>> Paul,
    >>
    >> When I was at the Seven Stock Show, I noticed that all of the
   rotors were
    >> cast iron. Has anyone made aluminum rotors? Is there too much
   thermal
    >> expansion to use aluminum? I was also thinking that the rotors
   could be
    >> made of a ceramic--low expansion, lighter weight, and possibly
   lower
    >> cost.
    >>
    >> Steve Brazil
    >>
    >> I think it is a heat issue. The rotors can run 500 F or more.
    >> Titanium seems to work but it is expensive.
    >>
    >>
    >> --
    >> Paul Lamar ...No rotor no motor.
    >
    >
    > Paul,
    >
    > That's interesting. Titanium likes heat and it's highly corrosion
    > resistant, although it has problems around metals like cadmium.
   It does
    > very well with investment casting. I have some very large
   investment cast
    > Ti parts around the shop at work--on the order of 50 lb. I would
   think a
    > rotor would be easy. Do the rotors wear out?
    >
    > I heard somebody at the show talking about a ceramic either rotor
   or seal
    > that they were using in a Formula Mazda car. I think one of the new
    > ceramics would be worth looking at.
    >
    > I don't know if anyone has done this, but the rotor could also be
   machined
    > in halves out of stainless steel, electron beam welded together then
    > finish
    > machined. This would make a very light, strong rotor although a
   precision
    > investment casting in stainless steel would be very close to this.
    >
    > Steve
    >
    > Yes rotors wear in the apex seal slots. They are good for 300,000
   miles
    > in a car and well over 2000 hours in aircraft service. They are
   hardened
    > only
    > at the ends of the slots. A chrome plated or totally hardened
   slot would
    > reduce the wear further. I don't know what the situation would be
   with
    > titanium rotors. I always thought that a aluminum rotors with steel
    > inserts for the apex seal slots might work. This is done on heavy
   duty
    > aluminum pistons with the piston ring slots in some aircraft engines.
    >
    > I also don't know what the life would be with ceramic apex seals.
    > I suspect it would further extend the life of the rotor slots.
    >
    > Also worn rotor slots can be ground out for 3 mm apex seals.
    >
    > Paul Lamar ...No rotor no motor.

   Steve,
   I believe I read somewhere that Ti doesn't wear well, if that's the
   case the
   apex slot could wear quickly. It is already a problem in steel -
   however a
   steel insert could be the solution. A replaceable slot insert would
   also be
   the solution in the steel rotor.

   BTW apart from the slot, I've never heard of a rotor being worn out, Ti
   would be a good investment.
   George (down under)

Ti is a great material except for the fact that it is notch sensitive
and "gummy". It doesnt like to be scratched or galled. It would make for
great side housing and rotor material if it werent for the fact that
anything that rubs against it will gall it up. Steel inserts are
definitely a possible solution but then you get into dissimalar metals,
their expansion rates and the induced press fit stresses involved. I was
thinking the possible use of cast titanium side housings in order to
avoid having to use the exhaust inserts on I/E side port design but I
havent found a surface treatment that would allow the housing to survive
the side seals scraping against it. Also still dont know if it would
survive the the heat in the exhaust port as Paul has quoted 1600F. Still
toying with ideas to see if anything is worth it.

Rob Woods

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