February 26, 1921 



HARDWOOD RECORD 



23 



What Is Good Kiln Drying? 



By Donald R. Brewster * 



Specialist in the Kiln Drying of Lumber 



(Continued from Fet. 10 Issue) 



After considerable experience in inspection work, I have come to 

 the conclusion that all kiln drying operations can be classified into 

 three groups. 



The first group I will call the "Foolproof Class." This class seeks 

 refuge from the bother of the kiln drying problem by working out a 

 method which will practically take care of itself with a minimum of 

 attention, small direct expenditure, and low-priced, unskilled labor. 

 Simplicity is the watchword of this class. They look at the drying 

 of lumber as they would look at the drying of the weekly wash on 

 Monday morning in the back yard — an essentially simple operation, 

 not deserving of any particular attention of thought. 



This class got along with air-dried lumber as long as they could. 

 When they finally became convinced that kiln drj-ing produced a 

 better product, they installed the kiln which promised to do the work 

 with the least amount of direct expense and attention. The simpler 

 the process, the better it suited them. They wanted their kilns 

 "foolproof" — so simple that any yard hand could operate them, and 

 so nearly automatic that the operation consisted merely of putting 

 lumber into the kiln, turning on the steam and taking the lumber out 

 again. Since this class has always neglected the drying operation 

 and the whole matter of moisture in wood, they have not in many 

 eases realized the large indirect losses which often result from this 

 simple foolproof process and have therefore been fairly well satisfied 

 with the results obtained. 



Example of "Foolprooflng" 



Not long ago, I visited a furniture plant which is a typical example 

 of the foolproof class of kiln operations. The plant was built some 

 40 years ago on the outskirts of a town which has now grown to be 

 a city for miles beyond. A large yard area was provided for air- 

 seasoning and it has always been the practice of this plant to leave 

 all stock in the yard on sticks for six months to a year before going 

 into the kilns. Progressive kilns were built 25 years ago, sufficient to 

 hold a month's supply of lumber with the plant running at maxi- 

 mum capacity. A limited heating surface was provided sufficient to 

 give a maximum temperature of about 135 degrees in the kilns. 



The method of operation at this plant was simplicity itself. The 

 lumber was never more than 2 inches thick, and mostly 1 inch. After 

 being first air-dried at the mill and then air-dried six months or 

 more in the yard, it was always dried down to a uniform moisture 

 content of from 12 to 15 per cent, when it was placed in the kiln. 

 The door was then closed and the heat turned on. With such a low 

 moisture content and such low temperatures, most species of lumber 

 may be kiln dried without much damage, in almost any kind of a 

 hot box or heated building. The stock at this plant was conse- 

 quently in fairly good condition when taken out at the end of a 

 month or six weeks in the kilns. It was always fully dried and 

 ready for use when needed, since it had been left in the kilns two 

 or three times as long as necessary to accomplish the drying. 



I have never visited a plant where the ideal of simplicity and fool- 

 proofness of kiln operation was more nearly attained than at this 

 furniture factory. Yard hands loaded and unloaded the kilns; the 

 engineer turned the steam on and off; the shop got the stock when 

 it was needed. No moisture tests were necessary, no casehardening 

 tests, no steaming treatments to relieve casehardening, no high- 

 priced, trained operator. The kilns practically ran themselves and 

 produced results which satisfied the plant. 



This system has its advantages, I will admit, yet it also has a very 

 great fault — a fault that is almost universally overlooked by the 



advocates of such foolproof kiln drying. That fault is unnecessary 

 cost. Let us take this same plant as an example. 



In the first place, preliminary yard drying for from six months to 

 a year required the carrying of from 500,000 to 700,000 feet of lum- 

 ber ahead at all times over and above the amount needed to provide 

 a reasonable reserve against delays in shipment. 



This stock was piled on valuable land in the industrial district, 

 and it is estimated that the value of the excess stock of lumber and 

 piling space would average at least $30,000 over the last ten years. 

 Interest, taxes, insurance and depreciation would at least be 8 per 

 cent, or $2,400 yearly. In addition, there would be an extra charge 

 for piling about 1/100,000 feet of lumber each year, which even at 

 pre-war prices would amount to at least 60 cents per thousand, or 

 $600 more. 



Now, coming to the kilns, we find that the kiln space provided is 

 more than twice the amount really needed. We will forget the 

 double investment in land and buildings and consider only the loss 

 from the heating and operation of double the kiln space required. 

 The costs of kiln operation were never kept separate at this plant, 

 so we can only estimate. We do know, however, that with pre-war 



a 



Test Sections Cut from Oak Lumber Being Kiln Dried 



