Epoxies

For 2-part epoxies use the general rule that every 10 °C added to cure conditions will reduce cure time by half. It is best to not exceed 150 °C. If the exothermic reaction disrupts the bond line (Bubbles/foams), heat bump for 2 hours at 65 °C, reduce mass of adhesive used, or gel at room temperature before heat bumping. You may also pre-heat the cartridge (50 °C) or parts (Up to 93 °C) to speed cure. Heating the cartridge however will decrease the products viscosity. Heat bumping epoxy can also provide denser cross-linking for better chemical and moisture resistance from an ambient cured sample. Suitability testing should always be implemented. Larger masses will have a larger exotherm which means more heat is released. For potting applications, this should be considered because it can melt the plastic substrate and cause shrinkage. A mass of 50 grams should not be exceeded.

Glass transition temperature (Tg) is the temperature at which plastics start to go from glassy solids to a rubbery soft material like a silicone. It is also interesting to know that epoxies are a thermoset. The will not reflow when heat is applied. A thermoplastic reflows when enough heat is applied.

The chemistry of these adhesives involves an exothermic reaction that releases heat. Therefore, caution should be taken when dispensing large volumes of adhesive. Temperature limits vary between 82 °C to 177 °C.

Epoxies can show a white cloudiness that can appear at the surface of the adhesive. This phenomena occurs when the amine in the hardener reacts with carbon dioxide from the air and settles on the part as a white salt. It is recommended to use a hardener formulated to minimize the blush problem or to use heat to accelerate the cure.