Toller wrote:
> Why doesn't it take as long to dry out as it did when the wood was fresh?
It's a question of where the water is (read Hoadley for details).
Water in timber can be either inside the cells or between them. When
you dry green timber the between cells water is first to move and it
doesn't start to shrink until amost all of this has gone and the
moisture inside the cells begins to diminish too.
If you steam dry timber, then it's impractical to put water back into
the cells and so the added steam sits between the cells. When drying it
after steaming, this is easily removed and the timber dries quickly.
However this is a different situation to steaming green timber, which
still contains water inside cells. That's why steaming green timber
works better anyway - inside the cells is still "wet" making bending
.easy, something which can't be replicated by adding steam to dry
timber. Obviously bent steamed green timber is still green afterwards,
so this takes just as long to dry after steaming as the green timber
would have done anyway.
One of the favoured bending timbers in the UK is ash. This is riven
(split) and steamed for bending while still green. Ash is know as
excellent firewood though, for its low moisture content while still on
the tree. Green ash bends well with little added steam, then dries
quickly afterwards.
It's not so much the moisture as the heat that makes a difference in
bending. By using steam it gets deeper into the wood since it will
wick up the water thus drawing in the heat. And since it's hot it
will evaporate quickly as well.
On Mon, 09 Oct 2006 02:28:26 GMT, "Toller" <[email protected]> wrote:
>After you steam bend wood, does it take time for the wood to dry out again?
>
>I have steamed wood to restore dents and it drys out pretty immediately, so
>I expect steam bending is similar, but why? Why doesn't it take as long to
>dry out as it did when the wood was fresh?
>
On Mon, 09 Oct 2006 02:28:26 GMT, "Toller" <[email protected]> wrote:
>After you steam bend wood, does it take time for the wood to dry out again?
>
>I have steamed wood to restore dents and it drys out pretty immediately, so
>I expect steam bending is similar, but why? Why doesn't it take as long to
>dry out as it did when the wood was fresh?
>
IIRC
In standing wood there are two types of moisture; Bound and Free. That
is--- either within the cell wall , or within the cell cavity. As the
wood dries the Free water will deplete first and there is some point
called Fiber Saturation Point, when the walls are holding a max amount
of moisture.
Steaming does not impart moisture within the cell walls but only in
and around the cell cavities...something like Free water in a standing
tree, I think.
Thus, just like the Free water leaves the tree shortly after cutting,
steam moisture departs rather quickly as well.
You might want to Google *wood moisture* and read up.