UNITED STATES DEPARTMENT OF AGRICULTURE 
wae, 
° Issued May 12, 1923 
Washington, D. C. Revised May, 1929 
KILN DRYING HANDBOOK 
By Rotr THELEN, In Charge, Section of Timber Physics, Forest Products 
Laboratory, Forest Service? 
CONTENTS 
Page | Drying schedules—Continued. Page 
1 PU OTS) Se 5 A SS a 1 General softwood schedules______._.._.---- 50 
MTC HE REOS) VHD, VO LS See Me TEN IGT SY Sapa Nee 2 Specialischedulessioa2 Sse U0 yh COMO ee Rea 53 
Moisture determination.__________________ 3 | Miscellaneous features of drying_______________ 62 
Distribution of moisture in stock during Oscillating ;scheduless 22k ae 62 
(Gls bafey Sees See yap ee a ae ae ere aa 5 Drying by superheated steam_____________ 62 
General principles of drying cod UU RCNA EAN 7 IDyevpenes sO 63 
Eeatemet hi eykellme ss aS ea a eS a GN 7 Binal moisture contents... 1a 64 
Souncessolheate e2-  e e 7 Steaming sap. gum 1200s se eee ea 66 
Pipe coils and other radiators_____________- 8 Seasoning specifications________-___________ 67 
Control of kiln temperature__-_-__..______- 12 Storage of kiln-dried stock_________________ 68 
EME Gey; 1, Che kel SE ee a 19 Moisture change in transit___._____________ 69 
Relative) humaldit yee tbe ot eee Saale LOM ely pes ot kilmss 2.22) Sen LEE ee ae 69 
Humidity-measuring instruments--______- 20 IEAROLTESSTivjiOy Kell ry Ss yey ale Neo pe 71 
Wontrolor kiln humidity 2 7 esr ee 24 Natural-circulation compartment kilns__._ 72 
Miteinemation im vheikilm 2025. oo sek ey eke 26 Condenser compartment kilns_____________ 74 
Production of circulation ----_- LM a i 27 Water-spray compartment kilns___________ 74 
Measurement and control of circulation____ 29 External-blower compartment kilns______- 75 
IRE), Oh GHG UIE Y OO aty 5 oe Oe ee al a ai 29 Internal-f an compartment kilns__._______- 75 
Mest oa Me CiELCUlatlIOM a=. 42a eel 30 Superheated-steam compartment kilns___. 77 
Divinsrandkdinyingystressesu. 21 see eee 3l Piling lumber for kiln drying_____-_______--___- 78 
Mioistune: cradiente-2- 255. se) Be ee 31 Ma G youn oye ee ac Esky 2 ah ec a 78 
Slap al eal Oia ete We isi i co oye Me ce Dae 32 IB Oe OUT es A Saas a ee A ae ee 80 
Drying defects caused by unevenskrinkage_ 33 ADokezey op hove Nal ial een ACME ema orca Nh 81 
SINOSSRUOLOCO Me yan yest n Mii oot nati fle i Lie! 37 Plt CHO LACTIC OMA ae NTE AR Mista ee Dee 82 
Key for determining from stress sections the Detailsvofalnvoperation=s]22. wi. Asian 83 
probable conditions in lumber during Reriodicinspection of kilmsus 2.2. ea aa 83 
SEASO MMT Se aus WN ak ee eel eae 39 Calibration and adjustment ofinstruments. 83 
SENESSPROIME CHOSE Ls soa Pay ee 39 Location of instrument bulbs_____________- 89 
General rules for steaming________--_--___- 42 The placing of kiln samples_______________- 91 
DTV IMCASCHOCUIES = ne wks ieee ey Say ee ee 43 AD o(zy Laub avh apy atam omar cel Os Mais Peteinie ces Bile 2 91 
IKSiTRS aD ES es eats Nd Nae Nac ea ee ea 44 Keil re Core Sis e W taiD UNA Ic ais pear eat 92 
Use of the drying schedules presented here__ 47 Hssentialtapparavusemse. esse eee 94 
General hardwood schedules.________--____ AQ ASACITS SOQ.S O TAIN eee 2) es hea at al Rn esa pee 95 
PURPOSE 
ii principal purpose of this publication is to present to the dry- 
kiln operator, in condensed and convenient form, the fundamental 
facts about the drying of wood that he must know in order to get 
1 Acknowledgment is made by the author to the members of the section of timber physics, 
both past and present, who are largely responsible for the development of the practical 
technic of kiln drying described in this bulletin. Further acknowledgment is made to 
the manufacturers of lumber, dry kilns, and kiln equipment who have assisted in obtaining 
and in commercial testing of the results presented here and in addition acknowledgment 
Is made to the University of Wisconsin. 
320060 29-1. i! 
