Volume 20, Issue 1 (January 1992)
Hydrochlorofluorocarbon (HCFC) Blowing Agents for Foam Insulation of Launch Vehicle Cryogenic Propellant Tanks
Two polyurethane spray-on foam insulations (SOFI) were evaluated with five hydrochlorofluorocarbon (HCFC) blowing agents each (HCFC-141b, HCFC-123, and three blends). Foams were evaluated by measuring bond and flatwise tension strengths at four temperatures, compression at ambient temperature, and substrate strain compatibility at liquid helium temperature. Additionally, foams were characterized for density, closed-cell content, oxygen index, and ablation under radiant heating. Compression strengths of RDB-1-152 (polyether polyol) exceeded those of SS-1825 SOFI (polyester polyether, blend). Highest compression and tensile strengths were for foams sprayed with HCFC-141b and strengths decreased with increasing HCFC-123 content in the blowing agent. No foam failures occurred adhesively at the aluminum substrate, but a high incidence of premature failures occurred in the knitline between successive spray layers. Process optimization studies will be conducted with the two best SOFI systems, RDB-1-152/HCFC-141b and RDB-1-152/30% HCFC-123: 70% HCFC-141b.