24 



HARDWOOD RECORD 



Nnvfinl>er 2."). 1921 



YARD AND KI LN 



c/^ Section Intended to Promote Efficiency^ 

 and Economy in Lumber Biding ^ 



Advantages of Automatic Kiln Drying 

 *By F. J. Lillis 



The kiln drying of lumber at the mill and factory is as important 

 as the banking of profits. Indeed, no small percentage of the 

 expense item in many plants is chargeable directly to improper 

 drying results. While substantial progress has been made in bet- 

 tering drying practices, many thousands of dollars are annually 

 being wasted because in many cases the impression still exists that 

 extensive loss and degrade are an unavoidable evil, and therefore 

 must be tolerated. 



The three preliminary considerations to proper drying are tem- 

 perature, humidity and circulation. The necessity for observing 

 these three factors and a more general understanding of their 

 operation is being gradually accomplished through education, and 

 yet one frequently will encounter here and there striking examples 

 of wrong practice in which these essentials are not given any 

 recognition whatsoever. For instance, the manager of a large 

 woodworking operation recently told the writer of a case which 

 had come under his observation. At this plant a large battery of 

 kilns was in use the year round. However, the lumber was packed 

 into these kilns without reference to its species or condition of dry- 

 ness and without sticks. According to the story told to the writer, 

 when the kilns were piled full to the ceiling, the doors were closed 

 and the steam valves opened wide. The temperature was then 

 allowed to go where it might for one week, no more, no less, regard- 

 less of the lumber. Then the steam valves were closed, the doors 

 opened and the process was finished. The informant told me that 

 due to ignoring the three cardinal principles of correct drying, it is 

 necessary to maintain a department at this plant to handle the 

 scrap lumber for kindling wood and other similar purposes. 



Now it so happened, according to my informant, that this system 

 resulted from an unfortunate misconception on the part of a 

 former employee of this company, who formed the idea (and car- 

 ried it through), that a series of tightly built, concrete boxes, 

 equipped with ordinary steam coils, would be adequate for all 

 drying purposes. His error lay in the fact that his conception of 

 the requirements of the drying art admitted the necessity of no 

 major principle beyond the direct application of dry heat. Had 

 he grasped the fundamental principles involved in accomplishing 

 the work required, this man would undoubtedly have constructed 

 a set of kilns of an entirely different nature. 



Because of the very heavy investment, these kilns are still being 

 utilized with resultant heavy loss, but when this company becomes 

 satisfied that it has found kilns offering the proper requirements of 

 circulation, temperature and humidity, which can be found in any 

 of the recognized makes, then the further steps necessary for proper 

 drying of lumber economically are very simple and can be expressed 

 in the following formula: Gradually removing the waste from the 

 interior outward. 



Under its present arrangement this company has been trying to 

 dry its lumber under just the reverse principle. It is almost 

 impossible to safely depend upon the human element to gradually 

 increase the temperature and at the same time gradually decrease 

 the percentage of humidity (in any form of compartment kilns or 

 charge kiln, such as the box kiln, pocket kiln, compartment kiln, 

 tower kiln, etc., in other words, a non-progressive kiln). Each 

 piece of stock throughout the kiln must be subjected to these 



Associated with the western office of C. J. TagUahue Manufacturinff Co. 



gradually changing conditions of heat and moisture during the 

 entire seasoning or drying process, in order to produce perfect 

 stock in a minimum time at a low cost, which result can be 

 attained in only one way, namely, through automatic control and by 

 means of a thermostat and humidostat combined, provided with 

 clock work for automatically regulating the temperature and the 

 humidity during any period of time desired. 



Removes Previous Case-Hardening 

 A preliminary period of saturating the lumber is taken care of be- 

 fore starting the clock movement so that any case-hardening existent 

 from previous air drying is removed. The stock is thus uniformly 

 saturated, making possible the uniform removal of moisture later, 

 furthermore, the stock thus heated affords uniform conductivity for 

 the subsequent moisture removal, so that when thus controlled the 

 moisture can be removed from the interior outwardly with certainty. 

 The next period of gradually decreasing humidity and increasing 

 temperature is then made free from worry, without waste of material, 

 time, labor or steam by means of this automatic controller, also thus 

 preventing the defects and losses (that cannot be overcome in any 

 other way) namely: 



Case-hardening is prevented because by this method it is simply 

 impossible for such surface hardening — due to the exterior drying 

 first and preventing escape of the interior moisture, to occur, because 

 this controller keeps the humidity and temperature changes both con- 

 stantly in step with each other, always as required to remove the 

 moisture of the stock from the interior of the stock outwardly. Other- 

 wise resulting in interior strains causing honeycombing or warping 

 of stock when rcsawed or shaped. 



Cupping is also overcome by this method, which is the only sure 

 way of securing uniform rates of drying, thereby achieving uniform 

 shrinkage and preventing strains which might result in cupping and 

 warping, even if such stock is of uniform moisture content when 

 furnished. 



Cliecking at the surface does not happen when this controller is 

 used because there is no unequal shrinkage when the simple, de- 

 pendable device automatically takes care of both humidity and tem- 

 perature every second of the twenty-four hours it is in use. 



The Wet and Dry Bulb method is used in connection with this auto- 

 matic controller. That is, tliis controller is provided with two thermo- 

 static bulbs, one of which is kept in a moistened condition in a very 

 simple manner. 



A wet finger feels cool if moved through the air and gives a good 

 example of the wet bulb principle. 



Evaporation requires heat and the wet finger consequently feels 

 cool because of the evaporation of the moisture. Just as the stove is 

 needed to supply the heat when rapid evaporation takes place in a 

 boiling tea kettle, heat is likewise needed for the slower evaporation 

 occurring at lower temperature as from the surface of the moistened 

 finger. Therefore, the moisture of the wet finger is evaporating, that 

 is — changing from liquid to vapor form "steals" heat from the finger. 

 Advantage is taken of a simple natural law, such as this in the case 

 of this time, temperature and humidity controlling device to get the 

 resultant close regulation of humidity. 



Both Wet and Dry Bulbs 



The controller has both a wet and dry bulb as already mentioned. 



These thermostatic bulbs contain a fluid very sensitive to temperature 



changes and the merest tendency toward a higher or lower temperature. 



The dry bulb affords the means for keeping the air temperature inside 



