[modeleng] Ally boiler

At 02:55 PM 10/24/06 +0100, you wrote:
>Is there any problem building a working steam boiler . . . . completely
from Aluminium.

Julian,
     I suppose it could best be said this way, if aluminum was such a
marvelous or even acceptable material for boilers everyone would build one.
 However in fact in my (many) years involved in model engineering I've
never known of a single aluminum boiler.  There may very well have been an
experimental one built here or there but to my knowledge there has been
none built for a model that was intended to be working and have a
reasonable life span.
     I am not a metalurgist, and there may very well be an ally alloy which
has fantastic properties, but two basic drawbacks come to mind.  First, the
strength of metals changes as temperatures rise, as with copper for
instance.  What is strong enough at 80=B0F may not be at 450=B0F, or in the
case of the firebox in excess of 1000=B0F.  I'd wager there is a significant
(and fatal) dropoff in tensile strength of ally above a certain temperature.
     Secondly, the phase change of water to steam creates a very aggressive
corrosive action at the point of change.  Copper and to a lesser extent
steel are able to withstand this action for long enough to give the boiler
a reasonably long life (10-25 years).  I would seriously doubt that an ally
alloy could last so long.
     In general it is not a very good idea.


Regards,
Harry Wade
Nashville  Tennessee

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