1、Designation: D792 08D792 13Standard Test Methods forDensity and Specific Gravity (Relative Density) of Plasticsby Displacement1This standard is issued under the fixed designation D792; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision
2、, the year 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 Department of Defense.1. Scope*1.1 These test methods des
3、cribe the determination of the specific gravity (relative density) and density of solid plastics in formssuch as sheets, rods, tubes, or molded items.1.2 Two test methods are described:1.2.1 Test Method AFor testing solid plastics in water, and1.2.2 Test Method BFor testing solid plastics in liquids
4、 other than water.1.3 The values stated in SI units are to be regarded as the standard.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices
5、and determine the applicability of regulatorylimitations prior to use.NOTE 1This standard is not equivalent to ISO 11831 Method A. This test method provides more guidelines on sample weight and dimension. ISO1183-1 allows testing at an additional temperature of 27 6 2C.2. Referenced Documents2.1 AST
6、M Standards:2D618 Practice for Conditioning Plastics for TestingD891 Test Methods for Specific Gravity, Apparent, of Liquid Industrial ChemicalsD4968 Guide for Annual Review of Test Methods and Specifications for PlasticsD6436 Guide for Reporting Properties for Plastics and Thermoplastic ElastomersE
7、1 Specification for ASTM Liquid-in-Glass ThermometersE12 Terminology Relating to Density and Specific Gravity of Solids, Liquids, and Gases (Withdrawn 1996)3E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test MethodIEEE/ASTM SI-10 Practice for Use of the Intern
8、ational System of Units (SI) (the Modernized Metric System)3. Terminology3.1 GeneralThe units, symbols, and abbreviations used in these test methods are in accordance with IEEE/ASTM SI-10.3.2 Definitions:3.2.1 specific gravity (relative density)the ratio of the mass of a given volume of the impermea
9、ble portion of the material at23C to the mass of an equal volume of gas-free distilled or de-mineralized water at the same temperature; the form of expressionshall be:Specific gravityrelative density!23/23Cor sp gr23/23C!1 These test methods are under the jurisdiction of ASTM Committee D20 on Plasti
10、cs and are the direct responsibility of Subcommittee D20.70 on Analytical Methods(Section D20.70.01).Current edition approved June 15, 2008Nov. 1, 2013. Published July 2008November 2013. Originally approved in 1944. Last previous edition approved in 20002008 asD792 - 00.D792 - 08. DOI: 10.1520/D0792
11、-08.10.1520/D0792-13.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 The last approved version of this hist
12、orical standard is referenced on www.astm.org.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately
13、, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive
14、, PO Box C700, West Conshohocken, PA 19428-2959. United States1NOTE 2This definition is essentially equivalent to the definition for apparent specific gravity and apparent density in Terminology E12, because thesmall percentage difference introduced by not correcting for the buoyancy of air is insig
15、nificant for most purposes.3.2.2 densitycubic metre of impermeable portion of the material at 23C. The form of expression shall be:D23,kg/m3(Notes 2-4)NOTE 3The SI unit of density, as defined in IEEE/ASTM SI-10, is kg/m3. To convert density in g/cm3 to density in kg/m3, multiply by 1000.NOTE 4To con
16、vert specific gravity 23/23C to density 23C, kg/m3, use the following equation:D23C,kg/m35sp gr23/23C3997.5Where 997.5 kg/m3 is the density of water at 23C.4. Summary of Test Method4.1 Determine the mass of a specimen of the solid plastic in air. It is then immersed in a liquid, its apparent mass up
17、onimmersion is determined, and its specific gravity (relative density) calculated.5. Significance and Use5.1 The specific gravity or density of a solid is a property that is conveniently measured to identify a material, to follow physicalchanges in a sample, to indicate degree of uniformity among di
18、fferent sampling units or specimens, or to indicate the averagedensity of a large item.5.2 Changes in density of a single material are due to localized differences in crystallinity, loss of plasticizer, absorption ofsolvent, or to other causes. It is possible that portions of a sample differ in dens
19、ity because of their differences in crystallinity,thermal history, porosity, and composition (types or proportions of resin, plasticizer, pigment, or filler).5.3 Density is useful for calculating strength-weight and cost-weight ratios.6. Sampling6.1 The sampling units used for the determination of s
