24 



HAKDWOOD RECORD 



Aliirih 111. l'.V2 



YARD AND KILN 



o^ Section Intended to Promote Efficiency^ 

 and Economy in Lumber Dicing ^ 



Kiln Drying 

 By C, 



A number of inquiries liave come to the writer recently concerning 

 the drying of Gum hinil>er, all of these correspondents wishing to avoid 

 "twisting and war])ing" of the boards. Some of these inquiries 

 mention "Bed Gum" only, others talk about "Tupelo." 



There are three members of the Gum Family and the best be- 

 haved of these, from the kiln drying standpoint, is the Red Gum, and 

 particularly the heart wood of this variety. The sapwood is more 

 inclined to try to walk away in the kiln, if not properly restrained 

 by physical force, or coaxed to behave by correct treatment. 



Next, in natural cusscdness conies the Tupelo Gum, nhi^h will 

 twist more readily than the Red variety, and finally the Black Gum. 



The writer has done considerable experimental and research work 

 on a large scale during the conmiercial drying of large quantities ot 

 Gum boards of all three varieties and in the hope that his experiences 

 may benefit some of the readers, will undertake to state his deductions 

 therefrom, of necessity in a more or less condensed form. 



Any Gum lumt>er, if it is to dry flat and witliout twisting, nnist 

 be piled so as to prevent any desire on the part of the boards to 

 move. The foundation must be strong and solid. Distance between 

 stickers and foundation supjmrts cannot be more than Iti" and should 

 preferably be about 14". Furthermore, boards of the same thick- 

 ness only should be piled into the same course. A reasonable amount 

 of sorting in this respect will pay well. 



Stickers simply must be of good stiff pine or hardwood and not 

 less tlum J" wide by 1" thick, and must be surfaced to uniform thick- 

 ness. The indifferent sticker of scrap lumber or edgings, cut l"xl" 

 or v\'orse, each piece having its individual thickness, positively will 

 not do with Gum, and should not be used on other lumber of value. 



Thus we dispose of the prime essential to good drying of Gum 

 lumber. If you fail in this, you may save the time of reading 

 further. 



Care Will Pay Dividends 



With reasonable care, end checking or splitting need not be feared 

 in the kiln with Gum lumber. The writer had caused the end splits of 

 many thousands of boards to be marked, to determine their possible 

 extension in the kiln, and has found that, with reasonable care these 

 splits remained in statu quo (as our legal friends would say), they 

 did not close up, as is the habit of oak, neither did they ojien further. 



The only difficulty with Gum lumber which is real, is its naturally 

 inborn cusscdness of wishing to turn around upon itself, when it 

 gets comfortably warm in the kiln, and then only, when the moisture 

 begins to dry ofE the surface fa.ster than it follows to the surface 

 from within the board. 



Close sticking with good stickers will hold the lumber when it 

 softens and becomes jdastic (as Gum will), when first introduced into 

 the kiln, and later, if any tendency to warping develops. 



Generally, the chief trouble is with the upper layers or courses of the 

 piles. For this there are two causes, the first, and most important, is 

 found in the fact that the drying conditions under the kiln ceiling 

 nearly always are very much more severe than in any other part of the 

 kiln. The temperature being higher, and the humidity much lower. 



How to Save the Upper Layers 



Therefore, if you would prevent the loss of the upper layers of 

 Gum lumber, you must maintain such a humidity under the kiln ceil- 

 ing as will prevent the drying of the surface moisture at a greater 

 rate than the rate of transfusion of this moisture from the center of the 

 boards. If this is done then the shrinkage strains will exhaust them- 

 selves in material still reasonaV)ly plastic. 



Gum Lumber 



J. M. 



The second, and less important reason (because in a large manner 

 offset by the correction of the first), is in the fact that there is no 

 weight above the upper layers sufficient to hold them down against 

 the tendency to twist. Careful adherence to the advice given in the 

 preceding paragrajih will of course reduce this tendency to warp, and 

 will in like measure reduce the necessity for physical restraint, against 

 twisting, of the upper courses of Gum lumber. 



I fully a]]i)reciate the difficulty of atteni]iting to read a hygrometer 

 on top of the piles of lumber in a kiln, at about 130° dry and 1:21° 

 wet bulb (75% R. H.). I have tried it, and .-iflcr the trial did not 

 ask anyoiu> else to do so. 



It, therefore, becomes necessary to make a suitable provision to 

 read the dry bulb and wet bulb temperatures ot the space directly 

 above the lumber, and as near as possible to the center of the kiln, 

 without entering the kiln for the purpose. This seemingly difficult 

 problem was solved in a simple, and fairly inexpensive manner. 



Use Gas Filled Extension 



The bulb of an ordinary j^cidnJiTr.; 1 lici niciTiii'tcr. Iiaviug a 25' 

 extension (important that this be filled with gas and not mercury), 

 was suspended in horizontal position, about 12" below the ceiling 

 of the kiln, in central location, and as far in (away from the door), 

 as the 25' extension would permit. A rigid pair of brackets held this 

 12" bulb in position. Over this bulb was wound loosely, but thoroughly 

 covering same, regular physicians gauze. Above the bulb thus held 

 horizontally, was arranged a jierforated %" jdpe, which would, when 

 water was forced into same, thoroughly aiul uiiifoiTiily wet tlio gauze 

 on the bulb. 



This sprinkling device was connected to a small reservoir suspended 

 on the side wall of the kiln, which would hold all of the water neces- 

 sary for one wetting of the gauze, and would therefore insure that 

 the water should be of kiln temperature, a condition not essential, but 

 desirable. The water was supplicil uiKtcr pressure tlirough a %" 

 pipe from the outside of the kiln, through a three-way cock, in such 

 a way that when the bulb was to be wetted down this cock was 

 opened, admitting water to the reservoir line, and after a few seconds 

 (the time necessary for the operation), the three way cock was closed 

 to the water supply, and the reservoir line was opened to the atmos- 

 phere, so as to absolutely prevent any continued dripping of water 

 on the gauze of the bulb. The respective levels of the three-way 

 cock and the reservoir were so arranged as to preclude syphoning 

 and emptying of the latter when open to atmosphere, and the connect- 

 ing pipe was trapped to prevent outdoor air from entering. 



The clock mechanism of the recorder was placed outside the kiln, 

 for convenient observation, on a level with the face of the observer. 

 A recorder with daily charts was used, but the weekly form will 

 answer fairly well. 



Method of Operation 



Operation was as follows; When dry, the gauze did not in the 

 least interfere with the dry bulb reading of the thermometer, which 

 was taken first, and which as a matter of fact was recorded on the 

 chart. Then the water was sent to the sprinkler above the bulb, and 

 the gauze was thoroughly soaked, when almost instantly, the pen arm 

 of the recorder began to move down on the scale, finding the true 

 wet bulb temperature in about 5 to 10 minutes, and holding same for 

 about 15 minutes, when it began to cree|i back to the dry bulb 

 temperature slowly, which it reached in about one hour after all the 

 water had dried out of the gauze. This operation was repeated about 

 .'i hours apart during the day, and the record chart clearly indicated 



