Specimen Preparation

Block Shear Test Specimens—The small-scale components to be joined were produced under laboratory conditions. Following thorough cleaning of the surfaces, the adhesive was applied exclusively to the air side of the glass, because scientific studies [4] have proved that the adhesion of acrylate adhe­sives is lower on the bath side. The radiation for curing the adhesive is transmit­ted from both sides for a period of 60 s with an intensity of about 60 mW/cm2 UV-A, measured at the position of the component to be joined.

Specimen Components—The adhesive joints at the frame corners were pro­duced at room temperature in the testing shed of the Institute for Building Con­struction. The areas to which adhesive was to be applied on both components— frame support and cantilever—were thoroughly cleaned with a mixture of ace­tone and isopropanol. Final, careful cleaning shortly before fitting the parts to­gether was carried out with a solvent-based cleaner supplied by the adhesive manufacturer.

The two individual parts of the sample component were aligned in a jig and fixed in position. The bottom and sides of the joint were sealed to prevent uncontrolled loss of the adhesive during application. The bottom seal, a trans­parent adhesive tape made from acrylate, remains in place, whereas the side seals are removed once the adhesive has cured.

The two adhesive joints at the frame corner were filled with adhesive one after the other. A flat nozzle with an oval cross section enables the viscous adhesive (vis­cosity approximately 17500 mPas) to be injected into the ~1.9-mm-wide gap pro­vided for the adhesive. A housing shields the working area against the ingress of unwanted daylight. Once the adhesive had been injected, intermittent exposure to low-energy radiation from UV fluorescent lamps on both sides followed (intensity at a distance of 7 cm: UV 1.8 mW/cm2, blue 3.5 mW/cm2; intensity at 12 cm: UV 1.3 mW/cm2, blue 2.9 mW/cm2). Three lamps positioned at a slight angle were placed on both sides. This meant that curing in the bottom part of the adhesive joint proceeded faster than in the top part of the joint, and that meant that the loss of ad­hesive, the volume of which decreases during curing, could be compensated for by the reserves of adhesive at the sides and top of the joint. Finally, brief exposure to radiation from a focused beam lamp with a high output (intensity at a distance of 60 cm: UV 12.7 mW/cm2, blue 67.9 mW/cm2) ensured that the final strength and stiffness were achieved. This production method was developed for the all-glass en­closure described in Ref [15] (see also “Previous Work" above). Comprehensive technology testing for this project revealed that the combination of low-intensity curing in the first stage and high-intensity curing in the second stage lead to a high bearing capacity, as well as to an excellent optical quality of the joint.