NNR IN RAPIDLY ROTATED METALS By - Nottingham eTheses ...

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with a minimum of tension but at higher rotation rates they were
most stable when the tension was increased to about 40 gm. The
tape used was 0.005" thick glass reinforced PTFE obtained from
Tygadure Ltd. Thinner tape was less able to withstand the rigors
of the rotors starting and stopping and thicker tape tended to
be too stiff. Metal tapes have proved more successful for rotors
with larger diameter axles.
The driving jets were constructed from brass or aluminium
with two or three equally spaced about each set of rotor flutes.
For starting a simple on/off switch was used with an air pressure
of around 100 psi. The rotors then quickly accelerated to a
stable spinning speed. The most efficient drive was achieved
using ä nozzle diameter of 0.025". The rotor flutes were cut to
a depth of 0.025" with 24 in each set. By placing the rotor so
that the propelling gas impinged against the curved face of the
flutes it was found that the rotors were sufficiently constrained
axially to make superfluous the use of any separate positioning
jets.
In theory the three-pad foil bearing is ideal for its purpose
because it supports the rotor equally in all directions about the
axis of rotation. However a two-pad system was found to be
equally efficient. This considerably facilitated the construct-
ion of a rig capable of supporting the rotors within the magnet
gap. Because the tapes had to be free to move, the foil guides
were rounded with a polished surface. They were glued separately
on to the two halves of the rig after machining. The full experi-
mental rig is shown in Figure 4.7, and Figure 4.8 shows the rotat-
ion rates achieved in it by a solid aluminium rotor.
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