Question

Give three methods for controlling the exotherm in foaming/casting. Explain how they work.

Answer 1

Proven methods for controlling exotherm:

If you do want to pour or cast a large volume of epoxy, here are several proven methods for minimizing heat buildup which have been developed over the years.

Pour the epoxy in timed, multiple batches.

Timing is important when doing multiple pours. Ideally, you want to wait for mild exotherm to peak and begin falling before mixing a new batch and pouring. Waiting too long could cause an insufficient bond between the two pours. Not waiting long enough can cause too much heat to build and cracks to propagate.

Work at cooler temperatures.

Cooler shop temperatures and cooling the epoxy itself will both work to your advantage in slowing cure and controlling epoxy’s exothermic reaction. A deeper pour can be accomplished with less heat buildup by starting with cooled epoxy and a cool substrate until the epoxy initially cures to a soft solid. Then you could expose it to room temp or higher to complete the cure.

Use heat sinks.

A heat sink is any object that can absorb lot of heat. If you are applying the epoxy into or over a heavy metal object, it will absorb much more heat than a lower-density object.

High-density fillers can also act as a heat sink, reducing exotherm by absorbing more heat than a low-density filler, and taking up more volume. This leaves less room for mixed resin and hardener, reducing the resulting heat reaction.

If the wrong epoxy/filler combination is used for a certain cure temperature, the epoxy may generate enough heat to smolder and burn. Adding more low-density filler will certainly reduce the amount of epoxy in a given volume, but the filler will act as an insulator instead of a heat sink