KILN DRYING HANDBOOK 49 
TaBLE 2.—General hardwood kiln-drying schedules 1 to 8 
(D=dry-bulb temperature; W=wet-bulb temperature; H=relative humidity) 
: : Schedule 1 Schedule 2 Schedule 3 Schedule 4 
Moisture content at which 
Chamees soowlkdl be wey |_-— —e ———eeee  eeeeeeeee 
per cent Tye Welw 18d Aa) Pe di eae Me soy Ae een Ttsieray IL eaggee th Tr 
Per Per Per Per 
°F,.|° F. | cent | ° F.|° F. | cent |° F. | ° F. | cent | ° F. | ° F. | cent 
A SOTETTONO seat tee oe whol 140 132 80 135 128 80 130 123 80 125 118 80 
ND vi a eal as 9 1 A a 145 135 75 140 130 75 185 126 7h) 130 121 75 
SAD) ocho os ese 150 137 70 145 133 70 140 128 70 135 123 70 
py yaaa ey er eR SIG BH Ng a Sk 155 136 60 150 132 60 145 128 60 140 123 60 
PADS Nae 8 A a en 160 135 50 155 131 50 150 127 50 145 122 50 
Tce SA SO e URC OTE Te e 165 127 85 160 124 35 155 124 40 150 120 40 
HOROMIA Tete 170 116 20 165 112 20 160 115 25 155 111 25 
hedule Schedule 6 Schedule Schedule 
Moisture content at which otoe : ql ecmle.® 
CMATICESES HOU NICHT Cl On a a 
ber cent Dy hua Nast MAT), WNT Letse yO) AG Wnms aa Mead Noayat lh ret 
Pe Per Pe er 
OS Oo SHE A CETiEe ick Be | OR | CEenE |i o BAS RW cent NOUR oe cent 
AION MN OVO sees et eo 120 113 80 115 108 80 110 105 85 105 101 85 
fl ES Ae ee 125 116 75 120 111 75 115 108 80 110 104 80 
Pak Ys Set aS i Pee Se 130 119 70 125 114 70 120 111 75 115 107 75 
FOG a So tek tal Bn US ea pe a 135 121 65 130 116 65 125 112 65 120 109 70 
AU) EMMY E Ro AER Web) 140 120 55 135 116 55 130 112 55 125 110 60 
il eee Ota Se ys ea 145 119 45 140 115 45 135 110 45 130 109 50 
ORO smMaAlek es eee ee 150 | 112 30 | 145 | 108 30 | 140; 108 35 | 135 | 107 40 
Study of these schedules draws attention to the fact that, for a 
given equilibrium moisture content, in the mild schedules the tem- 
peratures are lower and the humidities are higher than in the severe 
schedules. The moisture gradients, as a result, will be less steep with 
the milder schedules. Further, high final humidities preclude the 
possibility of drying to a low final moisture content. For example, 
the final conditions in Schedule 8, namely, 135° F. and 40 per cent 
humidity, correspond to an equilibrium moisture content of about 6 
per cent, and it would be impossible, under these conditions, to secure 
a final moisture content lower than this no matter how long the dry- 
ing was continued. Moreover, getting a moisture content less than 8 
per cent would take too long. When low final moisture-content values 
are desired with the mild schedules, therefore, it will be necessary to 
use final humidities lower than those shown. <A good rule to follow 
in doing this is to keep the kiln conditions 3 per cent below the cur- 
rent moisture content of the stock. The departure from the schedule 
will, in no event, need to be made until after the stock has passed 9 
per cent moisture content, since the final humidity in Schedule 8, 
the mildest one, already corresponds to an equilibrium moisture con- 
tent of 6 per cent, which is 3 per cent lower than the 9 per cent. 
32006 °—29———44 
