Monitoring of curing processes using air coupled ultrasonic system

Schober, Giovanni; SKZ - KFE gGmbH; Germany

Shober, G.; SKZ - KFE Gmbh; Germany
Werner, M.; SKZ - KFE Gmbh; Germany
Kolb, C.; SKZ - KFE Gmbh; Germany
Kremling, S.; SKZ - KFE Gmbh; Germany
Hochrein, T.; SKZ - KFE Gmbh; Germany

ID: ECNDT-0024-2018

There are only a few methodological approaches that allow the monitoring of curing processes of adhesives and sealants. Often, laboratory methods such as nuclear spin resonance technique or infrared spectroscopy are used. Main disadvantages are the lack of process capability, the low penetration depth and the high system costs. Ultrasonic methods, on the other hand, allow the monitoring of curing process directly during production with high temporal and spatial resolution, and thus offer several advantages compared with other measuring technologies.

The applicability was tested on various adhesives between plastic plates and on sealing compounds. In particular, one- and two-component adhesives and sealants, which cure by polycondensation and -addition reactions, and various thermoplastics as well as thermosets as carrier material, were used.

Using ultrasonic testing, the sound attenuation and sound velocity provide material-dependent information which can be directly correlated with the degree of curing. Also indirect measurements are possible by observing variables such as a temperature change during the chemical reaction. Due to the high acoustic impedance differences between the surrounding air and the materials to be examined, it is difficult to determine the exact sound attenuation and speed in the case of air-coupled ultrasound testing. Here, evaluation methods have been developed in order to determine characteristic values, for example based on group delay time and signal intensity, which allow conclusions similar to the absolute sound attenuation and speed.