Alarch 



1922 



HARDWOOD RECORD 



31 



tions required, and the air circulation in most is not sufficiently 

 active to produce uniformity of these necessary conditions to per- 

 fect drying, and therefore corrective measures must be resorted to 

 by further steaming, during and after the drying, in most cases. 



One of the conditions frequently arising because of insufficient 

 air circulation is that of mold, in greater or lesser degree. This 

 manifests itself frequently a short time after the drying has started, 

 and generally in lumber of heavier dimensions, such as must be 

 held for longer periods at high humidity. The fungus should be 

 destroyed as promptly as it appears, and this can best be done 

 only by a very quick heating of the lumber surface (not the 

 interior) to about 180 degrees with live steam. To use exhaust 

 steam for this purpose is entirely out of question, aud would only 

 aggravate the condition which it was intended to cure. 



The quicker the needed heat can be supplied to the surface of the 

 lumber the less will be the danger of any damage from this excess 

 heat. Live steam at boiler pressure, anywhere up to 175 pounds, 

 must be supplied in sudden and large quantity up to the point 

 when the extension thermometer shows 180 degrees, when the 

 steam must be promptly shut off. The temperature will drop with 

 reasonable rapidity. If the case of mold is very bad the steam 

 may be again turned on to bring up the temperature required 

 quickly, when it must be shut off at once. More than two such 

 heatings in rapid succession are not advisable. The lumber should 

 then cool in saturated air until it attains the same degree of tem- 

 perature which it had when the steaming began. Drying may then 

 be resumed. 



Cooling after steaming must be at 100 per cent humidity. 



No harm will come to the lumber from such brief steaming to 

 severe temperature; provided, that positively no drying is per- 

 mitted to take place during the cooling period. The importance of 

 this injunction cannot be overstated. 



Dampers, condensers, sprays or any other means for moisture 

 removal must be closed absolutely, and kiln doors cannot be 

 opened on any pretext whatever until the normal drying condition 

 (for the known moisture content of the lumber) has again been 

 reached, as evidenced by the correctly placed extension thermom- 

 eter. In this case 100 per cent humidity means saturation and 

 nothing less. If the operator fails to obey this injunction he will 

 surely make kindling for the furnace. 



The writer has frequently used live steam at 1.50 pounds gauge 

 pressure, superheated 100 degrees, and discharged into the kiln 

 through a l^^-inch pipe, valve wide open (where it was distributed 

 through the regular spray pipe system, in the shape of an H, all 

 perforations facing away from the lumber and towards the bottom 

 of the kiln), always with very good results and no damage to the 

 lumber, but much care was exercised in stopping at the right 

 moment, as indicated by a properly installed thermometer, with 

 bulb in center of inner pile, and still greater care was exercised 

 in the cooling of the lumber in fully saturated air. 



For Casehardening Use Boiler Pressure Steam 



If, as drying proceeds, surface checks appear, these should be 

 watched as the lumber approaches fiber saturation, when these sur- 

 face checks will begin to close. At this point another swift steam- 

 ing with live steam to about 150 degrees, followed by a slow cooling 

 period in saturated air, will remove any existing casehardening 

 of the outer shell of the boards, of which casehardening the men- 

 tioned surface checks were an indication, and will permit uniform 

 shrinkage as the fiber moisture goes out, thus preventing internal 

 checking or honeycombing. 



Final Steajning 

 A final steaming is not generally necessary, but if the lumber is 

 intended for such manufactured product as will not permit any 

 strains in the lumber without danger of warping, a brief but thor- 

 ough steaming of the dry lumber will prove advisable. Live steam 

 only should be used for this purpose, and the surface temperature 

 of the lumber should be raised to about 160 degrees, and after this 

 steaming the lumber should again be cooled in saturated air to the 

 temperature which it had when drying was finished. At this point 



Where does the 

 moist, warm air go? 



Up and around, in and out, over 

 every usable inch of every stick in 

 the Kiln. It's the only way to dry 

 lumber properly and the only way 

 to lessen degrade and more profits 

 for vou. And the 



HIGH HUMIDITY DRY KILN 



The Kiln with a circulation you can understand 



is the only Kiln that will do this right 

 because the circulation of this moist, warm 

 air is positive and complete. No guess- 

 work, no "trusting to luck" with accurately 

 controlled circulation, re-circulation, tem- 

 perature and humidity. 



Circulation is the nub of the wonderful re- 

 sults wherever Sturtevant Kilns are in- 

 stalled. Write for Catalog No. 282. 



B. F. STURTEVANT COMPANY 



HYDE PARK BOSTON MASSACHUSETTS 



