Singing Strut

[Doug Richards]

     David and list,
     
     I meant to look up the material properties today, but now I'm home 
     again (ol memory aint like it used to be).
     
     From what I remember as a welder years ago, cast iron has a very high 
     carbon content! I think the carbon content is even higher than tool 
     steel, although the grain structure is completely different.  If I 
     were to guess, the internal damping factor for Cast Iron is even lower 
     than steel (since it is so brittle).  As for struts, it's the strut 
     stiffness and mass that usually takes too much energy to excite.  Of 
     coarse, any structure will sing with the correct input...
     
     I will look the material properties tomorrow if anyone is interested.
     
     
     doug richards
     Associate Member #12550
     San Jose CA
     
     
______________________________ Reply Separator _________________________________
Subject: RE: Singing Strut
Author:  "David ilvedson" <ilvey@a.crl.com> at SMTP 
Date:    11/23/97 8:29 PM
     
     
> From:          "Robert W.Hohf" <rhohf@idcnet.com>
> To:            "pianotech@ptg.org" <pianotech@ptg.org> 
> Subject:       RE: Singing Strut
> Date:          Sun, 23 Nov 1997 19:24:27 -0600 
> Reply-to:      pianotech@ptg.org
     
Now that is interesting...I thought that cast iron naturally had 
a high level of graphite/carbon in it.  I didn't know? it was 
added for piano manufacturing.  Is this really true?
     
David ilvedson, RPT
Pacifica, CA
     
     
     
> 
> 
> A number of years ago I attended a very interesting and informative class 
> given by Henry(?) Wickham of the now defunct Wickham Foundry.  One of the 
> topics he covered was how the composition of the iron effects the resonance 
> of the casting.  Here is what I recall him saying (FWIW):  it is the 
> addition of carbon to the iron which reduces the resonance.  It seems that 
> one of the difficulties in the casting process is keeping the carbon 
> uniformly distributed in the molten metal.  When enough carbon migrates out 
> of a strut, the strut can sometimes resonate at a distinct  frequency.  If 
> this is true (it's been quite a few years),  it would seem to indicate that 
> a "singing strut" is not necessarily due to faulty design, but possibly 
> faulty casting.  However, none of this helps to solve the problem. 
> 
> Bob Hohf
> Wisconsin
> 
> 
>