1、Designation: D 785 08Standard Test Method forRockwell Hardness of Plastics and Electrical InsulatingMaterials1This standard is issued under the fixed designation D 785; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of la
2、st 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. Scope*1.1 This test method covers two procedure
3、s for testing theindention hardness of plastics and related plastic electricalinsulating materials by means of the Rockwell hardness tester.1.2 The values stated in SI units are to be regarded asstandard. The values given in brackets are for information only.1.3 This standard does not purport to add
4、ress 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.NOTE 1This test method and ISO 2039-2 are equivalent. Pr
5、ocedure Aof this test method is equivalent to the test method in the main body ofISO 2039-2. Procedure B of this test method is equivalent to the testmethod in the integral annex part of ISO 2039-2.2. Referenced Documents2.1 ASTM Standards:2D 618 Practice for Conditioning Plastics for TestingD 883 T
6、erminology Relating to PlasticsD 2240 Test Method for Rubber PropertyDurometerHardnessD 4000 Classification System for Specifying Plastic Mate-rialsE18 Test Methods for Rockwell Hardness of MetallicMaterialsE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Me
7、thod2.2 ISO Standards3ISO 2039-2 PlasticsDetermination of HardnessPart 2:Rockwell Hardness3. Terminology3.1 Definitions used in this test method are in accordancewith Terminology D 883.3.2 Definitions of Terms Specific to This Standard:3.2.1 indentation hardnessthe resistance of a material tosurface
8、 penetration or plastic deformation.4. Significance and Use4.1 A Rockwell hardness number is a number derived fromthe net increase in depth impression as the load on an indenteris increased from a fixed minor load to a major load and thenreturned to a minor load (Procedure A). A Rockwell alpha (a)ha
9、rdness number represents the maximum possible remainingtravel of a short-stroke machine from the net depth of impres-sion, as the load on the indenter is increased from a fixed minorload to a major load (Procedure B). Indenters are round steelballs of specific diameters. Rockwell hardness numbers ar
10、ealways quoted with a scale symbol representing the indentersize, load, and dial scale used. This test method is based on TestMethods E18. Procedure A (Section 11) yields the indentationof the specimen remaining 15 s after a given major load isreleased to a standard 10-kg minor load. Procedure B (Se
11、ction12) yields the indentation of the indenter into the specimenafter a 15-s application of the major load while the load is stillapplied. Each Rockwell scale division represents 0.002-mm0.00008-in. vertical movement of the indenter. In practice,the Rockwell hardness number is derived from the foll
12、owingrelationship:HR 5 130 2 e (1)where:HR = the Rockwell hardness number, ande = the depth of impression after removal of the majorload, in units of 0.002 mm. This relation only holdsfor the E, M, L, R, and K scales.1This method is under the jurisdiction of ASTM Committee D20 on Plastics andis the
13、direct responsibility of Subcommittee D20.10 on Mechanical Properties.Current edition approved March 1, 2008. Published March 2008. Originallyapproved in 1944. Last previous edition approved in 2003 as D785 - 03.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Cus
14、tomer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.1*A Summary of Changes
15、 section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.2 A Rockwell hardness number is directly related to theindentation hardness of a plastic material, with the higher thereading the harder th
16、e material. An a hardness number is equalto 150 minus the instrument reading. Due to a short overlap ofRockwell hardness scales by Procedure A, two different dialreadings on different scales may be obtained on the samematerial, both of which may be technically correct.4.3 For certain types of materi
17、als having creep and recovery,the time factors involved in applications of major and minorloads have a considerable effect on the results of the measure-ments.4.4 The results obtained by this test method are not gener-ally considered a measure of the abrasion or wear resistance ofthe plastic materia
18、ls in question.4.5 Indentation hardness is used as an indication of cure ofsome thermosetting materials at room temperature. Generally,an uncured specimen has a hardness reading below normal.4.6 Each Rockwell hardness scale in Table 1 is an extensionof the proceeding less severe scale, and while the
19、re is someoverlap between adjacent scales, a correlation table is notdesirable. Readings on one material may be satisfactory forsuch a table, but there is no guarantee that other plasticmaterials will give corresponding readings because of differ-ences in elasticity, creep, and shear characteristics
20、.4.7 Before proceeding with this test method, referenceshould be made to the specification of the material being tested.Any test specimen preparation, conditioning, dimensions,and/or testing parameters covered in the materials specificationshall take precedence over those mentioned in this test meth
21、od.If there are no material specifications, then the default condi-tions apply.5. Factors Affecting Reproducibility and Accuracy5.1 Rockwell hardness readings have been found reproduc-ible to 62 divisions for certain homogeneous materials with aYoungs modulus in compression over 3400 MPa 5 3 105psi.
