Epoxies

For 2-part epoxies use the general rule that every 10°C added to cure conditions will reduce cure time by half. However, it is advisable not to 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 is essential in all cases. Larger masses generate greater exothermic reactions, releasing more heat. For potting applications, this can pose risks such as melting the plastic substrate or causing shrinkage. Avoid exceeding a mass of 50 grams.

Glass transition temperature (Tg) is the temperature at which plastics begin to transition from glassy solids to a rubbery soft material similar to silicone. It is also interesting to know that epoxies are a thermoset meaning they will not reflow when heat is applied. A thermoplastic reflows when sufficient heat is applied.

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

Epoxies can exhibit a white cloudiness that can appear at the surface of the adhesive. This phenomenon 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 minimise the blushing issue or to use heat to accelerate the cure.