ASTM D4442-2007 Standard Test Methods for Direct Moisture Content Measurement of Wood and Wood-Base Materials《木材和木基材料的直接水分测量用标准试验方法》.pdf

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1、Designation: D 4442 07Standard Test Methods forDirect Moisture Content Measurement of Wood and Wood-Base Materials1This standard is issued under the fixed designation D 4442; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year

2、 of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 These test methods cover the det

3、ermination of themoisture content (MC) of solid wood, veneer, and otherwood-base materials, including those that contain adhesivesand chemical additives. The test methods below describeprimary (A) and secondary (B through D) procedures tomeasure moisture content:Method APrimary Oven-Drying MethodMet

4、hod BSecondary Oven-Drying MethodMethod CDistillation (Secondary) MethodMethod DOther Secondary Methods.1.2 The primary oven-drying method (Method A) is in-tended as the sole primary method. It is structured for researchpurposes where the highest accuracy or degree of precision isneeded.1.3 The seco

5、ndary methods (B through D) are intended forspecial purposes or under circumstances where the primaryprocedure is not desired or justified. In these procedures,moisture content values cannot be reported with an accuracygreater than integer percentage values. However, a greaterlevel of accuracy may b

6、e reported if the appropriate primaryprocedures are used.1.4 Distillation (secondary) method is intended for use withmaterials that have been chemically treated or impregnatedsuch that the oven-drying procedures introduce greater errorthan desired in the results.1.5 This standard does not purport to

7、 address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D9 Termin

8、ology Relating to Wood and Wood-Based Prod-uctsD 4933 Guide for Moisture Conditioning of Wood andWood-Based Materials3. Terminology3.1 Definition:3.1.1 moisture contentthe amount of water contained inthe wood, usually expressed as a percentage of the mass of theoven-dry wood (in accordance with Term

9、inology D9).3.1.1.1 DiscussionThe moisture content of wood or otherwood-based materials can be expressed on either as a percent-age of oven-dry mass of the sample (oven-dry basis) or as apercentage of initial mass (wet basis). The methods describedin this standard refer to the oven-dry basis. Becaus

10、e oven-drymass is used, moisture content values may exceed 100 %. Theterm moisture content when used with wood-based materialscan be misleading since untreated wood frequently containsvarying amounts of volatile compounds (extractives which areevaporated when determining moisture content). Definitio

11、n ofthe moisture content of wood is further complicated whendetermined by a thermal method because of thermal degrada-tion, which causes the final moisture-free mass to decreasefrom small but continuous losses.4. Significance and Use4.1 Moisture content is one of the most important variablesaffectin

12、g the properties of wood and wood-base materials. Theprocedures in these test methods are structured to permit thefull range of use from fundamental research to industrialprocessing. Method A is designed for obtaining the mostprecise values of moisture content consistent with the needs of1These test

13、 methods are under the jurisdiction of ASTM Committee D07 onWood and are the direct responsibility of Subcommittee D07.01 on FundamentalTest Methods and Properties.Current edition approved Nov. 15, 2007. Published December 2007. Originallyapproved in 1984. Last previous edition approved in 2003 as D

14、 4442 92 (2003).These test methods replace, in part, Test Methods D 2016, for Moisture Contentof Wood, discontinued 1989.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refe

15、r to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.the user. It also provides means of assessing variabilitycontributed by the oven or specimen hygroscopicity, or both. Inaddit

16、ion, criteria are described for defining the endpoint inoven-drying. Method A is the reference (primary) standard fordetermining moisture content of wood and wood-base materi-als. Methods B through D are secondary methods to permitrelatively simple procedures of measuring moisture content,but with l

17、ess precision than Method A. However, greaterprecision may be obtained with supporting data by using theappropriate procedures in Method A.5. Method AOven-Drying (Primary)5.1 Apparatus:5.1.1 OvenA forced-convection oven that can be main-tained at a temperature of 103 6 2C throughout the dryingchambe

18、r for the time required to dry the specimen to theendpoint shall be used. Ovens shall be vented to allow theevaporated moisture to escape.NOTE 1The ratio of sample mass to chamber volume and the airvelocity within the oven are not critical as long as temperature and relativehumidity within the oven

19、are constant. Room relative humidity should beless than 70 % relative humidity, at which condition the oven is at 1.7 %relative humidity. For best precision, drying should be carried out in aconstant relative humidity room with the relative humidity as low aspossible.5.1.2 BalanceBased on a 10-g (ov

20、en-dry) specimen,minimum readability of the balance shall be determined by thedesired reporting level of precision:Reporting Precision Level, MC, % Minimum Balance Readability, mg0.01 10.05 50.1 100.5 501.0 100For other oven-dry mass levels, the sensitivity requirementshall be scaled appropriately.5

