Active Standard ASTM D7050 | Developed by Subcommittee: D11.22
Book of Standards Volume: 09.01
Historical (view previous versions of standard)
Significance and Use
In accordance with Specification D2227, shipments of TSR10 and TSR20 must meet a minimum initial Wallace plasticity (Po) of 30 to be accepted. However, even with this minimum restriction, the uncured viscoelastic or “processability” properties are allowed to vary greatly. This variation in properties can significantly affect the quality and efficiency of a factory operation.
Bales of TSR10 or TSR20 which are lower in their uncured elastic quality (“soft” rubber) in some cases may impart better processing properties to tire innerliners, cushion gums, and sidewalls. “Soft” bales sometimes impart better building tack, better mold flow, and lower extrusion die swell with better dimensional stability. Also, these “soft” rubber bales may dissolve faster in solvents for adhesion dipping.
Bales of TSR10 or TSR20 that are higher in their uncured elastic quality (“hard” rubber) in some cases generate greater shearing during the initial stages of a factory mix, which result in a faster breakdown and a shorter mix cycle.
Therefore, in a factory operation, sometimes segregating TSR10 or TSR20 shipments into “soft” and “hard” categories can improve the efficiency and quality of a factory operation.
1.1 This practice covers the sorting of natural rubber bales of TSR10 or TSR20 in the factory according to their predicted processing performance based on differences in viscoelastic properties.
1.2 This practice determines which bales should be used in factory compounds which benefit from using “soft” natural rubber versus which work better with “hard” natural rubber.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
D1485 Practice for Rubber from Natural Sources--Sampling and Sample Preparation
D2227 Specification for Natural Rubber (NR) Technical Grades
D3194 Test Method for Rubber From Natural Sources--Plasticity Retention Index (PRI)
D6204 Test Method for Rubber--Measurement of Unvulcanized Rheological Properties Using Rotorless Shear Rheometers
ICS Number Code 83.060 (Rubber)