Meaning
Uncontrolled self-heating in a chemical system occurs when the rate of heat generation exceeds the capacity of the environment to remove it. Exotherm thermal runaway describes a condition where the temperature rise accelerates the reaction, which in turn generates more heat in a feedback loop. This phenomenon is a risk in the production of large composite structures and bulk chemical storage.
Energy Balance
Thermodynamics dictate the stability of a reacting mass based on the ratio of surface area to volume. During exotherm thermal runaway, the internal temperature of a part climbs rapidly while the exterior remains relatively cool. This internal heat cannot conduct to the surface fast enough to maintain equilibrium.
The resulting temperature spike can reach hundreds of degrees above the set point within minutes.
Mass Effect
Thick sections of material are more susceptible to heat accumulation than thin films. Engineers must calculate the critical thickness at which exotherm thermal runaway becomes likely for a given resin system. In a thin laminate, the high surface-to-volume ratio allows heat to dissipate into the tooling.
In a thick casting, the center of the mass acts as an insulator, trapping the energy and forcing the reaction toward a degrading conclusion.
Safety Limit
Mitigation strategies involve the use of retarded catalysts or staged heating cycles to manage the energy release. Detecting the early signs of exotherm thermal runaway allows operators to apply active cooling or pause the heating program. Failure to manage this risk leads to charred parts, cracked molds or fires in the manufacturing facility.
Monitoring the temperature at the core of the material provides the only reliable way to ensure the process remains within safe boundaries.
