Epoxy Adhesives
Epoxies are structural adhesives which come in one- and two-part systems. Epoxies provide unlimited gap-filling capabilities and cure through depth, excellent thermal- and chemical-resistance, high cohesive strength (strength within the adhesive), low shrinkage, good shear strength and peel strength. In addition, many epoxies are machineable and paintable. Epoxies also have formulating versatility, which easily can facilitate custom epoxy formulations.
Epoxies cure when covalent bonds between the epoxy resin and hardener are formed. Catalysts can be added to the epoxy system to increase the cure rate. Heat also can increase the cure rate of an epoxy adhesive system. Controlled heat application can increase the crosslinking density of the adhesive in the bond area, resulting in higher cured strengths.
There are a few limitations to epoxy adhesive systems. Epoxy systems tend to have a slow cure rate, with a fixture time between five minutes and two hours. Slow cure may be beneficial in a situation where it takes extended time to join parts after adhesive application or if parts need to be repositioned after being mated. Epoxies do exotherm during cure, so consideration needs to be taken if a manufacturer intends to use epoxies on highly sensitive parts. If a manufacture is bonding parts with a large bondline gap or parts which will endure high temperatures or harsh chemicals, epoxies may be a bonding solution3.