**7.1 Anaerobic curing mechanism**

When adhesive is applied onto one side of metal substrate, then adhesives contact with metal ion (Fe++, CU++) for some anaerobic initiator to be broken into free radicals which are unstable, but the presence of air to contact adhesive is stronger; therefore, it remains as a liquid. As a next step, when the other mating part comes in contact with the first part with adhesive in between, then more anaerobic initiators contact more metal ions to be broken into more free radicals, and at the same time, oxygen contact is blocked by both substrates, and then, those unstable free radicals react with a monomer nearby which becomes unstable, too, and then, it reacts with other monomers nearby, and gradually, all the monomers react and become polymerized (cure) (see **Figure 12**) [3, 4].

In case of inactive metal substrates that contain low metal ions such as Cu++ or Fe++ and have a slow reaction with photoinitiator and slow cure, an acceleration method such as primer or heating can be used to speed up the curing. Anaerobic adhesives become a very reliable thermoset plastic after cure [2].
