Open face vs. closed face pin blocks

[Delwin D Fandrich]

----- Original Message -----
From: "Phillip L Ford" <fordpiano@lycos.com>
To: <pianotech@ptg.org>
Sent: August 16, 2001 10:05 PM
Subject: Re: Open face vs. closed face pin blocks


> I checked my notes.  This is not from a handout but from a note that
> I wrote down myself.  Gray iron 35 ksi.  I could have made a mistake.
>
> I checked a couple of engineering references.  Representative numbers
> are:
>
> ASTM A 48  Class 20 to Class 60 with tensile strengths of
> 20000 to 60000 psi.
>
> So, 35000 psi is certainly well within this range.  It would depend on the
> specific 'recipe' that Kelly is using.  Also, I don't know if they use the
> same recipe for everyone's plates.

At the time Kelly was using the same mix for everybody. I don't know if that
has changed since the early 1990s. I wanted to move up to something in the
35,000 psi range for our plates and was told it couldn't be done.



> The different classes have different
> microstructure with some changes in various properties that certain
> manufacturers may want.  For instance, I believe damping capacity and
> machinability increase as you move down in class and strength, stiffness,
> and wear resistance go up as you move up in class.

This is essentially the case. The properties of gray iron castings depend
only partially on the actual mix. They also depend on several
characteristics of the casting process: how fast the iron is poured, how
fast it is allowed to cool, its cross-sections, etc. If you break up a piano
plate and test it for tensile strength you'll find that this varies
considerably from one area to another.

Del