28 



HARDWOOD RECORD 



July 10, 1922 



YARD AND tCILN 



qA Section Intended to Promote EfScienqyT' 

 and Economy in Lumber Drying ^ 



Advice on Selection of Dry Kilns Best Suited to Hardwood Lumber 



By C. J. Maural 

 {Continued from Issue of June 10) 



Specifications for Your Kiln 



The heating and air-circ-ulating provisions shoulii be such as to cause 

 the heated kiln air to ascend through the center chimney of the pile, 

 distributing itself laterally, between the courses, and emerging on the 

 outside of the pile, cooler and heavier, to descend once more to the 

 heating sj'stem. This air movement should be of sufficient volume 

 and velocity, to insure a uniform drying effect in all portions of the 

 piles. In this, for best result, the horizontal movement in the pile 

 must be short, but the lumber can be piled edge to edge if a proper 

 chimney duet is provided through center of pile. 



Adjustable automatic temperature control is very desirable. 



An automatic humidity control has been worked out and gives good 

 results with intelligent care, but the writer is not as yet in position to 

 recommend the general use of this delicate apparatus in regular service 

 around lumber yards. 



Manual humidity control must be positive and flexible, and it should 

 be possible to ascertain the temjjerature and humidity condition of 

 the kiln without entering it. 



The kiln should have two tracks, so placed as to provide a free space 

 of two feet in center, between the faces of the adjoining piles of 

 lumber. At the sides there should be a space of 18 inches between 

 the lumber and the respective walls. This would call for a net inside 

 width of nineteen feet. The inside length would depend ujpon the 

 predominance of the length of the lumber to be dried, and the com- 

 binations which may be formed of these various lengths. Generally 

 speaking, the length may be 60 feet or even more. 



Height, from top of rail to ceiling, should be not less than 11 feet, 

 and from top of rail to floor not less than 3 feet. 



It must be understood that you would sort to length, stick and pile 

 carefully, and charge any kiln with lumber of one species only, and, as 

 far as may be practicable, with but one thickness. 



Fire-proof construction is the only desirable one, if permanency is 

 required. 



Foundations should be to solid earth, of concrete, properly water- 

 proofed against moisture' absorption from without and from within. 

 Walls should be of brick, or tile and brick, or tile and concrete. Vit- 

 rified tUe, laid in water-proof cement mortar, is best for dividing walls. 

 These- should be 12 inches thick. Outside walls should be of same tile, 

 veneered with single 4-inch thickness of hard brick. 



The floor should be of concrete, about .3 inches thick, water proofed 

 against inside and outside moisture, and finished to smooth surface. 

 The roof should be flat and level, of reenfored tile and concrete con- 

 struction (Kahn System), tUe 8 inches thick with 2-inch thickness of 

 concrete over tUe, 4-inch concrete between tUe, and steel reenforcing 

 rods embedded in the concrete between tile. The pitch or water shed 

 of the roof to be formed with lean cinder concrete over the level roof 

 surface, and on top of the cinder concrete to be placed a regular tar 

 and gravel or Barrett specification roofing. 



Where End Piling Counts 



Good doors are very important. The more airtight the same can be 



made the better. Here is where some of the advantage of end piling 



comes in. It permits the use of two small doors instead of one as 



large as the entire end of the kiln. If the space between the lumber 



piles is two feet, then a 12-inch concrete and steel pier can be erected 

 between the tracks on center line of the kiln and steel door frames 

 installed, providing for a clearance of 6 inches on both sides of the 

 lumber cars. Six inches is ample with proper piling. This has been 

 proven in actual daily operation. It is not difficult to systematize the 

 piling to perfection. 



Canvas doors should never be used on hardwood kilns, either single 

 or double. Properly constructed doors supported on overhead carrier 

 (Hussey doors) are good, and heavy hinged doors of the refrigerator 

 type, equipped with heavy bar hinges and refrigerator level locks, are 

 better, provided same are hung in steel frames (angle or Z-bar con- 

 struction), properly anchored to the building structure, dear cjrpress, 

 kiln dried and carefully painted before, during and after construction, 

 is the best material for these doors. 



The heating system of hardwood kilns must first of all provide for 

 a continuous steam supply at a uniform pressure of not more than five 

 pounds or less than two pounds by gauge. Higher pressure steam is 

 not desirable for the heating of hardwood kilns, and whatever the 

 pressure decided upon may be, it must be supplied continuously and 

 uniformly. The low pressure will permit the use of any available 

 exhaust steam, which can be supplemented by live steam from the 

 boilers whenever insufficient. The pressure of the latter must be 

 reduced through a good reducing valve, and if the boiler pressure is 

 very high such reduction should be made in two stages. In laying out 

 the steam supply lines it is very essential to make the pipe sizes and all 

 valves and specialties correctly proportional to the volume of steam 

 which the same will have to pass at maximum servic*. This matter of 

 proportioning pipe sizes and laying out pipe lines is far more im- 

 portant with low pressure than with high, and it should receive com- 

 petent engineering attention, which must take into consideration all 

 local conditions of steam plant and ground levels, providing for proper 

 drainage of the condensate and its efficient return to the boilers. 



The Heating System 



The heating system of each kiln nmst be so designed and installed 

 as to provide an equal heat effect throughout the entire length of the 

 kiln, front, rear and center. This cannot be obtained from ordinary 

 "header" coUs, where the steam enters at one end of the header coil 

 and the condensate leaves at the opposite end. With such eoUs the 

 supply end will always be warmer by several degrees and will produce 

 an equivalent difference in the temperature of the kiln at the same 

 respective positions. 



Regardless of the employment of a good temperature control, the 

 heating system must be subdivided in such manner as to make manual 

 control possible and flexible in case of derangement of the automatic, 

 and the subdivisions must therefore be such as to enable the kiln 

 operator to obtain and hold any desired degree of temperature between 

 100° F. and 175° F. during any usual condition of the atmosphere, 

 from zero to 90° F. 



Continuous so-called "snake coils" are desirable, if properly spread 

 and inclined, and so are some forms of cast-iron radiation if properly 

 grouiiril and connected. 



No form of radiation can be effective without efficient and con- 

 tinuous drainage of the condensate forming therein, or without efficient 



