ASTM D4442-2016 Standard Test Methods for Direct Moisture Content Measurement of Wood and Wood-Based 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: D4442 16Standard Test Methods forDirect Moisture Content Measurement of Wood and Wood-Based Materials1This standard is issued under the fixed designation D4442; 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 () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope1.1 These test methods cover the

3、determination of themoisture content (MC) of wood, veneer, and other wood-basedmaterials, including those that contain adhesives and chemicaladditives. The test methods below describe primary (A) andsecondary (B through D) procedures to measure moisturecontent:Method APrimary Oven-Drying MethodMetho

4、d 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 second

5、ary methods (B through D) are intended forspecial purposes or under circumstances where the primaryprocedure (Method A) is not desired or justified. In theseprocedures, moisture content values cannot be reported with anaccuracy greater than integer percentage values (that is, lowerthan in Method A).

6、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 The values stated in SI units are to be regarded asstandard. No other units of measurement

7、 are included in thisstandard.1.6 This standard does not purport to 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 limitation

8、s prior to use.2. Referenced Documents2.1 ASTM Standards:2D9 Terminology Relating to Wood and Wood-Based Prod-uctsD4933 Guide for Moisture Conditioning of Wood andWood-Based Materials3. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this test method, referto Terminology D9.3.1.2 m

9、oisture contentthe amount of water contained inthe wood, usually expressed as a percentage of the mass of theoven-dry wood (in accordance with Terminology D9).3.1.2.1 DiscussionThe moisture content of wood or otherwood-based materials can be expressed either as a percentageof oven-dry mass of the sa

10、mple (oven-dry basis) or as apercentage of the original mass (wet basis). The methodsdescribed in this standard refer to the oven-dry basis. Becauseoven-dry mass is used, moisture content values may exceed100 %. The term moisture content when used with wood orother wood-based materials can be mislea

11、ding since theyfrequently contain varying amounts of volatile compounds(extractives that are evaporated when determining moisturecontent). Definition of the moisture content of wood is furthercomplicated when determined by a thermal method because ofthermal degradation, which causes the final moistu

12、re-free massto decrease from small but continuous losses.4. Significance and Use4.1 Moisture content is one of the most important variablesaffecting the properties of wood and wood-based materials.The procedures in these test methods are structured to permit1These test methods are under the jurisdic

13、tion of ASTM Committee D07 onWood and are the direct responsibility of Subcommittee D07.01 on FundamentalTest Methods and Properties.Current edition approved Nov. 15, 2016. Published November 2016. Originallyapproved in 1984. Last previous edition approved in 2015 as D4442 15. DOI:10.1520/D4442-16.T

14、hese test methods replace, in part, Test Methods D2016, 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, refer to the standards

15、 Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1the full range of use from fundamental research to industrialprocessing. Method A is designed for obtaining the mostprecise values of moisture c

16、ontent consistent with the needs ofthe user. It also provides means of assessing variabilitycontributed by the oven or specimen hygroscopicity, or both. Inaddition, criteria are described for defining the endpoint inoven-drying. Method A is the reference (primary) standard fordetermining moisture co

17、ntent of wood and wood-based mate-rials. Methods B through D are secondary methods to permitrelatively simple procedures of measuring moisture content,but with less precision than Method A.5. Method AOven-Drying (Primary)5.1 Apparatus:5.1.1 OvenA forced-convection oven that can be main-tained at a t

18、emperature of 103 6 2C throughout the dryingchamber 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

19、 temperature and relativehumidity within the oven 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

20、as low aspossible.5.1.2 BalanceBased on a 10 g (oven-dry) specimen, mini-mum 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 se

21、nsitivity requirementshall be scaled appropriately.5.2 Test MaterialAny conveniently sized wood or wood-based material can be used, consistent with the use of closedweighing jars (5.4.7) and the balance readability (5.1.2).NOTE 2If specimens contain any degree of volatilizable material otherthan wat

22、er, it may be necessary to either use Method C or run Method Aand 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 se

23、parate evaluation of the oven variability from that 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 tum

24、bled in a closed containeruntil thoroughly mixed. All 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 te

25、chniques describedunder 5.3.1.1 are used. Equilibration 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

26、 positions with respect to height, width,and depth of 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 5.3.1.3except t

27、hat specimens of any origin and size or shape can beused. 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 D4933.5.4.2 Store specimens in individual vapor-tight cont

28、ainers ifany delay could occur between sampling and weighing.5.4.3 Weigh the specimens using a balance consistent withthe desired precision (see 5.1.2).5.4.4 Preheat the oven to a temperature of 103 6 2C5.4.5 Place specimens in the oven within the volume testedfor oven precision.5.4.6 EndpointAssume

29、 that the endpoint has been reachedwhen the mass loss in a 3 h interval is equal to or less thantwice the selected balance sensitivity. For example, given aspecimen 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

