ASTM_D_518_-_99.pdf

Designation:D 518 99Standard Test Method forRubber DeteriorationSurface Cracking1This standard is issued under the fixed designation D 518;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year 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 This test method covers three test specimen proceduresthat estimate the comparative ability of rubber compounds towithstand the effects of normal weathering,or exposure in anatmosphere containing controlled amounts of ozone.It doesnot apply to testing of electrical insulation or other rubber partswhere high concentrations of ozone prevail due to electricaldischarge,nor to testing of material ordinarily classified ashard rubber.1.2 The values stated in SI units are to be regarded as thestandard.1.3 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 limitations prior to use.2.Referenced Documents2.1 ASTM Standards:D 1149 Test Method for Rubber DeteriorationSurfaceOzone Cracking in a Chamber2D 4575 Test Methods for Rubber Deterioration:ReferenceandAlternative Method(s)for Determining Ozone Level inLaboratory Test Chambers23.Summary of Test Methods3.1 Three test methods are used to measure ozone crackingresistance:SectionsMethod AExposure of Straight Specimens(Elongated)5 to8Method BExposure of Bent Looped Test Specimens9 to 12Method CExposure of Tapered Specimens(Elongated)13 to 173.2 Each test consists of continuously exposing rubber testspecimens,held under strain,to normal weather conditions orin an atmosphere containing controlled amounts of ozone.Specimens are exposed for definite periods of time and theirdeterioration observed as evidenced by the appearance andgrowth of cracks on the surfaces.3.3 Refer to Test Method D 4575 for the reference andoptional alternative test methods for the measurement of theozone partial pressure in laboratory test chambers.4.Significance and Use4.1 In the development of rubber compounds for use inapplications where ozone cracking is objectionable,it isnecessary to have a test in which simple comparative perfor-mance for resistance to cracking can be evaluated.This testmethod can be used for this performance comparison.4.2 This test method is not suited for use in purchasespecifications,not only because correlation with service life isuncertain,but because the results from duplicate specimenstested in different locations do not ordinarily give the samevalues.No exact relation between the results of the test andactual service performance is given or implied.The test isprincipally of value when used for comparisons between two ormore rubber compounds.METHOD AEXPOSURE OF STRAIGHTSPECIMENS5.Apparatus5.1 Mounting Block A rectangular wooden block shall beused for supporting the extended specimens.The block shall be140 mm(5.5 in.)wide and approximately 380 mm(15 in.)longand shall have a thickness of not less than 22 mm(0.875 in.).The block shall have the grain running lengthwise and shall besuitably reinforced on the back to prevent warping.Both of the380-mm edges of the face carrying the specimens shall berounded with a 3-mm(0.125-in.)radius.(Fig.1 shows thedetails of construction.)The block shall have a smooth finishand shall be painted with two coats of clear lacquer3or sparvarnish.5.2 FastenersAluminum tacks,or other suitable materialfasteners inert to ozone shall be used for fastening thespecimens to the edges of the wooden block.5.3 Angle Strips Right angled aluminum molding strips13 by 22 mm(0.5 by.0875 in.)and of approximately No.22gage thickness,for shielding the specimens where tacked andbent over the edges of the block.Strips made from commercialaluminum sheet of Alloy No.2-S are suitable.1This test method is under the jurisdiction ofASTM Committee D-11 on Rubberand is the direct responsibility of Subcommittee D11.15 on Degradation Tests.Current edition approved Nov.10,1999.Published December 1999.Originallypublished as D 518 38.Last previous edition D 518 86(Reapproved 1997).2Annual Book of ASTM Standards,Vol 09.01.3duPont clear lacquer,or its equivalent,has been found suitable for this purpose.1Copyright ASTM,100 Barr Harbor Drive,West Conshohocken,PA 19428-2959,United States.6.Test Specimens6.1 The test specimens shall be rectangular strips 25 mm(1in.)in width by 150 mm(6 in.)in length cut from standardlaboratory test sheets having a thickness of 1.9 mm(0.075 in.)minimum and 2.5 mm(0.100 in.)maximum.The“millinggrain”shall be in the lengthwise direction of the specimen.6.2 Duplicate test specimens shall be tested whenever pos-sible.7.Procedure7.1 Firmly fa