DRY-KIEN TEMPERATURE SCHEDUEES 
 
 ECR AIRCRAFT EUMBER 
 
 Revised June 1943 
 
 I UNIV. OF Ft LIB. 
 
 U.S. DEPOSITORY 
 
 No. 1360 
 
 UNITED STATES DEPARTMENT OF AGRICULTURE 
 FOREST SERVICE 
 FOREST PRODUCTS LABORATORY 
 Madison, Wisconsin 
 
 In Cooperation with the University of Wisconsin 
 
■ •- - LI : 
 
 -ctive in ; of aircrafl 
 
 th. It ha eei jmonstrated 
 
 are kept wit. oper limits, the strei bh be seriously reduced. 
 
 , aeycombin -, and other , -- , has 
 
 m to be no guarantee of the suitabilit" of wood for use in i ne 
 
 . 
 
 Drying Schedules 
 
 A edule usually specifies both the temreratures and relat' 
 
 humidities that are to be used at various stapes of the dry: 
 tei relative humidities are based on the current ncisture 
 
 of the stock. The I ore si: 1 roducts Laboratory prefers to make changes in t 
 peratures and relative humidities at specific .-.oisture content va" . , 
 uses this type of drying schedule almost exclusively . ir, 
 
 aber of a piven species and thickness has been dried i pecific kiln often 
 enough to establish the relationship between moisture content and the lc 
 of time the lumber has been in the kiln, a - .^erature schedule car. 
 adopt*-- 
 
 • 
 
 The te ures and relative humidities f.ive ryii le are 
 assumed to be ;e w Lc exist in the hottest an est zr Lin, 
 
 vledpe of the distribution of temperature 
 is . Successful drying cannot be ac Lin is in- 
 
 able of mainta^ he conditions s a drying 
 
 the length of the kiln on th Lde Lr enters 
 
 ^e as nearly uniform as possible, i should a 4- 
 
 duri ryi 3 exceed 10° 
 
 les 
 
 The succes: : ul use of a drying schedule based upon current moisture 
 t requires a system by which the moisture content of the lumber in t. s 
 
 nes of the charge can be determined with both ease and certainty. 
 . t system so far developed involves the use :iln sample . These are 
 • ely short pieces of the wettest, thickest, and sic - stock in 
 iln charge* ->mples are coated at both end? - -_• -> n t 
 
 material before being dried, Aft Bir i: Isture tit values ha-^ 
 
 samples are distributed in rucks located 
 
 — r reries of progress 
 
 ttion's defense e: ". tutes a 
 
 <.bora+ Lmeo« No. 135", "Aircrafl 
 41. 
 
 . L360 I -' - 
 
parts of the kiln where drying occurs most rapidly and most slowly, arid allowed 
 to dry with the rest of the kiln charge. Periodically, these samples are 
 weighed and returned to their respective locations in the kiln. The current 
 moisture content of each sample is calculated and this moisture content is as- 
 sumed to be at least as high as that of any "board in that part of the kiln in 
 which the sample is placed. 
 
 Kiln Temperatures 
 
 The temperatures permitted by tables 1 and 2 are based on thousands of 
 strength tests on material kiln dried in many experimental runs. Careful ad- 
 herence to these temperature schedules, together with proper regulation of the 
 relative humidity, may be expected to produce lumber that is fully equal in 
 strength properties and all other respects to the most carefully air-dried 
 stock. Since relative humidities in themselves do not affect the strength of 
 aircraft wood as long as they are high enough to prevent checking and honey- 
 combing, the relative humidity schedule is left to the discretion of the kiln 
 operator, whose judgment will be influenced by a desire to dry the stock as 
 rapidly as possible without kiln degrade. The specified temperatures are maxi- 
 mum values, and are to be changed from time to time in accordance with the 
 wetter half of the samples in the hottest location in the kiln.' 
 
 Mimeo. Ho. 1360 (Revised) 
 
 -2- 
 
Table 1. — Temporature sche dule. 
 