21、.2 Test MaterialAny conveniently sized wood or wood-based material can be used, consistent with the use of closedweighing jars (5.4.6) and the balance readability (5.1.2).NOTE 2If specimens contain any degree of volatilizable materialother than water, it may be necessary to either use Method C or ru

22、nMethod A and C concurrently.5.3 Calibration and StandardizationDetermination ofspecimen variability requires a separate measurement of thecontribution of variability within the oven.5.3.1 Determination of Oven VariabilityThis section per-mits a separate evaluation of the oven variability from that

23、ofspecimens distributed in the oven.5.3.1.1 Specimen Selection and PreparationDouglas-firshall be ground to sawdust and that fraction contained in a40/60 mesh screen used. The sample origin or drying history isnot critical. The sawdust shall be tumbled in a closed containeruntil thoroughly mixed. Al

24、l replicates shall be prepared at thesame time from the same batch of material. All material shallbe transferred and stored in air-tight weighing jars.5.3.1.2 EquilibrationThe moisture content of the speci-men is not important if the preparation techniques describedunder 5.3.1.1 are used. Equilibrat

25、ion is not required, althoughit is preferable that the material be as uniform as possible inmoisture content.5.3.1.3 Number and Location of SpecimensEach test shallconsist of a set of eight replicated specimens. These shall belocated at third-point positions with respect to height, width,and depth o

26、f the oven cavity. With this scheme four sampleswill be positioned on each of two shelves at one third and twothirds of the cavity height.5.3.2 Determination of Combined Specimen and OvenVariabilityProcedures are the same as 5.3.1.1-5.3.1.3 exceptthat specimens of any origin and size or shape can be

27、 used.Calculate variability by the equation in 5.5.2.5.3.3 ProcedureUse the primary oven-drying procedure(5.4).5.4 Procedure:5.4.1 Specimens to be equilibrated shall be processed as inGuide D 4933.5.4.2 Store specimens in individual vapor-tight containers ifany delay could occur between sampling and

28、 weighing.5.4.3 Weigh the specimens using a balance consistent withthe desired precision (see 5.1.2).5.4.4 Place specimens in the oven within the volume testedfor oven precision.5.4.5 EndpointAssume that the endpoint has beenreached when the mass loss in a 3-h interval is equal to or lessthan twice

29、the selected balance sensitivity. For example, givena specimen weight of 10-g and for a balance sensitivity of 1 mgchosen in 5.1.2 to allow reporting to a 0.01 % MC precision,the endpoint is assumed to have been reached when the changein weight is 2 mg or less in a 3-h period.5.4.6 Handling and Weig

30、hing ProceduresDried samplesshall be stored in a desiccator with fresh desiccant until theyhave reached room temperature. All weighings shall be carriedout using closed weighing jars.5.5 Calculations:5.5.1 Calculate moisture content as follows:MC,%5 A 2 B!/B 3 100 (1)where:A = original mass, g, andB

31、 = oven-dry mass, g.ExampleA specimen of wood weighs 56.70 g. After oven-drying, the mass is 52.30 g.MC,%5 56.70 2 52.30!/52.30 3 100 (2)5 4.40/52.30! 3 100 5 8.4 %NOTE 3If wood has been treated with a nonvolatile chemical and ifthe mass of the retained chemical is known, the moisture content may be

32、determined as follows:MC,%5 A 2 B!/D 3 100 (3)where:D = B minus mass of retained chemical in sample.5.5.2 Calculate variance of the specimens as follows:Sw25 Sow22 So2(4)D4442072where:Sw2= specimen material variance,So2= oven variance (from 5.3.1), andSow2= combined specimen and oven variance (5.3.2

33、).5.6 ReportReport the following information: nominaloven-dry mass, type of material, oven variance, specimenvariance, balance sensitivity, oven model and type, and anydeviation from the prescribed method. The number of decimalplaces reported shall not exceed the precision level (5.1.2).5.7 Precisio

34、n and Bias:5.7.1 Precision of MeasurementBy definition, the accu-racy of measurement has been set equal to the determinedprecision of test measurement, that is, there is no assumed biasof measurement due to the inability to accurately assessmoisture content. With this approach the actual accuracy ma

35、ybe poorer than the stated accuracy. At this time, no data areavailable from which to report typical variances in ovens orfrom specimen material.6. Method BOven-Drying (Secondary)6.1 Apparatus:6.1.1 OvenAn oven that can maintain 103 6 2C near thedrying endpoint shall be used.6.1.2 BalanceThe sensiti

