ASTM_D_7050_-_04_2019.pdf

Designation:D705004(Reapproved 2019)Standard Practice forRubber from Natural SourcesSampling and Sorting BalesBased on Predicted Processing Properties1This standard is issued under the fixed designation D7050;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()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This practice covers the sorting of natural rubber balesof TSR10 or TSR20 in the factory according to their predictedprocessing performance based on differences in viscoelasticproperties.1.2 This practice determines which bales should be used infactory compounds which benefit from using“soft”naturalrubber versus which work better with“hard”natural rubber.1.3 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade(TBT)Committee.2.Referenced Documents2.1 ASTM Standards:2D1485 Practice for Rubber from Natural SourcesSampling and Sample PreparationD2227 Specification for Natural Rubber(NR)TechnicalGradesD3194 Test Method for Rubber From Natural SourcesPlasticity Retention Index(PRI)D6204 Test Method for RubberMeasurement of Unvulca-nized Rheological Properties Using Rotorless Shear Rhe-ometers3.Significance and Use3.1 In accordance with Specification D2227,shipments ofTSR10 and TSR20 must meet a minimum initial Wallaceplasticity(Po)of 30 to be accepted.However,even with thisminimum restriction,the uncured viscoelastic or“processabil-ity”properties are allowed to vary greatly.This variation inproperties can significantly affect the quality and efficiency ofa factory operation.3.2 Bales of TSR10 or TSR20 which are lower in theiruncured elastic quality(“soft”rubber)in some cases mayimpart better processing properties to tire innerliners,cushiongums,and sidewalls.“Soft”bales sometimes impart betterbuilding tack,better mold flow,and lower extrusion die swellwith better dimensional stability.Also,these“soft”rubberbales may dissolve faster in solvents for adhesion dipping.3.3 Bales of TSR10 or TSR20 that are higher in theiruncured elastic quality(“hard”rubber)in some cases generategreater shearing during the initial stages of a factory mix,which result in a faster breakdown and a shorter mix cycle.3.4 Therefore,in a factory operation,sometimes segregatingTSR10 or TSR20 shipments into“soft”and“hard”categoriescan improve the efficiency and quality of a factory operation.4.Sampling4.1 Sample SizeThe number of samples to be selected torepresent the lot may be determined by the size of the lot asindicated in Practice D1485,Table 1.4.2 Alternatively,five bales from a 36-bale pallet may besampled.4.3 Samples from these bales should be taken from withinthe bale,not from the edges,because bale surface exposure tothe air will cause surface samples to not be representative ofthe rubber inside the bale.5.Lot Sorting5.1 The criteria for sorting should be based on a repeatablemeasure of uncured elasticity of the raw natural rubber.5.2 Measuring uncured elastic modulus G at 1 Hz,100%strain,100C in accordance with Test Method D6204,Part B,has been found to be an effective method for segregating“soft”natural rubber from“hard”natural rubber used in production.See also Test Method D3194.5.3 The segregating elastic modulus value GSEGis estab-lished as the criteria for separating“soft”natural rubber from“hard”natural rubber as shown in Fig.1.1This practice is under the jurisdiction ofASTM Committee D11 on Rubber andRubber-like Materials and is the direct responsibility of Subcommittee D11.22 onNatural Rubber.Current edition approved May 1,2019.Published June 2019.Originallyapproved in 2004.Last previous edition approved in 2014 as D7050 04(2014).DOI:10.1520/D7050-04R19.2For 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 Document Summary page onthe ASTM website.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards,Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade(TBT)Committee.1 5.4 The value assigned to GSEGwill depend on the factorysetting.It will be dependent on the type of different compoundsbeing mixed.A value must be assigned that will provide thebest balance for quality and cost effectiveness for each pro-duction plant site.6.Keywords6.1 hard rubber;na