Abstract
This paper describes an apparatus that measures three important rubber processing characteristics—the compounded viscosity, the scorch time and the time to optimum cure. The apparatus is called a Viscurometer and consists of a heated die chamber and a drive mechanism to rotate a biconical rotor in an oscillatory manner through a fixed arc of ±6°. A strain gage torque pickup is mounted as an integral part of the drive shaft and the torque to impose the strain of ±6° (35% shear strain) is measured. The frequency of this oscillation is 2 per minute. A torque vs. time trace is recorded on a strip chart recorder. Data in graphical form are presented to show that the compounded viscosity of NR and SBR stocks correlates well with typical Mooney viscosity values. The scorch time, as measured with the Viscurometer, also correlates well with Mooney scorch values. The apparatus can be used to predict optimum cure for typical production SBR and NR stocks with a one standard deviation precision of ±2 minutes. The apparatus can also be used to predict the cured modulus at full cure (or any other percentage) under some conditions. This use of the Viscurometer is, however, more complex than its use to predict the previously mentioned processing parameters. The complexity of this use is illustrated for some typical NR and SBR stocks.