20、pecific gravity (relative density) shall be representative of the quantityof product for which the data are required.6.1.1 If it is known or suspected that the sample consists of two or more layers or sections having different specific gravities,either complete finished parts or complete cross secti
21、ons of the parts or shapes shall be used as the specimens, or separatespecimens shall be taken and tested from each layer. The specific gravity (relative density) of the total part shall not be obtainedby adding the specific gravity of the layers, unless relative percentages of the layers are taken
22、into account.7. Conditioning7.1 ConditioningCondition the test specimens at 23 6 2C and 50 6 5 %50 6 10 % relative humidity for not less than 40 hprior to test in accordance with Procedure A of Practice D618, unless otherwise specified by the contract or relevant materialspecifications. In cases of
23、disagreement, the tolerances shall be 61C and 62 %65 % relative humidity.7.2 Test ConditionsConduct tests in the standard laboratory atmosphere of 23 6 2C and 50 6 5 %50 6 10 % relativehumidity, unless otherwise specified in this specification or by the contract or relevant material specification. I
24、n cases ofdisagreement, the tolerances shall be 61C and 62 %65 % relative humidity.TEST METHOD A FOR TESTING SOLID PLASTICS IN WATER (SPECIMENS 1 TO 50 g)8. Scope8.1 This test method involves weighing a one-piece specimen of 1 to 50 g in water, using a sinker with plastics that are lighterthan water
25、. This test method is suitable for plastics that are wet by, but otherwise not affected by water.9. Apparatus9.1 Analytical BalanceA balance with a precision of 0.1 mg or better is required for materials having densities less than 1.00g/cm3 and sample weights less than 10 grams. For all other materi
26、als and sample weights, a balance with precision of 1 mg or betteris acceptable (see Note 5). The balance shall be equipped with a stationary support for the immersion vessel above the balancepan (“pan straddle”).NOTE 5The balance shall provide the precision that all materials tested have three sign
27、ificant figures on density. In case that materials with differentdensities are tested on one single balance, use the balance that provides at least three significant figures for all materials concerned.NOTE 6To assure that the balance meets the performance requirements, check on zero point and sensi
28、tivity frequently and perform periodiccalibration.D792 1329.2 Sample Holder, corrosion-resistant (for example, wire, gemholder, etc.).9.3 SinkerA sinker for use with specimens of plastics that have specific gravities less than 1.00. The sinker shall: (1) becorrosion-resistant; (2) have a specific gr
29、avity of not less than 7.0; (3) have smooth surfaces and a regular shape; and (4) be slightlyheavier than necessary to sink the specimen. The sinker shall have an opening to facilitate attachment to the specimen and sampleholder.9.4 Immersion VesselA beaker or other wide-mouthed vessel for holding t
30、he water and immersed specimen.9.5 ThermometerA thermometer readable to 0.1C or better.10. Materials10.1 WaterThe water shall be substantially air-free and distilled or de-mineralized water.NOTE 7Air in water can be removed by boiling and cooling the water, or by shaking the water under vacuum in a
31、heavy-walled vacuum flask.(WarningUse gloves and shielding.) If the water does not wet the specimen, add a few drops of a wetting agent into the water. If this solution doesnot wet the specimen, Method B shall be used.11. Test Specimen11.1 The test specimen shall be a single piece of material with a
32、 size and shape suitable for the testing apparatus, provided thatits volume shall be not less than 1 cm3 and its surface and edges shall be made smooth. The thickness of the specimen shall beat least 1 mm for each 1 g of weight.Aspecimen weighing 1 to 5 g was found to be convenient, but specimens up
33、 to approximately50 g are also acceptable (see Note 8). Care shall be taken in cutting specimens to avoid changes in density resulting fromcompressive stresses or frictional heating.NOTE 8Specifications for certain plastics require a particular method of specimen preparation and should be consulted
34、if applicable.11.2 The specimen shall be free from oil, grease, and other foreign matter.12. Procedure12.1 Measure and record the water temperature.12.2 Weigh the specimen in air. Weigh to the nearest 0.1 mg for specimens of mass 1 to 10 g and density less than 1.00 g/cm3.Weigh to the nearest 1 mg f
