George Wright wrote:
     > It's my understanding that RotaMax has gone to a ceramic lining. I
     > confess to not have much background with this approach. At some
     > point, the lining will begin to transfer heat to the housing.
     > I'm wondering if there is a differential expansion between the
     > two materials and if this falls within the tolerances of the seals?

    You've hit upon one of the fundamental challenges, but missed the
    impact. The seals can move more than enough to accommodate thermal
    expansion. The problem is that aluminum (the housing substrate) has a
    rather high coefficient of thermal expansion, while all ceramics I know
    of (not that many) have fairly lower coefficients of thermal expansion.
    So as the engine heats up, the housing wants to separate from any
    ceramic coating on the inside of the housing. As a general rule,
    ceramics have great compressive strength, and lousy tensile strength.
    The expansion of the housing puts the liner under tensile stress. The
    coating, being thin and hard, generally fractures and de-bonds at this
    point.

    I'm no materials engineer ("but I play one on TV"), but I've got some
    lay ideas on ceramic/aluminum bonding that address this. Because of
    possible patentability, I'm not going to discuss it here.

     > My background with ceramic seals and liners was back in the late
     > 70's and early 80's when we used it for short-life turbines. The
     > application was expendible and you didn't require an engine that
     > had to live more than 150 hours (the darn things tended to be
     > lost for other reasons before 50 hours).

    And I bet that the turbine liners weren't bonded to a highly expansive
    substrate.


    Russell Kent

    I have seen a rotary engine that had ceramic coating on the
    rotors. The ceramic came off and destroyed the rotor housings wear
    surface.
    The rotors are low coef. of expansion iron no less.
    Dave Leonard has the engine. Dave can you please take some pictures
    of the rotor and the housing in question before you leave?

    Paul Lamar ...No rotor no motor.

    Technical ceramics has greatly surpassed the commode that squirts
    you in the butt.  Forty years ago at Corning Glass Works R&D,  I
    developed sheet glass with sufficient tensile strength to bend
    around a 16" diameter drum. Don't ask how much Corning spent on that
    project. The glass was great but the cost of the application was
    prohibitive.   The problem is that most of solutions we are
    discussing will cost $$$$!  So Paul, you need to go out and buy a
    lottery ticket for the big drawing tonight.
    Joel
    Over the Hill Materials Engr

I must be getting senile - I don't remember the substrate material in those
turbines.  They put the C in crude though.  On the other hand, they did what
they were supposed to do for the time they were supposed to do it and for a
fraction of the normal cost.  "horses for courses"!

george wright


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