 
 : Schedule numbers according to 
 
 thickness 
 
 Species 
 
 : Up to and 
 
 includij 
 
 ^S 
 
 • 
 
 : Greater 
 : than 3 
 : inches 
 
 
 : 1 
 
 : i nch 
 
 : 1-1/2 
 
 r inches 
 
 : 2 
 
 : inches 
 
 : 3 
 
 : inches 
 
 Softwoods: 
 
 
 
 
 ; 
 
 i 
 
 Baldcypresc 
 
 : 4 
 
 : 4 
 
 : 5 
 
 : 6 
 
 1 7 
 
 Douglas-fir 
 
 : 3 
 
 4 
 
 : 5 
 
 : 6 
 
 : 7 
 
 Fir, noble 
 red 
 
 : 2 
 r 3 
 
 : 3 
 1 4 
 
 1 4 
 
 1 5 
 
 : 6 
 : 6 
 
 : 7 
 : 7 
 
 Hemlock, western 
 
 l 4 
 
 i 
 
 5 
 
 : 6 
 
 : 6 
 
 : 7 
 
 Pine, northern white 
 ponderosa 
 red 
 sugar 
 western white 
 
 4 
 ' 4 
 
 2 
 ' 3 
 
 4 | 
 
 5 
 5 
 3 
 
 4 
 5 
 
 : 6 
 
 ; 6 
 
 I 4 
 
 5 
 
 6 
 
 : 7 
 : 6 
 : 6 
 : 6 
 : 7 
 
 : 8 
 1 7 
 : 7 
 : 7 
 : 8 
 
 Spruce, red 
 
 Sitka 
 
 white j 
 
 1 2 : 
 2 
 2 
 
 3 
 3 
 3 
 
 4 
 4 
 
 4 
 
 : 5 
 5 
 5 
 
 : 6 
 6 
 6 
 
 White-cedar, Port Orford : 
 
 2 i 
 
 3 : 
 
 4 
 
 5 
 
 6 
 
 Hardwoods: : 
 Ash, commercial white : 
 
 5 : 
 
 5 < 
 
 
 
 
 Birch, yellow : 
 
 5 : 
 
 5 i 
 
 
 ! 
 
 
 Cherry, black : 
 
 5 : 
 
 5 : 
 
 
 
 
 Khaya ("African mahogany") : 
 
 5 : 
 
 5 : 
 
 
 1 
 
 < 
 
 
 i'.ahogany, West Indies : 
 
 5 : 
 
 5 : 
 
 
 1 
 
 : 
 
 I 
 
 Maple, silver : 
 sugar : 
 
 3 : 
 3 : 
 
 3 : 
 3 : 
 
 i 
 
 ! 
 
 Oak, commercial red : 
 commercial white ; 
 
 8 J 
 8 : 
 
 8 : 
 8 ; 
 
 
 1 
 
 1 
 
 i 
 
 
 Sweotgum i 
 
 G : 
 
 6 : 
 
 
 
 
 Yellowpoplar : 
 
 3 : 
 
 4 : 
 
 5 : 
 
 6 
 
 7 
 
 .Walnut, black : 
 
 4 : 
 
 4 
 
 
 
 
 Mimeo, i:o. 1360 (Revised) 
 
Table 2. -.-Drying temperatures. 
 
 Moisture content 
 
 
 
 s 
 
 chedule number 
 
 
 
 1 
 
 : 2 
 
 3 
 
 i 4 : 5 : 6 
 
 : 7 i 
 
 8 
 
 Percent ! 
 
 o^ 4 
 
 ; oy t 
 
 °F. 
 
 
 ' °F. ,* 
 
 °r. 
 
 45 or more 
 
 i 140 
 
 : 135 
 
 : 130 
 
 : 125 
 
 i 120 
 
 ! 115 
 
 : 110 
 
 : 105 
 
 ^40 
 
 • 145 
 
 : 140 
 
 : 135 
 
 • 130 i 
 
 125 
 
 120 
 
 115 
 
 : 110 
 
 30 
 
 • 150 
 
 : 145 
 
 i 140 
 
 ', 135 
 
 130 
 
 125 
 
 : 120 
 
 : 115 
 
 25 
 
 155 
 
 150 i 
 
 ' 145 
 
 140 | 
 
 135 
 
 130 . 
 
 125 
 
 : 120 
 
 20 
 
 160 
 
 155 
 
 150 
 
 145 1 
 
 • 140 
 
 135 
 
 130 i 
 
 125 
 
 15 ! 
 
 165 
 
 160 1 
 
 155 • 
 
 150 
 
 145 
 
 140 
 
 135 
 
 ' 130 
 
 10 to final ! 
 
 « 170 ' 
 
 165 
 
 160 ' 
 
 155 - 
 
 150 
 
 145 
 
 140 
 
 135 
 
 —When the initial moisture content of the stock exceeds 40 percent, 
 the initial temperature should be maintained until the moisture 
 content reaches 40 percent, at which stage of the drying the 
 temperature may be increased 5° F, 
 
 &lmeo. No„ 1360 (Revised) 
 
IVERSITV OF FLORIDA 
 
 3 1262 08925 4386