35、or other specimens.12.3 If necessary, attach to the balance a piece of fine wire sufficiently long to reach from the hook above the pan to the supportfor the immersion vessel. In this case attach the specimen to the wire such that it is suspended about 25 mm above the vesselsupport.NOTE 9If a wire i
36、s used, weigh the specimen in air after hanging from the wire. In this case, record the mass of the specimen, a = (mass ofspecimen + wire, in air) (mass of wire in air).12.4 Mount the immersion vessel on the support, and completely immerse the suspended specimen (and sinkers, if used) inwater (see 1
37、0.1) at a temperature of 23 6 2C. The vessel must not touch sample holder or specimen. Remove any bubblesadhering to the specimen, sample holder, or sinker, by rubbing them with a wire. Pay particular attention to holes in the specimenand sinker. If the bubbles are not removed by this method or if b
38、ubbles are continuously formed (as from dissolved gases), theuse of vacuum is recommended (see Note 10). Determine the mass of the suspended specimen to the required precision (see 12.2)(see Note 11). Record this apparent mass as b (the mass of the specimen, sinker, if used, and the partially immers
39、ed wire in liquid).Unless otherwise specified, weigh rapidly in order to minimize absorption of water by the specimen.NOTE 10Some specimens may contain absorbed or dissolved gases, or irregularities which tend to trap air bubbles; any of these may affect the densityvalues obtained. In such cases, th
40、e immersed specimen may be subjected to vacuum in a separate vessel until evolution of bubbles has substantially ceasedbefore weighing (see Test Method B). It must also be demonstrated that the use of this technique leads to results of the required degree of precision.NOTE 11It may be necessary to c
41、hange the sensitivity adjustment of the balance to overcome the damping effect of the immersed specimen.12.5 Weigh the sample holder (and sinker, if used) in water with immersion to the same depth as used in the previous step (Notes12 and 13). Record this weight as w (mass of the sample holder in li
42、quid).NOTE 12If a wire is used, it is convenient to mark the level of immersion by means of a shallow notch filed in the wire. The finer the wire, the greaterthe tolerance is permitted in adjusting the level of immersion between weighings. With wireAwg No. 36 or finer, disregard its degrees of immer
43、sion and,if no sinker is used, use the mass of the wire in air as w.NOTE 13If the wire is used and is left attached to the balance arm during a series of determinations, determine the mass a with the aid of a tare onthe other arm of the balance or as in Note 9. In such cases, care must be taken that
44、 the change of mass of the wire (for example, from visible water)between readings does not exceed the desired precision.12.6 Repeat the procedure for the required number of specimens. Two specimens per sample are recommended. Determineacceptability of number of replicate test specimens by comparing
45、results with precision data given in Tables 1 and 2. Use additionalspecimens if desired.D792 13313. Calculation13.1 Calculate the specific gravity of the plastic as follows:sp gr23/23C5a/a1w 2b!where:a = apparent mass of specimen, without wire or sinker, in air,b = apparent mass of specimen (and of
46、sinker, if used) completely immersed and of the wire partially immersed in liquid, andw = apparent mass of totally immersed sinker (if used) and of partially immersed wire.13.2 Calculate the density of the plastic as follows:D23C,kg/m35sp gr23/23C3997.513.3 If the temperature of the water is differe
47、nt than 23C, use the density of water listed in Table 3 directly, or use the followingequations to calculate the density of water at testing temperature:M 5D/t (1)Dconversion to 23C!,kg/m3 (2)5sp gr ta/tw 3997.51tw 223!3M#andsp gr 23/235D conversion to 23C!/997.5 (3)where:M = slope,TABLE 1 Test Meth
48、od A Specific Gravity Tested in WaterMaterial Mean SrA SRB rC RDPolypropylene 0.9007 0.00196 0.00297 0.00555 0.00841Cellulose Acetate Butyrate 1.1973 0.00232 0.00304 0.00657 0.00860Polyphenylene Sulfide 1.1708 0.00540 0.00738 0.01528 0.02089Thermoset 1.3136 0.00271 0.00313 0.00767 0.02171Polyvinyl C
49、hloride 1.3396 0.00243 0.00615 0.00688 0.01947A Sr = within laboratory standard deviation for the individual material. It is obtained by pooling the within-laboratory standard deviations of the test results from all of theparticipating laboratories:Sr = (s1)2 + (s2)2 . . .+(sn )2/n1/2B SR = between-laboratories reproducibility, expressed as standard deviation:SR = Sr2 + SL21/2 whereSL is the standard deviation of laboratory means.C r = within-laboratory critical interval between two test results = 2.8 Sr.D R = betwe
