[CAUT] about magnets

[Ken Zahringer]

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OK, let=B9s see how much I can remember from =B3Elementary Strengths of
Materials=B2 from 1976.

Technically, springs don=B9t =B3wear out=B2.  The amount of force needed to bend
or compress a spring a given amount, it=B9s =B3rate=B2, is dependent on what the
spring is made of and it=B9s cross-section area.  In the absence of corrosion=
,
this doesn=B9t change.  What does happen is that if a spring is subject to a
constant stress, like a wippen spring that is slightly compressed when the
key is at rest, the shape of the spring will, over many years, conform to
that stress.  I have also seen this happen with upright hammer springs =AD yo=
u
unhitch the spring and it only moves a little bit, and it almost certainly
didn=B9t start out that way.  Effectively, then, the spring isn=B9t compressed
as far as it once was in it=B9s rest position, so it=B9s not exerting as much
force.  The distinction, I guess, is pretty academic.  From the player=B9s
point of view, the spring has worn out.

Of course, corrosion is also a factor in old springs, usually in the form o=
f
rust, and it does decrease the spring=B9s rate by degrading the metal.  And i=
f
you try to re-bend an old spring to regain it=B9s performance very many times=
,
you can weaken the metal some.  Like bending a coat hanger until it breaks.

Synthetic magnets do slowly lose their field over time, at least
theoretically.  However, given the quality of magnets available today, I
doubt that you could measure a change in the field after 100 years.

That=B9s all I remember.

Ken Z.


On 3/22/05 4:41 PM, "Ed Sutton" <ed440@mindspring.com> wrote:

> O, Great Minds of Caut!
> =20
> I have heard tell that Petrof is producing grand pianos with a magnetic
> assisted action, soon to arrive in our neighborhood.
> =20
> The magnets are installed in the wippen rail and wippen in repelling
> orientation so that the magnets lift the wippen similar to a wippen assis=
t
> spring.  The touchweight can be refined by adjusting the magnets similar =
to a
> screw regulated wipen assist spring.  Functionally it seems identical to =
a
> wippen assist spring.
> =20
> When I asked how it differed from a wippen assist spring I was told "Spri=
ngs
> wear out, but magnets last forever."  I would be interested in educated
> comments on that statement.  The magnets will be held continuously in
> opposition and "compression."  Will they grow weaker over years? decades?=
 or
> will they last forever?
> =20
> How does this compare with assist springs?  Do wippen assist springs grow
> weaker over time?  Faster than magnets?
> =20
> Jim Ellis, I thank you in advance!
> =20
> Sincerely,
> Ed Sutton
> =20
>=20


--=20
Ken Zahringer, RPT
Piano Technician
MU School of Music
297 Fine Arts
882-1202
cell 489-7529


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