Props of Imported Tropical Woods

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  • PROPERTIES OF IMPORTED TROPICAL WOODS1

    By

    _

    B. FRANCIS KUKACHKA, Botanist

    Forest Products Laboratory,2 Forest Service U.S. Department of Agriculture

    INTRODUCTION

    The descriptive text and tabular data compiledhere have been drawn freely from a wide varietyof sources, but special credit is due the publica-tions of the British Forest Products ResearchLaboratory and those of the Yale University Schoolof Forestry.

    Species descriptions are arranged alphabetical-ly by generic names. The generic name may befollowed by a specific name when the latter isthe sole or principal name used in the timbertrade. When a number of species are involvedand it is generally not practical to identify theprecise species from the wood alone, the genericname is followed by the designation spp.

    With well-established species only a singlecommon name has been applied, even though itmay have many local or vernacular names,particularly if the species has widespread distri-bution. Where two or three names are indicated,they usually refer to the name in use in theseveral areas of principal production. Commonnames which are inappropriately applied and aregenerally misleading have been avoided as muchas possible. The use of generic common names

    such as birch and teak in connection with totallyunrelated species is bad practice and only addsto already existing confusion of names in the wood-using industry.

    The pair of capital letters after the speciesname serves as a quick reference to the broadarea of origin as AF (Africa), AM (Latin America),and AS (Southeast Asia).

    An index of common names with their botanicalequivalents is included at the end of thisreport.

    The average weight of the woods described isgiven in pounds per cubic foot and at a moisturecontent of 12 percent, unless otherwise indicated.

    The term texture refers only to the diameterof the pores.

    Kiln schedules for foreign woods are given inBritish Forest Products Research LaboratoryLeaflet No. 42, Kiln-Drying Schedules, revised1959. The schedules differ somewhat from thosein Chapter 8 of Dry-Kiln Operators Manual,Agriculture Handbook 188 (1961). Table 1 (at endof report) lists the British schedule recommenda-tions for 4/4 to 6/4 lumber, the nearest U.S.

    1Presented at the Conference on Tropical Hardwoods held at theState University College of Forestry, Syracuse University,August 18-21, 1969.

    2The Laboratory is maintained at Madison, Wisconsin, in cooperationwith the University of Wisconsin.

  • schedule from the Dry Kiln Operators Manualfor these same sizes, and a suggested U.S.schedule for 8/4 stock.3

    Statements relative to durability refer only toheartwood and under conditions favorable todeterioration. Sapwood is always nondurable underexterior use conditions. Wood kept continuouslydry is not subject to attack by fungi although thesapwood of certain species may be attacked bypowder-post beetles.

    The term in-service, when mentioned, refersto the shrinkage and swelling or movement ofwood that may occur under conditions of use. Itrefers to interior use in the major part of theUnited States and the values, when cited, apply tounfinished wood. Finishes do not prevent move-ment but retard to varying degree the rate atwhich moisture is lost or gained. The valuesgiven in table 2 represent total shrinkage fromthe green to the ovendry state and are based onthe dimensions when green. Such values havelimited application and do not indicate the degreeof movement that may occur between differentlevels of relative humidity or the ratio of shrinkagethat occurs during different stages of drying. Itis unfortunate that so little movement data areavailable with respect to the species in everydayuse.

    The machining of wood perhaps presents moreproblems than any phase of conversion from thelog to finished product.. Lumber that is straightgrained and free of all defects is, of course, theideal material to the machine operator. Problemsbegin to mount when a user is confronted withthe necessity of machining species with which heis totally unfamiliar. With respect to tropicalspecies he will be confronted with considerablevariation in density, degree of interlocking andvariable grain, silica content, and tension wood,all of which can be very troublesome in speciesof lower density. Interlocked grain is character-istic of the majority of tropical species and pre-sents difficulty in the planing of quartered sur-faces unless attention is paid to cutting angles andsharpness of knives. Tension wood may accountfor rough surfaces, which may be referred to asfibrous, fuzzy, or torn. It is also frequentlyresponsible for the pinching effect on saws due

    to stress relief in the lumber during sawing andthe resulting burning and dulling of the teethThis particular difficulty is sometimes attributedto the presence of silica, even when silica is notpresent. Silica, when present, may have a pro-nounced dulling effect on all cutting edges andthis becomes more pronounced as the wood isdried to the usual in-service requirements.

