26 



HARDWOOD RECORD 



. iiilj.-r 111 lirj! 



YARD AND KILN 



c^ Section Intended to Promote Efficiency^ 

 and Economy in Lumber Drying ^ 



Suggestions Toward Improvement of Yard Drying Through Better Piling 



Bv Carl J. M aural 



Comparatively a very small amount of the hardwood lumber goes 

 direct from the saw to the dry kihi. Practically all of it is piled 

 in the open yard, either at the mill or at the factory, for storage 

 and for drying, so to remain during longer or shorter periods, dur- 

 ing all seasons of the year, before it finally reaches the kiln. The 

 considerable losses from degrade and decay which result are gener- 

 ally accepted as unavoidable, are frequently blamed to the suc- 

 ceeding kiln operation, and in the end are charged to the manu- 

 facturing cost. 



Much advance has been made during recent years in better under- 

 standing of the scientific conditions which produce good kiln dry- 

 ing, and in the practical application of these scientific facts to 

 systematic and successful control of large kiln drying operations. 

 The time-honored customs of yard arrangement and yard piling, 

 however, have not been affected by much desire for improvement, 

 and in most cases these operations are still following least resist- 

 ance. 



The writer notes witli appreciation of its importance the pro- 

 posed investigation of the subject of yard drying by the Forest 

 Products Laboratory, and hopes that it may meet with the co-opera- 

 tion and the success which the matter justly deserves from the 

 standpoint of conservation of natural resources alone, not to men- 

 tion that of the owner's profit. 



The suggestions herein presented make no claim to novelty, liut 

 the same are based on 

 facts, and on conclu- 

 sions which the w-riter. 

 h a s bee n able to 

 prove by the results 

 obtained by their 

 practical application 

 to a reasonably large 

 operation. 



For good and uni- 

 form drying and for 

 prevention of stain or 

 mold in lumber which 

 is piled in the open 

 yard, a free circula- 

 tion of air, sufficient- 

 ly humid, traveling at 

 ample velocity, with 

 uniform distribution 

 over all surfaces of 

 the lumber in the jnle, 

 is very essential, pre- 

 cisely the same as in 

 kiln drying. 

 Yard and Kiln Circu- 

 lation 

 While the require- 

 ments for uniform air 

 circulation are the 

 same in the yard pile 

 as in the kiln pile, the 

 natural tendency in 

 the yard pile in all 

 cases is " down- 

 ward," and in the 



kiln pile is "upward," except at the very beginning of the oyii'va- 

 tiou, before the kiln ])ile has become heated through, when the 

 circulation in tlie kiln ]iile likewise tends dow-nward. In tliis ten- 

 dency circulation will of course follow least resistance, and it can 

 be intelligently directed, l)v logical piling, and in the kiln by loca- 

 tion of condensers and ventilators or by the force of the water 

 sprays or that of fans. Improved piling alone is the only remedy 

 available in the yard for proper control and uniforiiL liistribiition 

 of the air circulation over the luml)er. 



In the piling for the yard as well as for the kiln it is very 

 important that the distance which the air must travel from the 

 point where it enters to the point where it leaves the pile shall not 

 be too great, in order that the gradually increasing moisture con- 

 tent of the air, as it passes between the lumber may not too closely 

 approach the saturation point, and thus prevent further absorption 

 of moisture from the lumber coming last in contact with this 

 saturated air. This error in piling would cause the lumber near 

 the exit of the air current to greatly "lag" in drying behind that 

 wliicli is located nearer the entry of the air into the pile. At this 

 point the air is slightly warmer and considerably less humid, there- 

 fore capable of absorbing moisture from the lumber surface more 

 re.adily. In fact it would be quite possible by injudicious piling 

 to incre.-ise the distance of .lir travel within a. pile to such an 

 extent ;is to cause a conilition of ]irolonged moisture saturation in 



a ]iortion of the pile 

 to the serious detri- 

 ment of the lumber. 



The difference of 

 actual moisture con- 

 tent between the air 

 entering and leaving 

 the luml)er pile de- 

 pends, first of all, 

 u])on the volume of 

 tiic ;iir wliicli p.asses 

 <i\"er a given lumber 

 area in .a unit of time 

 and next upon the 

 drying power of this 

 air when it is enter- 

 ing the pile, a n d 

 fin.'illy u |) o n t h e 

 amount (if moistures 

 wliicli the ] u m b e r 

 passes to its surface 

 in tlie same unit of 

 time and, therefore, 

 makes available for 

 absorption by the air 

 circulating over it. 



The greater the 

 s p a c e between the 

 lumber surfaces the 

 greater will be the 

 volume of air which 

 may jia.ss over the 

 same lumber surfaces, 

 provided that the 

 speed with whicli the 



South (Front) Face of Pile 



