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Aviation History
1957
1957 - 0207.PDF
«-"i-:;~ :-iff»:. •'^•~ S~?' JOZ FLIGHT, 15 February 1957 209 Typical of the large-diameter, thin-gauge finish-machining work at Briggs. Using vertical borers, the mounting flanges are being machined after assembly. According to the location of the work face, the parti are held in sturdy internal or external fixtures. (Right). Finish- machining en attachment flange for an Avon RA.7R reheat jet-pipe on a Morando-Tufi centre lathe. "HOT ENDS" . . . Sapphire introduced bigger components that were largelyfabricated from segmental, cylindrical or conical panels. This tendency is, of course, being perpetuated in the newer enginedesigns, although Bristol and Rolls-Royce so far appear to favour cannular combustion systems—that is, individual flame-tubeswithin an annular air casing. The change in engine design affects production organizationas well as the actual processes, since quantities are completely different when there is only one instead of, say, eight combus-tion chambers per engine. From the actual combustion components there followed workon tail-cones, jet-pipes, afterburners, turbine housings and such small units as nozzle boxes. The whole range, it will be seen,built up very wide experience in the handling of fabricated units in stainless steel and nickel alloys. Now, the rising pressure-ratios of engines have increasedstresses and temperatures to the point where light-alloy castings are no longer adequate for compressor-delivery casings. Briggsstep in here with their experience to produce fabricated steel units for the later Sapphires and the Olympus. Plant and Equipment. The aeronautical activities at Eastleighare concentrated under a single roof, with the offices on three floors along the frontage. Perhaps half of the production floorspace is occupied by machine tools, with the greater pan of the remainder divided between press tools, assembly fixtures, bat-teries of electric welding machines almost a hundred) and Argonarc booths. There is no separate machine shop in the usual sense, butone side of the factory is filled by lines of machine tools. Prin- cipally, these are vertical borers (Italian Pensottis for roughing,with the Swiss Schiess for finishing), centre and turret lathes, grinders, and milling machines. A Rigid Rorschach 360 deguniversal profile-copy miller and a Newall jig borer isolated in a glass "cabinet" are two very handsome special tools. A feature of this gas-turbine work is the large diameter andthin gauges of the majority of components. This necessitates the careful mounting of the parts so that they are rigid andnot subject to distortion while being worked. One method of achieving rigidity in a cylindrical component is to mount it on afixture with multiple eccentric clamps. During setting-up the job is revolved and measured by micrometer or vernier calipersto ensure that it is true and that there is no initial ovality. In general, the choice of horizontal or vertical turning dependsrather upon machine availability than upon any intrinsic advantage of one or other method. Many of the flanges are turned from centrifugally cast nickel-chrome alloy-steel pots, or "cheeses". Here, again, they may be (Left). "Pot" turning. Machining of inner exhaust-cone flanges from a centri- fugally cast cylindrical billet on a vertical borer. The weld joining the "pot" to the mild-steel machining base can just be discerned. (Below). A Schiess vertical boring mill fitted with Keller controls for reproducing curved tapers and other two-dimensional forms. Behind the component on the worktable can be seen the Mollart gear boxes, while the operator is turning to the electronic control cabinet.
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