Foundry Castings

[Alan R. Barnard]

I stand corrected.

"Modulus of elasticity?" I thought we didn't use that kind of language in
polite company.

Alan Barnard


----- Original Message -----
From: "Ron Nossaman" <RNossaman@cox.net>
To: <pianotech@ptg.org>
Sent: Tuesday, August 27, 2002 8:38 PM
Subject: Re: Foundry Castings



>Cast iron IS brittle but it will not deform nor compress under stress and
>tension the way steel, aluminum, and other metals do.

The modulus of elasticity of gray cast iron is lower than that of either
cast, or rolled steel. It is, if anything, more flexible than steel. It
just doesn't bend very far before it breaks.


>Nor does it expand and contract with changing temperatures as much as
>other metals. The key point is that it holds its shape and, most
>important, the critical string length dimensions.

This is correct. It is more dimensionally stable with temperature swings. I
make the difference in length changes for a 1 meter bar of each to be about
0.0044 millimeters (0.00017") for a 20°F change. If I did that right...
Just leaning against the piano will probably distort it at least that much,
especially with a cast iron plate <G>. In any case, I think the string
length dimensions would be relatively safe in either.


>I understand that cast aluminum was tried back in the 40's or so. It would
>sure be nice to find a different, lighter, less brittle material--then you
>wouldn't need such a heavy wood frame either.

Why wouldn't you?


>I'm guessing that a lot of the metal in the casting is just to make the
>plate "beefier" so it doesn't break so easily.
>
>Alan R. Barnard

I expect so, and to keep the flex to a minimum between struts.

Ron N