Microwave processing of adhesive joints using a temperature controlled feedback system

Previous experiments have shown that microwave curing of epoxies reduces the curing time and could lead to improvements in the mechanical properties of the cured epoxies, Precise temperature control is important as inadequate control may lead to thermal run-away, resulting in localized material damage. Consequently, the main objective of the present work is to use temperature for controlling the intensity of microwave radiation during the adhesive curing process. Using microwave energy delivered through a slotted waveguide at a frequency of 2.45 GHz, and with the power varied between 300 and 600 W, three engineering thermoplastics or adherends were joined by curing two types of two-pack epoxy adhesives. Subsequently, the bond strengths of the microwave cured samples were compared to those of the specimens cured in ambient conditions by subjecting the joined samples to shear loading. The results obtained indicate that the samples cured with microwave under a temperature feedback control protocol achieved higher bond strengths after curing for only a fraction of the time required for ambient curing, It can therefore be inferred that, with an adequate temperature control strategy, increased efficiency of curing, higher quality of adhesive joint, and improved bond strength can be achieved when joining thermoplastics. (C) 2000 Elsevier Science Ltd. All rights reserved.