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Author Topic: Wood science question - hysteresis  (Read 840 times)

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Offline Dan_Shade

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Wood science question - hysteresis
« on: February 26, 2016, 06:31:03 AM »
Does wood eventually acclimate to a point that it no longer changes with humidity changes?
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Offline WDH

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Re: Wood science question - hysteresis
« Reply #1 on: February 26, 2016, 07:19:24 AM »
No.  It will always change as the humidity changes.  If it has a finish on it that seals the wood in a stable environment, then the changes can be very small so as to not amount to much. 
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Offline Dan_Shade

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Re: Wood science question - hysteresis
« Reply #2 on: February 26, 2016, 01:12:38 PM »
Thanks, I have a video from Christian Becksvoort where he talks about how over time, the movement becomes smaller, I'll watch it again to provide a better reference.

I was wondering if museum curators of old furniture notice movement.
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Offline GeneWengert-WoodDoc

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Re: Wood science question - hysteresis
« Reply #3 on: February 26, 2016, 04:51:21 PM »
The movement continues forever.  What does change is the amount of movement when you change direction.  That is, with humidity that is drier, then more humid, then drier, etc.  with each change in direction, there is a lag before the moisture changes and a lag before the wood starts to shrink or swell.  This lag is called hysteresis.  So, it appears that the wood is more stable.  There is also a difference in swelling or shrinking if the humidity change is fast (more change) or slow.  However, the changes do not moderate with time...the change for a piece at a given RH change and from a certain moisture content is the same 10 years ago and this year.

All in all, it is the first change for a newly made piece of furniture that will be the largest.  The annual changes after the first six months will be smaller.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline Dan_Shade

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Re: Wood science question - hysteresis
« Reply #4 on: February 26, 2016, 05:00:08 PM »
Gene, does that mean that wood may eventually not respond to a change from 50% to 40% relative humidity?  Or that the dimensional changes occur more slowly.
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Offline GeneWengert-WoodDoc

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Re: Wood science question - hysteresis
« Reply #5 on: February 29, 2016, 07:22:22 AM »
If I have higher MC lumber that I dry to 7.5% MC (about 40% RH) and then increase the RH to 45% RH, the wood will essentially do nothing.  Then up to 50% RH, it might get to 8.5% MC.  Then if I go back to 45% RH, nothing will happen.  Then continue to 40% RH, maybe 8.0% MC.  Then 45% RH, nothing.  Then up to 50%, 8.5% MC.  Etc.  ad infinitum.  Lumber Size, speed of RH change, temperature, and coatings affect the speed but not the end point basically.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more


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