The use of adhesives (bonding) has many advantages in the industry. Compared with welding, it causes no material distortion and expensive equipment is not necessary. Also the bonded area needs no meticulous protection against possible accidents happening, in addition, parts which are sensitive to heat need not to be dismantled. The use of adhesives has asserted itself, particularly in the body area. E.g., due to the bonding of front and rear windscreens, the design of cars has changed in leaps and bounds. The disadvantage of using adhesives, is the more complex preparation of the surfaces to be glued and the sensitive reaction to certain operational demands. The glued seams react sensitively to temperature and tension and are particularly prone to peeling.
Glueing belongs in the category of cohesive bonding (like welding and soldering). A distinction is drawn between the cohesive forces (lat. cohaehere = joined together), for the bonding of the adhesive material, and the adhesion forces (lat. adhaehere = attaching), for the connection of the two materials. Of course, both forces should be as equal as possible. The chosen adhesion area must be large enough and suitably prepared to cope with the transference of the forces applied.
One problem is, that even the experts are never sure, whether the glue still has it's full chemical qualities. There is now an assistent from the 3M company, whereby one adds cetain colours, which only become visible when the product has aged: Blue for the hardener and yellow for the glue. Success is indicated if the mixture, after a suitable hardening period, turns green. 05/12