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HARDWOOD RECORD 



ditions of moisture, temperature and circulation. Again, however, 

 it was thought perfection had been attained and every concern 

 who had sold a foot of pipe for dry kilns advertised in bold head- 

 lines "moist air dry kilns will dry your lumber without degrad- 

 ing." Avoid such general statements. Tliey are misleading. It 

 is no more true that the haphazard introduction of moisture will 

 make efficient dry kilns than it is true that the haphazard method 

 of applying heat to the bake-oven kiln would produce elGciency'. 

 The terra moist air as applied to dry kilns, unless qualified by the 

 assurance of adequate control and regulation, has become so gen- 

 eral and indefinite that it is absolutely lacking in any real descrip- 

 tive force. The term is misleading and means nothing but the in- 

 troduction of a little artificial moisture in one way or another. 

 It bears no relation to the heat and ventilation which arc equally 

 important considerations. 



It has remained for the last four or five years to develop a dry 

 kiln in which careful attention has been given to the control of 

 operation and to the three absolutely essential functions of lum- 

 ber drying, viz., humidity or moisture, temperature or heat, and 

 ventilation or circulation. Unless all these three elements are 

 carefully considered in the preliminary designing of the building, 

 the selection of the building material, the proportion of radiation 

 furnished and the type of ventilation, the results can be no other 

 than haphazard. 



Two control methods are in general use today. These are the 

 so-called condensing kiln and the expansion kiln. The condensing 

 kiln has been designed on the basis of air recirculation — in other 

 words, the air in the kiln is circulating over and over and around 

 and around the lumber, and at certain regular intervals in this 

 circulation passes over cold water pipes or open water sprays 

 where some of the moisture is condensed from the circulating air. 

 The air thus relieved of part of its moisture passes on again to 

 • do additional duty in again absorbing moisture from the lumber 

 and yielding it to the condenser. If the moisture charged air is 

 exhausted from the kiln, instead of recirculated, and fresh air 

 is drawn in, it is obvious that nature will do, without charge, the 

 duty devolving on condensers in this type of kiln. The main- 

 tenance of temperature in the condensing medium is a very dif- 

 ficult matter. The cost of water used in condensers is excessive 

 and unnecessary. The corrosion and coating of pipes or spray 

 devices used for condensation will be a very serious item in run- 

 ning expense because there will be removed from the lumber large 

 amounts of acid and organic matter which will tend to rapidly 

 corrode any exposed surfaces. The tannic acid of oak and chest- 

 nut is especially harmful to the ironwork of any kiln wherein 

 humidity and heat are combined. 



The control of circulation in a condensing kiln is uncertain as 

 there is no draft from the outside which can be depended upon to 

 pull, and the recirculation must rely upon the application of heat 

 only. The advocates of condensing kilns claim the advantage of 

 independence from outside conditions, but it is a grave question 

 if this is not a serious disadvantage. In other words, the con- 

 densing kiln attempts to do artificially what nature will willingly 

 do if given a fair chance. 



The condensing kiln has been adopted by government depart- 

 ments for its experiments because it believes that it will serve to 

 control the conditions in the kiln more accurately than any other 

 method. They freely admit that it is an expensive type of kiln 

 to install, elaborate to operate and is so particular in its demands 

 for care and attention as to be impractical for the average wood- 

 worker who desires reasonably "fool proof" equipment. 



