1.3 / 3 76 . CONDITIONING AND STORING Or AIR-DRIED AND KILN-DRIED AIRCRAFT STOCK #l Revised May 1943 TtilS REPORT IS ONE CI A SERIES ISSUED TC AID THE NATION'S WAR PROGRAM Nc. 1370 UNITED STATES DEPARTMENT OF AGRICULTURE FOREST SERVICE FOREST PRODUCTS LABORATORY Madison, Wisconsin In Cooperation with the University of Wisconsin . ition: -:■ •-DRIED AIRCRAFT STOCKS i reparinp Air-dried Stock f» r Man u facture Usually air-dried stock is not in satisfactory condition for aircraft use, thus the common procedure is to place it in a kiln for fina; relief of casehardening stresses. If a kiln is not available and if suf- ficient storage space is available in sheds or rooms heated to or all above ordinary factory temperature, and time not important, be to store air-r^ri*^. lumber in such mom? until the moisture eon- • lies with the specific requirements . (See For-:' r iuctfl Lab- bory r . 1365, "Moisture Content of Aircraft Lumber"). 3efore use, however, any existing casehardeni -isses must be removed by a conditioning treatment in a kiln or in the s* f the relative humidity can be raised by temperature adjustments or by humi lification. The kiln od is described in Forest Products Labor . 1.567 -vised), "Kiln-Drying Essentials for Aircraft Stock". Low temperature conditioning can be accomplished similarly except that more bins sil] be Jed* Stock so room conditioned may then be used without kiln dryi The fol rules should be observed in room dry: (a) Piling . — File foundations should be designed to permit circulation below the ] lie j The lo.vest layer of lumber should be 18 inches above the flc-r. Piles should be 2 feet apart, net nearer than 2 feet to outr lis, and • more than 6 feet wide. Stock should be placed on 1-inch stickers when it is not over 6/4 inch thick. For thicker material of random le , 1-1/2-inch stickers should be used for greater stiffness and stre Stickars should be evenly aligned wit: spacing not to exceed 2 feet for stock up to and including 6/4 inch in thickness. (b) Circa la '.ion . --If e do not vary more than 5C I . beti sen fferent parts of the room, effective control of .istjre content can be obtained. Small fans may be used to circulate a : r sufficiently to keep tern .--ps relatively unifor . (c) Temperature, humidity, and moisture relqti ons . --By referr equ moisture content curve (see aecompa:. figure) trie necessary temperature and humidity conditions roqu ' a a desired constant moisture content readily can be determined. To haste- , the humid it be 15 percent bel b required to maintain the final moisture content specified* it it si be possible to secure the d< ' "m^erature and humidity conditions by controlling only > temperat urc . For conditioning- treatments, however, steam or wa* sprays miay be requir-. . .is mimeograph is nne of a Be'rles of r Labor • I -• to aid the Nation's - ». 1370 (Revised) Storage Aircraft lumber should be dried to meet moisture content and oasehardenii specifications, and subsequent storage should be relied upon merely to obtain additional benefits in the form of more nearly uniform transverse moisture distribution and further relief of casehardening stresses. For kiln-dried stock at least two weeks storage is desirable for this purpose, but to maintain the stock in satisfactory condition until used in the shop, the storage conditions should be controlled within the moisture-content range specified. The stock then may be either left on stickers or solid piled. Stock stored under uncontrolled conditions may become unsatisfactory regard- less of the method of piling, because a longitudinal moisture gradient may develop in a solid pile and a general moisture pick-up may occur in an open pile. Storage of all material before manufacture should be under conditions that will deliver the stock sound, free from seasoning defects, and at suitable moisture content. In order to reduce moisture changes or to secure wood at a given moisture content, it may be necessary to equip the storage shed, or factory, with humidity-control equipment so that the ran : ;e of mointure change may be controlled. The humidity should be so controlled that the moisture content of stoch other than propeller material cannot fall below 8 percent or rise above 12 percent, ^r one He r stoc v should be stored under conditions that maintain the moisture content betwe en ^ and J per cent . Effect of Storage on Defects Stock that has been dried to the acceptable moisture content, if kept dry, may be held for an indefinite period without deterioration from seasoning defects, such as checking, honeycombing, stain, and deca5'. Certain woods are subject to insect attack even alter drying. The Lyctus powder-post beetle attacks especially the seasoned sapwood of hickory, ash, and oak, and it also damages other hardwoods such es walnut, maple, cherry, elm, yellowpcplar, and sycamore. Other powder-post beetles attack both heartwood and sapwood, and both' hardwoods and softwoods. Stored stock that is subject to insect attack should be moved in rotation, so that none of it will remain exposed to infestation for an excessively long time. Such stock should be examined regularly and carefully, and borer-infested stock should be either heat-sterilized or destroyed. Infestation of adjacent stock is merely a matter of time if proper preventive measures are not observed. The larvae of the Lyctus beetles bore inward, giving little or nc early indication of their presence and thus making prompt recognition of infestatioi tly difficult. Borers eat holes from l/lS to i/4 inch in diameter and leave wood powder in them. Then a hole penetrates an exterior surface, the powder can be jarred out. Badly tunneled wood can easily be broken. Himeo No. 1370 (Revised) -2- Figure — Relation of the equilibrium moisture content cf rood to the relative humidity of the surrounding atmosphere at three temperatures. r^ X X X \ X i > 1 \ > \ 1 \ \ \ \ • VJ o % j t-^ — \ 1 \ 1 \ 1 1 \ 1 \ \ 1 1 \ 1 I \ \ t 1 * 1 ■ \ \ \ 1 \ V 1 /. ! % § <3n 8 1 -*4 o- ^ ^ ^ *0 ^ <^> (IN 30 H3d) aooM Nt 3Un±SI0lAl UNIVERSITY OF FLORIDA 3 1262 08926 8659