30、 to have been reached when the changein weight is 2 mg or less in a 3 h period.5.4.7 Handling and Weighing 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 Calculation

31、s:5.5.1 Calculate moisture content as follows:MC,%5 A 2 B!/B 3100 (1)where:A = original mass, g, andB = 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 3100 (2)54.40/52.30! 3100 5 8.4%NOTE 3If wood has been treated with a n

32、onvolatile chemical, or if awood-based material contains a large amount of non-wood chemicals thatcannot be neglected, and if the mass of the retained chemical(s) is known,the moisture content may be determined as follows:MC,%5 A 2 B!/D 3100 (3)where:D = B minus mass of retained chemical in sample.D

33、4442 1625.5.2 Calculate variance of the specimens as follows:Sw25 Sow22 So2(4)where:Sw2= specimen material variance,So2= oven variance (from 5.3.1), andSow2= combined specimen and oven variance (5.3.2).5.6 Report:5.6.1 Report the following information:5.6.1.1 Type of material,5.6.1.2 Description of

34、specimens and their nominal oven-dry mass,5.6.1.3 Oven variance,5.6.1.4 Specimen variance,5.6.1.5 Balance sensitivity,5.6.1.6 Oven model and type, and5.6.1.7 Any deviation from the prescribed method.5.6.2 The number of decimal places reported shall notexceed the precision level (5.1.2).5.7 Precision

35、 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, it is possible that th

36、eactual accuracy will be poorer than the stated accuracy. At thistime, no data are available from which to report typicalvariances in ovens or from 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

37、.2 BalanceThe sensitivity shall be a minimum of 0.1 %of the nominal oven-dry mass of the specimen (see 5.1.2).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 sp

38、ecimens contain any degree of volatilizable material otherthan water, it may be necessary to either use Method C, or run MethodsB 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

39、Procedure:6.4.1 Specimens to be equilibrated shall be processed as inGuide D4933.6.4.2 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

40、 Preheat the oven to a temperature of 103 6 2C andplace specimens in the oven.6.4.5 EndpointAssume that the endpoint has been reachedwhen no appreciable change is noted in final mass readingsmade at approximately 4 h intervals.NOTE 5As a guide, an air-dry wood specimen about 50 by 100 mm incross sec

41、tion and 25 mm along the grain will usually attain “constantmass” within 24 h when dried in a forced convection oven using thisprocedure.6.4.6 Handling and Weighing ProceduresDried samplesshall be weighed as soon as possible to minimize moistureuptake.6.5 Calculation of Moisture Content:6.5.1 Calcul

42、ate moisture content as follows:MC,%5 A 2 B!/B 3100 (5)where:A = original mass, g, andB = oven-dry 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 3100 (6)54.4/52.3! 3100 5 8.4Round to 8 % (see 1.3 and 6.7.1)NOTE 6If wood has been treat

43、ed with a nonvolatile chemical, or if awood-based material contains a large amount of non-wood chemicals thatcannot be neglected, and if the mass of the retained chemical(s) is known,the moisture content may be determined as follows:MC,%5 A 2 B!/D 3100 (7)where:D = B minus the mass of retained chemi

44、cal in sample.6.6 Report:6.6.1 Report the following information:6.6.1.1 Type of material,6.6.1.2 Description of specimens and their nominal oven-dry mass,6.6.1.3 Mean,6.6.1.4 Standard deviation,6.6.1.5 Number of specimens, and6.6.1.6 Any deviation from the method.6.6.2 Moisture content values shall

45、be integer only (see6.7.1).6.7 Precision and Bias:6.7.1 The precision is assumed to be no greater than 61%moisture content for any measurement unless the appropriateprocedures in Section 5 are used.6.7.2 The bias of this test method is unknown because thevalues are determined solely in terms of this

46、 test method itself.7. Method CDistillation7.1 Apparatus:7.1.1 Extraction FlaskA 500 mL flask and thimble holder,as shown in Fig. 1. It is acceptable to combine the flask andholder in one unit.7.1.2 CondenserA water-cooler condenser of the cold-finger type, as shown in Fig. 1, or of the straight-tub

47、e, Liebigtype.D4442 1637.1.3 Water TrapA glass tube preferably having an insidediameter of 9 to 10 mm and sealed 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 shoul

48、d be not greater than0.1 mL with the major divisions marked 1 to 10. The water trapshould be chemically clean 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

49、 it with sulfuric acid-chromic acidmixture. Rinse the clean trap with a silicone resin and, afterdraining for a few minutes, bake for 1 h at approximately200C.)7.1.4 Extraction CupEither a Wiley siphon cup of suitablesize or a basket made of approximately 45 mesh, stainless steelgauze and having the approximate dimensions of 42 mm inoutside diameter and 127 mm in length. The siphon cup isrecommended for borings from heavily treated piling. When asiphon cup is used, the loss of wood particles should beprevented either by placin