ASTM D6204-19a Measurement of Unvulcanized Rheological Properties of Rubber Using Rotorless Shear Rheometers

Scope:

ASTM D6204-19a test method is used to determine flow properties. These viscoelastic properties may relate to factory processing behavior. This test is used for quality control in rubber manufacturing processes. It is also used for research and development testing of raw rubber and rubber compounds. This test is also used for evaluating compound differences resulting from the use of different compounding materials. 

Test Procedure:

In ASTM D6204-19a test method, the flow properties of rubber are measured by a rheometer. A rheometer is a device used to measure how a liquid, suspension, or slurry flows in response to applied forces.

A rubber test specimen is placed in a die cavity, closed, and maintained at an elevated temperature. The die cavity is constructed by two dies, one of which is oscillated through a rotary amplitude. This produces a sinusoidal torsional strain in the test specimen, resulting in a sinusoidal torque, which measures the viscoelastic quality of the test specimen.  

These viscoelastic measurements are made based on (1) a frequency sweep, in which the frequency is programmed to change in steps under constant strain amplitude and temperature conditions, (2) a strain sweep, in which the strain amplitude is programmed to change, or (3) a temperature sweep, in which the temperature is programmed to either increase or decrease. Rheological properties are measured for each set of frequency, strain, and temperature conditions.

Specimen size:

The test specimen should be circular, with a diameter smaller than the test chamber of the instrument to be used. 

The test specimen is of proper size when a small bead of rubber compound is extruded uniformly around the periphery of the dies as they are closed. Undersized test specimens can cause low cavity pressure and low torque readings. Oversized test specimens cool the dies excessively during the early part of the test period, affecting the vulcanization characteristics.

Data:

Rheological properties of rubbers are reported.