belly tempering temperature
scp
"Wood handbook : wood as an engineering material"
http://www.treesearch.fs.fed.us/pubs/5734
[19-1] Plasticizing Wood
Principles of Plasticizing and Bending
In simple terms, the wood cell wall is a composite made of a
rigid cellulose polymer in a matrix of lignin and the hemicelluloses.
The lignin polymer in the middle lamella and S2
layer is thermoplastic; that is, it softens upon heating. The
glass transition temperature Tg of the lignin in the matrix is
approximately 170°C (338°F). Above the matrix Tg, it is
possible to cause the lignin to undergo thermoplastic flow
and, upon cooling, reset in the same or modified configuration.
This is the principal behind bending of wood.
The matrix can be thermoplasticized by heat alone, but the
Tg of the unmodified matrix is so high that some fiber decomposition
can occur if high temperatures are maintained for
a lengthy period. The Tg of the matrix can be decreased with
the addition of moisture or through the use of plasticizers
or softeners.
It appears that wood plasticizes at 338°F.
In that case, if you don't have a caul and are as impatient as me,
you can lower the heat gun temperature setting (7 out of 10 in my case)
and hold the gun rather close to the belly.
But the question is whether this bending temperature is
enough for heat treating (tempering) the belly.
http://en.wikipedia.org/wiki/Heat_treatment_of_wood
There are 3 similar European heat treatments: Retiwood, developed in
France, Thermowood, developed in Finland by VTT, and Platowood developed
in The Netherlands. These processes autoclave the treated wood,
subjecting it to pressure and heat, along with nitrogen or water vapour
to control drying in a staged treatment process ranging from 24 to 48
hours at temperatures of 180 to 230°C depending on timber species. These
processes increase the durability, dimensional stability and hardness of
the treated wood by at least one class; however, the treated wood is
darkened in colour, and there are changes in certain mechanical
characteristics: specifically, the modulus of elasticity is increased to
10%, and the modulus of rupture is diminished by 5% to 20%; thus, the
treated wood requires drilling for nailing to avoid splitting the wood.
Certain of these processes cause less of an impact than others in their
the mechanical effects upon the treated wood. Wood treated with this
process is often used for cladding or siding, flooring, furniture and
windows.
I might have asked the same question before.
What is the proper temperature for heat tempering the belly of a bow?
Is it the same for all kinds of wood?