ABSTRACT
At one time, there was some commercial consideration of using special aluminum extrusions as a substitution for wooden structurals in buildings. A large experimental program at Alcoa demonstrated that these neoprene-phenolic high-solids mastics were quite adequate in strength to be considered for bonding the large aluminum structurals to a variety of floor-and wall-sheaving materials. One important consideration was how fast would the bond strength develop under varying ambient temperature conditions? The data obtained by Minford (1341) using aluminum extrusions and fir plywood adherends is shown in Table 38. As solvent slowly dissipated from the bondline, the tensilepeel-strength of the joints increased. At curing temperatures below 75°F (24°C), joint strength development rate was unacceptably slow. Even at 75°F (24°C), the joint strength continued to increase over a 56-day test evaluation time. In another investigation, the author determined the lap-shear and tensile-peel values for 11 different commercial neoprene high-solids mastic cements for joining aluminum extrusions to fir plywood, as shown in Table 39. Results showed as much as a 5000Jo difference in lap-shear and tensile-peel strength values, yet all were equally recommended by their manufacturers' data sheets. The danger in selecting adhesives without specific test information utilizing
Table 38 Rate of Aluminum-to-Wood Joint Strength Build-up Under Various Temperature Conditions Using an 850Jo Solids Mastic Adhesive
Time (days) 1 2 4
14 28 56
0 9 9
6 8 9
12 14
12 22 40 66 93
120 All joints made with B. F. Goodrich PL-400 high solids rubber mastic and 6063-T6 aluminum extrusion and fir plywood. Source: Data from Ref. 1341.
