WORKING PROCEDURE 



The following instructions and illustrative sketches for working 

 timber dryers are derived mainly from the " Procedure for Kilns," 

 A.B.I. No. 255, of the Aeronautical Inspection Directorate, which pro- 

 cedure was drawn up and inaugurated by the writer during his service 

 with the Department. Permission to use this matter is gratefully 

 acknowledged to the Director, Brigadier-General Bagnal-Wilde. 



Many milhons of feet of aircraft timbers have been successfully treated 

 in accordance with this procedure under the supervision of the A.I.D. 

 Methodical working is all important. The timber must be carefully 

 stacked and arranged in the dryer, so that the circulating air is brought 

 into contact with all the boards and does not pass uselessly through gaps 

 in the piles. 



The pihng sticks, of which there should be a sufficient number of the 

 right size, must be dry. After a dryer has been at work for some time, 

 the sticks are naturally quite dry, but when starting a new installation 

 it often happens that new sticks are cut from green timber for immediate 

 use. These should be put in the dryer by themselves, and dried before 

 being used in stacking. If wet sticks are used, the strip across the plank 

 which has been in contact with the stick \vill probably be stained, and 

 will certainly be wetter than the remainder. Piling sticks i inch square 

 are the most useful size. Smaller ones should not be used even for 

 the thinnest material, as the circulation would be poor. For very 

 thick material it is often advisable to use sticks i| inch or even 2 inches 

 thick in the lower part of the pile, in order to assist the flow of air 

 through the piles. As a general rule, it may therefore be said that piUng 

 sticks should be i inch thick for planks up to 2 inches thick. For thicker 

 timber, 2-inch pihng sticks should be used in the lower part of the stack 

 (from floor to one-third of the height), and i-inch sticks for the remainder. 



The timber must be piled evenly, filling as far as possible the whole 

 cross section of the dryer. The circulating air will naturally take the 

 easiest course, and if free passages are left, the drying air will not come 

 into contact with all the timber, and the drjing wiU be uneven. Canvas 

 curtains should be placed across any unavoidable spaces, or some similar 

 device employed to ensure that the drying air is properly utihsed. 



With progressive dryers the boards should be stacked to pass through 



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