Wood

[Farrell]

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Well, that is more-or-less what I did Del. My aim was to calibrate a =
panel-type MC gauge, so RH and MC stability were my aims, not =
necessarily measuring rate of change. But I do have some data that might =
shed some light on this subject.

I took 2 to 6 blocks of wood (approx. 8 mm x 100 mm x 100 mm - my 0.01 =
scale only goes up to 100 grams, so I needed to stay with block of less =
than that - they were all between 50 and 95 grams) - mostly spruce, but =
some mahogany and hard maple (all pretty much reacted the same except =
the maple was slower to change MC overall). I placed blocks in my hot =
box and varied RH and left it at different levels for several days to be =
sure wood MC had stabilized. I would weigh blocks every day. Experiments =
ran (I actually did several) up to 34 days. If anyone wants the raw =
data, I can send it to you. Some approximations follow (I looked for a =
near-equilibrium conditions, a rise or fall of RH, and then =
near-equilibrium conditions again):

RH                DAYS   =3D    MC           =20
20% drop      2.5            2.7% drop
14% rise        5.0            1.3% rise
12% drop       5.0            1.3% drop
 9% rise          4.0            1.0% rise

These data represent fairly stable endpoint conditions (both hot box RH =
and MC, except for the 20% drop, the wood had not stabilized before the =
hot box RH went back up a bit, but MC did in fact drop 2.7% in 2.5 days, =
it had simply not yet reached equilibrium).

>From these data, it looks to me like wood looses moisture as easily as =
it gains it.

Terry Farrell =20

----- Original Message -----
From: "Don" <pianotuna@accesscomm.ca>

> Can someone suggest a better protocol for such an experiment?

----- Original Message -----=20
From: "Delwin D Fandrich" <pianobuilders@olynet.com>

Yes.

Put a piece of wood--since we're interested in piano tuning stability, =
let's
make it a Sitka spruce panel about 8 mm thick by, say 250 x 250 mm--in a
hermetically sealed environment stabilized at 70=BA F (or 90=BA F, or =
whatever,
just so the temperature remains stable throughout the experiment) and =
50%
RH. With the wood sample placed on a very precise and accurate scale,
monitor its weight until it has stabilized. Rapidly raise the RH to 70% =
and
periodically monitor and record the weight change over time until the =
weight
of the sample has again stabilized. Rapidly take the RH back down to =
50%,
again monitoring the weight change at the same time intervals. Following =
the
same procedure take the RH further down to 30% and then back up to 50%.

If you take weight readings frequently enough this should give you a =
pretty
good idea of the rate at which the sample absorbs and desorbs moisture. =
In
the end I expect you'll find it's about the same both ways.

Del

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