22、 Softer plastics and coarse-filled materials will have awider range of variation. A large ball indenter will distributethe load more evenly and decrease the range of test results(Note 2). The sensitivity of the instrument decreases with anincrease in the dial reading and becomes very poor for readin
23、gsof 100 and over due to the shallow indentation of the steel ball.It is desirable to use the smallest ball and highest load that ispractical because of this loss of sensitivity. Rockwell hardnessreadings over 115 are not satisfactory and shall not be reported.Readings between zero and 100 are recom
24、mended, but read-ings to 115 are permissible. For comparison purposes, it maybe desirable to take readings higher than 115 or lower than zeroon any single scale. In such cases, Rockwell hardness readingsmay be reported, but the corresponding correct readings shallfollow in parentheses, if possible.
25、Such alternate readings arenot always feasible when the specimen is subjected to con-stantly changing conditions or irreversible reactions.NOTE 2Molded specimens containing coarse fiber fillers, such aswoven glass fabric, will influence the penetration obtained. These varia-tions in hardness may be
26、reduced by testing with the largest ball indenterconsistent with the overall hardness of the material.5.2 If the bench or table on which a Rockwell hardnesstester is mounted is subject to vibration, such as is experiencedin the vicinity of other machines, the tester should be mountedon a metal plate
27、 with sponge rubber at least 25 mm 1 in.thick, or on any other type of mounting that will effectuallyeliminate vibration from the machine. Otherwise the indenterwill indent further into the material than when such vibrationsare absent.5.3 Dust, dirt, grease, and scale or rust should not beallowed to
28、 accumulate on the indenter, as this will affect theresults. Steel ball indenters that have nicks, burrs, or are out ofround shall not be used.5.4 The condition of the test equipment is an importantfactor in the accuracy of the test results. Dust, dirt or heavy oilact as a cushion to the load suppor
29、ting members of the testequipment and cause erroneous readings of the instrument dial.The shoulders of the instrument housing, indenter chuck, ballseat in the instrument housing, capstan, capstan screw, andanvil shoulder seat should be kept clean and true. The capstanand screw should be lightly oile
30、d. Pitted anvil surfaces may berefinished with 600 grit paper.5.5 Surface conditions of the specimen have a marked effecton the readings obtained in a test. Generally, a molded finishwill give a higher Rockwell reading than a machined face dueto the high resin content or filled materials or better o
31、rientationand lower plasticizer content of unfilled plastic materials.Injection mold specimens in such a way that sink marks andwarpage are minimized. Tubular or unsupported curved speci-mens are not recommended for plastic hardness testing. Suchcurved surfaces have a tendency to yield with the load
32、 andproduce an unsymmetrical indentation pattern.5.6 Many plastic materials have anisotropic characteristicswhich cause indentation hardness to vary with the direction oftesting. In such cases, the hardest face is generally that oneperpendicular to the molding pressure. Specimens with flash-ing on t
33、he side supported by the anvil also may give erroneousresults.5.7 Ambient temperature variations can significantly affecthardness for many materials.5.8 Rockwell hardness tests of the highest accuracy aremade on pieces of sufficient thickness so that the Rockwellreading is not affected by the suppor
34、ting anvil.Abulge, changein color, or other marking on the under surface of the testTABLE 1 Rockwell Hardness ScalesRockwellHardnessScale(Red DialNumbers)MinorLoad,kgMajorLoad,kgAIndenter Diameterin. mmR 10 60 0.5000 6 12.700 60.0001 0.0025L 10 60 0.2500 6 6.350 60.0001 0.0025M 10 100 0.2500 6 6.350
35、 60.0001 0.0025E 10 100 0.1250 6 3.175 60.0001 0.0025K 10 150 0.1250 6 3.175 60.0001 0.0025AThis major load is not the sum of the actual weights at the back of the frame butis a ratio of this load, depending on the leverage arm of machine. One make andmodel has a 25 to 1 leverage arm.D785082specimen
36、 closest to the anvil is an indication that the specimenis not sufficiently thick for precision testing. Stacking of thinspecimen is permitted provided they are flat, parallel, and freefrom dust or burrs. The precision of the test is reduced forstacked specimens, and results should not be compared t
