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Terahertz adhesive curing
Inline monitoring of the curing of applied adhesives using cost-effective terahertz methods
Project duration
From: 01.05.2022 To: 30.04.2024Description
The research project showed that process and quality control for curing monitoring of adhesives in an adhesive bond is possible and realisable, which could be demonstrated at the end of the project on components actually used in industry.In summary, all the objectives set were achieved or exceeded:
- A measurement setup was constructed that can take the THz and radar technology and can be moved to measure several samples. Furthermore, the measuring set-up was enclosed in order to set different climates and to enable effective extraction of the adhesive vapours, some of which are hazardous to health. Furthermore, heat lamps and dispensers were installed to enable a change in temperature and humidity in the measuring room.
- In-depth knowledge was gained about the interaction of THz and radar waves on curing adhesives with regard to attenuation effects due to absorption. These could be correlated with the manufacturer's information on characteristic curing times.
- An evaluation and prediction algorithm was developed that simulated the curing curves and can be used in the future. This enables predictions to be made about curing processes based on the historical processes stored in a database. This can have a considerable positive effect in industrial practice, as it is possible to say more precisely when the adhesive has cured sufficiently for the application.
- In addition to THz technology, radar technology based on a 300 GHz sensor also showed good results in monitoring adhesive curing. Even a very inexpensive 24 GHz in-house variant was able to monitor adhesive curing.
Overall, a broad portfolio of physically and chemically curing adhesives was analysed. With the exception of the polycondensation adhesives, it was possible to determine the feasibility of curing monitoring for all adhesives. As the curing curves correlated well with the characteristic curing times of the adhesive manufacturers and these were also validated with different reference methods such as rheology, DSC or IR spectroscopy, both THz and radar technology can be used in future to monitor the curing of applied adhesives. In particular, the curing process can vary depending on the ambient conditions, due to differences in temperature or humidity, or the geometric bonding situation, which can now be monitored directly inline or in the field using this measurement technology.
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