Singing Strut

[Roger Jolly]

At 06:12 AM 11/24/97 -0600, you wrote:
>I know Wickham went into it more in his class, but I just don't remember
much about it.  Maybe someone else can fill in more details.
>
>Bob Hohf
>Wisconsin
>
>----------
>From: 	David ilvedson[SMTP:ilvey@a.crl.com]
>Sent: 	Sunday, November 23, 1997 2:29 PM
>To: 	pianotech@ptg.org
>Subject: 	RE: Singing Strut
>
>
>
>> 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
>> 
>>Greetings All,
                I'm trying to recall imformation from my University
Metallurgy classes and after 30yrs its a bit hazy.  Carbon exist in cast
iron in what is refered to as free carbon. It does not bond to the iron
(ferrite) but floats in the cast as seperate crystals. The manner in which
the iron is smelted the amount of coke and the rate of cooling, will
determine the size and distrubution of the free carbon.  The carbon content
helps to determine the ridgity of the plate, piano plates are cooled quite
slowly compared to other castings, so that there will be consistancy
through out the cast, and to relieve many of the stresses that build up
during cooling.
  The free carbon also acts as a built in lubricant, part of the reason the
strings can slip through pressure bars.(graphite a type of carbon)
  Cooling cast iron too rapidly can create large inclusions into the material,
we have all seen these big pits on the V bars of smaller pianos. Rarely do
we see them on larger grands due to the fact the foundries tend to be much
more careful in the cooling stages, to ensure adequate stress relief.
Hope this sheds a little light.
Regards to all.>> 
>
>
>
Roger Jolly
University of Saskatchewan
Dept. of Music.