HARDWOOD RECORD 



1/ 



High Humidity Kiln Saves Case-Hardened 

 Lumber 



A large manufactur- 

 ing electrical concern 

 jnirchased a quantity 

 of quarter-sawed red 

 oak which was to be 

 used in one of its 

 pio.iucts. This was 

 the average air-dried 

 luml)e3- — that is t(j say, 

 tlie wood was dried in 

 the open by the natu- 

 ral atmosphere. It 

 was found, however, 

 that the finished elec 

 trical device was very erratic in operation and that there was consider- 

 able distortion. On investigating, it did not take very long to find 

 the trouble. 



The lumber used, showed a very poor condition of drying. Sam- 

 ples were then taken by experts and laboratory tests were made. 

 To make such tests, the wood is usually cut roughly like a tuning 

 fork. 



Figure 1 sliows what linppened to the testing samples after being 

 left in the laboratory for a few days. The samples were cut from 

 the lumber exactly as it was delivered from the mill. It will be 

 noticed that in every instance the tines of the fork closed together 

 at the top. The cause of such distortion is what is known as ' ' case- 

 hardening. ' ' 



Wlien any kind of lumber, whether red oak or not, manifests this 

 condition, it is indicative of overdrying of the surface of the wood, 

 the inner portions hardly being affected at all. Case-hardening will, 

 in every instance, curve the test fork towards the top. This is due 

 to the unequal stresses of the lumber which is dried to hardness on 

 the surface, yet hardly fit for use immediately below. 



With all this lumber 

 on hand, the electrical 

 concern had to do 

 something to remedy 

 conditions. Usually, 

 case-hardened lumber 

 is somewhat hopeless 

 of recovery, but the 

 wood was put into a 

 wellkuowu High Hu- 

 midity Dry Kiln to 

 see what benefit could 

 lie obtained. The re- 

 sult was not only grat- 

 ifying but indeed surprising. 



Figure 1 shows the same samples after they were taken out of the 

 kiln showing the tines approximately parallel. This is correct and 

 normal condition to test samples of properly dried and seasoned 

 lumber. As the samples showed up so well, all the lumber was put 

 into the kiln. 



From time to time, tests were again made and in every instance, it 

 was found that this High Humidity Dry Kiln was able to rectify 

 a rather bad example of the case-hardening of wood. The electrical 

 company was, therefore, able to use the wood which naturally saved 

 the concern quite a good deal of money, as the lumber was purchased 

 as air-dried stock which in reality it was. 



The saw mills can hardly guarantee the condition of lumber, but 

 they can promise that any particular lot has been left out in the 

 air for several months. What the wind, weather, and sun does to it, 

 can not l)e controlled by the seller. 



The buyer -sometimes takes a chance and for all ordinary purposes 

 the air dried stock is plenty good enough. But where special care 

 must be exercised as in electrical apparatus, the lumber mupt be free 

 from all danger of warping, shrinking or swelling. 



^H-^f 



You can lessen 

 this waste 



The Government Forest Service tells 

 us that only 33.5 per cent of the log is 

 converted into merchantable lumber. 

 Further that 16.3 per cent is lost in 

 subsequent manufacturing operations, 

 leaving only 17.2 per cent of clear 

 cuttings for the manufacturer. 



\A'ith a correctly operated 



'iJjft'v-, 



High Humidity 

 Dry Kiln 



The Kiln with the circula- 

 tion you can understand 



there is no check- 

 i n g, warping, 

 cracking, case- 

 hardening or hon- 

 eycombing. 



Consequently there 

 is little or no waste. 

 Because of this and 

 the confidence they 

 have in results, 

 some concerns put 

 their lumber in a 

 Sturtevant DRY 

 KILN already cut 

 to size. 



But there is more 

 about Sturtevant 

 Kilns in Bulletin 

 No. 282. 



Write for your 

 copy today. 



R P 



STURTEVANT 



COMPANY 



HYDE PARK 

 BOSTON, MASS. 



