated clamps automatically swing around to clamp brazing alloys such as Nicrobraz. If a very dry hydro cessory is a small mirror which can be clipped to any the large burner plate section in place. Micro-switches gen atmosphere is used, and if treatment is carried of the probes to make visible corners not in the line on both the bracket and line-up plug prevent starting out in a metal container, the surfaces are kept clean of sight. of the machine until the aft frame is properly clamped and brazing is satisfactory. in position. The operator then presses the cycle-button A G.E.C. 60 kilowatt vertical cylindrical furnace and the machine begins the operations. Hot-Closing Rivets with gas-tight container has given excellent results First, the cutting head moves into the part and bores when used for the process. It has effective loading It has long been known that cold heading of rivets and faces the forward flange. At completion, it retracts dimensions of 17 in. diameter by 4 ft. 10 in. deep and used in stressed assemblies leaves much to be desired, and the cradle assembly slides sideways to bring the can be used for all types of brazing in the temper owing to the serious disturbance to the structure of aft frame into line with two other cutting heads. ature range 700 deg. to 1,180 deg. C. The method of the headed metal, which is often so fatigued by the They move into the work, from opposite ends, and operation is as follows: process as to break away from the rivet stem im one head bores, counter-bores, chamfers and faces mediately any strain is imposed. the stiffencr bearing flange which is inside the barrel (a) After loading the stainless steel assemblies on of the aft frame. The other head bores, countcr-bores After a careful investigation of the problems in the support casting, the pot is scaled and im volved, Standard Resistance Welders Ltd., decided and faces the aft bearing housing, from the other mediately purged with the dry hydrogen pro to build a modified version of their successful vertical direction. When this is done the heads retract and the tective atmosphere. If it is considered desirable, slide head air-operated projection welder to hot-close cradle returns the part to the front of the machine. the pot may first be purged with nitrogen. rivets. Close automatic control was established over The three cutting heads which perform the machine (b) The pot is loaded into the furnace and thechargc such operating variables as electrode pressure, heating ing are equipped with thirteen tungsten carbide tools brought to the required temperature in the current and time. As a result the rivets were closed and are powered by separate 5-horscpowcr clectric controlled atmosphere and held at that more tightly than formerly, and the grain-flow in the motors. Each moves into the work on steel guide in the controlled atmosphere and held at rivet was practically undisturbed; the headed por under hydraulic pressure. In each head a cam opcratcd temperature for between 10 and 30 minutes, tions were uniform in size and shape, and the whole mechanism retracts and extends the various cutting depending upon the brazing alloy being used. process was carried out in a tenth of the usual time tools to perform the different machining operations 60 Aircraft Engineering
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: Feb 1, 1954
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