Fw: Wood

[Farrell]

I was expecting maybe at least Don might respond to this post I made a couple days ago. I see Don is back. What is your read on this?

Terry Farrell
  
----- Original Message ----- 
From: "Farrell" <mfarrel2@tampabay.rr.com>
To: "Pianotech" <pianotech@ptg.org>
Sent: Sunday, February 16, 2003 9:11 AM
Subject: Re: Wood


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   =    MC            
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  

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

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

----- Original Message ----- 
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 70º F (or 90º 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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