The best method of humidity control proved to be to reduce the
relative humidity of the air from 100 per cent (saturated steam) very
carefully at first and then more rapidly to 30 per cent in about four
days. If the change is too marked immediately after the steaming
period, checking will invariably result. Under these temperature and
humidity conditions the stock was dried from 15 per cent moisture,
based on the dry wood weight, to 6 per cent in five days' time. The
loss due to checking was about 5 per cent, based on the actual footage
loss, not on commercial grades.
=Final Steaming.=--From time to time during the test runs the material
was resawed to test for case-hardening. The stock dried in five days
showed slight case-hardening, so it was steamed at atmospheric
pressure for 36 minutes near the close of the run, with the result
that when dried off again the stresses were no longer present. The
material from one run was steamed for three hours at atmospheric
pressure and proved very badly case-hardened, but in the reverse
direction. It seems possible that by testing for the amount of
case-hardening one might select a final steaming period which would
eliminate all stresses in the wood.
Kiln-drying of Green Red Gum
The following article was published by the United States Forestry
Service on the kiln-drying of green red gum:
A short time ago fifteen fine, red-gum logs 16 feet long were received
from Sardis, Miss. They were in excellent condition and quite green.
It has been our belief that if the gum could be kiln-dried directly
from the saw, a number of the difficulties in seasoning might be
avoided. Therefore, we have undertaken to find out whether or not such
a thing is feasible. The green logs now at the laboratory are to be
used in this investigation. One run of a preliminary nature has just
been made, the method and results of which I will now tell.
This method was really adapted to the drying of Southern pine, and one
log of the green gum was cut into 1-inch stock and dried with the
pine. The heartwood contained many knots and some checks, although it
was in general of quite good quality. The sapwood was in fine
condition and almost as white as snow.
This material was edge-stacked with one crosser at either end and one
at the center, of the 16-foot board. This is sufficient for the pine,
but was absolutely inadequate for drying green gum. A special
shrinkage take-up was applied at the three points. The results proved
very interesting in spite of the warping which was expected with but
three crossers in 16 feet. The method of circulation described was
used. It is our belief that edge piling is best for this method.
Public-domain text, read in full here on John Shaqi.
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