In the late 1940's D Napier & Son had risen to the challenges of the new gas turbines that were required to replace piston engines. With the help of the Napier Research Station (NRS) at Liverpool state of the art axial compressors were tested and made available for in-house and outside customer use. The combined 'Blade Shop' and Napiercast Precision Investment Foundry at Park Royal 2 works in Mansfield Road had been the envy of other companies. Their output of Nimonic cast and machined turbine blades and their forged and machined aluminium bronze compressor blades were at the forefront of the technology of the time. These were finished to tight aerofoil and root tolerances on Napier-developed hydraulic 'PF' or precision finishing machines. The image on the right shows an invesment cast Nimonic turbine blade for Napier Gazelle. It clearly shows the fir tree roots which were hand finished. Much sub-contract work was also carried out by the Company for other British engines manufacturers.
When D Napier & Son's Aero Gas Turbine Division became the Napier Aero Engines Ltd on its way to be absorbed in Rolls-Royce the investment foundry went with it. On 2nd September 1964 it was sold as a working unit to Westlands at Stag Lane, Hayes (formerly Fairey Aviation) where it was re-established and operated as a viable plant for components using the lost-wax process.
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Fabricated Cooled Turbine Blades
The images to the right show a series of production stages to produce sheet metal Nimonic hollow blades. These blades were air cooled and the images clearly show the exit holes in the trailing edge where the cooling air was dumped back into the gas stream. The last two images show the larger hole where the cooling air entered the blade. By allowing cooling air through the blades the turbine could be run at many degrees over the melting point of the parent metal, and therefore increased the power output. Modern turbine engines are run well over the melting point of the blades (up to 2,100°K).
In later years these sheet metal blades had very small tubes fitted inside the blade in order to direct the cooling air to the most advantageous position, usually one third of the blade height from the root as shown below.
Another trial was made with ceramic cores in the cast blade to produce air passages. Development of these ceased after the takeover mentioned above and the removal of personnel to Stag Lane.
These blades were being tested by D Napier & Son in the late 1950s. An article in Model Engineer dated 1989 described turbine blades and the harsh environments in which they had to work. It stated that 25 years previously (i.e. 1964) "there were no cooled turbine blades". As you can see above Napiers were well ahead of the game!
Courtesy Michael Davidson NPHT