22 



HARDWOOD RECORD 



February 25. 1922 



YARD AND KILN 



cA Section Intended to Promote Efficiency^ 

 and Economy in Lumber Drying ^ 





Short Stones of tire Kiln 



By C. 



What cold air may do to hot lumber is best illustrated in relat- 

 ing the following experience which came to a very capable and 

 faithful operator of an extensive layout of dry kilns. 



In a kiln, containing approximately twenty thousand spoke billets 

 of southern oak, which had been long enough in drying to reach 

 about 35 percent of moisture content, through some blunder (prob- 

 ably careless piling), the forward piles collapsed, carrying a large 

 door with them. 



This accident occurred when the atmosphere was at about zero, 

 or just a little below. The clearing and repiling of the billets and 

 repairing of the kiln door occupied several hours. 



The operator, feeling* his responsibility in the matter, was pre- 

 occupied with the work of restoring the kiln contents and the door 

 to proper order, and thus completely lost sight of any possible con- 

 sequences to the lumber and any possible steps to prevent these 

 consequences, neither did he report the accident. 



He succeeded in suppressing general information about the mis- 

 hap, but was most unpleasantly surprised to find later that the 

 great majority of the billets in the kiln were hopelessly destroyed 

 for use other than kindling, because of severe checks and honey- 

 combs. In fact only about 28 percent of the total contents of the 

 kiln were finally found useful for the intended purpose. This not- 

 withstanding the operators firmly established prior success in per- 

 fect drying of this material with but nominal kiln loss. 



The money involved in the lumber being quite considerable, an 

 investigation was ordered, to establish facts, causes of the dam- 

 age, and prevention of a possible repetition of the disaster. 



The conclusions were that the damage was caused by the sudden 

 drying out of all surface moisture, and consequent deep caseharden- 

 ing, when the cold and very dry air came into contact with the hot 

 (11.5°) lumber. 



Serious damage to the lumber could have been prevented, or at 

 least very largely restricted, first, by immediate flooding of the 

 complete kiln contents with water from a fire hose, to cool the same 

 and to moisten the surface of the lumber, even to the extent of 

 forming an ice coating on the more exposed pieces, and next, by 

 thorough steaming, after repiling and door repairs had been accom- 

 plished. 



This and other similar experiences induce the writer to suggest, 

 in case of hardwood lumber, and more especially oak and black 

 walnut, that if the drying operation must be interrupted from any 

 cause, and if the lumber must be permitted to cool while its mois- 

 ture content is still above l.^j percent, then if this cooling takes 

 place in the kiln, all ventilation must be shut off completely, and 

 condensers if there be any, and the relative humidity of the kiln 

 air must be held constant at the point required by the then existing 

 moisture content of the lumber or above this point, and if no steam 

 is available with which to do so a water hose should be resorted to. 

 If on the other hand it were necessary to remove such lumber 

 while hot from the kiln, then this lumber should be thoroughly 

 drenched with water, until no further drying out takes place, and 

 its temperature has been reduced to approximately, or below, the 

 temperature of the atmosphere, or that of the place where this lum- 

 ber is to be temporarily located, until it can be placed into a kiln. 

 Even then the lumber should be carefully watched, and the wetting 

 operation repeated if any signs of drying, due to internal heat, 

 develop. 



—An Expensive Accident 

 J.M. 



Questions and Answers 



[Note: h'eailcrs of Hardwood Secord arc invited to submit their yard 

 and liln problems for answer in this column. — Thk Editor.] 



Question 5 — Dripping Eoof Over Transfer Pit? 

 The dry ends of our progressive kilns open onto a transfer pit, 

 beyond which is located the dry storage space. The roof over this 

 transfer pit persists in sweating and dripping during cool weather. 

 There is no ceiling below this roof, which is of wood construction 

 with tar and gravel over same. 



Our kilns have good doors of the llussey type, made of cypress 

 strips and asbestos roofing paper, and the same fit quite well. This 

 dripping is really getting serious, and we will thank you sincerely 

 for any expert advice which you may obtain for us. Our engineer 

 suggests a steam coil placed under the roof over the transfer pit. 



Superintendent. 

 Answer to Question 5 



From your description of the conditions I am inclined to reason 

 as follows: 



First — More humidity exists in the "dry" ends of your pro- 

 gressive kilns than jirobably should be there. It may pay you to 

 investigate this. 



Second — That, notwithstanding their good condition, your kiln 

 doors do not fit sufficiently air-tight on this end. Upon investiga- 

 tion 3'ou will probably find that these doors "bottom" on the rails, 

 and consequently fall away from the brackets and the lintels, or, 

 if they really do "hang" as they should, in the top brackets, that 

 the lintels have warped, or arc not strictly in line with the jambs. 

 It will be to your interest in several directions to have these doors 

 brought to a tight fit. 



Third — Your engineer is right in advising the steam coil, but this 

 can be very light in capacity. About four pipes, run the full length 

 of the transfer pit, will prove sufficient. These should be made up 

 into a continuous coil (snake type), which, however, must not be 

 over fifty feet long, and carefully hung as close to the roof as 

 possible, in such manner as to assist its easy drainage of eondesa- 

 tion, and must be equipped with an automatic air valve, connected 

 to an enlarged fitting at its outlet end, the air collecting in this 

 fitting to pass out through the air valve. 



It is important that such a coil should be no longer than fifty feet. 

 If the transfer pit in question is longer, divide the space into two 

 or three, and provide separate steam coils accordingly. 



Fourth — From your statements it would appear that your dry 

 storage space, connecting direct with the transfer pit, must be 

 insufficiently heated, and consequently too humid to serve its pur- 

 pose properly. A dry storage space cannot be termed dry unless its 

 humidity is held below the point where the wood can again absorb 

 moisture from the air. The humidity of such a dry storage room, 

 regardless of its temperature, must not exceed 20 per cent to 25 

 per cent, if you desire to hold the wood stored therein at a moisture 

 content of about 5 per cent. A small amount of heating surface, 

 properly placed, will accomplish this easily, and also will prevent 

 any possible roof dripping. Xylos. 



Question 6 — Dry kiln Doors? 

 I am designing a small woodworking plant, which is to contain 

 two lumber kilns. The owner will provide all heating arrange- 



