June 10. 1922 



HARDWOOD RECORD 



25 



built on the same premises, and operated in drying of identical 

 material. 



No Greater Steam Economy 



Economy in steam consumption is another fancied advantage 

 credited to progi'essive kilns. This is not based on fact, as can be 

 readily proven. The reverse is the case, caused by the frequent 

 opening and cooling. 



Aside from the inability to maintain proper drying conditions, 

 such as are required in drying hardwoods green from the saw, there 

 are other objections of importance to the progressive drying of hard- 

 wood. One of these is in the necessity for opening of both end doors, 

 full and wide, whenever a car is to be removed, the remaining 

 cars are to be progi-essed, and a fresh car to be introduced. All of 

 this takes considerable time to accomplish, even with a trained crew, 

 and it is warm work without a mechanical car moving device to assist, 

 and even then the time required approximately remains the same, 

 and just about long enough to destroy temperature and humidity con- 

 ditions throughout the length of the kiln (which it may take hours 

 to re-establish), and to start case hardening of the more exposed 

 portions of the piles. Where a mechanical car hauling device is em- 

 ployed, steam may be used to counteract the effects of the sudden 

 exposure to cooler air, but if the work has to be done with man power 

 such steaming is impractical. 



The impracticability of steaming the lumber properly, either at 

 the. start, or later to remedy incipient case hardening, in such kilns 

 has already been mentioned. 



The inquiry refers to a crosspiled, progressive kiln with longitudinal 

 circulation. Such a kiln would be very good at higli temperatures in 

 the drying of soft wood, but the writer cannot recommend it for the 

 purpose which is mentioned in the inquiry. The description given pre 

 sumes a ventilated type of kiln with fresh air supply at the discharge 

 end, and the moist air removal at the charge end. From the wording 

 of the statement, the gentleman making the inquiry seems to be under 

 the impression that the air entering at the hot end of the kiln would 

 travel squarely through the cross-section of the kiln, parallel to its 

 axis, and would jiass consecutively through all of the lumber piles in 

 its path. 



Unfortunately this is not so, because air, like all fluids, will follow 

 the path of least resistance. The air volume in this case is rela- 

 tively small, its velocity is low, and the resistance of the channels 

 through the lumber piles (between courses) is too great, at least 

 much greater than that of the free space around the lumber piles. 

 Under these circumstances the necessary circulation of air through 

 the respective lumber piles will be apart from the longitudinal scheme. 

 It will be local, caused and controlled by the difference in the gravity 

 of the air in actual contact witli the lumber, to which it delivers 

 heat, and from which it receives moisture in return, thereby becoming 

 cooler, denser and heavier, its weight further augmented by the 

 moisture which it absorbs, and thus it must eventually descend against 

 the ascending warmer and lighter air, passing in counter current 

 through the same channels, coming and going, unless there has been 

 made a provision in the piling of the lumber on the kiln cars, and in 

 maintenance of proper spaces between the kiln cars, for a coming ami 

 a going stream of air through the lumber. This can be helped by 

 ju-oviding a triangular, graduated chimney space through the center 

 of the lumber jdle, to enable an easy upward flow of the warmer and 

 lighter air, forcing the same sidewise through the sticker space between 

 courses. The horizontal travel of the air is thus reduced to about 

 half its length, since the air is able to ascend through the center of 

 the pUe, and the resistance is likewise reduced to one-half, thus 

 stimulating better circulation, where it is needed most — through the 

 lumber piles. The moisture taken from the lumber is diffused into the 

 general air circulation of the kiln by the descending air. This is how 

 the air movement works, or at least how it should work, in this type 

 of kiln. 



Drying Must Be Uniform 



So much in general explanation of the progressive kiln and its 

 adaptability to hardwood drying. Next, the writer wishes to call 

 attention to the urgent necessity for uniformity of the drying of all 

 the lumber on any kiln car, if the output of the kiln shall be at its 



Circulation 



The arrows show exactly how the moist, 

 warm air circulates around every piece of lum- 

 ber in the Kiln — drying it through and through, 

 without warping, checking or case-hardening. 



It is the continuous circulation that counts — 

 the constant movement of air; after the air has 

 put in its work across only 3^ feet, it is recon- 

 ditioned and again returns to circulate as shown 

 by the arrows : and this change is made every 

 nine seconds. 



It makes no difference what kind or grade 

 of lumber you put in : the accurately controlled 

 temperature, humidity — and circulation will 

 take care of it. 



Write for Catalog 382 



HIGH HUMIDITY 



THE KILN WITH A CIRCULATION YOU CAN UNDERSTAND 



HYDE PARK, BOSTON, MASSACHUSETTS 