37、o a testspecimen of standard thickness.6. Apparatus6.1 Rockwell Hardness Tester, in accordance with the re-quirements of Section 7. A flat anvil at least 50 mm 2 in. indiameter shall be used as a base plate for flat specimens.6.2 For Rockwell hardness testing, it is necessary that themajor load, whe
38、n fully applied, be completely supported by thespecimen and not held by other limiting elements of themachine. To determine whether this condition is satisfied, themajor load should be applied to the test specimen. If anadditional load is then applied, by means of hand pressure onthe weights, the ne
39、edle should indicate an additional indenta-tion. If this is not indicated, the major load is not being appliedto the specimen, and a long-stroke (PL) machine or less severescale should be used. For the harder materials with a modulusaround 5500 MPa 8 3 105psi or over, a stroke equivalent to150 scale
40、 divisions, under major load application, may beadequate; but for softer materials the long-stroke (250 scaledivisions under major load) machine is required.7. Test Specimen7.1 The standard test specimen shall have a minimumthickness of 6 mm 14 in. The specimen may be a piece cutfrom a molding or sh
41、eet. Care should be taken that the testspecimen has parallel flat surfaces to ensure good seating onthe anvil and thus avoid the deflection that may be caused bypoor contact. The specimen shall be at least 25 mm 1 in.square if cut from sheet stock, or at least 6 cm21 in.2 in areaif cut from other sh
42、apes. The minimum width shall be 13 mm12 in. plus the width of the indentation resulting from theconduct of a test using the chosen indenter.NOTE 3Specimen with a thickness other than 6 mm may be used if ithas been verified that, for that thickness, the hardness values are notaffected by the support
43、ing surface and that no imprint shows under thesurface of the specimen after testing. The specimen may be composed ofa pile-up of several pieces of the same thickness, provided that precautionis taken that the surfaces of the pieces are in total contact and not heldapart by sink marks, burrs from sa
44、w cuts, or other protrusions andprovided the hardness values are not affected by the stacking of thinspecimens.8. Calibration8.1 Check the Rockwell hardness tester periodically with asmall machinists level along both horizontal axes from a flatanvil for correct positioning. Minor errors in leveling
45、are notcritical, but correct positioning is desirable.8.2 The adjustment of speed-of-load application is of greatimportance. Adjust the dashpot on the Rockwell tester so thatthe operating handle completes its travel in 4 to 5 s with nospecimen on the machine or load applied by the indenter to theanv
46、il. The major load shall be 100 kg for this calibration. Whenso adjusted, the period taken for the mechanism to come to astop with the specimen in place will vary from 5 to 15 s,depending upon the particular specimen, the indenter, and theload used. The operator should check the instrument manualfor
47、 this adjustment.8.3 Select a standardized test block as near as possible to thehardness of the material being tested. If more than onehardness scale is used in testing, choose a standardized testblock for each scale used (Note 4). Make five impressions onthe test surface of the block. Compare the a
48、verage of these fivetests against the hardness calibration of the blocks. If the erroris more than 62 hardness numbers, bring the machine intoadjustment as described in 8.4 or in 5.3 and 5.4. If adjustmentcan not be achieved, more extensive servicing of the instru-ment may be needed.NOTE 4Standard t
49、est blocks for the R, L, E, K, and M scales areavailable from Wilson Instruments, 100 Royal Street, Canton, Ma 02021(A Division of Instron Corporation).8.4 Check the index lever adjustment periodically and makeadjustments if necessary. To adjust the index lever, place aspecimen (plastic with low creep or soft metal) on the anvil andturn the knurled elevating ring to bring the specimen in contactwith the indenter. Keep turning the ring to elevate the specimenuntil positive resistance to further turning is felt, which will beafter the 10-kg load is encounte
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