National Conference on Forest Products 59 
The great variation in seasonal draft kiln. There are several different 
weather conditions did not lend itself kilns of the forced-draft type, but the 
to uniform conditions necessary to best best known are the northwest blower 
results. This naturally led to experi- kiln and the new internal-fan kiln de- 
ments with artificial methods in an veloped by the Forest Products Labor- 
effort to produce constant conditions atory. 
requisite to favorable results. This When preparing our plans for the 
condition existed in the South and re- construction of our new western plant, 
] sulted in the development of the so- Wwe called upon the Forest Products 
called “Arkansas smoke kilns.” These Laboratory to make exliaustive tests 
smoke kilns, however, were extremely for us, and to give us the benefit of 
hazardous; and their use resulted in the results of such tests. We care- 
many fires and the destruction of fully considered the results of these 
property, as well as improperly dried tests, and after due deliberation de- 
lumber. The next development in the cided that the internal-fan kiln was 
Southern States was that of the “hot- the best kiln available for our pur- 
air kilns,” using hot-air furnaces. Doses. It is constructed so, as to 
This type of kiln, while less hazard- thermostatically control two of the 
ous than the old smoke kilns, and three elements entering into the dry- 
more ‘efficient, was very hazardous. ng of lumber (temperature and 
Many fires originated therein, result- humidity), and to mechanically con- 
ing in insurance rates, on such uits, trol the third, circulation. The other 
of 10 to 12 per cent. Steam kilns types of forced-draft kilns have con- 
were the natural successors of the trol of humidity and temperature, but 
earlier types. do not have mechanical control of 
The development of the thought of circulation; i. e., the ability to reverse 
artificial drying versus air drying of the circulation. We concluded we 
high-grade lumber was for the pur- could not secure even drying without 
pose, primarily, of reducing the losses control of circulation, and therefore 
through degradation due to checking, decided to adopt the kiln developed 
twisting, discoloration, and other air- by ‘the Forest Products Laboratory. 
seasoning degrades. ; ! The only remaining feature, in my 
In the earlier days it was thought judgment, to make these kilns perfect 
impossible to kiln-dry common grades Is the development of some character 
of lumber, but with the development 0f automatic control of circulation, 
of the steam kiln many of the op- under a time-clock arrangement, so as 
erators in the South began drying to eliminate entirely the human ele- 
their No. 1 common grades, for the ment in kiln drying. 
reason that this process reduced the We had one of the internal-fan type 
time that lumber had to be carried in Kilns installed at one of our southern 
stock, as well as the degrades inci- mills, and made a complete check of 
dent to air drying. Hventually the its operation as against our steam 
process proceeded to the point where Kilns in which we did not have control 
all grades of lumber, at some opera- Of the circulation, grading the lum- 
tions in the South, are kiln-dried, and ber green before charging the kiln, 
we are getting better results from this and grading it dry after discharging 
artificial means than were possible it from this kiln, with the result that 
from air drying. we came to the conclusion that by 
The matter of artificial drying has changing our 12 kilns at that plant 
been more or less in the process of over to the internal-fan type, at a cost 
evolution. One by one the difficulties hot to exceed $48,000, we could save 
have been overcome, until to-day we in that operation, through reduction 
have the new forced-draft kilns, which in degrades, $105,000 per year. 
give a more or less automatic and me- In other words, our experience, gen- 
chanical control of the necessary ele- erally speaking, has been that de- 
ments of drying lumber. In all meth- grades may be very materially re- 
ods of steam drying, we have had duced through the use of the internal- 
more or less control of two of the fan kiln, as compared with the ordi- 
three necessary elements to drying nary steam kiln. Our experience with 
lumber, e., humidity and tempera- this new kiln in our western operation 
ture— but we were dependent entirely has developed the fact that we are now 
On natural circulation; and of the drying lumber with practically no 
three elements entering into the dry- checking, cupping, twisting, warping, 
Ing process, possibly circulation is the splitting, or discoloration. Large and 
most important element, and on ac- loose knots that will check or loosen 
count of this situation there has been in air drying will do so with artificial 
developed what is known as the forced- drying. 
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