    Strength values are given in table 3 for greenwood and in table 4 for seasoned wood. Thevalues are based on the ASTM or 2-inch standard.The values published by the British Laboratoryin their Bulletin No. 50 are based on the 2-centi-meter standard and are not directly comparablewith those based on the 2-inch standard. TheBritish values cited in tables 3 and 4 have beenconverted to the 2-inch standard using the con-version factors recommended in their BulletinNo. 50.

    ALBIZIA FALCATARIA AsBatai

    This species, originally described from theMolucca Islands, is now commonly found incultivation throughout the tropics of the world.The tree has been utilized in Malaysia for theafforestation of degraded and idle lands, and inCentral America it is replacing the silk-oak(Grevillea ) and native species used for shadetrees in coffee plantations. This species hasshown remarkable growth in several plantationson the islands of Kaual and Hawaii. Data pre-sented here are based primarily on the timberobtained from these Hawaiian plantations.Synonyms of this species are A. moluccana and A. falcata.

    Heartwood and sapwood not clearly distingulsh-able in all trees; wood light colored with a verypale brown, pinkish, or yellowish cast. Deschreports the Malayan-grown wood with grain deeplyinterlocked and spiral: the texture rather coarseand even. The Hawaiian-grown material wasessentially straight-grained and, although inter-locking was noted, it was rather shallow. Thewood weighs about 24 pounds per cubic foot.

    American basswood (Tilia americana), of thesame average specific gravity as batai, exceeds

    Wis., provided this abstract of Leaflet No. 42 and the U.S.schedule suggestions. The British schedules may be purchasedfrom the British Information Service, 845 Third Avenue,New York, N.Y. 10022.

    3John McMillen of the U.S. Forest Products Laboratory, Madison,

    FPL 125 2

    Balaji IyerHighlightStatements relative to durability refer only toheartwood and under conditions favorable todeterioration.

    Balaji IyerHighlightSapwood is always nondurable underexterior use conditions. Wood kept continuouslydry is not subject to attack by fungi although thesapwood of certain species may be attacked bypowder-post beetles

  • the latter in static bending and compressionParallel to grain at the 12 percent moisturecontent level; batai is slightly superior withrespect to side hardness and maximum shearingstrength.

    In Malaya, batai is said to dry fairly rapidlywithout serious degrade; the most common defectobserved was bowing. Lumber of 5/4 thicknesswas air seasoned in 6 weeks and 4/4 materialwas well dried in 4 weeks. None of the materialwas reported to have developed any splits orchecks.

    The wood is said to be abrasive to saws, butbecause this species is not a silica accumulator,the dulling effect can be attributed to the pinchingand resulting burning of the saw teeth as tensionstresses are relieved in the lumber. Wood in thisdensity class would require sharp knives to ensurethe production of smooth surfaces in planing. Thefine sawdust produced when machining the drywood is said to be responsible for allergicresponses in certain individuals. Responses notedhave been sneezing and tearing.

    The wood is not durable under exterior con-ditions. It has been treated by the open-tank pro-cedure and absorptions of 5 pounds of creosote-diesel fuel mixture were obtained in Malayantests.

    Because this species has some degree ofimportance as an ornamental tree and in silvi-cultural practice, the lumber has been utilizedon a relatively small scale and only for localpurposes. Because of its rapid growth, it wouldappear to have promise as a plantation speciesfor lumber and veneer purposes. For plantationpurposes it would be highly desirable to selectstrains which are relatively straight grained,since there appears to be considerable variationin the species with respect to degree of inter-locking grain. This species requires a morethorough evaluation of its inherent tension stres-ses.

    The Australian Laboratory reports the follow-ing potential problems in veneer production basedon four billets from the Solomon Islands: Endpopping on crosscutting of logs; high output ofnarrow veneer, woolliness of veneer surfaceswhen the knife edge is blunt or poorly prepared;buckling and splitting of veneer containing tensionwood; shortage of face veneer through end splits:and bow distortion of plywood due to tension wood.One billet contained brittleheart and two billetscontained a severe form of tension wood,

    3

    ALBIZIA LEBBEKKokko, Siris

    AS

    Albizia lebbek. which is native to India, Burma,Pakistan, Malaya, and the Andaman Islands hasfrequently and very erroneously bee