36、vity shall be a minimum of0.1 % of the nominal oven-dry mass of the specimen (see5.1.2).6.2 Test MaterialAny conveniently sized wood or wood-based material can be used, however, the balance readabilityshall be consistent with the desired precision (see 5.1.2 and5.3).NOTE 4If specimens contain any de

37、gree of volatilizable materialother than water, it may be necessary to either use Method C, or runMethods B and C concurrently.6.3 Calibration and StandardizationNo specific tests arerequired unless greater precision than integer moisture contentvalues are desired. See 6.7.6.4 Procedure:6.4.1 Specim

38、ens to be equilibrated shall be processed as inGuide D 4933.6.4.2 Store specimens in individual vaportight containers orwrapping if any delay could occur between sampling andweighing.6.4.3 Weigh the specimens using a balance consistent withthe desired precision (see 6.1.2).6.4.4 EndpointAssume that

39、the endpoint has beenreached when no appreciable change is noted in final massreadings made at approximately 4-h intervals.NOTE 5As a guide, an air-dry solid wood specimen about 50 by 100mm in cross section and 25 mm along the grain will usually attain“constant mass” within 24 h when dried in a forc

40、ed convection oven usingthis procedure.6.4.5 Handling and Weighing ProceduresDried samplesshall be weighed as soon as possible to minimize moistureuptake.6.5 Calculation of Moisture Content:6.5.1 Calculate moisture content as follows:MC,%5 A 2 B!/B 3 100 (5)where:A = original mass, g, andB = oven-dr

41、y mass, g.ExampleA specimen of wood weighed 56.7 g. Afteroven-drying, the mass was 52.3 g.MC,%5 56.7 2 52.3!/52.3 3 100 (6)5 4.4/52.3! 3 100 5 8.4Round to 8 % see 1.3 and 6.7.1!NOTE 6If wood has been treated with a nonvolatile chemical and ifthe mass of the retained chemical is known, the moisture c

42、ontent may bedetermined as follows:MC,%5 A 2 B!/D 3 100 (7)where:D = B minus the mass of retained chemical in sample.6.6 ReportReport the following information: Mean, stan-dard deviation, number of specimens, and any deviation fromthe method. Moisture content values shall be integer only (see6.7.1).

43、6.7 Precision and Bias:6.7.1 The precision is assumed to be no greater than6 1%moisture content for any measurement unless the appropriateprocedures in Section 5 are used.6.7.2 No bias calculations may be made from this proce-dure.7. Method CDistillation7.1 Apparatus:7.1.1 Extraction FlaskA 500-mL f

44、lask and thimbleholder, as shown in Fig. 1. The flask and holder may becombined in one unit.7.1.2 CondenserA water-cooler condenser of the cold-finger type, as shown in Fig. 1, or of the straight-tube, Liebigtype.7.1.3 Water TrapA glass tube preferably having an insidediameter of 9 to 10 mm and seal

45、ed at one end. If a trap withstopcock is used, the stopcock shall be securely fastened inplace. The graduated portion of the tube shall have a capacityof 10 mL. The smallest graduation should be not greater than0.1 mL with the major divisions marked 1 to 10. The water trapshould be chemically clean

46、so that the shape of the meniscus atthe end of the test is the same as at the beginning. (The trapmay be coated with a silicone resin to give a uniform meniscus.To coat the trap, first clean it with sulfuric acid-chromic acidmixture. Rinse the clean trap with a silicone resin and, afterdraining for

47、a few minutes, bake for 1 h at approximately200C.)7.1.4 Extraction CupEither a Wiley siphon cup of suit-able size or a basket made of approximately 45 mesh, stainlesssteel gauze and having the approximate dimensions of 42 mmin outside diameter and 127 mm in length. The siphon cup isrecommended for b

48、orings from heavily treated piling. When asiphon cup is used, the loss of wood particles should beprevented either by placing a conical screen at the bottom ofthe siphon cup or by putting the chips or borings in a wiregauze basket which is then placed inside the siphon cup.7.1.5 Hot Plate:D44420737.

49、1.6 Weighing BottleThe weighing bottle shall have aground glass stopper and be of sufficient size to contain thewire extraction cup or Wiley siphon described in 7.1.4.7.1.7 RodA rod approximately 3 mm in diameter made ofsome material to which water does not adhere such asTFE-fluorocarbon resin.7.1.8 OvenThe oven shall be maintained at a temperatureof 103 6 2C.7.1.9 Desiccator:7.1.10 BalanceThe balance shall have a sensitivity of0.01 g.7.1.11 Increment Borer:7.2 Reagents and Materials:7.2.1 DesiccantCalcium chloride, silica g