June 10, 1919 



Hardwood Record — Veneer & Panel Section 



21 



Kiln -Drying Specifications for Lumber 



By H. D. Tiemann, M. E., M. F.* 

 Editor's Note 



The following article is based on experiments regarding airida 

 fit the treatment of lumber for any other cabinet work. 



lumber and is j-'ublished because the conclusion 



Brashness, internal stresses, and hidden checks pro- various species. On the effect of various treatments and 

 duced by poor drying may be passed undiscovered in temperatures upon their properties, and develop meth- 

 the most rigid inspection, since they cannot always be ods of kiln-drying woods from the green condition, 

 determined by direct examination of the material. The The Signal Corps specifications'!' were prepared on the 



basis of this previous know^ledge of 

 drying and of the mechanical prop- 

 erties of woods. The results of a 

 few preliminary tests made in April 

 and May, 1917, upon some airplane 

 material of partly air-dried spruce 

 and ash were also taken into ac_- 

 count. 



Necessity for More Elxact Knowledge 

 as to Strength 



It was evidently desirable, hovi?- 

 ever, to establish definitely and be- 

 yond all question what effect would 

 be produced upon the strength of 

 the wood by methods of drying 

 given in the specifications, and to 

 obtain more exact knowledge about 

 the limiting conditions for each 

 species of wood as regards the se- 

 verity of treatment beyond which it 



FIGURE 1. GENERAL VIEW OF DRV KILNS BUILT BY THE SIGNAL CORPS AT VANCOUVER, 

 WASH., AND USED FOR KILNDRVING AIRPLANE WING BEAM STOCK DURING THE WAR. 

 THIS PICTURE SHOWS THE FIRST LOADS OF WING BEAMS BEING REMOVED FROM THE KILN. 



drying process itself is, therefore, of 

 prime importance, not only for the 

 saying of material through the 

 avoidance of due waste from injuries 

 in drying, but even more so for the 

 assurance that the material which 

 passes inspection shall be free from 

 subtle defect or possible weaknes.s. 

 For this reason it has become neces- 

 sary to draw up very careful specifi- 

 cations for the drying operations 

 themselves, and to place inspectors 

 at the kilns to see that the operations 

 are conducted in accordance with 

 the specifications. The need for this 

 was realized when the airplane pro- 

 gram was undertaken at the begin- 

 ning of the war, and the Forest 

 Products Laboratory of the U. S. 

 Forest Service, Madison, Wiscon.sin, 

 was looked to for the necessary information. would be unsafe to go. This called for exhaustive 



The Forest Service had for many years conducted ex- drying and strength tests, which w^ere at once under- 

 haustive experiements on the mechanical properties of taken at the Forest Products Laboratory. Shipment of 



SEVEN LOADS OF DOUGLAS FIR WING BEAM STOCK IN THE SORTING SHED 

 READY TO BE LOADED INTO THE KILNS. 



'Physicist and Dry Kiln Specialist, 

 Forest Service, Madison, Wis. 



Forest l*roducts Laboratory, JJ. S, 



t Specification 20,.S(HJ-.\ for Kiln-Drying .Airplane Stock, -^ir Service, LT. S. 

 War Department. 