The expansion Iciln is the latest development of the lumber dry- 

 ing art. In this kiln we have adequate control of the heat, humid- 

 ity and the circulation. Humidity control means that the water 

 vapor in the atmosphere of the kiln can be increased or decreased 

 at will. The lumber on entering the kiln can be immersed in a 

 hot fog W'hich will be an absolute safeguard against caseharden- 

 ing and its attendant evils. This hot fog, which is maintained to 

 a more or less degree through the entire drying process, is an 

 absolute preventive of fire in the kiln. It is impossible to light 



a match or carry a lighted candle or lantern in this type of kiln, 

 as the fog is too dense to permit a flame to live. This fog, -when 

 properly combined with heat and pressure, may be forced into the 

 lumber in such a way that the free moisture can be rapidly 

 vaporized and the moisture contained in the cells can be heated 

 and expanded so that the cell walls will be opened, the check 

 valves loosened and the opportunity afforded for the removal 

 of all organic matter. To refer again to our analogy in the 

 kitchen; if a potato is steamed or boiled it will expand to the full 

 limit of its skin and usually crack or open tlie skin. At the same 

 time the steamed potato is drier at the center than the baked 

 specimen. Lumber with cells thus expanded and opened has lost 

 its power of contraction, because the sap cells are empty. Is it 

 not clear that lumber thus dried will not be shrunken and there- 

 fore cannot swell or change dimension appreciably after leaving 

 the kiln? 



In absence of this hot fog, or in a bakeoven kiln, these sap cells 

 will be shrivelled up with contents dried to a granulated form. 

 This dried and shrivelled cell when exposed to moisture will again 

 swell. Consequently bake-oven dried lumber will shrink because 

 its sap cells shrivel and it will again swell because its shrivelled 

 cells will swell when exposed to moisture. 



Let us think what this means to woodworkers. It means that 

 when the lumber is dried by the humidity or expansion process 

 the interior trim placed in a building will not show the usual 

 shrink or swell. Doors, wainscoting, bookcases and every part 

 of the handsome and expensive woodwork that is popular in the 

 up-to-date office and home could be made with imperceptible joints 

 and the elaborate arrangements designed by architects for conceal- 

 ing shrinkage and swelling in panels, frames and lapped joints 

 could be eliminated. 



Think what it would mean to manufacturers of panels and glued-up 

 stock if they could know that the heavy centers would be uni- 

 formly dry and would not shrink or swell; if they could know 

 that the tendency to twist and warp when resawing was removed. 

 Think what it would mean in the cabiuei trade if case parts, drawers 

 and doors could be fitted snug and true, without the necessity and 

 expense of refitting; if parts could be fastened rigidh' together 

 without danger of changing from shrinking and swelling. 



It means that woodwork which, because of its variable shrink- 

 age in different climates has been displaced by pressed steel which 

 has no change of dimension in moist localities, can again come 

 into its own, superseding this selfsame steel, which is subject to 

 such severe temperature expansion. The thoughts suggested by 

 this line are far reaching. 



Another point in the expansion kiln is the fact that with con- 

 trolled circulation and temperature it will be possible to elim- 

 inate not only the shrinkage but also the degrading of the lumber 

 which has been one of the most wasteful features in a woodwork- 

 ing plant. Checking ends, surfaces and around knots and swirls 

 has been a serious source of loss. Not only has the checking been 

 expensive, but even more waste has been caused by the tools tearing 

 the surface in dressing. Degrading is eliminated because the 

 absence of shrinkage has removed the internal stress and strain 

 that causes all cheeking and honeycombing; the absence of case- 

 hardening has avoided the hard crust that dulls edge tools and 

 that leads to twisting and cupping when surfacing, ripping or 

 resawing, and that causes unnecessary labor cost. If the waste 

 caused by degrading in dry kilns could be computed it would be 

 found to reach an enormous sum — sufficient to pay annually for the 

 installation of dry kilns, built, equipped and operated on a scien- 

 tific basis. 



The efficient ventilation of a dry kiln has been notoriously dis- 

 regarded by the practical woodworker. Apparently any inlet or 

 any outlet would be deemed sufficient, no matter where located, 

 or how large. It is obvious to those who have followed us that 

 effective circulation can never be obtained except by the admission 

 of fresh or dry air and the removal of the dead or saturated air 

 in accordance with natural laws. No practical man would think 

 of having an outlet for' saturated air at any height along the side 



