Reading the cure curve: what your rheometer is actually telling you

Vulcanization is the chemistry that turns soft, sticky raw rubber into a strong, elastic, durable material by cross-linking the polymer chains — usually with sulfur. Get the cure wrong and the part is either under-cured (weak, sticky, poor recovery) or over-cured (brittle, reverted).

The instrument that measures this is a rheometer, which holds a small sample at vulcanization temperature and oscillates it, recording torque as cross-links form. The resulting cure curve is the single most important QC test in rubber manufacturing. The numbers that matter: ML (minimum torque — how the uncured compound flows), MH (maximum torque — stiffness of fully cured rubber), ts1/ts2 (scorch time — your processing safety window), and tc50/tc90 (time to 50% and 90% cure — how long to mold the part).