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The Mooney viscometer has been the principal instrument used to control the processability of synthetic rubber production for the past 30 years. The oscillating-disk cure meter is now becoming the principal instrument for determining the vulcanization characteristics of standard compounds of raw rubbers and compounding materials and of factory compounds used for rubber products. Therefore, a large amount of effort has been expended in their standardization. Nevertheless, both instruments which have certain similarities are affected by the following factors that still cause variability among instruments: 1. temperature of the rubber in the die cavity, 2. friction between the oscillating or rotating stem and the stationary lower die, 3. slippage at the rubber-metal interfaces, 4. the pressure on the rubber during test, and 5. scale calibration.
This paper summarizes past and recent studies on these factors and indicates from recent findings the direction for further standardization.
Measurements of the disk temperature in the oscillating-disk cure meter were made. These measurements indicated that the clearance between the oscillating or rotating stem and the lower die is critical for temperature uniformity. Also, the present design of the upper die in ASTM Measurement of Curing Characteristics with the Oscillating Disk Cure Meter (D 2084-71T) substantially reduces the rate of heat transfer to the specimen. However, the design is reasonably effective for applying pressure on the specimen which reduces slippage at the rubber-metal interfaces. Other means of applying pressure may be used. Slippage also depends on the torque at the rubber-metal interfaces. In the Mooney viscometer, torque can be reduced by decreasing the speed of the rotor or by increasing the temperature. In the cure meter, torque is most effectively reduced by keeping the amplitude of oscillation as small as practical.
elastomers, standardization, vulcanizing, viscometers, test equipment, oscillating-disk cure meter, processability
Technologist, National Bureau of Standards, Washington, D.C.
Consultant on Engineering Standards, National Bureau of Standards, Washington, D.C.