Page 243 - The Jet Engine

Manufacture

17. Forging calls for a very close control of the
temperature during the various operations. An
exceptionally high standard of furnace control
equipment, careful maintenance and cleanliness of
the forging hammers, presses and dies, is essential.
Fig. 22-4 Automatic investment casting. 18. Annular combustion rings can be cold forged to
exacting tolerances and surfaces which alleviates
the need for further machining before welding
16. The high operating temperatures at which the together to produce the combustion casing.
turbine discs must operate necessitates the use of
nickel base alloys. The compressor discs at the rear 19. H.P. compressor casings of the gas turbine
end of the compressor are produced from creep- engine are forged as rings or half rings which, when
resisting steels, or even nickel base alloys, because assembled together, form the rigid structure of the
of the high temperatures to which they are subjected. engine. They are produced in various materials, i.e.,
The compressor discs at the front end of the stainless steel, titanium and nickel alloys.
compressor are produced from titanium. The higher
strength of titanium at the moderate operating tem- CASTING
peratures at the front end of the compressor,
together with its lower weight provides a consider- 20. An increasing percentage of the gas turbine
able advantage over steel. engine is produced from cast components using

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