May 10, I'.iin 



HARDWOOD RECORD 



20a 



the difference in the drying conditions in the kiln are so pronounced 

 that this method is uncertain. Tliis practice wlien ajiplied to the 

 commercial drying of heavy green oak has resulted in exorbitant 

 losses. 



The whole dry kilning operation is linked 141 uitli the amount of 

 moisture in wood and obviou.sly the operation of the kiln must be on 

 that basis. 



It is a well established fact tliat there is a point in the drying 

 process around which the entire drying schedule should center. It 

 is the point which marks the dividing line between green and par- 

 tially seasoned wood. Up to this point the drying condition must 

 be moderate and constant, after which the drying may take place more 

 rapidly. Technically this point in the drying is called the fiber 

 saturation point and practically it corresponds roughly to moisture 

 content of 25 per cent based on the bone dry weight of the wood. 



There is no way of knowing when the lumber in the kiln is ready 

 to stand higher temperature except by knowing how much moisture 

 there is left in the wood. The number of days that the lumber has 

 been in the kiln is of slight importance and no significance in this 

 connection. 



The one criterion of regulation is the moisture content of the lumber 

 and its fitness to withstand more severe drying conditions and never 

 the number of days that the lumber has been in the kiln. 



It Pays to Watch Behavior of Lumber During Kiln-Drying 



Brain work in connection with kiln operation shows up more than 

 anywhere else in watching the effect of the drying on the condition 



of the stock itself. To go into a warm, moist kiln especially on a 

 hot summer day and look for surface checks and other defects is not 

 the most agreeable thing in the world, but it is worth while when a 

 kiln load of expensive lumber is at stake. In tlie old time kiln opera- 

 tion to spend any time in the dry kiln was never thought of, in fact, 

 in most kilns there is no way to get into the kiln except the main 

 door be opened thereby letting out the heat and exposing the lumber. 



A furniture man, when consulted regarding his troubles in kiln- 

 drying green oak, was urged to cut a small door in the large kiln 

 door so that the operator could get in easily to watch the condition 

 ot the stock from day to day. His contention in opposition was that a 

 small door was a nuisance; that it was continuously getting out of 

 repair and that it so weakened the big door that it would go to pieces 

 in 2 or 3 years. The stock in his dry-kiln cost him around $1,000, 

 he could have built a new kiln door, when the oH one was too weak, 

 for $100, but the lumber in the kiln, according to this business man 's 

 reasoning, was not worth the kiln door. It is a matter of record that 

 his $1,000 worth of oak was a total loss, but that his kiln door is 

 still in good condition. 



What are some of the things that can be seen by watching the 

 stock? The answer is — practically all of the things that result in 

 losses of lumber during kiln-drying. Symptoms can be seen and they 

 can be fought just as a physician fights the symptoms of disease. If 

 the temperature in the kiln is too high and the lumber too green, the 

 stock checks and case-hardens. Maybe the class of work is such 

 that a few surface checks do not count. Maybe the operator knows 

 that the checks will close during the remainder of the drying. What 



Tenj/on 

 CompreMion 



Aj/iyhi-jurface check hajdeye/oped inf'O a 

 deep c/teci hecauje of ^00 rap'd dryma from 

 i'he surface 

 Mffhij jfaye fhe oah/de /j in tension 



CornpreJi3/on 

 Tenj/on 



Surface c/iecfi be^injfo c/oje aj drying 

 confinuej due fo fhe comprejjion fhafha.s 

 been .sefup on fhe oa/i?/de oppo,siny fhe 

 tension on fhe inj/de far/y .jfa^e of 

 casehardening 



Co/nppejj/on 



T^r}s.o/^ 



'Surface check near'y c/ased aj drying pro- 

 ceeds ^fill fariher and case/iardening m- 

 crea~se^. 



Comprejj/on 



Tension 



ZV 

 ^Surface check enfire/y c/ojetf 6y f/>e 

 force of compression on oufer jurfac^j. 

 cornprejsion confmaej fo increase even offer 

 c/ieck IS ciojedaf surface and causes fhe 

 'pinching /n 'of fhe check. 

 Thij /J ffe iiirie fo sfeam fo re/iere cajeharden- 

 mo 



Compre.sjion 



TenuSi on 



Co/nprej^/on 



; Tension 



Pi nching m becomes more severe due 

 fo increas/ng force ofcompressicn en 

 oufside due ro severe cajenardenin^. 



Final sfo^e of honeycombing rtsu/iing 

 front imprcfitr c/oJure ofiurface check 

 dofe -fhe off-Jef alonq l-he c/rain. Which is a 

 surface condifion or'noneycomhing 



Stages in the devolopmont of honey-combitig from a surface check wh ich has developed oarI.\ in the drying and allowed to close up without proper 

 steaming treatment In the dry kiln. The application of steam at the pro per time prevents honey-oombing. 



The sketches above are to be regarded as imaginary cross-sections cut through the same check during successive stages in the drying. 



