Theory and Method
Vulcanization builds sulfur or peroxide crosslinks between polymer chains, and each new crosslink raises the shear modulus of the compound. A rotorless curemeter tracks that stiffness rise in real time. The lower die oscillates through a fixed arc, typically ±0.5° at 1.67 Hz, while the specimen transmits the resulting shear strain to the stationary upper die. A temperature-compensated torque transducer on the upper die records the reaction torque, which stays proportional to the shear modulus of the sample throughout the reaction.
Plotting that torque against time produces the cure curve. Minimum torque (ML) reflects the viscosity of the uncured stock, maximum torque (MH) reflects final crosslink density, and the difference MH minus ML indicates the extent of cure. Scorch times ts1 and ts2 mark the onset of crosslinking, while t10, t50, and t90 give the times to reach 10%, 50%, and 90% of the total torque rise. Molders set press cycles from t90. A falling torque after MH signals reversion, which the reversion (TR) calculation quantifies.
The oscillation is sinusoidal, so the torque response splits into an elastic component in phase with the strain (S') and a viscous component out of phase (S''). Their ratio, tan delta, describes the balance between stored and dissipated energy during cure. Removing the rotor eliminates the thermal mass that slowed temperature recovery in oscillating disc designs, and the sealed cavity keeps porosity from distorting the torque signal. The variable frequency option (0.001 to 50 Hz) extends the QualiMDR™ A to frequency and strain sweeps.
